Transport in Plants (3.1.3): OCR A Level Biology Exam Questions by Topic

OCRExchange and TransportExam Questions
Written by Tom Whitburn

Transport in plants is one of the longest topics in the Year 12 OCR A course, and it turns up on every paper. Spec point 3.1.3 asks you to explain why large plants need a transport system, to know the structure of xylem and phloem in roots, stems and leaves, and to follow water from the soil, through the plant and out of the stomata. You also need the adaptations of xerophytes and hydrophytes, the mechanism of translocation, and practical work with stained sections, dissected stems and the potometer.

Most lost marks here come from loose wording. The examiners' reports keep pointing to the same slips: naming a cell when the question asks for a tissue (or the other way round), writing "water is lost" instead of water vapour, saying "waxy cuticle" without "thick", and calling sucrose loading "active transport of sucrose" instead of explaining the proton pump and cotransporter.

Work through the eighteen questions below in order. They start with recall of the vascular tissues, move on to water movement, transpiration and translocation, and finish with practical and potometer questions. If you'd like to go through questions like these with me each week, my OCR A masterclasses run on Wednesdays at 5.15pm for Year 12 and on Tuesdays at 6.30pm or Thursdays at 5.15pm for Year 13.

What you need from GCSE

Each question on this page assumes you're secure on these GCSE ideas. If any of them feels shaky, look it up before you start.

  • Xylem carries water and mineral ions from the roots to the leaves; phloem carries dissolved sugars made in photosynthesis around the plant.
  • Water enters root hair cells by osmosis and leaves the plant as water vapour through the stomata. This loss is called transpiration.
  • Transpiration is faster when it is warmer, brighter, windier or less humid.
  • Guard cells open and close the stomata, which also let carbon dioxide in for photosynthesis.
  • Large organisms have a smaller surface area to volume ratio than small ones, so diffusion alone can't supply all their cells.

Key terms

These words come up in the questions and mark schemes. Examiners expect you to use them exactly.

  • Xylem vessel: a dead, hollow cell with lignified walls and no end walls, joined end to end to carry water and mineral ions; pits let water move sideways.
  • Sieve tube element: a living phloem cell with no nucleus, joined end to end through sieve plates with sieve pores; it carries assimilates such as sucrose.
  • Companion cell: the cell next to a sieve tube element, linked to it by plasmodesmata, with many mitochondria to supply ATP for loading sucrose.
  • Apoplast and symplast pathways: water moving through cell walls and the spaces between them (apoplast), or through the cytoplasm and plasmodesmata (symplast).
  • Casparian strip: a waterproof band in the walls of endodermis cells that blocks the apoplast pathway and forces water into the symplast.
  • Transpiration: the loss of water vapour from the leaves, mainly through the stomata; a consequence of gas exchange.
  • Transpiration stream: the movement of water from the roots, up the xylem, to the leaves.
  • Cohesion and adhesion: hydrogen bonds holding water molecules to each other (cohesion) and to the xylem walls (adhesion).
  • Xerophyte: a plant adapted to dry conditions, such as a cactus or marram grass.
  • Translocation: the energy-requiring movement of assimilates in the phloem from a source to a sink by mass flow.

What these questions cover (OCR 3.1.3)

The questions test these learning outcomes from the OCR A Level Biology A specification (H420):

  • (a) the need for transport systems in multicellular plants (size, metabolic rate and SA:V)
  • (b)(i) the structure and function of the vascular system in the roots, stems and leaves of herbaceous dicotyledonous plants (xylem vessels, sieve tube elements and companion cells)
  • (b)(ii) the examination and drawing of stained sections of plant tissue to show the distribution of xylem and phloem (PAG1)
  • (b)(iii) the dissection of stems, both longitudinally and transversely, and their examination to demonstrate the position and structure of xylem vessels (PAG2)
  • (c)(i) the process of transpiration and the environmental factors that affect transpiration rate
  • (c)(ii) practical investigations to estimate transpiration rates (the potometer (PAG5))
  • (d) the transport of water into the plant, through the plant and to the air surrounding the leaves (apoplast and symplast pathways, cohesion, adhesion)
  • (e) adaptations of plants to the availability of water in their environment (xerophytes and hydrophytes)
  • (f) the mechanism of translocation (active loading at the source, removal at the sink)

How to use this page

Write your answer on paper before you open the mark scheme. Allow about 1.2 minutes per mark: the 18 questions are worth 40 marks, so about 48 minutes in total. Then mark your answer strictly against the mark scheme and read the examiners' tip underneath it. If you'd rather print the questions, download the PDF pack.

Vascular tissues

Question 1

A level Paper 1 · June 2022 · Q16(a) · 3 marks · Easy

Explain, with examples of transported substances, why multicellular plants need transport systems.

Question explaining that dicotyledons include oak trees and dandelions and asking why multicellular plants need transport systems, using examples of transported substances.
Show the mark scheme Mark scheme: up to two explanations (long distances, diffusion too slow, small SA:V) and up to two examples (water and ions from roots to other parts, sucrose from source to sink, hormones).

Tap an image to open it full size.

From the examiners' report: Give each example in full: what is carried, and from where to where, such as water from the roots to the leaves. Sucrose, not glucose, travels in the phloem, and a whole large plant has a small SA:V.

Question 2

A level Paper 3 · June 2018 · Q1(b) · 2 marks · Easy

Identify the tissues at M and N in a cross section of an onion root.

Fig. 1: light micrograph of a cross section of an onion root with the central vascular tissue; label M points to large xylem cells and N to smaller phloem cells.
Show the mark scheme Mark scheme: M is xylem, N is phloem. Xylem vessels, sieve tubes or companion cells are not allowed because they are cells, not tissues.

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From the examiners' report: The question asks for tissues, so write xylem and phloem. Vessels, elements and sieve tubes are cells and didn't score.

Question 3

A level Paper 3 · June 2025 · Q1(a) · 2 marks · Medium

Name the cells labelled A and B in a root section.

Photomicrograph of a transverse section through a dicotyledonous root, with A labelling a small cell in the phloem and B a large cell in the xylem.
Show the mark scheme Mark scheme: A is a sieve tube element, B is a xylem vessel (xylem cell allowed).

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From the examiners' report: This time the question asks for cells, so 'phloem' wasn't enough: A is a sieve tube element and B is a xylem vessel. Always check whether you're asked for a cell or a tissue.

Question 4

A level Paper 1 · June 2022 · Q16(b)(ii) · 2 marks · Medium

State two functions of the xylem (structure A) in a leaf section.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Fig. 16.1: light micrograph of a transverse section through a dicotyledon leaf, magnification ×120, with A labelling the xylem in the midrib and B the phloem.
Show the mark scheme Mark scheme: transport of water or named ions; mechanical or structural support. 'Strength' alone is ignored.

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From the examiners' report: Give two different functions: transport and support. Transport of water and transport of ions count as one function.

Question 5

AS Paper 1 · June 2019 · Q24(c)(i) · 3 marks · Medium

Identify the vessel wall, lumen and pit on a section through xylem.

Fig. 24: drawing of a cross section through xylem tissue from a stem, with a 20 micrometre scale bar; A labels a thick vessel wall, B the empty space inside a vessel and C a gap linking two neighbouring vessels.
Show the mark scheme Mark scheme: A vessel wall (lignified wall allowed), B lumen, C (bordered) pit. 'Cell' is not allowed.

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From the examiners' report: Use the xylem words: vessel wall (not cell wall), lumen (not hollow tube) and pit. Plasmodesmata link living cells, so they aren't found in xylem vessels.

Question 6

AS Paper 1 · June 2019 · Q24(c)(ii) · 1 mark · Medium

Suggest why mosses don't need roots or xylem.

Question stating that mosses do not have xylem and rarely grow more than a few centimetres tall, and asking why they don't need roots or xylem.
Show the mark scheme Mark scheme: large surface area to volume ratio, or the distance water and mineral ions travel is short. 'Larger' or 'higher' SA:V is not allowed; support is ignored.

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From the examiners' report: Link the small size to a large SA:V and a short distance for water to travel. Answers about support or damp habitats didn't score.

Question 7

AS Paper 1 · June 2024 · Q22(b)(i) · 2 marks · Medium

Identify tissues E and F on a drawing made from a stained stem section.

Drawing made from a light micrograph of a transverse section of a stem, showing a vascular bundle with F labelling the outer tissue, E a thin band of cells and G the inner tissue.
Show the mark scheme Mark scheme: E is cambium (meristem allowed), F is phloem. Stem cells and phloem sieve tubes are not allowed.

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From the examiners' report: In a vascular bundle in a stem, phloem is on the outside, xylem on the inside and cambium between them. Many students labelled F as xylem.

Question 8

AS Paper 1 · June 2024 · Q22(b)(ii) · 2 marks · Hard

Explain two ways the xylem (tissue G) is adapted for its function.

Question asking for two ways tissue G is adapted for its function, with numbered answer lines.
Show the mark scheme Mark scheme: pits let water move sideways; lignified vessel walls for support or to stop collapse; no end walls for a continuous water column; narrow vessels for capillarity; lignin for adhesion. 'Cell' walls and phloem not allowed.

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From the examiners' report: 'Explain' means link each feature to its job: lignified vessel walls stop the vessel collapsing, no end walls give a continuous column of water. Say 'vessel walls', not 'cell walls'.

Water transport and transpiration

Question 9

AS Paper 1 · June 2024 · Q22(c) · 3 marks · Medium

Complete sentences about the apoplast pathway, the Casparian strip and plasmodesmata.

Sentences with three gaps: in the apoplast pathway water moves through the blank of plant cells; at the endodermis it is blocked by the blank; in the symplast pathway it moves between cells through channels called blank.
Show the mark scheme Mark scheme: cell walls, Casparian strip, plasmodesmata. Phonetic spellings allowed.

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From the examiners' report: In the apoplast pathway water moves through the cell walls themselves, not the 'spaces between cell walls'. Learn to spell Casparian strip and plasmodesmata.

Question 10

A level Paper 1 · June 2023 · Q21(a)(i) · 2 marks · Easy

Describe what is meant by the transpiration stream.

Question about a 1933 study of coloured dyes in the transpiration stream of sycamore trees, asking what is meant by the term transpiration stream.
Show the mark scheme Mark scheme: movement of water from the roots to the leaves.

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From the examiners' report: Say where the water starts and finishes: from the roots to the leaves. 'Through the xylem' alone misses the second mark, and you don't need cohesion-tension here.

Question 11

A level Paper 1 · June 2023 · Q21(b)(iii) · 2 marks · Medium

Explain why plants in high light intensity need more water than plants in shade.

Question asking why plants growing in high light intensity require more water than plants in shade at the same temperature.
Show the mark scheme Mark scheme: more photosynthesis (light-dependent reaction); more stomata open for gas exchange or carbon dioxide entry; more transpiration so more water vapour lost by evaporation.

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From the examiners' report: Link the chain: more light, more photosynthesis, stomata open wider for carbon dioxide, so more water vapour is lost. Plants in shade still photosynthesise, just more slowly.

Question 12

AS Paper 1 · June 2024 · Q22(d) · 2 marks · Hard

Explain two ways xerophytes are adapted to prevent water loss.

Question stating that xerophytes are adapted to dry environments and asking for two ways they are adapted to prevent water loss.
Show the mark scheme Mark scheme: rolled or small leaves or spines reduce the surface area for transpiration; thick waxy cuticle; sunken stomata, hairs or rolled leaves trap water vapour and reduce the water potential gradient; fewer stomata; hinge cells.

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From the examiners' report: Explain how each feature cuts transpiration: rolled leaves reduce the surface area, sunken stomata trap water vapour. All plants have a waxy cuticle, so say thick waxy cuticle.

Question 13

AS Paper 1 · June 2018 · Q25(d)(i) · 2 marks · Medium

Suggest why trees further from a river have hairier leaves.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Question stating that students found a positive correlation between the distance of trees from a river and mean leaf hair density, asking for reasons.
Show the mark scheme Mark scheme: further from the river there is less water; hairs trap water vapour, reduce transpiration and reduce the water vapour potential gradient. 'Hairs prevent water loss' is not allowed.

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From the examiners' report: Make two linked points: less water is available further from the river, and the hairs trap water vapour so transpiration is reduced. Hairs don't absorb water from the air.

Translocation

Question 14

A level Paper 3 · June 2025 · Q1(c) · 3 marks · Easy

Describe how carbohydrates move from palisade cells into companion cells.

Question stating that carbohydrates made in palisade cells are transported in phloem to sinks such as roots, and asking how they move from palisade cells into companion cells.
Show the mark scheme Mark scheme: transported as sucrose; through plasmodesmata (symplast) or cell walls (apoplast); protons pumped out of the companion cell; sucrose cotransported in with protons; active loading. 'Active transport of sucrose' is not allowed.

Tap an image to open it full size.

From the examiners' report: Name sucrose, give the pathway to the phloem, then explain active loading: protons are pumped out and sucrose comes back in with them by cotransport. 'Active transport of sucrose' wasn't credited.

Question 15

AS Paper 1 · June 2025 · Q24(a) · 3 marks · Hard

Find and correct three errors in a student's notes on loading sucrose into companion cells.

Three incorrect revision-note statements about companion cell membranes: channel proteins pump protons; cotransporters carry protons and glucose; cotransporters use ATP to change shape.
Show the mark scheme Mark scheme: channel should be carrier proteins; glucose should be sucrose; cotransporters use the proton gradient, not ATP.

Tap an image to open it full size.

From the examiners' report: Protons are pumped out by carrier proteins, sucrose (not glucose) is loaded, and the cotransporter is driven by protons diffusing back in down their gradient, not by ATP.

Practical and potometer

Question 16

AS Paper 2 · June 2017 · Q2(a) · 2 marks · Medium

Describe how to observe the position of xylem vessels in celery stalks.

Question asking how students could observe the position of xylem vessels in the leaf stalks (petioles) of celery.
Show the mark scheme Mark scheme: stand the stalks in dye, then cut a transverse section; or cut a thin cross section, add a stain and look with a microscope on low power. Longitudinal cuts are ignored.

Tap an image to open it full size.

Question 17

AS Paper 2 · June 2023 · Q2(c) · 2 marks · Medium

Modify the potometer set-up to test the effect of air movement on transpiration.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Question asking how to modify the potometer apparatus in Fig. 2.1 and Fig. 2.2, a leafy shoot with a clear plastic dome and water spray, to find how air movement affects transpiration.
Show the mark scheme Mark scheme: remove the plastic dome and spray bottle; use a fan at different distances or different speeds.

Tap an image to open it full size.

From the examiners' report: Change only the variable you're testing: take off the plastic dome as well as adding a fan at different speeds or distances, or humidity becomes a second variable.

Question 18

A level Paper 3 · June 2024 · Q3(c)(i) · 2 marks · Hard

Calculate the rate of transpiration from a potometer bubble that moves 18 mm in 30 minutes.

Diagram of a potometer with a leafy shoot, water reservoir, screw clip and a capillary tube with a scale in mm; the bubble moves 18 mm in 30 minutes in tubing of diameter 1 mm; use volume = pi r squared l.
Show the mark scheme Mark scheme: radius 0.5 mm, squared is 0.25, times pi times 18 gives 14.1 mm cubed in 30 minutes, times 2 gives 28 mm cubed per hour.

Tap an image to open it full size.

From the examiners' report: Halve the diameter to get the radius, square it, then convert from per 30 minutes to per hour by doubling. Give the answer to 2 or 3 significant figures and show your working.

Where students lose marks (from OCR examiners' reports and mark schemes)

Each point below is followed by wording that gained marks.

  • Tissue or cell? Check the question: Asked for tissues, some students wrote xylem vessels or sieve tubes and lost the marks. Asked for cells, most wrote 'phloem', which is a tissue.

    ✔ Gains credit: Tissues: "xylem" and "phloem". Cells: "sieve tube element" and "xylem vessel".

  • Xylem has pits, not plasmodesmata: On a section of xylem, students wrote 'cell wall', 'hollow tube' and 'plasmodesmata' for the labelled parts.

    ✔ Gains credit: "Vessel wall" (or "lignified wall"), "lumen" and "(bordered) pit".

  • Mosses are small, so their SA:V is large: Some wrote that mosses have a 'larger' or 'higher' SA:V, which wasn't allowed, or wrote about support instead.

    ✔ Gains credit: "Large surface area to volume ratio" or "the distance water and mineral ions need to travel is short".

  • Transpiration loses water vapour: Answers said plants in bright light 'lose more water' without saying it leaves as vapour through open stomata.

    ✔ Gains credit: "More stomata open to allow entry of carbon dioxide" and "increases transpiration so more water vapour is lost".

  • Every plant has a cuticle; xerophytes have a thick one: Students wrote 'waxy cuticle' or 'stomata on the underside', which are true of most plants, and 'small leaves' without surface area.

    ✔ Gains credit: "Thick(er) waxy cuticle to reduce transpiration" and "rolled leaves, to reduce the surface area for transpiration".

  • Active loading, not active transport of sucrose: 'Sucrose is actively transported into the companion cell' was not credited.

    ✔ Gains credit: "Protons actively pumped out of the companion cell" and "co-transport of sucrose with protons into the companion cell".

  • The cotransporter runs on protons, not ATP: Few students spotted that the cotransporter in companion cells doesn't use ATP, and many confused it with the proton pump.

    ✔ Gains credit: "Carrier proteins" pump protons; the cotransporter "uses the proton gradient to cotransport the sucrose".

  • Take the dome off when you add the fan: Most students used a fan at different settings but left the plastic dome on, so humidity changed as well.

    ✔ Gains credit: "Remove plastic dome / spray bottle" and "place fan at different distances / set to different speeds".

Download the questions

Download the PDF pack (18 questions, mark schemes at the end)

Keep practising

Questions, mark schemes and examiners' report extracts © OCR.

Tom Whitburn
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