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Diffusion, osmosis and active transport
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Substances move in and out of cells all the time. Three processes explain how.
Diffusion
Diffusion is the net movement of particles from a higher to a lower concentration.
It is passive: no energy from respiration is needed.
Example: oxygen diffusing from the lungs into the blood.
It is passive: no energy from respiration is needed.
Example: oxygen diffusing from the lungs into the blood.
Osmosis
Osmosis is the diffusion of water across a partially permeable membrane, from a dilute solution to a more concentrated one.
In a strong salt solution, plant cells lose water and become flaccid; in pure water they gain water and become turgid.
In a strong salt solution, plant cells lose water and become flaccid; in pure water they gain water and become turgid.
Active transport
Active transport moves substances against a concentration gradient (low to high).
It needs energy from respiration and carrier proteins.
Example: root hair cells absorbing mineral ions from the soil.
It needs energy from respiration and carrier proteins.
Example: root hair cells absorbing mineral ions from the soil.
A potato cylinder goes from 2.50 g to 2.20 g in salt solution. Find the percentage change in mass.
- Change = 2.20 − 2.50 = −0.30 g
- −0.302.50 × 100
- = −12%
Answer: −12%
Diffusion: high to low concentration, passive. Osmosis: water across a partially permeable membrane. Active transport: low to high, needs energy from respiration.
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