Q.Different cells have different sizes. Arrange the following cells in an ascending order of their size. Choose the correct option among the followings.
i. Mycoplasma
ii. Ostrich eggs
iii. Human RBC
iv. Bacteria

Cell Size And Shape Variation

It is tempting to picture "a cell" as one standard, microscope-sized dot — but the real range of cell sizes in nature is closer to the range between a grain of sand and a beach ball. At one extreme sits Mycoplasma, the smallest cell known, measuring only a fraction of a micrometre. At the other extreme sits a single ostrich egg, which — however strange it sounds — is itself one enormous single cell, big enough to see and hold in your hand. Everything else in biology, including your own red blood cells, falls somewhere on the vast scale between these two points.

A scale worth memorising

Rather than exact measurements, it helps to anchor a handful of approximate benchmarks in increasing order:

Putting these in ascending order — Mycoplasma, then bacteria, then a human red blood cell, then the ostrich egg — captures just how many orders of magnitude separate the smallest and largest cells that exist.

Shape follows function

Size is only half the story — cells also vary enormously in shape, and this variation is rarely random. As a general principle, the shape a cell takes on tends to match the specific function it has to perform:

• Red blood cells are biconcave discs, a shape that increases their surface area for gas exchange while keeping them flexible enough to squeeze through narrow capillaries.
• Nerve cells are among the longest cells in the body, drawn out into thin, elongated processes precisely because their job is to carry electrical signals over long distances.
• Columnar epithelial cells are tall and narrow, an efficient shape for lining a surface such as the gut, where absorption and secretion happen across that lining. …