Reviewing SCERT Class 8 Basic Science Solutions and Kerala Syllabus Class 8 Basic Science Chapter 8 Origin of Life, Origin of Living Things Question Answer Notes Pdf can uncover gaps in understanding.
Class 8 Basic Science Chapter 8 Origin of Life, Origin of Living Things Question Answer Notes
Class 8 Basic Science Chapter 8 Notes Kerala Syllabus Origin of Life, Origin of Living Things Question Answer
Origin of Life, Origin of Living Things Class 8 Questions and Answers Notes
Let’s Assess
Question 1.
Write which of the given statements are not related to eukaryotes.
a) A clear nuclear membrane is seen.
b) Cell organelles have no membranous covering.
c) Genetic material is found inside the nuclear membrane.
d) Organelles that perform various functions are seen.
Answer:
b) Cell organelles have no membranous covering.
Question 2.
Arrange the timeline properly.
Answer:
Question 3.
Match the following.
Answer:
a) Urey- Miller – Amino acids
b) Joan Oro – Nitrogenous bases
c) Sidney Fox – Proteinoid
d) Oparin-Haldane – Theory of Chemical evolution
Basic Science Class 8 Chapter 8 Question Answer Kerala Syllabus
Answers to the indicators on page no. 125
Question 1.
Characteristics of the primitive Earth’s atmosphere
Answer:
- High temperature.
- Hydrogen, methane, carbon dioxide, hydrogen sulfide, ammonia, water vapour.
- No free oxygen.
Question 2.
Formation of Ocean
Answer:
The condensation of steam, prolonged rainfall and the formation of oceans. The ocean is formed by dissolving varidus substances.
Question 3.
Energy sources that assist the formation of biomolecules.
Answer:
Sunlight, Lightning, Ultraviolet Rays, Volcanic Eruptions.
Question 4.
Formation of primitive cell
Answer:
The condensation of steam, prolonged rainfall and the formation of o’ceans. The ocean is formed by dissolving various substances. Simple organic particles were formed in the seawater. Then, complex organic particles were formed from simple organic particles. A complex molecule called nucleic acid and a fat layer were formed. Then, a primitive cell capable of self-replication was formed.
Question 5.
Completed table 8.1
Answer:
| Indicators | Conditions in the primitive Earth | Experimental set-up |
| Gases | Hydrogen, Methane, Carbon dioxide, Hydrogen sulphide, Ammonia, Water vapour. | Methane, ammonia, hydrogen, Water vapour. |
| Energy source for chemical synthesis | Sunlight, Lightning, Ultraviolet Rays, and Volcanic Eruptions. | Energy from an electric spark through electrodes |
Question 6.
Analyse illustration 8.5 based on the indicators and record your inferences in the Science Diary
Answer:
Prokaryotic cell: A few cell organelles, Cell organelles have no membranous covering, Membrane-bound nucleus absent.
Eukaryotic cell: Many cell organelles, Organelles with a membranous covering, Membrane-bound nucleus present.
Question 7.
Analyse illustration 8.6 from the textbook page number 128 and prepare a note on it.
Answer:
The eukaryotic cell engulfs the small aerobic bacteria. Instead of digesting the small cell, it protects it. These eventually become mitochondria. The eukaryotic cell engulfs the tiny photosynthetic bacteria. Instead of digesting the photosynthetic bacteria, it protects them and gradually transforms them into chloroplasts.
Question 8.
Completed Table 8.2, Pg.no. 129
Answer:
| Indicators | Prokaryotic cell | Eukaryotic cell |
| Structure | Simple | Complex |
| Nucleus | Membrane-bound nucleus absent | Well-defined nucleus with a membrane covering |
| Cell organelles such as mitochondria and chloroplasts | Absent | Present |
Question 9.
Analyse the timeline (Table 8.3) from Textbook Pg.no. 130, and prepare’ a note based on it.
Answer:
4 – 4.6 billion years ago: Origin of the Earth
3.5 – 2.5 billion years ago: Formation of the first life. Single-celled prokaryotes with simple structures
2.5 – 541 million years ago: Multicellular organisms called eukaryotes
541 – 252 million years ago: Plants and animals on land
252 – 66 million years ago: Dinosaurs
66 million years ago to the present: Emergence of mammals, evolution of humans
Question 10.
Conclusions drawn from the analysis of Illustration 8.7 on page 131 of the textbook
Answer:
Suppose we are preparing a calendar assuming the age of the universe to be just one year. One second in the said calendar is equivalent to approximately 438 years. Conclusions drawn from analyzing a model of the cosmic calendar:
The universe is born at exactly 00.00 on January 1st
August 1st Solar System, Earth
September 22nd Emergence of life
October 12th Prokaryotes
November 9th Eukaryotes
December 18th Vertebrate
December 20th Land Plants
December 26th Dinosaurs
December 27th Mammals
December 31st, 11.52 PM – Human
According to the cosmic calendar, man was born in the last moments of the last day of the year. This shows how recent the emergence of man is in the chronology of the universe.
Class 8 Basic Science Chapter 8 Question Answer Extended Activities
Question 1.
Make a model of the Urey-Miller experimental setup using the materials available from the surroundings and display it at the science corner.
Question 2.
Prepare a digital model/chart of the Cosmic calendar including more information and exhibit in the classroom.
Origin of Life, Origin of Living Things Class 8 Notes
Class 8 Basic Science Origin of Life, Origin of Living Things Notes Kerala Syllabus
- Scientists believe that life originated on Earth about 3.5 billion years ago.
- Theories related to the origin of life – Panspermia theory, Chemical evolution theory
- Harold Urey, Stanley Miller, Sydney Fox, and Joan Oro are some of the scientists who contributed to the field of the origin of Life.
- The simple structured cells, which were formed in the beginning, are called prokaryotes, and Eukaryotic cells with more complex structures are evolved from prokaryotic cells.
- As part of the evolutionary process, the formation of a nuclear membrane was the key feature of eukaryotic cells. Additionally, membrane-bound organelles were evolved, enabling them to perform specialised functions.
- Around 3.8 billion years ago, primitive living cells were formed from the molecules present in Earth’s oceans. By 3.5 billion years ago, prokaryotic cells had evolved.
- Approximately 2.5 billion years ago, the occurrence of photosynthesis led to the release of oxygen into the atmosphere. Later, eukaryotic, cells with organelles such as mitochondria and chloroplasts were evolved. Over time, simple multicellular organisms appeared around 800 million years ago, followed by more complex life forms.
- The Cosmic Calendar is a depiction that helps to easily understand the chronology from the creation of the universe to the origin of human beings.
INTRODUCTION
The quest to understand the origins of life is one of the most profound and challenging scientific endeavours. It delves into the fundamental question of how inanimate matter transitioned into the complex, self-replicating systems we recognise as living organisms. This field encompasses two closely related yet distinct concepts: the origin of life and the origin of living organisms.
The origin of life, often referred to as abiogenesis, explores the initial emergence of life from non-living chemical compounds. This involves understanding the conditions on early Earth—its atmosphere, oceans, and energy sources – that could have facilitated the formation of fundamental organic molecules like amino acids, nucleotides, and fatty acids. It further investigates how these simple building blocks could have self-assembled into more complex polymers (proteins, nucleic acids) and eventually organised into self-replicating systems enclosed by primitive membranes, forming the very first “protocells or primitive cells.”
The origin of living things, on the other hand, broadly refers to the subsequent evolution and diversification of these initial life forms into the vast array of organisms we see today, from the simplest bacteria to complex multicellular plants and animals. While the origin of life focuses on the first step, the origin of living things traces the evolutionary journey, driven by natural selection, adaptation, and genetic changes, that led to the incredible biodiversity on Earth. This includes the development of complex cellular structures (eukaryotes), the emergence of multicellularity, and the evolution of different modes of nutrition and reproduction.
Together, these two areas of inquiry seek to unravel the complete narrative of life’s emergence and evolution on our planet, providing insights into our own existence and the potential for life elsewhere in the universe. In this chapter, we will learn about these concepts.
ORIGIN OF LIFE
- Millions of years ago, life on Earth was very different from what we see today.
- Living things evolved in many ways, depending on changes in external factors such as habitat, climate, and food availability, as well as changes in the internal components of living cells, and the living things we see today were formed.
- Scientists believe that life originated on Earth about 3.5 billion years ago.
- Some of the simpler organisms released oxygen through photosynthesis, which led to the formation of more complex organisms.
- Complex plants and animals evolved. Over time, organisms evolved into the modern-day
- Theories related to the origin of life – Panspermia theory, Chemical evolution theory
| Panspermia Theory Life originated elsewhere in the universe and was accidentally transported to Earth in the form of microorganisms or spores. These microscopic particles are referred to as Panspermia. |
| Chemical Evolution Theory The Chemical Evolution Theory explains that life originated as a result of changes in the combination of chemical substances in the ocean under the unique conditions of the primitive Earth. |
- Although many theories explaining the origin of life have emerged over time,-the theory of chemical evolution is the one that is most supported by evidence and has received the most acceptance in the scientific world.
- Some of the scientists who contributed to this field:
Harold Urey, Stanley Miller: They together proved that the fundamental units responsible for the origin of life can form from simple gases.
Sydney Fox: Proved that molecules similar to proteins can be synthesised artificially.
Joan Pro: Adenine, one of the key building blocks of nucleic acids, was artificially synthesised. - Among the many experimental evidence supporting the theory of chemical evolution, the most notable is the Urey-MiUer experiment.
- The Urey-Miller experiment was conducted by artificially recreating the conditions of the primitive Earth in a laboratory.
- The Urey-Miller experiment demonstrated that organic molecules can form from inorganic components under suitable conditions.
FROM PRIMITIVE CELLS TO COMPLEX ORGANISMS
- The primitive cell is composed of nucleic acids capable of self-replication and a lipid layer covering it.
- Primitive forms like bacteria evolved from this primitive cell.
- These simple structured cells, which were formed in the beginning, tire called prokaryotes.
- Eukaryotic cells with more complex structures evolved from prokaryotic cells.
| Prokaryotic cell • A few cell organelles. • Cell organelles have no membranous covering. • Membrane-bound nucleus absent. |
| Eukaryotic cell • Many cell organelles. • Organelles with membranous covering • Membrane-bound nucleus present. |
- The eukaryotic cell engulfs the small aerobic bacteria. Instead of digesting the small cell, it protects it. These eventually become mitochondria.
- The eukaryotic cell engulfs the tiny photosynthetic bacteria. Instead, of digesting the photosynthetic bacteria, it protects them and gradually transforms them into chioroplasts.
- In prokaryotes, genetic material is scattered within the cytoplasm.
- As part of the evolutionary process, the formation of a nuclear membrane was the key feature of
eukaryotic cells. Additionally, membrane-bound organelles were evolved, enabling them to perform
specialised functions. - Around 3.8 billion years ago, primitive living cells were formed from the molecules present in Earth’s oceans. By 3.5 billion years ago, prokaryotic cells had evolved.
- Approximately 2.5 billion years ago, the occurrence of photosynthesis led to the release of oxygen into the atmosphere. Later, eukaryotic cells with organelles such as mitochondria and chloroplasts were evolved. Over time, simple multicellular organisms appeared around 800 million years ago, followed by more complex life forms.
Cosmic calendar
- The Cosmic Calendar is a depiction that helps to easily understand the chronology from the creation of the universe to the origin of human beings.
- Suppose we were creating a calendar assuming the age of the universe to be just one year. One second in that calendar would be equivalent to approximately 438 years.
- According to the cosmic calendar, man was born in the final moments of the last day of the year.
The process of evolution is the cause of present biodiversity. It is difficult to predict the direction of evolution as it is an accidental phenomenon.