STPM BIOLOGY – TERM 3

Chapter 3: Selection and Speciation Part B: Essays 1. (a) Define the term genetic drift, and explain how it occurs in a population. (b) Explain the concept of adaptive radiation, using specific examples.

[ 8 marks] [ 7 marks] (Johor 2012)

2. (a) What is meant by species? Explain the problems faced in the definition of species. (b) Explain how the isolation mechanism helps in the formation of new species.

[ 5 marks] [ 10 marks] (Johor 2008)

3. (a) Describe the genetic and environmental factors that cause variation in organisms. (b) Explain the importance of variation in a population.

[ 12 marks] [ 3 marks] (Kelantan 2012)

4. With the aid of graphs and suitable examples, explain briefly: (a) Stabilising selection (b) Directional selection (c) Disruptive selection 5. (a) Explain the role of isolating mechanisms in the evolution of new species. (b) Describe an explain, using an example, the process of artificial selection.

[ 15 marks] (NS 2009) [ 8 marks] [ 7 marks ] (Pahang 2012)

6. (a) What is meant by species? [ 2 marks] (b) Explain the problems that exist in defining species. [ 5 marks] (c) Explain how different species could maintain their identities through isolating mechanism. [ 8 marks] (Terengganu 2011)

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SELECTION AND SPECIATION ANSWER SCHEME ( ESSAY ) Section B: Essay 1. (a) - Genetic drift is a process where the allele frequency in a small population changes over time, as a result of some events. - Occur commonly in population undergoing Founder effect and bottleneck effect. - Founder effect occurs when a small population is separated from original population. - The gene pool is likely to be different from that of the original population. - Over several generations, this founding population given rise to a new allele frequency that is different from the original population. - This pioneer population becomes a new species which cannot breed with the original population. - Bottleneck effect occurs when a population undergoes a dramatic decrease in size due to natural disasters. - Disaster randomly eliminates a major proportion of population. - The small population survives has a different gene pool with the original population. - Reproduction of this new population gives rise to an allele frequency that is different from original population. - Examples are cheetah population due to overhunting by human, disease, drought, elephant seal over hunted by human. Max: 8m (b) - Adaptive radiation is the gradual change of an ancestral species to a number of diverse species, each of which occupies a new habitat or ecological niche. An example is the Darwin finches in Galapagos island. - The original population is the mainland ground finch, with shirt straight beak to crush seeds. - The ground finch population occupies ecological niche without competition. - As the population increases, intraspecific competition also increases. Natural selection results in finches adapting to new unoccupied habitat to survive. - 14 species of finches occupying new ecological niches finally took advantage of the various food sources available in the island, namely ground finch, cactus finch, insectivorous finch and woodpecker finch. - Adaptive radiation gives rise to divergent evolution. Max: 7m Total: 15 m

2. (a) - Species is a group of organisms that have similar morphological and physiological characteristics and can interbreed with one another to produce fertile offspring. - Species which reproduce asexually cannot be categorized. - Extinct fossilized organisms cannot be categorized based on their reproductive capability. - Certain plant species can form hybrids with other species through polyploidy. - Some organisms have a life complex life cycle with different morphological and physiological characteristics during their life cycle. - Speciation is a continuous process and it is difficult to classify intermediate organisms. - Mutation can occur in a population and mutants lose their ability to produce fertile offspring. Such mutants are often mistakenly considered to be of another species. - Reproductive compatibility of populations that do not exist together in time cannot be evaluated. Max: 4m Chapter 3: Selection and Speciation 1

(b)

- Ex of prezygotic mechanisms are ecological / habitat isolation, temporal isolation, behavioural isolation, mechanical isolation and gametic isolation. - Ex of postzygotic mechanisms are hybrid inviability, hybrid sterility and hybrid breakdown. Max: 10m Total 15m

3. (a)

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Zygote produced has numerous combination of genotypes.

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Max: 12 m (b)

Max: 3m Total: 15m

4. (a) Stabilising selection

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Directional selection

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Disruptive selection

Max: 3 x 5m Total: 15m

5. (a)

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Max: 8m (b)

Max: 7m Total: 15m

6. (a)

(b)

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(c)

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