IGCSE · Practice questions · Leaf structure

Every layer has a job.

Six original Cambridge-style questions on the external features of leaves, labelling a leaf section and explaining how the cuticle, epidermis, mesophyll, stomata and veins adapt a leaf for photosynthesis.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Structure, then function.

Large surface area: absorbs more light. Thin: short diffusion distance for carbon dioxide.
Top to bottom: cuticle, upper epidermis, palisade, spongy mesophyll with air spaces, lower epidermis with stomata.
Vascular bundle: xylem brings water and ions; phloem takes sucrose away.
Always link each structure to light, carbon dioxide, water or the products.

Recall

[2 marks]

State two external features of most leaves and explain how each is an adaptation for photosynthesis.

Large surface area, so more light can be absorbed (and more surface for gas exchange). ✓
Thin, so carbon dioxide has a short distance to diffuse to the mesophyll cells (and light reaches all the cells). ✓

Recall

[4 marks]

List, in order from the upper surface to the lower surface, the layers you would see in a section through a dicotyledonous leaf.

Waxy cuticle, then upper epidermis. ✓
Palisade mesophyll. ✓
Spongy mesophyll with air spaces (vascular bundles run between the mesophyll layers). ✓
Lower epidermis with guard cells and stomata, then the lower cuticle. ✓

Explain

[3 marks]

Explain how the palisade mesophyll is adapted for photosynthesis.

Palisade cells are close to the upper surface, where light intensity is highest. ✓
They contain many chloroplasts, with chlorophyll to absorb light. ✓
They are tall and closely packed, so many cells fit into the layer and absorb most of the light. ✓

Explain

[4 marks]

Describe the pathway taken by a molecule of carbon dioxide from the air to a chloroplast in a palisade cell, and explain how the leaf is adapted to make this quick.

Carbon dioxide diffuses in through an open stoma, controlled by guard cells. ✓
It diffuses through the air spaces of the spongy mesophyll. ✓
It dissolves in the moist surface of a mesophyll cell and diffuses into the cell and its chloroplast. ✓
The leaf is thin and the air spaces are connected, giving a short diffusion distance and a large internal surface area. ✓

Data

[3 marks]

A student counted stomata in the same area (0.1 mm²) of the upper and lower surfaces of five leaves. Means: upper surface 4, lower surface 26. (a) Calculate the mean number of stomata per mm² on the lower surface. (b) Suggest an advantage of having most stomata on the lower surface.

(a) 26 ÷ 0.1 = 260 stomata per mm². ✓
(b) The lower surface is shaded and cooler, so less water evaporates through the stomata. ✓
The upper surface is left free for light to reach the palisade cells, while gas exchange still happens through the many lower stomata. ✓

Analysis

[3 marks]

A vascular bundle in a leaf contains xylem and phloem. Explain the role of each in photosynthesis, and identify which is on the upper side of the bundle.

Xylem brings water, a raw material for photosynthesis, and mineral ions such as magnesium to the leaf. ✓
Phloem carries away sucrose made from the glucose produced in photosynthesis. ✓
In a leaf the xylem is on the upper side of the vascular bundle, with the phloem below it. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.