1. 1
   A commercial trout farm keeps thousands of fish in large net cages in a reservoir. The farm manager regularly checks water quality and takes steps to prevent losses to predators and disease.

   (a)

   Which method is used to prevent losses of fish to predators such as herons and otters?

   [1 mark]

   • ACovering the cages with netting to physically exclude predators
   • BIncreasing the amount of food given to the fish each day
   • CRemoving waste products from the water more frequently
   • DSelectively breeding the fish for faster growth

   (b)

   The farm manager keeps the fish at a lower stocking density than the cages could hold at maximum. What is the main reason for this?

   [1 mark]

   • ATo increase the amount of waste ammonia produced by the fish
   • BTo maintain a high enough dissolved oxygen concentration for all the fish to respire aerobically
   • CTo increase competition between the fish for food
   • DTo reduce the rate at which the fish grow

   (c)

   Explain why the farm manager removes waste products from the water regularly.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A market gardener grows sweet peppers in a heated glasshouse fitted with supplementary lighting and a carbon dioxide burner, to increase yield outside the normal growing season.

   (a)

   The market gardener uses a carbon dioxide burner to raise the carbon dioxide concentration inside the glasshouse. Why does this increase the yield of the pepper plants?

   [1 mark]

   • ACarbon dioxide increases the rate of respiration, releasing more energy for growth
   • BCarbon dioxide raises the temperature inside the glasshouse, speeding up enzyme reactions
   • CCarbon dioxide is a raw material for photosynthesis, so increasing its concentration increases the rate of photosynthesis
   • DCarbon dioxide reduces water loss by transpiration, leaving more water for growth

   (b)

   The glasshouse is also heated to keep the temperature well above outdoor levels throughout the year. What is the main reason increasing temperature, within limits, increases crop yield?

   [1 mark]

   • AHigher temperature reduces the rate of respiration, saving glucose for growth
   • BHigher temperature increases the concentration of carbon dioxide in the air
   • CHigher temperature stops pests and pathogens surviving in the glasshouse
   • DHigher temperature increases the rate of enzyme-controlled reactions such as photosynthesis, up to the optimum

   (c)

   Suggest why the market gardener must be careful not to raise the glasshouse temperature much above the plants' optimum.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A poultry breeder wants to develop a broiler chicken that reaches a high body mass in a short time using less feed, to reduce the cost of production.

   (a)

   Describe how the poultry breeder could use selective breeding, over several generations, to produce chickens that grow quickly to a high body mass using less feed.

   [3 marks]

   (b)

   After many generations of this selective breeding programme, the flock shows very little variation in growth rate. Suggest why this reduced variation occurs, and explain one disadvantage it could cause for the flock.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   At a pharmaceutical manufacturing plant, technicians grow large batches of genetically modified bacteria in an industrial fermenter to produce human insulin, which is purified and packaged as a medicine for people with diabetes.

   (a)

   Explain, referring to restriction enzymes, ligase enzymes, a plasmid vector and the term 'transgenic', how the gene for human insulin was originally inserted into bacteria to create the genetically modified strain now used at the plant.

   [6 marks]

   (b)

   Explain why each of the following conditions must be carefully controlled inside the fermenter for the genetically modified bacteria to grow and produce insulin efficiently: aseptic (sterile) conditions, nutrient supply, temperature and pH, and oxygen supply/agitation.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A student investigates how the amount of sugar added to a bread dough affects how much the dough rises. She prepares three identical dough samples with different sugar concentrations and leaves each covered in a warm oven for 30 minutes.

   (a)

   Which gas produced by the yeast during anaerobic respiration causes the bread dough to rise?

   [1 mark]

   • AOxygen
   • BCarbon dioxide
   • CNitrogen
   • DEthanol vapour

   (b)

   The student finds that, up to a point, the dough with the highest sugar concentration rises fastest. Why does the yeast inside the dense dough respire anaerobically rather than aerobically?

   [1 mark]

   • AThere is little or no oxygen available inside the dense dough, so the yeast respires without oxygen
   • BYeast cells cannot respire aerobically under any conditions
   • CAnaerobic respiration releases more energy per glucose molecule than aerobic respiration
   • DThe warm temperature of the oven prevents aerobic respiration from occurring

   (c)

   Explain why the dough sample with the highest sugar concentration produced the largest volume of gas within the 30 minutes.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A horticultural company wants to mass-produce a rare, disease-free variety of banana plant that shows resistance to a fungal disease, using small pieces of tissue taken from a single parent plant.

   (a)

   What is the term for the small pieces of plant tissue taken from the parent plant and used to start micropropagation?

   [1 mark]

   • AZygotes
   • BSpores
   • CCuttings
   • DExplants

   (b)

   The explants are grown on a nutrient gel medium in sterile test tubes. Why must these conditions be kept sterile (aseptic)?

   [1 mark]

   • ATo increase the rate of mitosis in the explant cells
   • BTo provide the explants with carbon dioxide for photosynthesis
   • CTo prevent microorganisms such as bacteria and fungi from contaminating and infecting the explants
   • DTo stimulate the explants to undergo meiosis and produce genetic variation

   (c)

   Explain why all the banana plants produced by this micropropagation process are genetically identical to the parent plant and to each other.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A rose breeder wants to develop a new variety with an especially strong scent, and cross-breeds roses with the most fragrant flowers over several generations.

   (a)

   Describe how the rose breeder could use selective breeding, over several generations, to increase the strength of scent in a variety of roses.

   [3 marks]

   (b)

   After many generations of selective breeding for scent, the roses have become more susceptible to a fungal leaf disease than older varieties. Suggest, with reference to genetic variation, why this has happened, and suggest one way the breeder could reduce this problem in future breeding.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A biotechnology company keeps a herd of cloned female rabbits, all genetically modified to produce a human blood-clotting protein in their milk, which is extracted and purified for use as a medicine.

   (a)

   Describe how scientists could produce a cloned rabbit that is genetically identical to a single transgenic donor rabbit already known to produce the human protein in its milk.

   [6 marks]

   (b)

   Explain one advantage of using cloned transgenic mammals, such as these rabbits, to produce a human protein in their milk compared with using genetically modified bacteria grown in a fermenter, and explain why every rabbit in the cloned herd produces the same protein.

   [6 marks]

   Total for question 8: 12 marks

End of questions