Q.Multicellular organisms have division of labour. Explain.

In a multicellular organism the body is built from many cells rather than one, and these cells are not all alike — they differ in size, shape and the particular activity each performs. In general the shape of a cell tends to match the function it carries out. Because of this specialisation:

• Different groups of cells take on different jobs, so no single cell has to do everything.
• Each type of cell becomes suited to its task; for example, long narrow columnar cells line surfaces, biconcave red blood cells suit their role, and long nerve cells are built for their function.
• The overall work of staying alive is shared out, with each set of cells contributing its own part. …

Living things are all made of cells. Some organisms exist as a single cell and are called unicellular; a lone cell of this kind can lead an independent existence and carry out every essential function of life by itself. Others, such as human beings, are multicellular — their bodies are made of many cells working together. When a body is built from many cells, an important possibility opens up that a single-celled organism does not have: the cells need not all be the same, and they need not all do the same work.

Cells in fact differ enormously in size, shape and activity. They may be disc-like, polygonal, columnar, cuboid, thread-like or irregular — for example round biconcave red blood cells, branched and long white blood cells, long narrow columnar epithelial cells, and among the longest of all, the nerve cells. A key principle links these forms to their jobs: the shape of a cell generally tends to match the function it performs. This is the basis of division of labour.

• Because the cells are specialised, different groups of them can be set aside for different functions. One kind of cell need not attempt every task; it can be built and shaped for the one job it does best. …

Method: State the general principle before giving the specific illustration

"Explain" questions built around a named concept (here, division of labour) score best when they open with a one-sentence general definition of the concept, and only then bring in specific illustrations — jumping straight to examples without ever stating the underlying principle leaves the answer reading like a list of facts rather than an explanation.

Structure this kind of answer in three moves: first, state the enabling condition (a multicellular body has many cells, so they need not all be identical — a single-celled organism has no such option); second, state the general rule that follows (cell shape tends to match the function it performs, so different jobs get assigned to differently shaped, specialised cells); third, ground the rule with one or two concrete examples — enough to illustrate, not an exhaustive c …