Movement Of Substances Into And Out Of Cells Flashcards
Diffusion
Net movement of particles from an area of higher concentration to an area of lower concentration down a concentration gradient
Examples of diffusion
- gas exchange
Osmosis
Net movement of water particles from an area of higher water potential to an area of lower water potential, across a partially permeable membrane. This is down a water potential gradient
Examples of osmosis
- root hair cells absorbing water
Active transport
Net movement of particles from an area of a lower concentration to an area with a higher concentration, against a concentration gradient. Requires a transporter energy, using up ATP.
Factors affecting rate of movement of substances
Concentration gradient, temperature, distance, surface area :volume ratio
Distance
As the distance increases, the rate of diffusion decreases as the molecules have further to move
Temperature
As the temperature increases, the rate of diffusion increases because the particles have more kinetic energy and they are able to move faster
Concentration gradient
The steeper the concentration gradient, the faster the rate of movement of molecules
Surface area : volume ratio
The larger the surface area : volume ratio, the greater the surface area over which movement of molecules can take place
Why do unicellular organisms rely on diffusion for movement of substances in and out of cells
- The small size of the unicellular organisms means that there is a very small diffusion distance from the outside of the organism to the centre of the organism
- making diffusion sufficient to supply the cell with materials for metabolism
- A transport system is not needed
Why do multicellular organisms need a transport system?
- diffusion is not sufficient to supply all cells in a multicellular organism with the materials it requires
- they have transport systems to distribute materials close to the cells that are in need and then diffusion takes over from there
