Summary Coordinated Science - IGCSE - Biology - Movement In and Out of Cells

Chapter 2 - Movement In and Out of Cells
I. Diffusion
 The net movement of molecules and ions from a region of higher
concentration to a region of lower concentration down a concentration
gradient until they reach equilibrium




Concentration Gradient - occurs when the concentration of particles (solute) in higher in
one area than in another



 Diffusion is the simplest way to transport substances in living organisms
 Organisms use diffusion in many ways
 obtaining nutrients
 expelling waste
 movement between cells
 Factors that may affect diffusion
Size of molecules The smaller/lighter the molecule, the faster the rate of diffusion
(mass)

Concentration The greater the difference in the concentration, the quicker the rate
difference of diffusion
 Low concentration = less molecules = less collision
 High concentration = more molecules = more collision

Temperature The higher the temperature, the faster the rate of diffusion
→ particles have higher kinetic energy, therefore they move
quicker and mix more quickly

,  Real-life examples
Oxygen diffuse across from the
alveoli to the blood vessels in the
lungs




Water molecules diffuse out of
the plant leaves into the air
→ Transpiration




Carbon dioxide diffuses into the
plant leaf during photosynthesis

Oxygen diffuses out of the plant
leaf during photosynthesis