2.17 Root hair cells, xylem and phloem
6 exam questions worth 14 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Explain how a root hair cell is adapted to absorb water.
Mark scheme
- long extension / hair (1)
- gives a large surface area (for osmosis) (1)
Model answer
A root hair cell has a long thin extension that gives a large surface area, so more water can enter by osmosis.
Mineral ions are taken into root hair cells by active transport.
Explain why active transport is needed, and why root hair cells have many mitochondria.
Mark scheme
- ions are at a lower concentration in the soil than in the cell (1)
- so they must move against the concentration gradient (1)
- active transport needs energy from respiration (in mitochondria) (1)
Model answer
The concentration of mineral ions is lower in the soil than inside the root hair cell, so the ions must move against their concentration gradient. Active transport needs energy, which is released by respiration in the mitochondria.
Which statement about xylem is correct?
Choose one answer.
Correct Not quite: the answer is It is made of dead cells strengthened with lignin
Mark scheme
D
Model answer
D: xylem is made of dead cells strengthened with lignin.
Give two ways that xylem is adapted to carry water.
Mark scheme
Any two from:
- no end walls / hollow tube (so water flows easily) (1)
- dead cells / no cytoplasm (1)
- walls strengthened with lignin (so they do not collapse) (1)
Model answer
Xylem cells have no end walls, forming a continuous hollow tube, and their walls are strengthened with lignin so the tubes do not collapse.
What is translocation?
Mark scheme
- the movement of (dissolved) sugars / sucrose (1)
- in / through the phloem (1)
Model answer
Translocation is the movement of dissolved sugars around the plant in the phloem.
Compare the structure and function of xylem and phloem.
Mark scheme
- xylem dead cells, phloem living cells (1)
- xylem has no end walls / is a hollow tube, phloem has sieve plates (1)
- xylem strengthened with lignin (1)
- xylem carries water and mineral ions, phloem carries dissolved sugars (1)
- xylem: upwards only; phloem: up and down (1)
Maximum 4 marks
Model answer
Xylem is made of dead cells with no end walls, forming hollow tubes strengthened with lignin, while phloem is made of living cells joined by sieve plates. Xylem carries water and mineral ions upwards from the roots, while phloem carries dissolved sugars both up and down the plant.
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