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How can we smell our dinner being made in the room next door? • diffusion Diffusion • Diffusion is the movement of particles from a region where they are concentrated to a region where they are less concentrated • No energy is needed for Diffusion to take place. It is a Passive process. • It is important in the movement of substances between cells and inside cells (occurs only over short distances, no more than 1mm) • Hence, larger organisms will require Transport systems as well i.e. circulatory system in humans Osmosis • Osmosis is the movement of water molecules across a semi-permeable membrane, from an area of high concentration of water molecules to an area of low concentration of water molecules. Cell Membrane & Osmosis • The cell membrane controls movement of substances into and out of the cell • It is semi-permeable i.e. it allows small molecules like water, carbon dioxide and oxygen through by diffusion but stops larger ones. • Where energy is required to move molecules in and out of cells is called Active transport Osmoreregulation • Our cells contain sugar and salt at certain • • concentrations. If these concentrations change, action is taken by cells to counteract the changes and return to the normal balanced state. This balancing action is called Osmoregulation. Osmosis in Animal Cells Animal Cells in Pure water • Red blood cells have 1% salt • concentration in them. What would happen if a red cell is placed in pure water? Animal cells in Salt water • What would happen if a red cell is placed in a very salty solution? • The Cytoplasm swells up with • Experiences a loss of water water and eventually the cell may burst and die. which causes the cell to shrivel up. Osmosis in Plant Cells Plant Cells in Pure Water Plant Cells in Salt Solution • Onion cells have Salt and • What happens if an onion cell • The cytoplasm & vacuole fill • The cytoplasm & vacuole lose Sugar in their cytoplasm. • What happens if an onion cell is placed in pure water? • up with water, which stretches the cell. The cell wall prevents the cell from bursting and the cell is said to be Turgid. is placed in a very salty solution? • water. The cell membrane comes away from the cell wall, the cell is said to be Plasmolysed. Turgid describes a plant cell in which the cell wall is rigid, due to the cytoplasm pushing out against it as it fills with water. Osmotic pressure is the main cause of support in plant leaves (Without water the cell walls are not strong enough to support the weight of the plant, and so it Wilts) Osmosis in Food Preparation • Naturally occurring chemicals like salt, sugar and • • • fruit juice will preserve foods by osmosis. Salt is the oldest and most common method of preserving fish and meats. Water moves, by osmosis, from the cells into the salt solution, causing the tissues to become dehydrated, which destroys bacteria. Sugars are used to preserve fruits (jams/tinned fruit) • • Active Transport More In order for Large molecules to move across the cell solute membrane they must do so at certain ‘gates’ and the molecules cell has to use energy to do this. These ‘gates’ are proteins within the cell membrane, which pump the molecules across, often against the concentration gradient (from where there is less to where there is more of the substance) Fewer solute molecules SOLUTE CONCENTRATION GRADIENT • Active Transport is the movement of substances across a cell membrane against a concentration gradient, using energy from respiration.