AQA AS Biology

Topic Questions

3.1 Adaptations for Gas Exchange

1a1 mark

Complete the following sentence. 

The size of an organism is ___________ proportional to its surface area to volume ratio.

1b1 mark

In an experiment using agar blocks immersed in a diffusion solution, the blocks are made up containing sodium hydroxide and universal indicator solution. Suggest a suitable solution to immerse these blocks in to examine diffusion.

1c2 marks

Two organisms are described in Table 1

Table 1

  Organism A Organism B
Surface Area / cm2 18 970 79.8
Volume / dm3 70 0.019
SA:VOL ratio    


Complete
Table 1 by calculating the missing surface area to volume ratios. Do not include units. 

1d2 marks

Table 1 from part c) shows two organisms, A and B. One of these is a mouse, the other is a human. Work out which animal is represented by A. Give a reason for your answer.

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2a2 marks

Describe and explain one example of how the human breathing system is adapted to achieve sufficient gas exchange despite humans’ low surface area-to-volume ratio.

2b2 marks

A molecule of oxygen would diffuse into a single-celled prokaryotic cell and reach the centre of the cell quicker than it would reach the centre of a single, eukaryotic cell. Explain why.

2c1 mark

Basal Metabolic Rate (BMR) is a measure of the amount of energy expended by that organism within a given period of time when the organism is at rest. Suggest one variable that can be measured as a way of determining BMR.

2d1 mark

Describe the relationship between Basal Metabolic Rate and the mass of an organism.

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3a2 marks

Explain why plants have, in general, a much lower Basal Metabolic Rate than animals.

3b2 marks

A mouse’s resting heart rate can be 5 times faster than a human’s at a similar body temperature of 37°C. Explain why. 

3c2 marks

A spherical-shaped, single-celled organism, like certain species of coccus bacteria, is ideally suited to carry out gas exchange by simple diffusion. Explain why.

3d1 mark

Name the small pores that have evolved on the surface of certain insect species that are used for breathing. 

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4a3 marks

Figure 1 shows the parts of the breathing system of a certain species of insect. 

Figure 1

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Label the structures shown in Figure 1 with the letters A, B, C, D, E and F as follows:

 

Structure Label
Muscle tissue A
Spiracle B
Trachea C
Tracholes D
Air sac E
Exoskeleton F

4b1 mark

Referring to the diagram shown in Figure 1, identify the structure that provides the pressure changes required for increased breathing in an insect.

4c1 mark

All insects possess a rigid exoskeleton with a waxy coating that is impermeable to gases. Suggest why insects do not use this outer surface for gas exchange with the air.

4d2 marks

In plants, guard cells change to cause stomata to open and close at different times of day. Describe the nature of the change that guard cells undergo when stomata close at night.

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5a1 mark

Gas exchange is required in all organisms, and certain organisms called xerophytes have evolved ways to allow gas exchange to occur even in harsh conditions. Define the word, ‘xerophyte’.

5b1 mark

Terrestrial insects have a small body so are susceptible to water loss through being exposed to direct sunlight and high temperatures. Identify a feature of their bodies, which they share with plants’ leaves, that reduces water loss.

5c2 marks

The agave (Agave americana) is a plant that lives in hot, arid regions of Central and South America. Agaves have very few stomata per cm2 of leaf surface compared to other plants. Identify one advantage and one disadvantage of the agave having few stomata per cm2 of leaf surface. 

5d1 mark

Many species closely related to the agave belong to the Cactus genus. Name one other adaptation, observed in cacti, that limits water loss through transpiration.

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1a2 marks

Figure 1 below is a transmission electron micrograph of a cross section through the gill lamellae of a fish. 

Figure 1

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The line marked X in Figure 1 measures 0.65 cm, and the scale bar measures 1.5 cm. Calculate the diffusion distance for a molecule of oxygen travelling from the water to a red blood cell along the line marked X.

1b3 marks

The length of the diffusion distance calculated in part a) is one way in which fish gills are adapted for gas exchange. Another adaptation is that they have a countercurrent system. Explain what this means and how it acts as an adaptation for gas exchange.

1c2 marks

A group of researchers investigated the effect of an insecticide called Nuvan on the gills of fish. Some of their results are shown in Figure 2 below. 

Figure 2

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State what can be concluded from Figure 2 about the effects of Nuvan on fish.

1d3 marks

A local environmental campaign group claimed that the results shown in Figure 2 should  lead to a total ban on the use of Nuvan by farmers. Evaluate this claim.

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2a6 marks

A student wanted to investigate the effect of changing the surface area : volume ratio on the rate of diffusion in agar blocks. They decided to use agar made up with sodium hydroxide and the pH indicator phenolphthalein. The agar was cut up into cubes with sides of length 5, 10, 20, 30, and 40 mm. 

Explain how the student could use this agar to investigate the effect of surface area : volume ratio on the rate of diffusion. 

2b2 marks

Table 1 below shows the results that the student gained during their experiment.

Table 1

Cube side length (mm) Surface area : volume ratio Time taken for diffusion (s)
5 1.2 366
10 0.6 894
20 0.3 1680
30   2568
40 0.15 3546

Calculate the surface area : volume ratio of a cube with a side length of 30 mm

2c4 marks

Use the information in Table 1 and your answer to part b) to plot a graph of surface area : volume ratio against time for diffusion (s).

2d1 mark

Use the results in parts b) and c) to explain why most single celled organisms are limited to a diameter of around 100 μm.

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3a3 marks

Figure 1 shows cross sections through two xerophytic leaves taken under a light microscope. 

Figure 1

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Describe and explain features shown in Figure 1 that are xerophytic in nature.

3b2 marks

A student who wanted to investigate stomata looked at a lower leaf surface under a microscope. Their field of view is shown in Figure 2 below. 

The diameter of the microscope’s field of view was 1.4 mm and the lower leaf had a total surface area of 220 mm2.

Figure 2

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Use the information provided and Figure 2 to calculate the total number of stomata on the lower surface of the student’s leaf. Give your answer to the nearest whole number. 

3c2 marks

The student looked at data on the density (stomata per mm2) of spruce tree stomata at different altitudes. The data are shown in Figure 3 below. 

Figure 3

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Explain why ‘stomatal density’ is used here rather than ‘number of stomata’ as calculated in part b).

3d3 marks

Describe and suggest an explanation for the relationship between stomatal density and  altitude shown in Figure 3.

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4a2 marks

Figure 1 below shows the relationship between body mass and gill surface area in a species of shark. 

Figure 1

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Explain how increasing gill surface can cause the change in body mass shown in Figure 1.  

4b2 marks

A theory called the gill oxygen limitation theory (GOLT) states that the surface area of fish gills increases more slowly than fish metabolic requirements as body size increases. 

State how the graph provides support for the GOLT and suggest how this might affect fish growth.

4c3 marks

Figure 2 shows how the concentration of dissolved oxygen in water changes with temperature. 

Figure 2

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Use Figure 2 to predict and explain how climate change is likely to affect fish growth in the future. Refer to the ideas of the GOLT described in part b) in your answer.

4d3 marks

Scientists who disagree with the GOLT have several arguments, one of which is that the largest fish in the world, the whale shark, is found in tropical waters. The whale shark is a slow-moving filter feeder that comes to the sea surface to feed while spending long periods diving to deeper waters. Male whale shark growth levels off as they reach sexual maturity, while females grow slowly throughout their lives. 

Use the information provided to suggest and explain how scientists who argue for the GOLT might respond to the argument that the whale shark provides evidence against their theory. 

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5a3 marks

Figure 1 below shows some of the events taking place in the gas exchange system of an insect over time. 

Figure 1

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Explain the changes to gas concentration and spiracles shown in Figure 1.  

5b1 mark

In some insects the interval between spiracle opening can be a long time. Suggest why this discontinuous method of breathing might be advantageous to these insects.

5c3 marks

There are several mechanisms used by aquatic insects to allow them to continue breathing oxygen while underwater. Two of these methods are shown in Figure 2 below. Method A uses an air bubble, while method B uses a layer of air called a plastron which forms around a series of incompressible hairs. Note that both oxygen and nitrogen can diffuse across the air-water interface.

Figure 2 

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The bubble shown in method A in Figure 2 is sometimes known as a ‘compressible gill’ and only allows insects to dive for a short period of time. Use Figure 2 to suggest why this is the case.

5d3 marks

Method B in Figure 2 is a plastron, or an incompressible gill, and allows insects to dive indefinitely. Suggest how the plastron enables this. 

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1a2 marks

As the size of an organism increases, its surface area to volume ratio decreases, meaning that larger organisms often require specialised cells and systems to ensure the efficient transport of essential substances and waste products to and from respiring tissues.

Despite being very small, insects like the one in Figure 1 below require a specialised breathing system.

Explain why this is the case.

Figure 1

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1b3 marks

Figure 2 below shows the tracheal system of an insect.

Describe how oxygen in the tracheole reaches the muscle cells of the insect.

Figure 2

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1c4 marks

Some insects are very active flyers. After a period of time the flying muscles respire anaerobically and the products of anaerobic respiration accumulate in the cells.

Explain how this affects the supply of oxygen to the flying muscles.

1d3 marks

Spiracles are openings in the exoskeletons of insects. They possess valves that give insects the ability to open and close their airways.

A research scientist investigated how the concentration of oxygen in the air affects the rate at which spiracles open (number of times per minute) in lice.

Figure 3 below shows the number of times the spiracles of a single louse open in a minute when it is exposed to different concentrations of oxygen.

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Describe and explain the results seen in Figure 3.

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2a3 marks

Marram grass is an example of a xerophytic plant found on sand dunes throughout the UK.

Marram leaves have the ability to roll up into an almost cylindrical shape.

Figure 1 below shows the leaf in this rolled-up position.

Figure 1

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Describe and explain three features seen in Figure 1 that help to reduce water lost by evaporation.

2b2 marks

Privet is a plant often used for garden hedgerows in the UK.

A scientist was investigating the number of stomata on the leaves of a privet plant. Using a microscope they measured the number of stomata in the field of view for the top surface and underside of 12 leaves.

Their results are seen in Table 1 below.

Table 1

Leaf Number Top Surface of Leaf Underside of Leaf
Number of stomata in field of view Number of stomata in field of view
1 0 36
2 0 45
3 0 48
4 0 37
5 0 40
6 0 46
7 0 39
8 0 37
9 0 40
10 0 46
11 0 40
12 0 38
Mean    
Standard deviation    

Complete the table by calculating the mean and standard deviation for both sets of data.

2c2 marks

Suggest two reasons why it would not be beneficial for a plant to have stomata on the top surface of its leaves.

2d2 marks

For the data in Table 1 the scientist simply counted the number of stomata in the field of view.

Suggest a better way of counting the stomata, give units.

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3a2 marks

When first hatched, the young tadpoles of some toad species are less than 1.5 mm long. 

Explain how these young tadpoles are able to get enough oxygen to their cells without developed gills.

3b3 marks

A researcher calculated the surface area of a large number of toad eggs. She calculated the mean surface area to be 10.12 mm2. Toad eggs are generally spherical.

She calculated the surface area using the following equation: 4πr2

Use this equation to calculate the mean diameter of a toad egg.

Give your answer to 3.s.f.

3c2 marks

The researcher calculated the ratio of surface area to mass for the eggs, tadpoles and adult toads. She also determined the mean rate of oxygen uptake by eggs and tadpoles.

Their results are shown in Table 1 below.

Table 1

Stage of toad development Mean rate of oxygen uptake (µmol g-1 h-1) Surface area to Mass ratio
Egg 6.1 2567 : 1
Tadpole 1.2 319 : 1
Adult Toad No information 150 : 1

The researcher measured surface area to mass ratio instead of surface area to volume ratio. Suggest two practical advantages of this.

3d3 marks

The researcher was unable to make a conclusion about the relationship between the stages of development and metabolic rate in toads.

Use Table 1 to explain why they were unable to come to a conclusion.

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4a4 marks

Explain how the structure of a fish gill is adapted for the efficient uptake of oxygen.

4b3 marks

Figure 1 below illustrates the relationship between gill surface area and body mass for three different species of fish (X,Y and Z).

Figure 1

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Describe and explain the relationships between gill surface area and mass shown Figure 1.

4c2 marks

Predict the relationship between water temperature and the gill surface area.

4d3 marks

Describe and explain how the countercurrent system within fish gills leads to efficient gas exchange.

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5a2 marks

Figure 1 below shows a single-celled organism called Chlamydomonas. It is found in ditches and fresh water ponds.

Figure 1

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Fill in Table 1 below by naming two structures shown in Figure 1 that are found in both animal and plant cells, and two that are found in plant cells only.

Table 1

Found in Plant and Animals cells Found in Plant cells only
   
   
5b2 marks

Suggest why Chlamydomonas would not survive in a saltwater environment.

5c2 marks

Chlamydomonas measures roughly 20 µm across and is of a spherical shape. It’s volume is 4,188.8 µm3, calculate it’s surface area (SA) and SA:volume ratio. 

Give your answers to one decimal place.

5d3 marks

Chlamydomonas has several adaptations that help it to achieve an efficient rate of photosynthesis. Use Figure 1 to explain what these adaptations are.

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