Q1.
What similarities do you find in Fig. 2.3c and Fig. 2.3d?
Answer
The stained onion peel under the microscope (Fig. 2.3c) looks exactly like the wall made of bricks (Fig. 2.3d).
- Both are built from many small units of nearly the same shape — nearly rectangular cells, and rectangular bricks.
- The units are packed closely together with no space between them, in neat rows.
- Each unit has its own clear boundary — the cell wall in the peel, the edge of the brick in the wall.
- The whole structure is far bigger than any one unit, but it is made only of those repeated units.
Why the book uses this picture: it fixes the central idea of the chapter in one image — the cell is the basic unit of life, just as the brick is the basic unit of a wall. You cannot understand a wall by studying mortar; you understand it by studying one brick and then how the bricks are put together. The same is true of a leaf, an onion or your own body.
Tip: the safranin does not create the cells — it only stains them a pinkish colour so that their boundaries stand out against the background. The glycerin keeps the peel from drying and makes the picture clearer.