Lesson 5 of 5 / Cell structure and organisation
How specialised cells do their jobs
How does a structure make a cell better at its function?
I can explain adaptations of root hair cells, muscle cells and mature mammalian red blood cells.
I can explain specialised cell adaptations.Syllabus
Syllabus K224 / K225, Topic 1(d). Explain specialised cell adaptations.
About 5 min
Make a guess. You are not marked.
A mature red blood cell in your body has no nucleus. What would you expect this to do?
Show the answer
Leave more room inside the cell for haemoglobin.
Without a nucleus, more of the cell is filled with haemoglobin, so each cell can carry more oxygen.
The key idea
An adaptation answer needs a chain: a named structure, the advantage it provides and the function that benefits.
Specialised cells have features that help them perform particular functions. Compare the three cells and look for a structure that changes how well the cell does its job.
Explore the idea
Follow structure to function
- Structure: Long, narrow extension
- Benefit: More membrane surface in contact with soil water
- Function: Greater absorption of water and mineral ions
Original simplified diagrams, not to scale. The pale centre of the red blood cell shows its thinner region; it is not a nucleus or a hole.
Explanation
A root hair cell has a long, thin part that grows out into the soil. This gives a larger surface area of membrane touching the soil water. With more surface, the cell can absorb more water and mineral ions.
Muscle cells contract again and again, so they need a steady supply of energy. They often have many mitochondria. Aerobic respiration in the mitochondria releases the energy needed for contraction.
A mature red blood cell has no nucleus. This leaves more space for haemoglobin, the protein that carries oxygen. Its shape, a disc that dips in on both sides, gives a large surface area and a short distance for oxygen to diffuse. It can also bend to squeeze through narrow capillaries.
Naming a feature is not yet an explanation. "Many mitochondria" becomes an explanation when you add "so more aerobic respiration releases more energy for contraction". Always end with the job of the cell in the question.
Step by step
- 1
Name the job
For example, a muscle cell contracts; a red blood cell transports oxygen.
- 2
Choose a relevant structure
Select mitochondria for energy supply or lack of a nucleus for more haemoglobin space.
- 3
Explain the benefit
Link increased surface area, space or energy supply to the named job.
Worked example
Comparing two muscle samples
Two equally sized muscle cell samples have different numbers of mitochondria. Sample A contracts repeatedly for longer periods. Suggest why A has more mitochondria.
One way to explain it
Repeated contraction requires a sustained supply of energy. More mitochondria allow greater capacity for aerobic respiration, releasing energy for contraction when oxygen and respiratory substrates are available.
Why this answer works
- Identify the greater demand for contraction.
- Connect mitochondria with aerobic respiration.
- Explain energy supply without saying that mitochondria create energy.
Watch out for this
A student says: "A root hair absorbs more because it has a larger volume." What is wrong with this?
Show the answer
Its long projection increases the membrane surface area in contact with the soil. The relevant advantage is more surface for absorption, not simply a larger volume.
Check your understanding
Why does a mature mammalian red blood cell lack a nucleus?
Show the answer
To leave more space for haemoglobin to carry oxygen.
Connect the missing nucleus to additional space for haemoglobin, then to oxygen transport.
Exam-style questions
Check your understanding
Which feature of a root hair cell most directly increases the rate of water uptake?
Show the answer
A long extension that gives a large surface area
A larger surface area in contact with soil water gives more water uptake per second.
Quick recall
How does a structure make a cell better at its function?