OCR A-Level Biology: Biodiversity, Classification and Evolution

A species of ground beetle lives on shingle beaches. The beetles vary in body colour from pale grey to dark brown. On clean shingle the pale beetles are well camouflaged from bird predators, but a nearby stretch of beach has become covered in dark seaweed debris washed up after a change in tides. Over several generations on the debris-covered beach, the proportion of dark beetles has risen sharply.

Describe and explain how natural selection has led to this change in the beetle population. In your answer you should refer to the origin of the variation, the selection pressure, and how the allele frequencies change over generations.

(6 marks)

A student investigated the plant biodiversity of an area of upland heath using random quadrats. The total number of individuals of each species across all the quadrats is shown below.

Plant species	Number of individuals (n)
Ling heather	36
Bilberry	20
Gorse	14
Bell heather	6
Tormentil	4
Total (N)	80

Simpson's Index of Diversity is given by:

$D = 1 - \sum\left(\frac{n}{N}\right)^2$D=1−∑(Nn​)2

(a) Calculate Simpson's Index of Diversity (D) for this heath. Show your working and give your answer to 2 decimal places. (4 marks)

(b) A second heath nearby gave a value of D = 0.42. Explain what these two values tell you about the biodiversity of the two heaths. (2 marks)

Scientists compared the amino acid sequence of a conserved respiratory protein in a small mammal, species P, with the equivalent protein in four other animal species (Q, R, S and T). The protein is 108 amino acids long in every species. The table shows the number of amino acid differences between species P and each of the other species.

Species compared with P	Number of amino acid differences
Q	4
R	9
S	22
T	31

(a) Using the data, state which species is most closely related to species P and which is most distantly related. Explain your reasoning. (3 marks)

(b) Explain why a conserved protein that changes only slowly is more useful than a rapidly changing one for working out distant evolutionary relationships. (2 marks)

A rare orchid survives as just two small, isolated populations on a single hillside. A conservation team is deciding whether to maintain the orchids in their natural habitat (in situ) while also storing seed from both populations in a seed bank (ex situ).

A team member argues that because the two populations are so small, their genetic diversity is very low, and that this low genetic diversity puts the species at risk in the long term.

Suggest and explain why low genetic diversity could make this orchid species more vulnerable, and give one advantage of also keeping seed in a seed bank. (5 marks)

The sand-diving lizard lives in a hot desert. Biologists have recorded the following features of the lizard.

Feature	Description
W	Pale, sand-coloured skin that reflects sunlight
X	Produces highly concentrated urine, losing very little water
Y	Buries itself in cooler sand during the hottest part of the day

Classify features W, X and Y as anatomical, physiological or behavioural adaptations, and for feature Y explain how it helps the lizard survive. (4 marks)

In the three-domain system of classification, organisms are divided into the domains Bacteria, Archaea and Eukarya. This replaced an earlier system in which all prokaryotes were placed in a single group.

State the type of molecular evidence that led to the separation of Archaea from Bacteria, and explain why classification systems such as this one change over time. (3 marks)