worked solutions
model answers
, Oxford Cambridge and RSA
Wednesday 18 June 2025 – Morning
A Level Biology A
H420/03 Unified biology
Time allowed: 1 hour 30 minutes
You can use:
* 1 8 4 8 9 4 4 5 5 8 *
• a scientific or graphical calculator
• a ruler (cm/mm)
* H 4 2 0 0 3 *
Please write clearly in black ink. Do not write in the barcodes.
Centre number Candidate number
First name(s)
Last name
INSTRUCTIONS
• Use black ink. You can use an HB pencil, but only for graphs and diagrams.
• Write your answer to each question in the space provided. If you need extra space use
the lined pages at the end of this booklet. The question numbers must be clearly shown.
• Answer all the questions.
• Where appropriate, your answer should be supported with working. Marks might be
given for using a correct method, even if your answer is wrong.
INFORMATION
• The total mark for this paper is 70.
• The marks for each question are shown in brackets [ ].
• Quality of extended response will be assessed in questions marked with an asterisk (*).
• This document has 28 pages.
ADVICE
• Read each question carefully before you start your answer.
© OCR 2025 [601/4260/1] OCR is an exempt Charity
DC (WW/CB) 345392/5 Turn over
for more: tyrionpapers.com
, 2
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]
© OCR 2025
for more: tyrionpapers.com
, 3
(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.
..........................................................................................................................................................
..................................................................................................................................................... [1]
© OCR 2025 Turn over
for more: tyrionpapers.com
model answers
, Oxford Cambridge and RSA
Wednesday 18 June 2025 – Morning
A Level Biology A
H420/03 Unified biology
Time allowed: 1 hour 30 minutes
You can use:
* 1 8 4 8 9 4 4 5 5 8 *
• a scientific or graphical calculator
• a ruler (cm/mm)
* H 4 2 0 0 3 *
Please write clearly in black ink. Do not write in the barcodes.
Centre number Candidate number
First name(s)
Last name
INSTRUCTIONS
• Use black ink. You can use an HB pencil, but only for graphs and diagrams.
• Write your answer to each question in the space provided. If you need extra space use
the lined pages at the end of this booklet. The question numbers must be clearly shown.
• Answer all the questions.
• Where appropriate, your answer should be supported with working. Marks might be
given for using a correct method, even if your answer is wrong.
INFORMATION
• The total mark for this paper is 70.
• The marks for each question are shown in brackets [ ].
• Quality of extended response will be assessed in questions marked with an asterisk (*).
• This document has 28 pages.
ADVICE
• Read each question carefully before you start your answer.
© OCR 2025 [601/4260/1] OCR is an exempt Charity
DC (WW/CB) 345392/5 Turn over
for more: tyrionpapers.com
, 2
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]
© OCR 2025
for more: tyrionpapers.com
, 3
(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.
..........................................................................................................................................................
..................................................................................................................................................... [1]
© OCR 2025 Turn over
for more: tyrionpapers.com
