OCR A-Level Biology: Manipulating Genomes, Cloning, Biotechnology and Ecosystems

A biotechnology company wants to produce a human therapeutic protein by transferring the gene that codes for it into bacteria, creating a transgenic strain that can be grown in a fermenter.

Describe and explain how the company could use recombinant DNA technology to produce bacteria that contain and express the human gene. In your answer you should refer to how the gene is obtained, how it is inserted into a vector, how the vector enters the bacteria, and how transformed bacteria are identified.

(6 marks)

Ecologists studied energy flow through a grassland food chain made up of grass, field voles (primary consumers) and weasels (secondary consumers). They estimated the energy entering each trophic level, and the energy lost from each level by respiration and by faeces and other losses, over one year. The data are shown below.

Trophic level	Energy entering level / kJ m⁻² yr⁻¹	Energy lost in respiration / kJ m⁻² yr⁻¹	Energy lost in faeces and other losses / kJ m⁻² yr⁻¹
Producers (grass)	24 000	9 600	8 880
Primary consumers (voles)	5 520	3 700	1 270
Secondary consumers (weasels)	550	—	—

The efficiency of energy transfer between two trophic levels is given by:

$\text{efficiency} = \frac{\text{energy available at higher level}}{\text{energy available at lower level}} \times 100\,\%$efficiency=energy available at lower levelenergy available at higher level​×100%

(a) Using the energy entering each level, calculate the percentage efficiency of energy transfer from primary consumers to secondary consumers. Show your working and give your answer to 2 significant figures. (2 marks)

(b) The efficiency of transfer from voles to weasels is higher than the efficiency of transfer from grass to voles. Using the data, explain why energy transfer between these animal trophic levels can be more efficient than transfer from producer to primary consumer. (4 marks)

In a disputed-parentage investigation, DNA from a child, the mother and two men (P and Q) was amplified at a single variable-number tandem repeat (VNTR) locus and separated by gel electrophoresis. Each person inherits one allele from each parent, so each shows up to two bands at this locus. The sizes of the fragments (bands) detected for each individual are given below. Smaller fragments travel further through the gel.

Individual	Fragment sizes detected / kbp
DNA size ladder	2.0, 3.0, 4.0, 5.0, 6.0
Mother	3.0 and 5.0
Child	4.0 and 5.0
Man P	2.0 and 6.0
Man Q	4.0 and 6.0

(a) State which fragment in the child must have been inherited from the biological father, and explain how the data show this. (2 marks)

(b) Using the data, determine whether man P or man Q is the more likely biological father, and explain your reasoning. (3 marks)

A food company wants to produce a sugar-reduced fruit juice continuously. They have an expensive enzyme that breaks down a sugar in the juice into less-sweet products. They plan to immobilise the enzyme by trapping it inside porous calcium alginate beads, pack the beads into a column, and run the juice slowly through the column so that finished juice flows out of the bottom.

Using your knowledge of immobilised enzymes, suggest and explain the advantages of this design compared with simply mixing the free enzyme into a tank of juice. (5 marks)

A coastal nature reserve contains an area of species-rich chalk grassland that is home to several rare orchids and butterflies. The grassland is not a natural climax community: if left alone it would undergo succession, with shrubs and then woodland replacing the grassland. To keep the rare grassland species, the wardens allow a flock of sheep to graze the area each year.

Using your knowledge of succession, explain how grazing by the sheep keeps this area as grassland and prevents it changing into woodland. (4 marks)

In the nitrogen cycle, several groups of soil microorganisms convert nitrogen between different chemical forms. Farmers want soil to contain plenty of nitrate for their crops.

Describe the role of nitrifying bacteria in the nitrogen cycle, and explain why waterlogging a field reduces the amount of nitrate available to crops. (3 marks)