Cambridge O Level Biology 5090: Transport in flowering plants (5090) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover Topic 7, Transport in flowering plants, of the Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4): section 7.1 Uptake and transport of water and ions and section 7.2 Transpiration and translocation. The syllabus is not tiered. Questions 3, 4, 11 and 12 use practical contexts; a calculator is useful for questions 4 and 11.

Learn the content first with the study guide and revision notes.

Questions

1. Describe what is meant by transpiration. [2]

2. Water moves from the soil to the leaves of a plant.

(a) State one feature of a root hair cell that increases water uptake, and explain how it does so. [2] (b) Outline the pathway taken by water from a root hair cell to the cells inside a leaf. [3]

3. A student wants to find which tissue carries water up a stem.

(a) Describe a method the student could use, including a suitable stain. [4] (b) State where the stain would appear in a transverse section of the stem. [1] (c) Suggest why the stem should be cut under water before it is placed in the stain. [1]

4. (calculator allowed) A potometer was used to measure water uptake by a leafy shoot at three temperatures. The bubble moved along a capillary tube with a cross-sectional area of 0.8 mm². Each reading was taken over 4 minutes.

Temperature / °C	Distance moved by bubble in 4 min / mm
10	12
20	22
30	38

(a) Calculate the rate of bubble movement, in mm per minute, at 10 °C and at 30 °C. [2] (b) Calculate the volume of water taken up per minute at 30 °C. Give your units. [2] (c) Explain the effect of temperature on the rate of transpiration. [2] (d) State one variable, other than the shoot, that should be kept constant. [1]

5. Transpiration rate changes with the weather.

(a) Explain why transpiration is slower when the air is humid. [2] (b) Explain why transpiration is faster on a windy day. [2]

6. A pot plant is left on a sunny windowsill on a hot day without being watered. By the afternoon its leaves are drooping. Explain how this wilting occurs. [4]

7. Explain the mechanism by which water moves upwards in the xylem of a tall plant. [4]

8. Potato plants store starch in tubers underground.

(a) Describe translocation. [2] (b) Identify whether a potato tuber is a source or a sink (i) in summer, when the leaves are photosynthesising, and (ii) in spring, when new shoots are growing from it. Give a reason for each answer. [4]

9. A transverse section of a non-woody dicotyledonous organ shows a ring of vascular bundles near the outside, with a band of cells outside them. In each bundle, tissue X faces the centre and tissue Y faces the outside.

(a) State whether this is a root or a stem, and give a reason. [2] (b) Identify tissue X and tissue Y. [1] (c) Name the band of cells between the bundles and the outer surface. [1]

10. Xylem vessels are adapted to their functions.

(a) State two functions of xylem. [2] (b) Explain how each of these features adapts xylem vessels for their functions: (i) walls thickened with lignin; (ii) cells joined end-to-end with no cross walls. [4]

11. (calculator allowed) Four similar leaves were treated with grease (which waterproofs a surface) and hung up in the same room for 48 hours.

Leaf	Surface greased	Mass at start / g	Mass after 48 h / g	Percentage loss in mass
A	none	2.50	1.75	30.0
B	upper only	2.40	1.74	27.5
C	lower only	2.60	2.47
D	both	2.50	2.43

(a) Explain why the results are compared as percentage loss in mass, not mass lost. [1] (b) Calculate the percentage loss in mass for leaves C and D. [2] (c) Explain how leaf A lost mass. [2] (d) What do the results show about the distribution of stomata? Use data in your answer. [2] (e) Suggest why leaf D still lost some mass. [1]

12. Plan an investigation, using a potometer, into the effect of light intensity on the rate of transpiration of a leafy shoot. [7]

Answers

1. The loss of water vapour [1] from the leaves of a plant (through the stomata) [1]. [2] Examiner insight: “loss of water” alone is unlikely to score; the word vapour and the link to leaves are what the marks look for.

2. (a) Long, thin extension (hair) [1], which gives a large surface area for water to enter by osmosis [1]. (Accept: cell sap with a lower water potential than the soil water, so water enters by osmosis.) (b) From root hair cells through the root cortex cells [1], into the xylem, which carries water up the root and stem to the leaf veins [1], then into the mesophyll cells [1]. [5] Examiner insight: the pathway is marked as a sequence, so a correct list in the wrong order, or one that skips the cortex, loses credit.

3. (a) Stand a leafy stem (e.g. celery) in a coloured stain such as eosin [1]. Leave it for a few hours in warm, bright conditions so water is drawn up [1]. Cut thin transverse sections at several heights with a sharp blade [1]. Examine the sections with a hand lens or microscope to see which tissue is stained [1]. (b) In the xylem of the vascular bundles [1]. (c) To stop air entering the xylem and blocking the flow of water [1]. [6] Examiner insight: a method answer needs the stain named and the sectioning step; “put it in dye and look” covers only one point.

4. (a) 10 °C: 12 ÷ 4 = 3.0 mm per minute [1]. 30 °C: 38 ÷ 4 = 9.5 mm per minute [1]. (b) Volume per minute = 9.5 × 0.8 [1] = 7.6 mm³ per minute [1]. (c) As temperature rises the rate increases [1], because water molecules have more kinetic energy, so they evaporate from mesophyll cell surfaces and diffuse out of the stomata faster [1]. (d) Any one: light intensity; wind speed (air movement); humidity; time allowed for the shoot to settle [1]. [7] Examiner insight: a volume needs mm³ as the unit, and a rate needs “per minute”; an answer with no units is usually not given the accuracy mark.

5. (a) Humid air already contains more water vapour [1], so the concentration gradient between the air spaces in the leaf and the outside air is smaller and water vapour diffuses out more slowly [1]. (b) Wind blows away water vapour from around the leaf surface [1], keeping the concentration gradient steep, so diffusion out through the stomata is faster [1]. [4] Examiner insight: each part needs the cause and the gradient link; “less diffusion” alone gives half the credit at most.

6. High temperature and bright light increase transpiration [1]. Water is lost from the leaves faster than it is taken up from the dry soil [1]. The cells lose water and become flaccid / lose turgor pressure [1]. They no longer press against each other to support the leaves and soft stem, so these droop [1]. [4] Examiner insight: use flaccid or turgor; “the plant runs out of water” is too vague for the cell-level marks.

7. Water evaporates from the mesophyll cells and diffuses out through the stomata (transpiration) [1]. Water moves from the xylem into the mesophyll cells to replace it, creating a transpiration pull [1]. Water molecules are held together by forces of attraction between them [1], so a continuous column of water is drawn up the xylem from the roots [1]. [4] Examiner insight: the pull starts at the leaves; “sucked up by the roots” does not match the mechanism asked for.

8. (a) The movement of sucrose and amino acids in the phloem [1], from sources, where they are produced or released, to sinks, where they are used or stored [1]. (b) (i) Sink [1]: it receives sucrose from the leaves and stores it (as starch) [1]. (ii) Source [1]: it releases stored food, carried to the growing shoots where it is used [1]. [6] Examiner insight: each identification needs its reason to gain the second mark; “sink because it is underground” is not a reason.

9. (a) Stem [1], because the vascular bundles are in a ring near the outside, not in the centre [1]. (b) X is xylem and Y is phloem [1]. (c) Cortex [1]. [4] Examiner insight: both tissues must be correct for (b); swapping xylem and phloem in a stem bundle loses the mark.

10. (a) Transport of water and mineral ions [1]; support [1]. (b) (i) Lignin makes the walls strong and rigid [1], so the vessels support the plant and do not collapse as water is pulled up [1]. (ii) There are no cross walls, so the cells form a long continuous tube [1] and water can flow in an unbroken column from root to leaf without obstruction [1]. [6] Examiner insight: name the feature and then the function it serves; a feature with no “so that” link is unlikely to gain the second mark in each pair.

11. (a) The leaves had different starting masses, so percentage loss allows a fair comparison [1]. (b) C: (2.60 − 2.47) ÷ 2.60 × 100 = 5.0% [1]. D: (2.50 − 2.43) ÷ 2.50 × 100 = 2.8% [1]. (c) Water evaporated from the surfaces of the mesophyll cells into the air spaces [1], and the water vapour diffused out through the stomata [1]. (d) Most stomata are on the lower surface [1]: greasing the lower surface cut the loss from 30.0% to 5.0%, but greasing the upper surface only reduced it to 27.5% [1]. (e) Any one: the grease did not seal the surface completely; water was lost from the cut leaf stalk [1]. [8] Examiner insight: “use data” means quoting figures; a conclusion with no numbers is likely to gain only one mark.

12. Fit a leafy shoot into the potometer under water, with airtight joints [1]. Place a lamp 10 cm from the shoot, with a beaker of water between as a heat filter [1]. After a few minutes to settle, measure the distance the bubble moves in 5 minutes [1]. Repeat at 20, 30 and 40 cm with the same shoot [1]. Keep temperature, wind speed and humidity constant (same room, no fan) [1]. Take three readings at each distance and calculate a mean [1]. Calculate rate as distance ÷ time and plot rate against lamp distance [1]. [7] Examiner insight: a plan is credited for the variable changed, what is measured and what is controlled; a lamp also heats the shoot, so the heat filter matters.

Where marks are usually lost

• Writing that water evaporates from the stomata instead of from mesophyll cell surfaces.
• Giving the effect of a factor without the reason (concentration gradient or stomatal opening).
• Missing out root cortex cells or mesophyll cells in the water pathway.
• Describing a wilted plant without flaccid or turgor.
• Placing phloem on the inside of a stem vascular bundle.
• Forgetting the heat filter or the settling time in a potometer plan.

Next steps

• Recap with the transport in flowering plants revision notes.
• Re-read any weak sections in the study guide.
• Go back to the Cambridge O Level Biology hub or tick off outcomes on the printable checklist.
• Try all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028, version 4 (Cambridge University Press & Assessment), section 7 Transport in flowering plants.