IGCSE · Practice questions · Respiration in cells

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Six original Cambridge-style questions on what respiration is, what living things use the energy for, and planning and analysing an investigation into the effect of temperature on respiration in yeast.

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

Respiration releases energy.

Respiration happens in all living cells; breathing is only the movement of air.
Seven uses: muscle contraction, protein synthesis, cell division, active transport, growth, nerve impulses, constant body temperature.
Yeast and temperature: rate rises to an optimum (about 35 to 40 °C), then falls as enzymes denature.
Fair test: same yeast mass, sugar volume and concentration, time; equilibrate in the bath first.

Recall

[4 marks]

State four uses of the energy released by respiration in the human body.

Any four of: muscle contraction; protein synthesis; cell division; active transport; growth; the passage of nerve impulses; maintaining a constant body temperature. ✓

Explain

[2 marks]

A student writes: "Respiration is breathing in oxygen and breathing out carbon dioxide." Explain why this is wrong.

Respiration is the chemical reactions inside cells that break down nutrient molecules (such as glucose) to release energy. ✓
Breathing (ventilation) is only the movement of air into and out of the lungs; it supplies oxygen for, and removes carbon dioxide from, respiration. ✓

Data

[4 marks]

Flasks of yeast in sugar solution were kept in water baths for 10 minutes and the carbon dioxide released was collected.

Temperature / °C	10	20	30	40	50	60
CO₂ / cm³	20	40	80	123	18	1

(a) Describe the results. (b) Explain the results above 40 °C.

(a) The volume of carbon dioxide increases from 20 cm³ at 10 °C to a maximum of 123 cm³ at 40 °C (it doubles for each 10 °C rise from 10 to 30 °C). ✓
Above 40 °C it falls sharply, to 1 cm³ at 60 °C. ✓
(b) Respiration is controlled by enzymes; at high temperature the enzymes are denatured (their shape changes) so they no longer work. ✓
So the rate of respiration falls and the yeast cells are killed, releasing little or no carbon dioxide. ✓

Analysis

[4 marks]

Plan an investigation to find the effect of temperature on the rate of respiration of yeast.

Put the same mass of yeast and the same volume and concentration of sugar solution into flasks; leave each in a water bath at a different temperature (for example 20, 30, 40, 50 °C) until it reaches that temperature. ✓
Collect the gas in a gas syringe or upturned measuring cylinder (or count bubbles) over a fixed time, such as 10 minutes. ✓
Calculate the rate as volume of carbon dioxide per minute. ✓
Control the type of sugar, time and yeast; repeat each temperature and calculate a mean. ✓

Explain

[3 marks]

Germinating peas were placed in vacuum flask A and boiled peas, rinsed in disinfectant, in vacuum flask B. After three days flask A was 6 °C warmer than flask B. Explain these results and the reason for each step of the method.

The germinating peas respire, and some of the energy released is lost as heat, so flask A warms up. ✓
The boiled peas are dead and do not respire; flask B is the control. ✓
Disinfectant kills microorganisms on the boiled peas so that their respiration does not warm flask B; the vacuum flask reduces heat loss. ✓

Recall

[2 marks]

Suggest why the cells of a root hair and the cells of a growing shoot tip both need a lot of energy from respiration.

Root hair cells take up mineral ions by active transport, which needs energy. ✓
Shoot tip cells are dividing and growing, and they make proteins (protein synthesis), which needs energy. ✓

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.