AS 2 2024-style comparison question · 5 marks
Compare the process of gas exchange in a fish gill with that in an insect tracheal system.
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CCEA AS Biology 2024 past paper and mark scheme
Summer 2024 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 2024
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 2024 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 2024 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 2024 questions with mark schemes
Question styles that carried the most marks in the Summer 2024 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 2 2024-style comparison question · 5 marks
Compare the process of gas exchange in a fish gill with that in an insect tracheal system.
Command word: Compare — how to answer itMark scheme — 5 creditworthy points
- Both have a large surface area for diffusion (gill lamellae / many tracheoles)
- Both have short diffusion distances / thin exchange surfaces
- Fish use a counter-current flow between water and blood to maintain a concentration gradient along the whole lamella
- Insects have no respiratory pigment or blood transport of oxygen; oxygen diffuses directly to the tissues via tracheoles
- Insects ventilate by abdominal pumping and control water loss with spiracles; fish ventilate by continuous one-way water flow over the gills
Full-mark answer
Both surfaces have a very large surface area — the many gill filaments and lamellae in a fish, and the extensive branching tracheoles in an insect — and in both the exchange surface is thin, giving a short diffusion distance. The fish maintains its concentration gradient by counter-current flow, with water and blood flowing in opposite directions so that a gradient exists along the whole length of the lamella, whereas the insect has no respiratory pigment and no blood transport of oxygen: oxygen diffuses directly from the tracheoles into the respiring tissues. Ventilation also differs — the fish maintains a continuous one-way flow of water over the gills, while an insect ventilates by abdominal pumping movements and closes its spiracles to limit water loss.
Examiner insight: This is 'compare', so each point must mention both organisms in the same sentence. Two separate paragraphs describing each in turn is the most common way marks are lost here.
AS 2 2024-style transport question · 5 marks
Explain how tissue fluid is formed at the arterial end of a capillary and how most of it returns to the blood.
Command word: Explain — how to answer itMark scheme — 5 creditworthy points
- At the arterial end the hydrostatic pressure of the blood is high
- This forces water and small solutes out through the capillary wall — ultrafiltration
- Plasma proteins are too large to leave, so they remain in the capillary
- At the venous end hydrostatic pressure has fallen, and the remaining plasma proteins give a lower (more negative) water potential in the capillary
- Water re-enters by osmosis; excess tissue fluid drains into the lymphatic system and returns to the blood
Full-mark answer
At the arterial end of a capillary the hydrostatic pressure of the blood is high, and this forces water and small dissolved solutes such as glucose and ions out through the capillary wall to form tissue fluid. Plasma proteins are too large to pass through, so they stay in the capillary. By the venous end the hydrostatic pressure has fallen because fluid has been lost, while the plasma proteins left behind give the blood a lower, more negative water potential than the tissue fluid. Water therefore moves back into the capillary by osmosis. The excess tissue fluid that does not return drains into the lymphatic vessels and is eventually returned to the blood at the subclavian vein.
Examiner insight: Both pressures must be named — hydrostatic and the water potential effect of plasma proteins. The lymphatic route is a separate mark.
AS 2 2024-style phagocytosis question · 5 marks
Explain how a phagocyte destroys a bacterium, and explain why this response is described as non-specific.
Command word: Describe — how to answer itMark scheme — 5 creditworthy points
- The phagocyte is attracted to chemicals released by the bacterium (chemotaxis) and binds to its antigens
- The cell surface membrane engulfs the bacterium by endocytosis, forming a phagosome
- Lysosomes fuse with the phagosome and release lysozymes / hydrolytic enzymes
- The enzymes hydrolyse the bacterium and the soluble products are absorbed into the cytoplasm
- It is non-specific because the same process and the same enzymes act on any pathogen, regardless of its antigens
Full-mark answer
A phagocyte is attracted along a concentration gradient of chemicals released by the bacterium and by the products of the immune response, and attaches to antigens on the bacterial surface. The cell surface membrane then extends around the bacterium and engulfs it by endocytosis, enclosing it in a vesicle called a phagosome. Lysosomes move towards the phagosome and fuse with it, releasing hydrolytic enzymes such as lysozyme that hydrolyse the bacterial cell wall and contents. The soluble products are absorbed into the cytoplasm of the phagocyte and the antigens may then be displayed on its surface. The response is non-specific because the phagocyte uses the same mechanism and the same digestive enzymes on any pathogen it meets, rather than responding to one particular antigen.
Examiner insight: The phagosome-lysosome fusion is a distinct mark from the enzymes. For the last mark you must contrast with antigen specificity, not just say 'it attacks everything'.
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 2024 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 2024 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.