Gas exchange

21

Describe three ways fish gills are adapted for efficient gas exchange.

Explain why insects can function with open circulatory systems.

The largest fish is the whale shark. Whale sharks have an average mass of 20 tonnes.

The largest marine mammal is the blue whale. Blue whales have an average mass of 150 tonnes.

Use your knowledge of gas exchange and circulatory systems to suggest why marine mammals can grow to a much larger size than fish.

Explain how the structure of haemoglobin allows it to transport oxygen from the lungs to the tissues.

Cats are mammals.

A light micrograph of a section through the trachea of a cat is shown in Fig. 1.1.

Name the tissues labelled A and B in Fig. 1.1.

Name the two types of cell in the box labelled C in Fig. 1.1 and outline their functions.

Alveoli increase the surface area to volume ratio (SA:V) in the lungs of cats and other mammals.

An alveolus in the lung of a cat has:

• a spherical shape

• a diameter of 0.13 mm

• a surface area of 0.053 mm².

Calculate the SA:V of this alveolus. Use the formula: volume of sphere = r³

Explain why the large SA:V of alveoli is an advantage to mammals.

The nervous system of a cat coordinates a response to stop objects becoming stuck in their throat.

Sensory receptors at the back of the throat detect the stimulus of a large piece of food or a ball of hair pressing on the tissue. The response is shown in Fig. 1.2.

Fig. 1.2

Sensory neurone

in the throat
medulla oblongata

Explain two conclusions that can be drawn from Fig. 1.2 about the type of nervous response shown.

The graphs, A to D, represent gas exchange in bony fish.

The graphs show the oxygen saturation in blood in the lamellae and water flowing over the lamellae.

Which graph, A to D, shows the relationship between blood oxygen saturation and distance along the lamellae?

Your answer

The table compares the features of airways in the lungs.

Complete the table by putting a tick (✓) in each box if the feature is present and a cross (8 the feature is absent in each structure.

The first row has been completed for you.

Question 21(b) begins on page 30

Ventilation of the lungs creates air movements that can be measured and recorded.

Name the apparatus used to measure and record these air movements.

The trace below shows a recording of ventilation movements from an individual subject.

Use the trace to estimate the maximum value for tidal volume during the first minute.

After 60 seconds, the subject was told to breathe in as deeply as possible and then breathe out fully.

Use the trace to calculate the vital capacity of the subject.

* Compare and contrast the mechanism of expiration during the first 60 seconds of the trace with the mechanism of expiration when the subject was told to breathe out fully.

Additional answer space if required.

Complete the following statements about exchange surfaces.

Use the correct terms selected from the list below.

circulatory system concentration gradient diffusion pathway

flow of air lung capacity surface area

surface area to volume ratio ventilation

Large organisms have a large........ but they

have a small........ This means they need

a specialised exchange surface and a........

Two features of an efficient exchange surface are:

1. A good blood supply to maintain the........

2. A short........

Many organisms have evolved specialised gas exchange surfaces. One feature of these structures is their large surface area to volume ratio.

Describe how the structures of the insect tracheal system and fish gills provide a large surface area for gas exchange.

insect tracheal system........

The lugworm, Arenicola marina, is a species of segmented worm that lives in burrows in damp sand. They have hair-like external gills that increase the surface area available for gas exchange.

Many other species of segmented worm do not have external gills.

Suggest why lugworms have evolved external gills