Diffusion & Osmosis

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diffusion works down the concentration gradient (from an area of high concentration to low concentration). • Individual cells may be adapted to make diffusion easier and more rapid. The most common adaptation is to increase the surface area of the cell membrane. Diffusion & Osmosis Example of diffusion for respiration: The oxygen you need for respiration passes form the air in your lungs into your red blood cells through the cell membranes by diffusion. The oxygen moves down the concentration gradient from a region of high oxygen concentration to a region of low oxygen concentration. Osmosis: Remember: • A dilute solution of sugar contains a high concentration of water (the solvent). It has a low concentration of sugar (the solute). • A concentrated sugar solution contains a relatively low concentration of water and a high concentration of sugar. *In osmosis, water moves from a dilute solution (high concentration of water molecules) to a concentrated solution (fewer water molecules in a given volume) across the membrane of a cell. Study Smarter Create the best notes with StudySmarter.de https://app.studysmarter.de/studyset/12936274/summary/69971780/edit Okto 2000 2/6 09/04/2023, 18:39 (a) glass tube initial level (b) concentrated sugar solution water (hypotonic to cell) partially permeable membrane bag concentrated sugar solution water (hypertonic to cell) partially permeable membrane bag Study Smarter Diffusion & Osmosis sugar molecules . water molecules final level https://app.studysmarter.de/studyset/12936274/summary/69971780/edit water moves into the bag by osmosis Figure 1 A model of osmosis in a cell. In (a) the model cell is in a hypotonic solution. In (b) the model cell is in a hypertonic solution water moves out of the bag by osmosis Create the best notes with StudySmarter.de Okto 200 3/6 09/04/2023, 18:39 hypotonic solution isotonic solution hypertonic solution animal cell H₂O H₂O burst Definition H₂O normal H₂O shrivelled If the concentration gradient of solutes in the solution outside the cell is the same as the internal concentration, the solution is isotonic to the cell. • If the concentration of solutes in the solution out of the cell is higher than the internal concentration, the solution is hypertonic to the cell. • If the concentration of solutes in the solution outside the cell is lower than the internal concentration, the solution is hypotonic to the cell. Diffusion & Osmosis If the solution outside the cell becomes much more dilute (hypotonic) than the cell contents, water will move in by osmosis. • The cell will swell and may burst. If the solution outside the cell becomes much more concentrated (hypertonic) than the cell contents, water will move out of the cell by osmosis. • Cytoplasm will become too concentrated and will shrink/shrivel up and can no longer survive. Study Smarter Create the best notes with StudySmarter.de https://app.studysmarter.de/studyset/12936274/summary/69971780/edit Axta 240 4/6 09/04/2023, 18:39 Osmosis in plants: plant cell H₂O H₂O turgid (normal) flaccid plasmolysed H₂O H₂O Study Smarter Plants rely on osmosis to support their stems and leaves. When water moves into plant cell by osmosis, this causes the vacuole to swell, which presses the cytoplasm against the plant cell wall. The pressure builds up until no more water can physically enter the cell - this pressure is known as turgor which makes the cell hard and rigid. When water leaves the cell, as the solution surrounding the cell is hypertonic, the cell will become flaccid as there is no pressure on the cell walls. *In animal cells, if the cell swells, it will burst as there is no cell wall to protect it but in plant cells, as there is a cell wall, the cell will not burst. *Only plant cells can be turgid, animal cells cannot. Diffusion & Osmosis Turgid - When plant cells are firm because their vacuoles are filled with water Energy is needed for active transport, which is produced from respiration through the mitochondria. Active transport moves substances from a more dilute solution to a more concentrated solution (against concentration gradient). Active transport allows plant root hairs to absorb mineral ions required for healthy growth from very dilute solutions in the soil. • Active transport enables sugar molecules used for cell respiration to be absorbed from lower concentrations in the gut into the blood where the concentration of sugar is higher. • Membrane is not required. Requires carrier proteins in the membrane. Flaccid - When plant cells lose water and the cell contents no longer push outward the cell wall. Active transport: Cells are moved against a concentration gradient, across a partially permeable membrane. Cells are moved from an area of low concentration to high concentration. Example Hair root cells, cells lining human gut Create the best notes with StudySmarter.de https://app.studysmarter.de/studyset/12936274/summary/69971780/edit Akt 2000 5/6 09/04/2023, 18:39 Example Partially permeable membranes: . Red blood cells ● potato • Onion Study Smarter Diffusion & Osmosis Create the best notes with StudySmarter.de https://app.studysmarter.de/studyset/12936274/summary/69971780/edit Akt 2000 6/6