Adaptations for Gas Exchange (AQA AS Biology)

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

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

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.

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.

Figure 3

Describe and explain the results seen in Figure 3.

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

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

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

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

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

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.

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.

A researcher calculated the surface area of a large number of toad eggs. She calculated the mean surface area to be 10.12 mm^2. 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.

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

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

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.

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

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

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

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

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

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

Figure 1

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

Suggest why Chlamydomonas would not survive in a saltwater environment.

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.

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

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

Figure 1

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.

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.

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

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

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.

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. 

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

Table 1

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

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

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

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

Figure 1

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

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

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. 

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

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

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

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

Figure 1

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

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. 

Suggest how the data in Figure 1 provides support for the GOLT and suggest how this might affect fish growth.

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

Figure 2

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.

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. 

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

Figure 1

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

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.

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 

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.

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