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CIE iGCSE Co-Ordinated Science B8.3 Transpiration Exam Style Questions Paper 3

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Question

Fig. 1.1 shows a part of a cross-section of a plant stem.
(a) On Fig. 1.1, draw a label line and the letter Y to identify the part of the stem that transports sucrose.
(b) Sucrose is a type of carbohydrate.
Complete the sentences about carbohydrates in plants.
Plants make carbohydrates using the process of ………………………………………………………………
This process requires water and ……………………………………………………………… in the presence of …………………………. energy and chlorophyll.
(c) Water travels through the plant from the roots to the leaves.
Complete the flow chart to show the pathway of water through a plant.
(d) Water evaporates inside the leaves to form water vapour. Water vapour is then lost from the leaves.
(i) State the name of the process that describes the loss of water vapour from leaves.
(ii) Circle the part where water vapour exits the leaf.
cuticle         palisade         stomata         vascular bundles

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B8.1 — Xylem and phloem (Part (a))
• Topic B6.1 — Photosynthesis (Part (b))
• Topic B8.2 — Water uptake (Part (c))
• Topic B8.3 — Transpiration (Part (d))

▶️ Answer/Explanation

(a) Correct line drawn and labelled Y on the phloem tissue in the vascular bundle.
Sucrose is transported in the phloem, which is part of the vascular bundle in the stem. The label line should point to the phloem region.

(b) Plants make carbohydrates using the process of photosynthesis.
This process requires water and carbon dioxide in the presence of light energy and chlorophyll.
Photosynthesis is the process by which plants synthesise carbohydrates from carbon dioxide and water using light energy absorbed by chlorophyll in chloroplasts.

(c) roots → root hair cells → root cortex cells → xylem → leaves → mesophyll cells
Water enters through root hair cells by osmosis, passes through the cortex to the xylem, travels up the stem, and reaches the mesophyll cells in the leaves where it is used for photosynthesis or evaporates.

(d)(i) Transpiration
Transpiration is the loss of water vapour from the leaves of a plant, mainly through stomata.

(d)(ii) Stomata
Stomata are small pores on the leaf surface through which water vapour diffuses out of the leaf during transpiration.

Question

(a) Fig. 10.1 is a diagram of the gas exchange system in humans.
State the names of the parts labelled A, B and C in Fig. 10.1.
(b) Describe three ways the composition of expired air is different from inspired air.
(c) Gases move across the gas exchange surface by diffusion.
Place ticks (✓) next to all the statements that correctly describe diffusion.
(d) Gas exchange also occurs in plants.
(i) State the name of the part of the leaf where water vapour exits.
(ii) State the term used to describe when water evaporates and then diffuses out of a leaf.
(iii) State two factors that increase the rate of water loss from a leaf.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B11.1 — Gas exchange in humans (Parts (a)–(c))
• Topic B8.3 — Transpiration (Part (d))

▶️ Answer/Explanation

(a) A – trachea; B – bronchus; C – alveoli

The trachea (windpipe) leads into the bronchi, which branch into smaller tubes ending in the alveoli.
Gas exchange with the blood takes place at the alveoli.

(b) Expired air contains more carbon dioxide, less oxygen, and more water vapour

Oxygen is used up by the body during respiration, so expired air contains less of it than inspired air.
Carbon dioxide is produced by respiration, so expired air contains more of it.
Water vapour is added to the air as it passes through the moist respiratory passages, so expired air contains more water vapour.

(c)

Diffusion is the net movement of any particles (not only water) due to their random motion.
It occurs down a concentration gradient (from high to low concentration), not against it, and does not require energy from respiration.
It can occur across a cell membrane, such as at the alveoli or in plant leaves.

(d)(i) Stoma / stomata

Water vapour exits the leaf through small pores called stomata, usually located on the underside of the leaf.

(d)(ii) Transpiration

Transpiration is the term for the evaporation of water from inside the leaf followed by its diffusion out through the stomata.

(d)(iii) Increase in temperature; decrease in humidity

Higher temperature increases the rate of evaporation of water from leaf cells, speeding up transpiration.
Lower humidity increases the concentration gradient between the leaf and the air, speeding up diffusion of water vapour out of the leaf.

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