BioenergeticsOxford AQA IGCSE Biology: Topic test

1. 1
   A gardener digs up potato tubers from her allotment in autumn and finds them firm and full of starch, while nearby sugar beet roots store their food mainly as sugar rather than starch.

   (a)

   Why do plants convert glucose into starch for storage rather than storing it as glucose?

   [1 mark]

   • AStarch is insoluble, so it does not affect the concentration of cell contents by osmosis
   • BStarch is soluble and easily transported around the plant
   • CStarch contains more energy per gram than glucose
   • DStarch can be used directly in respiration without being broken down

   (b)

   Besides making starch for storage, which other substance can plants make from glucose, using nitrate ions absorbed from the soil?

   [1 mark]

   • ACellulose
   • BFat/oil
   • COxygen
   • DProtein

   (c)

   State two other uses of the glucose produced during photosynthesis, besides being converted into starch or used for respiration.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A gardener notices that pea seeds sown in a flooded plant pot, where very little oxygen can reach them, germinate slowly and produce a faint smell of alcohol, unlike seeds sown in a well-drained pot of the same soil.

   (a)

   Which type of respiration is most likely occurring in the seeds in the flooded pot?

   [1 mark]

   • AAerobic respiration, because oxygen is available
   • BAnaerobic respiration, because oxygen is in short supply
   • CPhotosynthesis, because light is available
   • DNo respiration is taking place

   (b)

   Which word equation correctly represents anaerobic respiration in the flooded pea seeds?

   [1 mark]

   • Aglucose -> ethanol + carbon dioxide
   • Bglucose + oxygen -> carbon dioxide + water
   • Cglucose -> lactic acid
   • Dcarbon dioxide + water -> glucose + oxygen

   (c)

   Explain why much less energy is transferred when the seeds respire anaerobically compared with aerobic respiration.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A patient recovering from surgery to remove a damaged section of small intestine is being monitored by doctors, who explain how digested food is absorbed into the blood and then transported around the body by the circulatory system.

   (a)

   Describe how starch, protein and fat are digested into smaller, soluble molecules that can be absorbed into the blood, naming the type of molecule each is broken down into.

   [3 marks]

   (b)

   Describe how the digested food substances, once absorbed into the blood in the small intestine, are transported to the rest of the body, referring to blood plasma and the double circulatory system.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A biology teacher explains to a class how the body breaks down a meal of pasta (rich in starch) and how the energy released from the digested food is then used by the body's muscles during exercise.

   (a)

   Explain how enzymes such as amylase break down starch in the digestive system, referring to the shape of the enzyme's active site and the effect of temperature on enzyme action.

   [6 marks]

   (b)

   Explain what happens to the sugars absorbed from the digested pasta once they reach the muscles during exercise, describing both aerobic and anaerobic respiration and the changes that occur in the body to support this.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A school canteen worker tests a sample of soup for the presence of different food groups, using Benedict's solution to test for reducing sugars and iodine solution to test for starch.

   (a)

   What colour change would indicate that the soup contains starch, when iodine solution is added?

   [1 mark]

   • ABlue-black to orange-brown
   • BColourless to purple
   • COrange-brown to blue-black
   • DBlue to brick-red precipitate

   (b)

   When Benedict's solution is heated with a food sample and turns from blue to a brick-red precipitate, what does this indicate?

   [1 mark]

   • AThe sample contains starch
   • BThe sample contains protein
   • CThe sample contains lipid
   • DThe sample contains a reducing sugar

   (c)

   Describe how the canteen worker could test whether the soup contains any lipid (fat).

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A diver takes a deep breath before swimming underwater, then, on surfacing, breathes out forcefully. A doctor uses this to explain to trainee lifeguards how breathing in and out is brought about by movements of the ribcage and diaphragm.

   (a)

   What happens to the volume and pressure inside the thorax when the diver breathes in?

   [1 mark]

   • AVolume decreases and pressure increases
   • BVolume increases and pressure decreases
   • CVolume and pressure both increase
   • DVolume and pressure both decrease

   (b)

   Which combination of muscle movements causes the diver to breathe in?

   [1 mark]

   • AIntercostal muscles relax and the diaphragm flattens
   • BIntercostal muscles relax and the diaphragm domes upwards
   • CIntercostal muscles contract, pulling the ribcage up, and the diaphragm contracts and flattens
   • DIntercostal muscles contract and the diaphragm domes upwards

   (c)

   Explain why the alveoli in the diver's lungs are well adapted for the rapid diffusion of oxygen into the blood.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A food scientist investigates why a protease enzyme, used to tenderise meat in a marinade, works well at the warm temperature and slightly acidic pH of the marinade, but stops working when the marinade is boiled.

   (a)

   Explain, in terms of enzyme structure, why boiling the marinade stops the protease enzyme working.

   [3 marks]

   (b)

   Describe the structure of a protein molecule and explain how proteins in the meat are broken down by the protease enzyme.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A dietitian advises an athlete on planning a balanced diet that provides enough carbohydrate, protein, fat, vitamins, minerals, fibre and water for both training and recovery, while also explaining how digestive enzymes will break this food down for the body to use.

   (a)

   Describe what is meant by a 'balanced diet' and explain why an athlete in intensive training might need a different balance of nutrients compared with someone who is not very active.

   [6 marks]

   (b)

   Explain how the digestive enzymes amylase, protease and lipase each break down a different type of food in the athlete's diet, and explain why bile is important for the digestion of fats.

   [6 marks]

   Total for question 8: 12 marks

End of questions