Free Transport in plants questions for AS Level Biology (9700), part of Transport & disease. Each question has the answer and the marking points an examiner would look for.
Generate a full Transport in Plants worksheet →All Transport & disease questionsXerophytes have adaptations that reduce water loss.
1 Hairs increase air movement over the stomata.
2 Having more stomata reduces transpiration.
3 Sunken stomata trap moist air, reducing the water potential gradient.
Which statements are correct?
Answer: D
Which term is described by this statement?
“Movement of sucrose solution in phloem down a hydrostatic pressure gradient.”
Answer: D
Which row describes the pathways and mechanism of water movement through a plant?
| pathway in cortex mostly | blocked at endodermis by | mechanism in xylem | |
|---|---|---|---|
| A | apoplast | plasmodesmata | cohesion–tension |
| B | vacuolar | Casparian strip | root pressure only |
| C | symplast | Casparian strip | active transport |
| D | apoplast | Casparian strip | cohesion–tension |
Answer: D
Sucrose is transported in phloem by mass flow.
Describe how sucrose is loaded into phloem sieve tubes.
Explain how a hydrostatic pressure gradient develops in the phloem.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | H⁺ pumped out; co-transport companion cells actively pump H⁺ out B1 H⁺ diffuse back with sucrose B1 via co-transporter proteins B1 | 3 |
| (b) | water enters at source; leaves at sink loading sucrose lowers water potential so water enters by osmosis at the source B1 unloading at the sink reduces pressure there B1 | 2 |
This question is about transport in plants.
Describe the pathways taken by water from the root hair cell to the xylem.
Explain how water moves up the xylem by cohesion–tension.
Describe two features of xylem vessel elements that adapt them for transport.
Describe two features of a xerophyte and explain how each reduces water loss.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | apoplast through cell walls; symplast through cytoplasm and plasmodesmata; Casparian strip forces into symplast at endodermis apoplast pathway through cell walls B1 symplast pathway through cytoplasm via plasmodesmata B1 at the endodermis the Casparian strip blocks the apoplast so water enters the symplast B1 | 3 |
| (b) | evaporation from leaves lowers water potential; water pulled up; H bonds cohesion between water molecules; adhesion to walls; continuous column under tension water evaporates from mesophyll cells and diffuses out of stomata B1 this creates tension that pulls water up the xylem B1 hydrogen bonds between water molecules (cohesion) keep the column continuous B1 adhesion to the xylem walls helps B1 | 4 |
| (c) | no end walls (continuous tube); lignified, waterproof, prevents collapse; pits Any 2 of: no end walls so form a continuous tube; lignified walls withstand tension / prevent collapse; pits allow lateral movement B2 | 2 |
| (d) | rolled leaves / sunken stomata trap humid air; thick cuticle; hairs rolled leaves / sunken stomata / hairs trap moist air, reducing the water potential gradient B1 thick waxy cuticle reduces evaporation B1 | 2 |
Water moves through the leaf by the apoplast and symplast pathways.
Distinguish between the apoplast and symplast pathways.
Explain the role of the Casparian strip in the endodermis.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | cell walls vs cytoplasm via plasmodesmata apoplast: through cell walls and spaces B1 symplast: through cytoplasm and plasmodesmata B1 | 2 |
| (b) | blocks apoplast; water enters symplast suberin blocks the apoplast pathway B1 water and ions must enter the symplast, so uptake is controlled B1 | 2 |
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