On the wild sideEdexcel A-Level Biology A: Topic test

1. 1
   A vertical farm grows lettuce in a sealed warehouse under LED lamps that are switched on for 16 hours and off for 8 hours in every 24 hours. The air is enriched with carbon dioxide while the lamps are on.

   (a)

   In a lettuce chloroplast, where are the enzymes that catalyse the Calvin cycle found?

   [1 mark]

   • AIn the stroma
   • BIn the thylakoid membranes, bound to the photosystems
   • CIn the inner membrane of the chloroplast envelope
   • DIn the lumen of the thylakoids, where protons accumulate

   (b)

   In the light-dependent reactions, what is the immediate source of the electrons that replace those lost from chlorophyll in photosystem II?

   [1 mark]

   • AThe reduction of carbon dioxide
   • BThe hydrolysis of ATP
   • CThe photolysis of water
   • DThe oxidation of reduced NADP

   (c)

   Explain why carbon fixation in the Calvin cycle stops soon after the lamps are switched off.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A limestone quarry was abandoned in 1940. Today its floor is covered by a mixture of grassland, scrub and young woodland, and the quarry is used by many species of bird, insect and plant.

   (a)

   Which feature is typical of a pioneer species that colonises bare quarry rock?

   [1 mark]

   • AA need for a deep, humus-rich soil
   • BThe ability to tolerate extreme conditions and grow with almost no soil
   • CThe ability to grow in the deep shade beneath a canopy
   • DLarge, heavy seeds that germinate slowly

   (b)

   Which term describes all the living organisms of all the species in the quarry?

   [1 mark]

   • APopulation
   • BHabitat
   • CEcosystem
   • DCommunity

   (c)

   Explain why species diversity increased as the quarry changed from bare rock to scrub.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Marine ecologists measured the productivity of a kelp forest off the coast of California over one year. The kelp had a gross primary productivity (GPP) of 4800 kJ m⁻² year⁻¹ and its respiration used 1900 kJ m⁻² year⁻¹. Sea urchins that graze the kelp had a net productivity of 232 kJ m⁻² year⁻¹.

   (a)

   Calculate the net primary productivity of the kelp, and the percentage of its gross primary productivity that is lost in respiration. Show your working.

   [3 marks]

   (b)

   Calculate the efficiency of energy transfer from the kelp to the sea urchins, and explain two reasons why this efficiency is less than 100%.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A company grows the single-celled alga Nannochloropsis in large outdoor ponds and converts the harvested algae into biodiesel. The energy needed to pump, harvest and process the algae comes from the electricity grid, which is supplied mainly by burning natural gas. This energy input is equal to 60% of the chemical energy contained in the biodiesel produced.

   (a)

   Explain how the light energy absorbed by the algal chloroplasts is converted into chemical energy stored in carbohydrate.

   [6 marks]

   (b)

   Evaluate the claim that using algal biodiesel instead of fossil diesel reduces the net amount of carbon dioxide added to the atmosphere.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   The concentration of methane in the atmosphere has risen from about 0.7 parts per million before the Industrial Revolution to about 1.9 parts per million today. Important sources include flooded rice paddies, the guts of cattle and landfill sites.

   (a)

   Which process is mainly responsible for the methane released from flooded rice paddies?

   [1 mark]

   • AAerobic respiration by the rice plants
   • BPhotosynthesis in the rice leaves
   • CAnaerobic decomposition of organic matter by microorganisms in the waterlogged soil
   • DComplete combustion of the rice stems

   (b)

   Which statement is a limitation of climate models used to predict future global temperature?

   [1 mark]

   • AMany factors interact and some feedback effects are not fully understood, so the models rely on assumptions
   • BModels cannot use any data from the past
   • CModels assume that greenhouse gas emissions will stay constant
   • DModels take account of carbon dioxide only

   (c)

   Explain how an increase in the concentration of methane in the atmosphere contributes to an increase in global temperature.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   Cichlid fish live in a small, deep crater lake in East Africa. Fish living in shallow water are mainly yellow and mate only with yellow fish, while fish living in deeper water are mainly blue and mate only with blue fish. There is no physical barrier between the two groups in the lake.

   (a)

   Which statement defines evolution?

   [1 mark]

   • AA change in the phenotype of an individual during its lifetime
   • BThe appearance of new alleles in response to a change in the environment
   • CThe survival of the largest individuals in a population
   • DA change in the allele frequencies of a population over successive generations

   (b)

   The two groups of cichlids are becoming separate species within the same lake. What is this type of speciation called?

   [1 mark]

   • AAllopatric speciation
   • BSympatric speciation
   • CStabilising selection
   • DThe founder effect

   (c)

   Explain how a new advantageous allele that arises by mutation in a population of fish can become more common over many generations.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A student estimates the population of wild bluebells in a woodland of area 8000 m². She places 40 quadrats, each 0.5 m × 0.5 m, in the woodland and counts the bluebell plants in each. The total number of bluebells counted in all 40 quadrats is 156. Bluebells flower in April and May, before the leaves of the trees fully open and shade the woodland floor.

   (a)

   Calculate an estimate of the number of bluebells in the whole woodland. Show your working.

   [3 marks]

   (b)

   Describe how the student should position the quadrats to avoid bias, and explain, in terms of niche, how bluebells and trees can live in the same woodland.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   In the Pyrenees an alpine plant lives only above 2000 m, on cool, damp, rocky slopes. It grows on several separate mountain tops, each separated from the others by lower, warmer valleys where the plant cannot survive. Over the last 40 years the mean temperature in the mountains has risen by 1.5 °C and summer rainfall has decreased.

   (a)

   Explain how this climate change may affect the distribution and the life cycle of the alpine plant and of the insects that pollinate it.

   [6 marks]

   (b)

   Explain how, if the populations on different mountain tops stay isolated for many thousands of years, new species of the plant could form.

   [6 marks]

   Total for question 8: 12 marks

End of questions