iGCSE Biology (0610)-8.3 Transpiration - iGCSE Style Questions Paper 3

Question

(a) A student investigated the effect of windspeed on the rate of transpiration.
The student placed a fan at different distances from a plant shoot and measured the distance the air bubble moved in three minutes.
The distance the air bubble moved can be used to calculate the rate of water uptake, which is equivalent to the rate of transpiration.
Fig. 5.1 shows the apparatus the student used.

Table 5.1 shows their results.

(i) Calculate the rate of water uptake when the fan is 0.6 m from the plant shoot.
Give your answer to two decimal places.
Space for working.

(ii) Using the information in Fig. 5.1 and Table 5.1, complete the sentences by writing a word or phrase in the spaces to describe the results.
As the fan is moved further away from the shoot, the windspeed …………………………………… and the …………………………………… moved by the air bubble decreased.
During transpiration water evaporates from the surfaces of the …………………………………… cells into the air spaces inside the leaf. The water vapour diffuses out of the leaf through the …………………………………… . This causes water to move through the capillary tube causing the air bubble to move towards …………………………………… .

(iii) State one other factor that affects the rate of transpiration.

(b) State two uses of water in a plant.

(c) Explain why the leaf can be described as an organ.

▶️ Answer/Explanation

Solution

(a)(i) Ans: 0.11 mm per second

From Table 5.1, at 0.6 m, the distance moved is 20 mm in 3 minutes (180 seconds). The rate is calculated as \( \frac{20}{180} \approx 0.11 \, \text{mm per second} \).

(a)(ii) Ans: decreased ; distance ; mesophyll ; stomata ; shoot/plant/left/leaf

As the fan moves further, windspeed decreases, reducing the air bubble’s movement. Water evaporates from mesophyll cells, diffuses through stomata, and pulls water towards the shoot.

(a)(iii) Ans: temperature/humidity/light intensity

Higher temperature increases transpiration by speeding up evaporation, while humidity and light also influence the rate.

(b) Ans: Any two from: photosynthesis, solvent, transport, support, germination.

Water is essential for photosynthesis, acts as a solvent for nutrients, and provides structural support via turgor pressure.

(c) Ans: A leaf is a group of tissues performing specific functions.

Leaves contain multiple tissues (e.g., xylem, phloem, mesophyll) working together for photosynthesis and gas exchange, qualifying them as organs.

Question

(a) Complete the sentences about transpiration using words from the list.
Each word may be used once or not at all.
decomposition phloem evaporation root hair cells mesophyll stomata
Transpiration is the loss of water vapour from leaves.
Water moves from the surface of ………………………………………. cells into the air spaces by ………………………………………. .
Then the water vapour diffuses out of the leaf through the ………………………………………. .

(b) A student investigated transpiration.
Fig. 3.1 is a diagram of the apparatus used in the investigation.

• The student watered the plant before the investigation started.
• She measured the mass of water lost every five minutes.
• The mass of water lost represents the rate of transpiration.
• She took measurements in still air and with a fan moving air past the plant.
• She plotted her results on a graph as lines labelled A and B.
Fig. 3.2 shows the results.

(i) Calculate the difference in the mass of water lost between the results for A and the results for B at 30 minutes.
(ii) Calculate the percentage increase in water loss shown for A between 10 minutes and 20 minutes.
Give your answer to the nearest whole number.
Space for working.
(iii) The student repeated the investigation using the fan at half‑speed.
Draw a line on Fig. 3.2 to show the result you would expect when the fan is at half‑speed.

▶️ Answer/Explanation

Solution

(a) mesophyll ; evaporation ; stomata ;

Explanation: Water evaporates from the surface of mesophyll cells into air spaces. The water vapour then diffuses out of the leaf through the stomata.

(b)(i) 4 (g) ;

Explanation: At 30 minutes, line B shows ~8 g and line A shows ~4 g. The difference is \(8 – 4 = 4\) g.

(b)(ii) 65 (%) ;

Explanation: For line A, at 10 minutes, mass lost = ~2.6 g, and at 20 minutes = ~4.3 g. Percentage increase is \(\frac{4.3 – 2.6}{2.6} \times 100 \approx 65\%\).

(b)(iii) line between A and B at all times ; faster initial rate, followed by a slower rate ;

Explanation: At half-speed, transpiration rate is intermediate, so the line should lie between A (still air) and B (full fan speed).

(c) any one from: temperature ; humidity ; light intensity ;

Explanation: Higher temperature increases evaporation, while high humidity reduces the transpiration rate. Light intensity affects stomatal opening.

iGCSE Biology (0610)-8.3 Transpiration – iGCSE Style Questions Paper 3

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