Explain how active transport allows a plant root hair cell to absorb mineral ions from the soil, even when the concentration of mineral ions in the soil water is lower than inside the cell.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Active transport moves mineral ions against a concentration gradient, from the low concentration in the soil water into the higher concentration inside the root‑hair cell.
The process requires energy, supplied as ATP released from cellular respiration.
Carrier proteins in the plasma membrane bind the ions and use the energy to change conformation, allowing the ions to be transported into the cell.
Thus the plant can absorb the ions it needs even when their concentration inside the cell is already higher than in the soil.
The process requires energy, supplied as ATP released from cellular respiration.
Carrier proteins in the plasma membrane bind the ions and use the energy to change conformation, allowing the ions to be transported into the cell.
Thus the plant can absorb the ions it needs even when their concentration inside the cell is already higher than in the soil.
Examiner tips
- Use the phrase ‘against a concentration gradient’ to show understanding of direction. Mention ATP as the energy source. Identify carrier proteins as the transporters. Explain the result – absorption despite lower external concentration.
Common mistakes
- Confusing passive diffusion with active transport. Forgetting to mention ATP or energy. Not specifying that the ions move from soil into the cell.
Mark scheme (5 marks)
- Active transport moves mineral ions against a concentration gradient (from low to high concentration)
- Active transport requires energy (in the form of ATP / released from respiration)
- Carrier proteins in the cell membrane are used to transport the mineral ions into the cell
- The mineral ions move from the soil water into the root hair cell
- This allows the plant to absorb ions it needs even when their concentration is already higher inside the cell than in the soil
Key terms in this question
active transport · mineral ions
Related
- All AQA A-Level Biology (7402) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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