Gas Exchange Flashcards
(35 cards)
Where does gas exchange occur?
Occurs over a gas exchange surface – a boundary between the outside environment and the internal environment of an organism.
Most gas exchange surfaces have two things in common that increase the rate of diffusion:
1.They have a large surface area
2.They are often thin just one layer of epithelial cells this provides a short diffusion pathway across the gas exchange surface.
Gas exchange in single-celled organisms
absorb and release gases by diffusion through their cell-surface membranes.
relatively large surface area, thin surface, and a short diffusion pathway – so there is no need for a specialised gas exchange system.
Gas exchange in fish
Lower concentration of oxygen in water than in the air. So, fish have special adaptions to get enough of it.
The gas exchange surface is the gills.
Structure of gills:
-Water, containing oxygen, enters the fish through its mouth and passes out through the gills.
-Each gill is made of lots of thin plates called gill filaments, which give a large surface area for exchange of gases (and so increase the rate of diffusion).
-The gill filaments are covered in lots of tiny structures called 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, between the water and the blood.
Blood flows in the gills:
Blood flows through the lamellae in one direction and water flows over them in the opposite direction. This is called a counter-current system.
The reason for counter-current system
The water with a relatively high oxygen concentration always flows next to blood with a lower concentration of oxygen.
Means that a steep concentration gradient is maintained between the water and the blood – so as much oxygen as possible diffuses from the water into the blood.
Gas exchange in dicotyledonous plants
Main gas exchange surface is the surface of the mesophyll cells in the leaf.
Gases move in and out through special pores in the epidermis (mostly the lower epidermis) called stomata.
Guard cells control the opening and closing the stomata.
No active ventilation is required as the thinness of the plant tissues and the presence of stomata helps to create a short diffusion pathway
Structure of a leaf:
Waterproof cuticle
Upper epidermis - layer of tightly packed cells
Palisade mesophyll layer - layer of elongated cells containing chloroplasts.
Spongy mesophyll layer - layer of cells that contains an extensive network of air spaces.
Stomata - pores (usually) on the underside of the leaf which allow air to enter.
Guard cells - pairs of cells that control the opening and closing of the stomata.
Lower epidermis - layer of tightly packed cells
Gas exchange in insects
Terrestrial insects have microscopic air-filled pipes called tracheae which they use for gas exchange.
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.
Carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere. Insects use rhythmic abdominal movements to move air in and out of the spiracles.
Control of water loss
If insects are losing too much water, they close their spiracles using muscles. They also have a waterproof, waxy cuticle all over their body and tiny hairs around their spiracles, both of which reduce evaporation.
Control of water loss
If insects are losing too much water, they close their spiracles using muscles. They also have a waterproof, waxy cuticle all over their body and tiny hairs around their spiracles, both of which reduce evaporation.
What happens to plant stomata during the day
Plants’ stomata are usually kept open during the day to allow gaseous exchange. Water enters the guard cells, making them turgid, which opens the stomatal pore. If the plant starts to get dehydrated, the guard cells lose water and become flaccid, which closes the pore
Stomata skunk in pits to trap water vapour, reducing the concentration gradient of water between the leaf and the air……..
This reduces evaporation of water from the leaf.
A layer of ‘hairs’ on the epidermis…….
to trap water vapour round the stomata.
Curled leaves with the stomata inside…..
Protecting them from the wind (windy conditions increase the rate of diffusion and evaporation).
A reduced number of stomata………
so there are fewer places for water to escape.
Thicker waxy, waterproof cuticles on leaves and stems……
To reduce evaporation.
Gas exchange in humans: Passage of Air
- Nose / mouth
- Trachea (windpipe)
- Bronchi
- Bronchioles
- Alveoli
Structure of the gas exchange system
Air enters the trachea (windpipe).
The trachea splits into two bronchi – one bronchus leading to each lung. Each bronchus then branches off into smaller tubes called bronchioles.
Bronchioles end in small ‘air sacs’ called alveoli. This where gases are exchanged. The rib cage, intercoastal muscles and diaphragm all work together to move air in and out.
Intercoastal muscles
Found between the ribs.
There are actually two layers: external and internal intercoastal muscles.
Ventilation
Consists of inspiration and expiration.
It’s controlled by the movements of the diaphragm, internal and external intercoastal muscles and ribcage.
What happens during inspiration?
The external intercoastal and diaphragm muscle contract. This causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thoracic cavity.
The volume of the thoracic cavity increases, the lung pressure decreases to below atmospheric pressure. Air will always flow from an area of higher pressure to an area of lower pressure.
Is an active process – it requires energy.
What happens during expiration?
The external intercoastal and diaphragm muscles relax.
Ribcage moves downwards and inwards, and the diaphragm curves upwards again.
Volume of the thoracic cavity decreases, causing the air pressure to increase to above atmospheric pressure. Air is forced down the pressure gradient and out of the lungs.
Normal expiration is a passive process – it doesn’t require energy.
