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Students can Download Chapter 5 Evolution Notes, Plus Two Zoology Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Zoology Notes Chapter 5 Evolution

Origin Of Life
In the solar system, earth was originated 4.5 billion years back. There was no atmosphere on early earth.

Water vapour, methane, carbondioxide and ammonia are found on the surface

The UV rays from the sun broke up water into Hydrogen and Oxygen. Oxygen combined with ammonia and methane to form water, CO₂ and others.

Life originated four billion years. Earlier it was believed that life originated from non living things. This is the theory of spontaneous generation.

Later Louis Pasteur demonstrated that life comes only from pre-existing life. He showed that in presterilised flasks, life did not come from killed yeast while in another flask open to air, new living organisms arose from ‘killed yeast’.

Oparin and Haldane proposed that the first form of life that arose from pre-existing non-living organic molecules (e.g. RNA, protein, etc.) and it is followed by chemical evolution.

In 1953, S.L. Miller, an American scientist created similar conditions in a laboratory He created electric discharge in a closed flask containing CH4, H2, NH3 and water vapaur at 800°C. He observed the formation of amino acids.

The first non-cellular forms of life could have originated 3 billion years back i.e RNA, Protein, Polysaccharides, etc…

Later the first cellular forms (single-celled) were originated. These were occurred in water environment only.
Diagrammatic Representation of Miller’s Experiment:

Evolution Of Life Forms – A Theory
Charles Darwin was conducted a voyage ship called H.M.S. Beagle round the world and reach the conclusion that existing living forms share similarities not only among themselves but also with life forms that existed millions of years ago. There has been gradual evolution of life forms.

According to the concept of reproductive fitness, those who are better fit in an environment, produce more progeny than others and survived more. He called it as natural selection an important mechanism of evolution.

In the same time Alfred Wallace naturalist of Malay Archepelago had the same conclusion as Darvin, that all the existing life forms share similarities and share common ancestors.

What Are The Evidences For Evolution?
Evidence of evolution of life comes from fossils that found in sedimentary rocks. Different-aged rock sediments contain fossils of different life-forms. They represent extinct organisms (e.g., Dinosaurs).This type of evidence is called paleontological evidence.

Analysing the comparative anatomy and morphology, shows similarities and differences among organisms of today and those that existed years ago.

Example of homologous organs in (a) Plants and (b) Animals:

For example whales, bats, Cheetah and human share similarities in the pattern of bones of forelimbs (similar anatomical structure).

It contains the bones like humerus, radius, ulna, carpals, metacarpals and phalanges. The same structure developed along different directions due to adaptions to different needs. So they have different functions.

These structures are homologous. This type of evolution is called divergent evolution. Other examples are vertebrate hearts or brains and the thorn and tendrils of Bougainvillea.

Wings of butterfly and of birds anatomically dissimilar but they perform similar functions. These are analogous structures arise due to convergent evolution.

Other examples are the eye of the octopus and of mammals or the flippers of Penguins and Dolphins: Sweet potato (root modification) and potato (stem modification) etc.

Another evidence supporting evolution by natural selection comes from England. Before industrialisation there are more white-winged moths on trees than dark-winged.

This is due to white-coloured lichen covered the trees – in that background the white winged moth survived But after industrialisation, there were more dark-winged moths in the same area because the tree trunks became dark due to industrial smoke and soots.

Under this condition the white-winged moth did not survive due to predators, dark-winged or melanised moth survived.

Lichen are pollution indicators they cannot grow in areas that are polluted. Hence, moths that were able to camouflage themselves.

What Is Adaptive Radiation?
In this, the small black birds -Darwin’s Finches are examples. Darwin found that there were many varieties of finches in the same island.

Their original seed-eating features are changed and become insectivorous and Variety of beaks of finches that Darwin found in Galapagos Island vegetarian finches.

Here the evolution starting from a point and radiating to other areas of geography (habitats) is called adaptive radiation.

Another example is Australian marsupials. A number of different marsupials evolved from an ancestral stock within the Australian island.

Placental mammals in Australia also exhibit adaptive radiation i.e they evolved into varieties (e.g., Placental wolf and Tasmanian wolf marsupial).

Variety of beaks of finches that Darwin found in Galapagos Island:

Biological Evolution
The importance of Darwinian theory of evolution lies in natural selection.

A colony of bacteria (say A) growing on a given medium show variation in terms of feed component. A change in the medium composition results the population (say B) that can survive under the new conditions.

Here the fitness of B is better than that of A under the new conditions. Nature selects for fitness. Adaptive ability is inherited. It has a genetic basis. Fitness is the ability to adapt and get selected by nature.

Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution Before Darwin, Lamarck had conducted experiments and proposed the use and disuse of organs.

He gave the examples of Giraffes who in an attempt to forage leaves on tall trees had to adapt by elongation of their necks. As they passed on this acquired character of elongated neck to succeeding generations.

The work of Thomas Malthus on populations was influenced Darwin For example, natural resources are limited, populations are stable in size except for seasonal fluctuation.

The population size grow exponentially if reproduced maximally. Darwin was pointed that variations which are heritable, when the resource utilisation better for few, they reproduce more progeny. Hence for a period of time survivors leave more progeny and there would be a change in population characteristics.

Mechanism Of Evolution
Mendel had studied only inheritable ‘factors’ influencing phenotype, But Hugo deVries conducted experiments on evening primrose and proposed the idea of mutation. Mutations are random and directionless while Darwinian variations are small and directional.

Mutation leads to speciation called as saltation (single step large mutation).

Hardy-Weinberg Principle
Diagrammatic representation of the operation of natural selection on different traits:

(a) Stabilising
(b) Directional and
(c) Disruptive

According to Hardy-Weinberg principle allele frequencies in a population are stable and is constant from generation to generation. This is called genetic equilibrium. Sum total of all the allelic frequencies is 1.

For example, p and q represent the frequency of allele A and allele a. The frequency of AA individuals in a population is simply p2. The frequency of p appear on both the chromosomes of a diploid individual, Similarly of aa is q2, and of Aa is 2pq.

Hence, p2 + 2pq + q2 = 1. This is a binomial expansion of (p+q)2.

Disturbance in genetic equilibrium, or Hardy – Weinberg equilibrium, i.e., change of frequency of alleles in a population affected by five factors.

These are gene migration or gene flow, genetic drift, mutation, genetic recombination and natural selection.

When migration of population occurs, gene frequencies change in the original as well as in the new population. If the same change occurs by chance, it is called genetic drift.

Sometimes the change in allele frequency is different in the new sample of population that they become a different species. The original drifted population becomes founders and the effect is called founder effect.

The variation due to mutation or variation due to recombination during gametogenesis, or due to gene flow or genetic drift results in changed frequency of genes and alleles in future generation.

Natural selection lead to the stabilisation	(more individuals acquire mean character value)
directional	more individuals acquire value other than the mean character value)
disruptive	More individuals acquire peripheral character value at both ends of the distribution curve

A Brief Account Of Evolution
About 2000 million years ago (mya) the first cellular forms of life appeared on earth. From this the cells with membranous envelop evolved and developed Some of these cells had the ability to release O₂. Slowly single-celled organisms became multi-cellular life forms.

In 500 mya, invertebrates were formed Jawless fish evolved around 350 mya. Sea weeds and few plants evolved around 320 mya. In 350 mya Fish with stout and strong fins evolved

In 1938, a fish caught in South Africa happened to be a Coelacanth which was thought to be extinct. These animals called lobefins evolved into the first amphibians that lived on both land and water.

The amphibians evolved into reptiles. They lay thick shelled eggs. Their modern descendents are the turtles, tortoises and crocodiles.

In the next 200 millions years reptiles of different shapes and sizes dominated on earth.In this period Giant ferns (pteridophytes) were present.

Land reptiles dinosaurs (biggest i.e., Tyrannosaurus rex) went back into water to evolve into fish like reptiles 200 mya (e.g. Ichthyosaurs). About 65 mya, the dinosaurs suddenly disappeared from the earth.

After the reptiles, mammals evolved on this earth. The first mammals were like shrews. Their fossils are small sized. Mammals were viviparous and protected their unborn young inside the mother’s body.

There were in South America mammals resembling horse, hippopotamus, bear, rabbit, etc. Due to continental drift, when South America joined North America, these animals were overridden by North American fauna.

Due to the same continental drift pouched mammals of Australia survived because of lack of competition. Some mammals live wholly in water are Whales, dolphins, seals and sea cows.

Origin And Evolution Of Man

Students can Download Chapter 10 Vector Algebra Notes, Plus Two Maths Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Maths Notes Chapter 10 Vector Algebra

Introduction
Physical quantities we deal are of two types, one that can be specified using a single real number which gives its magnitude and the other which involves the idea of direction as well as magnitude. The first type is called scalar quantity and the second is vector quantity. In this chapter we analyses the basic concepts about vectors, various operations, and their algebraic and geometrical properties.

I. Types of vectors

1. Equal Vectors: Vectors having same magnitude and direction regardless of the positions of their initial points.
2. Collinear Vectors: Vectors which are parallel to the same line, irrespective of their magnitude and direction.
3. Like and Unlike Vectors: Collinear vectors having same direction are like vectors and opposite direction are unlike vectors.
4. Unit Vectors: Vectors with magnitude unity.

II. Component form of a vector
Let i, j, k be the unit vectors along the x-axis, y-axis, z-axis respectively. The point P(x, y, z) be a point in space. Then the position vector of the point P can be expressed in component form as
1. If li + mj + nk is unit vector, then l,m,n are direction cosines along the vector.
2. If P (a, b, c) is a point on space, then a, b, c are direction ratios and

are direction cosines along the vector \(\overline{O P}\).

III. Addition of Vectors

\(\overline{A B}+\overline{B C}+\overline{C A}=\overline{0}\) is known as triangle law of vector addition.

IV. Multiplication of a vector by a scalar
Let \(\bar{a}\) = a₁i + a₂j + a₃k be a vector and λ be a scalar. Then the product of the vector \(\bar{a}\) by a scalar is denoted by λ\(\bar{a}\) and the new vector formed has a magnitude λ|\(\bar{a}\)|.
λ\(\bar{a}\) = λa₁i + λa₂j + λa₃k

V. Vector joining two points
If P(a₁, a₂, a₃) and Q(b₁, b₂, b₃) are two points, then the vector joining P and Q is the vector \(\overline{P Q}\).
ie: \(\overline{P Q}\) = (b₁ – a₁)i + (b₂ – a₂)j + (b₃ – a₃)k

VI. Section Formula
If \(\bar{a}\) and \(\bar{b}\) be the position vectors of the points A and B respectively, then the position vector of the point P which divides AB in the ratio l:m

VII. Dot (Scalar) Product of vectors

VIII. Cross (vector) Product of Vectors

Geometrical meaning of vector product.

• \(\bar{a} \times \bar{b}\) is a vector perpendicular to \(\bar{a}\) and \(\bar{b}\).
• \(|\bar{a} \times \bar{b}|\) gives the area of a parallelogram with adjacent sides \(\bar{a}\) and \(\bar{b}\).

• i × i = j × j = k × k = 0,
• i × j = k, j × k = i, k × i = j
• j × i = -k, k × j = -i, i × k = -j

IX. Box (Scalar Triple) Product of Vectors

Properties:
1. Since \(\bar{b} \times \bar{c}\) is a vector, \([\bar{a} \bar{b} \bar{c}]\) is a scalar quantity.

2. |\([\bar{a} \bar{b} \bar{c}]\)| is the volume of the parallelopiped with a adjacent sides vector \(\bar{a}, \bar{b}, \bar{c}\).

3. If \(\bar{a}\) = a₁i + a₂j + a₃k; \(\bar{b}\) = b₁i + b₂j + b₃k and \(\bar{c}\) = c₁i + c₂j + c₃k, then

4. if \(\bar{a}, \bar{b}, \bar{c}\) be any three vectors, then \([\bar{a} \bar{b} \bar{c}]\) = \([\bar{b} \bar{c} \bar{a}]=[\bar{c} \bar{a} \bar{b}]\) (cyclic permutation of three vectors does not change the value of the scalar triple product).

5. In scalar triple product, the dot and cross can be interchanged.ie,

6. If any two vectors are interchanged the sign of box product is changed but magnitude remains the same.

7. If any two vectors are equal or proportional then the value of box product is zero.

8. Three vectors \(\bar{a}, \bar{b}, \bar{c}\) are coplanar if and only if \([\bar{a} \bar{b} \bar{c}]\) = 0.

Students can Download Chapter 4 Molecular Basis of Inheritance Notes, Plus Two Zoology Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Zoology Notes Chapter 4 Molecular Basis of Inheritance

The Dna
DNA is a long nucleotides polymer of deoxyribonucleotides.

1. Structure of Polynucleotide Chain:
A nucleotide has three components

1. Nitrogenous base
2. Pentose sugar (ribose in case of RNA, and deoxyribose for DNA), and
3. Phosphate group.

There are two types of nitrogenous bases.

Purines	Adenine and Guanine
Pyrimidines	Cytosine, Uracil and Thymine

Cytosine is common for both DNA and RNA and Thymine is present in DNA.

Uracil is present in RNA at the place of Thymine.

A nitrogenous base is linked to the pentose sugar through a N – glycosidic linkage to form a nucleoside, When a phosphate group is linked to 5′-OH of a nucleoside through phosphor ester linkage, to form nucleotide. Two nucleotides are linked through 3′-5′ phosphodiester linkage to form a dinucleotide.

Polynucleotide chain has at one end a free phosphate moiety at 5′-end of ribose sugar and other end of the polynucleotide chin the ribose has a free 3′-OH group The backbone in a polynucleotide chain is formed due to sugar and phosphates.

RNA has an additional-OH group present at 2′-position in the ribose and the uracil is found at the place of thymine.

Acidic nature of DNA was first identified by Friedrich Meischer in 1869 and it called as ‘Nuclein’.

Data from the X-ray diffraction studies conducted by James Watson and Francis Crick, Maurice Wilkins and Rosalind Franklin showed that DNA has Double Helix structure.

Erwin Chargaff showed that ratios between Adenine and Thymine and Guanine and Cytosine are constant and equals one

Each strand from a DNA acts as a template for synthesis of a new strand. The two double stranded DNA thus, produced would be identical to the parental DNA molecule.

The salient features of the Double-helix DNA are

(i) It is made of two polynucleotide chains, where the backbone is sugar-phosphate, (ii) The two chains have anti-parallel polarity, ie. 51 and 31 strands. (iii) The bases in two strands are paired through hydrogen bond. Adenine forms two hydrogen bonds with Thymine and Guanine is bonded with Cytosine with three H- bonds. (iv) The two chains are coiled in a right-handed fashion. The pitch of the helix is 3.4 nm. (v) The plane of one base pair stacks over the other in double helix.

Francis Crick proposed the Central dogma in molecular biology, which states that the genetic information flows from DNA to RNA and RNA to protein. But in some viruses the flow of information is reverse direction, that is from RNA to DNA.

2. Packaging of DNA Helix:
In E. coli, they do not have a defined nucleus it is termed as ‘nucleoid’. The DNA in nucleoid is organised in large loops held by proteins.

In eukaryotes, this organisation is much more complex. Here the positively charged, basic proteins called histones are associated with DNA.

Histones are rich in the basic amino acid residues lysines and arginines. Histones are organised to form a unit of eight molecules called as histone octamer.

The beads-on-string structure in chromatin is packaged to form chromatin fibers that are further coiled and condensed at metaphase stage of cell division to form chromosomes.

The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called Nucleosome. It contains 200 bp of DNA helix.

Nucleosomes constitute the repeating unit of a structure in nucleus called chromatin, it is thread-like stained (coloured) bodies seen in nucleus. The nucleosomes in chromatin are seen as ‘beads-on- string’ structure when viewed under electron microscope (EM).

The packaging of chromatin at higher level with proteins that are called as Non-histone Chromosomal (NHC) proteins.

In a typical nucleus, some region of chromatin are loosely packed (euchromatin) and more densely packed (Heterochromatin). Euchromatin is transcriptionally active chromatin, whereas heterochromatin is inactive.

The Search For Genetic Material
This is the work of identification of DNA that acts as a genetic material and responsible for inheritance.

Transforming Principle:
In 1928, Frederick Griffith, in a series of experiments with Streptococcus pneumoniae (bacterium responsible for pneumonia), showed the trasformation in the bacteria.

For this, Streptococcus pneumoniae (pneumococcus) bacteria are grown, on a culture plate, some produce smooth shiny colonies (S) (mucous polysaccharide coat) while others produce rough colonies (R).

Mice infected with the S strain (virulent) die from pneumonia infection but mice infected with the R strain do not develop pneumonia.

When Griffith was injected heat-killed S strain into mice, bacteria did not kill them. But he injected a mixture of heat-killed S and live R bacteria, the mice died and he recovered living S bacteria from the dead mice.

Biochemical Characterisation of Transforming Principle:
Oswald Avery, Colin MacLeod, and Maclyn McCarty worked on the ‘transforming principle’ of Griffith’s experiment and noticed that DNA alone from S bacteria caused R bacteria to become transformed.

They also discovered that protein-digesting enzymes (proteases) and RNA-digesting enzymes (RNases) did not affect transformation.

But the digestion with DNase inhibited transformation.

They concluded that the transforming substance was not a protein or RNA but DNA is the hereditary material.

1. The Genetic Material is DNA:
Alfred Hershey and Martha Chase (1952) grew bacteriophages on a medium that contained radioactive phosphorus and some others on medium that contained radioactive sulfur.

Viruses grown in the presence of radioactive phosphorus contained radioactive DNA but not radioactive protein because DNA contains phosphorus but protein does not. Similarly, viruses grown on radioactive sulfur contained radioactive protein but not radioactive DNA because DNA does not contain sulfur.

After the infection the viral coats were removed from the bacteria by agitating them in a blender. It is concluded that proteins did not enter the bacteria from the viruses. But the DNA is the genetic material that passed from virus to bacteria.

The Hershey-Chase experiment:

2. Properties of Genetic Material (DNA versus RNA):
A molecule that act as a genetic material must possess the following features

(i) It should be able to generate its replica (Replication). (ii) It should chemically and structurally be stable. (iii) It should provide the scope for slow changes (mutation) that are required for evolution. (iv) It should be able to express itself in the form of ‘Mendelian Characters’.

The 2-OH group present at the nucleotide in RNA is a reactive group and makes RNA labile and easily degradable. Therefore, DNA is less reactive and structurally more stable when compared to RNA.

Therefore, among the two nucleic acids, the DNA is a better genetic material.
The presence of thymine at the place of uracil also gives additional stability to DNA.
In fact, RNA being unstable, mutate at a faster rate. So the viruses having RNA genome having shorter life span mutate and evolve faster.

Rna World
RNA is genetic material as well as a catalyst. But it is reactive and hence unstable. Therefore, DNA has evolved from RNA with chemical modifications that make it more stable.

Replication
Watson and Crick (1953) proposed replication of DNA. They suggested that the two strands separate and act as a template for the synthesis of new complementary strands.

Waste-click model for semiconservative DNA replication:

1. The Experimental Proof:
DNA replicates in semi conservative manner was first shown in Escherichia coli by Matthew Meselson and Franklin Stahl performed the following experiment in 1958:

After the completion of replication, each DNA molecule have one Watson-Crick model for parental and one newly synthesised strand. This is termed as semiconservative DNA replication. semiconservative DNA replication.

They grew E. coli in a medium containing 15NH4Cl. The result was that 15N was incorporated into newly synthesised DNA .This heavy DNA molecule could be distinguished from the normal DNA by centrifugation in a cesium chloride (CsCl) density gradient.

Then they transferred the cells into a medium with normal 14NH4Cl and took samples at various definite time intervals as the cells multiplied, and extracted the DNA that remained as double-stranded helices.

The DNA that was extracted from the culture one generation after the transfer from 15N to 14N medium [E. coli divides in 20 minutes] had a hybrid DNA.
(Separation of DNA by Centrifugation):

DNA extracted from the culture after another generation [that is after 40 minutes, II generation] was composed of equal amounts of this hybrid DNA and of ‘light’ DNA.

In an another experiment radioactive thymidine is incorporated into DNA and was observed the semi conservative replication of DNA in Vicia faba (faba beans) by Taylor and colleagues in 1958.

2. The Machinery and the Enzymes:
In E. coli, the process of replication takes place with the help of DNA-dependent DNA polymerase, because it uses a DNA template to catalyse the polymerization of deoxynucleotides.

E. coli that has only 4.6 × 106 bp completes the process of replication within 38 minutes. Deoxyribonucleoside triphosphates have double role. Besides acting as substrates, they provide energy for polymerization reaction same as in case of ATP.

Initially the replication occur within a small opening of the DNA helix (origin of replication) called as replication fork. The DNA- dependent DNA polymerases catalyse polymerization only in one direction, that is 5¹-3’.

Here on one strand (the template with polarity 3’-5′), the replication is continuous, while on the other (the template with polarity 5′-3′), it is discontinuous. The discontinuously synthesized fragments are later joined by the enzyme DNA ligase.

In eukaryotes, the replication of DNA takes place at S-phase of the cell-cycle. A failure in cell division after DNA replication results into polyploidy(a chromosomal anomaly).

Transcription
The process of copying genetic information from one strand of the DNA into RNA is termed as transcription. In transcription only a segment of DNA is copied into RNA.

Only single stranded RNA is produced by transcription process. If the two RNA molecules are produced simultaneously it would be complementary to each other, hence would form a double stranded RNA. This would prevent the translation.

1. Transcription Unit:
DNA has three regions as transcription unit

1. A Promoter
2. The Structural gene
3. A Terminator

The two strands have opposite polarity and the DNA-dependent RNA polymerase catalyse the polymerisation in only one direction, that is, 5′-3′, the strand that has the polarity 3′-5’acts as a template, and is also referred to as template strand.

The other strand which has the polarity (5′-3′) and the sequence same as RNA (except thymine at the place of uracil), is displaced during transcription. This strand (which does not code for anything) is referred to as coding strand.
For example

3′-AT GC ATGC ATGC ATGC ATGC ATGC -5′ Template Strand 5′-TACGTACGTACGTACGTACGTACG-3′ Coding Strand

The promoter is located towards 5′ – end (upstream) of the structural gene. It provides binding site for RNA polymerase.

The terminator is located towards 3′ – end (downstream) of the coding strand and it usually defines the end of the process of transcription.

2. Transcription Unit and the Gene:
A gene is the functional unit of inheritance. The DNA sequence coding for tRNA or rRNA molecule also define a gene.

Cistron is a segment of DNA coding for a polypeptide, the structural gene in a transcription unit is called as monocistronic (mostly in eukaryotes) or polycistronic (mostly in bacteria or prokaryotes).

eukaryotes, the structural genes have interrupted coding sequences – the genes in eukaryotes are split. The coding sequences are exons. The exons are interrupted by introns.

3. Types of RNA and the process of Transcription:
In bacteria, there are three major types of RNAs:

• mRNA (messenger RNA)
• tRNA (transfer RNA), and
• rRNA (ribosomal RNA).

All three RNAs are needed to synthesise a protein in a cell. The mRNA provides the template, tRNA brings aminoacids and reads the genetic code, and RNAs play structural and catalytic role during translation.

DNA- dependent RNA polymerase that catalyses transcription of all types of RNA in bacteria. RNA polymerase binds to promoter and initiates transcription (Initiation). It uses nucleoside triphosphates as substrate and polymerises in a template and follow the rule of complementarity.

Once the polymerases reaches the terminator region, the nascent RNA and RNA polymerase falls off. This results in termination of transcription.

RNA polymerase catalyse all the three steps, which are initiation, elongation and termination.

The RNA polymerase bind with initiation factor and termination-factor to initiate and terminate the transcription, respectively.

In bacteria, the mRNA does not require any processing and transcription and translation take place in the same compartment.

In eukaryotes, there are 3 RNA polymerases in the nucleus. The RNA polymerase I transcribes rRNAs (28S, 18S, and 5.8S).

RNA polymerase III is responsible for transcription of tRNA, 5srRNA, and snRNAs (small nuclear RNAs).

The RNA polymerase II transcribes precursor of mRNA, the heterogeneous nuclear RNA (hnRNA).

Heterogeneous nuclear RNA contain both the exons and the introns and are non-functional. Hence, it is subjected to a process called splicing where the introns are removed and exons are joined together hnRNA undergo two additional processing called as capping and tailing. In capping an methyl guanosine triphosphate is added to the 5’-end of hnRNA. In tailing, adenylate residues (200-300) are added at 3′-end in a template. It is the fully processed hnRNA, called as mRNA, that is transported out of the nucleus for translation.

Genetic Code
The process of translation requires transfer of genetic information from a polymer of nucleotides to a polymer of amino acids.
codons for various aminoacids:

For this, George Gamow, who proposed only 4 bases they have to code for 20 amino acids, the code should constitute a combination of bases.

The code should be made up of three nucleotides( triplet) and in various combination would generate 64 codons, 4³ (4 × 4 × 4) Marshall Nirenberg’s cell-free system for protein synthesis helped the code to be deciphered.

Severo Ochoa enzyme- polynucleotide phosphorylase was also helpful in polymerising RNA with defined sequences.

The salient features of genetic code are: (i) The codon is triplet. 61 codons code for amino acids and 3 codons do not code for any amino acids, hence they function as stop codons. (ii) One codon codes for only one amino acid, hence, it is unambiguous and specific. (iii) Some amino acids are coded by more than one codon, hence the code is degenerate. (iv) The codon is read in mRNA in a contiguous fashion. There are no punctuations. (v) code is nearly universal: for example, from bacteria to human UUU would code for Phenylalanine (phe). Some exceptions to this rule have been found in mitochondrial codons, and in some protozoans. (vi) AUG has dual functions. It codes for Methionine (met), and it also act as initiator codon.

1. Mutations and Genetic Code:
Deletions and rearrangements in a segment of DNA result in loss or gain of a gene function.

Example of point mutation is a change of single base pair in the gape for beta globin chain that results in the change of amino acid residue glutamate ‘to valine. It results sickle cell anemia.

Insertion or deletion of one or two bases, changes the reading frame from the point of insertion or deletion. Such mutations are referred to as frame-shift insertion or deletion mutations.

2. tRNA- the Adapter Molecule:
Francis Crick proposed that an adapter molecule would bind to specific amino acids. tRNA has an anticodon loop and an amino acid accepter end to which it binds to amino acids. tRNAs are specific for each amino acid.

For initiation, there is another specific tRNA that is referred to as initiator tRNA. There are no tRNAs for stop codons.

Two-dimensional structure of tRNA looks like a clover-leaf. But in three-dimensional structure of tRNA looks like inverted L.

Translation
Translation is the process of polymerisation of amino acids to form a polypeptide. The order and sequence of amino acids are defined by the sequence of bases in the mRNA. The amino acids are joined by a bond which is known as a peptide bond. Formation of a peptide bond requires energy.

The activation of amino acids with ATP and linked to tRNA- a process commonly called as charging of tRNA or aminoacylation of tRNA. If two such charged tRNAs are brought close together the peptide bond is formed.

The ribosome also acts as a catalyst (23S rRNA in bacteria is the enzyme- ribozyme) for the formation of peptide bond.

A translational unit in mRNA is start codon (AUG) and the stop codon. mRNA also has some additional sequences that are not translated they are called as untranslated regions (UTR). The UTRs are present at both 5′-end (before start codon) and at 3′-end (after stop codon). They are required for efficient translation process.

The ribosome consists two subunits; a large subunit and a small subunit. For initiation, the ribosome binds to the mRNA at the start codon (AUG) that is recognised only by the initiator tRNA.

In elongation , amino acid linked to tRNA, and bind to the codon in mRNA by forming complementary base pairs with the tRNA anticodon. The ribosome moves from codon to codon along the mRNA.

Amino acids are added one by one and translated into Polypeptide. At the end, a release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.

Regulation Of Gene Expression
The Lac operon:
In eukaryotes, the regulation is possible in

1. transcriptional level (formation of primary transcript),
2. processing level (regulation of splicing),
3. transport of mRNA from nucleus to the cytoplasm,
4. translational level.

For example E. coli synthesised the enzyme beta-galactosidase in the medium if the disaccharide, lactose is present.

Enzyme breakdown the lactose into galactose and glucose; the bacteria use them as a source of energy. The development and differentiation of embryo into adult organisms are also a result of the coordinated regulation of expression of several sets of genes.

In a transcription unit, the activity of RNA polymerase at a promoter is regulated by proteins. These regulatory proteins act both positively (activators) and negatively (repressors). The promoter regions of prokaryotic DNA is regulated by the interaction of adjacent operators. Each operon has its specific operator and specific repressor.

For example, lac operator is present only in the lac operon and it interacts specifically with lac repressor only.

1. The Lac operon:
The function of lac operon was first shown by Jacob and Monod.

In lac operon the structural gene is regulated by a promoter and regulatory genes. Such arrangement in bacteria is called as operon.

Other examples are trp operon, ara operon, his operon, val operon, etc.

The lac operon consists of one regulatory gene (i gene) and three structural genes (z, y, and a).

The i gene codes for the repressor of the lac operon. The z gene codes for beta-galactosidase. The y gene codes for permease, which increases permeability of the celt to beta galactosides. The a gene codes for transacetylase.

Hence, all the three gene products in lac operon are required for metabolism of lactose. Lactose (inducer) is the substrate for the enzyme beta-galactosidase and it regulates switching on and off of the operon.

In the presence of an inducer, such as lactose, the repressor is inactivated by the inducer. Then RNA polymerase bind to the promoter and transcription proceeds. Regulation of lac operon by repressor is referred to as negative regulation.

Human Genome Project
This is mainly aims to find out the complete DNA sequence of human genome If two individuals differ, then their DNA sequences should also be different, at least at some places.

Human Genome Project was launched in the year 1990 (HGP). Human genome consists of approximately 3 × 109 bp.

Goals of HGP (i) Identify 20,000-25,000 genes in human DNA; (ii) Determine the sequences of the 3 billion chemical base pairs. (iii) Store this information in databases; (iv) Improve tools for data analysis; (v) Transfer related technologies to other sectors, such as industries; (vi) Address the ethical, legal, and social issues (ELSI) that may arise from the project.

HGP was coordinated by the U.S. Department of Energy and the National Institute of Health. The project was completed in 2003.

This project also aims to solve challenges in health care, agriculture, energy production, environmental remediation.

Methodologies:
For sequencing, the total DNA from a cell is isolated and converted into random fragments of relatively smaller sizes and cloned in suitable host using vectors. The cloning resulted into amplification of each piece of DNA fragment so that it could be sequenced with ease.

The commonly used hosts are bacteria and yeast, and the vectors are called as BAC (bacterial artificial chromosomes), and YAC (yeast artificial chromosomes). The fragments are sequenced using automated DNA sequencers that was developed by Frederick Sanger.

These sequences are then arranged based on some overlapping regions present in them. Alignment of these sequences are done with computer based programs. These sequences are annotated and assigned to each chromosome. The sequence of chromosome 1 was completed only in May 2006.

Another task was the construction of genetic and physical maps on the genpme. This was made possible by knowing the polymorphism of restriction endonuclease recognition sites, and some repetitive DNA sequences.

1. Salient Features of Human Genome:

(i) The human genome contains 3164.7 million nucleotide bases. (ii) The average gene consists of 3000 bases. The largest known human gene is dystrophin consist of 2.4 million bases. (iii) The total number of genes is estimated at 30,000. The 99.9 per cent nucleotide bases are exactly the same in all people. (iv) The functions are unknown for over 50 per cent of discovered genes. (v) Less than 2 percent of the genome codes for proteins. (vi) Repeated sequences make up very large portion of the human genome. (vii) Repetitive sequences are stretches of DNA sequences that are repeated many times, sometimes hundred to thousand times (viii) Chromosome 1 has most genes (2968), and the Y has the fewest (231) (ix) Scientists have identified about 1.4 million locations where single base DNA differences (SNPs – single nucleotide polymorphism, pronounced as ‘snips’) occur in humans.

Dna Fingerprinting
The 99.9 per cent of base sequence among humans is the same. The genetic differences between two individuals is calculated by comparing the two sets of 3 × 10⁶ base pairs.

It is the identification of differences in some specific regions in DNA sequence called as repetitive DNA,
These repetitive DNA are separated from bulk genomic DNA as different pegks during density gradient centrifugation.

The bulk DNA forms a major peak and the other small peaks are referred to as satellite DNA. Depending on base composition, length of segment, and number of repetitive units, the satellite DNA is classified into many categories,

1. Micro-satellites,
2. Mini-satellites etc.

These sequences do not code for any proteins and show high degree of polymorphism. DNA from every tissue (such as blood, hair-follicle, skin, bone, saliva, sperm etc.), of an individual show the same degree of polymorphism, they become very useful identification tool in forensic applications.

The polymorphisms are inheritable from parents to children DNA fingerprinting is the basis of paternity testing, in case of disputes.

The polymorphism in DNA sequence is the basis of genetic mapping and DNA fingerprinting, Polymorphism arises due to mutations. Allelic sequence variation results inheritable mutation.

Such variation are observed in non coding DNA sequence. These mutations accumulating generation after generation, and form one of the basis of variability/polymorphism.

The different types of polymorphisms ranging from single nucleotide change to very large scale changes. For evolution and speciation, such polymorphisms play very important role.

The technique of DNA Fingerprinting was initially developed by Alec Jeffreys. He used a satellite DNA as probe. It is called as Variable Number of Tandem Repeats (VNTR).

The technique, is based on Southern blot hybridisation using radiolabeled VNTR as probe.

It involves

1. isolation of DNA,
2. digestion of DNA by restriction endonucleases,
3. separation of DNA fragments by electrophoresis,
4. transferring (blotting) of separated DNA fragments to synthetic membranes, such as nitrocellulose or nylon,
5. hybridisation using labelled VNTR probe, and
6. detection of hybridised DNA fragments by autoradiography.

The VNTR belongs mini-satellite.lt is the small DNA sequence. Its copy number varies from chromosome to chromosome in an individual. The numbers of repeat show very high degree of polymorphism.

The size of VNTR varies in size from 0.1 to 20 kb. So after hybridisation with VNTR probe, the autoradiogram gives many bands of differing sizes.

These bands give a characteristic pattern for an individual DNA. It differs from individual to individual in a population except in the case of monozygotic (identical) twins.

Students can Download Chapter 8 Environmental Issues Notes, Plus Two Botany Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Botany Notes Chapter 8 Environmental Issues

Air pollution
Pollutants are harmful substances that affect growth and yield of crops and cause premature death of plants. In animals they affect the respiratory system and causes diseases.

Smoke stacks of thermal power plants, smelters and other industries release particulate and gaseous air pollutants together with harmless gases, such as nitrogen, oxygen, etc.

Electrostatic precipitator:

These are separated using electrostatic precipitator which can remove over 99 per cent particulate matter present in the exhaust from a thermal power plant.

At high voltage the electrons produced in an instrument are attached to dust particles giving them a net negative charge. These charged dust particles are attracted by collecting plates. Then reducing the velocity of air between the plates which help the dust to fall.

Scrubber is an instrument that remove gases like sulphur dioxide present in the exhaust.

According to Central Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter (PM 2.5) are adversely affect the lungs followed by breathing and respiratory symptoms, irritation, inflammations and results premature death.

Automobiles are the largest source of air pollution in big cities .It is avoided by using lead-free petrol or diesel and catalytic converters, (platinum-palladium and rhodium as the catalysts) for reducing emission of poisonous gases.

The exhaust when passes through the catalytic converter, the unburnt hydrocarbons are converted into carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively.

If once fitted the catalytic converter, there must be used unleaded petrol because lead in the petrol inactivates the catalyst.

1. Controlling Vehicular Air Pollution:
A Case Study of Delhi:
Analysis showed that in 1990s, Delhi ranked fourth among the 41 most polluted cities of the world. The serious air pollution problems in Delhi was reduced after filing public interest litigation (PIL) in the Supreme Court of India. After that Delhi govt, orderd of using compressed natural gas (CNG) in public transport, i.e., buses.

CNG is better than diesel. It bums most efficiently. CNG is cheaper than petrol or diesel and cannot be adulterated like petrol or diesel.

The supply of CNG for major distribution centres through pipelines is difficult. In the meantime Delhi govt, is also taken parallel steps for reducing vehicular pollution that is to

Control pollution in big cities:

1. Avoid the use of old vehicles
2. Use of unleaded petrol
3. Use of low-sulphur petrol and diesel
4. Use of catalytic converters in vehicles,
5. Application of strict pollution level norms for vehicles, etc.

The new auto fuel policy introduced by the Government of India is to reduce the sulphur and aromatic content in petrol and diesel fuels.

Euro II norms aims that amount of sulphur to be controlled at 350 parts-per-rhillion (ppm) in diesel and 150 ppm in petrol.

The goal, according to the roadmap, is to reduce sulphur to 50 ppm in petrol and diesel and bring down the level to 35 percent. For these purpose, vehicle engines should be upgraded.

The Bharat Stage II (equivalent to Euro-ll norms) is applicable to all automobiles throughout the country from April 1, 2005.

Euro III emission specifications brought out in 11 cities from April 1, 2005and later the Euro-IV norms by April 1, 2010.

Analysis shows that, great reduction in CO₂ and SO₂ level in Delhi between 1997 and 2005. In India, the Air (Prevention and Control of Pollution) Act came into force in 1981, but was amended in 1987 to include noise as an air pollutant. It causes psychological and physiological disorders in humans.

The sound level above 150 dB arises due to the jet plane or rocket take off, damage ear drums and permanently impairing hearing ability. Noise also causes sleeplessness, increased heart beating and altered breathing pattern in humans.

It is necessary to reduce noise by using sound absorbing materials in industries. Govt, laws are there to reduce noise pollution around hospitals and schools by avoiding the use of air – horns, restriction in the use of loudspeakers etc.

Water Pollution And Its Control
To safeguard water resources, Government of India has passed the Water (Prevention and Control of Pollution) Act, 1974. It helps to maintain the water bodies clean.

1. Domestic Sewage and Industrial Effluents:
About 0.1 per cent impurities present in domestic sewage unfit for human use. Domestic sewage mainly contains biodegradable organic matter, which is decomposed by bacteria and other micro-organisms. The amount of organic matter present in sewage can be measured by Biochemical Oxygen Demand (BOD).

For the biodegradation of organic matter by micro-organisms require plenty of oxygen, it results in sharp decline in dissolved oxygen. This causes mortality of fish and other aquatic creatures.

Presence of large amounts of nutrients in waters also causes excessive growth of planktonic(free-floating) algae, called an algal bloom which gives colour to the water bodies. Algal blooms cause lose of the water quality and fish mortality. Some are toxic to human beings and animals.
Effect of sewage discharge on some important characteristics of water:

Presence of excessive nutrients cause water hyacinth (Eichhornia crassipes), to grow in plenty, it causes blocks in our waterways. These are plants of the world’s most problematic aquatic weed called Terror of Bengal’. They grow abundantly in eutrophic water bodies, and lead to an imbalance in the ecosystem of the water body.
View of algal bloom:

Sewage from homes and hospitals contain undesirable pathogenic microorganisms it causes outbreak of serious diseases, such as dysentery, typhoid, jaundice, cholera, etc.

Domestic sewage from industries like petroleum, paper manufacturing, metal extraction and processing, chemical manufacturing, etc. contains as mercury, cadmium, copper, lead, etc.

Clorinated toxic hydrocarbons such as DDT, BHC etc present in industrial waste waters passes through successive trophic levels of food chain and causes accumulation. This is called Biomagnification.

The concentration of DDT is increased at successive trophic levels, it starts at 0.003 ppm in water, it can ultimately can reach 25 ppm in fish-eating birds, through biomagnification.

High concentrations of DDT disturb calcium metabolism in birds, which causes the thinning of eggshell and their premature breaking, causing decrease in bird populations.

Eutrophication is the natural aging of a lake by nutrient enrichment of soil. It occurs when nitrates and phosphates reaches water bodies by run off water.
Biomagnification of DDT in aquatic food chain:

Pollutants from man’s activities like effluents from the industries and homes can accelerate the aging process. This phenomenon is called Cultural or Accelerated Eutrophication. It causes depleting oxygen content of water and results the death of fish and other aquatic organisms.

Heated (thermal) wastewaters from thermal power plants destroy the growth of aquatic organisms. But it promote the growth of aquatic organisms in cold waters.

2. A Case Study of Integrated Waste Water Treatment:
An example of such an initiative was put into practice at the town of Areata, situated along the northern coast of California. Biologists from the Humboldt State University, and the townspeople created an integrated water treatment process within a natural system.
The cleaning occurs in two stages-

(a) The conventional sedimentation, filtering and chlorine treatments. After this stage, lots of dangerous pollutants like dissolved heavy metals are there. (b) The biologists developed a series of six connected marshes over 60 hectares of marshland. Appropriate plants, algae, fungi and bacteria were seeded into this area, which neutralise, absorb and assimilate the pollutants. Hence, as the water flows through the marshes, it gets purified naturally. The marshes of Arcta rich in biodiversity especially fishes, animals and birds. So the Friends of the Areata Marsh (FOAM) were responsible for safeguarding of this wonderful project.

Ecological sanitation:
It is a sustainable system for handling human excreta, using dry composting toilets. This is a practical, hygienic, efficient and cost-effective solution to human waste disposal.

Here human excreta is recycled and reduces the need for chemical fertilisers. This is the basis of ‘EcoSan’ toilets in many areas of Kerala and Sri Lanka.

Solid Wastes
Solid wastes especially municipal solid wastes are wastes from homes, offices, stores, schools, hospitals, etc. contain, comprise paper, food wastes, plastics, glass, metals,rubber, leather, textile, etc. These are subjected to Sanitary landfills in which wastes are dumped in a depression after packed and covered with dirt everyday because burning is not practicable.

In metros Landfills are not really a good solution since the amount of garbage generation increased largely that these sites are getting filled too. Also there is danger of seepage of chemicals, etc., from these landfills polluting the underground water resources.

All wastes are categorised into three types –

(a) bio-degradable, (b) recyclable and (c) the non-biodegradable

Kabadiwallahs and rag-pickers doing the of separation of materials for recycling. The biodegradable materials are put into deep pits in the ground for natural breakdown.

State Governments had decided to reduce the use of plastics and use of eco-friendly packaging. It is done by use of natural fibre carry-bags and avoid polythene bags.

1. Case Study of Remedy for Plastic Waste:
A plastic sack manufacturer Ahmed Khan in Bangalore has found a solution for problem of accumulating plastic waste. About 8 years ago, in collaboration with R. V. College of Engineering and the Bangalore City Corporation, he realised that the

Polyblend, a fine powder of recycled modified plastic, is mixed with the bitumen that is used to lay roads.

Bitumen is a water repellant substance helps to increase road life. The raw material for creating Polyblend is any plastic film waste that brought about by rag pickers.

Incinerators are used to remove the wastes from hospitals, it contain disinfectants and other harmful chemicals, and also pathogenic micro-organisms.

Electronic wastes (e-wastes) mainly contains irreparable computers and other electronic goods. It is generated in the developed world and are exported to developing countries, mainly to China, India and Pakistan where metals like copper, iron, silicon, nickel and gold are recovered during recycling process. In developing countries, during the recycling process workers are exposed to toxic substances.

So recycling is the only solution for the treatment of e-wastes. it is carried out in an environment-friendly manner.

Agro-chemicals And Their Effects
In the period of green revolution use of inorganic fertilizers, pesticides, herbicides, fungicides, etc. has increased crop production manifold. These chemical substances are toxic to other micro organisms in the soil and affect the terrestrial ecosystems. It also adversely affects the aquatic ecosystem and result the eutrophication of water bodies.

1. Case Study of Organic Farming:
Ramesh Chandra Dagar, a farmer in Sonipat, Haryana, in his agriculture land, he included

• Bee-keeping
• Dairy management
• Water harvesting, and
• Composting as a chain of processes, which support each other.

It is an example of sustainable agricultural method. There is no need to use chemical fertilisers for crops, as cattle excreta (dung) are used as manure. Crop waste is used to create compost, which can be used as a natural fertiliser or can be used to generate natural gas for satisfying the energy needs of the farm.

Radio Active Wastes
Nuclear energy is useful in many ways especially to generate electricity. But the disasters that occurred as accidental leakage in the Three Mile Island and Chernobyl incident and safe disposal of radioactive wastes are the main problems.

It was also realised that nuclear energy radiation is damaging to biological organisms, because it causes mutations. At high doses, nuclear radiation is lethal but at lower doses, it creates various disorders and cancer. Storage of nuclear waste must done in shielded containers buried within the rocks, about 500 m deep below the earth’s surface.

Greenhouse Effect And Global Warming
The term ‘Greenhouse effect’ has been derived from a phenomenon that occurs in a greenhouse. It looks like a small glass house and is used for growing plants especially during winter. It does not allow heat to escape.

The greenhouse effect is a naturally occurring phenomenon that is responsible for heating of Earth’s surface and atmosphere. If greenhouse effect is not there, the average temperature at surface of Earth would have been -18°C rather than the present average of 15°C.

The incoming raditions of sunlight reaches the earth’s surface re-emits heat in the form of infrared radiation but part of this does not escape into space as atmospheric gases (e.g., carbon dioxide, methane, CFC and nitrogen oxides) absorb a major fraction of it.

The molecules of these gases radiate heat energy, and a major part of which again comes to Earth’s surface, thus heating it up once again This cycle is repeated many a times. This leading to global warming.

During the past century, the temperature of Earth has increased by 0.6° C. This rise in temperature leads to the occurance of El Nino effect that is the melting of polar ice caps and Himalayan snow caps. It causes rise in sea level and submerge many coastal areas.

To reduce the emission of green house gases it is necessary to

1. Cutting down use of fossil fuel
2. Improving efficiency of energy usage
3. Reducing deforestation
4. Planting trees and slowing down the growth of human population.

Ozone Depletion In The Stratosphere
There are two type of ozone that is ‘bad’ ozone, formed in the lower atmosphere (troposphere) that harms plants and animals. ‘Good’ ozone- this ozone is found in the upper part of the atmosphere (stratosphere), and it acts as a shield and absorbing ultraviolet radiation from the sun.

UV rays are harmful to living organisms since DNA and proteins of living organisms absorb it, and breaks the high energy chemical bonds within these molecules.

The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU).
Ozone hole in antartica area It is measured by Dobson unit:

Ozone gas is continuously formed by the action of UV rays on molecular oxygen, and also degraded into molecular oxygen in the stratosphere.

The balance between production and degradation of ozone in the stratosphere is disrupted due to
chlorofluorocarbons (CFCs).

The CFC produced in the upper part of the atmosphere is degraded by the action of UV. It splits and release active clorine. This active clorine destroys ozone and makes holes.

It was first noticed in Antarctic region.

UV-B and UV-C causes DNA damage and mutation. It causes aging of skin, damage to skin cells and various types of skin cancers. In human eye, cornea absorbs UV-B radiation and causes inflammation of cornea, called snow-blindness, cataract, etc.

To reduce the emission of CFCs and other ozone depleting chemicals, an international treaty was formed known as the Montreal Protocol, signed at Montreal (Canada) in 1987.

Degradation By Improper Resource Utilisation And Maintenance
The important improper resource utilisation practices are
(1) Soil erosion and desertification:
The fertility of top-soil is lost due to over-cultivation, unrestricted grazing, deforestation and poor irrigation practices, resulting in arid patches of land. It result in the creation of desert.

(2) Waterlogging and soil salinity:
Irrigation without proper drainage of water leads to waterlogging in the soil. It also causes the deposition of salts on the land surface or starts collecting at the roots of the plants. This increased salt content and reduce the growth of crops and damaging to agriculture.

Deforestation

At the beginning of the twentieth century, forests covered about 30 per cent of the land of India. By the end of the century, it shrunk to 19.4 per cent, whereas the National Forest Policy (1988) of India has recommended 33 per cent forest cover for the plains and 67 per cent for the hills.

Deforestation occurs due to growing human population for timber, firewood, and several other purposes. Slash and burn agriculture, commonly called as Jhum cultivation in the north-eastern states of India, has also contributed to deforestation.

The ash is used as a fertiliser and the land is then used for farming or cattle grazing. The farmers then move on to other areas and repeat this process.
The consequences of deforestation are

1. Increased carbon dioxide concentration in the atmosphere
2. Loss of biodiversity due to habitat destruction
3. Disturbs hydrologic cycle
4. Causes soil erosion, and lead to desertification

Reforestation is the process of restoring a forest that once existed but was removed.

1. Case Study of People’s Participation in Conservation of Forests:
In 1731, the king of Jodhpur in Rajasthan asked one of his ministers to arrange wood for constructing a new palace. The minister and workers went to a forest near a village, inhabited by Bishnois, to cut down trees. Bishnois are opposed the act of ministers. Of which Amrita Devi-.her three daughters and hundreds of other Bishnois followed her, and thus lost their lives saving trees.

The Government of India has recently established the Amrita Devi Bishnoi Wildlife Protection Award for individuals or communities from rural areas that have shown extraordinary courage and dedication in protecting wildlife.

Another movement started at Garhwal Himalaya in 1974 was – Chipko Movement, here local women showed enormous bravery in protecting trees from the axe of contractors.

In 1980s Government of India has introduced the concept of Joint Forest Management (JFM) this is helpful to local communities for getting benefit of various forest products (e.g., fruits, gum, rubber, medicine, etc.) and thus the forest can be conserved in a sustainable manner.

Students can Download Chapter 9 Differential Equations Notes, Plus Two Maths Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Maths Notes Chapter 9 Differential Equations

Introduction
An equation involving derivatives of a dependent variable with respect to one or more independent variables is called a Differential Equation. In this chapter we study the method formation of a Differential Equation and solving of a Differential Equation.

I. Degree and Order of a DE
Order of a DE is defined as the order of the highest order derivative of the dependent variable with respect to the independent variable involved in the given DE.

Degree of a DE is defined as the exponent of highest differential coefficient appearing in the equation provided the equation is made into polynomial form in all differential coefficient.

II. Formation of a DE
To form a DE from a given function we differentiate the function successively as many times as the number of arbitrary constants in the equation and eliminate the arbitrary constant.

III. Solution of a DE
1. Variable Separable Type:
A DE of the form mdx = ndy Where m is a function in x alone or a constant and n is a function y alone or a constant.
Solution is ∫mdx = ∫ndy + c.

2. Homogeneous DE:
A DE of the form \(\frac{d y}{d x}=\frac{f(x, y)}{g(x, y)}\), where f(x, y) and g(x, y) are homogeneous equations in x and y. Solution is put y = vx ⇒ \(\frac{d y}{d x}=v+x \frac{d v}{d x}\) after simplification DE will be converted into variable separable type.

3. Linear DE:
A DE of the form \(\frac{d y}{d x}\) + Py = Q, where P and Q dx are function in x alone or a constant.
Solution is IF = e^∫Pdx
⇒ y(IF) = ∫Q(IF)dx + c.

A DE of the form \(\frac{d x}{d y}\) + px = Q, where P and Q are function in y alone or a constant.
Solution is IF = e^∫Pdy
⇒ x(IF) = ∫Q(IF)dy + c.

Students can Download Chapter 2 Sexual Reproduction in Flowering Plants Notes, Plus Two Botany Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Botany Notes Chapter 2 Sexual Reproduction in Flowering Plants

Flower – A Fascinating Organ Of Angiosperms
Flower shows aesthetic, ornamental, social, religious and cultural importance. They are used as symbols for conveying human feelings such as love, affection, happiness, grief etc.

Pre-Fertilisation: Structures And Events
The Hormonal and Structural changes leads to the differentiation and development of the floral primordium.

In the flower the male reproductive structure is the androecium, it consists of a whorl of stamens. The female reproductive structure is gynoecium, it consists of pistils.

1. Stamen, Microsporangium and Pollen Grain:
A typical stamen consist of the long and slender stalk called the filament, and the bilobed structure called the anther. The number and length of stamens are variable in flowers of different species.

A typical angiosperm anther is bilobed i.e. dithecous.
It is a four-sided (tetragonal) structure consisting of four microsporangia located at the corners, two in each lobe. The microsporangia develop further and become pollen sacs.

Structure of microsporangium:
In young condition anther consist of cells called the sporogenous tissue. It is surrounded by four wall layers.

1. Epidermis
2. Endothecium
3. Middle layers
4. Tapetum.

The outer three wall layers shows protective function and help in breaking of anther to release the pollen. The innermost wall layer is the tapetum possessing more than one nucleus. It nourishes the developing pollen grains.

Microsporoqenesis:
During the development of anther, cells of the sporogenous tissue undergo meiotic divisions to form microspore tetrads. This is called microsporogenesis.

At maturity the microspores dissociate from each other and develop into pollen grains.

Pollen grain:
Pollen grain has hard outer layer called the exine, it is made up of sporopollenin (resistant organic material- not degraded by enzyme).

Exine surface shows Germ pores through which pollen tube come out. Exine shows different patterns and designs.

Pollen grains are well preserved as fossils because of the presence of sporopollenin.

The inner wall of the pollen grain is called the intine. It is thin and continuous layer made up of cellulose and pectin. The cytoplasm of pollen grain is surrounded by a plasma membrane.

When the pollen grain mature, it contains two cells, the bigger vegetative cell and the smaller generative cell.

About 60 per cent of angiosperms, pollen grains are shed at 2-celled stage. In the remaining species, the generative cell divides mitotically and give rise to the two male gametes before pollen grains are shed (3-celled stage).

Pollen grains of many species cause severe allergies and bronchial infections leading to chronic respiratory disorders- asthma, bronchitis, etc. For example Parthenium or carrot grass causes pollen allergy.

Pollen grains are nutritious
The pollen tablets are used as food supplements. In western countries pollen products are used as tablets and syrups. Pollen consumption is important to increase the performance of athletes and race horses.

Pollen products

The viability of pollen grains is important in the success of fertilisation. The period of viability of pollen grains is variable and depends on the temperature and humidity.

In some cereals such as rice and wheat, pollen grains lose its viability within 30 minutes of their release, and in some members of Rosaceae, Leguminosae and Solanaceae, they maintain viability for months.

Pollen grains can be stored for years in liquid nitrogen (-1960C). Such stored pollen can be used as pollen banks for future use.

2. The Pistil, Meqasporangium (ovule) and Embryo sac:
The gynoecium is the female reproductive part. It consist of a single pistil (monocarpellary) or more than one pistil (multicarpellary). If more than one pistils are fused togetherthey are called syncarpous or free they are called apocarpous.

Each pistil has three parts the stigma, style and ovary. The stigma is the place where pollen grains falls. The style is the elongated slender part beneath the stigma.

The broad basal part of the pistil is the ovary. Inside the ovary is the ovarian cavity (locule). The placenta is located inside the ovarian cavity. The number of ovules in an ovary are different. It is one (wheat,paddy, mango) to many (papaya, water melon, orchids).

The Megasporangium (Ovule):
The ovule is a small structure attached to the p|acenta by means of a stalk called funicle. The body of the ovule fuses with funicle in the region called hilum (junction between ovule and funicle).

Each ovule has one or two protective envelopes called integuments. It covers entire ovule except at the tip where a small opening called the micropyle.

Opposite the micropylar end, is the chalaza, representing the basal part of the ovule. Enclosed within the integuments is a mass of cells called the nucellus.

Cells of the nucellus have abundant reserve food materials. Embryo sac or female gametophyte is located at there.

Ovule structure

Megasporoqenesis:
It is the process of formation of megaspores from the megaspore mother cell. A single megaspore mother cell (MMC) is differentiates in the micropylar region of the nucellus.

It is a large cell containing dense cytoplasm and a prominent nucleus. The MMC undergoes meiotic division to form female gametophyte.

In most flowering plants, only one megaspore is functional while other three degenerates. Functional megaspore develops into the female gametophyte (embryosac). This is termed as monosporic development.

The nucleus of the functional megaspore undergoes three repeated mitotic division to form 8 nucleate embryosac. After the 8-nucleate stage, cell walls are formed leading to the organisation of the typical female gametophyte or embryo sac.

Six of the eight nuclei are surrounded by cell walls and organised into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell.

Three cells are arranged at the micropylar end and constitute the egg apparatus. It consists of two synergids and one egg cell. The synergids have special cellular thickenings at the micropylartip called filiform apparatus, it helps to guide the pollen tubes into the synergid.

Three cells at the chalazal end are called the antipodals. The large central cell has two polar nuclei.

Angiosperm embryo sac at maturity is 8-nucleate and 7-celled.

3. Pollination:
It is the transfer of pollen grains to the stigma of a pistil.

Kinds of Pollination:
Depending on the source of pollen, pollination is divided into three types,
(i) Autogamy:
It is the transfer of pollen grains from the anther to the stigma of the same flower. In such flowers pollen release and stigma receptivity are at the same time and the anthers and the stigma should lie close to each other.

Some plants such as Viola, Oxalis, and Commelina produce two types of flowers – chasmogamous flowers (exposed anthers and stigma) and cleistogamous flowers (do not open flower). Cleistogamous flowers possible to the seed-set even in the absence of Pollinators.

Cleistogamous flowers

(ii) Geitonogamy:
Transfer of pollen grains from the anther to the stigma of another flower of the same plant. Functionally geitonogamy is a type of crosspollination but it is genetically similar to autogamy since the pollen grains come from the same plant.

(iii) Xenogamy:
Transfer of pollen grains from anther to the stigma of a different plant. This type of pollination occurs between genetically different species.

Agents of Pollination:
Pollination takesplace with abiotic (wind and water) and biotic (animals) agents. Majority of plants use biotic agents for pollination.

Wind pollination:
Pollen grains are light and non-sticky. They possess well-exposed stamens and feathery stigma. Such flowers have a single ovule in each ovary and numerous flowers packed into an inflorescence.
Example -corn cob – Here stigma and style which wave in the wind to trap pollen grains. Wind-pollination is more common in grasses.

Wind pollinated plant with well expesed stamens

Water Pollination:
Water Pollinated plants are mostly monocotyledons. In the lower plants such as algae, bryophytes and pteridophytes required water for the transport of male gametes and fertilisation.

Some examples of water pollinated plants are Vallisneria and Hydrilla (fresh water) and Zostera (marine sea- grasses).

In Vallisneria, the female flower reach the surface of water by the long stalk and the male flowers or pollen grains are released on to the surface of water. The anthers eventually reach the female flowers and the stigma.

In seagrasses, female flowers are submerged in water and the pollen grains are released inside the water. Pollen grains are long and ribbon like, some of them reach the stigma and results pollination.

In a majority of aquatic plants such as water hyacinth and water lily, the flowers emerge above the level of water and are pollinated by insects or wind.

In most of the water-pollinated species, pollen grains are protected from wetting by a mucilaginous covering. Both wind and water pollinated flowers are not very colourful and do not produce nectar.

Animal pollination:
Animals pollinating agents are Bees, butterflies, flies, beetles, wasps, ants, moths, birds (sunbirds and humming birds) and bats.

Bees are the dominant biotic pollinating agent.
Larger animals such as some primates (lemurs), arboreal (tree-dwelling) rodents, or even reptiles (gecko lizard and garden lizard) have also been reported as pollinators in some species.

Features of animal pollinated flowers are Flowers are large, colourful, fragrant and rich in nectar, the small flowers are clustered Into an inflorescence to make them conspicuous.

The flowers pollinated by flies and beetles secrete foul odours to attract these animals. Flowers in turn provide rewards to the animals in the form of Nectar and pollen grains.

In some species flower provide safe places to lay eggs. Eg-tallest flower of Amorphophallus (Flower- 6 feet in height).

The plant Yucca and moth cannot complete their life cycles without each other. The moth deposits its eggs in the locule of the ovary and the flower in turn gets pollinated by the moth. The larvae of the moth come out of the eggs as the seeds start developing.

Outbreeding Devices
In plants the continued self-pollination result in inbreeding depression. Flowering plants have some devices to prevent self pollination and to promote cross pollination.

1. In some species, pollen release and stigma receptivity are not at the same time.
2. In some other species, the anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower. Both these devices prevent autogamy.
3. In some other species self-incompatibility is the genetic mechanism Here pollen cannot germinate on the stigma of the same flower or other flowers of the same plant by inhibiting pollen germination or pollen tube growth in the pistil.
4. Another device to prevent self-pollination is the production of unisexual flowers. If both male and female flowers are present on the same plant such as castor and maize (monoecious), it prevents autogamy but not geitonogamy.

In papaya, male and female flowers are present on different plants. This condition prevents both autogamy and geitonogamy.

Pollen-pistil Interaction:
After pollination, the pistil recognize pollen of the wrong type( incompatible )or the right type(compatible). If it is of the right type, the pistil accepts the pollen and promotes post-pollination events that leads to fertilisation. If the pollen is of the wrong type, the pistil rejects the pollen by preventing pollen germination on the stigma or the pollen tube growth in the style.

Pollen-pistil interaction is a kind of dialogue mediated by chemical components of the pollen interacting with those of the pistil.

Pollen tube grows through the tissues of the stigma and style and reaches the ovary. The generative cell divides and forms the two male gametes during the growth of pollen tube in the stylar region.

Then it enters into the ovule through the micropyle and reaches the synergids. It is reported that filiform apparatus present at the micropylar part of the synergids guides the entry of pollen tube.

Artificial hybridization:
It is the method for the crop improvement programme. It aims for the creation of’superior’ varieties.lt is done by emasculation and bagging techniques.

Anthers are removed by using forceps before the dehiscence of anther of female parent that bears bisexual flowers. This step is called as emasculation. It is covered with a bag of suitable size, to prevent contamination of its stigma with unwanted pollen. This process is called bagging. When the stigma of bagged flower attains receptivity, mature pollen grains collected from anthers of the male parent are dusted on the stigma, and the flowers are rebagged, and the fruits allowed to develop.

Emasculation is not necessary for unisexual flowers. Here female flower buds are bagged before the flowers open. When the stigma becomes receptive, pollination is carried out using the desired pollen and the flower rebagged.

Double Fertilisation
By the help of filifiorm apparatus the pollen tube releases the two male gametes into the cytoplasm of the synergid. Then it fuses with the egg cell to form diploid zygote. This process is called syngamy.

The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid primary endosperm nucleus (PEN). This type of fusion contains three haploid nuclei, it is called triple fusion.

Therefore syngamy and triple fusion take place in an embryo sac, the phenomenon is called as Double fertilization. The central cell after triple fusion becomes the primary endosperm cell (PEC) and develops into the endosperm while the zygote develops into an embryo.

Post-Fertilisation: Structures And Events
Double fertilization leads to the development of endosperm and embryo, maturation of ovule into seed and ovary into fruit. These are called as post-fertilisation events.

1. Endosperm:
It serve as nutrition for the developing embryo. In most plants, the PEN undergoes successive nuclear divisions to give rise to free nuclei. This stage of endosperm development is called free-nuclear endosperm. Later cell wall formation occurs and the endosperm becomes cellular.

The tender coconut contains free-nuclear endosperm and the surrounding white kernel is the cellular endosperm. Some times the endosperm completely consumed by the developing embryo (e.g., pea, groundnut, beans) before seed maturation or it is persist in the mature seed (e.g. castor and coconut) and be used up during seed germination.

2. Embryo:
The micropylarend of the embrysac sac contains zygotes which divide only after the endosperm is formed. The early stages of embryo development (embryogeny) are similar in both monocotyledons and dicotyledons.

The zygote gives rise to the proembryo and subsequently to the globular, heart-shaped and mature embryo.

Dicotyledonous embryo consists of an embryonal axis and two cotyledons. The portion of embryonal axis above cotyledons is the epicotyl, which terminates with the plumule. The cylindrical portion below the cotyledons is hypocotyl that terminates at its lower end in the radical or root tip. The root tip is covered with a root cap.

Embryos of monocotyledons possess only one cotyledon. In the grass family the cotyledon is called scutellum that rs situated towards one side of the embryonal axis. At its lower end, the embryonal axis consists of radical and root cap enclosed by sheath called coleorhiza.

The portion of the embryonal axis above the level of attachment of scutellum is the epicotyl. Epicotyl has a shoot apex and a few leaf primordia enclosed by a sheath called the coleoptile.

3. Seed:
In angiosperms, the seed is the fertilised ovule. Seeds are formed inside fruits. It consists of seed coat, cotyledon and an embryo axis. The cotyledons stores food reserves.

Non-albuminous seeds have no endosperm because it consumed during embryo development (e.g., pea, groundnut). Albuminous seeds retain endosperm because it is not completely used up in embryo development (e.g., wheat, maize, barley, castor, sunflower).

In some seeds such as black pepper and beet, the remnants of nucellus are persistent. This persistent nucellus is called the perisperm

The micropylar region facilitates entry of oxygen and water into the seed during germination. As the seed matures, its water content is reduced and metabolic activity of the embryo slows down. This inactive state of embryo is called dormancy.

If seed get suitable conditions, they germinates. During the embryo development ovules mature into seeds, the ovary develops into a fruit, integuments of ovules develops into seed coats and ovary wall becomes wall of fruit called pericarp.

Many fruits have evolved mechanisms for dispersal of seeds.

1. In some species such as apple, strawberry, cashew, etc., the thalamus develops to form fruit. Such fruits are called false fruits 2. Fruits develops only from the ovary, they are called true fruits. 3. In some species fruits develop without fertilization, they are called. Parthenocarpic fruits, eg- Banana. Parthenocarpy cgn be induced by the use of growth hormones. Such fruits are seedless.

Dehydration and dormancy of mature seeds are important for storage So this is advantageous and to be used as food through out the year and also to raise crop in the next season.

In some species, the seeds lose viability within a few months but some seeds can remain alive for hundreds of years.

• The oldest seed is lupine, Lupinus arcticus excavated from Arctic Tundra.
• The seed germinated and flowered after of 10,000 years of dormancy.
• The 2000 years old viable seed – Date palm, Phoenixdactylifera discovered during the archeological excavation at King Herod’s palace near the Dead Sea.

Apomixis And Polyembryony
In some flowering plant species of Asteraceae and grasses produce seeds without fertilisation, it is called apomixis.

Apomixis is a form of asexual reproduction that mimics sexual reproduction. In some species, the diploid egg cell is formed without reduction division and develops into the embryo without fertilisation.

But in a few species of Citrus and Mango, the nucellar cells surrounding the embryo sac develop into the embryos. In such species each ovule contains many embryos. The occurrence of more than one embryo in a seed is called polyembryony.

Hybrids are widely used in cultivation as food and vegetable crops because of increased productivity, but their production is expensive for the farmers.

If these hybrids are made into apomicts, there is no segregation of characters in the hybrid progeny. So the farmers can use these apomictic seeds to raise new crop year after year without losing the desirable characters.

Students can Download Chapter 7 Ecosystem Notes, Plus Two Botany Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Botany Notes Chapter 7 Ecosystem

Ecosystem – structure And Function
Interaction of biotic and abiotic components form the physical structure that is characteristic for each type of ecosystem. Different types of plant and animal species of an ecosystem gives its species composition. Life of species occupying different strata is called stratification For example, trees occupy top vertical strata of a forest, shrubs and herbs and grasses occupy the bottom layers.

The components of the ecosystem are seen to function as a unit, they are

(i) Productivity; (ii) Decomposition; (iii) Energy flow; and (iv) Nutrient cycling.

Productivity
The primary energy source for functioning of an ecosystem is solar energy.

The amount of food energy produced by a particular trophic level per unit area in a time or rate of biomass production is called productivity.

It is highest in a coral reef of aquatic ecosystems and in tropical rain forest of terrestrial ecosystems
Productivity is of two types

(a) Primary productivity:
It refers to the productivity at producer level. It is divided into two

1. Gross primary productivity – It refers to total photosynthesis i.e total amount of food formed by the producers
2. Net primary productivity – It refers to gross production minus losses by respiration and decomposition.

(b) Secondary productivity:
It is defined as the rate of formation of new organic matter by consumers. The annual net primary productivity of the whole biosphere is approximately 170 billion tons (dry weight) of organic matter.

Decomposition

Decomposition is the process by which complex organic compounds are broken into simpler and inorganic substances.

Decomposition is a complex process of enzymatic reaction and involves the step-wise degradation of detritus (dead organic matter and excreta of animals and plants). It involves following processes.

Fragmentation of detritus:
Leaching:
It is process by which simple and water soluble compounds like simple sugars and inorganic nutrients move downward along with percolating gravitational water.

Catabolism:
It is the enzymatic break down of organic compound.

Humification:
It is process by which simplified detritus is changed into dark coloured amorphous substance called humus.

Mineralisation:
It involves the release of inorganic subtances (Water, C02, etc) and other nutrients (NH4+, Ca++, Mg++, K+, etc.) in the soil.
Decomposition cycle in terrestrial ecosystem:

Decomposition is largely an oxygen-requiring process. The rate of decomposition is controlled by chemical composition of detritus and climatic factors.

Decomposition rate is slower if detritus is rich in lignin and chitin, and quicker, if detritus is rich in nitrogen and water-soluble substances like sugars.

Warm and moist environment favour decomposition whereas low temperature and anaerobic condition inhibit decomposition and accumulation of organic materials.

Energy flow
Of the incident solar radiation less than 50 percent of it is photosynthetically active radiation (PAR). Plants capture only 2-10 percent of the PAR. solar energy captured by plants flows through different organisms of an ecosystem.

Energy flow is the key function of an ecosystem. It is determined by two basic laws of thermodynamics.

First law of thermodynamics states that energy is neither created nor destroyed, but can betransffered from one component to another, or transformed from one state to another.

Second law of thermodynamics states that every energy transformation involves degradation or dissipation of energy from a concentrated to a dispersed form due to metabolic functions. Dissipation of energy occures as heat. The remaining energy used in the synthesis of plant biomass.

Producers in a terrestrial ecosystem, include herbaceous and woody plants and an aquatic ecosystem are species like phytoplankton, algae, and higher plants. The energy trapped by the producer is passed on to a consumer.

They are hence called consumers. If animals feed on the producers, they are called primary consumers (herbivores.), and if the animals eat other animals which in turn eat the plants they are called secondary consumers.

The consumers that feed on these herbivores are carnivores, i.e primary carnivores Those animals that depend on the primary carnivores for food are called as secondary carnivores.
A simple grazing food chain (GFC) is depicted below:

The detritus food chain (DFC) begins with dead organic matter. It is made up of decomposers which are heterotrophic organisms, mainly fungi, and bacteria. They get energy from dead organic matter or detritus. These are also known as saprotrophs.

In an aquatic ecosystem, energy flow occurs through GFC. In a terrestrial ecosystem, a much larger fraction of energy flows through the detritus food chain than through the GFC.

Detritus food chain is connected with the grazing food chain at some levels: some animals in an ecosystem are Omnivores, eg-cockroaches, crows, etc. These natural interconnections of food chains make it a food web.
Trophic levels in an ecosystem:

The different steps of food chain is known as trophic level. Producers belong to the first trophic level, herbivores (primary consumer) to the second and carnivores (secondary consumer) to the third. The amount of energy decreases at successive trophic levels. Detritus or dead biomass that serves as an energy source for decomposers.

Each trophic level has a certain mass of living material at a particular time called as the standing crop. The standing crop is measured as the mass of living organisms (biomass).

In food chain the energy transfer from one trophic level to the next is 10%.

Energy flow through different trophic levels:

Ecological pyramids
An ecological pyramid is a graphical representation of an ecological parameter, like number or biomass or accumulated energy at different trophic levels in a food chain in as ecosystem.
The three ecological pyramids are

(a) pyramid of number; (b) pyramid of biomass and (c) pyramid of energy.

The idea of ecological pyramids was developed by Charles Elton. An ecological pyramid may be upright (taping towards the tip) or inverted (widens towards the tip).

The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top level consumer.

In most ecosystems, all the pyramids, of number, of energy, and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores. Also energy at a lower trophic level is always more than at a higher level.

The pyramid of biomass in sea is inverted because the biomass of fishes is more than Phytoplankton. Pyramid of energy is always upright, because energy level decreases in successive trophic level some energy is always lost as heat at each step.

Ecological Succession
The successive replacement of biotic communities in an area over a period of time is known as ecological or biotic succession.

The first community to inhabit area is called pioneer community while the last and stable community in an area is called climax community. The intermediate communities between the pioneer and climax communities are called transitional or serai communities.

Basic types of succession:
Primary succession:
Primary succession which starts from the primitive substratum, where there was no previously any sort of living matter e.g. land formed by volcanic lava, development of forest climax on a barren land may take about 1,000 years.

Secondary Succession:
Secondary succession which starts from previously built up substrata with already existing living matter. Such areas include burned or cut forests, flooded lands, etc. such successions are comparatively more rapid. Time taken is about 50 – 100 years in case of a grassland and about 100 – 200 years for a forest.

1. Succession of Plants:
Depending mainly upon the nature of the environment succession is of two types hydrarch-starting in regions where water is in plenty, xerarch- where moisture is present in minimal amounts such as dry deserts, rocks, etc.

If succession occurs in medium water conditions, they are called mesarch.

Xerarch It involves the ecological succession on bare rock surfaces. The various stages in the ecological succession in a xerarch are (1) Crustose lichens stage – It forms the poineer community in a lithosere and is represented by lichen species. These produce organic acids which cause weathering of rocks. (2) Foliose lichens stage – It includes the lichens with leafy thalli. (3) Moss stage – It is characterised by growth of mosses (4) Herbs stage – short plant with soft stem (5) Shrub stage – medium sized plant with soft stem (6) Forest stage – It is the climax community depends upon the nature of climate eg a rain forest in a moist tropical area; a coniferrous forest or deciduous forest in temperature area; a grassland in area with less rainfall etc.

Hydrarch:
It involves the ecological succession in the newly formed pond or lake.

(a) phytoplankton stage. (b) Submerged plant stage. Hydrilla, Vallisneria, Utricularia (c) Submerged free floating plant Stage -It includes nymphaea.nelumbium, etc. (d) Reed swamp stage. It is also called amphibious stage It includes the plant species like sagittaria, Typha etc. (f) Marsh – meadow stage. It is mainly formed of plant species like Carex (sedge). They form a mat-like vegetation towards the centre of the pond (g) Scrub stage. In this stage the area is invaded by some shrubby plants which can tolerate bright sunlight as well as waterlogged conditions (h) Forest stage. It is the climax community

Nutrient Cycling

The amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc. present in the soil at any given time, is referred to as the standing state.

It varies in different kinds of ecosystems. Nutrients are continuously exchanged between organisms and their physical environment. These exchanges are called nutrient cycling / biogeochemical cycles.
Nutrient cycles are of two types:

1. gaseous and
2. sedimentary

Cycles of gaseous matter are called gaseous cycles. The reservoir of gaseous matter is atmosphere, (e.g.,
nitrogen, carbon cycle).

Cycles of mineral matter are called Sedimentary cycles. The reservoir of mineral matter is lithosphere, (e.g., sulphur and phosphorus cycle.)

1. Ecosystem – Carbon Cycle:
Carbon cycling occurs through atmosphere, ocean and through living and dead organisms. The amount of carbon fixed in the biosphere through photosynthesis annually is 4 × 1013 kg. Decomposition of dead organic matter and fossil fuel, through respiratory activities, burning of wood, forest fire, deforestation and volcanic activity releasing CO₂ in the atmosphere.
Carbon cycle in biosphere:

2. Ecosystem – Phosphorus Cycle:
Phosphorus is a major component of biological membranes, nucleic acids, and cellular energy transfer systems. The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates.

When rocks are weathered, minute amounts of these phosphates dissolve in soil solution and are absorbed by the roots of the plants. The waste products and the dead organisms are decomposed by phosphate-solubilising bacteria releasing phosphorus.

Ecosystem Services
The products of ecosystem processes are named as ecosystem services, for example,

healthy forest ecosystems purify air and water, mitigate droughts and floods, cycle nutrients, generate fertile soils, provide wildlife habitat, maintain biodiversity, pollinate crops, provide storage site for carbon and also provide aesthetic, cultural and spiritual values.

Robert Constanza and his colleagues have very recently tried to put price tags on nature’s life-support services. Researchers have put an average price tag of US $ 33 trillion a year on these fundamental ecosystems services. It is nearly twice the value of the global gross national product GNP which is US $ 18 trillion. Out of the total cost of various ecosystem services.

The soil formation accounts for about 60 per cent, and contributions of other services like recreation and nutrient cycling, are less than 10 per cent each. The cost of climate regulation and habitat for wildlife are about 6 per cent each.

Students can Download Chapter 3 Principles of Inheritance and Variation Notes, Plus Two Zoology Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Zoology Notes Chapter 3 Principles of Inheritance and Variation

Mendel’s Laws Of Inheritance
Gregor Mendel, conducted hybridisation experiments on garden peas and proposed the laws of inheritance in living organisms.

Mendel selected 14 true-breeding pea plant varieties, as pairs with contrasting traits.

Inheritance Of One Gene
Mendel crossed tall and dwarf pea plants to study the inheritance of one gene. He collected the seeds produced as a result of this cross and grew them to generate plants of the first hybrid generation. This is called the Filial progeny or the F1.

The F1 progeny plants were tall. Mendel then self-pollinated the tall F1 plants and to raise the second Filial generation The result was that 3 tall and 1 dwarf.

Based on these observations,
Mendel proposed that ‘factors’ (genes) transmitted from parent to offspring through the gametes, over successive generations.

Genes which code for a pair of contrasting traits are known as alleles, i.e., they are alternative forms of the same gene.

Figure: A Punnett square used to understand a typical monohybrid cross conducted by Mendel between true-breeding tall plants and true-breeding dwarf plants.

According to Mendels experiment, true breeding tall are identical or homozygous TT and true breeding dwarf pea variety are also homozygous tt.

TT and tt are called the genotype of the plant while the terms tall and dwarf are the phenotype.

The production of gametes and the formation of the zygotes in the F1 and F2 plants can be understood from a diagram called Punnett Square.

The possible gametes are written on two sides, usually the top row and left columns. All possible combinations are represented in boxes below in the squares.

In the cross of tall TT(male) and dwarf tt (female) plants, the gametes produced by them are represented by T and t respectively. The all F₁ is Tt progeny.

The F₁ plants of genotype Tf are self-pollinated. They produces gametes of the genotype T and fin equal proportion. When fertilisation takes place, the pollen grains of genotype T have a 50 percent chance to pollinate eggs of the genotype T, as well as of genotype t.

At F2, 3/4th of the plants are tall ,(of which 1/2 are Tt and only 1/4th are TT) and 1/4th are dwarf tt, i.e., phenotypic ratio is 3:1. and the genotypic ratio is 1 : 2 : 1.

From the Punnet square it is clearthat 1/4th of the random fertilisations lead to TT, 1/2 lead to Tt and 1/4th to tt.

For determining the genotype of a tall plant at F2, Mendel crossed the tall plant from F2 with a dwarf plant. This is called a test cross.

Diagrammatic representation of a test cross:

Based on his observations on monohybrid crosses Mendel proposed two general rules first law is Law of Dominance and the Second Law or Law of Segregation.

1. Law of Dominance:

(i) Characters are controlled by discrete units called factors.

(ii) Factors occur in pairs.

(iii) In a dissimilar pair of factors one member of the pair dominates (dominant) the other (recessive).

The law of dominance explains the ratio of 3:1 in F2.

2. Law of Segregation:

According to these law the parents contain two alleles, during gamete formation, alleles of a pair segregate from each other and the gamete receives only one of the two alleles.

A homozygous parent produces all gametes that are similar while a heterozygous one produces two kinds of gametes.

Non mendelian inheritance:
a. Incomplete Dominance:
F1 phenotype not resemble either of the two parents The inheritance of flower colour in the dog flower (snapdragon or Antirrhinum sp.) is a good example.

In a cross between true-breeding red-flowered (RR) and true breeding white-flowered plants (rr), the F1 (Rr) was pink.


Explanation of the concept of dominance:
Here the normal allele produces the normal enzyme that is needed for the transformation of a substrate S the modified allele is responsible for production of –

1. the normal/less efficient enzyme, or
2. a non-functional enzyme, or
3. no enzyme at all

In the case(i), the modified allele is equal to the unmodified allele,

Figure: Results of monohybrid cross in the plant Snapdragon, where one allele is incompletely dominant over the other allele.

But in the case (ii) and (iii) if the allele produces a non-functional enzyme or no enzyme, the phenotype may be effected.

The unmodified (functioning) allele, which represents the original phenotype is the dominant allele and the modified allele is the recessive allele. So the recessive trait arise due to non-functional enzyme or because no enzyme is produced.

b. Co-dominance
Here F1 generation resembles both parents. A good example is different types of red blood cells that determine ABO blood grouping in human beings.

ABO blood groups are controlled by the gene I. The gene (I) has three alleles I^A, I^A and i. The alleles I^A and I^B produce a slightly different form of the sugar while allele i doesn’t produce any sugar.

So I^A and I^B are completely dominant over i, and when I^A and i are present only I^A expresses and when I^B and i are present I^B expresses.

when I^A and I^B are present together they both express their own types of sugars: this is because of codominance.

ABO blood grouping is a good example of multiple alleles. Here a single gene produce more than one effect.

For example, starch synthesis in pea seeds is controlled by one gene. It has two alleles (B and b). Starch is synthesised by BB homozygotes and bb homozygotes have lesser efficiency in starch synthesis.

After maturation of the seeds, BB seeds are round and the bb seeds are wrinkled. Heterozygotes produce
round seeds, and so B seems to be the dominant allele. But, the starch grains produced are of intermediate size in Bb seeds.

Inheritance Of Two Genes
Mendel crossed pea plant seeds with yellow colour and round shape and seeds of green colour and wrinkled shape. Yellow colour was dominant over green and round shape dominant over wrinkled.

Y for dominant yellow seed colour and y for recessive green seed colour, R for round shaped seeds and r for wrinkled seed shape. The genotypes of the parents are RRYY and rryy.

The gametes RY and ry unite on fertilisation to produce the F1 hybrid RrYy. When Mendel self hybridised the F1 plants and found that the ratio in F2 is 9:3:3:1.

Phenotypic ratio: round yellow(9) : round green(3) : wrinkled yellow (3) : wrinkled green(1).
Figure: Result s of a dihybrid cross where the two parents differed in two pairs of contrasting traits: seed colour and seed shape.

1. Law of Independent Assortment:
Based on dihybrid crosses (crosses between plants differing in two traits) Mendel proposed Law of Independent Assortment.

The law states that when two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters’.

In the dihybrid cross the phenotypes round-yellow; Wrinkled- yellow; round- green and wrinkled- green appeared in the ratio 9:3:3:1.

The segregation of 50 percent R and 50 per cent ris independent from the segregation of 50 percent Y and 50 percent y. Therefore, 50 percent of the r bearing gamete has Y and the other 50 percent has y.

Similarly, 50 percent of the R bearing gamete has Yand the other 50 percent hasy. Thus there are four genotypes of gametes (four types of pollen and four types of eggs). The four types are RY, Ry, rY and ry.

2. Chromosomal Theory of Inheritance:
According to Mendel law, factors (genes) are discrete units, but its existence was not proved In 1900, three Scientists (de Vries, Correns and von Tschermak) independently rediscovered Mendel’s results on the inheritance of characters.

Walter Sutton and Theodore Boveri noted that the behaviour of chromosomes was parallel to the behaviour of genes and used chromosome movement to explain Mendel’s laws.

The chromosomes as well as genes occur in pairs. The two alleles of a gene pair are located on homologous sites on homologous chromosomes. During Anaphase of meiosis I, the two chromosome pairs can align at the metaphase plate independently of each other. So the pairing and separation of a pair of chromosomes would lead to the segregation of a pair of factors they carried.

Sutton united the chromosomal segregation with Mendelian principles and called as chromosomal theory of inheritance.

Experimental proof for the chromosomal theory of inheritance was given by Thomas Hunt Morgan and his colleagues. This led to discovery that variation occurs during sexual reproduction His studies were conducted on tiny fruit files, Drosophila melanogaster.

They have short life cycle (two weeks), and a single mating could produce a large number j of progeny flies. The male and female flies are distinguishable and hereditary variations can be seen.

3. Linkage and Recombination:
Morgans dihybrid crosses in Drosophila reveals genes that are sex-linked.

For example yellow-bodied, white-eyed females crossed with brown-bodied, red-eyed males and intercrossed their F1 progeny. The F2 ratio was different from the expected 9:3:3:1. Because the two genes are not segregated independently located on the X same chromosome.

They found that some genes were very tightly linked (showed very low recombination), while others were loosely linked (showed higher recombination).

For example the genes for the white and yellow were very tightly linked and showed only 1.3 per cent recombination while white and miniature wing showed 37.2 per cent recombination.

His student Alfred Sturtevant found that frequency of recombination between gene pairs on the same chromosome is equivalent to the distance between genes and ‘mapped’ their position on the chromosome.

Sex Determination
Henking (1891) studied the spermatogenesis in an insects and X body. The ‘X body’ of Henking was given the name X-chromosome (sex chromosome).

Grasshopper is an example of XO type of sex determination in which the males have only one X-choromosome besides the autosomes, whereas females have a pair of X-chromosomes.

Insects and mammals including man:
XY type of sex determination is seen where both male (XY- heterogametic) and female (XX- homogametic) have same number of chromosomes. Both males and females bear same number of autosomes. i.e males have autosomes plus XY, while female have autosomes plus XX.

Male heterogamety:
In XO type and XY type, males produce two different types of gametes, Such types of sex determination mechanism is seen in drosophila and human male respectively.

Female heterogamety:
In birds the total number of chromosome is same in both males and females. But females produce two types of gametes.

Female birds have one Z and one W chromosome, where as males have a pair of Z-chromosomes besides the autosomes.

1. Sex Determination in Humans:
Out of 23 pairs of chromosomes, 22 pairs are same in both males and females; these are the autosomes. A pair of X-chromosomes are present in the female, whereas X and Y chromosome are present in males.

During spermatogenesis two types of gametes are produced of which 50 per cent carry the X- chromosome and the rest 50 per cent has Y-chromosome besides the autosomes.

Females produce only one type of ovum with an X-chromosome. In case the ovum fertilises with a sperm carrying X-chromosome the zygote develops into a female (XX) and with Y-chromosome results into a male offspring.

Thus the genetic makeup of the sperm that determines the sex of the child.

Mutation
It is the sudden change in the genetic make up of an organism. The loss (deletions) or gain (insertion/ duplication) of a segment of DNA, result in alteration in chromosomes. Alteration in chromosomes results in abnormalities or aberrations.

If the mutation also arise due to change in a single base pair of DNA. This is known as point mutation. Eg- sickle cell anemia.

Deletions and insertions of base pairs of DNA, causes frame-shift mutations.

There are many chemical and physical factors that induce mutations. They are called as mutagens. Eg- physical mutagen – UV radiations.

Genetic Disorders
1. Pedigree Analysis:
It is the study of the family history of inheritance of a particular trait. Such an analysis of traits in a several of generations of a family is called the pedigree analysis. For this the standard symbols are used.

In human beings it helps to trace the inheritance of a specific trait, abnormality or disease. A number of disorders in human beings have been found to be associated with the inheritance of altered genes or chromosomes.

2. Mendelian Disorders:
Genetic disorders are classified into two categories. Mendelian disorders and Chromosomal disorders.

Mendelian disorders (dominant or recessive) arise by alteration or mutation in the single gene.

Eg-Haemophilia, Cystic, fibrosis, Sickle-cell anaemia, Ctflour blindness, Phenylketonuria, Thalesemia, etc.

The pattern of inheritance can be traced in a family by the pedigree analysis.

Haemophilia:
Haemophilia is the X-linked recessive trait that is transmitted from carrier female to male progeny in the zig-zag manner (Sex linked recessive disease) This is the bleeders disease mainly observed in family of Queen Victoria.

In an affected individual a simple cut will result in non-stop bleeding. The heterozygous female (carrier) for haemophilia transmit the disease to sons.

Sickle-cell anaemia:
This is an autosome linked recessive trait transmitted from parents to the offspring when both the partners are carrier for the gene. The disease is controlled by a single pair of allele, HbA and HbS.

The homozygous individuals for HbS (Hb^SHb^S) show the diseased phenotype. Heterozygous (Hb^AHb^S) individuals are carrier of the disease.

The defect is caused by the substitution of Glutamic acid by Valine at the sixth position of the beta globin chain of the haemoglobin molecule.

It is due to the single base substitution at the sixth codon of the beta globin gene from GAG to GUG.

The mutant haemoglobin molecule under low oxygen tension causing the change in the shape of the RBC from biconcave disc to elongated sickle like structure.

Phenylketonuria:
This is an autosomal recessive trait. This is due to the deficiency of enzyme that converts the amino acid
phenylalanine into tyrosine. As a result of this phenylalanine is accumulated and converted into phenylpyruvic acid.

Accumulation of these in brain results in mental retardation. These are also excreted through urine.

3. Chromosomal disorders:
Failure of segregation or non-disjunction of chromosomes during cell division results in the gain or loss of a chromosome(s), called aneuploidy. For example

Down’s syndrome is the gain of extra copy of chromosome 21 and Turner’s syndrome is due the loss of an X chromosome in human females.

Failure of cytokinesis results in an increase in a whole set of chromosomes in an organism. This phenomenon is known as polyploidy. This is mainly seen in plants.

If an additional copy of a chromosome is added. This is called trisomy Eg- Down’s Syndrome and Klinefelter’s syndrome or lack of copy of a chromo^ome( monosomy) Eg- Turner’s syndrome.

Down’s Syndrome: (Trisomy of 21):
The affected individual is short statured with small round head, furrowed tongue and partially open mouth. Palm is broad with characteristic palm crease. Physical, psychomotor and mental development is retarded.

Klinefelter’s Syndrome:
This is due to the trisomy of sex chromosome 44 autosomes+XXY. Individuals show feminine development i.e development of breast, i.e., Gynaecomastia Such individuals are sterile.

Turner’s Syndrome:
This is due to absence of one of the X chromosomes, i.e. 44 autosomes+ XO, Such females are sterile. The ovaries are rudimentary and lack other secondary sexual characters.

Students can Download Chapter 6 Organisms and Populations Notes, Plus Two Botany Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Botany Notes Chapter 6 Organisms and Populations

Organism And Its Environment

The annual variations in the intensity and duration of temperature, resulting in distinct seasons. These variations together with annual variation in precipitation (precipitation includes both rain and snow) responsible for the formation of major biomes such as desert, rain forest and tundra.

Regional and local variations within each biome lead to the formation of a wide variety of habitats.

The existence of life not only in favourable habitat but it occurs in scorching Rajasthan desert, rain-soaked Meghalaya forests, deep ocean trenches, torrential streams, permafrost polar regions, high mountain tops, boiling thermal springs, and stinking compost pits.

1. Major Abiotic Factors:
Temperature:
The average temperature on land varies seasonally, it decreases from the equator towards the poles and from plains to the mountain tops. It ranges from minus degree Celsius in polar areas and high altitudes to more than 50°C in tropical deserts in summer.

It is clear that mango trees cannot grow in temperate countries like Canada and Germany, and the snow leopards are not found in Kerala forests.

Actually temperature affects the kinetics of enzymes which influence the basal metabolism, activity and other physiological functions of the organism.

A few organisms can tolerate and thrive in a wide range of temperatures they are called eurythermal, but majority of them are restricted to a narrow range of temperatures they are called stenothermal.

Water:
The productivity and distribution of plants is dependent on water. For aquatic organisms the quality (chemical composition, pH) of water is important.

The salt concentration (salinity in parts per thousand), is less than 5 per cent in inland waters, 30 – 35 per cent the sea and > 100 per cent in some hypersaline lagoons.

Some organisms can tolerate wide range of salinities, they are called euryhaline but others are restricted to a narrow range they are called stenohaline.

Freshwater animals cannot live for long in sea water and vice versa because of the osmotic problems.

Light:
It is an important factor for photosynthesis.

Small plants (herbs and shrubs) growing in forests are adapted to photosynthesise under very low light conditions because of tall canopied trees. Many plants require sunlight for the initiation of photoperiodic flowering.

Animals require the diurnal and seasonal variations in light intensity and duration (photoperiod) fortiming their foraging, reproductive, and migratory activities. The spectral quality of solar radiation is important for life.

The UV component of the spectrum is harmful to many organisms while other colour components of the visible spectrum are important for marine plants living at different depths of the ocean.

Soil:
The nature and properties of soil dependent on the climate and the weathering process. The characteristics of the soil determine the water holding capacity.

These characteristics, pH, mineral composition, and topography determine the vegetation in any area. In the aquatic environment, the sediment-characteristics determine the type of benthic animals in ocean.

2. Responses to Abiotic Factors:
During the course of millions of years many species would have evolved constant internal (within the body) environment that permits maximum efficiency of biochemical reactions and physiological functions that results overall ‘fitness’ of the species.

Some organism maintain the constant internal environment when the external environmental conditions changes it is called homeostasis.

A person is able to do his/her work in temperature is 25°C when it is extremely hot or cold outside. It could be achieved at home, in the car while travelling, and at workplace by using an air conditioner in summer and heater in winter. Here the person’s homeostasis is maintained by artificial means.

How do other living organisms cope with the situation?
(i) Regulate:
Some organisms maintain their homeostasis by keeping up constant body temperature, constant osmotic concentration, etc.

Birds, mammals, and some lower vertebrate and invertebrate species are capable of such regulation i.e thermoregulation and osmoregulation. This is the characteristics of mammals to live in Antarctica or in the Sahara desert.

In summer season body of man sweat, it provide cooling effect. In Winter season, vyhen the temperature is much lower than 37°C, man start to shiver, a kind of exercise which produces heat and raises the body temperature. Plants do not have such mechanisms to maintain internal temperatures.

(ii) Conform:
Majority of animals and all plants cannot maintain a constant internal environment.

Thermoregulation is energetically expensive for many organisms. This is true for small animals like shrews and humming birds. Small animals have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; so they have to spend much energy to generate body heat through metabolism. That is why very small animals are rarely found in polar regions.

If the stressful external conditions are remain only for a short duration, the organism has two other alternatives.

(iii) Migrate:
The organism move temporarily from the stressful habitat to a more favourable area and return when stressful period is over. Some persons moving from Delhi to Shimla in summer season. During winter some birds from Siberia and other extremely cold northern regions migrate to Keolado National Park (Bhartpur) in Rajasthan.

(iv) Suspend:
In bacteria, fungi and lower plants produce thick walled spores during unfavourable Conditions. They germinate in suitable environment.

In higher plants the seeds and vegetative reproductive structures are dormant during adverse condition and germinate after getting favourable moisture and temperature.

In animals, especially bears go into hibernation during winter. Some snails and fish go into aestivation to avoid summer. Under unfavourable conditions many zooplankton species in lakes and ponds are subject to diapause, a stage of suspended development.

3. Adaptations:
Some organisms are subjected to physiological and behavioural adjustments. These responses are called adaptations Kangaroo rat in North American deserts is capable of meeting all its water requirements through its internal fat oxidation. It has the ability to concentrate its urine.

Desert plants have a thick cuticle on their leaf surfaces and stomata arranged in deep pits to minimise water loss through transpiration. They also have CAM pathway in which they open stomata during night and closed during day time.

Opuntia, their leaves are reduced to spines and the flattened stems do photosynthesis. Mammals of colder climates have shorter ears and limbs to minimise heat loss. This is an Allen’s Rule In the polar seas aquatic mammals like seals have a thick layer of fat (blubber) below their skin that acts as an insulator and reduces loss of body heat.

In high altitude, some organism feels altitude sicknes due to low atmospheric pressure and low 02. Its symptoms include nausea, fatigue, and heart diseases. But, gradually get adapted and stop experiencing altitude sickness by increasing red blood cell production, decreasing the binding capacity of hemoglobin and by increasing breathing rate.eg- Many tribes live in the high altitude of Himalayas.

Archaebacteria seen in hot springs and deep sea hydrothermal vents where temperature is more than 1000°C.

Many fish thrive in Antarctic waters where the temperature is below 0°c. A large variety of marine invertebrates and fish live at great depths in the ocean where the pressure could be > 100 times the normal atmospheric pressure.

Desert lizards keep their body temperature constant by behavioural means. They bask in the sun and absorb heat when their body temperature drops, but move into shade when the surrounding temperature starts increasing.

Some species are capable of burrowing into the soil to escape from the above-ground heat.

Populations
1. Population Attributes:
Population has birth rates and death rates. The rates are expressed as the change in numbers with respect to the members of the population. If in a pond there are 20 lotus plants last year and through reproduction 8 new plants are added, so the current population is 28, birth rate is 8/20 = 0.4 offspring per lotus per year.

If 4 individuals in a laboratory population of 40 fruit flies died in a week, the death rate in the population during that period is 4/40 = 0.1 individuals per fruit fly per week.

Another attribute of a population is sex ratio. A population at any given time is composed of individuals of different ages. If the age distribution is plotted for the population, the resulting structure is called an age pyramid.

The shape of the pyramid indicates the growth status of the population i.e

1. growing,
2. stable and
3. declining.

Another important attribute of population is population Representation of age pyramids for human population density (designated as N) Total number is the measure of population density, it is difficult to determine if the counting is impossible.

In an area, if there are 200 Parthenium plants but only a single huge banyan tree with a large canopy, the population density of banyan is low when compared to that of Parthenium. In such cases, the per cent cover or biomass is the measure of the population size.

Number of fish caught pertrap is good measure of its total population density in the lake. The tiger census in our national parks and tiger reserves is based on pug marks and fecai pellets.

2. Population Growth:
Changes in population density that determined by four basic processes, natality, immigration mortality, and emigration.

1. Natality refers to the number of births during a given period
2. Mortality is the number of deaths in the population during a given period.
3. Immigration is the movement of individuals into the population
4. Emigration is the movement of individuals out of the population.

N is the population density at time t, then its density at time t + 1 is
Nt + 1 =Nt + [(B + I) – (D + E)]
Population density increase if the number of births plus the number of immigrants (B + I) is more than the number of deaths plus the number of emigrants (D + E).

If a new habitat is just being colonised, immigration contribute to population growth than birth rates.

Growth Models:
(i) Exponential growth:
When the resources in the habitat are unlimited, each species has the ability to grow in number. Here the population grows in an exponential or geometric fashion.

Population growth curve a when responses are not limiting the growth, plot Is exponential, b when responses are limiting the growth, plot is logistic, K ts carrying capacity

If in a population of size N, the birth rates are represented as b and death rates as d, then the increase or decrease in N during a unit time period t (dN/dt) will be

dN/dt = (b – d) × N (b – d) = r, then dN/dt = rN

r is called the ‘intrinsic rate of natural increase’it is important for assessing impacts of any biotic or abiotic factor on population growth.

The above equation shows the exponential or geometric growth and results J-shaped curve The integral form of the exponential growth equation as

N_t = Population density after time t, N₀ = Population density at time zero, r = intrinsic rate of natural increase, e = the base of natural logarithms (2.71828).

(ii) Logistic growth:
Limited resources leads to competition between individuals and the ‘fittest’ individual will survive and reproduce. Governments of many countries introduced restraints to limit human population growth.

In nature, a given habitat has resources to support a maximum possible number, beyond which no further growth is possible. This is called as nature’s carrying capacity (K) for that species in that habitat.

So the population growth in limited resources show initially a lag phase, followed by phases of acceleration and deceleration and finally an stationary phase, and the population density reaches the carrying capacity.

A plot of N in relation to time (t) results in a sigmoid curve. This type of population growth is called Verhulst-Pearl Logistic Growth equation. It is represented by
dN/dt = rN\(\frac{(K-N)}{K}\)
Where N = Population density at time t
r = Intrinsic rate of natural increase
K= Carrying capacity

3. Life History Variation:
Populations evolve to maximise their reproductive fitness, called as Darwinian fitness. Some organisms breed only once in their lifetime (Pacific salmon fish, bamboo) while others breed many times during their lifetime (most birds and mammals). Some produce a large number of small-sized offspring (Oysters, pelagic fishes) while others produce a small number of large-sized offspring (birds, mammals).

4. Population Interactions:
It occurs between species. Interspecific interactions arise from the interaction of populations of two different species. It is beneficial, detrimental or neutral (neither harm nor benefit) to one of the species or both. Assigning a ‘+’sign for beneficial interaction, sign for detrimental and 0 for neutral interaction,
Population Interactions

Both the species benefit in mutualism and both lose in competition. In both parasitism and Predation one species is benifitted and the other is harmed (host and prey).

In commensalism one species is benefitted and the other is neither benefitted nor harmed. In amensalism one species is harmed whereas the other is unaffected.

(i) Predation:
In predation, the energy stored at consumer level from plants are transferred to the next. So the consumer level energy transfer mainly takes place from prey to predator. For example prey is deer and predator is tiger.

The introduction of prickly pear cactus into Australia causes the spreading of these plants into millions of hectares. Later the cactus was controlled by cactus-feeding predator (a moth) from its natural habitat. This is an example of Biological control methods.

Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. In an American Pacific Coast, the starfish Pisaster is an important predator.

In a field experiment, when all the starfish were removed from intertidal area, more than 10 species of invertebrates became extinct within a year, because of interspecific competition.

If a predator overexploits its prey, it become extinct. Later predator become extinct for the lack of food. This is the reason why predators in nature are ‘prudent’.

Prey species also have defense mechanism to reduce the impact of predation. Some species of insects and frogs are cryptically-coloured (camouflaged) so the prey cannot be detected easily by the predator. If the prey is poisonous, it cannot be attacked by the predators. Eg- Monarch butterfly is distasteful to its predator (bird).

Plants have evolved some morphological and chemical defences against herbivores. Thorns (Acacia, Cactus) are morphological defence. Many plants produce and store chemicals that affect the herbivores digestion, reproduction and finally kill it.

The weed Calotropis produces poisonous cardiac glycosides and that affect cattle or goats browsing on this plant. Chemical substances that extract from plants (nicotine, caffeine, quinine, strychnine, opium, etc.,) are defences against grazers and browsers.

(ii) Competition:
The competition mainly for resources that takesplace among same species and different species. For example flamingoes coming into shallow South American lakes compete with resident fishes for their common food, the zooplankton in the lake.

In interference competition, the feeding efficiency of one species is reduced due to other species, even if resources (food and space) are abundant. So, in competition the fitness of one species is lower in the presence of another species.

According to Gause, when resources are limiting the competitively superior species eliminate the other species, This is an example of competitive exclusion.

When the goats introduced in the Galapagos island, Abingdon tortoise become extinct due to the greater browsing efficiency of the goats.

Another evidence of competition in nature is called ‘competitive release’. Some species restricted to small geographical area because of the presence of a competitively superior species.

Connell’s elegant field experiments showed that on the rocky sea coasts of Scotland, the larger and competitively superior barnacle Balanus dominates the intertidal area, and eliminates the smaller barnacle Chathamalus.

Actually the herbivores and plants are more adversely affected by competition than carnivores.
Gause’s Competitive Exclusion Principle’ states that two closely related species competing for the same resources cannot co-exist, as a result competitively inferior one is eliminated.

Some species shows ‘resource partitioning’.that is, if two species compete for the same resource, they avoid competition by choosing different times for feeding or different foraging patterns.

MacArthur showed that five closely related species of warblers living on the same tree were able to avoid competition and co-exist due to behavioural differences in their foraging activities.

(iii) Parasitism:
Many parasites are host-specific. Some parasites evolved special adaptations such as the

loss of unnecessary sense organs, presence of suckers to cling on to the host, loss of digestive system and high reproductive capacity.

The life cycles of parasites consist of one ortwo intermediate hosts or vectors to facilitate parasitisation. The human liver fluke depends on two intermediate hosts to complete its life cycle. The malarial parasite needs a vector (mosquito) to cause disease in other hosts.

Majority of the parasites reduce the survival, growth and reproduction of the host and reduce its population density.

Parasites that feed on the external surface of the host organism are called ectoparasites. Examples are the lice on humans and ticks on dogs. Ectoparasite copepods affect many marine fishes Chlorophyll-less Cuscuta a parasitic plant that absorbs nutritive materials from the host plant. Endoparasites that live inside the host body at different sites (liver, kidney, lungs, red blood cells, etc.). The life cycles of endoparasites are more complex. Their reproductive potential is more but their morphological and anatomical features are simple.

In Brood parasitism parasitic bird lays its eggs in the nest of its host and the host incubate them. The eggs of the parasitic bird resemble the host’s egg in size Examples of brood parasitism are cuckoo (koel) and the crow.

(iv) Commensalism:
This is the interaction in which one species benefits and the other is neither harmed nor benefited. An epiphytic orchid on a mango branch, and barnacles growing on the back of a whale get benefit. But the mango tree and the whale is neither harmed nor benefited.

The cattle egret and grazing cattle is an example of commensalism. Another example of commensalism is the interaction between sea anemone with stinging tentacles and the clown fish.

(v) Mutualism:
In this interaction both partner species are benefitted. Examples are Lichens (between a fungus and algae), mycorrhizae (between fungi and the roots of higher plants). The fungi help the plant in the absorption of essential nutrients from the soil while the plant in turn provides the energy-yielding carbohydrates.

Some examples of mutualism are found in plant-animal relationships. Plants need animals for pollinating their flowers and dispersing their seeds. Plants offer rewards in the form of pollen and nectar for pollinators and juicy and nutritious fruits for seed dispersers.

Co-evolution occurs between the flower and its pollinator species. In many species of fig trees, pollination is done by wasp. The female wasp uses the fruit not only for egg laying but uses the developing seeds within the fruit for nourishing its larvae.

The Mediterranean orchid- Ophrys. petal of its flower shows the similarity with female bee in size, colour and markings. The male bee is attracted and ‘pseudocopulates’ with the flower, When this same bee pseudocopulates’ with another flower, it transfers pollen to it and thus, pollinates the flower.