IGCSE · Practice questions · Water uptake

Follow the water.

Six original Cambridge-style questions on root hair cells, why surface area matters, the pathway of water through root, stem and leaf, and planning and interpreting a stain investigation.

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

Hair, cortex, xylem, mesophyll.

Root hair cells: absorb water (osmosis) and mineral ions (active transport).
Large surface area increases uptake of water and mineral ions.
Pathway: root hair cells → root cortex cells → xylem → mesophyll cells.
Stain test: the dye moves with the water, so it marks the xylem.

Recall

[3 marks]

State two functions of root hair cells and explain how their shape helps.

They absorb water from the soil (by osmosis). ✓
They absorb mineral ions such as nitrate and magnesium (by active transport). ✓
The long, thin hair gives a large surface area, which increases the rate of uptake of water and mineral ions. ✓

Recall

[3 marks]

Outline the pathway taken by a water molecule from the soil to a mesophyll cell in a leaf.

It enters a root hair cell. ✓
It passes through the root cortex cells into the xylem in the centre of the root. ✓
It travels up the stem and into the leaf in the xylem, then passes into the mesophyll cells. ✓

Analysis

[4 marks]

Plan an investigation, using a suitable stain, to show the pathway of water through the above-ground parts of a plant.

Stand a freshly cut celery stalk with leaves (or a white flower) in a beaker of water containing a dye such as food colouring or eosin. ✓
Leave it in the light for a few hours (warm conditions increase transpiration, so the dye rises faster). ✓
Look for coloured strands in the stalk and colour in the leaf veins (or petals). ✓
Cut thin transverse slices with a sharp blade and view with a hand lens: the coloured dots show where the xylem is. ✓

Data

[3 marks]

A student measured how far up a celery stalk the dye had travelled.

Time / min	0	20	40	60
Distance / mm	0	30	62	90

(a) Calculate the mean rate of movement of the dye over 60 minutes. (b) Suggest one change that would make the dye rise faster, and explain why.

(a) 90 ÷ 60 = 1.5 mm per minute. ✓
(b) Put the plant in a warmer place, or in moving air (a fan). ✓
This increases the rate of transpiration, so water (carrying the dye) is pulled up the xylem faster. ✓

Explain

[2 marks]

Gardeners move seedlings with a ball of soil around the roots. Explain why.

Pulling a seedling out of the soil tears off many delicate root hairs. ✓
This reduces the surface area for water uptake, so the seedling cannot take in enough water and wilts; the soil ball protects the root hairs. ✓

Explain

[2 marks]

Explain why a transverse slice of a celery stalk that has stood in red dye shows red dots only near the outside, while the rest of the slice is uncoloured.

The dye moves only with the water, which travels in the xylem. ✓
The xylem is in vascular bundles arranged in a ring near the outside of the stalk, so only those bundles are stained. ✓

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.