3.3 Topic 3 - 3.3.2 Gas exchange Flashcards
1What are two things most gas exchange surfaces have in common? + one extra
1] A large surface area.
2] Thin [often just one layer of epithelial cells] = short diffusion pathway across gas exchange surface.
3] They also maintain a steep concentration gradient of gases across the exchange surface.
What do single-celled organisms exchange gases across? + how?
Their body surface.
They do this by absorbing and releasing gases by diffusion through their outer surface.
Single-celled organisms have a relatively large what? thin what? and short what?
Large surface area, thin surface and a short diffusion pathway.
Why is there no need for a gas exchange system in single-celled organisms?
As oxygen can take part in biochemical reactions as soon as it diffuses into the cell.
What system do fish use for gas exchange?
Counter-current system.
True or false? There is a lower concentration of oxygen in water than in air.
True.
How does the counter-current system work for gas exchange in fish?
[5 steps]
1] Water containing oxygen enters the fish through its mouth and passes out through the gills.
2] Each gill is made of 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 surface area 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. 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.
Counter-current system simple terms:
Blood flows through the lamellae in one direction and water flows over in the opposite direction. 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.
What would a counter-current system graph look like?
y-axis = oxygen concentration
x-axis = distance along gill plate
blood horizontal line up
water horizontal line down
What is each gill made of?
Lots of thin plates called gill filaments, which give a big surface area for exchange of gases
What are the gill filaments covered in?
Lots of tiny structures called lamellae, which increase the surface area even more.
The lamellae have lots of ….. ……….. and a …. ……. ….. of cells.
Blood capillaries and a thin surface layer of cells.
What do insects use to exchange gases?
Tracheae.
What are tracheae?
Microscopic air-filled pipes which are used for gas exchange in insects.
How does air move into the tracheae?
Through pores on the surface called spiracles.
In the tracheae does oxygen travel up or down the concentration gradient towards the cells?
Down to the cells.
What do the tracheae branch of into?
Smaller tracheoles which have thin, permeable walls and go to individual cells = oxygen diffuses directly into the respiring cells - the insects circulatory system does not transport O2.
True or false for gas exchange in insects? CO2 from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere.
True.
What do insects use to move air in and out of the spiracles?
Rhythmic abdominal movements.
Where do dicotyledonous plants exchange gases?
At the surface of the mesophyll cells in the leaf.
What do plants need CO2 for? + what does this produce as waste?
Photosynthesis, which produces O2 as a waste gas.
Where do gases move in and out of in the mesophyll cells?
Through special pores in the epidermis called stomata [singular = stoma].
What can the stomata do?
The stomata can open to allow exchange of gases, and close if the plant is losing too much water
What cells control the opening and closing of the stomata?
Guard cells.
True or false? Insects and plants can control water loss.
True.
Exchanging gases tends to make you lose water, plants and insects have evolved adaptations to minimise water loss without reducing gas exchange too much.
If insects are losing too much water, what will they do?
Close their spiracles using muscles.
What features do plants have to reduce evaporation?
A waterproof, waxy cuticle all over their body and tiny hairs around their spiracles.
What happens to the guard cells when water enters?
They go turgid, which opens the stomatal pore.
What happens to the guard cells if a plant starts to get dehydrated?
They lose water and become flaccid, which closes the pore.
What are the plants called which are adapted for life in warm, dry or windy habitats where water loss is a problem?
Xerophytes.
What are the 5 examples of adaptations xerophytes have?
- Stomata sunk in pits.
- A layer of hairs on the epidermis.
- Curled leaves with the stomata inside.
- Reduced number of stomata.
- Waxy, waterproof cuticles.
How does xerophytes having stomata sunk in pits help reduce water loss?
They 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.
How does xerophytes having a layer of hairs on the epidermis help reduce water loss?
They trap moist air round the stomata.
How does xerophytes having curled leaves with the stomata inside help reduce water loss?
This helps to protect them from wind [windy conditions increase the rate of diffusion and evaporation].
