Exam questions rarely say “this is a plant cell”. They hand you a micrograph or a short description and expect you to work it out, then explain how the cell’s structure suits its job. Both of those are skills you can practise, and both follow a fixed order.
📚 What you need to know
Identify a cell type by asking a short series of questions in a fixed order.
The first question is always: is the DNA inside a nucleus? That splits prokaryote from eukaryote.
Then look for a cell wall, then for chloroplasts.
Size is useful evidence: a few µm suggests a prokaryote, tens of µm a eukaryote.
To explain a specialised cell, link one named structure to one named job.
Use evidence from the image or the stem — never from memory alone.
Working out what you are looking at
Do not guess from the overall look. Ask the questions in this order and the answer falls out.
The order matters. Asking about the wall first would put bacteria and plants in the same box, since both have one.
The evidence to look for
What you can see
What it tells you
DNA loose in the cytoplasm, no internal membranes
Prokaryotic
A clear nucleus and other membrane-bound organelles
Eukaryotic
Rigid straight edges and a thick outer layer
A cell wall, so plant, fungal or prokaryotic
Green oval structures with internal stacks
Chloroplasts, so a plant cell in a lit tissue
One large space filling most of the cell
A permanent vacuole, so most likely a plant cell
Rounded, flexible outline with no outer layer
An animal cell
Scale bar showing a length of 1 to 5 µm
Prokaryotic size range
Absence is weaker evidence than presence. A root cell has no chloroplasts, but it is still a plant cell. So if you cannot see chloroplasts, look for the wall and the vacuole before you decide — and say in your answer which feature you used.
Linking structure to function
The second skill is explaining why a cell is built the way it is. Every answer has the same two halves: name the feature, then say what it lets the cell do.
Notice how often the adaptation is about surface area or about making room. Those two ideas cover a large share of specialised cells.
The sentence that scores
This cell has [named structure], which means [what it can do], so it can [carry out its job]
Try it on a root hair cell. It has a long thin extension (structure), which greatly increases the surface area in contact with soil water (what it can do), so water and mineral ions are absorbed faster (its job). Three clauses, three marks.
Worked examples
WE 1
Identify a cell from a micrograph
A micrograph shows a cell 40 µm across with straight edges, a nucleus pushed to one side and one large space filling the middle. Identify the cell type and justify your answer. (3 marks)
Step 1: eukaryote or prokaryote
It has a nucleus and is 40 µm across, so it is eukaryotic.
Step 2: is there a wall
The straight rigid edges indicate a cell wall, which rules out an animal cell.
Step 3: the deciding feature
One large central space is a permanent vacuole, and it has pushed the nucleus to the edge, which points to a plant cell.
A plant cell — nucleus, wall and a large permanent vacuolequote the numbers and features from the stem; that is what “justify” means
WE 2
Explain an adaptation
Explain how the structure of a red blood cell suits its function. (3 marks)
Feature 1: no nucleus
A mature red blood cell has no nucleus, leaving more room for haemoglobin, so it carries more oxygen.
Feature 2: the shape
Its biconcave shape gives a larger surface area, so oxygen diffuses in and out more quickly.
Feature 3: flexibility
It is small and flexible, so it can squeeze through narrow capillaries.
No nucleus, biconcave shape, flexible — all serving oxygen transporteach mark is one structure plus one consequence, so never give a bare list
WE 3
Deduce a cell type from a description
A cell is 3 µm long, has a wall, and its DNA forms a single circular loop lying in the cytoplasm. Deduce the cell type and give two pieces of evidence. (3 marks)
Step 1: the deduction
It is a prokaryotic cell.
Step 2: evidence one
The DNA is circular and lies free in the cytoplasm, so there is no nucleus.
Step 3: evidence two
At 3 µm it sits in the usual prokaryotic range of 1 to 5 µm.
Prokaryotic — circular naked DNA, no nucleus, and only 3 µm longthe wall alone proves nothing here, since plants and fungi have one too
💡 Exam tips
Always ask about the nucleus first. It is the cleanest split.
Quote evidence from the image or stem, including any measurements given.
For adaptations, write structure then consequence then function.
Surface area and available space explain a huge number of adaptations.
Say which feature you used to decide — the reasoning earns marks, not just the name.
Watch for plant cells with no chloroplasts, such as root cells.
⚠ Common mistakes
Deciding from the wall alone. Plants, fungi and bacteria all have one.
Naming a structure with no function. Half an answer scores half the marks.
Ignoring the scale bar. Size is often the easiest evidence in the question.
Assuming no chloroplasts means not a plant. Root and stem cells have none.
Saying a cell “is designed” for its job. Say adapted or suited instead.
Giving general facts instead of reading the image. The marks are for evidence in front of you.
Up next: Drawing Cells (Skills) — the rules for a biological drawing, and how to put a magnification on your own diagram.
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