B3 1.1 Active Transport
- Substances are sometimes absorbed against a concentration gradient by active transport.
- Active transport uses energy from respiration.
- Cells can absorb ions from very dilute solutions and move molecules through cell membranes using active transport.
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B3 1.2 Exchange Of Gases In The Lungs
- Your breathing system takes air into and out of your body.
- Oxygen from the air diffuses into your bloodstream and carbon dioxide diffuses out.
- The alveoli of the lungs provide a large, moist surface area with a rich blood supply and thin walls to make diffusion as effective as possible.
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B3 1.3 Exchange In The Gut
- The villi in the small intestine provide a large surface area with an extensive network of capillaries. This makes them well adapted to absorb the products of digestion by diffusion and active transport.
- In material exchanges, the surface area : volume ratio is always important - a big surface area is vital for successful diffusion.
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B3 1.4 Exchange Of Materials In Other Organisms
- Whatever the organism, gas and solute exchange depends on a large surface area, moist surfaces, short diffusion distances and a large concentration gradient.
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B3 1.5 Exchange In Plants
- Plants have stomata which allow them to obtain carbon dioxide from the atmosphere.
- Carbon dioxide enters the leaf by diffusion. Leaves have a flat thin shape and internal air spaces to increase the surface area available for diffusion.
- Most of the water and mineral ions needed by a plant are absorbed by the root hair cells which increase the surface area of the roots.
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B3 1.6 Transpiration
- The loss of water vapour from the surface of plant leaves is known as transpiration.
- Water is lost through the stomata which are opened and closed by guard cells to let in carbon dioxide for photosynthesis.
- Water is pulled up through the xylem from the roots to replace the water lost from the leaves in the transpiration stream.
- Transpiration is more rapid in hot, dry, windy or light conditions.
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