AS 1 2025-style enzyme question · 6 marks
Explain the effect of increasing temperature on the rate of an enzyme-controlled reaction.
Marked instantly, no account needed
CCEA AS Biology 2025 past paper and mark scheme
Summer 2025 is part of the current CCEA GCE Biology (2016) specification, so every question style in it is still examinable. The papers and mark schemes themselves are published by CCEA; BioCCEA is an independent study tool and is not endorsed by CCEA.
What you sit in AS 2025
AS 1: Molecules and Cells
AS 1 written paper (1 hour 30 minutes)
Biological molecules, enzymes, cell structure, transport across membranes, cell division, nucleic acids and the immune response.
AS 1 topic list and exam focusAS 2: Organisms and Biodiversity
AS 2 written paper (1 hour 30 minutes)
Gaseous exchange, transport in plants and mammals, adaptation, biodiversity, classification, sampling and human impact.
AS 2 topic list and exam focusAS 3: Practical Skills in AS Biology
AS 3 practical booklet plus a written practical-skills paper (1 hour)
Planning, manipulating apparatus, recording, processing and evaluating experimental data at AS level.
AS 3 topic list and exam focus
How to sit the 2025 paper properly
- 1Print the paper and sit it in one block, to time, with no notes. A paper done in pieces tells you nothing about your exam performance.
- 2Mark it with the official CCEA mark scheme in front of you and award a mark only where the scheme's point is actually made.
- 3Log every dropped mark by unit topic, not by question number, so patterns appear across papers.
- 4Rewrite the two worst answers in full, using mark-scheme wording, then re-mark them.
- 5Come back to the same paper three weeks later and redo only the questions you lost marks on.
Sit the AS 2025 style questions
Answer each one under exam conditions. Your wording is marked against every mark scheme point before the full-mark answer appears.
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These questions are written in the style of the CCEA GCE Biology (2016) papers and are not reproduced from any live paper. CCEA owns the copyright in its question papers and mark schemes — always download the official paper and mark scheme from CCEA and use these worked answers alongside them. BioCCEA is an independent study tool and is not endorsed by CCEA.
Worked AS 2025 questions with mark schemes
Question styles that carried the most marks in the Summer 2025 papers, each with the full list of creditworthy mark scheme points, a model answer at full marks, and the marking point candidates most often missed.
AS 1 2025-style enzyme question · 6 marks
Explain the effect of increasing temperature on the rate of an enzyme-controlled reaction.
Command word: Explain — how to answer itMark scheme — 6 creditworthy points
- As temperature increases the kinetic energy of the molecules increases
- More frequent successful collisions between enzyme and substrate / more enzyme–substrate complexes form
- Rate increases up to the optimum temperature
- Above the optimum, hydrogen (and ionic) bonds in the enzyme break
- The tertiary structure changes so the active site is no longer complementary to the substrate — denaturation
- Fewer enzyme–substrate complexes form, so the rate falls, and denaturation is permanent
Full-mark answer
As temperature increases, the kinetic energy of both enzyme and substrate molecules increases, so they move faster and there are more frequent successful collisions. More enzyme–substrate complexes form per second, so the rate of reaction increases up to the optimum temperature. Above the optimum, the increased vibration breaks the hydrogen and ionic bonds holding the enzyme's tertiary structure, so the shape of the active site changes and it is no longer complementary to the substrate. Fewer enzyme–substrate complexes can form and the rate falls sharply. Because the bonds cannot reform in the correct arrangement, denaturation is permanent.
Examiner insight: 'The enzyme is killed' is never credited — enzymes are not alive. Name the bonds that break; 'the enzyme changes shape' alone does not secure the denaturation mark.
AS 1 2025-style protein synthesis question · 5 marks
Describe how a molecule of mRNA is produced from a gene, and explain why the mRNA is shorter than the gene.
Command word: Describe — how to answer itMark scheme — 5 creditworthy points
- DNA helicase breaks hydrogen bonds and the double helix unwinds, exposing the template strand
- Free RNA nucleotides align with complementary bases on the template strand (uracil pairs with adenine)
- RNA polymerase joins the nucleotides by phosphodiester bonds to form pre-mRNA
- Pre-mRNA is spliced: introns are removed and exons joined together
- The mRNA is therefore shorter than the gene because the non-coding introns have been removed
Full-mark answer
DNA helicase breaks the hydrogen bonds between the two DNA strands so the double helix unwinds and the template strand is exposed. Free RNA nucleotides align opposite their complementary bases on the template strand, with uracil pairing with adenine, and RNA polymerase joins them together by phosphodiester bonds to form pre-mRNA. The pre-mRNA is then spliced, so the non-coding introns are removed and the coding exons are joined together. The finished mRNA is shorter than the gene because the introns present in the DNA are not present in the mature mRNA.
Examiner insight: The uracil–adenine detail and the named enzymes are both credited. Explain the length difference using introns explicitly — 'only part of the gene is copied' is not enough.
AS 1 2025-style carbohydrates question · 6 marks
Explain how the structure of starch, glycogen and cellulose is related to their functions.
Command word: Explain — how to answer itMark scheme — 6 creditworthy points
- Starch is a mixture of amylose (unbranched, helical) and amylopectin (branched), both made of alpha-glucose joined by glycosidic bonds
- It is compact and insoluble, so it does not affect water potential and is a good storage molecule in plants
- Glycogen is also made of alpha-glucose but is more highly branched than amylopectin
- More branches mean more ends for hydrolysis, so glucose is released rapidly to meet the high metabolic demand of animals
- Cellulose is made of beta-glucose, with alternate molecules inverted, giving straight unbranched chains
- Hydrogen bonds between chains form microfibrils of high tensile strength, so cellulose gives strength to plant cell walls
Full-mark answer
Starch consists of amylose, an unbranched chain of alpha-glucose that coils into a helix, and amylopectin, which is branched; both are compact and insoluble, so large amounts can be stored in a plant cell without affecting its water potential. Glycogen is also a polymer of alpha-glucose but is much more highly branched, and because each branch provides another end for hydrolysis, glucose can be released very rapidly to meet the high metabolic demands of an animal. Cellulose is a polymer of beta-glucose in which alternate molecules are inverted, so the chains are straight and unbranched. Many hydrogen bonds form between adjacent chains, holding them together as microfibrils with high tensile strength, which is why cellulose is suited to providing strength and support in plant cell walls.
Examiner insight: Every structural point must be tied to a function, and the alpha/beta distinction is essential for the cellulose marks.
These questions are written in the style of the CCEA GCE Biology (2016) papers and are not reproduced from any live paper. CCEA owns the copyright in its question papers and mark schemes — always download the official paper and mark scheme from CCEA and use these worked answers alongside them. BioCCEA is an independent study tool and is not endorsed by CCEA.
Download the official CCEA paper and mark schemePractise the AS 2025 paper in the app
These open BioCCEA with AS already selected, so you can sit questions in this paper's style and have them marked against the CCEA mark scheme.
Get your 2025 answers marked
Photograph a written answer from this paper and see it marked line by line in CCEA mark-scheme language, with the exact phrase you needed to earn each missing mark.