Commonly Confused Command Words (Edexcel IGCSE Biology): Revision Note

A student measured their heart rate before, during and after a period of exercise.

Describe the changes in the student's heart rate during and after exercise.

[2]

Zero-mark answer:

• Their heart rate increases in order to pump more blood around the body

• This supplies the muscles with more oxygen and glucose for respiration

Full-mark answer:

• During exercise, the heart rate increases from 72 beats/min to about 160 beats/min and then levels off [1 mark]

• After exercise, the heart rate decreases back to 72 beats/min [1 mark]

The zero-mark answer explains why the heart rate increases, but it does not describe how the heart rate changes, and so scores nothing; it has not met the requirements of the question.

The full-mark answer makes two mark-worthy points describing the change and using the data given.

Food handlers are told to wash their hands before preparing food.

Explain why washing hands before preparing food reduces the spread of disease.

[2]

Zero-mark answer:

• You would wash your hands with soap and warm water for 20 seconds

• You would then dry them before you touch any food

Full-mark answer:

• Hands can carry pathogens / infectious microorganisms [1 mark]

• Washing removes / kills the pathogens, so they are not passed on to the food and eaten [1 mark]

The zero-mark answer describes how to wash your hands, but the question asks why it matters. Describing the method, however accurately, does not earn marks.

The full-mark answer gains two marks for two separate biological ideas. First, it identifies the problem: pathogens can be present on the hands. Second, it explains how washing solves it: removing the pathogens breaks the route by which they would be transferred to the food and eaten.

Scientists studied the number of red blood cells in people living at different altitudes. The table shows their results.

Discuss the relationship between altitude and the number of red blood cells.

Use the data in the table and your own knowledge in your answer.

[4]

One-mark answer:

• As altitude increases, the number of red blood cells increases [1 mark]

Full-mark answer:

• The mean number of red blood cells increases from 4.8 × 10¹² to 5.3 × 10¹² in 1 litre of blood as altitude increases from 0 m to 2400 m [1 mark]

• There is less oxygen available at higher altitude [1 mark]

• More red blood cells means that more oxygen can be transported to cells for aerobic respiration [1 mark]

• The samples at altitude are much smaller than the sample at sea level, so the results at altitude are less reliable [1 mark]

The one-mark answer describes the trend, but it quotes no data, gives no biology to explain the trend and says nothing about the quality of the data.

The full-mark answer makes four separate points for four marks. It uses the data, explains the trend with biology and comments on the sample sizes.

The photograph below shows a snowshoe hare, a small mammal native to North America.

Snowshoe hare (Lepus americanus), D. Gordon E. Robertson, converted to black and white, CC BY-SA 3.0, via Wikimedia Commons (opens in a new tab)

Suggest how two adaptive features, visible in the photograph, aid snowshoe hare survival in their environment.

[2]

Zero-mark answer:

• It is adapted to the cold

• It has a good sense of smell to avoid predators

Full-mark answer:

• It has white fur to camouflage it from predators [1 mark]

• It has large feet so it doesn't sink in the snow [1 mark]

The zero-mark answer gives a generic point ("adapted to the cold") that does not identify any feature of the hare. Its second point may be true, but a sense of smell cannot be seen in the photograph, and the question asks for visible features.

The full-mark answer applies knowledge to the specific scenario. The student has not been taught about snowshoe hares, but they use what they know about adaptive features to identify two features and say how each aids survival. They refer to the specific photograph of the hare and its environment throughout.

Note that there are many more correct answers available than the two given here.

A student counted the bubbles of carbon dioxide released by yeast at different temperatures. Their results are shown in the table below.

Predict the number of bubbles per minute at 35 °C.

[1]

Zero-mark answer:

• More bubbles, because the yeast respires faster when it is warmer

Full-mark answer:

• 26 bubbles per minute [1 mark]

Any value from 21 to 31 would be accepted.

The zero-mark answer gives a reason, but the question asks for a number of bubbles per minute, and no value has been predicted.

The full-mark answer uses the pattern in the table. 35 °C lies between 30 °C and 40 °C, so the number of bubbles lies between 20 and 32, and a value near the midpoint, 26, fits the pattern best.