Flashcards · 0610 · Topic 3

Movement into and out of cells flashcards

14 cards on Topic 3, subtopics 3.1 to 3.3. Pick a subtopic or study them all.

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Diffusion: The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, as a result of their random movement.
Four factors that affect the rate of diffusion: Surface area, temperature, concentration gradient, distance.
Does diffusion need energy from respiration?: No. The energy comes from the kinetic energy of the particles' random movement.
How could you investigate the effect of surface area on diffusion?: Cut agar blocks of different sizes containing an indicator, place them in a solution that changes the indicator colour, and time how long the colour change takes to reach the centre of each block.

Osmosis (Core statement): Water diffuses through partially permeable membranes by osmosis. Water moves into and out of cells by osmosis through the cell membrane.
Why is water important as a solvent in organisms?: Substances dissolve in it, so it is needed for digestion, excretion and transport.
How are plants supported by water?: The pressure of water inside the cells presses outwards on the cell wall.
Osmosis investigation with dialysis tubing: Fill the tubing with sugar solution, place it in water, and measure the change in mass (or the level in a capillary tube). Water enters by osmosis, so mass increases.
Osmosis (Extended definition)Extended: The net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane.
Turgid, turgor pressure, flaccid and plasmolysisExtended: In a dilute solution a plant cell gains water and becomes turgid, pressing on the wall (turgor pressure). In a concentrated solution it loses water and becomes flaccid; if enough is lost the membrane pulls away from the wall (plasmolysis).

Active transport: The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (against a concentration gradient), using energy from respiration.
Which of diffusion, osmosis and active transport needs energy?: Only active transport. It is also the only one that moves substances against a concentration gradient.
Why do root hair cells need active transport?Extended: To take up mineral ions from the soil when the ion concentration in the soil is lower than inside the root hair cell.
What moves molecules or ions across the membrane in active transport?Extended: Protein carriers in the cell membrane, using energy from respiration.