Gas Exchange

Question 1

Most gas exchange have two things in common, what are these?

Answer 1

1. They have a large surface area

2. They’re thin - this provides a short diffusion pathway across the exchange surface

Question 2

What do fish use for gas exchange?

Answer 2

Fish use a counter-current system for gas exchange

Question 3

How do fish use the counter-current system for gas exchange?

Answer 3

1. Water, containing oxygen, enters the fish through its mouth and passes through the gills
2. Each gill is made from lots of thin plates called gill filaments, which give a big surface area for exchange of gases
3. The gill filaments are covered in lots of tiny structures called lamellae, which increase the SA even more
4. The lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion
5. Blood flows through the lamellae in one direction and water flows over in the opposite direction - this is 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 4

What do insects use to exchange gases?

Answer 4

Tracheae

Question 5

How do insects use tracheae for gas exchange?

Answer 5

1. Air moves into the tracheae through pores on the surface called spiracles
2. Oxygen travels down a concentration gradient towards the cells
3. The tracheae branch off into smaller tracheoles which have thin, permeable walls and go into individual cells. This means oxygen diffuses directly into respiring cells
4. Carbon dioxide from the cells move down its own concentration gradient towards the spiracles to be released into the atmosphere
5. Insects use rhythmic abdominal movements to move air in and out of the spiracles

Question 6

Where does gas exchange occur in plants?

Answer 6

In dicotyledonous plants, gas exchange occurs at the surface of the mesophyll cells

Question 7

How do plants exchange gases?

Answer 7

The main gas exchange surface is the mesophyll cells inside the leaf - they’re adapted for their function as they have a large surface area. Gases move in and out through pores in the epidermis called stomata. The stomata can open to allow exchange of gases, and close if the plant is losing too much water. Guard cells control the opening and closing of stomata

Question 8

What do insects do if they’re losing too much water?

Answer 8

They close their spiracles using muscles. They also have a waterproof, waxy cuticle all over their body and tiny hairs around the spiracles, both which reduce evaporation

Question 9

What do plants do if they’re losing too much water?

Answer 9

Plants stomata are usually kept open during the day to allow for gaseous exchange. Water enters the guard cells, making them turgid, which opens the stomatal pores. If the plant starts to get dehydrated, the guard cells lose water and become flaccid, which closes the pore

Question 10

Some plants are adapted too warm, dry and windy habitats. What are these called?

Answer 10

Xerophytes

Question 11

What are some adaptations of xerophytes?

Answer 11

1. Stomata sunk in pits that trap moist air, reducing the concentration gradient of water between the leaf and the air. This reduces the amount of water diffusing out of the leaf and evaporating away
2. A layer of ‘hairs’ on the epidermis - to trap moisture around the stomata
3. Curled leaves with the stomata inside, protecting them from the wind - windy conditions increase the rate of diffusion and evaporation
4. A reduced number of stomata so there are fewer places for water to evaporate
5. Waxy, waterproof cuticles on leaves and stems to reduce evaporation