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| Question | Answer |
| What is the cell membrane composed of? | Phospholipids and proteins. |
| What is the cell membrane known to be? | Selectively permeable-it only allows molecules that are small enough to pass through it. |
| What is a concentration gradient? | A difference in concentration of a substance. |
| Describe what passive transport of a substance is | The movement of its molecules from a region of high concentration to a region of low concentration, down a concentration gradient. This does not require additional energy. |
| Give two examples of passive transport | Diffusion and osmosis. |
| What is the difference between diffusion and osmosis? | Osmosis is the movement of water through a selectively permeable membrane, whereas diffusion is the movement of a substance. |
| Give three examples of substances that enter most cells through diffusion | Oxygen, glucose and amino acids. |
| Give two examples of substances that leave most cells through diffusion | Carbon dioxide and urea. |
| Why is diffusion important? | It helps to provide the cell with raw materials and helps to remove waste products. |
| Describe what active transport of a substance is | The movement of molecules from a region of low concenration to a region of high concentration against a concentration gradient. This requires additional energy (ATP). |
| Why does active tranpsort require additional energy? | To allow membrane proteins to move molecules against the concentration gradient. |
| What happens to an animal cell in a hypotonic solution? | Water is taken into the cell through osmosis and it bursts. |
| What happens to an animal cell in a hypertonic solution? | Water will be lost by osmosis and the cell shrinks. |
| What happens to an animal cell in an isotonic solution? | No gain or loss in water, and therefore the cell remains unchanged. |
| What happens to a plant cell if it is placed in a hypotonic solution? | It will take up water by osmosis and become turgid-the vacuole swells and cell membrane and cytoplasm are pushed against the cell wall. |
| What happens to a plant cell placed in a hypertonic solution? | It will lose water by osmosis and become plasmolysed-vacuole shrinks, and the cell membrane pulls away from the cell wall, tissue is flaccid. |
| Describe the role of protein molecules in osmosis and active transport | In osmosis, protein molecules allow the passage of water molecules in pores. In active transport, proteins act as carriers. |
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