Absorption and Secretion State the definition of diffusion.

1. Absorption and Secretion • State the definition of diffusion. • Molecules move from a higher concentration to a lower concentration down a concentration gradient • Explain how diffusion could be used by a cell to absorb molecules. •  The substance must be at a higher concentration outside the cell for it to diffuse into the cell • Give two examples of molecules that would enter a cell by diffusion. • Glucose amino acids oxygen

2. Explain how diffusion could be used by a cell to pass molecules out.The molecules must have a higher concentration inside the cell compared to outside  • Give two examples of molecules that would be passed out of a cell by diffusion. • carbon dioxide urea  • State the definition of osmosis. •  Water molecules moving from a higher concentration to a lower concentration passing through a selectively permeable membrane • Explain what would happen if an animal cell was surrounded by a solution with a higher water concentration. • Water molecules would moveinto the cell by osmosis from high concentration outside cell and it would burst as it only has a plasma membrane

3. Explain what would happen if a plant cell was surrounded by a solution with a higher water concentration. • Water molecules would move into the plant cell by osmosis from high concentration outside cell and it would become turgid as it has a cell wall to prevent it bursting • In both cases above which solution can be called hypotonic? The surrounding solution or the cytoplasm of the cell? • The solution surrounding the cell is hypotonic to the cell sap • Why do plant cells and animal cells react differently to this higher water concentration outside the cell? • Plant cells have a cell wall made of the carbohydrate cellulose which prevent the cell from bursting

4. Explain what would happen if an animal cell was surrounded by a solution with a lower water concentration. • Water molecules would move out of the cell by osmosis from high concentration inside cell and the animal cell would shrivel up • Explain what would happen if a plant cell was surrounded by a solution with a lower water concentration. • Water molecules would move out of the cell by osmosis from high concentration inside cell and the plant cell would become plasmolysed and membrane moves away from the cell wall • Explain the following terms • Hypertonic This is a liquid that has a lower water concentration • Isotonic This is liquids with equal water concentration • HypotonicThis is a liquid with a higher water concentration

5. List two components of a plasma membrane. • phospholipid bi layer and proteins • List two different proteins found in a plasma membrane. •  protein pores and carrier proteins • Explain why the plasma membrane is based on the fluid mosaic model. •  Fluid because the phospholipid layers are moving • Mosaic because the proteins produce a pattern in the phospholipid layers • Why is the plasma membrane described as selectively permeable? • It only allows small soluble substances to pass through

6. How could each component of the plasma membrane be destroyed in an experiment? • When the cells are heated to above 50 oC the proteins in the plasma membrane become denatured • If the cells are immersed in alcohol the phospholipid layer is destroyed • Label the diagrams below of a plasma membrane. • Label the phospholipid bi layer, carrier proteins and protein pore • Describe the structure of the cell wall. • Cell wall is made of cellulose fibres  • Is the cell wall selectively permeable like the plasma membrane? • The cell wall is full permeable

7. Explain the term selective ion uptake (active transport). • This is when a cell takes in certain molecules(ions) against a concentration gradient using energy from aerobic respiration • Give an example of an ion that would be taken into a cell by this method. • sodium potassium • Why is it called selective? •  It will take in more of one ion than another •  What are the main differences between selective ion uptake compared to diffusion and osmosis? • Diffusion and osmosis do not use energy as the molecules move down a concentration gradient

8. Label the phagocyte blood cell engulfing a bacteria using phagocytosis. • Make sure you have labelled the following in the diagram above: • Lysosomes Food vacuole • What is the role of the lysosomes in phagocytosis? • They contain digestive enzymes to breakdown the engulfed bacteria •  Explain pinocytosis. • A method of certain cells taking in liquids

9. NB You should be able to discuss the following: Experiment to measure the water concentration of cell sap using plant tissue. Experiment to investigate the chemical nature of the plasma membrane Interpret data concerning solute concentration in aquatic organisms in their environment. List the 5 main techniques that cells use to absorb or secrete substances. Diffusion Osmosis (water) Active transport (selective ion uptake) needs energy Phagocytosis using the organelle called lysosomes Pinocytosis