Class 10 Biology Chapter 2 Notes Kerala Syllabus Paths of Evolution Questions and Answers

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SSLC Biology Chapter 2 Notes Questions and Answers Pdf Paths of Evolution

SCERT Class 10 Biology Chapter 2 Paths of Evolution Notes Pdf

SSLC Biology Chapter 2 Questions and Answers – Let Us Assess

Question 1.
Two illustrations related to human evolution are given below. Based on the theory of natural selection, find out the correct one and explain the reason.

Answer:
The correct illustration is A. Humans and monkeys evolved from a common ancestor. As per the theory of natural selection, through over production, variations, struggle for existence, survival of the fittest and natural selection, new species are evolved from a common ancestor.

• Over production – Organisms produce more offsprings than environment can support.
• Variations – Organisms show differences from each other in most features such as the size, immunity and seed production. These variations can be favourable or harmful to the organisms.
• Struggle for existence – Limitation of resources including food, shelter and mates will lead to competition among organisms.
• Survival of the fittest – Organisms with favourable variations survive in the struggle for existence. They reproduce more effectively and create new generations.
• Natural selection – Favourable variations are passed on to the next generations. More variations accumulate over time leading to the creation of organisms that are unable to reproduce within the species. They evolve as new species.

Question 2.
Although dolphins have a larger brain than that of humans, the level of thinking, language skills and social relationships are higher in humans. Evaluate this statement based on the following indicators.
• Difference in the structure of the brain.
• Influence of natural selection
Answer:
• Difference in the brain structure: Human brains have a highly developed neocortex responsible for language, reasoning and creativity which the dolphins lack.
• Influence of natural selection: Favourable variations such as bipedalism, tool-making and language development helped humans survive and evolve socially and intellectually.

Question 3.
Redraw the figure of the neuron and label the following parts by writing their names.

(a) The part of the neuron that receives impulses from the adjacent neuron
(b) Part that contains neurotransmitter
(c) Part that acts as an insulator.
Answer:

Question 4.
Darwin failed to explain the reasons of variation even though he argued that variations occur continuously in organisms. Evaluate this statement based on the findings of Neo Darwinism.
Answer:
Darwin’s theory of evolution has been subjected to criticism because Charles Darwin had no idea about the genetic basis of variations and inheritance. However, with the discoveries of Gregor Mendel and the concepts about chromosomes and genes, it was recognised that the causes of variations that lead to evolution were genetic changes, genetic recombination during sexual reproduction, and gene flow. Later Darwinism became uncritically rationalised as more evidences and further studies from the fields of population genetics, palaeontology, environmental science, etc. were added to Darwinism to form Neo Darwinism.

Neo-Darwinism explains that variations arise due to:

• Mutations – sudden changes in the genetic material (DNA) that can be inherited.
• Genetic recombination – the reshuffling of genes during sexual reproduction (e.g., crossing over during meiosis).
• Gene flow – exchange of genes between populations.
• Environmental influences – which may cause gene expression to change.

Question 5.
Observe the illustration and answer the questions.

(a) Identify the nerves A and B.
(b) Are messages being exchanged between A and B? Explain.
Answer:
(a) A – Sensory nerve,
B – Motor nerve

(b) The neuron that connects the sensory neurons and motor neuron is called interneuron which generates quick responses according to the sensory impulses. Hence, messages are being exchanged between A and B.

Question 6.
A table that includes the parts of the spinal cord and their functions is given below. Arrange column B appropriately in accordance with column A of the table.

Answer:

A. Part	B. Functions/ Peculiarities
Central canal	Fluid present here nourishes the spinal cord
White matter	Neurons with myelin sheath are numerous
Dorsal root	Transmits impulses to the spinal cord
Grey matter	Cell body of neurons are numerous

Question 7.
Based on the information obtained from fossils, some human ancestors and their characteristics are given below. Find out the one which is arranged correctly from the given Answers.

A. Part	B. Functions/Peculiarities
A. Homo habilis	i. buried dead bodies
B. Homo neanderthalensis	ii. able to stand upright on two legs
C. Astralopithecus	iii. made tools with stones using their hands
d. Homo erectus	iv The skeletal structure confirms bipedalism

(a) A : i, B : ii, C : iii, D : iv
(b) A : iii, B : i, C : iv, D : ii
(c) A : iii, B : iv, C : ii, D : i
(d) A : iv, B : i, C : iii, D : ii
Answer:
(b) A : iii, B : i, C : iv, D : ii

A. Part	B. Functions/Peculiarities
A. Homo habilis	iii. made tools with stones using their hands
B. Homo neanderthalensis	i. buried dead bodies
C. Astralopithecus	iv The skeletal structure confirms bipedalism
d. Homo erectus	ii. able to stand upright on two legs

Question 8.
Examine the information mentioned in the boxes labelled as P, Q, R, S. Identify the part of the brain associated with them and choose the correct Answer.

(a) P – Medulla oblongata Q – Pons R – Hypothalamus S – Thalamus
(b) P – Pons Q – Hypothalamus R – Medulla oblongata S – Cerebrum
(c) P – Hypothalamus Q – Cerebrum R – Thalamus S – Pons
(d) P – Thalamus Q – Cerebrum R – Hypothalamus S – Medulla oblongata
Answer:
(c) P – Hypothalamus Q – Cerebrum R – Thalamus S – Pons

Question 9.
Complete the table by including the following in the appropriate columns.
• Only long-necked giraffes survive
• Use and Disuse
• Natural selection
• Variations acquired in the life span
• Through continuous use, giraffe’s neck elongates
• Inheritance of variations

Answer:

Lamarckism	Darwinism
• Use and disuse	• Only long necked giraffes survive
• Variations acquired in the life span	• Natural selection
• Through continuous use, giraffe’s neck elongates	• Inheritance of variations

Biology Class 10 Chapter 2 Notes Kerala Syllabus Paths of Evolution

Answer of Indicators – Page 37
Question 1.
What was the treatment given initially to cure the disease? What was its result?
Answer:
He was given a series of antibiotics for six weeks and then a special antibiotic for 33 weeks. Ten months after starting treatment, a culture of the lung fluid and a chest X-ray confirmed that the tuberculosis was cured, and the treatment was completed.

Question 2.
Why didn’t the disease get cured even after giving treatment for the second time?
Answer:
Two months later, the young man was again admitted to the hospital with the same symptoms. Despite having treated with various antibiotics as done previously, he died due to breathing difficulty after 10 days. Further examination revealed that the disease got relapsed as the tuberculosis bacteria were activated again.

Question 3.
How did the tuberculosis bacteria acquire resistance to antibiotics?
Answer:
To find out where these antibiotic-resistant bacteria came from, the DNA of these bacteria was compared with the DNA of tuberculosis bacteria previously isolated and stored from the same patient. It was found that a mutation in a specific gene caused the bacteria to become resistant to the antibiotic.

Question 4.
What will happen if this bacteria transmit this ability to their next generations?
Answer:
If this ability of mutated bacteria is passed on to their next generations, the next generation of bacteria will also be resistant to antibiotics.

Answers of Indicators – Page 38
Question 5.
Changes in the environment
Answer:
Food from the ground became scarce.

Question 6.
Formation of acquired character
Answer:
The giraffe’s neck elongates as it stretches its neck to reach for leaves from higher branches due to food scarcity.

Question 7.
Inheritance of acquired characters
Answer:
Acquired characters were transmitted through generations, leading to the emergence of giraffes with longer necks

Question 8.
Survival of giraffes with longer and shorter necks in a changed environment.
Answer:
In the changed environment, food was only available in the taller trees. Only giraffes with longer necks survived because they could eat leaves from the taller branches. Giraffes with shorter necks died out because they could not eat leaves from the taller branches. According to Lamarck’s theory, only giraffes with longer necks survived.

Answers of Indicators – Page 41
Question 9.
Diversity of finch’s beak
Answer:
There are about fourteen different species of finches in the Galapagos Islands. Some of them are ground finches, cactus finches, and tree finches. The main difference between these species is the shape and size of their beaks. The beaks of mediumsized seed-eating finches are different from those of large seed-eating finches and insect-eating finches.

Question 10.
Cause of diversity
Answer:
The beaks are the main means of obtaining food.

Question 11.
The way in which diversity influences survival
Answer:
Birds with beaks of suitable shape or size, depending on the availability of food resources in the environment, will survive and produce more offspring.

Answers of Indicators – Page 47
Question 12.
Compare LUCA and MRCA?
Answer:
Biodiversity on Earth is the result of a process called speciation, in which new species arise from a common ancestor. It is estimated that all species evolved from a Last Universal Common Ancestor (LUCA) and that different species may have a Most Recent Common Ancestor (MRCA).

Question 13.
Which is the category of organism that is nearest to fungi? Why?
Answer:
Animalia, Fungi and members of the phylum Animalia are eukaryotes, and both groups cannot make their own food like plants. Both store energy as glycogen (plants store it as starch).

Question 14.
What are the circumstances that lead to the formation of variations in organisms?
Answer:
Genetic changes, natural selection, genetic recombination during sexual reproduction, and gene flow.

Question 15.
How do these circumstances lead to the formation of species?
Answer:
Members of a species can reproduce and produce offspring that are different, but they remain a single species. If members of a species are separated from each other by environmental factors or other factors, many variations can accumulate over time. When the members of a species become unable to reproduce new offspring mutually, they will evolve into different species.

Answers of Indicators – Page 48
Question 16.
Which organisms has the most evolutionary relationship with humans? Why?
Answer:
Chimpanzee has the most evolutionary relationship with humans because there is no difference in the amino acids of the beta chain of the haemoglobin molecule.

Question 17.
Which organism has a distant evolutionary relationship with humans? Why?
Answer:
Rat has a distant evolutionary relationship with humans because there is a difference of 31 amino acids in the beta chain of the haemoglobin molecule of rat when compared to humans.

Question 18.
How does molecular biology help to find out the evolutionary relationship among organisms?
Answer:
The evolutionary relationships of organisms can be determined by comparing the sequence of nucleotides in an organism’s DNA and the sequence of amino acids in its proteins with those of other organisms. The evolutionary tree depicts similarities and differences at the molecular level, combined with knowledge from anatomical comparisons and fossil studies. This is the most modern way to understand evolutionary history.

Question 19.
Analyse the given illustration 2.5 on Page 48 of the textbook and draft your inferences from the comparative study of DNA.

Answer:

• The DNA sequences of chimpanzees and humans show the highest percentage of similarity, indicating that humans share a very close evolutionary relationship with chimpanzees. This supports the idea that chimpanzees and humans have a very recent common ancestor compared to other primates.
• The DNA similarity between chimpanzees and gorillas is slightly lower, suggesting that gorillas are also closely related but diverged from a common ancestor earlier than humans.
• The similarity between chimpanzee DNA and monkey DNA is even less, meaning monkeys share a more distant evolutionary relationship with chimpanzees and humans.
• This comparative study of DNA sequences is strong molecular evidence of evolution, showing how species have diverged from common ancestors over time.

Answers of Indicators – Page 51
Question 20.
Two categories of Anthropoidea
Answer:
Cercopithecoidea and Hominoidea

Question 21.
Common category including apes and humans.
Answer:
Primates

Question 22.
Page 53, Complete the table based on the members in the human evolutionary path

Answer:

Human	Cranial capacity	Characteristics
Sahelanthropus tchadensis	350 cm3	1. The first link in the human evolutionary series. 2. Fossils have been excavated from Tchad in Africa. 3. Almost complete fossils of organisms belonging to this group have been obtained from Africa. 4. The skeletal structure confirms bipedalism.
Astralopethecus	450 cm3	• Fossils are obtained from Africa. • Large skull. • Made tools with stones using hands. • Lived in small groups. • Began hunting
Homo habilis	600 cm3	• Fossils are obtained from Africa, Asia and Europe. • They were able to walk upright on two legs. • Large forehead, omnivores, used excellent stone weapons for hunting
Homo erectus	900 cm3	• Contemporaries of modern man. • Fossils have been found from Germany. • They had small, sloping forehead and thick eye brows. • They buried dead bodies.
Homo neanderthalensis	1450 cm3	• Modern man. • They acquired technology and agricultural methods. • They domesticated animals and built cities. • They are culturally the most evolved category.

Question 23.
Table 2.3 on Page 59 of the textbook

Answer:

Part	Functions
Cerebrum	• Plays an important role in problem solving, planning and voluntary movements. • Centre of memory, intelligence, thinking and imagination. • Provides various sensory experiences
Cerebellum	Helps to maintain equilibrium of the body by coordinating muscular activities.
Thalamus	• Acts as the relay station of messages to and from the cerebrum. • Pain killers act on this part of the brain
Hypothalamus	Helps in maintaining homeostasis by regulating body temperature, hunger, thirst and emotions.
Mid brain	• Initial assessment of messages regarding vision and hearing. • It has a role in the movement of eyes and eyebrows.
Pons	• Coordinates the muscular activities of the eye and the face. • Regulates the rate of ventilation.
Medulla oblongata	Controls involuntary activities like heartbeat, ventilation, vomiting, cough, sneezing etc.

Question 24.
Illustration 2.14 on Page 60 of the textbook

Answer:

Answers of Indicators given in Textbook Page 61
Question 25.
Parts of the synapse
Answer:

• Synaptic knob: It is the tip of the axon which contains vesicles that is filled with neurotransmitters
• Synaptic cleft: It is the small gap present between neurons.
• Post Synaptic membrane: It is the tip of the dendrites which contains receptors for receiving the neurotransmitters

Question 26.
Transmission of impulses through the synapse
Answer:
When the impulses reach the synaptic knob, the synaptic knob secretes neurotransmitters to the synaptic cleft. These neurotransmitters binds with the receptors of the post synaptic membrane and stimulates that neuron.

Question 27.
Role of the synapse in controlling the direction and speed of the impulses
Answer:
Synapses transmit the impulses to only one direction and increases the speed of the impulses.

Question 28.
Table 2.4 on Page 63 of the textbook

Answer:

Neurons	Functions
Sensory neuron	It carries impulses from different parts of the body to the brain and spinal cord
Motor neuron	Impulses from brain and spinal cord are sent to different parts of the body
Interneuron	It connects sensory neuron and motor neuron. It generates quick responses according to the sensory impulses.

Question 29.
Table 2.5 on Page 63 of the Textbook

Answer:

Nerve	Building block	Functions
Sensory nerve	Sensory neuron	Transmits messages from different parts of the body to the brain and spinal cord (central nervous system).
Motor nerve	Motor neuron	Transmits instructions from the central nervous system (brain and spinal cord) to the organs.
Mixed nerve	Both sensory neuron and motor neuron	It carries impulses to and from the brain and spinal cord.

Question 30.
Table 2.6 on Page 64 of the Textbook – Sympathetic and Parasympathetic system – A comparison

Answer:

Organ/part	Sympathetic system	Parasympathetic system
Pupil of the eye	Dilates	Constricts
Salivary gland	Decreases production of saliva	Increases production of saliva
Bronchiole	Expands	Constricts
Heart	Increases heartbeat	Decreases heartbeat
Adrenal gland	Increases hormone production	No direct influence
Stomach	Slows down the process of digestion	Stimulates the process of digestion
67 Small intestine	Slows down peristalsis	Increases peristalsis
Urinary bladder	Retains urine	Empties urine

Answers of Indicators given in Textbook Page 66
Question 31.
Parts included in the reflex arc
Answer:
Receptor, Sensory neuron, Inter neuron, Motor neuron, Muscle

Question 32.
Functions performed by each part
Answer:

Part	Functions
Receptor	Generate impulses
Sensory neuron	Carries impulses to the spinal cord
Inter neuron	The neuron that connects the sensory neuron and motor neuron. It generates quick responses according to the sensory impulses
Motor neuron	Carries the information from spinal cord to related muscles
Muscle	Withdraws the hand by the action of muscles

Question 33.
Significance of reflex actions
Answer:
Reflex actions are significant because they provide quick, involuntary responses to stimuli, often protecting an organism from harm or danger. They are crucial for survival, allowing for rapid reactions to potentially dangerous situations without conscious thought.

Answers of Indicators given in Textbook Page 67
Question 34.
Compare the nervous system of Hydra and that of Planaria
Answer:
In hydra, the nervous system consists of a neural network with no control centre, whereas in the case of Planaria, a pair of nerve ganglia is present in the head region, which coordinates the instructions.

Question 35.
Peculiarity of the nervous system of insects
Answer:
In insects, the neurons in the head region unite to evolve into a clear and somewhat developed brain. The ganglia of paired nerve fibres emerging from this are seen in each segment.

Std 10 Biology Chapter 2 Notes – Extended Activities

Question 1.
Prepare the human evolutionary tree by including maximum organisms and exhibit it in the class.

Question 2.
Not only the origin of life but mass extinctions also had occurred on Earth. Collect more information about these and organise a seminar.
Answer:
Seminar Topic: The Origin of Life and Mass Extinctions on Earth

Main Topics
The Origin of Life on earth
a) Early Earth: Earth formed 4.6 billion years ago. Early Earth had no oxygen – full of volcanic gases and lightning.

b) How Life Might Have Started: Primordial Soup Theory: Simple chemicals in oceAnswer: formed basic life molecules (A.I. Oparin, J.B.S. Haldane) Miller – Urey Experiment: Proved life-
building molecules could form in early Earth conditions.

c) Timeline of Life: Earth forms – 4.6 billion years ago, First life – 3.5 billion years ago, Oxygen appears – 2.5 billion years ago, First animals – ~600 million years ago. Dinosaurs appear – ~230 million years ago

Mass extinctions on Earth
a) What is a Mass Extinction – A massive loss of species in a short period of time. Has happened 5 times in Earth’s history – called the Big Five.

b) The Big Five Mass Extinctions:

• Ordovician Ice age – 444 mya ( million years ago) 85% lost
• Devonian (Oxygen drop in oceAnswer:) – 375 mya 75% lost
• Permian (“The Great Dying”) (Volcanic eruptions) – 252 mya 96% lost
• Triassic (Climate change) – 201 mya 80% lost
• Cretaceous ( Asteroid hit Earth) – 66 mya 76% lost (Dinosaurs)

c) Sixth Mass Extinction (Happening Now?) Caused by human activities: Deforestation, Pollution, Climate change, Poaching & overfishing Scientists say thousands of species are vanishing every year.

How Extinction Leads to New Life?
After each extinction, new species evolve to take over. Dinosaurs went extinct. Mammals and humams evolved. Earth has seen birth, survival, and death of life many times. But this time, we are the reason for the destruction. Let’s become the generation that protects life, not ends it.

Question 3.
Prepare a script for a short play to clarify the protection of the nervous system and present the play in schools and public places.

Question 4.
Make a model of a nerve cell by using various materials such as beads of different colours, thin wires, woollen yarn etc. and present in the class.

Question 5.
Is artificial intelligence a challenge to the human brain? Organise a debate on this.
Answer:
Subject – Is artificial intelligence a challenge to the human brain?
FOR the Motion (AI is a challenge to the human brain)

Sample points for speakers:

• Al systems can now solve problems, process data, and make decisions with lightning speed often more accurately than the smartest humans.
• Digital assistants like Siri, Google Assistant, and ChatGPT can pull up massive amounts of data in a split second something our brains cannot compete with.
• Automation powered by Al is transforming industries and replacing jobs, making certain human skills redundant.
• Al has stepped into creative fields – it can write poems, paint pictures, and compose music. Aren’t those traditionally human traits?
• Advanced Al learns from patterns, adapts to new information, and never tires unlike the human brain, which needs rest and is prone to error.
• If left unchecked or used irresponsibly, AI has the potential to outgrow our control, raising real concerns about safety and ethics.

AGAINST the Motion (AI is not a challenge to the human brain)
Sample points for speakers

• Al is a product of human innovation it only functions within the limits set by human programmers.
• Unlike humans, Al cannot feel empathy, understand moral values, or experience joy, pain, or love.
• Machines lack a soul. They cannot appreciate beauty, feel inspiration, or dream of a better world.
• The human mind is full of creativity, emotion, intuition, and imagination qualities no machine can replicate.
• Al is a powerful tool that supports human progress in fields like medicine, education, and science – it doesn’t threaten our existence.
• Intelligence is more than logic and memory – it includes compassion, wisdom, and the ability to make ethical decisions. That is uniquely human.

SUGGESTED FORMAT:

• Moderator Introduction (sets the stage)
• Opening statements (2 to 3 minutes per speaker)
• Rebuttals (1 to 2 minutes each)
• Audience questions
• Concluding remarks
• Judges or audience vote

Paths of Evolution Class 10 Notes

Paths of Evolution Notes Pdf

• Doctors, public health experts and scientists are warning that the most reliable antibiotics currently available are ineffective against bacteria known as superbugs.
• Jean-Baptiste Lamarck was a French biologist who pioneered early discussions of the evolution of life. Later, scientists demonstrated that spontaneous mutations are not inherited because they do not alter the genetic makeup of organisms.
• The foundation of modern evolutionary theories is the theory of natural selection, or Darwinism, presented by the English naturalist Charles Darwin.
• Charles Darwin was influenced by the beak diversity of the finches of the Galapagos Islands to formulate the idea of evolution. Some of the finches of the Galapagos Islands include the ground finch, the cactus finch, and the tree finch.
• The main ideas of Darwinism are overproduction, variation, competition for existence, and survival of the fittest, Natural selection.
• Lamarckism – the environment causes variation in organisms.
• Darwinism – the environment selects for favourable variations in organisms.
• With the addition of evidence and further studies from the fields of population genetics, palaeontology, and ecology to Darwinism, Darwinism became more rational than it was criticized.
• Biodiversity on Earth was formed through a process called speciation, in which new species arise from a common ancestral species.
• It is assumed that all species evolved from a Last Universal Common Ancestor (LUCA) and that different species may have a Most Recent Common Ancestor (MRCA).
• The evolutionary relationships of organisms can be determined by comparing the sequence of nucleotides in the DNA of an organism and the sequence of amino acids in proteins with those of other organisms.
• The evolutionary tree depicts similarities and differences at the molecular level, combined with knowledge from anatomical comparisons and fossil studies. It is the most modem way to understand evolutionary history.
• The bones in a human hand, a cat’s forelegs, a whale’s flipper, and a bat’s wing are similar. But these organs differ in their external structure and function.
• Fossils are the remains or traces of ancient organisms.
• Evidence provided by fossils – Evolution is a gradual process. Intermediate fossils prove the evolutionary relationships between organisms. It has been proven that many organisms that lived on Earth have become extinct.
• The common ancestors of monkeys, apes, and humans in the mammalian order were members of the order primates.
• Common characteristics of primates – a thumb that can be opposed to the other fingers, binocular vision, a large and developed brain, flat claws instead of sharp claws, and flexible limbs and joints.
• Cercopithecoidea – the group that includes monkeys, small brains, and tails
• Hominoidea – the group that includes humans, large brains, and no tail
• Links in human evolutionary history Sahelathropus tchadensis, Australopithecus, Homo habilis, Homo erectus, Homo neanderthalensis, Homo sapiens.
• The increase in brain size over the past 3 to 4 million years is a major trend in human evolution.
• The nervous system plays a major role in controlling and coordinating vital functions. The nervous system includes the brain, spinal cord, and nerves.
• Nerve cells, or neurons, are the basic building blocks of the nervous system.
• The parts of neurons are the cell body, dendrons, dendrites, axon, axonite, and synaptic knob.
• More than half of the brain and spinal cord are composed of ependymal cells, oligodendrocytes, microglial cells, Schwann cells, and astrocytes. These are neuroglial cells.
• The various functions of neuroglial cells include providing nutrients to nerve cells. Removing waste products. Acting as immune cells. Maintaining the homeostasis of the nervous system. Helping to repair and regenerate damaged nerve tissue.
• In some neurons, a sheath called myelin is found around the axon. The main functions of the myelin sheath are to act as an insulator and increase the speed of transmission of messages, to provide nutrition to the nerve cell, and to protect the axon from external damage.
• In the brain and spinal cord, the myelin sheath is produced by oligodendrocytes, and in the nerves, the myelin sheath is produced by Schwann cells.
• A group of nerve cells is surrounded by a sheath. Such parts, which appear spherical, are called ganglions.
• In the brain and the spinal cord, the part where myelinated neurons with are more abundant is called the white matter. The part where the cell bodies and parts of the neurons without a myelin sheath are seen is called the grey matter.
• The nervous system is broadly classified into the central nervous system and the peripheral nervous system. The central nervous system includes the brain and spinal cord, and the peripheral nervous
  system includes 12 pairs of cranial nerves and 31 pairs of spinal nerves that connect the central nervous system to the organs. It also includes receptors and nerve ganglia.
• The brain and spinal cord are covered by the three-layered Meninges.
• The cerebrospinal fluid is the fluid that is filled in between the inner membranes of the meninges, in the cavities of the brain and in the central canal of the spinal cord. Ependymal cells play a role in the formation of cerebrospinal fluid.
• Cerebrospinal fluid performs the following functions: Provides oxygen and nutrients to the tissues, eliminates wastes, regulates the pressure, and protects from external injuries.
• The various parts of the brain include cerebrum, cerebellum, thalamus, hypothalamus and brain stem (midbrain, pons and medulla oblongata).
• The spinal cord is the part of the central nervous system seen as the continuation of the medulla oblongata. It transmits messages from different parts of the body to the brain and transmits instructions from the brain to the different parts of the body.
• The messages transmitted through the neuron are called nerve impulses.
• The part where an impulse is transferred from one neuron to another is called a synapse.
• Synapses transmit the impulses to only one direction and increase the speed of the impulses.
• The cerebral cortex of the brain of mammals is modified into a complex structure of a six-layered neocortex. It is more developed in humans as compared to other mammals.
• There are three types of neurons, which include sensory neurons, motor neurons and intemeurons.
• Nerves are made up of the axons of a group of neurons covered with a layer of fat and connective tissue. The three types of nerves are sensory nerve, motor nerve and mixed nerve.
• Autonomous nervous system is a part of the peripheral nervous system that regulates body activities by itself. The autonomous nervous system includes the sympathetic nervous system and the parasympathetic nervous system.
• The sympathetic system equips the body to respond during emergency situations.
• The parasympathetic system prepares the body to relax and perform routine functions such as digestion.
• Reflex actions are reactions that occur spontaneously and involuntarily in response to stimuli.
• The pathway through which impulses are transmitted in a reflex action is called a reflex arc.
• The different parts of reflex action include receptor, sensory neuron, inter neuron, motor neuron and muscle.
• Evolution is the prolonged process of the origin of complex multicellular organisms from simple, unicellular ones. It also gives a remarkable transition from simple nervous structures to highly complicated nervous systems.

INTRODUCTION

THEORIES OF EVOLUTION
Jean Baptiste Lamarck was a French biologist who pioneered early discussions of evolution. Lamarck’s ideas are known as Lamarckism (the theory of the inheritance of acquired characteristics). Modem evolutionary views are based on the theory of natural selection, or Darwinism, presented by the English naturalist Charles Darwin. Charles Darwin was influenced by the diversity of the beaks of finches on the Galapagos Islands to formulate the idea of evolution. In 1859, Darwin expanded and presented his ideas in the book ‘On the Origin of Species’. Initially, Darwin’s observations were opposed by society at the time, but as more evidence emerged, his theory of evolution gained widespread acceptance.

EVIDENCES OF EVOLUTION
There is a wealth of evidence supporting the theory of evolution. From the comparative study of molecules in organisms to the distribution of organisms on Earth, the study of the relationships between organisms helps us understand the relationships between them. The evolutionary tree depicts similarities and differences at the molecular level, combined with knowledge from anatomical comparisons and fossil studies. It is the most modem way to understand evolutionary history.

HUMAN EVOLUTION
Human evolution is a long-term process. The common ancestors of apes and humans in the mammalian order were primates. Fossils play a crucial role in unravelling the history of human evolution. The increase in brain size over the past 3 to 4 million years has been a major trend in human evolution. Brain size has nearly tripled in 2 million years. This has given humans complex social behaviours, the ability to make tools, use language, and engage in higher cognitive functions. Brain size has helped humans adapt to changing environments, develop culture, and use sophisticated technologies. Brain development laid the foundation for the transition from small-brained ancestors to Homo sapiens.

HUMAN NERVOUS SYSTEM
The nervous system plays a major role in controlling and coordinating vital functions. The nervous system includes the brain, spinal cord, and nerves. Neurons are specialized cells that are capable of receiving stimuli and forming appropriate messages. More than half of the brain and spinal cord are composed of ependymal cells, oligodendrocytes, microglial cells, Schwann cells, and astrocytes. These are neuroglial cells. Neuroglial cells that have the ability to divide are unable to receive stimuli or transmit messages. In evolutionarily advanced humans, an appropriate nervous system functions to form and coordinate physical responses to external and internal changes. The nervous system is divided into the central nervous system and the peripheral nervous system. The central nervous system includes the brain and spinal cord. The peripheral nervous system includes 12 pairs of cranial nerves and 31 pairs of spinal nerves that connect the central nervous system to the organs, as well as the nerves and ganglia.

Nerve impulses are messages transmitted through nerve cells. For a nerve impulse to reach one part of the body to another, it must travel through many neurons. The synapse is the part that transmits the impulse from one neuron to another. Synapses transmit impulses in only one direction and increase the speed of the impulses. In mammals, the cerebral cortex in the brain has transformed into a complex structure called the neocortex with 6 layers. The neocortex is the most developed in humans compared to other mammals. The autonomic nervous system, which is part of the peripheral nervous system, plays a role in controlling various bodily functions that occur outside of our conscious level.

Evolution has also provided a remarkable transition from simple nervous structures to highly complex nervous systems. This evolution of the nervous system has led to the adaptation of organisms to diverse environments and their survival. Complex brain development has played a crucial role in humans dominating nature and enabling unparalleled cognitive and technological progress. The presence of the neocortex, which has developed through long-term evolution, and the higher mental functions such as language, intelligence, and creativity that it makes possible, distinguish humans from other species.

ANTIMICROBIAL RESISTANCE

• A mutation in a specific gene has made bacteria resistant to antibiotics.
• Doctors, public health experts and scientists are warning that the most reliable antibiotics currently available are ineffective against bacteria known as superbugs.

LAMARCKISM (THEORY OF INHERITANCE OF ACQUIRED CHARACTERS)

• Jean Baptiste Lamarck was the French biologist who initiated early discussions related to biological evolution.
• The ideas of Lamarck are known as Lamarckism (Theory of Inheritance of Acquired Characters).
• Later, scientists proved that acquired characters do not impart change in the genetic structure of organisms and therefore, are not inherited.

DARWINISM

• The foundation of modern evolutionary theories is the theory of natural selection, or Darwinism, formulated by the English naturalist Charles Darwin.
• Charles Darwin was born on 12 February 1809, at Shrewsbury, England, into a family of well-educated background.
• In 1831, at the age of 22, he embarked on a 5-year voyage on the ship HMS Beagle for cartographical purposes. During this voyage, Darwin explored areas including South America, Australia, and the Galapagos Islands.
• Returning to England in 1836, Darwin analysed the specimens and observations he had made and deeply studied them by correspondence with other scientists through letters.
• Thomas Malthus, an English economist and demographer, argued that when the human population grows rapidly, food production will not increase in accordance with that, and it may lead to problems such as poverty, disease, and war. This perspective of Malthus had greatly influenced Darwin, too.
• While Darwin continued with his studies in 1858, he noticed the evolutionary studies of the British naturalist Alfred Russell Wallace.
• The papers of Darwin and Wallace were presented at a science conference.
• In 1859, he elaborated and presented his ideas in the book ‘On the Origin of Species’.
• Although his observations were initially opposed by society, as more and more evidence emerged, Darwin’s theory of evolution gained widespread acceptance.
• Darwin’s theory of evolution is a key scientific idea used in medicine, agriculture, and environmental science, apart from biology.
• Charles Darwin was influenced to formulate the theory of evolution by observing the diversity in the beaks of finches at the Galapagos Islands.

• There are about fourteen different species of finches in the Galapagos archipelago. Ground, cactus and tree finches are some among them.
  • Ground finches – seed eaters and ground dwellers
  • Cactus finches – cactus eaters and eat seeds.
  • Tree finches – shelter in trees and are insectivorous.
• The beaks of medium-sized seed-eating finches are different from those of large seed-eating and insecteating ones.
• Birds with beaks of suitable shape or size, depending on the availability of food resources in the environment, will survive and produce more offspring.

CHARACTERISTICS OF DARWINISM

• Overproduction: Organisms produce more offspring than environment can support
• Variations: Organisms show differences from each other in most features such as size, immunity and seed production. These variations can be favourable or harmful to the organisms.
• Struggle for existence: Limitation of resources, including food, shelter and mates, will lead to competition among organisms.
• Survival of the fittest: Organisms with favourable variations survive in the struggle for existence. They reproduce more effectively and create new generations.
• Natural selection: Favourable variations are passed on to the next generations. More variations accumulate over time, leading to the creation of organisms that are unable to reproduce within the species. They evolve into new species.

LAMARCKISM vs DARWINISM

• Lamarckism says that the environment causes variations in organisms.
• Darwinism argues that the environment selects the favourable variations in organisms.

NEO DARWINISM

• Darwin’s theory of evolution has been subjected to criticism because Charles Darwin had no idea about the genetic basis of variations and inheritance.
• However, with the discoveries of Gregor Mendel and the concepts about chromosomes and genes, it was recognised that the causes of variations that lead to evolution were genetic changes, genetic recombination during sexual reproduction and gene flow.
• Later on, Darwinism became uncritically rationalised as more evidences and further studies from the fields of population genetics, palaeontology, environmental science, etc. were added to Darwinism to form Neo Darwinism.

RESEARCH & EVOLUTION

• Many modem researches are being conducted, related to evolution as in the case of evolutionary clinical medicine which makes use of the ideas of evolution in health care. E.g., it studies how bacteria or vimses evolve over time to become drug resistant, which can lead to the creation of new methods for the treatment or the improvement of the existing ones.
• Personalised medicine is designed by looking at an individual’s genes and family genetic history.
• DNA studies and artificial intelligence help doctors to understand about diseases and to find new ways to resist them.

PECIATION, LUCA & MRCA

• Biodiversity on Earth originated through a process known as speciation, in which new species arise from a common ancestor.

• It is thought that all species have descended from a Last Universal Common Ancestor (LUCA), and different species might have a Most Recent Common Ancestor (MRCA).
• Although members of a population can produce offspring with differences through reproduction, they
  remain as a single species.
• If the members of a population get isolated from each other by ecological or other factors (mutation, natural selection, genetic recombination etc.) several variations might accumulate over time.
• When the members of a species become unable to reproduce new offspring mutually, they will evolve into different species.

EVIDENCES QF EVOLUTION
The evidences that support the theory of evolution where the studies ranging from the comparative study of biomolecules to the distribution of organisms on earth helps to understand the interrelationship among organisms.

MOLECULAR BIOLOGY

• The evolutionary relationship of organisms can be found out by comparing the sequence of nucleotides in the DNA and the sequence of amino acids in proteins in an organism with those of other organisms.
• Globin is the protein molecule of the respiratory pigment haemoglobin.
  The arrangement of amino acids in the beta chain of the haemoglobin molecule in humans, as compared to other organisms, is given in Table 2.1.

Organism	Difference in the amino acids of the beta chain as compared to humans
Chimpanzee	0
Gorilla	1
Rat	31

From the given table, it can be analysed that chimpanzee has the most evolutionary relationship with humans because there is no difference in the amino acids of the beta chain of the haemoglobin molecule and rat has the distant evolutionary relationship with humans because there is a difference of 31 amino acids in the beta chain of the haemoglobin molecule of rat when compared to humans.

The similarities and differences at the molecular level, along with the knowledge obtained from comparative anatomy and palaeontology, are correlated to depict the evolutionary tree, which is the most modem tool to understand the evolutionary history.

COMPARATIVE ANATOMY

The above image shows the forelimbs of man (used for grasping), cat (used for walking), flippers of whale (used for swimming) and wings of bat (used for flying). Though these structures perform different functions, their internal bone structure is similar. They are examples of homologous organs, where they have the same basic skeletal structure, but their functions differ based on the needs of the organism. These animals likely evolved from a common ancestor with a generalised limb structure.

FOSSIL EVIDENCES

• Fossils are the remains or traces of ancient organisms.

• Evidence provided by fossils – Evolution is a gradual process. Intennediate fossils prove the evolutionary relationships between organisms. It has been proven that many organisms that lived on Earth became extinct.

HUMAN EVOLUTION

• Human evolution is a prolonged process that continues for a very longer period of time.
• The common ancestors of mammals such as monkeys, apes, and humans belonged to the group of primates.
• Common characteristics of primates – a thumb that can be opposed to the other fingers, binocular vision, a large and developed brain, flat claws instead of sharp ones, and flexible limbs and joints.
• The organisms that are included in the human evolutionary tree are monkey, gibbon, orangutan, gorilla, chimpanzee and humans.

• • Anthropoidea is a suborder of primates consisting of monkeys, apes and humans.
  • Anthropoidea is further classified into Cercopithecoidea and Hominoidea.
  • Cercopithecoidea includes monkeys which has small sized brain and also has a tail.
  • Hominoidea includes gibbon, orangutan, gorilla, chimpanzee and humans which have big sized brain and they do not have a tail.
• Fossils play a vital role in disclosing the history evolution.
• The scientific world has succeeded in explaining the history of human evolution based on the available fossils

• In the last 3 to 4 million years, increase in the brain capacity is a major trend in human evolution.
• Over the course of 2 million years, the size of the brain has been nearly tripled which gave complex social behavior, to make tools, to use language, and to perform higher-level cognitive functions.
• The increase in cranial capacity has also helped man to adapt to changing environments, develop culture and to use advanced technologies.
• Brain development laid the foundation for the transition from ‘small-sized’ ancestors to Homo sapiens.

HUMAN NERVOUS SYSTEM

• Nervous system plays a major role in controlling and coordinating the vital functions of the body.
• Nervous system consists of brain, spinal cord, nerves and receptors

NEURONS

• They are also known as nerve cells which are the basic building blocks of the nerv ous system.
• Neurons are the structural and functional unit of the nervous system.
• Neurons are specialized cells which have the capability of receiving stimuli from the surroundings and form suitable messages.

• The centre of the neuron is known as cell body or cyton where cell membrane, cytoplasm, nucleus and cell organelles are seen.
• Dendrons are fine fibres arising from the cell body.
• Dendrites are the branches of dendrons.
• The messages received by the dendrites from the adjacent neurons are transmitted to cyton through the dendrons.
• Axon is the longest fibre from the cell body.
• Axonites are the branches of axon.
• The impulses from the cell body reaches the axonites through axons.
• Synaptic knob is a knob-like structure seen at the tip of the axonite.
• Synaptic knob secretes specialized chemicals known as neurotransmitters (e.g., Acetylcholine) which helps in transferring chemical messages to its adjacent neuron.

NEUROGLIAL CELLS

• More than half of the brain and spinal cord are made up of ependymal cells, oligodendrocytes, microglial cells, Schwann cells, and astrocytes. These are neuroglial cells.

• Neuroglial cells, which are capable of division, are unable to receive stimuli or transmit messages.
• The various functions of neuroglial cells include providing nutrients to nerve cells, removing waste products, acting as immune cells, maintaining the balance of the nervous system and helping to repair and regenerate damaged nerve tissue.
• In some neurons, the axon is covered by a layer called myelin sheath which is made up of a shiny white fat called myelin.

• The major functions of the myelin sheath are to increase the speed of transmission of messages, it acts as an insulator, to provide nourishment to the neuron and to protect the axon from external injuries.
• Myelin sheath in the brain and spinal cord are formed of specialized cells called oligodendrocytes.
• Myelin sheath in the nerves is formed of specialized cells called Schwann cells.

White matter: The part of the brain and spinal cord where myelinated neurons is more abundant in number. Grey matter: The cell bodies and parts of the neurons where myelin sheath is not seen is called the grey matter.

• Humans, who have evolved to a higher level, have a nervous system mechanism that produces and coordinates bodily reactions to both internal and external changes.

Classification of Nervous system

Illustration 2.10 Parts of the nervous system

BRAIN AND SPINAL CORD

• The brain and spinal cord is covered by the three-layered membrane known as the meninges.
• Cerebrospinal fluid is the fluid which is filled in between the inner membranes of the meninges, in the cavities of the brain and in the central canal of the spinal cord.
• Ependymal cells play an important role in the formation of cerebrospinal fluid.
• The functions of cerebrospinal fluid in the central nervous system are as follows:
  • Provides oxygen and nutrients to the tissues of the brain.
  • Eliminates wastes
  • Regulates the pressure
  • Protects from external injuries
• The various parts of the brain include Cerebrum, Cerebellum, Thalamus, Hypothalamus, Brain Stem (Mic brain, Pons, Medulla oblongata).

• Cerebrum:

1. It is the largest part of the brain.
2. Outer part is called the cortex because grey matter is seen, and the inner part is called the medulk because white matter is seen.
3. It plays an important role in problem solving, planning and voluntary movements.
4. It is also the centre of memory, intelligence, thinking and imagination.
5. It also provides various sensory experiences.

• Cerebellum:

1. It is the second largest part of the brain.
2. It is located behind and below the cerebrum.
3. It helps to maintain equilibrium of the body by coordinating muscular activities.

• Thalamus:

1. It is seen in the inner part of the brain.
2. It acts as a relay station of messages to and from the cerebrum.
3. Pain killers act on this part of the brain.

• Hypothalamus: It helps in maintaining homeostasis by regulating body temperature, thirst and emotions.

• Midbrain:

1. It is the centre of initial assessment of messages regarding vision and hearing.
2. It also has a role in the movement of eyes and eyebrows.

• Pons:

1. It coordinates the muscular activities of the eye and the face.
2. It regulates the rate of ventilation.

• Medulla oblongata: It controls involuntary activities like heartbeat, ventilation, vomiting, cough, sneezing, etc.

SPINAL CORD

• Spinal cord is a part of the central nervous system which is the continuation of medulla oblongata.
• Spinal cord transmits messages from different parts of the body to the brain and transmits instructions from brain to the different parts of the body.

• In the spinal cord, grey matter is seen inside, and white matter is seen outside.
• The part of the spinal cord which is filled with cerebrospinal fluid is called the central canal.
• Dorsal root: It transmits messages from different parts of the body to the spinal cord.
• Ventral root: It transmits instructions from spinal cord to different parts of the body.

TRANSMISSION OF NERVE IMPULSES

• The messages which are transmitted through the neurons are called nerve impulses.
• All cells, including neurons have an electric charge. The inner side of the cell membrane has a negative charge, compared to their outer side. When stimulated, positive ions from outside the cell membrane enter the cell, causing a temporary charge variation in that region.
• For a nerve impulse to be transmitted from one body part to the other, it needs to travel through different neurons.
• Synapse is the part where an impulse is transferred from one neuron to another neuron.

• Synaptic knob: It is the tip of the axon which contains vesicles that is filled with neurotransmitters.
• Synaptic cleft: It is the small gap between neurons.
• Post – synaptic membrane: It is the tip of the dendrites which contains receptors for receiving the neurotransmitters.
• The synaptic knob secretes neurotransmitters to the synaptic left when the impulses reach there, and these neurotransmitters bind with the receptors of the post synaptic membranes and stimulates the neuron.
• The function of synapse is to transmit the impulse to only one direction and to increase the speed of impulses.

Neocortex

The cerebral cortex of the mammalian brain is modified into a complex structure which is six-layered. It is known as neocortex. It is more developed in humans when compared to other mammals. Approximately 16 billion neurons are present in the human neocortex. An average of about 7000 synapses are created with each other. Advanced mental processes such as thinking, decision¬making, learning, recalling, etc. are possible only with the help of the synapses of the neocortex. When we learn new things or gain new experiences, the number of these synapses increases, making our brain more efficient and effective.

DIFFERENT TYPES OF NEURONS

There are three different types of neurons:
✓ Sensory neurons: It carries impulses from different parts of the body to the brain and spinal cord.
✓ Motor neurons: The messages from the brain and spinal cord are transmitted to different parts of the body.
✓ Interneurons: It is the neuron which connects both sensory neuron and motor neuron. It generates quick responses according to the sensory impulses.

NERVES
They are made up of the axons of a group of neurons which is covered with a layer of fat and connective tissue. Based on the peculiarities of the building blocks, nerves are of three different types: Sensory nerve, motor nerve and mixed nerve.
✓ Sensory nerve: It is made up of sensory neurons. It carries instructions from different parts of the body to the central nervous system (brain and spinal cord).
✓ Motor nerve: It is made up of motor neurons. It transmits instructions from the central nervous system (brain and spinal cord) to different parts of the body.
✓ Mixed nerve: It is made up of both sensory neurons and motor neurons. It carries impulses to and from the brain and spinal cord.

AUTONOMOUS NERVOUS SYSTEM

• It is a part of the peripheral nervous system that regulates the body’s activities by itself.
• It includes the sympathetic nervous system and the parasympathetic nervous system.
• The sympathetic nervous system equips the body to respond during emergency situations.
• The parasympathetic nervous system prepares the body to relax and perform routine functions such as digestion.
• The role of the autonomous nervous system, which is a part of the peripheral nervous system, is to regulate various physiological activities that take place beyond our consciousness.

SPONTANEOUS RESPONSES

• Reflex actions are reactions that occur spontaneously and involuntarily in response to stimuli.
• Reflex actions can originate from both the spinal cord and the brain.
• The reflex arc is the pathway through which impulses are transmitted in a reflex action.

PRECAUTIONS AND HABITS TO BE FOLLOWED FOR THE PROTECTION OF THE NERVOUS SYSTEM
✓ Use a helmet, seat belt, etc. while riding a motor bike/driving.
✓ Take necessary precautions while playing.
✓ Taking bath in stagnant water may cause infections. Therefore, avoid such situations.
✓ Those who engaged in jobs with the risk of brain injuries must use safety equipment such as helmets and safety belts.
✓ Avoid habits such as smoking, alcohol consumption and drug abuse. Do exercises.
✓ Lack of adequate sleep can affect brain function, which leads to memory loss, anxiety, difficulty in learning and hinders emotional development. Therefore, it is essential to sleep for at least 8 – 10 hours a day.

NERVOUS SYSTEM IN DIFFERENT ORGANISMS
The structure of the nervous system differs according to the complexity of organisms.

• Evolution is the prolonged process by which simple, unicellular organisms give rise to complex, multicellular ones.
• A notable transition from simple nervous structures to extremely complex nervous systems is also provided by evolution.
• The nervous system’s evolution is what allows organisms to adapt to and survive in a variety of environments.
• Human dominance over nature was made possible by the development of a complex brain, which also allowed for special advancements in cognition and technology.
• Humans differ from other organisms due to the presence of a neocortex that was developed over a long period of evolution and the resulting higher mental processes of language, intelligence, and creativity.
• Human sense organs do not have the same proficiency compared to other organisms, despite having a more developed brain and this can only be evaluated only when the relation between sense organs and the brain is analysed. Sensations provided together by the sense organs and brain are also to be understood.