By the end of this lesson
- Explain differentiation using changes in gene expression.
- Link specialised cell structures to their functions.
- Explain why division of labour benefits a multicellular organism.
BIG QUESTION
If nearly every cell contains the same genome, why can a neurone not do the job of a red blood cell?
Cell identity depends on which genes are expressed, which proteins are produced and how structure becomes adapted to function.
Differentiation changes cell identity
differentiationThe process by which an unspecialised cell becomes specialised for a particular function. is the process by which an unspecialised cell develops specialised structures and functions. Most cells in one organism contain the same genome, but they express different combinations of genes.
Different gene expression produces different proteins. Those proteins alter cell structure, metabolism and interactions, creating cells suited to particular roles. The DNA sequence does not usually need to change for differentiation to occur.
Specialisation creates division of labour
A multicellular organism benefits when different cells perform particular tasks efficiently. This division of labourDifferent specialised cells, tissues or organs carrying out different functions so the whole organism works more efficiently. allows tissues and organs to carry out functions that one general-purpose cell could not sustain at the same rate.
The benefit comes with dependence: a neurone relies on blood cells for oxygen, gut cells for absorbed nutrients and support cells for a stable environment.
Animal-cell adaptations
A red blood cellA biconcave blood cell with no nucleus, packed with haemoglobin, that carries oxygen from the lungs to body tissues. has a biconcave shape for a large surface-area-to-volume ratio, haemoglobin to bind oxygen and no nucleus when mature, leaving more space for haemoglobin. A neuroneA nerve cell, specialised to carry electrical impulses quickly around the body. has a long axon for transmission over distance, branched dendrites for connections and often a myelin sheath that electrically insulates the axon and increases conduction speed.
A ciliated epithelial cellA cell lining the airways with tiny hair-like cilia that beat to sweep mucus, and the dust and bacteria trapped in it, away from the lungs. has motile cilia that move mucus along airways; nearby goblet cells produce the mucus. A sperm cellThe male gamete, with a flagellum for movement, many mitochondria in the midpiece, a haploid nucleus and an acrosome containing enzymes involved in fertilisation. has a flagellum for movement, many mitochondria in the midpiece, a haploid nucleus and an acrosome containing enzymes involved in fertilisation.
Plant-cell adaptations
A root hair cellA root epidermis cell with a long extension that gives a large surface area for absorbing water by osmosis and mineral ions by active transport. has a long projection that increases surface area for absorption, a thin wall that shortens the diffusion pathway and many mitochondria to support active transport of mineral ions. Water uptake is by osmosis; mineral-ion uptake may require active transport.
A palisade mesophyllThe layer of tall, closely packed cells near the upper surface of a leaf, containing many chloroplasts; the main site of photosynthesis. is positioned near the upper surface of a leaf and contains many chloroplasts. Its elongated form and close packing help expose chloroplasts to light while leaving exchange pathways through neighbouring tissues.
Specialisation has limits
Some differentiated cells retain the ability to divide, while others do not. Mature mammalian red blood cells lack nuclei; many neurones do not normally divide. Stem cells provide replacement cells in selected tissues.
A good explanation of adaptation is causal. “It has many mitochondria” is description; “many mitochondria support a high rate of aerobic respiration, releasing energy for active transport” explains why the feature is useful.
Adaptation must be linked to function
Each row follows feature → process → advantage.
| Cell | Adaptation | Functional advantage |
|---|---|---|
| Red blood cell | Biconcave; packed with haemoglobin; no nucleus when mature. | Rapid oxygen exchange and high oxygen-carrying capacity. |
| Neurone | Long axon, branched dendrites and insulating myelin. | Carries impulses over distance and connects with many cells. |
| Ciliated epithelial cell | Motile cilia on its exposed surface. | Moves mucus containing trapped particles towards the throat. |
| Sperm cell | Flagellum, many mitochondria, acrosome and haploid nucleus. | Reaches and fertilises an egg, contributing one chromosome set. |
| Root hair cell | Long projection, thin wall and many mitochondria. | Absorbs water and mineral ions efficiently. |
| Palisade mesophyll cell | Many chloroplasts; elongated and close to the upper leaf surface. | Absorbs light and carries out photosynthesis rapidly. |
Language that earns precision
- differentiation
- The development of specialised structures and functions in a cell.
- specialised cell
- A cell adapted to perform a particular function.
- gene expression
- The process by which information in a gene is used to make a functional product.
- division of labour
- Different cells or tissues performing different tasks within a system.
- adaptation
- A feature that improves performance of a function in a particular context.
Common misconceptions
Claim: Differentiated cells have different genes.
Correction: Most have the same genome but express different combinations of genes.
Claim: Ciliated cells make mucus.
Correction: Goblet cells produce mucus; ciliated epithelial cells move it.
Claim: Root hair cells absorb all mineral ions by diffusion.
Correction: Mineral ions may be absorbed by active transport when moving against a concentration gradient.
Claim: Every adaptation is beneficial in every context.
Correction: A feature is advantageous for a particular function and may carry trade-offs.
Match the answer to the command word
State the visible or named feature accurately.
Link feature → process → benefit; do not stop after naming the adaptation.
Pair similarities or differences directly and keep the same basis of comparison.
Recall, apply, then justify
Recall, apply, then justify (continued)
Explain how differentiation can produce two cell types from cells containing the same genome.
Hint
Connect genes, proteins and structures.
Suggested marking points
- Different genes are switched on or expressed in the cells.
- Different proteins are produced.
- The proteins lead to different structures and functions.
Explain two adaptations of a root hair cell for uptake from soil.
Hint
Give two feature–benefit links.
Suggested marking points
- Long projection gives a large surface area for absorption.
- Thin wall gives a short pathway for water movement.
- Many mitochondria support aerobic respiration.
- Released energy supports active transport of mineral ions.
Explain why loss of cilia can increase the risk of lung infection.
Hint
Track mucus, pathogens and removal.
Suggested marking points
- Mucus traps pathogens and particles.
- Cilia normally move mucus towards the throat.
- Without effective cilia, contaminated mucus accumulates and pathogens are less efficiently removed.
A red blood cell has no nucleus. Explain one advantage and one limitation.
Hint
Think about internal space and genetic control.
Suggested marking points
- More internal space is available for haemoglobin.
- This increases oxygen-carrying capacity.
- Without a nucleus it cannot express genes in the usual way or divide.
- It has limited protein replacement and repair.
Evaluate the statement: “Specialisation makes a cell better.”
Planning hint
Define “better,” then consider performance, trade-offs and dependence.
What a strong design includes
- Specialisation improves efficiency at a particular function.
- Examples should link adaptations to that function.
- Specialisation can reduce other capabilities, such as division or independent survival.
- Cells become dependent on other specialised cells and organ systems.
- A justified conclusion should replace “better” with “better adapted to a specified role.”