Wednesday 19 June 2024 – Morning
A Level Biology A
H420/03 Unified biology
Time allowed: 1 hour 30 minutes
You can use:
• a scientific or graphical calculator
• a ruler (cm/mm)
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 begiven
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 24 pages.
ADVICE
• Read each question carefully before you start your answer.
OCR is an exempt Charity
Turn over
, 2
1 Escherichia coli is a bacterium that is used widely in scientific experiments and in biotechnology.
(a) This is a transmission electron micrograph of E. coli.
A
(i) Name the structure labelled A.
A ...................................................................................................................................................... [1]
(ii) Based on your knowledge, estimate the diameter of the E. coli cell.
(b) A student carries out a serial dilution of an E. coli culture.
This is the method the student uses:
• Transfer 10 cm3 of E. coli culture to a sterilised test tube from an original culture that has avolume
of 50 cm3.
• Carry out four 10-fold serial dilutions. Each dilution involves transferring 1 cm3 of culture fromone
test tube to another test tube containing 9 cm3 of distilled water.
• Transfer 1 cm3 of the final 10 cm3 diluted culture to an agar plate. Evenly spread 1 cm3 ofliquid
across the plate using a sterilised spreader.
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