Energy Flow, Ecosystems and the EnvironmentEdexcel International A Level Biology: Topic test

1. 1
   A green alga grows in a pond in bright sunlight, and bubbles of oxygen collect among its filaments. Its cells contain chloroplasts.

   (a)

   Which process in the chloroplasts of the alga makes ATP using light energy?

   [1 mark]

   • AOxidative phosphorylation
   • BPhotophosphorylation
   • CSubstrate-level phosphorylation
   • DPhotolysis

   (b)

   The oxygen released by the alga comes from

   [1 mark]

   • Athe reduction of carbon dioxide in the Calvin cycle.
   • Bthe breakdown of glucose in respiration.
   • Cthe hydrolysis of ATP to ADP and phosphate.
   • Dthe photolysis of water.

   (c)

   Explain why the alga needs photolysis of water for non-cyclic photophosphorylation to continue.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A market gardener grows lettuces in a glasshouse that is lit artificially for 16 hours each day. During the 8-hour dark period the lights are off.

   (a)

   In which part of a chloroplast does carbon fixation take place?

   [1 mark]

   • AThe stroma
   • BThe thylakoid membrane
   • CThe thylakoid space
   • DThe outer membrane

   (b)

   Which compound is the first stable product when carbon dioxide is fixed by RuBP in a lettuce leaf?

   [1 mark]

   • AGlyceraldehyde 3-phosphate (GALP)
   • BRibulose bisphosphate (RuBP)
   • CGlycerate 3-phosphate (GP)
   • DGlucose

   (c)

   Explain why the Calvin cycle in the lettuce leaves slows down and then stops soon after the lights are switched off.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student separated the photosynthetic pigments in a kale leaf extract by thin layer chromatography. The solvent front moved 9.0 cm from the pencil origin line. The distances moved from the origin by the pigment spots were: carotene 8.1 cm, xanthophyll 6.3 cm, chlorophyll a 5.4 cm and chlorophyll b 4.5 cm. Carotene and xanthophyll are accessory pigments.

   (a)

   Calculate the Rf value of chlorophyll b. Explain why Rf values, rather than the distances moved by the spots, are used to identify pigments.

   [3 marks]

   (b)

   Explain how the accessory pigments increase the rate of photosynthesis of the kale leaf.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A grower of tomatoes in a glasshouse measured the rate of photosynthesis under different conditions. At 25 °C and low light intensity, increasing the carbon dioxide concentration from 0.04% to 0.10% did not change the rate. At 25 °C and high light intensity, the same increase in carbon dioxide concentration raised the rate considerably. With high light intensity and 0.10% carbon dioxide, raising the temperature from 25 °C to 35 °C raised the rate further, but at 45 °C the rate fell sharply.

   (a)

   Explain these results.

   [6 marks]

   (b)

   Evaluate whether the grower should add extra carbon dioxide, supplementary lighting and heating to the glasshouse to increase the yield of tomatoes.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   Ecologists studied a salt marsh on an estuary. Seawater floods the lowest part of the marsh twice a day, and the soil there is very salty and waterlogged. Soil salinity falls steadily with distance from the sea. Cord grass, Spartina, is the only plant found close to the sea. Further inland several other plant species grow, and Spartina is rare.

   (a)

   Which term describes all the populations of different species living and interacting in the salt marsh?

   [1 mark]

   • APopulation
   • BHabitat
   • CCommunity
   • DNiche

   (b)

   The ecologists want to find out how the distribution of plant species changes with soil salinity. Which method is most suitable?

   [1 mark]

   • APlace quadrats at regular intervals along a transect running inland from the sea, and measure salinity at each quadrat.
   • BPlace quadrats at random positions across the whole marsh and measure salinity once for the whole marsh.
   • CPlace one quadrat at the sea edge and one at the inland edge only.
   • DCount every Spartina plant in the marsh.

   (c)

   Suggest why Spartina is found close to the sea but is rare further inland.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A single species of cichlid fish colonised a small crater lake. Several thousand years later two species live in the lake. One feeds on algae in the shallow water and the other feeds on small invertebrates in the deep water. The two types can interbreed when kept together in a tank, but in the lake each fish chooses a mate of its own colour, and the males of the two types have different colours.

   (a)

   Which term describes the formation of two species from one within the same lake?

   [1 mark]

   • AAllopatric speciation
   • BStabilising selection
   • CConvergent evolution
   • DSympatric speciation

   (b)

   Which change is most important in allowing the two groups of fish to become separate species?

   [1 mark]

   • AThe same mutation occurring in every fish at the same time
   • BA reduction in gene flow between the groups, because they no longer mate with each other
   • CFish in deep water inheriting features that their parents gained by using them
   • DAll fish in one group moving to a different lake

   (c)

   Explain how natural selection could lead to the algae-eating fish evolving a jaw shape different from that of the original colonists.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A limestone quarry stopped working 60 years ago. At first the floor was bare rock. Today there are patches of lichen and moss on the rock, an area of grassland, an area of hazel and birch scrub, and a few small oak trees. In the scrub area, ecologists measured a gross primary productivity (GPP) of 13 000 kJ m⁻² year⁻¹, with plant respiration (R) of 8 200 kJ m⁻² year⁻¹. The energy incorporated into the biomass of primary consumers in the scrub was 480 kJ m⁻² year⁻¹.

   (a)

   Describe how the quarry floor changed from bare rock to the scrub stage.

   [3 marks]

   (b)

   Calculate the net primary productivity (NPP) of the scrub and the percentage of NPP that is transferred into the biomass of primary consumers. Suggest one reason why this percentage is less than 100%.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   Direct measurements at a mountain observatory show that the mean annual concentration of atmospheric carbon dioxide rose from 316 ppm in 1959 to 415 ppm in 2020. Over the same period the mean global surface temperature rose by about 1 °C. A commentator argues that this correlation does not show that carbon dioxide has caused the warming. Climate models that include rising emissions predict a further rise of 2 °C to 4 °C by 2100. A separate report, funded by a group of fossil fuel companies, concludes that the warming is mainly natural, whereas an independent university team that reviewed the same data concludes that it is mainly anthropogenic.

   (a)

   Evaluate the commentator's argument and the reliability of the model predictions.

   [6 marks]

   (b)

   Evaluate how far the source of a conclusion on a controversial climate issue should affect how much weight it is given. Describe how knowledge of the carbon cycle can be used to reduce atmospheric carbon dioxide.

   [6 marks]

   Total for question 8: 12 marks

End of questions