SPM Biology Paper 2 (4551/2)

What Paper 2 tests

Paper 2 tests how well you can explain, apply and analyse biology in writing. It rewards precise wording and complete answers, and it is where diagram labelling, processes and essay structure earn or lose marks.

The three sections

How to approach Paper 2

1. In Section A, answer using the exact keywords; a vague phrase rarely gets the mark.
2. For essays, plan the marking points first, then write in full sentences that hit each one.
3. Label diagrams with straight lines and correct terms; a wrong label scores nothing.
4. Match your answer length to the marks, a 4-mark question needs about four distinct points.
5. Watch the time: Section A is worth the most, so do not lose it by over-writing an essay.

Common mistakes

Reading the command words

The command word at the start of a part decides the shape of the answer. 'State' or 'name' rewards a single correct term with no explanation, while 'explain' scores only when you give the reason or mechanism; writing a description where the question asks you to explain is one of the most common ways to lose Section A marks.

How the structured section is marked

Section A is marked analytically: each answer is broken into independent marking points, and you earn one point for every correct, relevant idea up to the marks shown for the part. A wrong extra point is usually ignored, but a statement that contradicts a correct one can cancel it, so keep each answer clean and to the point.

Section A often includes data-response parts, built around a graph, table or diagram. Read values from the data with their units when you describe a trend, then give the biological reason separately, because the description and the explanation are almost always two different marks.

Choosing and planning an essay

Section B and Section C each offer a choice of questions, and you answer one from each. Read every part of both options before you choose, because the question that looks easier at the start sometimes ends with a part you cannot complete.

Pick the option where you can score across every part, not only the opening.

An essay is still marked point by point, so jot the marking points as a short list before writing. Answer the parts in order, give each idea its own sentence or numbered point, and add a labelled diagram where it earns marks, a correct labelled diagram of a structure such as the nephron or the heart can earn its marks faster than prose.

Worked exam-style question

Question. Figure 1 shows the rate of photosynthesis of a water plant measured at increasing light intensity, while temperature and carbon dioxide concentration were kept constant. The rate rose steeply at first, then levelled off and stayed constant as the light intensity increased further.

(a) Name the gas whose rate of release could be used to measure the rate of photosynthesis. (b) Describe the relationship between light intensity and the rate of photosynthesis shown in Figure 1.

(c) Explain why the rate levelled off at high light intensity. (d) State two variables that had to be kept constant for the comparison to be fair.

Model answer. (a) Oxygen. (b) As light intensity increases, the rate of photosynthesis increases, then becomes constant and levels off at high light intensity.

(c) At high light intensity, light is no longer the limiting factor; another factor, such as carbon dioxide concentration or temperature, now limits the rate, so raising the light intensity further does not increase it. (d) Any two of: temperature, carbon dioxide concentration, and the species or mass of the water plant.

Source:SRC-FORMAT

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