Form 4:
Evolution kcse questions

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1. State the difference between Lamarckian and Darwinian theories of evolution

- Lamarckian theory- a character acquired in the life of an organism which is favourable in its adaptation to the environment is inherited.

- Darwinian Theory – As a result of variations, some organisms become better adapted to the environment. They therefore survive better and mature giving rise to more adapted off springs.

- The less adapted organisms die before maturity hence been eliminated from the environment.

- The less adapted organisms die before maturity hence are eliminated from the environment.

2. Two populations of the same species of birds were separated over a long period of time by an ocean. Both populations initially fed on insects only. Later it was observed that one population fed entirely on fruits and seeds. Although insect were available. Name this type of evolutionary change.

Adaptive radiation / divergent evolution

3. Explain why Lamarck’s theory of evolution is not accepted by biologists today

- Evidence does not support Lamarck’ theory.

- Acquired characteristics are not inherited/inherited ,characteristics are found in reproductive cells only.

4. State three pieces of evidence that support the theory of evolution. ( 3 marks)

Fossils/ (records), palaeontology, Geographical distribution, comparative anatomy/taxonomy; cell biology; comparative serology; comparative embryology; comparative immunology.

5. state two advantages of natural selection to organisms ( 2 marks)

-Assists to eliminate disadvantageous characteristics / perpetuate advantageous characteristics.

- Allow better-adapted organisms to survive (adverse changes) in environment/less adapted organisms are eliminated by adverse changes in the environment.

6. Give a reason why each of the following is important in the study of evolution

(i) Fossils records

Gives evidences of types of plants, animals organism that existed at certain geological age/ long ago.

(ii) Comparative anatomy

Gives evidence of relationship among organism / common ancestry of a group of organisms.

7. Describe how natural selection brings about adaptation of a species to its environment ( 6 marks)

Nature selects those individuals who are sufficiently well adapted; rejects those that are poorly adapted

8. Explain how the process of evolution may result to the formation of new species

- For a new species to be formed, a population of organisms must become completely isolated or separated from the others;over long period of time so that any new variation that rise will not therefore flow to other population.

- Geographical isolation – this is due to physical barriers e.g. oceans / seas / deserts

- Ecological Isolation- a barrier resulting form the occupation of different types of habitats from the original type.

- For reasons of feeding/ predation / breeding as well as environmental changes (e.g. climate and vegetation which may result in population living in different habitats so becoming, ecologically separated from one another)

- Behavioural isolation alteration in behaviour proceeding mating which include courtship behaviour / lack of attraction between males and females in different chemicals / pheromoes / coloration /songs e.t.c

Reproduction isolation: a barrier to successful mating between individuals of population; due to structural differences in reproductive organs as well as failure in fertilization/ incompatibility.

Genetic isolation – Even if fertilization takes place the zygote may be inferior / fails to develop; however if the zygote develops the offspring may be inferior or sterile.

9. What is meant by

(a) organic evolution ( 1 mark)

It is the emergence of present forms of organisms gradually from pre-existing ones some of which no longer exists).

(b) continental drift ( 1 mark)

It is the drifting apart of the continents from one land mass (Pangaea).

10. Explain continental drift as an evidence of evolution ( 3 marks)

Current continents existed as one large landmass/pangea/Laureshia Guondaland.The present continent drifted leading to isolation of organisms.Organisms in each continent evolved along different lines hence emergence of new species.Each group adapted to different set of environmental conditions.

11. (a) What is adaptive radiation? ( 2 marks)

When organisms of the same origin become adapted (modified) in different ways in order to fit in the environment. The organisms are separated due to natural factors.

(b) Give a reason why organisms become resistant to drugs ( 1 mark)

When an organism is exposed to drug for sometime it becomes modified (adapted) to living in presence of the drug. The offspring produced therefore survive in presence of the drug. Hence drug resistant.

12. Distinguish between the following terms

(a) Homologous structures

Structures / organs that have arisen from a common ancestor but they have assumed different functions

(b) Analogous structures ( 4 marks)

Structures/organs that have originated from different ancestors but they perform the same function.

13. (a) What is meant by natural selection?

Natural selection is a process where nature selects those organisms that are well adapted to the prevailing environmental conditions enabling them to survive to reproductive maturity. Those organisms that are poorly adapted die young leaving no offspring and their characteristics are eventually eliminated from the population.

(b) Explain the role played by mutation in evolution ( 5 marks)

Mutation brings about new hereditary characteristics (or hereditary variation) in a species. Some of the new characteristics are favourable but others are unfavorable. Favourable characteristics enable the organism possessing them to compete better in the struggle for existence. The result is that most of them survive to adulthood and give rise to offspring of the next generation. Since characteristics resulting from mutation are inheritable they are passed on to new generation. On the other hand, only very few of those organisms with unfavorable characteristics survive to adulthood and give rise to young ones. The final result is that the favourable characteristics are propagated in the population giving rise to organisms that are better adapted to the environment. The unfavorable characteristics are gradually weeded out and may eventually get eliminated from the population.

14. Define the following terms

(a) Hybrid

A hybrid is an offspring of across between different varieties or breeds of the same species.

(b) Hybrid vigour

Hybrid vigour refers to the improved qualities, such as increased yields, fertility, resistance to diseases and toughness seen in offspring of different.

15. The peppered moth exists in two varieties, which are genetically controlled. The dark variety is found predominantly in industrial cities and the white variety is found predominantly in rural areas. Explain how this pattern of distribution supports the theory of evolution by natural selection ( 6 marks)

The peppered moth usually on trunks and branches of trees, industrial cities are normally dark in colour due to deposits of soot and other pollutants. A white moth resting on such a trunk or branches is highly conspicuous and is easily picked and eaten by preying birds. A dark moth resting at the same places is effectively camouflaged by the dark background and is not easily seen by preying birds.

- In rural areas, tree trunks and branches are normally white in colour due to growth of lichens. A white moth resting on such a trunk or branch is effectively camouflaged by the white background and is not easily seen by preying birds. A dark moth resting at the same place is highly conspicuous and is easily picked and eaten by praying birds.

- Therefore, dark moths are adapted for survival in industrial areas. Here most of them reach maturity and reproduce more dark moths. On the other hand, only a few white moths survive to maturity and reproduce in industrial areas. In rural areas, most white moths survive to maturity and reproduce more white moths. Here only a few dark moths survive to maturity and reproduce.

16. Explain what is meant by the following concepts

(a) Special creation (2 marks)

Special creation is a concept which proposes that all living things were made by God at a specific time and have remained unchanged since.

(b) Organic evolution (2 marks)

Organic evolution is a concept which proposes that all living things arose from a few ancient simpler forms through gradual modification.