Energy for biological processesEdexcel A-Level Biology B: Topic test

1. 1
   A bumblebee must raise the temperature of its flight muscles to about 30 °C before it can take off on a cold morning. It does this by contracting its flight muscles without moving its wings. The muscle cells respire aerobically.

   (a)

   In which part of a flight muscle cell does the Krebs cycle take place?

   [1 mark]

   • ACytoplasm
   • BMitochondrial matrix
   • CInner mitochondrial membrane
   • DSpace between the two mitochondrial membranes

   (b)

   What happens to the energy released from glucose by respiration in the shivering muscle?

   [1 mark]

   • AAll of it is transferred to ATP.
   • BAll of it is released as heat.
   • CSome is transferred to ATP and the rest is released as heat.
   • DSome is transferred to ATP and the rest is stored permanently in NADH.

   (c)

   Explain why contracting the flight muscles without moving the wings warms the bee.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Mature mammalian red blood cells have no nucleus and no mitochondria. They obtain their ATP only by breaking down glucose to pyruvate in the cytoplasm, and they then convert the pyruvate to lactate.

   (a)

   How many molecules of ATP are used to phosphorylate one hexose sugar at the start of glycolysis?

   [1 mark]

   • A2
   • B1
   • C3
   • D4

   (b)

   Which statement explains why red blood cells cannot carry out the link reaction and the Krebs cycle?

   [1 mark]

   • AThey have no nucleus, so they cannot make the enzymes.
   • BThey contain no oxygen.
   • CThey have no ribosomes in the cytoplasm.
   • DThey have no mitochondria, which contain the enzymes of these stages.

   (c)

   A red blood cell breaks down $4.0 \times 10^{6}$ glucose molecules by glycolysis. Calculate the net number of ATP molecules produced.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Oligomycin is an antibiotic that binds to ATP synthase in the inner mitochondrial membrane and blocks the passage of protons through the enzyme. Researchers added oligomycin to isolated, well-oxygenated mitochondria that were supplied with pyruvate and ADP.

   (a)

   Describe how ATP is made by chemiosmosis in a normal mitochondrion.

   [3 marks]

   (b)

   Explain why the addition of oligomycin reduces the rate at which the mitochondria take up oxygen.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A Weddell seal can dive for more than 20 minutes. Its swimming muscles contain a large store of oxygen bound to myoglobin, but during a long dive this store runs low and blood flow to the muscles is reduced. After the dive, the lactate concentration in the seal's blood rises briefly.

   (a)

   Describe how the swimming muscles of the seal make ATP from glucose when oxygen is available.

   [6 marks]

   (b)

   Explain how the seal's muscles can keep contracting when the oxygen store has run out, and why this cannot continue indefinitely.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   Red seaweeds live at depths of about 30 m, where the light is mainly blue-green because water absorbs longer wavelengths. Their cells contain chlorophyll a and other pigments that absorb blue-green light strongly.

   (a)

   What does an action spectrum for a seaweed show?

   [1 mark]

   • AThe rate of photosynthesis at different wavelengths of light
   • BThe wavelengths of light absorbed by a single pigment
   • CThe wavelengths of light reflected by the seaweed
   • DThe intensity of different wavelengths at 30 m depth

   (b)

   Where in a chloroplast are the photosynthetic pigments found?

   [1 mark]

   • AIn the stroma
   • BIn the outer envelope
   • CIn the starch grains
   • DIn the thylakoid membranes

   (c)

   Explain the advantage to the seaweed of having several different photosynthetic pigments.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   RUBISCO is an enzyme in the stroma of the chloroplasts of a wheat leaf. It is the enzyme that fixes carbon dioxide during photosynthesis.

   (a)

   Which compound combines with carbon dioxide in the reaction catalysed by RUBISCO?

   [1 mark]

   • AGlycerate 3-phosphate (GP)
   • BGlyceraldehyde phosphate (GALP)
   • CRibulose bisphosphate (RuBP)
   • DReduced NADP

   (b)

   Which pair of products of the light-dependent stage is used in the Calvin cycle?

   [1 mark]

   • AOxygen and ATP
   • BReduced NADP and ATP
   • CGALP and ATP
   • DReduced NADP and RuBP

   (c)

   A mutation lowers the activity of RUBISCO in the leaf. Predict and explain the effect on the concentration of RuBP in the chloroplast stroma.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   Isolated chloroplasts were suspended in a buffer containing the blue dye DCPIP, which becomes colourless when it accepts electrons. A tube of chloroplasts in bright light turned colourless within minutes. An identical tube kept in the dark stayed blue.

   (a)

   Explain why the DCPIP became colourless in the light.

   [3 marks]

   (b)

   Chloroplasts in a tube containing no NADP can still make ATP in the light. Explain how.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A vertical farm grows lettuce indoors under LED lamps that emit only red and blue light. Temperature and light intensity are kept constant, and the carbon dioxide concentration in the air is raised to 0.1%. The farmer says the plants make glucose faster than lettuce grown in outdoor fields.

   (a)

   Explain why LEDs that emit only red and blue light can support photosynthesis effectively.

   [6 marks]

   (b)

   Explain how raising the carbon dioxide concentration increases the rate of photosynthesis, and why the rate eventually stops increasing.

   [6 marks]

   Total for question 8: 12 marks

End of questions