IGCSE Coordinated Science: Movement in and out Cells Movement in and out Cells 1. Define diffusion Diffusion is the term for the net movement of molecules down a concentration gradient from a region of higher concentration to a region of lower concentration as a result of their randommovement. 2. Describe the importance of diffusion of gasses and solutes and of water as a solvent. Gases ● Necessary for gas exchange in all living organisms ● Necessary for obtaining Carbon Dioxide and releasing oxygen during photosynthesis. Solutes (liquids) ● Dissolved salts dissolve through root hair cell. ● Absorption of dissolved food material in many organisms, like amoeba, bacteria and fungi is carried out through diffusion. ● Some digested food material is absorbed by diffusion Water as a solvent ● Plants cannot obtain minerals unless they are dissolved in water ● Enzymes and hormones cannot be secreted unless they are dissolved in water ● Excretory products cannot be excreted unless they are dissolved in water. 3. Define osmosis (Supp. only) Osmosis the diffusion of water molecules from a region of their higher concentration (dilute solution) to a region of their lower concentration (concentrated solution), through a partially permeable membrane. 4. Describe the importance of osmosis in the uptake of water by plants, and its effectson plant and animal tissues. The importance of osmosis Plants gain water through osmosis in their roots from the soil. Without a water potential gradient,water will be loss from the roots . Plant cells contain vacuoles, which, if not full with water, will cause the cell to become flaccid. If all the cells in a leaf become flaccid, the whole
leaf will become flaccid, hence causing the plant to wilt . Plant cells therefore need water to remain turgid and keep firm.If an animal cell surrounded with a high water potential, osmosiswill take place, and if the water is not expelled some way or another, the cell will burst. This is because an animal cell doesn’t have a cell wall to keep it strong. If an animal cell is surrounded with low water potential, the water in the cytoplasm will diffuse outwards, causing the cell to shrink. 5. Describe and explain the importance of a water potential gradient in the uptake of water by plants. The water potential determines whether the plant cell would be turgid or plasmolysed. Since title says “uptake”, it means the plant cell taking in water. If the surroundings has a higher water potential than the plant cell, water molecules moves into the plant cell via osmosis. When the plant cell has sufficient water, it becomes turgid. The cell wall prevents the cell from bursting. Turgor pressure is exerted when the plant cell is swollen. This keeps the plant upright.