Gas Exchange and Exchange of Substances
- Created by: India.02
- Created on: 11-05-19 19:39
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- Gas Exchange
- Lungs
- Transfer oxygen to the blood and to remove waste CO2
- Contains millions of little air sacs called alveoli - where gas exchange takes place
- Alveoli have an enormous surface area - 75m*2 in humans - they also have a moist lining for dissolving gases, very thin walls and a good blood supply
- Villi
- Small projections inside the small intestine - increase surface area in a big way so that digested food is absorbed much quicker into the blood
- They have a single layer of surface cells and a very good blood supply to assist quick absorption
- Leaves
- Carbon dioxide diffuses into the air spaces within the leaf, then it diffuses into the cells - where photosynthesis happens
- Underneath of the the leaf is the exchange surface - covered in small holes called stomata which the CO2 diffuses through
- Oxygen and water vapour also diffuse out through the stomata - water vapour lost from all over the surface but mainly through stomata
- Water vapour evaporates from cells inside the leaf and escapes by diffusion - higher concentration inside the leaf than outside
- Size of stomata controlled by guard cells - close stomata if plant is losing water faster than it is being replaced by the roots - without guard cells the plant would wilt
- Flattened shape of leaf increases area of exchange surface so that it is more effective
- Walls of the cells inside the leaf forma another exchange surface - air spaces inside the leaf increase the area of this surface so there is more chance for CO2 to get into cells
- Gills
- Water (containing oxygen) enters the fish through its mouth and passes out through the gills - oxygen diffuses from the water into the blood in the gills and CO2 diffuses from the blood into he water
- Each gill is made of thin plates called gill filaments - big surface area for exchange of gases
- Filaments covered in tiny structures called lamellae - increase surface area more
- Lamellae have lots of blood capillaries to speed up diffusion - thin surface layer of cells to minimise the distance that the gases have to travel
- Blood flows through lamellae in one direction and the water flow over in the opposite direction - maintains large concentrationgradienj between water and blood
- Concentration of oxygen in the water is always higher than that in the blood - as much oxygen diffuses from the water into the blood
- Lungs
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