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A Level Biology: Transport in plants MCQs — Biology

20 multiple-choice questions on A Level Biology: Transport in plants from Biology, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

1. Companion cells contain many mitochondria to

  1. store sucrose
  2. make lignin
  3. carry out photosynthesis
  4. provide ATP for active loading of sucrose

Answer: D) provide ATP for active loading of sucrose

Explanation: Loading uses ATP. AS & A Level Biology · Topic 7 Transport in Plants · 7.1 Structure of transport tissues

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2. Sieve plates are found in

  1. phloem sieve tubes
  2. companion cells
  3. xylem vessels
  4. the endodermis

Answer: A) phloem sieve tubes

Explanation: Sieve plates are perforated end walls. AS & A Level Biology · Topic 7 Transport in Plants · 7.1 Structure of transport tissues

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3. Adhesion in the xylem is the attraction between

  1. sucrose and water
  2. xylem and phloem
  3. water molecules themselves
  4. water molecules and the cellulose of the walls

Answer: D) water molecules and the cellulose of the walls

Explanation: Water H-bonds to wall molecules. AS & A Level Biology · Topic 7 Transport in Plants · 7.2 Transport mechanisms

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4. Proton pumps in companion cells

  1. pump water into the phloem
  2. make ATP
  3. pump sucrose directly into the xylem
  4. use ATP to pump H⁺ out of the cell

Answer: D) use ATP to pump H⁺ out of the cell

Explanation: They create the proton gradient. AS & A Level Biology · Topic 7 Transport in Plants · 7.2 Transport mechanisms

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5. Rolled leaves in marram grass reduce water loss by

  1. increasing air movement
  2. increasing surface area
  3. opening stomata wider
  4. trapping humid air around the stomata

Answer: D) trapping humid air around the stomata

Explanation: Humid air lowers the gradient. AS & A Level Biology · Topic 7 Transport in Plants · 7.2 Transport mechanisms

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6. Which is a sink for assimilates?

  1. Mature leaf in sunlight
  2. Developing seed
  3. Stomata
  4. Xylem vessel

Answer: B) Developing seed

Explanation: Sinks use or store sucrose. AS & A Level Biology · Topic 7 Transport in Plants · 7.2 Transport mechanisms

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7. In translocation, sucrose is loaded into companion cells by

  1. osmosis
  2. cotransport with hydrogen ions
  3. simple diffusion
  4. endocytosis

Answer: B) cotransport with hydrogen ions

Explanation: H⁺/sucrose cotransporters. AS & A Level Biology · Topic 7 Transport in Plants · 7.2 Transport mechanisms

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8. Water moves up the xylem as a continuous column mainly because of

  1. osmosis in the leaves only
  2. active transport into xylem vessels
  3. cohesion between water molecules caused by hydrogen bonds
  4. translocation

Answer: C) cohesion between water molecules caused by hydrogen bonds

Explanation: Cohesion–tension. AS & A Level Biology · Topic 7 Transport in Plants · 7.2 Transport mechanisms

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9. Mass flow in phloem occurs because

  1. hydrostatic pressure is higher at the source than at the sink
  2. transpiration pulls sap upwards
  3. sucrose diffuses through sieve plates
  4. pressure is higher at the sink

Answer: A) hydrostatic pressure is higher at the source than at the sink

Explanation: Sap flows down the pressure gradient. AS & A Level Biology · Topic 7 Transport in Plants · 7.2 Transport mechanisms

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10. Which is an adaptation of xerophytes?

  1. Many large stomata on the upper surface
  2. Sunken stomata
  3. Large, flat, thin leaves
  4. A thin cuticle

Answer: B) Sunken stomata

Explanation: Sunken stomata trap humid air. AS & A Level Biology · Topic 7 Transport in Plants · 7.2 Transport mechanisms

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11. The apoplast pathway is movement of water through

  1. phloem sieve tubes
  2. cytoplasm via plasmodesmata
  3. cell walls and intercellular spaces
  4. vacuoles only

Answer: C) cell walls and intercellular spaces

Explanation: Apoplast = walls. AS & A Level Biology · Topic 7 Transport in Plants · 7.2 Transport mechanisms

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12. Which feature of xylem vessels allows water to move sideways?

  1. Plasmodesmata
  2. Pits
  3. Sieve plates
  4. Companion cells

Answer: B) Pits

Explanation: Pits are unlignified areas. AS & A Level Biology · Topic 7 Transport in Plants · 7.1 Structure of transport tissues

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13. Transpiration is

  1. evaporation of water from mesophyll cell walls and diffusion of vapour out through stomata
  2. uptake of water by root hairs
  3. active transport of ions
  4. movement of sucrose in phloem

Answer: A) evaporation of water from mesophyll cell walls and diffusion of vapour out through stomata

Explanation: Definition of transpiration. AS & A Level Biology · Topic 7 Transport in Plants · 7.2 Transport mechanisms

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14. Water enters the sieve tube at the source because

  1. sucrose lowers the water potential of the sap
  2. sucrose raises water potential
  3. transpiration pulls it in
  4. active transport pumps water

Answer: A) sucrose lowers the water potential of the sap

Explanation: Water follows by osmosis. AS & A Level Biology · Topic 7 Transport in Plants · 7.2 Transport mechanisms

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15. In the midrib of a leaf, the xylem is found

  1. in the stomata
  2. below the phloem
  3. on the upper side of the vascular bundle
  4. in the lower epidermis

Answer: C) on the upper side of the vascular bundle

Explanation: Xylem is uppermost in leaf bundles. AS & A Level Biology · Topic 7 Transport in Plants · 7.1 Structure of transport tissues

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16. The Casparian strip forces water into the symplast pathway because it contains

  1. lignin in the cortex
  2. suberin, which is waterproof
  3. pectin
  4. cellulose, which is permeable

Answer: B) suberin, which is waterproof

Explanation: Suberin blocks the apoplast. AS & A Level Biology · Topic 7 Transport in Plants · 7.2 Transport mechanisms

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17. In the stem of a herbaceous dicot, vascular bundles are arranged

  1. scattered randomly
  2. only in the epidermis
  3. in the centre in an X shape
  4. in a ring near the outside

Answer: D) in a ring near the outside

Explanation: Stem bundles form a ring. AS & A Level Biology · Topic 7 Transport in Plants · 7.1 Structure of transport tissues

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18. Lignin in xylem walls

  1. strengthens the vessel and prevents collapse
  2. makes vessels living
  3. allows sucrose transport
  4. forms sieve plates

Answer: A) strengthens the vessel and prevents collapse

Explanation: Lignin provides strength and waterproofing. AS & A Level Biology · Topic 7 Transport in Plants · 7.1 Structure of transport tissues

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19. Sieve tube elements have no nucleus so that

  1. there is little obstruction to the flow of sap
  2. they can divide
  3. they can photosynthesise
  4. they can store water

Answer: A) there is little obstruction to the flow of sap

Explanation: Fewer contents means easier flow. AS & A Level Biology · Topic 7 Transport in Plants · 7.1 Structure of transport tissues

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20. In a dicot root, the xylem is

  1. in the centre in a star or X shape
  2. above the phloem in the midrib
  3. in a ring near the outside
  4. absent

Answer: A) in the centre in a star or X shape

Explanation: Root xylem is central. AS & A Level Biology · Topic 7 Transport in Plants · 7.1 Structure of transport tissues

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