This definitions covers Key Terms: Cell Transport within Cell Transport for GCSE Biology. Diffusion, osmosis, active transport, factors affecting transport, surface area to volume ratio, and practical investigations It is section 11 of 18 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
Topic position
Section 11 of 18
Practice
18 questions
Recall
20 flashcards
📖 Key Terms: Cell Transport
- Diffusion
- The net movement of particles from an area of higher concentration to an area of lower concentration, down a concentration gradient. It is a passive process — no energy is required.
- Osmosis
- The movement of water molecules only, from an area of higher water concentration (dilute solution) to an area of lower water concentration (concentrated solution), through a partially permeable membrane. Osmosis is a passive process — it requires no energy. Note: osmosis is related to diffusion but is distinct because it involves only water molecules moving through a partially permeable membrane.
- Active Transport
- The movement of substances from an area of lower concentration to an area of higher concentration — against the concentration gradient. Active transport requires energy in the form of ATP, supplied by mitochondria.
- Concentration Gradient
- The difference in the concentration of a substance between two areas. The steeper the gradient (bigger the difference), the faster the rate of diffusion or osmosis.
- Partially Permeable Membrane
- A membrane that allows some molecules (e.g. water) to pass through but not others (e.g. large solute molecules). Also called a semi-permeable membrane. The cell membrane is partially permeable.
- Turgid
- A plant cell that has absorbed water by osmosis. The vacuole is full, pushing against the cell wall and making the cell firm and swollen. Turgid cells provide structural support to plants.
- Plasmolysed
- A plant cell that has lost so much water by osmosis that the cell membrane has pulled away from the cell wall. This happens in very concentrated (hypertonic) solutions.
- Flaccid
- A plant cell that has partially lost water so it is limp but not yet plasmolysed. The vacuole is smaller, and the cell wall is no longer under pressure. Flaccid cells cause wilting.
Must Memorise — Diffusion: Movement of particles from HIGH to LOW concentration (down the gradient). No energy needed. Any particles.
Must Memorise — Osmosis: Movement of WATER ONLY through a PARTIALLY PERMEABLE MEMBRANE from dilute to concentrated solution. No energy needed.
Must Memorise — Active Transport: Movement from LOW to HIGH concentration (AGAINST the gradient). Requires ATP energy from mitochondria. Uses protein carriers in the membrane.