AS 1 2022-style membrane question (reduced-content series) · 6 marks
Explain how the structure of the cell surface membrane relates to its function in controlling the movement of substances.
Marked instantly, no account needed
CCEA AS Biology 2022 past paper and mark scheme
Summer 2022 is part of the current CCEA GCE Biology (2016) specification, so every question style in it is still examinable. Reduced content — check what was removed before using it as a full mock. 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 2022
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 2022 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 2022 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 2022 questions with mark schemes
Question styles that carried the most marks in the Summer 2022 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 2022-style membrane question (reduced-content series) · 6 marks
Explain how the structure of the cell surface membrane relates to its function in controlling the movement of substances.
Command word: Explain — how to answer itMark scheme — 6 creditworthy points
- Phospholipid bilayer with hydrophilic heads outward and hydrophobic tails inward
- Small, non-polar molecules such as oxygen diffuse directly through the bilayer
- Polar molecules and ions cannot pass through the hydrophobic core
- Channel proteins allow facilitated diffusion of ions down a concentration gradient
- Carrier proteins change shape to transport specific molecules, by facilitated diffusion or active transport
- Active transport uses ATP to move substances against the concentration gradient; cholesterol regulates fluidity
Full-mark answer
The membrane is a phospholipid bilayer with hydrophilic phosphate heads facing the aqueous solutions on each side and hydrophobic fatty acid tails facing inwards. Small, non-polar molecules such as oxygen and carbon dioxide are lipid-soluble and diffuse straight through the bilayer, whereas polar molecules and ions cannot cross the hydrophobic core. These pass instead through channel proteins, which allow facilitated diffusion down a concentration gradient, or through carrier proteins, which change shape to move specific molecules across. Carrier proteins also carry out active transport, using ATP to move substances against their concentration gradient. Cholesterol between the phospholipids regulates the fluidity of the membrane, keeping it stable and limiting the leakage of polar substances.
Examiner insight: Every structural feature must be paired with what it lets through. 'The membrane is partially permeable' on its own is not creditworthy at this level.
AS 1 2022-style DNA question (reduced-content series) · 6 marks
Describe the structure of DNA and explain how semi-conservative replication produces two identical molecules.
Command word: Describe — how to answer itMark scheme — 7 creditworthy points
- Two polynucleotide strands, antiparallel, held by hydrogen bonds between complementary bases
- Each nucleotide is a deoxyribose sugar, a phosphate and a base, joined by phosphodiester bonds in the backbone
- A pairs with T (two hydrogen bonds) and C pairs with G (three hydrogen bonds)
- DNA helicase breaks the hydrogen bonds and the strands unwind and separate, each acting as a template
- Free DNA nucleotides align with complementary bases on each template strand
- DNA polymerase joins adjacent nucleotides by phosphodiester bonds
- Each new molecule contains one original and one new strand, so base sequences are identical - semi-conservative
Full-mark answer
DNA consists of two antiparallel polynucleotide strands wound into a double helix. Each nucleotide is made of deoxyribose, a phosphate group and an organic base, and the nucleotides in a strand are joined by phosphodiester bonds to form a sugar-phosphate backbone. The two strands are held together by hydrogen bonds between complementary bases, with adenine pairing with thymine by two hydrogen bonds and cytosine pairing with guanine by three. During replication DNA helicase breaks these hydrogen bonds so that the strands unwind and separate, and each strand acts as a template. Free DNA nucleotides align opposite their complementary bases, and DNA polymerase joins adjacent nucleotides together by phosphodiester bonds. Each of the two molecules produced contains one original strand and one newly synthesised strand, which is why replication is described as semi-conservative, and because base pairing is complementary the two molecules have identical base sequences.
Examiner insight: Both named enzymes and both bond types are credited. The definition of semi-conservative must mention one old and one new strand per molecule.
AS 2 2022-style gas exchange and disease question · 5 marks
Explain how the alveoli are adapted for efficient gas exchange, and explain the effect of emphysema on gas exchange.
Command word: Explain — how to answer itMark scheme — 5 creditworthy points
- Very large total surface area provided by millions of alveoli
- Alveolar epithelium and capillary endothelium are both one cell thick, giving a very short diffusion distance
- Dense capillary network and ventilation maintain a steep concentration gradient for oxygen and carbon dioxide
- In emphysema the walls between alveoli break down, reducing the surface area available for diffusion
- Loss of elastic tissue means the lungs cannot recoil, so less air is exhaled and the gradient is reduced - breathlessness / lower oxygen uptake
Full-mark answer
The lungs contain millions of alveoli, which together give a very large surface area for diffusion. The alveolar epithelium is only one cell thick and lies against capillary endothelium that is also one cell thick, so the diffusion distance is extremely short. A dense network of capillaries continually removes oxygenated blood and delivers blood high in carbon dioxide, and ventilation continually replaces the air in the alveoli, so steep concentration gradients for both gases are maintained. In emphysema the walls between adjacent alveoli break down, so the alveoli merge into larger air spaces and the surface area available for gas exchange is greatly reduced. The loss of elastic tissue also means the lungs cannot recoil properly, so less air is forced out during expiration, the concentration gradients are less steep and the patient becomes breathless because oxygen uptake into the blood falls.
Examiner insight: Three adaptations, each with its reason, then two clear consequences of emphysema. 'Alveoli are damaged' with no reference to surface area or elasticity does not score.
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 2022 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 2022 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.