1.18 Active transport
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Which statement describes active transport?
Choose one answer.
Correct Not quite: the answer is The movement of particles from a low to a high concentration, using energy from respiration
Mark scheme
C (The movement of particles from a low to a high concentration, using energy from respiration)
Model answer
C: The movement of particles from a low to a high concentration, using energy from respiration. Active transport moves substances against the concentration gradient and needs energy from respiration.
Explain why root hair cells use active transport to take in mineral ions.
Mark scheme
- the concentration of mineral ions is lower in the soil than in the root hair cell (1)
- so the ions must move against the concentration gradient, which diffusion cannot do (1)
Model answer
The concentration of mineral ions is lower in the soil than in the root hair cell, so the ions have to move against the concentration gradient. Diffusion cannot do this, so active transport is needed.
Root hair cells contain many mitochondria.
Explain why.
Mark scheme
- mitochondria release energy / carry out aerobic respiration (1)
- the energy is needed for active transport (of mineral ions) (1)
Model answer
Mitochondria release energy by respiration. This energy is needed for active transport of mineral ions into the cell.
Give two differences between diffusion and active transport.
Mark scheme
Any two from:
- diffusion is from high to low concentration; active transport is from low to high concentration (1)
- diffusion does not need energy; active transport needs energy from respiration (1)
- active transport uses carrier proteins; diffusion does not (1)
Model answer
Diffusion moves particles from a high to a low concentration without using energy, but active transport moves them from a low to a high concentration and uses energy from respiration.
The table shows the concentration of nitrate ions in the soil water and in a root hair cell.
| Place | Concentration (arbitrary units) |
|---|---|
| Soil water | 0.2 |
| Root hair cell | 1.4 |
Nitrate ions move from the soil into the root hair cell.
Name the process that moves them and explain how you know.
Mark scheme
- active transport (1)
- the ions move from a low concentration to a higher concentration / against the concentration gradient (1)
- this needs energy from respiration, which diffusion does not use (1)
Model answer
The process is active transport. The nitrate concentration is lower in the soil (0.2) than in the cell (1.4), so the ions are moving against the concentration gradient. This needs energy from respiration.
A plant growing in waterlogged soil does not take up enough mineral ions.
Explain why.
Mark scheme
- there is little oxygen in waterlogged soil (1)
- so the root cells carry out less aerobic respiration (1)
- so there is less energy available for active transport of mineral ions (1)
Model answer
Waterlogged soil contains little oxygen, so the root cells cannot respire aerobically very well. They release less energy, so less active transport of mineral ions can take place.
Describe the differences between diffusion, osmosis and active transport.
Mark scheme
- diffusion: net movement of particles from a high to a low concentration, with no energy needed (1)
- osmosis: diffusion of water from a dilute to a concentrated solution through a partially permeable membrane (1)
- active transport: movement of substances from a low to a high concentration / against the concentration gradient (1)
- active transport needs energy from respiration, but diffusion and osmosis do not (1)
Model answer
Diffusion is the net movement of particles from a higher to a lower concentration and needs no energy. Osmosis is the diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane, and also needs no energy. Active transport moves substances from a lower to a higher concentration, against the concentration gradient, and needs energy from respiration.
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