# Exam-Style Questions: Gas Exchange

1. a) (i) Give one similarity between the way in which oxygen from the atmosphere reaches a muscle in an insect and the way it reaches a mesophyll cell in a leaf.

(ii) Give one difference in the way in which carbon dioxide is removed from a muscle in an insect and the way in which it is removed from a muscle in a fish.

(2 marks)

The diagram shows the way in which water flows over the gills of a fish.

The graph below shows the changes in pressure in the buccal cavity and in the opercular cavity during a ventilation cycle.

b) Use the graph to calculate the rate of ventilation in cycles per second.

(1 mark)

c) For most of this ventilation cycle, water will be flowing in one direction over the gills explain the evidence from the graph that supports this.

(2 marks)

d) Explain how the fish increases pressure in the buccal cavity.

(2 marks)

(Marks available: 7)

Answer outline and marking scheme for question: 1

Give yourself marks for mentioning any of the points below:

a) (i) Diffuses (directly to cells concerned).

(ii) Transported in blood of a fish/lost through gills in fish/through tracheae/spiracle in insect.

(2 marks)

b) 100 (cycles per minute)

(1 mark)

c) Water will flow from high pressure to low pressure; pressure in buccal cavity is higher than in opercular cavity.

(2 marks)

d) Muscles surrounding buccal cavity contract; mouth shuts; floor of buccal cavity rises/volume decreases.

(2 marks)

(Marks available: 7)

2. The diagram shows a chamber set up for an investigation into the movement of woodlice in response to humidity.

Eleven chambers were set up, each with a different relative humidity obtained by using different concentrations of a solution in the base of the chamber. A woodlouse was placed in each chamber.

The rate of movement was recorded. This was repeated ten times for each of the chambers using different woodlice each time, and the means were plotted on a graph.

a) Explain how the response shown increases the chance of survival of woodlice in natural conditions.

(2 marks)

b) (i) Suggest why woodlice were kept in a dry environment for a short time before the investigation was carried out.

(ii) suggest why different woodlice were used each time.

(2 marks)

c) (i) name the type of behaviour observed in this investigation.

(2 marks)

(Marks available: 6)

Answer outline and marking scheme for question: 2

Give yourself marks for mentioning any of the points below:

a) Move faster in environment where they are more likely to desiccate/dry/slower in environments where no dehydration occurs; increases chance of finding suitable environment/remaining in a favourable environment.

(2 marks)

b) (i) To make them more active (at the beginning of the experiment) animals all in same state of hydration at beginning.

(ii) Natural variation in response/large sample enable the typical response to be found.

(2 marks)

c) (i) kinesis

(ii) (Rate of movement) related to intensity of a stimulus.

(2 marks)

(Marks available: 6)

3. The drawing shows a 24-hour cycle for the opening and closing of stomata from the same plant.

a) Explain how this opening and closing of stomata is adventageous to the plant.

(2 marks)

b) The diagram shows the potassium (K+) ion concentrations in the cells around an open and closed stoma in Commelina. The concentrations are in arbitrary units.

(i) Explain how the movement of K+ ions accounts for the opening of the stoma.

(ii) Explain how K+ ions are moved against a concentration gradient.

(5 marks)

(Marks available: 7)

Answer outline and marking scheme for question: 3

Give yourself marks for mentioning any of the points below:

a)

Open during the day to allow entry of carbon dioxide;

Closed at night/midday to reduce transpiration/evaporation/water loss.

b)

(i) K+ ions move into guard cells;

Water potential of guard cells becomes more negative;

Water enters;

How uptake of water causes stoma to open;

(ii) Energy/respiration/ATP/active transport;

Intrinsic proteins/carriers/channels.

(5 marks)

(Marks available: 7)