Lesson 6 of 6 / Cell structure and organisation
How specialised cells do their jobs
How does a structure make a cell better at its function?
In this lesson: Explain adaptations of root hair cells, muscle cells and mature mammalian red blood cells.
About 5 min
The key ideaAn 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, narrow extension into the soil. This increases the surface area of its cell membrane in contact with soil water, allowing greater absorption of water and mineral ions. The extension changes the available absorbing area; it does not give the cell a pump for water.
Muscle cells contain contractile structures and often many mitochondria. Aerobic respiration in the mitochondria releases energy needed for contraction. Cells that contract repeatedly require a continuing energy supply, so the number of mitochondria is linked to the demand of their work.
A mature mammalian red blood cell has no nucleus, leaving more space for haemoglobin, the protein that carries oxygen. Its biconcave shape provides a large surface area relative to its volume and a short diffusion distance for oxygen. It is flexible, helping it pass through narrow capillaries.
Listing a feature is not yet an explanation. "Many mitochondria" becomes an explanation when linked to more aerobic respiration and energy for contraction. The same structure can support different jobs in different cells, so finish with the function 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.
Is this true? "A root hair absorbs more because it has a larger volume."
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.