1. 1
   A commercial farm grows algae in large clear tanks as a novel protein source. The tanks are kept at a constant warm temperature and constantly supplied with carbon dioxide-enriched air, but light intensity is provided by banks of LED lights above each tank.

   (a)

   Which raw materials do the algae use in photosynthesis to produce glucose and oxygen?

   [1 mark]

   • ACarbon dioxide and water
   • BOxygen and glucose
   • CNitrogen and water
   • DCarbon dioxide and oxygen

   (b)

   If the LED lights are dimmed to a very low light intensity while carbon dioxide and temperature remain in plentiful supply, which factor will most likely limit the rate of photosynthesis?

   [1 mark]

   • ACarbon dioxide concentration
   • BLight intensity
   • CTemperature
   • DWater availability

   (c)

   Explain why, once light intensity is high, increasing it further may not increase the rate of photosynthesis in the tanks.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student examines a thin transverse slice cut from a young stem of a garden plant under a microscope. She identifies two types of transport tissue: one made of dead, hollow, lignified cells arranged end to end, and another made of living cells with perforated end walls next to companion cells.

   (a)

   Which of the two tissues identified consists of dead, hollow, lignified cells?

   [1 mark]

   • APhloem
   • BCompanion cells
   • CXylem
   • DGuard cells

   (b)

   What is the main function of the living tissue with perforated end walls described?

   [1 mark]

   • ATransport of water and dissolved mineral ions
   • BTransport of sucrose around the plant
   • CPhotosynthesis
   • DGas exchange

   (c)

   Explain why xylem cells, but not phloem cells, are dead at maturity, in relation to how each tissue transports its contents.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student ties a small sealed plastic bag around a single leaf (of known surface area 40 cm²) on a potted plant, without removing the leaf from the plant, and leaves it in place for 2 hours. She collects the water that condenses inside the bag and finds it has a mass of 0.6 g. She repeats the identical setup on a leaf of the same size on an identical plant placed in front of a small desk fan, and after 2 hours collects 1.8 g of condensed water in that bag.

   (a)

   Calculate the rate of water loss, in g per cm² per hour, from the leaf that was not exposed to the fan.

   [3 marks]

   (b)

   Calculate the rate of water loss, in g per cm² per hour, from the leaf placed in front of the fan, and explain, in terms of stomata and diffusion, why air movement increases the rate of transpiration.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A seed company treats dormant seeds with a gibberellin spray to encourage synchronised germination for commercial planting. Once germinated, the young seedlings rely on food stores in the seed, transported to the growing regions of the embryo, until the first true leaves expand and begin photosynthesising.

   (a)

   Explain how treating the seeds with gibberellin would help to encourage synchronised germination, and evaluate why this might be commercially useful for the seed company compared with allowing the seeds to germinate naturally without treatment.

   [6 marks]

   (b)

   Explain how food stores in the seed reach the growing regions of the embryo before the first true leaves can photosynthesise, and explain what must happen to the seedling's transport system once photosynthesis begins.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A gardener notices that a houseplant kept on a windowsill has all its stems curving strongly towards the window, while the same plant kept in the centre of a room under uniform ceiling lighting grows upright with stems spread evenly in all directions.

   (a)

   Which hormone is mainly responsible for the plant's stems curving towards the window?

   [1 mark]

   • AAuxin
   • BGibberellin
   • CEthene
   • DInsulin

   (b)

   In which region of the stem does the highest concentration of auxin build up when light comes from one direction only?

   [1 mark]

   • AThe illuminated side of the stem
   • BThe centre of the stem equally
   • CThe root tip only
   • DThe shaded side of the stem

   (c)

   Explain how the uneven distribution of auxin described above causes the stem to bend towards the window.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   In early spring, bluebells growing on a woodland floor flower and grow rapidly while the leafless tree canopy above still allows plenty of light to reach the ground. By early summer, once the trees are in full leaf and shade the woodland floor heavily, the bluebells have died back for the year.

   (a)

   Photosynthesis is best described as which type of reaction?

   [1 mark]

   • AExothermic
   • BCombustion
   • CNeutralisation
   • DEndothermic

   (b)

   Which limiting factor most likely restricts the bluebells' rate of photosynthesis once the tree canopy is in full leaf?

   [1 mark]

   • ACarbon dioxide concentration
   • BTemperature only
   • CLight intensity
   • DWater availability only

   (c)

   Explain, in terms of reactants and products, why photosynthesis is described as an endothermic reaction.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A biology class compares two leaves collected from the same tree: a sun leaf from a branch high in full sunlight, and a shade leaf from a lower branch that receives much less direct light. The sun leaf is thicker, smaller and has a smaller surface area than the shade leaf, which is thinner, larger and has a bigger surface area for its mass.

   (a)

   Explain why the shade leaf has evolved a larger surface area than the sun leaf, in terms of the leaf's need to photosynthesise effectively in low light.

   [3 marks]

   (b)

   Explain why the sun leaf, growing in full sunlight, has evolved to be thicker with a smaller surface area than the shade leaf, considering both its need to reduce water loss and its high light availability.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A crop scientist is breeding a new variety of wheat intended for a region with intense sunlight but limited rainfall. The new variety has narrower leaves with a thicker waxy cuticle and fewer stomata on its upper leaf surface than the standard variety, while its rate of photosynthesis under bright light remains similar to the standard variety.

   (a)

   Explain how the structural adaptations described (narrower leaves, thicker cuticle, fewer stomata on the upper surface) would help the new wheat variety to survive in a region with limited rainfall, and explain why these adaptations might create a disadvantage for the plant in gas exchange.

   [6 marks]

   (b)

   Given that the new variety's rate of photosynthesis under bright light remains similar to the standard variety despite having fewer stomata, suggest and evaluate two possible explanations for how the plant compensates for having fewer stomata, referring to limiting factors.

   [6 marks]

   Total for question 8: 12 marks

End of questions