Summary - Crossing membranes - a level biology ocr A year 1 and AS

Crossing membranes
Summary
Contains overview of:
Diffusion
Factors that affect diffusion
Ficks law
Simple diffusion
Facilitated diffusion
Active transport
Cytosis
bulk transport
phagocytosis
pinocytosis
receptor mediated endocytosis
water potential
osmosis




Selectively permeable – only allow certain substances to pass through

diffusion
 When, until equilibrium is reached, particles are moved drown the
concentration gradient
 When the particles are at equilibrium, they do not stop moving as they still
retain kinetic energy, but there is no longer any net diffusion
 Diffusion is a Passive process which means that it does not require cellular
energy (ATP), but solely relies on the kinetic energy of the particles

Factors that affect diffusion
1. Temperature
A higher temperature causes an increase win kinetic energy, this
means that the rate of diffusion is increased.
2. Concentration gradient
The steeper the concentration gradient, the greater the rate of
diffusion
3. Surface area
The greater the surface area the greater the rate of diffusion