A-Level Biology Topic 7: Transport in Plants MCQs – 30 Practice Questions with Answers (Cambridge 9700)
Free practice for Cambridge A-Level Biology 9700 on transport in plants, with every question followed by a short explanation to help you check your understanding.
Xylem, Phloem and Tissue Distribution
Q1. Which feature best suits a xylem vessel element for carrying water?
- (A) It has a large nucleus and dense cytoplasm
- (B) It is filled with chloroplasts for photosynthesis
- (C) It has sieve plates at each end
- (D) It is dead and hollow, with lignified walls
Show Answer
Answer: D – Xylem vessel elements are dead, hollow and lignified, forming an open tube for water.
Q2. Which feature is true of a phloem sieve tube element?
- (A) It is dead, with thick lignified walls
- (B) Living, with no nucleus and sieve plates
- (C) It carries only water from roots to leaves
- (D) It is found only in roots
Show Answer
Answer: B – Sieve tube elements are living cells with no nucleus and sieve plates joining them end to end.
Q3. What is the role of a companion cell?
- (A) It supports and loads a sieve tube element
- (B) It stores water in the leaf during dry conditions
- (C) It opens and closes stomata
- (D) It produces pollen
Show Answer
Answer: A – Companion cells support sieve tube elements and load assimilates into them.
Q4. In a transverse section of a herbaceous dicotyledonous stem, how are vascular bundles arranged?
- (A) Scattered throughout the ground tissue
- (B) In a single central strand only
- (C) In a ring around the stem
- (D) Only in the epidermis
Show Answer
Answer: C – In a herbaceous dicotyledonous stem the vascular bundles form a ring.
Q5. In a transverse section of a herbaceous dicotyledonous root, where is the xylem found?
- (A) Only in the outer epidermis
- (B) In a ring just under the epidermis
- (C) Only inside leaf veins
- (D) In the centre, with phloem between its arms
Show Answer
Answer: D – In a dicotyledonous root the xylem forms a central star, with phloem between the arms.
Q6. In a leaf vein, how are xylem and phloem usually positioned relative to each other?
- (A) Phloem above xylem in every vein
- (B) Xylem above phloem
- (C) Xylem and phloem mixed in one tissue
- (D) Phloem in the centre and xylem outside it
Show Answer
Answer: B – In a leaf vein the xylem is normally above the phloem, towards the upper leaf surface.
Q7. Why do xylem vessel elements have pits in their walls?
- (A) Pits allow sideways movement
- (B) Pits block all water movement
- (C) Pits store sugars
- (D) Pits produce new vessel elements
Show Answer
Answer: A – Pits are thin areas where water can pass sideways out of a vessel.
Q8. Why do companion cells contain many mitochondria and dense cytoplasm?
- (A) To carry out photosynthesis
- (B) To store starch grains
- (C) To supply energy for loading
- (D) To absorb light for the leaf
Show Answer
Answer: C – Loading assimilates needs energy, so companion cells have many mitochondria.
Q9. Which tissue carries water and mineral ions from roots to leaves?
- (A) Phloem only
- (B) Xylem
- (C) Epidermis only
- (D) Cortex only
Show Answer
Answer: B – Xylem carries water and dissolved mineral ions upwards through the plant.
Q10. Which tissue carries assimilates such as sucrose from sources to sinks?
- (A) Xylem vessels only
- (B) Epidermis
- (C) Cortex
- (D) Phloem sieve tubes
Show Answer
Answer: D – Phloem sieve tubes carry assimilates from sources to sinks.
Water Uptake and the Transpiration Stream
Q11. What is the apoplast pathway?
- (A) Through cell walls and spaces
- (B) Movement through the cytoplasm of living cells only
- (C) Movement inside xylem vessels only
- (D) Movement through the nucleus of each cell
Show Answer
Answer: A – The apoplast pathway runs through cell walls and intercellular spaces.
Q12. What is the symplast pathway?
- (A) Movement through dead xylem vessels
- (B) Movement through the soil only
- (C) Through cytoplasm via plasmodesmata
- (D) Movement through the air spaces of a leaf
Show Answer
Answer: C – The symplast pathway passes through the cytoplasm of cells linked by plasmodesmata.
Q13. What is the role of the Casparian strip in the root?
- (A) It pumps water into the leaf
- (B) It forces water into the symplast at the endodermis
- (C) It opens stomata in the leaf
- (D) It stores mineral ions in the cortex of the root for later use
Show Answer
Answer: B – The waterproof Casparian strip blocks the apoplast route, so water must enter cells at the endodermis.
Q14. Which material makes the Casparian strip waterproof?
- (A) Suberin
- (B) Cellulose only
- (C) Chlorophyll
- (D) Starch
Show Answer
Answer: A – The Casparian strip contains suberin, which is waterproof.
Q15. What is transpiration?
- (A) The uptake of water by root hairs from the surrounding soil
- (B) The movement of sugars in phloem
- (C) The opening of stomata at night
- (D) Evaporation from leaves, then vapour diffusion out
Show Answer
Answer: D – Transpiration is evaporation from internal leaf surfaces followed by diffusion of vapour out of the leaf.
Q16. How does hydrogen bonding help move water up the xylem?
- (A) It breaks water molecules apart
- (B) It prevents water from entering roots through the epidermis
- (C) Cohesion transmits the transpiration pull upwards
- (D) It turns water into sugar
Show Answer
Answer: C – Cohesion from hydrogen bonding holds the water column together under tension.
Q17. What is adhesion in the context of water movement in xylem?
- (A) The attraction between water molecules themselves
- (B) The attraction between water molecules and cellulose in cell walls
- (C) The sticking together of xylem vessels
- (D) The closing of stomata
Show Answer
Answer: B – Adhesion is the attraction of water to cellulose in the walls of xylem vessels.
Q18. Water moves from the soil into a root cell. In terms of water potential, in which direction does it move?
- (A) From higher water potential to lower water potential
- (B) From lower water potential to higher water potential
- (C) Only when both potentials are equal
- (D) From the xylem back into the soil
Show Answer
Answer: A – Water moves from a region of higher water potential to a region of lower water potential.
Q19. Which adaptation of a xerophytic leaf reduces water loss by transpiration?
- (A) A thin cuticle and wide open stomata
- (B) Large flat leaves with no hairs
- (C) Sunken stomata and a thick cuticle
- (D) The loss of all stomata
Show Answer
Answer: C – Sunken stomata, a thick cuticle and rolled leaves all reduce water loss in xerophytes.
Q20. How do leaf hairs help a xerophytic plant conserve water?
- (A) They absorb sunlight for photosynthesis
- (B) They pump water into the leaf
- (C) They open stomata wider
- (D) They trap moist air near the leaf
Show Answer
Answer: D – Hairs trap moist air, lowering the diffusion gradient for water vapour out of the leaf.
Translocation in Phloem
Q21. Which substances are transported as assimilates in phloem?
- (A) Water and mineral ions only
- (B) Sucrose and amino acids dissolved in water
- (C) Oxygen and carbon dioxide only
- (D) Starch grains alone
Show Answer
Answer: B – Assimilates such as sucrose and amino acids move in phloem dissolved in water.
Q22. What is a source in translocation, and what is a sink?
- (A) A source supplies assimilates and a sink uses or stores them
- (B) A source stores water and a sink makes sugars
- (C) A source is always a root and a sink is always a leaf
- (D) A source absorbs light and a sink absorbs water
Show Answer
Answer: A – A source, such as a leaf, supplies assimilates, while a sink uses or stores them.
Q23. How do companion cells load assimilates into sieve tubes?
- (A) By simple diffusion only
- (B) By opening stomata
- (C) By proton pumps and cotransport
- (D) By breaking down the sieve plates
Show Answer
Answer: C – Proton pumps create a gradient used by cotransporter proteins to load assimilates.
Q24. What drives mass flow in phloem sieve tubes?
- (A) Evaporation from leaves
- (B) The beating of a heart
- (C) Active transport in roots only
- (D) A hydrostatic pressure gradient from source to sink
Show Answer
Answer: D – Mass flow moves down a hydrostatic pressure gradient from source to sink.
Q25. At a sink, what happens to assimilates in the sieve tube?
- (A) They are stored in the leaf forever
- (B) They are removed for use or storage
- (C) They are turned back into water
- (D) They are pumped back to the source unchanged
Show Answer
Answer: B – Removal of assimilates at the sink lowers solute concentration and pressure, maintaining flow.
Q26. Why does loading sucrose at a source raise the pressure in a sieve tube?
- (A) It cools the sieve tube
- (B) It blocks the sieve plates
- (C) Water enters by osmosis, raising pressure
- (D) It removes all water from the sieve tube completely
Show Answer
Answer: C – Sucrose loading lowers water potential, so water enters by osmosis and pressure rises.
Q27. A plant is kept in dry soil. What is the most likely effect on the transpiration stream?
- (A) Uptake and xylem flow fall
- (B) Flow up the xylem increases sharply
- (C) Phloem stops carrying sucrose permanently
- (D) Leaves produce more water
Show Answer
Answer: A – Less soil water means less uptake, so the transpiration stream slows.
Q28. Which combination correctly matches tissue to its main transport role?
- (A) Phloem carries water, xylem carries sucrose
- (B) Xylem carries sucrose, phloem carries water only
- (C) Epidermis carries sucrose, cortex carries water
- (D) Xylem carries water, phloem carries assimilates
Show Answer
Answer: D – Xylem carries water and mineral ions, while phloem carries assimilates.
Q29. Why is the Casparian strip important for controlling what enters the xylem?
- (A) It allows all solutes to pass freely
- (B) It forces passage through endodermis cells
- (C) It prevents water from ever reaching the xylem
- (D) It stores sugars in the root
Show Answer
Answer: B – By blocking the apoplast route, the strip forces passage through endodermis cells.
Q30. Which sequence correctly describes water movement from soil to leaf?
- (A) Soil to xylem, up the xylem, out of the leaf
- (B) Soil, phloem to leaf, xylem to root, out through stomata
- (C) Leaf, xylem to root, soil to phloem, out through the cuticle only
- (D) Soil, leaf air spaces, xylem, phloem, out through roots
Show Answer
Answer: A – Water crosses the root by apoplast or symplast routes, rises in xylem, and leaves by transpiration.
Work through any questions you missed again, then revise those areas before moving on to the next topic.