3. movement of substances Flashcards
what are the five different types of transport in and out of the cell?
1) Simple diffusion (Passive process)
2) Facilitated diffusion (Passive process)
3) Osmosis (Passive process)
4) Active Transport (Active – require ATP energy)
5) Bulk transport (endocytosis and exocystosis) (Active – require ATP energy)
What is meant by ‘water potential’?
This is a measure of the tendency of water molecules to move across a partially permeable membrane.
The symbol used for water potential is the Greek letter psi, Ψ
What is osmosis?
- Osmosis is very similar to diffusion but ONLY refers to the movement of water particles.
Osmosis is the net random movement of water molecules from an region of high water potential to a region of low water potential (= down a water potential
gradient) across a partially permeable membrane - Pure water has a water potential of zero. Ψ = 0
Factors that affect the rate of osmosis
- water potential gradient
- thickness of the exchange surface
- surface area of the exchange surface
Water potential gradient
The higher the water potential gradient, the faster the rate of osmosis. As osmosis occurs, the difference in water potential either side of the membrane decreases,
so the rate of osmosis levels off over time.
Thickness of the exchange surface
The thinner the exchange surface the shorter the pathway the water molecules have to travel. This increases the rate of osmosis.
Surface area of the exchange surface
The greater the surface area of the partially permeable membrane the more area water molecule have to cross the membrane.
This increases the rate of osmosis.
Hypotonic solution
- A solution with MORE water in it than
solute, compared to another solution.
Hypertonic solution:
- A solution with MORE solute in it than
water, compared to another solution.
Isotonic solution
- Two solutions/cells that have the same
water potential
Osmosis in plant cells
Osmosis in animal cells
