IGCSE · Practice questions · Active transport

Pumping the wrong way, on purpose.

Six original Cambridge-style questions comparing diffusion, osmosis and active transport, explaining ion uptake by root hairs and interpreting data on the effect of oxygen on ion uptake.

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

Against the gradient, with energy.

Active transport: lower to higher concentration, through a membrane, using energy from respiration.
Extended: protein carriers move the molecules or ions across.
Root hairs: water in by osmosis, mineral ions in by active transport.
Anything that stops respiration (no oxygen, a poison, low temperature) slows active transport.

Recall

[3 marks]

Define active transport.

The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration. ✓
That is, against a concentration gradient. ✓
Using energy released by respiration. ✓

Analysis

[3 marks]

State three differences between diffusion and active transport.

Diffusion is down a concentration gradient; active transport is against it. ✓
Diffusion uses the kinetic energy of the particles; active transport needs energy from respiration. ✓
Diffusion does not need carrier proteins (or a membrane); active transport needs protein carriers in a cell membrane. ✓

Explain

[4 marks]

Extended. Explain how a root hair cell absorbs nitrate ions from the soil, and why the plant needs them.

The concentration of nitrate ions in the soil water is lower than in the root hair cell, so they cannot be absorbed by diffusion. ✓
Protein carriers in the cell membrane bind nitrate ions and move them into the cell, against the concentration gradient. ✓
This uses energy released by respiration in the many mitochondria of the root hair cell. ✓
Nitrate is used to make amino acids, and so proteins, for growth. ✓

Data

[4 marks]

Barley roots were placed in a solution of potassium ions, with and without air bubbled through. The table shows the ion uptake after 3 hours.

Condition	Potassium uptake / arbitrary units
air bubbled through	48
nitrogen bubbled through (no oxygen)	6

(a) Calculate how many times greater the uptake was with air. (b) Explain the difference.

(a) 48 ÷ 6 = 8 times greater. ✓
(b) With air the root cells have oxygen for aerobic respiration, which releases energy. ✓
The energy is used by protein carriers to take up potassium ions by active transport, against the concentration gradient. ✓
Without oxygen, little energy is released, so active uptake almost stops; the small uptake may be by diffusion. ✓

Explain

[2 marks]

Farmers drain waterlogged fields. Suggest why crops grow poorly in waterlogged soil.

Waterlogged soil has little air (oxygen) between the particles, so root cells cannot respire aerobically. ✓
Less energy is released for active transport, so the roots take up fewer mineral ions such as nitrate, and growth is reduced. ✓

Recall

[3 marks]

Extended. Glucose is absorbed from the small intestine by diffusion and by active transport. Explain why active transport is needed as well as diffusion.

Diffusion only moves glucose into the blood while its concentration in the gut is higher than in the blood. ✓
Once the concentration in the gut falls below that in the blood, glucose must be moved against the gradient. ✓
Active transport, using energy from respiration and protein carriers, absorbs this remaining glucose so none is wasted. ✓

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.