References only, not question text. Open Official paper ↗ where Cambridge publishes the paper,
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school. “Paper 42” means Paper 4, variant 2.
Practice questions
Original questions written by HomiLabs in the style of the exam, with answers and mark schemes. They are not
Cambridge past paper questions and have not been reviewed by Cambridge. Try each one before opening the answer.
Q1Transpiration & factors · Core · Paper 1 style · 1 mark
(a)In which set of conditions will a sunflower plant lose water vapour fastest?[1]
Show answer
(a) C warm, dry, windy
High temperature increases evaporation, low humidity gives a steep water vapour concentration gradient and wind removes water vapour from around the leaf. B is humid, which reduces the gradient.
Q2Transpiration & factors · Core · Paper 2 style · 4 marks
(a)Define the term transpiration.[2]
(b)Name the pores in the leaf through which most water vapour leaves.[1]
(c)State one way in which transpiration is useful to a plant.[1]
Show answer
(a) Loss of water vapour from the leaves (by evaporation of water at the surfaces of the mesophyll cells) followed by diffusion of water vapour through the stomata.
B1 loss of water vapour from leaves / aerial parts; B1 evaporation from mesophyll cell surfaces and diffusion out through stomata
(b) Stomata
B1
(c) Pulls water and mineral ions up the xylem / cools the leaves / supplies water for photosynthesis and support.
B1 any one
Q3Transpiration & factors · Core · Paper 4 style · 3 marks
A student uses a potometer in which the leafy shoot is fixed into a rubber bung, a capillary tube with a scale is attached and a water reservoir with a tap is connected to the tube.
(a)State why the joints of the potometer were sealed with petroleum jelly.[1]
(b)State how the student could return the bubble to the start of the scale between readings.[1]
(c)Suggest why the student waited 5 minutes after changing conditions before starting a new reading.[1]
Show answer
(a) To make them airtight / stop air leaking in or water leaking out.
B1
(b) Open the tap of the water reservoir / syringe to push water in.
B1
(c) To let the shoot adjust to the new conditions so the rate is steady.
B1
Q4Transpiration & factors · Core · Paper 2 style · 5 marks
Transpiration rate of a rubber plant at different relative humidities (temperature kept at 25 °C).relative humidity / % | rate of transpiration / arbitrary units30 | 8.445 | 6.960 | 5.175 | 3.290 | 1.6
(a)Describe the effect of relative humidity on the rate of transpiration. Use figures from the table.[2]
(b)Calculate the decrease in rate between 30 % and 90 % humidity.[1]
(c)Predict the rate at 100 % humidity and explain your prediction.[2]
Show answer
(a) As humidity increases, rate decreases: from 8.4 at 30 % to 1.6 at 90 %.
B1 inverse trend; B1 data quote with units
(b) 6.8 arbitrary units
B1 8.4 − 1.6
(c) Very close to zero (but probably not zero); the air is saturated, so there is almost no concentration gradient for water vapour to diffuse out.
B1 near zero / below 1.6; B1 no / tiny concentration gradient
Q5Transpiration & factors · Standard · Paper 1 style · 1 mark
(a)[1]
Show answer
(a) B the rate of water uptake by the shoot
The bubble moves as the shoot takes up water. Most of this water is lost in transpiration, but some is used in photosynthesis or kept in cells, so A is not exactly what is measured.
Q6Transpiration & factors · Standard · Paper 4 style · 7 marks
A student set up a bubble potometer with a leafy shoot of a guava plant. A small electric fan was placed 50 cm from the shoot. The distance moved by the air bubble was recorded in 4 minutes at each fan setting.Fan setting | distance moved by bubble / mm | time / minoff | 12 | 4low | 27 | 4high | 44 | 4
(a)Calculate the rate of bubble movement in mm per minute for each fan setting.[2]
(b)Describe and explain the effect of wind speed on the rate of transpiration shown by these results.[3]
(c)State two variables that must be kept constant.[2]
(b) As wind speed increases, the rate increases (3.0 → 11.0 mm/min). Wind blows away water vapour near the leaf, keeping a steep concentration gradient, so water vapour diffuses out of stomata faster.
B1 trend with figures; B1 wind removes water vapour from around leaf / reduces humidity near leaf; B1 steeper gradient so faster diffusion through stomata
(c) Light intensity; temperature (also: same shoot / humidity / distance of fan).
1 mark each for any two valid
Q7Transpiration & factors · Standard · Paper 2 style · 4 marks
(a)Explain why the rate of transpiration increases when the temperature rises.[2]
(b)Explain why the rate of transpiration decreases on a humid day in Karachi.[2]
Show answer
(a) Water molecules gain kinetic energy, so more water evaporates from mesophyll cell surfaces and water vapour diffuses out faster.
B1 more evaporation / molecules move faster; B1 faster diffusion of water vapour out of stomata
(b) The air outside the leaf already contains much water vapour, so the concentration gradient between the air spaces and the outside air is smaller and diffusion is slower.
B1 high water vapour concentration outside; B1 smaller concentration gradient so slower diffusion
Q8Transpiration & factors · Standard · Paper 4 style · 5 marks
A potted chilli plant was watered and its pot and soil surface were sealed in a plastic bag. It was placed on a balance in a sunny courtyard. At 9 am its mass was 412.0 g. At 3 pm its mass was 397.6 g.
(a)Calculate the mass of water lost in 6 hours.[1]
(b)Calculate the percentage of the starting mass that was lost. Give your answer to 2 decimal places.[2]
(c)Calculate the mean rate of water loss in g per hour.[1]
(d)Explain why the pot and soil were covered with a plastic bag.[1]
Show answer
(a) 14.4 g
B1 412.0 − 397.6
(b) 3.50 %
M1 14.4 ÷ 412.0 × 100; A1 3.50 %
(c) 2.4 g/h
B1 14.4 ÷ 6
(d) So that mass lost is due to transpiration from the plant only, not evaporation from the soil.
B1
Q9Transpiration & factors · Standard · Paper 2 style · 4 marks
(a)Describe the effect of increasing light intensity on the rate of transpiration.[1]
(b)Explain your answer to (a).[2]
(c)Suggest why a plant transpires very little at night.[1]
Show answer
(a) Rate increases (up to a point).
B1
(b) In light the stomata open (wider), so more water vapour can diffuse out of the leaf.
B1 stomata open in light; B1 more water vapour diffuses out
(c) Stomata are closed in the dark (and it is cooler).
B1
Q10Transpiration & factors · Challenge · Paper 1 style · 1 mark
(a)Four similar leaves were treated with petroleum jelly, which is waterproof, and hung up for two days. Leaf 1: no jelly. Leaf 2: jelly on the upper surface. Leaf 3: jelly on the lower surface. Leaf 4: jelly on both surfaces. Apart from leaf 4, which leaf lost the least mass?[1]
Show answer
(a) C leaf 3
Most stomata are on the lower surface of a typical dicot leaf, so blocking the lower surface stops most water vapour loss. Leaf 2 still loses water through the many lower stomata.
Q11Transpiration & factors · Challenge · Paper 4 style · 5 marks
In a potometer the air bubble moved 36 mm along a capillary tube in 4 minutes. The radius of the capillary bore is 0.5 mm.
(a)Calculate the volume of water taken up by the shoot in mm³. Use the formula volume = πr²l. Give your answer to 3 significant figures.[2]
(b)Calculate the rate of water uptake in mm³ per minute, to 3 significant figures.[1]
(c)Explain why the cut end of the shoot was cut under water before it was put in the potometer.[2]
Show answer
(a) 28.3 mm³
M1 π × 0.5² × 36; A1 28.3 mm³
(b) 7.07 mm³/min
B1 28.27 ÷ 4
(c) To prevent air entering the xylem vessels, which would block the water column and stop water being drawn up.
B1 stops air entering xylem; B1 air bubble would block water flow / break water column
Q12Transpiration & factors · Challenge · Paper 2 style · 5 marks
On a very hot afternoon in Multan in June, a farmer notices that his cotton plants have drooping leaves, even though the soil is slightly damp. By the next morning the plants look normal again.
(a)Explain why the plants wilted.[3]
(b)When wilting occurs, the stomata close. Give one advantage and one disadvantage to the plant of closing its stomata.[2]
Show answer
(a) Water was lost by transpiration faster than it was absorbed by the roots; cells lost water and became flaccid (lost turgor); so the leaves and stems were no longer supported.
B1 transpiration rate greater than water uptake; B1 cells lose turgor / become flaccid; B1 loss of support
(b) Advantage: reduces water loss. Disadvantage: less carbon dioxide enters, so less photosynthesis (also less cooling / less mineral transport).
B1 advantage; B1 disadvantage
Q13Transpiration & factors · Challenge · Paper 4 style · 6 marks
(a)Plan an investigation to find out how temperature affects the rate of transpiration of a leafy shoot. Your plan should include what you would change, measure and keep the same.[6]
Show answer
(a) Use a potometer; vary temperature (e.g. 15, 20, 25, 30, 35 °C in a temperature-controlled room or incubator, checked with a thermometer); measure distance bubble moves in a fixed time; calculate rate; keep light intensity, humidity, air movement and same shoot constant; allow time to adjust; repeat and calculate mean.
1 mark each for any six of: potometer / mass loss method; at least 5 temperatures stated with range; how temperature is controlled (heater / room / incubator, check with thermometer); dependent variable: bubble distance in fixed time (or mass lost); calculate rate; same shoot / same leaf area; constant light intensity; constant humidity / wind; acclimatise before timing; repeat at each temperature and find mean
Q14Transpiration & factors · Challenge · Paper 2 style · 4 marks
A cactus growing in the Thar Desert has leaves reduced to spines, a thick waxy cuticle and stomata sunk in pits in a thick green stem.
(a)Suggest how each feature reduces water loss: (i) leaves reduced to spines (ii) a thick waxy cuticle (iii) stomata sunk in pits.[3]
(b)Suggest why the cactus stem is green.[1]
Show answer
(a) (i) smaller surface area for transpiration (ii) waterproof layer reduces evaporation from the surface (iii) humid air is trapped in the pit, reducing the concentration gradient
1 mark each
(b) The stem carries out photosynthesis instead of the leaves (contains chloroplasts).
B1
Q15Water uptake & root hairs · Core · Paper 1 style · 1 mark
(a)What is the correct pathway taken by water as it moves through a plant?[1]
Water enters root hair cells, crosses the cortex to the xylem, travels up in the xylem and then enters mesophyll cells. B is wrong because water moves in xylem, not phloem.
Q16Water uptake & root hairs · Core · Paper 2 style · 4 marks
(a)State where root hairs are found on a root.[1]
(b)Seedlings that are pulled out and replanted often wilt. Suggest why.[2]
(c)Suggest how a gardener can reduce wilting when moving seedlings.[1]
Show answer
(a) Just behind the root tip.
B1
(b) Root hairs are damaged / torn off when the seedlings are pulled up; so the surface area for water absorption is reduced.
B1 root hairs damaged; B1 less surface area / less water absorbed
(c) Move them with a ball of soil around the roots / water well / move in the evening.
B1
Q17Water uptake & root hairs · Standard · Paper 2 style · 4 marks
(a)Explain how water moves from the soil into a root hair cell.[3]
(b)Explain why root hair cells are able to absorb a lot of water.[1]
Show answer
(a) By osmosis; from a higher water potential in the soil (dilute solution) to a lower water potential in the cell sap; through the partially permeable cell membrane.
B1 osmosis; B1 higher to lower water potential (soil → cell); B1 partially permeable membrane
(b) Many long root hairs give a large surface area.
B1
Q18Water uptake & root hairs · Standard · Paper 2 style · 5 marks
(a)Nitrate ions are absorbed by root hair cells even when their concentration in the soil is lower than in the cell. Name this process.[1]
(b)Explain why the root hair cells need oxygen for this process.[2]
(c)Suggest why plants in waterlogged soil take up fewer mineral ions.[2]
Show answer
(a) Active transport
B1
(b) Active transport needs energy; energy is released by aerobic respiration, which uses oxygen.
B1 needs energy; B1 from (aerobic) respiration
(c) Waterlogged soil has little oxygen (air spaces filled with water), so root cells respire less aerobically and release less energy for active transport.
B1 less oxygen in soil; B1 less respiration / energy for active transport
Q19Water uptake & root hairs · Challenge · Paper 2 style · 4 marks
A farmer in Faisalabad added far too much fertiliser to a field of young wheat plants. A few days later the plants wilted, although the soil was moist.
(a)Use the term water potential to explain why the plants wilted.[3]
(b)Suggest what the farmer should do to help the plants recover.[1]
Show answer
(a) The fertiliser made the soil solution very concentrated, with a lower water potential than the root cells; water moved out of the root cells into the soil by osmosis; so less water reached the leaves and cells lost turgor.
B1 soil water potential lower than root cells; B1 water leaves root cells by osmosis / cannot enter; B1 cells / plant lose turgor
(b) Water the field heavily to dilute the fertiliser.
B1
Q20Water uptake & root hairs · Challenge · Paper 2 style · 5 marks
(a)Describe how water moves from the root hair cell to the xylem.[2]
(b)Explain how water moves up the xylem to the leaves.[3]
Show answer
(a) By osmosis from cell to cell across the root cortex, down a water potential gradient (each cell has a lower water potential than the one before).
B1 through cortex cells; B1 osmosis / water potential gradient
(b) Water evaporates from mesophyll cells and is lost by transpiration; this creates a pull (tension) on the water in the xylem; water molecules stick together (cohesion) so a continuous column is drawn up.
B1 transpiration / evaporation at leaves; B1 creates pull / suction; B1 water molecules stick together / continuous column
Q21Xylem & phloem structure · Core · Paper 4 style · 4 marks
A celery stalk with leaves was stood in water containing red dye. After some time, a thin slice was cut across the stalk and viewed with a hand lens. Small red spots were seen in a ring near the outside of the stalk.
(a)Name the tissue that the dye travelled through.[1]
(b)The dye moved 84 mm up the stalk in 30 minutes. Calculate the mean rate of movement in mm per minute.[2]
(c)Suggest how the student could make the dye travel faster.[1]
Show answer
(a) Xylem
B1
(b) 2.8 mm/min
M1 84 ÷ 30; A1 2.8 mm/min
(c) Place it in a warm / bright / windy place, or near a fan, to increase transpiration.
B1
Q22Xylem & phloem structure · Standard · Paper 1 style · 1 mark
(a)Which description of xylem vessels is correct?[1]
Show answer
(a) B dead, hollow tubes strengthened with lignin
Xylem vessels are dead cells joined end to end with no cross walls, forming hollow tubes with lignified walls. A describes phloem sieve tubes.
Q23Xylem & phloem structure · Standard · Paper 2 style · 6 marks
(a)State two functions of xylem.[2]
(b)Explain how two features of xylem vessels are related to their functions.[4]
Show answer
(a) Transports water and mineral ions; provides support.
1 mark each
(b) No cross walls / hollow (no cytoplasm), so water flows freely as a continuous column; lignin in walls makes them strong, giving support and stopping collapse under tension; narrow tubes help the water column hold together.
For each of two features: B1 feature, B1 linked function
Q24Xylem & phloem structure · Challenge · Paper 2 style · 5 marks
(a)Describe the positions of xylem and phloem in (i) a transverse section of a dicot stem and (ii) a transverse section of a dicot root.[4]
(b)State the name given to the strand containing xylem and phloem in a leaf.[1]
Show answer
(a) (i) Stem: vascular bundles in a ring near the outside; xylem towards the centre (inside), phloem towards the outside. (ii) Root: xylem in the centre (often star / X shaped); phloem in groups between the arms of the xylem.
Stem: B1 bundles in a ring, B1 xylem inner, phloem outer. Root: B1 xylem central, B1 phloem between xylem arms
(b) Vein / vascular bundle
B1
Q25Translocation · Core · Paper 1 style · 1 mark
(a)What is translocation?[1]
Show answer
(a) B movement of sucrose and amino acids in phloem from sources to sinks
Translocation is the movement of sucrose and amino acids in the phloem from regions of production or release (sources) to regions of storage or use (sinks). A is water transport in xylem.
Q26Translocation · Standard · Paper 2 style · 5 marks
(a)Define the terms source and sink.[2]
(b)In sugar cane, sucrose is stored in the stem. State the source and the sink in a sugar cane plant during growth.[2]
(c)Name the tissue in which sucrose is moved.[1]
Show answer
(a) Source: part of the plant that releases sucrose / amino acids (e.g. where they are made). Sink: part where they are used or stored.
Q27Translocation · Standard · Paper 2 style · 5 marks
(a)In spring a stored potato tuber starts to sprout new shoots. Explain why the tuber acts as a source at this time.[2]
(b)Later in summer the potato plant forms new tubers. Explain why the new tubers are sinks.[2]
(c)Explain why translocation can occur in both directions in a plant, unlike water transport.[1]
Show answer
(a) Stored starch is broken down to sucrose; the sucrose is transported in phloem to the growing shoots (sinks), which cannot yet photosynthesise enough.
(b) Sucrose from the leaves is transported to them and converted to starch for storage.
B1 receive sucrose from leaves; B1 stored as starch
(c) Sources and sinks can be above or below each other (and change with season), so phloem carries substances up and down.
B1
Q28Translocation · Challenge · Paper 2 style · 7 marks
A ring of bark, including the phloem, was carefully removed all the way round the trunk of a young apple tree. After some weeks the bark just above the ring had swollen.
(a)Explain why the bark above the ring swelled.[3]
(b)Suggest why the leaves above the ring did not wilt for several weeks.[2]
(c)Predict what would happen to the roots after a long time, and explain.[2]
Show answer
(a) The ring removed the phloem (which is in the bark); sucrose moving down from the leaves could not pass the ring; sucrose built up above the ring, and the extra sugar caused water to enter / extra growth, so the bark swelled.
B1 phloem removed; B1 sucrose transport (down from leaves) blocked; B1 accumulation above ring
(b) The xylem, which is deeper in the stem (wood), was not removed, so water still reached the leaves.
B1 xylem intact / inside the bark; B1 water still transported up
(c) The roots would die; they receive no sucrose for respiration, so they cannot release energy (and eventually the whole tree dies).
B1 roots die / stop growing; B1 no sugar for respiration
Q29Transpiration & factors (option) · Challenge · Paper 2 style · 8 marks
A student hung a cut leafy shoot of a neem tree from a balance with its cut end in a sealed flask of water (the water surface was covered with oil). She recorded the mass every hour, first in still air and then with a fan blowing.
(a)Describe how the student's results could be used to show the effect of the fan.[2]
(b)Without the fan the shoot lost 1.8 g in 3 hours. With the fan it lost 3.3 g in 3 hours. Calculate the percentage increase in the rate of water loss caused by the fan.[2]
(c)Explain fully how water moves from the xylem in a leaf to the air outside, and why moving air speeds this up.[4]
Show answer
(a) Compare the mass lost per hour with and without the fan; the rate with the fan is higher.
B1 compare rates / mass loss; B1 under the same other conditions
(b) 83.3 %
M1 (3.3 − 1.8) ÷ 1.8 × 100; A1 83.3 %
(c) Water passes from xylem into mesophyll cells by osmosis; it evaporates from the surfaces of mesophyll cells into air spaces; water vapour diffuses out through stomata down a concentration gradient; moving air removes water vapour near the stomata, keeping the gradient steep.
1 mark each for four: osmosis into mesophyll; evaporation from cell surfaces into air spaces; diffusion of water vapour through stomata; down a concentration gradient; wind removes water vapour / maintains gradient
Q30Transpiration & factors (option) · Challenge · Paper 2 style · 7 marks
Measurements on a rice plant in a field in Punjab on a clear summer day showed that water loss rose from 8 am to a peak at 2 pm and then fell. Water uptake by the roots followed a similar pattern but reached its peak about an hour later.
(a)Explain why water loss from the plant is greater at 2 pm than at 8 am.[3]
(b)Explain why the rate of water uptake by roots lags behind the rate of transpiration in the early afternoon.[2]
(c)State two ways in which a hot, dry climate could be a problem for a crop such as rice, which needs a lot of water.[2]
Show answer
(a) Higher light intensity, so more stomata open wider; higher temperature, so faster evaporation and diffusion; lower humidity at midday, so steeper concentration gradient.
1 mark each for three of: more light so stomata open wider; higher temperature, more evaporation; molecules have more kinetic energy / diffuse faster; lower humidity / steeper gradient
(b) Water is first lost from the leaves, creating the pull; it takes time for the pull to be transmitted down the xylem and for water to cross the root, so uptake reaches its peak later.
B1 loss from leaves comes first / drives uptake; B1 time for pull to travel / delay in uptake
(c) Plants may wilt / lose turgor; stomata close so less photosynthesis and lower yield; more irrigation water needed.
1 mark each for any two
Similar questions
Questions that test the same subtopic in different years, grouped so you can work on one skill at a time.
References only: find each question in its paper (official link where available, otherwise through your school).
