Co-ordination and response questions

Co-ordination and response syllabus

Questions on co-ordination and response can test recall, calculations, explanations, diagrams, data handling and practical skills. You should be able to:

• 2.80 understand how organisms are able to respond to changes in their environment
• 2.81 understand that homeostasis is the maintenance of a constant internal environment, and that body water content and body temperature are both examples of homeostasis
• 2.82 understand that a co-ordinated response requires a stimulus, a receptor and an effector Flowering plants
• 2.83 understand that plants respond to stimuli
• 2.84 describe the geotropic and phototropic responses of roots and stems
• 2.85 understand the role of auxin in the phototropic response of stems Humans
• 2.86 describe how nervous and hormonal communication control responses and understand the differences between the two systems
• 2.87 understand that the central nervous system consists of the brain and spinal cord and is linked to sense organs by nerves
• 2.88 understand that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses
• 2.89 understand the role of neurotransmitters at synapses
• 2.90 describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object
• 2.91 describe the structure and function of the eye as a receptor
• 2.92 understand the function of the eye in focusing on near and distant objects, and in responding to changes in light intensity
• 2.93 describe the role of the skin in temperature regulation, with reference to sweating, vasoconstriction and vasodilation
• 2.94 understand the sources, roles and effects of the following hormones: adrenaline, insulin, testosterone, progesterone and oestrogen 2.95B understand the sources, roles and effects of the following hormones: ADH, FSH and LH

How to answer co-ordination and response questions

1. State the stimulus, receptor, co-ordinator and effector when describing a response pathway.
2. Keep nervous and hormonal responses distinct, including their speed, duration and route.
3. For homeostasis, identify the monitored variable and explain how negative feedback restores the set point.
4. Use labelled diagrams and data values to support explanations of the eye, nervous system or plant responses.

Co-ordination and response example questions and worked answers

These examples show how information in a diagram, graph or experimental context becomes part of a complete exam answer.

Example 1: Explaining binocular vision in predators

Adapted from January 2023, Paper 2B · Question 2(b)(iv)

Question 1

A student investigates if using one eye or using two eyes is better for judging the distance of objects. The student uses the plastic block shown in the diagram. The block has a grid where six different coloured pins can be placed as shown in the diagram.

This is the student’s method.

• place one pin into the lines of each column and row so that each pin is a different distance from the front of the grid
• ask a volunteer to close one eye
• hold the grid in front of the volunteer so they can see the coloured pins but not the grid
• ask the volunteer to call out the colour of the pins in order of distance, from nearest to furthest
• record the number of pins that the volunteer identifies correctly
• repeat eight more times, each time moving the pins to different positions in the grid

The student does the experiment again with both eyes open.

After nine trials, the student summarises the number of correctly identified pins.

Table 2: correctly identified pins

Summary	Using one eye	Using both eyes
Mode	3	6
Median	2	6

The field of view is the area that an animal can see with their eyes. The diagram shows the field of view for a cat.

Explain why predators, such as cats, have two forward facing eyes. Use the information in the diagram and Table 2 to support your answer.

Final answer

The diagram shows a large area seen by both eyes. The results show better distance judgement with both eyes, as more pins were identified in the correct order. This helps a predator locate and catch its prey.

Mark scheme points

Any three of the following points are needed for three marks. The first three form the answer above.

1. M1 A large area is seen by both eyes; the visual fields overlap.
2. M2 Distance judgement is better with two eyes, supported by more pins identified correctly (or a higher mode or median) with both eyes.
3. M3 Better distance judgement helps the predator locate, chase or catch prey.
4. M4 Alternatively, predators do not need a wide field of view to see behind them because they are not usually preyed upon.

Explanation

The diagram shows that the forward-facing eyes have an overlapping region, so a large area is seen by both eyes. The table supports the advantage of using both eyes: the volunteer identified more pins in the correct distance order, showing better distance judgement. A predator can use this judgement to locate and catch prey.

Common mistakes

• Saying only that predators have a “larger field of view” is not enough: describe the overlapping area seen by both eyes.
• Most candidates scored at least one mark; stronger answers linked the area seen by both eyes to judging distance from prey. Make that link explicit rather than mentioning the field of view alone.

Example 2: Graphing a snail’s response to repeated stimuli

Adapted from June 2024 (R), Paper 1B · Question 6(b)(i)

Question 2

A reflex is a rapid response to a stimulus.

The photograph shows an African land snail.

(Source: © MYN / JORIS VAN ALPHEN / NATURE PICTURE LIBRARY / SCIENCE PHOTO LIBRARY)

When an African land snail is touched on its eyestalk, the snail goes back into its shell. The snail then remains in its shell for a period of time.

A student investigates the effect that repeatedly touching the eyestalk has on the time the snail remains in its shell.

This is the student’s method.

• gently touch the eyestalk of a snail with a cottonwool bud so that the snail goes back into its shell
• measure the time the snail remains in its shell
• after the snail has come back out of its shell, touch the eyestalk again so that the snail goes back into its shell again
• measure the time the snail remains in its shell
• repeat the stimulus six more times

The student’s results are shown in the table.

Stimulus number	Time snail remains in its shell in seconds
1	12
2	12
3	10
4	11
5	10
6	7
7	5
8	3

Plot a graph to show the effect of stimulus number on the time the snail remains in its shell.
Join your points with ruled, straight lines.

Final answer

Label the horizontal axis Stimulus number and the vertical axis Time / seconds. Use linear scales that cover at least half of the grid. Plot the points (1, 12), (2, 12), (3, 10), (4, 11), (5, 10), (6, 7), (7, 5) and (8, 3), then join each consecutive point with a ruled straight line. Do not extend the line beyond the first or last point.

Mark scheme points

1. M1 Use linear scales on both axes, covering at least half of the grid.
2. M2 Join the plotted points with straight lines; do not extrapolate beyond the first or last point.
3. M3 Put stimulus number on the horizontal axis and time on the vertical axis.
4. M4 Label both axes and include the unit on the vertical axis: for example, “Stimulus number” and “Time / seconds”.
5. M5 Plot all eight points correctly, within half a square of their correct positions.

Explanation

A linear scale increases by the same amount for each equal step along an axis. Put the stimulus number on the horizontal axis because it is the stimulus being changed, and the time in seconds on the vertical axis because it is being measured. Plot each table value as a coordinate, then use straight line segments to connect the points in order. Stop at the first and last points rather than extending the line.

Common mistakes

• The examiner report notes that marks were lost when axes were not labelled, points were not all joined by straight lines, or the line was extended beyond the first and last points. Check each of these before finishing.
• Do not draw bars: the points should be plotted and joined with ruled straight lines.

Practise Co-ordination and response questions

Build a focused practice set from this part of the Edexcel IGCSE Biology syllabus.