Movement in and out of the Organisms IGSCE 0610

Movement in and out of the Cells
Course: Biology IGCSE 0610

Unit 2

2.1 Diffusion

-Diffusion: A passive transport system in which particles move from a region of higher
concentration to a region of lower concentration, down a concentration gradient through a
partially permeable membrane.




-Factors affecting rate of diffusion:

Particle Size: Greater particle size means slow rate of diffusion
Diffusion distance: A smaller distance means diffusion will be quicker
Permeability: A more permeable surface will allow more diffusion
Concentration Gradient: A higher gradient means that diffusion will be quicker
Temperature: Higher temperatures allow more diffusion
Diffusion Medium: Diffusion is fastest is slowest in solids but fastest in liquids

-Examples of Diffusion in Animal Cells:




Oxygen moves from alveolar air space in lungs to blood
Carbon dioxide moves from blood to alveolar air space in the lungs
Useful food substances move from bloodstream to small intestine
Urea moves from bloodstream to kidney tubules

, -Examples of diffusion in plant cells:




Carbon dioxide diffuses in via stomatal opening
Oxygen diffuses out via stomata
Water vapor diffuses out through transpiration via stomata

2.2 Osmosis

-Osmosis: The net movement of water molecules from a region of higher to a region of lower
water potential through a partially permeable membrane.