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LESSON B1 · EXPLAINER
Cell Structure and Specialisation
You started as one cell. Now you have about 200 different kinds. How?
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Explore in 3D
Cells in 3D
Rotate the cell and highlight each part. These models are simplified and not to scale.
Step 2 · Read
Key notes
Copy these into your notebook in your own words — that is how they stick.
Nucleus
Contains chromosomes (DNA); controls cell activities and inheritance.
Cell membrane
Partially permeable; controls entry and exit of substances.
Cytoplasm
Site of most chemical reactions.
Mitochondria
Aerobic respiration — release of energy (ATP). More in active cells (muscle, sperm).
No nucleus (DNA loop), plasmids, cell wall; may have flagellum, capsule, pili.
Specialisation
Structure adapted to function; allows division of labour and efficiency in multicellular organisms.
Levels
Cells → tissues → organs → organ systems → organism.
EXAM TIPS & COMMON MISTAKES
“List FOUR structures common to plant and animal cells”: membrane, nucleus, cytoplasm, mitochondria (ribosomes also accepted).
Drawing a plant cell (up to 9 marks!): large, clear single lines, labels on the right, no shading, title and magnification.
Onion epidermis cells have no chloroplasts — they are not exposed to light. Iodine stains the nucleus; methylene blue stains animal cells.
A muscle cell has MORE mitochondria than a cheek cell because it needs more energy.
Step 2 · Learn from examples
Worked examples & study resources
The kind of support a teacher gives after the lesson: worked examples to attempt first, a board illustration, key terms, common misconceptions and memory aids.
Worked example 1
Plant cell or animal cell?
Under the microscope a student sees cells with a cell wall, a nucleus, a large central vacuole but no chloroplasts. (a) Are these plant or animal cells? (b) Suggest where they came from. (c) Explain why there are no chloroplasts.
Try it in your notebook first, then reveal the solution one step at a time.
List the features that only plant cells have: cellulose cell wall, large permanent vacuole, chloroplasts.
The cells have a wall and a large vacuole, so they are plant cells — animal cells have neither.
Not every plant cell has chloroplasts. Cells that are not exposed to light — roots, or the inner layers of an onion bulb — do not photosynthesise, so they have none.
So a likely source is onion epidermis or a root.
Answer. (a) Plant cells (cell wall + large central vacuole). (b) Onion bulb epidermis or root tissue. (c) These cells are not in the light, so they do not carry out photosynthesis and do not need chloroplasts.
Examiner’s tip. Never use “has no chloroplasts” as proof that a cell is from an animal. The cell wall and large vacuole are the reliable plant features.
Worked example 2
Linking structure to function in specialised cells
Explain how (a) a root hair cell and (b) a red blood cell are adapted to their functions.
Try it in your notebook first, then reveal the solution one step at a time.
State the function first, then link each feature to it with “so that” or “which”.
Root hair cell — function: absorb water and mineral ions from the soil. Its long, thin extension gives a large surface area for absorption; its thin wall gives a short distance; it has many mitochondria to release energy for the active transport of minerals.
Red blood cell — function: carry oxygen. Its biconcave shape gives a large surface area for oxygen to diffuse in and out; it has no nucleus, leaving more room for haemoglobin; haemoglobin combines with oxygen; it is small and flexible so it squeezes through capillaries.
Answer. (a) Long extension → large surface area; thin wall; many mitochondria for active transport of minerals. (b) Biconcave → large surface area; no nucleus → more haemoglobin; haemoglobin carries oxygen; flexible → fits through capillaries.
Examiner’s tip. A feature with no link to function scores nothing. “Biconcave shape” alone = 0; “biconcave shape gives a large surface area for oxygen to diffuse” = 1 mark.
On the board · What each structure does
Structure
Function
Plant cell
Animal cell
Nucleus
Contains DNA; controls the cell’s activities
✓
✓
Cell membrane
Partially permeable; controls what enters and leaves
✓
✓
Cytoplasm
Where most chemical reactions take place
✓
✓
Mitochondrion
Aerobic respiration releases energy
✓
✓
Cell wall (cellulose)
Support; stops the cell bursting
✓
✗
Large permanent vacuole
Stores cell sap; keeps the cell turgid
✓
✗ (small, temporary)
Chloroplast
Photosynthesis
✓ (green parts)
✗
Ticks show where each structure is found. Bacteria are different again: no nucleus (DNA lies free in the cytoplasm) and no mitochondria.
Key terms
Organelle
A structure with a specific job inside a cell, e.g. nucleus, mitochondrion.
Cell membrane
Partially permeable layer that controls movement in and out of the cell.
Cell wall
Rigid cellulose layer outside the membrane of plant cells.
Specialisation
A cell’s structure being adapted to one particular function.
Tissue
A group of similar cells carrying out the same function.
Organ
Several tissues working together, e.g. leaf, heart.
Organ system
Several organs working together, e.g. the digestive system.
Common misconceptions
✗ Plant cells have chloroplasts instead of mitochondria.✓ Plant cells have mitochondria too. They respire all the time; chloroplasts are only in cells that photosynthesise.
✗ The cell wall controls what enters the cell.✓ The wall is fully permeable. The cell membrane is the partially permeable barrier.
✗ Bacteria have a nucleus.✓ Bacteria have no true nucleus: their DNA lies loose in the cytoplasm, often with small rings called plasmids.
Memory aid
Plant cells have three extras — remember “WVC”: Wall, big Vacuole, Chloroplasts.
Real-life link
Sickle cell disease is common in Caribbean populations of African descent. A changed haemoglobin makes red blood cells sickle-shaped: they carry less oxygen and can block capillaries — a clear example of a cell’s shape deciding how well it works.
Try this
Build a model cell: a clear bag of gel or jelly for the cytoplasm, a plum or grape for the nucleus, and beans for mitochondria. Put it in a box to turn it into a plant cell — what does the box represent?
Play & practise
Games
4 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness.
Step 3 · Practise
Paper 1 practice — multiple choice
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better.
Step 4 · Apply
Paper 2 practice — structured questions
Write full answers, then reveal the mark scheme and tick the points you earned (16 marks in total). Your answers are saved on this device.
Based on CSEC P2 May/June 2026, Question 1(a)–(f)
Question 1 [9 marks]
Students prepared slides of cheek cells and onion epidermis cells for microscope examination, using methylene blue and iodine.
(a) List FOUR structures common to both animal and plant cells. [4]
MARK SCHEME — (a) (max 4)
(b) Suggest an aim for the experiment. [1]
MARK SCHEME — (b) (max 1)
(c) State ONE reason why methylene blue and iodine were used. [1]
MARK SCHEME — (c) (max 1)
(d) Suggest why no chloroplasts were seen in the onion cells. [1]
MARK SCHEME — (d) (max 1)
(e) Suggest TWO precautions when carrying out the experiment. [2]
MARK SCHEME — (e) (max 2)
Based on CSEC P2 May/June 2023, Question 1(b)–(c)
Question 2 [7 marks]
Bacteria have structures suited to infecting other organisms. Humans have many specialised cells.
(a) Explain how EACH helps a bacterium: flagellum, slime capsule, cell wall. [3]
MARK SCHEME — (a) (max 3)
(b) State ONE structural difference between (i) red blood cells and skin cells; (ii) skin cells and nerve cells. [2]
MARK SCHEME — (b) (max 2)
(c) Explain why cell specialisation is important in multicellular organisms. [2]
MARK SCHEME — (c) (max 2)
Your progress
Lesson readiness
0% READY
Not started
Video watched (20%)0%
Multiple choice (40%)0%
Structured (40%)0%
Sources
Where this topic appears in CSEC papers
Find these in your own past-paper booklets for extra timed practice. The practice above is adapted from them.
CSEC P1 2021, 2022, 2023, 2024 — Items 12–14 (organelles; wall vs membrane; muscle vs cheek cell)
CSEC P1 May/June 2022 Item 43; 2023 Item 46; 2024 Item 43 (structure common to two specialised cells)