Biology Topic
Cell Membrane and Concentration Gradients
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Study focus - 3 things
- The cell membrane controls what enters and leaves the cell
- A concentration gradient is the difference in concentration between two areas
- Substances often move from high concentration to low concentration, unless energy is used
Section 1The cell membrane
The cell membrane is a thin boundary around the cell. It protects the cell and controls the movement of substances like oxygen, water, glucose, and waste. It is described as partially permeable because it lets some substances pass through but blocks others.
Section 2Concentration means amount in a space
Concentration tells you how crowded particles are in a certain area. If there is a lot of sugar dissolved in a little water, the sugar concentration is high. If there is only a little sugar in a lot of water, the sugar concentration is low.
Section 3What a concentration gradient is
A concentration gradient exists when one side has more particles than the other side. Particles naturally spread down the gradient, from high concentration to low concentration. This helps explain diffusion and osmosis.
Section 4Why this matters in cells
Cells need useful substances to enter and waste substances to leave. The cell membrane and concentration gradients help control this movement. Without this control, cells could lose too much water, take in harmful substances, or fail to get enough oxygen and food.
Examples
A cell has more oxygen outside it than inside it. Which way will oxygen tend to move?
Oxygen will move into the cell because it moves down the concentration gradient, from higher concentration outside to lower concentration inside.
A membrane lets water pass through but blocks large starch molecules. What word describes this membrane?
It is partially permeable because only some substances can pass through it.
Now let's water it
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