Division of Labour in Multicellular Animals

It means the body's total work is divided. Instead of one cell doing everything, different cells and tissues each do one special task. For example, muscle cells help in movement and nerve cells carry messages. Because each part does one job well, the whole body works in a better and more coordinated way.

In a unicellular organism, the single cell performs all functions — digestion, respiration and reproduction — by itself. In a multicellular animal, these same basic functions are carried out by different groups of cells. So the key difference is: unicellular = one cell does all jobs; multicellular = many cells share the jobs.

NCERT lists four levels: cells, tissues, organs and organ systems. Similar cells with intercellular substance form a tissue; tissues form an organ like the stomach or heart; organs with a common function form an organ system like the digestive system. Each level splits up the work, so this is division of labour built into levels of organisation.

Because they have millions or billions of cells. If every cell tried to do every job, the work would be slow and disorganised. By splitting the work, activities become more efficient and better coordinated, and this helps the survival of the body as a whole. NCERT states this directly.

Sponges show only a little. Their cells are arranged as loose cell aggregates (cellular level of organisation), and some division of labour occurs among the cells. Higher animals show much more division of labour because their cells are organised into tissues, organs and organ systems.

They are closely linked but not identical. Levels of organisation name the four steps — cell, tissue, organ, organ system. Division of labour is the reason these levels exist: at each level the work is split so the body runs efficiently. NCERT says these four levels 'split up the work' and exhibit division of labour.

It is the opening idea of Class 11 Biology, Chapter 'Structural Organisation in Animals'. It also connects to 'Animal Kingdom', where sponges show cellular level and higher phyla show organ and organ-system levels.

The digestive system: the stomach, intestine and other organs each handle one part of digestion, while muscle tissue moves food and glandular tissue makes enzymes. No single cell does all of this — the work is divided among many tissues and organs.

Because it makes all activities more efficient and better coordinated. When millions of cells share the work correctly, the body as a whole survives. This is a favourite one-line NEET statement, so learn it as written in NCERT.