Exchange and Transport Systems - Gas Exchange AND Gas Exchange in Humans Flashcards
What are the two adaptations of gas exchange surfaces?
1) They have a large surface area
2) They’re thin (often only just one layer of epithelial cells.
This provides a short diffusion pathway across the gas exchange surface.
The organism also maintains a steep concentration gradient of gases across the exchange surface.
All of these features increase the rate of diffusion.
How do single-celled organisms exhange gases? (2)
1) They absorb and release gases through 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).
What’s the name of the system fish use for gas exchange?
Why do they use this?
Counter-Current
Used because there’s a lower concentration of oxygen in water than air, so fish have special adaptations to get enough of it.
Explain the counter-current system for gas exchange in fish.
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.
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This is called a counter-current system.
It maintains a large concentrationg radient 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.
How does gas exchange occur in insects?
The Tracheal System:
1) Insects have microscopic, air-filled pipes called tracheae which they use for gas exchange
2) Air moves into the tracheae through pores on the surface called spiracles
3) Oxygen travells down the concentration gradient towards the cells
4) 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.
5) Carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere.
6) Insects use rhythmic abdominal movements to move air in and out of the spiracles.
How do insects limit water (and oxygen) loss?
2/3
1) The closing of spiricles using muscles
2) They have a waterproof waxy cuticle all over their body and tiny hairs surrounding spiracles to trap water / reduce evaporation
3) Air sacs surrounding trachea which allows store of oxygen if spiracles have to be closed for too long. (This one isn’t in the textbook - may not need to know)
Where do dicotyledonous plants exchange gases?
Explain this function.
At the surface of the mesophyll cells.
Plants need CO2 for photosynthesis, which produces O2 as a waste gas. They need O2 for respiration, which produces CO2 as a waste gas.
The main gas exchange surface is the surface of the mesophyll cells in the leaf. They’re well adapted for their function – they have a large surface area.
The mesophyll cells are inside the leaf. Gases move in and out through special pores in the epidermis called stomata (stoma sing.)
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 the stomata.
How do plants control water loss?
Plants’ stomata are usually kept open during the dayto allow gaseous exchange.
Ions (e.g. K+) enter the guard cells, making water potential more negative so water follows by osmosis making guard cells turgid, which opens the pores.
When ions exit / guard cells become dehydrated, water potential is more positive so water exits by osmosis making guard cells flaccid, which closes the pores.
What is a xerophyte?
A plant specially adapted for life in warm, dry or windy habitats, where water loss is a problem.
What are some xerophytic adaptions? (4)
- 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 lead and evaporating away. - A layer of ‘hairs’ on the epidermis
- again to trap moist air around the stomata
- Curled leaves with the stomata inside,
protecting them from wind
(windy conditions increase the rate of diffusion and evaporation) - A reduced number of stomata,
so there are fewer places for water to escape
What is ventilation?
Breathing in and out
Describe the mechanism of inspiration.
External intercostal and diaphragm muscles contract
Ribcage moves upwards and outwards
and diaphragm flattens, increasing volume and thoracic cavity
As the volume increases, the lung pressure decreases (to below atmospheric pressure)
Air will always flow from high to low pressure (down pressure gradient) so are flows from trachea into lungs
ACTIVE process – requires energy
Describe the mechanism of passive expiration.
How does this differ when its forced / active?
External intercostal and diaphragm muscles relax
Ribcage moves downwards and inwards
and diaphragm curces again, decreasing volume of thoracic cavity
As the volume decreases, the lung pressure increases (to above atmospheric pressure)
Air is forced down the pressure gradient and out of lungs.
PASSIVE process – doesn’t require energy.
When it’s forced (e.g. blowing out birthday candles),
external intercostal muscles relax
and INTERNAL intercostal muscles contract,
pulling the ribcage further down and in.
During this time, the movement of the two sets of intercostal muscles is said to be antagonistic (opposing).
Describe the function of gas exchange at the alveoli.
There’s a huge number of alveoli in the lungs,
which means there’s a big surface area for exchanging substances oxygen and carbon dioxide.
The alveoli are surrounded by a network of capillaries.
Oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endithelium (a type of epithelium that forms the capillary wall), and into haemoglobin in the blood. (Movement down a diffusion gradient.)
CO2 diffuses into the alveoli from the blood, and is breathed out.
How are alveoli adapted for gas exchange?
1) A thin exchange surface – the alveolar epithelium is only one cell thick.
This means there’s a short diffusion pathway (which speeds up diffusion).
2) A large surface area – the large number of alveoli means there’s a large surface area for gas exchange.
3) Very dense capillary network covering it – shorter diffusion pathway and easier acess to blood supply
4) Steep concentration gradient between the oxygen in the alveoli and the carbon dioxide in the capillaries, which increases the rate of diffusion.
This is constantly maintained by the flow of blood and ventilation.
5) The lining of the alveoli is moist, which allows gases to dissolve, which then allows them to diffuse across the lining.
6) Good ventilation
