Lesson focus: specialised cellA cell with a special shape or features that help it do one job, like a red blood cell carrying oxygen. have features whose effects support a particular function.
Build feature–effect–function explanations for sperm, red blood and root-hair cells.
Build on earlier learning
Plant and animal cellsRevisit organelle functions before explaining how specialised cells differ.
You will be successful when you can…
- Identify features of three specialised cells.
- Link each feature to a direct effect.
- Connect the effect to cell function.
- Recognise trade-offs and avoid purpose-language.
Words that carry the science
- specialised cell
- A cell with features suited to a particular function.
- adaptation
- An inherited feature that increases effectiveness in a context.
- haemoglobin
- Protein in red blood cells that binds oxygen.
- flagellum
- Tail-like structure producing movement in a sperm cell.
- surface area
- Total exposed area available for exchange or contact.
Explain adaptation as a causal chain
01Feature is not enough
A strong explanation follows feature → effect → function. “A sperm has a flagellumA tail that some cells, such as sperm cells, use to swim.” names a feature; “the flagellum generates movement, helping it travel towards an egg” explains its effect.
Avoid saying a cell “wanted” a feature. Variation and selection produce adaptationA feature that helps a living thing survive where it lives, like a camel's wide feet for walking on sand. over generations.
02Three grounded examples
A sperm cell has a flagellum and many mitochondria. A root-hair cell has a long extension increasing surface areaThe total area of the outside of an object, where things can touch or pass through. for water and mineral-ion uptake.
A mature human red blood cell contains haemoglobinThe red substance in red blood cells that carries oxygen., has a biconcave shape giving large surface area and short diffusion distance, and lacks a nucleus and mitochondria, leaving more internal space and not consuming the oxygen it transports. In short: the red blood cell is full of haemoglobinThe red substance in red blood cells that carries oxygen., which carries oxygen. Its dimpled disc shape gives it a large surface area, so oxygen can get in and out quickly. It has no nucleus, so there is more room for haemoglobinThe red substance in red blood cells that carries oxygen..
03Specialisation brings trade-offs
Losing a nucleus increases room for haemoglobin but prevents a mature red blood cell from dividing or repairing itself fully. Specialisation improves one role while limiting others.
Compare the evidence and avoid treating a typical example as a universal rule.
- Sperm cellFlagellum generates movement; mitochondria release energy for motility.
- Red blood cellBiconcave shape and haemoglobin support oxygen loading and transport.
- Root-hair cellLong extension increases membrane area for uptake from soil.
- Palisade cellMany chloroplasts support light absorption and photosynthesis.
Build the full chain
Explain how the biconcave shape of a red blood cell supports oxygen transport.
- Name the feature: biconcave disc.
- State the effect: large surface-area-to-volume ratio and short diffusion distance.
- Connect to process: oxygen can diffuse across the membrane rapidly.
- Connect to function: efficient oxygen loading and unloading.
How to make the reasoning visible: Each arrow must be scientifically defensible; “better” alone hides the mechanism.
Adaptation evidence cards
Complete the missing link in each chain.
| Cell | Feature | Direct effect | Function |
|---|---|---|---|
| Sperm | Flagellum | Propels the cell | Movement towards egg |
| Red blood cell | Haemoglobin | Binds oxygen reversibly | Oxygen transport |
| Root-hair | Long extension | Greater surface area | Water/mineral uptake |
| Palisade | Many chloroplasts | More light-absorbing machinery | Photosynthesis |
Why is “red blood cells have no nucleus so they can move faster” weak?
Give one trade-off of sperm specialisation.
Pick one cell from the table. Write a chain: feature → what it does → job.
Check your understanding
Answer from memory, then check against the suggested answer.
What protein carries oxygen in red blood cells?
What does a root-hair extension increase?
What does a flagellum do?
What is a specialised cell?
Why do palisade cells have many chloroplasts?
An unfamiliar cell makes and exports much protein. Predict two abundant structures.
Explain why a highly specialised cell may depend on other cells.
Why does a sperm cell have many mitochondria?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A red blood cell carries oxygen around the body. Answer the parts to explain how it is good at this.
What substance fills the cell and carries oxygen?
(1)What does its dimpled disc shape give it? How does this help?
(1)Which part is missing from a red blood cell? Why does this help?
(1)So how much oxygen can it carry?
(1)Total for this question: 4 marks
Command word: For each feature, say what it is and how it helps.