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Photosynthesis and transport in plants
6 MDCAT Biology questions with answers and explanations.
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The light reactions of photosynthesis take place in the:
- 1 Stroma
- 2 Thylakoid membranes
- 3 Mitochondria
- 4 Cytoplasm
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Correct answer: Thylakoid membranes
Light is absorbed by chlorophyll in the thylakoid membranes of the grana. The Calvin cycle happens in the stroma.
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Which enzyme fixes carbon dioxide in the Calvin cycle?
- 1 Amylase
- 2 Catalase
- 3 RuBisCO
- 4 ATP synthase
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Correct answer: RuBisCO
RuBisCO attaches carbon dioxide to ribulose bisphosphate, the first step of carbon fixation.
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Water moves up the xylem mainly because of:
- 1 Root pressure alone
- 2 Transpiration pull and cohesion
- 3 Active transport in xylem vessels
- 4 Osmosis in the leaf only
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Correct answer: Transpiration pull and cohesion
Water evaporating from leaves pulls a continuous column of water upward. Cohesion between water molecules keeps the column unbroken.
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Stomata open when the guard cells become:
- 1 Flaccid
- 2 Plasmolysed
- 3 Turgid
- 4 Dead
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Correct answer: Turgid
When guard cells take up water and become turgid, their shape bends and the pore opens.
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Which substance is mainly transported in the phloem?
- 1 Water and minerals
- 2 Sucrose
- 3 Starch
- 4 Oxygen
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Correct answer: Sucrose
Phloem carries sucrose from sources, such as leaves, to sinks, such as roots and fruits. This is called translocation.
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Auxins promote:
- 1 Seed dormancy
- 2 Cell elongation
- 3 Leaf fall
- 4 Fruit ripening only
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Correct answer: Cell elongation
Auxin makes cells in the shoot elongate. Uneven auxin on two sides of a shoot causes bending toward light (phototropism).