Specialised cells and their adaptations
Biology · Key Stage 3 · The School
Built for one job
A SPECIALISED cell has a shape and structure suited to one particular job, not a general one. This is a repeated pattern in biology: shape follows function. Once you see the pattern in one cell, you can predict roughly what an unfamiliar cell's shape is for.
Three cells, three jobs
A NERVE CELL is long and thin, sometimes over a metre in humans, so a signal can travel a long distance fast. A RED BLOOD CELL has no nucleus and is shaped like a dimpled disc, which leaves more room inside to carry oxygen and gives it a larger surface for gas to cross. A SPERM CELL has a long tail and is packed with mitochondria, giving it the energy to swim to an egg.
Root hair cells and sperm cells
A ROOT HAIR CELL has a long, thin extension that greatly increases its surface area, so it can absorb more water and minerals from the soil. Compare this to the sperm cell's tail: both increase what the cell can do — one absorbing more, one swimming faster — by changing shape rather than by changing what the cell is made of.
Given an unfamiliar cell's description, you can often work out its job. A cell described as "flattened, with a very thin membrane, found lining the lungs" is almost certainly built for GAS EXCHANGE — a thin, flat shape puts the least possible distance between the air and the blood. A cell described as "packed tightly with chloroplasts, near the top surface of a leaf" is built to catch as much LIGHT as possible for photosynthesis. Structure and function are the same question asked two ways: what does this shape make possible, and what job would need exactly that?