Biology

NIOS Class 12 Biology Chapter 1 Terminal Exercises

The chapter NIOS Biology Origin and Evolution of Life Class 12 introduces students to how life began on Earth and the gradual processes that led to evolution. It explains early theories, fossil evidence, Darwin’s work, and modern concepts of natural selection.

This chapter builds a foundation for understanding biodiversity and the continuity of life. With solved terminal exercises, students can revise effectively and prepare well for their NIOS Class 12 exams.

NIOS Biology Origin And Evolution Of Life Class 12 Solutions

1. Explain the most valid theory about origin of life on Earth. How did Miller and Urey verify the chemosynthesis theory of evolution?

The Chemosynthetic theory is the most valid theory of the origin of life on Earth. According to the Chemosynthetic theory, life might have originated at first on Earth through a series of combinations of chemical substances in the distant past, and it all happened in water.

Stanley Miller and Harold C. Urey in 1953 set up an experiment with an air-tight apparatus in which four gases (NH₄, CH_4, H₂, and H₂O) were subjected to an electric discharge for one week. On analysing the liquid, they found a variety of organic substances such as amino acids, urea, acetic acid, and lactic acid in it. This proved the Chemosynthetic Theory of Origin of Life.

2. Differentiate between Darwinism and Neo-Darwinism.

Darwinism, proposed by Charles Darwin, explains evolution through the theory of natural selection. According to him, organisms produce more offspring than can survive, and due to the struggle for existence, only those with favourable variations survive and reproduce, while the unfit are eliminated. However, Darwin could not explain the source of variations.

Neo-Darwinism, also called the Modern Synthetic Theory, is a modification of Darwin’s theory in the light of Mendelian genetics. It states that the unit of evolution is the population (gene pool) and not the individual. Variations arise due to mutations and genetic recombination, which are heritable. Natural selection acts on these variations, leading to differential reproduction, and reproductive isolation ensures the formation of new species.

Darwinism stressed natural selection without explaining variations, whereas Neo-Darwinism explains evolution through natural selection along with genetic variations and heredity.

3. Explain the synthetic theory of evolution.

Modern synthetic theory is regarded as the most valid theory of evolution. According to Darwin, when the environment changes, new adaptations get selected in nature, and after many generations, sufficient characteristics will have been changed so as to alter the species into a new one (Origin of Species).

Darwin talked about variation but did not know about the sources of variation. With progress in genetics, the sources of variation were discovered, and Darwin’s original theory of Natural Selection was modified.

According to this theory:

The unit of evolution is ‘population’, which has its own gene pool. The gene pool is the group of all the different genes of a population.
Heritable genetic changes appear in the individuals of a population. These heritable changes or variations occur due to small mutations in the genes or in the chromosomes and their recombinations.
Natural selection selects the variations that help in adapting to the environment.
A change in the genetic constitution of a population selected by natural selection is responsible for the evolution of a new species, since through the interaction of variation and Natural Selection, more offspring with favourable genetic changes are born. This is called ‘differential reproduction’.
Once evolved, Reproductive Isolation helps in keeping species distinct.

5. Substantiate the idea of evolution through molecular evidence.

Molecular Evidence of Evolution

All organisms have a cell as the basic unit of life. The cell is made of biomolecules common to all organisms.
Ribosomes, the cellular organelles, are of universal occurrence in organisms.
DNA is the hereditary material of all organisms, except for some viruses.
ATP is the molecule that stores and releases energy for biological processes.
The same 22 amino acids form the constituents of proteins of almost all organisms.
The genetic code is universal (exceptions are very few).
The central dogma, which deals with the transfer of genetic information in cells, is the same.
The basic steps of transcription and translation for protein synthesis are similar in all organisms.
The sequence of nucleotides, such as that for the promoter gene (TATA box), is common to all organisms.

6. Classify the following animals: earthworm, roundworm, frog, and human beings.

	Earthworm	Roundworm	Frog	Human Beings
Kingdom	Animalae	Animalae	Animalae	Animalae
Phylum	Annelida	Nematyhelminthes	Chordata	Chordata
Class	Oligochaeta	Nematoda	Amphibia	Mammalia
Order	Terricalae	Ascaroidea	Anura	Primates
Family	Megascolicidae	Ascaridae	Ranidae	Hominidae
Genus	Pheretima	Ascasis	Rana	Homo
Species	posthuma	lumbricoides	tigrina	sapiens

7. Write the scientific names of

(i) Mango (ii) Man (iii) Cat (iv) Tiger

Mango: Mangifera indica
Man: Homo sapiens
Cat: Felis domestica
Tiger: Panthera tigris

8. How does a virus increase in number? Show only by explanatory diagrams.

A virus can reproduce only when inside living cells.

A virus cannot reproduce by itself. For its reproduction, it needs to enter the cell of some organism. The host cell uses the raw material and enzymes, and energy-generating machinery of the host cell to produce its own DNA. Several virus particles are thus formed inside the host cell. The host cell bursts to release the new virus particles.

9. Give a schematic diagram of the five-kingdom classification.

10. State the criteria on which the five-kingdom classification is based.

R.H. Whittaker in 1969 suggested the five-kingdom classification, which is based on the following three criteria.

(i) The presence or absence of a well-defined nucleus.

(ii) Unicellular or multicellular

(iii) Mode of nutrition