Diffusion, Osmosis and Active Transport
- The movement of water from a dilute solution to a more concentrated solution.
- The water must pass through a partially permeable membrane.
- Osmosis is passive.
- Substances move from a high concentration to a low concentration.
- Substances must be either soluble or a gas.
- This is how oxygen leaves the leaf.
- Substances move against the concentration gradient.
- Particles move from a low concentration to a high concentration.
- Requires energy to take place.
- This is how plants take in minerals through their roots.
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Exchange surfaces in humans
- The surface area of the lungs is increased by the alveoli.
- The surface area of the small intestine is increased by the villi.
Exchange in the lungs
- The epithelium of the alveoli is very thin, which shortens the diffusion distance.
- There are capillaries running over the surface of the alveoli, which removes carbon dioxide and takes oxygen to the cells for respiration.
- The alveoli aid gaseous exchange by providing a large surface area, having a moist surface and having a copious blood supply.
Exchange in the gut
- Villi and microvilli increase the surface area of the small intestine. This increase in surface area aids the absorbtion of digested products.
- The villi have a rich blood supply which produces a steep concentration gradient for efficient diffusion.
- Villi also have a thin wall (around 1 cell thick) which shortens the diffusion distance.
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Gas Exchange in Plants
- Gasses diffuse in and out of the stomata, found on the underside of the leaves.
- Leaves have a large surface area.
- Air spaces within the leaves increases the surface area inside.
- Guard cells control the size of the stomata.
Inside a leaf
- Upper epidermis
- Chloroplast - palisade layer
- Xylem, phloem and air spaces - spongey layer
- Stomata and guard cells - lower epidermis
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Different Adaptions for Gas Exchange
- Worms breathe through their skin (no lungs)
- Insects breathe through spiracles on the sides of their bodies (no lungs)
- Dolphins breathe through their blowholes (lungs)
- Land snails breathe through their mantle, a thin layer of tissue (lungs)
- Water snails breathe through their gills (lungs)
- Gasses diffuse across the surface of amoeba.
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Gas Exchange in Plants 2
- Transpiration is the loss of water from the leaves through the stomata.
- Plants lose water in the form of water vapour.
- Capillary action is when water moves up the plant via fibres in the xylem.
- Water molecules are cohesive, they stick together.
Speeding it up
- Flatter, thinner leaves
- Hot, dry, windy weather
- Larger stomata
- More stomata
Slowing it down
- Humid climate
- Small stomata
- Fewer stomata
- Waxy leaves
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Heart and Circulation
- (Through the veins) From lungs --> left atrium --> left ventricle --> (through arteries) body tissues --> (through veins) right atrium --> right ventricle --> (through arteries) lungs.
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