Specialised Cells and Their Functions
In 2014, CSIRO researchers measured nerve cells from a blue whale spine that stretched over 2 metres in length — the longest single cells of any animal ever recorded, each one carrying a signal along the whale’s body.
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Q1 · The cells in your eye, your toe and your blood all came from one original cell. Why do you think they end up looking so different?
Q2 · If you had to design a cell to deliver oxygen all around the body, what shape and features would you give it?
● Know
- What "specialised cell" means
- The structure and job of five specialised cells: red blood cell, neuron, sperm, palisade, root hair
- That cells in multicellular bodies are not all the same
● Understand
- Why a red blood cell has no nucleus and is biconcave
- Why a neuron is so long
- Why a palisade cell is stuffed with chloroplasts
● Can do
- Match each specialised cell to its job
- Explain how a cell's shape suits its function
- Apply "structure fits function" to a new cell example
- Specialised
- Haemoglobin
- Neuron
- Flagellum
- Surface area
- A whip-like tail that helps a cell swim
- Red protein that carries oxygen in blood
- The total outer area of a cell
- A nerve cell with a long axon
- Built for one specific job
Hold a red blood cell and a nerve cell side by side in your imagination: one is a tiny flat disc the size of a full stop, the other is a thread that could stretch the length of your arm — and both are single cells doing completely different jobs. Here are five classic examples.
| Cell | Job | Key features |
|---|---|---|
| Red blood cell | Carry oxygen around the body | No nucleus (more room for oxygen), biconcave shape (more surface area), packed with haemoglobin |
| Neuron (nerve cell) | Carry electrical signals fast | Very long axon (up to 1 m), thin so signals travel quickly |
| Sperm cell | Swim to and fertilise an egg | Long flagellum (tail) for swimming, midpiece packed with mitochondria for energy |
| Palisade mesophyll cell | Run photosynthesis in leaves | Tall column shape, packed with chloroplasts on the sunlit upper layer of the leaf |
| Root hair cell | Absorb water and minerals from soil | Long thin extension increases surface area for water uptake |
Notice the pattern: every odd feature has a clear reason. Structure fits function.
- Red blood cell
- Neuron
- Sperm cell
- Palisade cell
- Root hair cell
- Swim to and fertilise an egg
- Absorb water and minerals from soil
- Carry oxygen around the body
- Run photosynthesis in the leaf
- Carry electrical signals around the body
A red blood cell does one job: pick up oxygen in your lungs, deliver it to every part of your body, then return for more. To do that job well it has three weird features:
- No nucleus. When a red blood cell is finished growing, it ejects its nucleus. This frees up space — letting it pack in roughly 270 million haemoglobin molecules, each one carrying oxygen.
- Biconcave shape (like a flattened doughnut without the hole). This shape gives more surface area for oxygen to enter and leave, and lets the cell bend through narrow blood vessels.
- Full of haemoglobin — the red protein that grabs onto oxygen. Without haemoglobin, blood couldn't carry oxygen at all.
Trade-off: because it has no nucleus, a red blood cell can't divide or repair itself. So they only live about 120 days, and your bone marrow has to keep making fresh ones.
Three more cells where the shape gives the job away:
- Neuron — a nerve cell. Has a long thin extension called an axon that can stretch from your spine to your toe. Why? So a single cell can carry a signal that far without any handover. The faster and longer the axon, the quicker your reflexes.
- Sperm cell — a male reproductive cell shaped like a tiny tadpole. It has a long flagellum (tail) that whips side to side to push it forward, and its midpiece (just behind the head) is packed with mitochondria to power the long swim to the egg.
- Root hair cell — a plant cell on the outside of a young root. It grows one super-long thin extension that pokes between soil particles. This dramatically increases surface area, so water and dissolved minerals can be sucked in faster.
In every case, the cell solves a job through its shape. Long for distance. Tailed for swimming. Hairy for absorbing.
A has a long axon to carry electrical signals fast. A cell has a flagellum to help it swim. A hair cell has a long extension that gives it a large area for absorbing water.
Now a plant example. Just under the top surface of a leaf is a layer of tall, column-shaped cells called palisade mesophyll cells. They are the plant's main sunlight collectors.
Two clever design choices:
- Column shape. Standing tall and tightly packed lets more cells fit into the sunlit upper layer per square millimetre.
- Stuffed with chloroplasts. A single palisade cell can contain dozens (sometimes hundreds) of chloroplasts. More chloroplasts means more photosynthesis, which means more glucose for the plant.
This is why a leaf is green on top and paler underneath — the chloroplast-packed palisade cells live near the upper surface where the sunlight is brightest.
Every specialised cell you've met follows the same rule:
The shape and features of a cell match the job it has to do.
This is called structure-function fit. It is one of the most important ideas in biology — and you'll see it everywhere from here on:
- Inside cells (chloroplasts have stacks for catching light, mitochondria have folds for more reactions)
- In organs (your lungs have millions of tiny sacs for huge surface area)
- In whole animals (cheetahs have long legs for speed; koalas have specialised teeth for tough gum leaves)
So when you see a weird-looking cell, the first question to ask is: "What job does this shape make easier?"
A ciliated cell lines your windpipe (the tube leading to your lungs). It has hundreds of tiny hair-like extensions called cilia that wave back and forth. Predict: what job is this cell doing, and why does its shape make sense? Write 1–2 sentences, then reveal.
How close was your prediction?
Nice — you read the cell's shape and worked out the job.
That's okay — cilia are an unusual feature. The key idea: hairs that wave usually mean "sweep stuff along".
At the start of the lesson you were asked why a nerve cell in your spinal cord can be over a metre long.
Now that you've learned about structure-function fit, write your full answer. What job does that length serve? How does being stretched out help it do its work faster?
Q1. Name three specialised cells from this lesson and state the main job of each. (3 marks)
Q2. Describe THREE features of a red blood cell and explain how each helps it carry out its job. (4 marks)
Q3. A scientist discovers a new cell with a long whip-like tail and many mitochondria. Predict what job this cell does and justify your answer using the idea of structure-function fit. (4 marks)
Answers
▾MCQ 1
C — Ejecting the nucleus frees up space, so the cell can pack in millions of haemoglobin molecules and carry more oxygen.
MCQ 2
A — A long axon means one neuron can carry the signal across a long distance (e.g. spine to toe) quickly and without handoff.
MCQ 3
D — Mitochondria release the energy that powers the sperm's flagellum, which it needs to swim a long way to reach the egg.
MCQ 4
B — Palisade cells live on the sunlit upper layer of the leaf where light is brightest. Many chloroplasts means lots of photosynthesis.
MCQ 5
C — A long thin extension increases the surface area in contact with soil, so the cell can absorb water and minerals much faster.
Short Answer 1
Model answer: Accept any three. For example: red blood cell — carries oxygen around the body. Neuron — carries electrical signals. Sperm — swims to fertilise the egg. Palisade mesophyll — runs photosynthesis. Root hair — absorbs water and minerals from soil.
Short Answer 2
Model answer: (1) No nucleus — frees up internal space, so the cell can be packed with haemoglobin to carry more oxygen. (2) Biconcave shape — gives more surface area for oxygen to enter and leave, and lets the cell bend to squeeze through narrow blood vessels. (3) Full of haemoglobin — the red protein that grabs onto oxygen so it can be transported around the body.
Short Answer 3
Model answer: The cell is probably built for swimming. A long whip-like tail (flagellum) is what cells use to push themselves through fluid, just like a sperm cell does. Many mitochondria provide the energy needed for the constant motion of the tail. So the structure of this cell — tail plus lots of mitochondria — fits a function of self-powered swimming. It could be something like a sperm cell, or a single-celled organism such as a flagellate protist that lives in water.