9700 · 4.2
Movement into and out of cells flashcards
Revision flashcards for Cambridge 9700 Movement into and out of cells (syllabus 4.2). Flip, recall, then mark a real past-paper question.
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What is osmosis?
The net movement of water molecules from a region of higher water potential to a region of lower water potential, across a partially permeable membrane.
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What is active transport?
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration (against a concentration gradient), using metabolic energy (ATP) and carrier proteins.
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Define water potential (Ψ).
The measure of the potential energy of water molecules, indicating the tendency of water to move. Pure water has a Ψ of 0 kPa. It is affected by solutes (solute potential, Ψs) and pressure (pressure potential, Ψp).
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What is the role of a carrier protein in facilitated diffusion?
It binds to a specific molecule (e.g., glucose), changes its shape (conformational change), and transports the molecule across the membrane down its concentration gradient.
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What happens to an animal cell when placed in a hypotonic solution?
It gains water by osmosis, swells, and may burst (undergo lysis) because it has no cell wall to withstand the increase in hydrostatic pressure.
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What is plasmolysis?
The process in a plant cell where the protoplast (cell membrane and its contents) shrinks and pulls away from the cell wall due to water loss by osmosis in a hypertonic solution.
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What is the difference between phagocytosis and pinocytosis?
Both are forms of endocytosis. Phagocytosis ('cell eating') is the bulk intake of solid material. Pinocytosis ('cell drinking') is the bulk intake of external fluid with dissolved solutes.
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How does the sodium-potassium pump work?
It's an active transport mechanism that uses ATP to pump 3 sodium ions (Na+) out of the cell and 2 potassium ions (K+) into the cell, both against their respective concentration gradients.