Gas Exchange

Question 1

Give two features that most gas exchange surfaces have in common.

Answer 1

1) They have a large surface area.
2) They’re thin (often just one layer of epithelial cells) this provides a short diffusion pathway across the gas exchange surface.

Question 2

How can single celled organisms exchange gases across their body structure?

Answer 2

1) Single-celled organisms absorb and release gases by diffusion through their outer surface.
2) They have a relatively large surface area, a thin surface and a short diffusion pathway (oxygen can take part in biochemical reactions as soon as it diffuses into the cell) so there’s no need for a gas exchange system.

Question 3

Why do fish need special adaptions to get enough oxygen?

Answer 3

Ther’s a lower concerntration of oxygen in water than there is in air.

Question 4

How is the gas exchange surface of a fish adapted for its function?

Answer 4

• Each gill is made of lots of thin plates called gill filaments,
  which give a big surface area for exchange of gases.
• The gill filaments are covered in lots of tiny structures called
  lamella (plural = lamellae) which increase the surface area even more.
• The lamellae have lots of blood capillaries and a thin
  surface layer of cells to speed up diffusion.

Question 5

Describe counter-current flow.

Answer 5

Water, containing oxygen, enters the fish through its mouth and passes out through the gills. Blood flows through the lamellae in one direction and water flows over in the opposite direction. This is called a counter-current system. It maintains a large concentration gradient between the water and the blood. The concentration of oxygen in the water is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood.

Question 6

Draw a diagram of countercurrent flow.

Answer 6

Question 7

Draw and label a section of a fish’s gill.

Answer 7

Question 8

What does countercurrent look like on a graph?

Answer 8

Question 9

3) Give three adaptations that many insects have to help them minimise water loss.

Answer 9

E.g. they can use muscles to close their spiracles, if they’re losing too much water. They have a waterproof, waxy cuticle all over their body to reduce evaporation. They have tiny hairs around their spiracles to reduce evaporation.

Question 10

Describe an insects site of gas exchange.

Answer 10

Insects have microscopic air-filled pipes called tracheae which they use for gas exchange. The tracheae branch off into smaller tracheoles which have thin, permeable walls and go to individual cells.

Question 11

Explain how carbon dioxide is exchanged between an insect’s cells and its external environment.

Answer 11

Carbon dioxide moves down a concentration gradient from respiring cells into the tracheoles. It then continues to move down a concentration gradient as it passes through the tracheae and out of the spiracles to the external environment.

Question 12

Explain why an insects circultory system dosen’t need to transport oxygen.

Answer 12

• Air moves into the tracheae through pores on the surface called spiracles.
• Oxygen travels down the concentration gradient towards the cells.
• The tracheae branch off into smaller tracheoles which have thin, permeable walls and go to individual cells. This means that oxygen diffuses directly into the respiring cells. the insect’s circulatory system doesn’t transport O₂.

Question 13

How do insects move air in and out of the spiricals?

Answer 13

Insects use rhythmic abdominal movements to move air in and out of the spiracles.

Question 14

Label a diagram of an insect

Answer 14