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Download 03 Movement in and out of cells
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Transcript
Movement in and out of cells Cells need to take in oxygen and nutrients for respiration. They also need to remove waste products such as CO2. The cell membrane controls movement of materials. Generally, this is determined by the size of the molecule. Smaller molecules move through more easily and quickly. Diffusion the movement of molecules from an area of high concentration to an area of low concentration until the molecules are in equilibrium (evenly mixed) molecule High concentration Low concentration Molecules move down a concentration gradient (high to low) until the molecules are in equilibrium. Then, diffusion stops. - No energy is required - Only occurs with gases and liquids (not solids) - Examples of materials which move in and out of cells by diffusion: . Oxygen and carbon dioxide in the lungs . Antibodies diffuse in the placenta . Glucose . Amino acids . Small molecules like solutes and gases (e.g. glucose, amino acids and oxygen moving into cell and carbon dioxide moving out). Page 1 of 5 Osmosis A form of diffusion but only involves water molecules. Only occurs across a partially permeable membrane. Partially permeable membrane only allows certain molecules to pass across it, generally it is only small molecules that can pass through. Definition of osmosis Osmosis is the movement of water molecules from an area of high water potential to an area of low water potential (concentration) across a partially permeable membrane. The rate of diffusion is increased across a shorter distance and if the concentration gradient is steeper. Partially permeable weak sucrose solution membrane strong sucrose solution high water potential OSMOSIS (many water molecules) low water potential (few water molecules) Osmosis in plant and animal cells Cytoplasm contains water Animal Cell Cell placed in solution with much less water potential than cytoplasm Cell placed in a very high water potential (e.g. water) water moves into cell by osmosis cell bursts (lysed) Page 2 of 5 cell loses water cell shrinks (crenated) Plant Cell cell wall vacuole cell membrane Cell placed in a very high water potential (e.g. water) Cell placed in solution with much less water potential than cytoplasm Cytoplasm and vacuole lose water. The cell membrane may pull away from the cell wall as water is lost. This is called plasmolysis. The cell is called plasmolysed. Cell swells but does not burst because the cell wall resists the increased pressure (cell wall is strong and flexible). The cell is turgid Active Transport substance carrier molecule OUTSIDE ATP cell membrane ADP INSIDE Substance combines with carrier molecule Carrier transports substance across membrane using energy from ATP Page 3 of 5 Substance is released into cell Active transport moves molecules against the concentration gradient. against concentration gradient Low concentration High concentration NEEDS ENERGY – unlike diffusion, which does not. ATP needs a protein carrier molecule to carry the molecules across the membrane. can be used to carry into/out of a cell - Adenosine triphosphate provides ‘free’ energy for cells to do ‘work’ universal energy carrier in molecules e.g. Active transport and muscle contraction ATP is produced by respiration – by breaking down glucose ADP + P A P P P broken down A P P + P + ‘free’ energy for ‘work’ High energy bond ADP is Adenosine diphosphate. Examples of active transport Kidney glucose leaves blood passes into the kidney but must be reabsorbed into the blood. Tubule Blood Method High glucose concentration No glucose Diffusion Equal glucose concentration Equal glucose concentration No glucose No diffusion High glucose concentration Active transport Root Hair Cells Minerals may be taken in from the soil using active transport when the concentration in the soil is lower than that of the root hair cell. Page 4 of 5 Endocytosis / Exocytosis Some cells can take in (endocytosis) or expel (exocytosis) solid particles or drops of fluid through the cell membrane. Endocytosis occurs in single celled ‘animals’ such as paramecium when they feed or in certain white blood cells when they engulf in bacteria called phagocytosis. Exocytosis takes place in the cells of some glands. A secretion forms vacuoles or granules in the cytoplasm and these are expelled through the cell membrane to do their work outside the cell. nucleus bacterium Cell membrane Endocytis (phagocytosis) in a white blood cell vacuole Enzyme released Exocytosis in a gland cell Page 5 of 5