AQA B3 Notes

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Topic 1 - Exchange of materials

  • Osmosis - diffusion of water from an area of low solute concentration to an area of high solute concentration through a partially permeable membrane (which only allows water to pass through)

  • Osmosis in animals restores the balance of water entering and leaving a cell:

  • If solute concentration outside cell is lower than solute concentration inside the cell, water moves in and the cell becomes turgid so it may burst (hypotonic osmosis)

  • If solute concentration outside cell is higher than solute concentration inside the cell, water moves out and the cell becomes plasmolysed so it may shrink and shrivel (hypertonic osmosis)

  • If solute concentration outside cell is fairly equal to the concentration inside the cell, water moves in and  out of the cell at the same rate so the cell retains its normal shape (isotonic osmosis)

  • Osmosis in plants allows water to move into cells to support leaves and stem:

  • Plant cells have a strong cellulose cell wall on the outside of the cell membrane. This supports the cell and stops it bursting when it gains water by osmosis.

  • A plant cell in a dilute solution-Water enters the cell by osmosis. The cytoplasm pushes against the cell wall and the cell becomes turgid.

  • A plant cell in a concentrated solution-Water leaves the cell by osmosis. The cytoplasm pulls away from the cell wall (plasmolysis) and the cell becomes flaccid and the plant wilts and may die.

  • Active Transport-this allows cells to move substances against a concentration gradient but unlike diffusion which is a passive process, it requires energy from respiration by the cell

  • It transports dissolved substances from low to high concentration

  • Active transport is carried out by a series ofprotein carriers within the cell membrane. These have a binding site, allowing a specific dissolved substance to bind to the side of the membrane where it is at a lower concentration.

  • Energy from respiration then changes the shape of the protein so that it releases the substance onto the other side of the membrane.

  • Examples of Active transport in plants and animals:

  • Root hair cells in plant roots use active transport to absorb mineral ions (such as nitrates) from the soil - even though there are lower concentrations of minerals in the soil than there are within the root hair cell.

  • Small intestine villi cells use active transport alongside diffusion to maximise the absorption of glucose and other substances, eg minerals.

  • Sports drinks

  • What happens when you exercise:

  • When you exercise you release energy by respiration to make your muscles contract and move your body, using up sugar. You also sweat to keep your body temperature stable.The more you sweat, the more water and mineral ions you lose. This can affect the concentration of your body fluids. If the body fluids become concentrated water will leave your cells by osmosis. The cells will become dehydrated.

  • If the water and mineral ions you lose in sweating are not replaced, the mineral ion/water balance

Comments

snickersbar

great for revision

snickersbar

hope everyone finds it helpful:))))))

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