1. 1
   A marine biologist studies how brown seaweed cells absorb iodide ions from the surrounding seawater. Inside the seaweed cells, the iodide ion concentration is far higher than in the seawater outside.

   (a)

   By which process are the iodide ions absorbed into the seaweed cells against their concentration gradient?

   [1 mark]

   • AActive transport
   • BDiffusion
   • COsmosis
   • DTranspiration

   (b)

   If the biologist treats the seaweed cells with a poison that stops respiration, what would happen to the rate of iodide ion uptake?

   [1 mark]

   • AIt would increase, because more energy would be available
   • BIt would decrease, because active transport needs energy from respiration
   • CIt would stay the same, because active transport does not need energy
   • DIt would reverse, with iodide leaving the cells

   (c)

   Explain why the uptake of iodide ions by active transport requires energy from respiration, unlike diffusion of a substance down its concentration gradient.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A detergent manufacturer tests a biological washing powder containing a protease enzyme, designed to break down protein stains such as blood from clothing, across a range of water temperatures from 20\u00b0C to 80\u00b0C.

   (a)

   What happens to the protease enzyme's active site at 80°C, well above its optimum temperature?

   [1 mark]

   • AIt becomes a better fit for the substrate
   • BIt stays exactly the same shape
   • CIt changes shape (denatures), so the substrate no longer fits
   • DIt splits into two separate enzymes

   (b)

   Proteins, such as those in the blood stain, are broken down by the protease into which smaller units?

   [1 mark]

   • AFatty acids and glycerol
   • BSimple sugars
   • CNucleotides
   • DAmino acids

   (c)

   Explain why the detergent is less effective at removing the blood stain at 80°C, even though enzyme reactions are usually faster at higher temperatures.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A plant scientist dissects a tomato fruit and examines a thin slice under a microscope, then explains to students how the tomato's cells are organised into tissues, and how the cells in the fruit's skin are specially adapted for their function.

   (a)

   State the levels of organisation between a single cell in the tomato and the whole plant, in order from smallest to largest, and give one example of a tissue found in the tomato fruit.

   [3 marks]

   (b)

   Describe the structure of the cell wall and the vacuole in a typical plant cell, such as one from the tomato's skin, and explain how each contributes to keeping the fruit firm.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A sports physiologist studies a swimmer competing in a 400 m race. In the final lap her leg muscles cannot get enough oxygen from her blood to meet demand, and she experiences muscle fatigue. Afterwards, the physiologist compares this with the metabolism of yeast used in brewing, which respires without oxygen inside sealed fermentation vessels.

   (a)

   Explain the differences between the anaerobic respiration taking place in the swimmer's leg muscles and the anaerobic respiration taking place in the yeast, including word equations for each, and explain why aerobic respiration releases more energy than either.

   [6 marks]

   (b)

   Explain how the swimmer's alveoli are adapted to supply her muscles with as much oxygen as possible during the race, and describe two ways her breathing changes during intense exercise.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A florist places cut chrysanthemum stems in water containing a blue dye, then later cuts across a stem to see which tissue carried the dye upward. She also compares how quickly identical flowers wilt in a warm, dry, windy room and in a cool, humid, still room.

   (a)

   Which plant tissue is found to have carried the blue dye up the stem?

   [1 mark]

   • AXylem
   • BPhloem
   • CEpidermis
   • DCambium

   (b)

   Which term describes the loss of water vapour from the surface of the flowers' leaves, which is fastest in the warm, dry, windy room?

   [1 mark]

   • AOsmosis
   • BTranspiration
   • CTranslocation
   • DRespiration

   (c)

   Explain two reasons why the flowers in the warm, dry, windy room wilt faster than those in the cool, humid, still room.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A dermatologist explains to a patient that the body excretes waste products through three different organs: the lungs, the kidneys and the skin, and describes what each organ removes.

   (a)

   Which waste product is removed mainly by the lungs?

   [1 mark]

   • AUrea
   • BExcess salts
   • CCarbon dioxide
   • DExcess water only

   (b)

   Which structure in the kidney filters the blood under pressure, the first stage of urine formation?

   [1 mark]

   • AThe loop of Henle
   • BThe collecting duct
   • CThe ureter
   • DThe Bowman's capsule and glomerulus

   (c)

   State two substances found in sweat, and explain why sweating is classed as excretion even though its main role is cooling the body.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A swimmer dives into a cold outdoor pool. Receptors in her skin detect the drop in temperature and, within seconds, the blood vessels near the skin surface narrow, reducing blood flow to the skin, while she also begins to shiver.

   (a)

   Explain, using the terms stimulus, receptor and effector, how the swimmer's body detects and responds to the cold water by narrowing the blood vessels near her skin.

   [3 marks]

   (b)

   Explain how vasoconstriction and shivering both help to reduce heat loss and maintain the swimmer's core body temperature.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A crop scientist grows barley seedlings in a controlled growth chamber, testing how light intensity, carbon dioxide concentration and temperature each affect the rate of photosynthesis, before investigating how a barley-based recovery meal (barley porridge with milk) is digested by an athlete after training.

   (a)

   Give the balanced chemical symbol equation for photosynthesis, and explain how each of light intensity, carbon dioxide concentration and temperature can act as a limiting factor on the rate of photosynthesis in the barley seedlings.

   [6 marks]

   (b)

   Explain what happens to the starch and protein in the athlete's barley porridge and milk as they pass through the alimentary canal, naming the enzymes involved and their products.

   [6 marks]

   Total for question 8: 12 marks

End of questions