Gas Exchange Flashcards
Where does gas exchange occur?
Over a gas exchange surface.
What is a gas exchange surface?
A boundary between the outside environment and the internal environment of an organism.
What do organisms need for diffusion across a gas exchange surface?
Oxygen and carbon dioxide (makes diffusion quicker).
What increases the rate of diffusion over gas exchange surfaces?
- They have a large surface area
* They are thin (often just one layer of epithelial cells).
What does a thin gas exchange surface provide?
A short diffusion pathway across the gas exchange surface.
What do single-celled organisms not require for gas exchange?
A specialised gas exchange system.
Why do single-celled organisms not require a gas exchange system?
- They have a relatively large surface area
* A thin surface, thus a short diffusion pathway
Where does gas exchange occur in single-celled organisms?
They absorb and release gases by diffusion through their cell-surface membranes.
Where does gas exchange occur in fish?
In the gills
Why does gas exchange occur in the gills of a fish?
Because the gills are specially adapted to get enough oxygen.
Why do fish gills need to be adapted to get enough oxygen?
Because there is a lower concentration of oxygen in water than in air.
How does gas exchange occur in fish?
Water containing oxygen enters the fish through its mouth and passes out through the gills.
What do gills have which are beneficial to gas exchange?
A large surface area for gas exchange.
Why do gills have a large surface area for gas exchange?
- Each gill is made of lots of thin plates called gill filaments.
- These gill filaments are covered in lots of tiny structures called lamellae.
How do the lamellae in gills increase the rate of diffusion further?
- They increase the surface area even more.
- They have lots of blood capillaries.
- They have a thin surface layer of cells.
What do fish gills look like?
image
What system do gills have that ensure a high rate of diffusion?
The counter-current system.
What is the counter-current system in fish gills?
- The blood flows through the lamellae in one direction.
* The water flows over the lamellae in the opposite direction.
What does the counter current system do in gills?
It ensures that the water with a relatively high oxygen concentration always flows next to blood with a lower oxygen concentration.
How does the counter-current system ensure a high rate of oxygen diffusion from water to blood in gills?
Because it maintains a steep concentration gradient between the water and the blood.
What does the counter-current system in gills look like?
Image
How does gas exchange occur in dicotyledonous plants?
Gases move in and out through special pores in the lower epidermis called stomata.
Where does gas exchange occur in dicotyledonous plants?
Mesophyll cells in the leaf (well adapted with a large surface area).
What do the stomata do during gas exchange in dicotyledonous plants?
Stomata open to allow gas exchange and close if the plant is losing too much water.
What does gas exchange in dicotyledonous plants look like?
image
Where does gas exchange in insects occur?
They have microscopic air filled pipes called trachea.
How does gas exchange occur in the trachea of insects?
- Air moves into the trachea through pores on the surface called spiracles.
- Oxygen travels down he concentration gradient towards the cells.
- The trachea branch off into smaller trachioles.
Why do the trachea branch off into trachioles during gas exchange in insects?
Because they go to individual cells and they have thin, permeable walls, so oxygen diffuses directly into respiring cells.
How is the carbon dioxide released during the gas exchange of insects?
Carbon dioxide from the respiring cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere.
How do insects move air into and out of the spiracles?
Through rhythmic abdominal movements.
What does gas exchange across the trachea of insects look like/
image
What does gas exchange often lead to?
Water loss
What adaptations do insects have that minimise water loss during gas exchange?
- They close their spiracles using muscles.
* They have a waterproof waxy cuticle over their body and tiny hairs (reducing evaporation).
What adaptations do plants have that minimise water loss during gas exchange?
The opening and closing of their stomata:
- Stomatal pores stay open when water enters the guard cells, making them turgid
- Stomatal pores close when guard cells lose water, becoming flaccid, thus closing the pore (when plants are dehydrated).
What are xerophytic plants?
Plants that are specially adapted for life in warm, dry or windy habitats, where water loss is a problem.
What are some adaptations of xerophytic plants?
- Sunken stomata
- Layer of hairs around the epidermis
- Curled leaves with the stomata inside
- Reduced number of stomata
- Thicker, waxy, waterproof cuticles on leaves and stems
Why do sunken stomata in xerophytes reduce water loss?
Because they trap water vapour, reducing the concentration gradient of water between the leaf and the air, reducing evaporation.
Why do layers of hair around the epidermis in xerophytes reduce water loss?
This traps water vapour around the stomata, again reducing the concentration gradient between the leaf and air, redcuing evaporation.
Why do curled leaves with the stomata inside in xerophytes reduce water loss?
This protects the stomata from the wind, decreasing diffusion and evaporation of water.
Why does a reduced number of stomata in xerophytes reduce water loss?
Because there are less places for water to escape from.
Why do thicker, waxy, waterproof cuticles on leaves and stems in xerophytes reduce water loss?
Because this reduces evaporation.
