Selection (Cambridge O Level Biology)

All commercial breeds of sheep belong to the species Ovis aries.

Define the term species.

The Merino is a breed of sheep that is farmed mainly for its wool. The wool is very thick and is made of lots of very thin hairs.

Fig. 1 shows a female Merino sheep with her newborn lamb.

Fig. 1

The presence of hair is a feature that is only found in mammals.

State two other features that distinguish mammals from all other vertebrates.

Merino sheep in South Africa have high quality wool with very thin hairs.

Breeders in New Zealand have used selective breeding programmes to improve the wool of their sheep to match the quality of South African wool.

Describe the steps that breeders would take to breed sheep that have wool with very thin hairs.

Explain how natural selection differs from selective breeding.

Compare natural selection with artificial selection.

Selective breeding is an example of artificial selection. 

The Wild Mustard plant has undergone extensive selective breeding for hundreds of years.

Fig. 1 shows the outcome of this selective breeding and the traits that have been selected for. 

Fig. 1 

Outline how selective breeding of the Wild Mustard plant has led to the development of the Kale plant. 

Streptomycin is an antibiotic. 

Table 1 shows results scientists collected from a study examining the effect of streptomycin on a bacterial population over fifteen generations.

The bacterial population consisted of organisms of two variants (X and Y).

Table 1

Describe and explain the data shown in Table 1. 

Explain the process that has led to the results shown by variant X in Table 1.