GCSE Bio unit 1.3/1.3 (AQA - Transport in cells)

Diffusion

The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.

Substances transported across cell membranes by diffusion in humans

Oxygen and carbon dioxide during gas exchange, and urea from cells into blood plasma for excretion in the kidney.

Three factors that affect the rate of diffusion

The difference in concentrations (concentration gradient), the temperature, and the surface area of the membrane.

Surface area to volume ratio in single-celled organisms

Relatively large, allowing sufficient transport of molecules into and out of the cell to meet metabolic needs.

Four structural features that increase the effectiveness of an exchange surface

A large surface area, a thin membrane for a short diffusion pathway, an efficient blood supply, and proper ventilation.

Osmosis

The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

What is active transport

The movement of substances from a more dilute solution to a more concentrated solution against a concentration gradient, requiring energy from cellular respiration.

Process by which mineral ions are absorbed into plant root hairs from dilute soil water

Active transport in plants

Process that allows sugar molecules to be absorbed from lower concentrations in the gut into higher concentrations in the blood

Active transport in the digestive system