Diffusion
| English | Chinese | Pinyin |
|---|---|---|
| diffusion | 扩散 | kuò sàn |
| concentration gradient | 浓度梯度 | nóng dù tī dù |
| surface area | 表面积 | biǎo miàn jī |
How things move in and out of cells
- Cells constantly take in oxygen and food, and get rid of waste — without any pumps.
- Much of this happens by diffusion 扩散: things simply spreading out.
Diffusion is the net movement of particles from a region of:
Particles move down the concentration gradient.
Diffusion requires energy from the cell.
Diffusion is passive — it needs no energy from the cell.
Diffusion is the ______ movement of particles down a concentration gradient.
Particles move both ways, but the net flow is high to low.
What diffusion is
- Diffusion is the net movement of particles from a region of high concentration to a region of low concentration.
- It happens because particles are always moving randomly, and it needs no energy from the cell.
Particles move down the concentration gradient 浓度梯度 until evenly spread.
Diffusion
net movement: high → low
Particles spread down the gradient, from where they're crowded to where they're sparse.
In a respiring cell, oxygen diffuses:
Oxygen is used up inside, so it diffuses in down the gradient.
Diffusion in living things
- Oxygen diffuses into cells for respiration; carbon dioxide diffuses out.
- In the lungs, gut and leaves, diffusion moves substances across surfaces.
Plasmolysed cells: the contents have pulled away from the cell walls
Which increase the rate of diffusion? (Select all that apply.)
A thicker barrier slows diffusion; the others speed it up.
What affects the rate
- Steeper concentration gradient → faster diffusion.
- Higher temperature → faster (particles move faster).
- Larger surface area 表面积 and shorter distance → faster.
Diffusion is the NET movement. Particles move both ways, but more move from high to low concentration. Once evenly spread, movement continues but there is no net change.
Diffusion: particles spread from higher to lower concentration, down the gradient
You've got it
- diffusion = net movement from high to low concentration; no energy needed
- it supplies oxygen and removes carbon dioxide in cells
- rate rises with a steeper gradient, higher temperature, more surface area, shorter distance