1. 1
   A biology class sets up three test tubes, each containing pond water with hydrogencarbonate indicator and a sprig of pondweed, then places them at different light intensities for an hour.

   (a)

   If the rate of photosynthesis exceeds the rate of respiration in a tube, the carbon dioxide concentration in the water falls. What colour does hydrogencarbonate indicator turn when carbon dioxide concentration falls?

   [1 mark]

   • APurple
   • BYellow
   • CRed-orange (no change)
   • DBlack

   (b)

   In the tube kept in complete darkness, the indicator turns yellow after an hour. What does this indicate about the gas exchange occurring in that tube?

   [1 mark]

   • ANo gas exchange has taken place in the tube
   • BCarbon dioxide concentration has decreased because photosynthesis exceeds respiration
   • COxygen concentration has increased because photosynthesis exceeds respiration
   • DCarbon dioxide concentration has increased because respiration exceeds photosynthesis

   (c)

   Explain why the tube kept at a certain intermediate light intensity showed no colour change in the hydrogencarbonate indicator at all.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A heavy smoker visits her doctor complaining of breathlessness on exertion. The doctor explains how smoking damages the gas exchange system.

   (a)

   Which gas is normally exchanged from the air in the alveoli into the blood in the surrounding capillaries?

   [1 mark]

   • ANitrogen
   • BCarbon dioxide
   • COxygen
   • DCarbon monoxide

   (b)

   Which substance found in cigarette smoke combines with haemoglobin in red blood cells, reducing the blood's ability to carry oxygen?

   [1 mark]

   • ANicotine
   • BCarbon monoxide
   • CTar
   • DOxygen

   (c)

   Explain how smoking increases a person's risk of developing coronary heart disease.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student monitors her own breathing rate at rest and then again immediately after running up several flights of stairs, noticing it becomes much faster and deeper.

   (a)

   Describe the roles of the intercostal muscles and the diaphragm in bringing air into the lungs during inhalation.

   [3 marks]

   (b)

   Explain how the structure of the alveoli is adapted for efficient gas exchange, which allows the student's blood to take up enough oxygen during exercise.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Environmental scientists studying a patch of woodland next to a busy factory measure gas exchange in the leaves of nearby trees at different times of day, alongside air pollution readings.

   (a)

   Explain how the structure of a leaf and its stomata are adapted for gas exchange, and how the net exchange of carbon dioxide and oxygen by the leaf changes between day and night.

   [6 marks]

   (b)

   The scientists also compare the woodland data with local hospital records showing higher rates of respiratory illness among factory workers exposed to air pollution and cigarette smoke. Explain how ventilation moves air into and out of the human lungs, and describe the biological consequences of smoking on the gas exchange system and circulatory system.

   [6 marks]

   Total for question 4: 12 marks

End of questions