2.5 diffusion Flashcards
What are all cells surrounded by?
Partially permeable membranes
What do partially permeable membranes do?
Control material entry and exit
Why do all cells need to import substances?
To survive and export waste materials
What are the three processes by which substances move across membranes?
Diffusion
Osmosis
Active transport
What can movement across membranes be?
Passive or active
What does all movement require?
Energy
Where does passive movement utilise its energy from?
The natural movement of particles
is diffusion passive or active?
Passive
Define diffusion:
The passive movement of molecules down a concentration gradient, from an area of high concentration to an area of low concentration across a membrane until there is no more net movement and equilibrium had been reached
Give an example of diffusion in the body:
Respiration occurs at gaseous exchange surfaces, oxygen diffuses from the capillaries to the alveoli
What sort of molecules diffuse quickly through the phospholipids?
Small Jon polar molecules such as oxygen and carbon dioxide
What is fick’s law?
Rate of diffusion is proportional to = (surface area x difference in concentration) ÷ length if diffusion path
The shorter the diffusion pathway…
… The faster diffusion happens
What is the length of diffusion path?
Membrane thickness
What affect will increasing the surface area across which particles diffuse have?
Increase in rate of diffusion
What effect will increasing the size of the concentration gradient have?
Increase the rate of diffusion
What effect will increasing the distance over which diffusion takes place have?
Decrease rate of diffusion
Why does respiration occur quickly?
Because alveoli and capillarity are one cell thick so oxygen is able to quickly diffuse
What factors affect the rate of diffusion?
Temperature Concentration difference Thickness of exchange surface Surface area Nature of plasma membrane Size and nature of diffusing molecule
What effect does increasing temperature have on the rate of diffusion?
The higher the temperature the faster the rate of diffusion as molecules have more kinetic energy so they move faster
The greater the concentration difference between the two areas…
The faster the rate of diffusion
The thinner the exchange surface…
The faster the rate of diffusion as the shorter the distance particles have to travel
The larger the surface area of the membrane…
The faster the rate of diffusion
