BIOLOGY 2 Marks Questions

1. Gene migration/ gene flow.
2. Genetic drift.
3. Mutation.
4. Genetic recombination.
5. Natural selection.

1. Australopithecus.
2. Homo habilis.

• Brachiosaurus and Stegosaurus lived early in the history.
• Tyrannosaurus and Triceratops lived later.

1. They were probably not taller than four feet.
2. They walked upright.
3. They hunted with stone weapons, but essentially ate fruits.

• Evolution is not a direct process in terms of determinism.
• As the environment changes, due to meteorological, biological and other physical activities, the organisms which are better adapted to the changed environment are selected by nature in a much lesser time scale.
• It is also true for natural selection and evolution of antibiotic-resistant strains of bacteria in a time scale of months.
• So, evolution is a stochastic process based on chance events in nature and chance mutation in the organism.

• Ernst Haeckel proposed embryological support for organic evolution.
• It was disapproved by Ernst Von Baer.
• He noted that embryos never pass through the adult stage of other animals.

1. Rhyniaceae.
2. Psilophytaceae (in a restricted and revised sense).
3. Trimerophytaceae.

1. Distribution of fossil gives information about habitat of an organism.
2. Establishes phylogenetic links.
3. Some fossils provide evidence of connecting link.
4. Age of the organisms can be determined by fossils.
5. Fossils also throw light on morphology and anatomy of past life.

1. The geological time period in which the organisms existed.
2. That life forms varied over time and certain life forms are restricted to certain geological time spans.
3. That new forms of life have appeared at different times in the history of earth.

1. Hearts of humans and monkeys.

3. Thorns of Bougainvillea and tendrils of Cucurbits.

These are homologous structures as they have similar anatomical structures, but perform different functions.

• Homology: Tendrils of Cucurbita and thorns of Bougainvillea.

• Analogy: Sweet potato (root modification) and potato (stem modification) to store food.

1. There are limited natural resources.
2. Populations are stable in size except for seasonal fluctuations.
3. Varying characteristics in members of a population, i.e. no two members of a population are identical even though they look superficially similar.
4. Variations are generally inherited.
5. Population size has two facts, i.e. theoretically it grows exponentially if everybody reproduced maximally but in reality, population size is limited, due to the competition among the individual for resources. Those, which are better adapted could survive and will reproduce at the cost of others, i.e. who are less adapted in the environment.

• The forelimbs of whales, bats and cheetah (or bat, horse and humans) are the result of divergent evolution.
• Divergent evolution is the evolutionary process, where the same structure develops along different directions in different groups of organisms as adaptations to different needs.
• The structures evolved are homologous organs; homology indicates common ancestry.
• Thorns of Bougainvillea and tendrils of Cucurbits are also homologous structures.

• S.L. Miller used this set-up.
• The electrodes (a) are used to create an electric discharge, similar to the lightning in the primitive earth; it was to provide energy.
• The formation of amino acids proved the chemical evolution, which preceded the origin of life.

1. New life forms arise and evolve in due course of time.
2. All the existing forms of life share certain similarities and common ancestors.
3. These ancestors lived at different periods in the history of earth.
4. The geological history closely correlates with the biological history.

1. The graph depicts disruptive natural selection. This type of selection tends to eliminate intermediate types.
2. The other two types of natural selection are,

1. Directional selection Large number of individuals acquire value other than mean character value.
2. Stabilising selection Large number of individuals acquire mean character value.

1. Dryopithecus.
2. Ramapithecus.
3. Australopithecus.
4. Homo habilis.
5. Homo erectus.
6. Cro-Magnon man.
7. Homo sapiens.

• Water vapour, methane, carbon dioxide and ammonia that were released from the molten mass covered the surface.
• The UV rays from the sun broke up water into hydrogen and oxygen.
• The lighter hydrogen escaped into the atmosphere.
• Oxygen combined with ammonia and methane to form carbon dioxide and other gases.
• Later ozone was formed from the oxygen.

1. Psilophyton.
2. Seeds and ferns.
3. Chlorophyte ancestor.
4. Ferns, conifers and seed ferns.
5. Tracheophyte ancestor.
6. Chlorophyte ancestor.

1. Convergent evolution.
2. Convergent evolution.
3. Convergent evolution.
4. Divergent evolution.