Leaf structure and factors affecting photosynthesisIB MYP Sciences: Subtopic test

1. 1
   A botanist in Costa Rica examines a thin slice of a leaf under a microscope. She identifies the layers of cells, working from the upper surface of the leaf downwards, and notes the structures that allow the leaf to carry out photosynthesis.

   (a)

   Which layer of the leaf contains the most chloroplasts and is the main site of photosynthesis?

   [1 mark]

   • AWaxy cuticle
   • BSpongy mesophyll
   • CLower epidermis
   • DPalisade layer

   (b)

   What is the main function of the stomata?

   [1 mark]

   • ATo carry water from the roots to the leaf
   • BTo absorb light energy
   • CTo allow gases to enter and leave the leaf
   • DTo make the leaf waterproof

   (c)

   Explain how the waxy cuticle helps the leaf.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A sunflower leaf has tiny pores on its lower surface. Each pore is surrounded by a pair of guard cells that can change shape. The leaf also contains veins, which are made of xylem and phloem tissue.

   (a)

   Which statement describes the function of xylem in the leaf?

   [1 mark]

   • AIt carries sugars away from the leaf
   • BIt carries water and minerals to the leaf from the roots
   • CIt carries oxygen to the cells
   • DIt absorbs light energy

   (b)

   What happens when the guard cells take in water and become swollen?

   [1 mark]

   • AThe stoma opens
   • BThe stoma closes
   • CThe leaf becomes waterproof
   • DThe chloroplasts move to the roots

   (c)

   Describe the role of the phloem in the leaf.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates how light intensity affects the rate of photosynthesis in a piece of pondweed. She places the pondweed in a beaker of water containing dissolved sodium hydrogencarbonate. She places a lamp at different distances from the beaker and counts the bubbles of gas released from the cut stem in one minute. She records 52 bubbles per minute with the lamp 10 cm away, 30 at 20 cm, 18 at 30 cm, 10 at 40 cm and 8 at 50 cm.

   (a)

   Identify the independent variable, the dependent variable and one control variable in this investigation.

   [3 marks]

   (b)

   Describe the trend in the results, explain it, and evaluate the method by suggesting one weakness and one improvement.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A commercial grower in northern Europe grows tomatoes in a large glasshouse. In winter she heats the glasshouse with gas burners, switches on lamps and adds extra carbon dioxide to the air. She finds that the tomato yield rises, but the heating and lighting bills are very high and the burners release carbon dioxide into the atmosphere.

   (a)

   Explain how light intensity, carbon dioxide concentration and temperature can each limit the rate of photosynthesis, and why increasing one of them may eventually stop increasing the rate.

   [6 marks]

   (b)

   Discuss the economic, social and environmental implications of the grower's methods, and justify a conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions