1 3 movement of substances into and out of cells

Diffusion is the spreading out of particles in a solution or a gas, resulting in net movement of particles from a region of higher concentration to a region of lower concentration.

A concentration gradient is a difference in concentration between two regions.

False. Diffusion is a passive process that occurs when molecules spread out due to their random movement.

Osmosis is the diffusion of water molecules from a region of higher water concentration (dilute solution) to a region of lower water concentration (solution with a high solute concentration), through a partially permeable membrane.

True. Only water can be transported by osmosis.

The type of concentration difference that leads to osmosis is a difference in water concentration between two regions. This can also be referred to as water potential.

True. Osmosis must take place across a partially permeable membrane. If water moves in any other way, e.g. water vapour moving out of a leaf via the stomata, this is diffusion.

If an animal cell is placed into a strong sugar solution (with a lower water concentration than the cell) it will lose water by osmosis and will shrivel up.

A plant cell placed in distilled water will gain water by osmosis and swell up. The cell wall will prevent the cell from bursting.

The independent variable in the osmosis and potato practical is the solute concentration of the solution in which the potato cylinders are placed.

The potato cylinders are blotted with paper towels before weighing to remove any surface water that could affect the mass measurement.

True. Potato cylinders placed in distilled water will gain mass due to the movement of water into the cells by osmosis. This will occur because distilled water has a higher water concentration than potato cell cytoplasm.

Examples of control variables in the osmosis and potato practical include:

True. If a potato cylinder does not change mass, it means the solution it is in has the same concentration as the cell cytoplasm, so there is no overall movement of water by osmosis.

Repeating the experiment with multiple potato cylinders allows for the identification and exclusion of anomalous results when calculating the mean.

Percentage change in mass of potato cylinders in the osmosis and potato practical can be calculated using the formula: percentage change = (change in mass ÷ starting mass) x 100

Active transport is the movement of particles across a cell membrane from a region of lower concentration to a region of higher concentration; this requires energy.

False. Active transport moves particles against a concentration gradient.

Energy for active transport is released by respiration.