Topic 3: SA:vol ratio

Question 1

What is the relationship between the size of an object and its surface area to volume ratio?

Answer 1

The larger an organism is, the smaller its surface area compared to its volume and the larger the distance from the middle to the outside.

Question 2

Why is it sufficient for small organisms such as amoeba to exchange gases across their surface, rather than requiring a special exchange system (like the lungs?)

Answer 2

Small organisms have a very large surface area in comparison to their volume. This means that there is a big surface for the exchange of substances, but also there is a smaller distance from the outside of the organism to the middle of it. As a result, the very small organism can simply exchange substances across its surface by diffusion.

Question 3

List examples of adaptations that larger organisms have to meet the demands that help make the exchange across surfaces more efficient.

Answer 3

1.Villi and microvilli
2.Alveoli and bronchioles 3.Spiracles and tracheoles 4.Gill filaments and lamellae 5.Thin wide leaves
6.Many capillaries

Question 4

Describe process of inspiration

Answer 4

External intercostal muscles contract to pull the ribs up and out

Intercostal muscles relax

Diaphragm contracts to move down and flattens

Air pressure in lungs initially drops. As air moves in it raises above atmospheric pressure

Lung volume increases

Air moves into lungs as the atmospheric pressure is higher than that of the thorax

Question 5

Describe process of expiration

Answer 5

External intercostal muscles relax

internal intercostal muscles contract and pull the ribs down and in

diaphragm relaxes to move up and dome

initially greater than atmospheric -pressure.. drops as air moves out

lung volume decreases

air moves out of the lungs as the pressure in the thorax is higher than that of the atmosphere