O-Level Biology 5090 Paper 2

In the examination:

Read the instructions carefully and answer the right number of questions from the right sections.

Do not answer more questions than are needed, as this will not gain you more marks in the examination.

Plan your time according to the marks for each question. For example, a question worth three marks requires less time and a shorter answer than one worth 10 marks. If a question has several parts, then the parts with more marks will need more time and more developed answers.

Do not leave out questions or parts of questions. Remember, no answer means no mark. Identify the command words - you could underline or highlight them• Identify the other key words and perhaps underline them too• Try to put the question into your own words to understand what it is really asking.

Read all parts of a question before starting your answer. Think carefully about what is needed for each part. You will not need to repeat material.

Paper 2 advice:

The number of marks for each question or question part often gives you a clue about how many separate points you need to make in your answer.

Structured questions contain many parts. Often later parts can depend on the answer to earlier parts.

Answer the question being asked. For example, if the question asks you to name ‘three other cell structures’, do not write down the cell structures which are given in the question.

Know the biological terms used in the questions.

Keep an eye on the time. Make sure you have time to answer all the questions and return at the end to check your answers.

Key ConceptsThis chapter covers how to describe cell structure and how to interpret microscope images/diagrams in Paper 2. You need to be able to compare prokaryotic vs eukaryotic cells, name key structures, and identify what a microscope diagram is showing.

Cell types you must separate

Prokaryotic cells: no nucleus; DNA is in cytoplasm in a region called the nucleoid.

Eukaryotic cells: nucleus present; DNA inside the nucleus; usually have membrane-bound organelles.

Microscope basics (what exam diagrams ask)

Light microscope: uses visible light; can see cells and some organelles (limited resolution).

Electron microscope: uses electrons; much higher resolution; shows finer internal detail.

Magnification vs resolution

Magnification = how many times bigger.

Resolution = ability to distinguish two close points as separate.

Structure-function links (common Paper 2 marking style)

Cell membrane: controls entry/exit (selective permeability).

Mitochondria: site of aerobic respiration (ATP production).

Ribosomes: protein synthesis.

Chloroplasts (plant cells): photosynthesis.

Vacuole (plant): large vacuole for storage; helps maintain cell turgor.

Typical diagram interpretation

Identify boundaries (cell membrane vs cell wall).

Look for nucleus (eukaryotes) and no nucleus (prokaryotes).

Match organelles to typical shapes in diagrams (e.g., mitochondria = bean/oval with folds).

Before you continue: After studying this chapter, can you clearly state 3 differences between prokaryotic and eukaryotic cells?

Key TermsNucleoid - Region in prokaryotic cytoplasm where DNA is located (no nucleus).

Nucleus - Eukaryotic control centre containing DNA, surrounded by a nuclear envelope.

Membrane-bound organelles - Organelles enclosed by membranes (e.g., mitochondria, chloroplasts).

Magnification - How many times larger an image appears than the specimen.

Resolution - The ability to distinguish two points as separate.

Electron microscope - Microscopy using electrons for much higher resolution than a light microscope.

Light microscope - Microscopy using visible light; lower resolution than electron microscopy.

Worked ExamplesExample 1: Identify cell type from featuresScenario: A diagram shows DNA but no nucleus; small circular DNA region; no membrane-bound organelles.

Check for nucleus: none shown → prokaryotic.

Check DNA location: in cytoplasm region (nucleoid) → matches prokaryotic.

Conclusion: label as prokaryotic.

Example 2: Choose the best microscopeScenario: The question asks for the microscope that would show the detailed structure of mitochondria clearly.

Mitochondria have fine internal detail (cristae).

Electron microscope gives much higher resolution.

Answer: electron microscope, not light microscope.

Practice Questions1. An exam diagram labels “cell wall” and “chloroplast”. Explain what type of cell it is and what these structures suggest about the cell’s functions.

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