2025 OCR A-LEVEL BIOLOGY A H420/03 Unified Biology Question Paper & Mark Scheme (Merged) June 2025 [VERIFIED]

2025 OCR A-LEVEL BIOLOGY A H420/03 Unified Biology Question Paper & Mark Scheme (Merged) June
2025 [VERIFIED]

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1 The roots of plants contain a variety of cells and tissues.

(a) The photomicrograph shows a transverse section through the root of a herbaceous
dicotyledonous plant.




A




B




Name the cells labelled A and B in the photomicrograph.

A .......................................................................................................................................................

B .......................................................................................................................................................
[2]




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(b) The outer surface of a root is made up of root epidermal cells.

A root hair cell is a type of root epidermal cell that has a hair‑like extension called a root hair.

A typical root epidermal cell has a surface area to volume ratio (SA: V) of 0.3 : 1.

A root hair cell has a higher SA: V than a typical root epidermal cell.

The diagram shows a root hair cell. The diagram is not to scale.



Root hair




The root hair has:
• a diameter of 10 µm
• a length of 800 µm.

(i) Calculate the SA: V of the root hair.

Assume the root hair is cylindrical.

Use the equations:

Surface area of cylinder = 2πr(r + l )

Volume of cylinder = πr 2l




SA: V of root hair = ............................................................. [3]

(ii) State how a high SA: V helps a root hair cell perform its function.


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. ....................................................................................................................................................... [1]




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