An Overview Of Cell

fig: Animal Living Cell

The onion cell which is a typical plant cell, has a distinct cell wall as its outer boundary and just within it is the cell membrane.

Cells that have membrane bound nuclei are called eukaryotic whereas cells that lack a membrane bound nucleus are prokaryotic.

In both prokaryotic and eukaryotic cells a semi-fluid matrix called cytoplasm occupies the volume of the cell.

The cytoplasm is the main arena (zone) of cellular activities in both the plant and animal cells. Various chemical reactions occur in it to keep the cell in the 'living states'.

Besides the nucleus, the eukaryotic cells have other membrane bound distinct structures called organelles like the endoplasmic reticulum (ER), the golgi complex, lysosomes, mitochondria, microbodies. The prokaryotic cells lack such membrane bound organelles.

Ribosomes are non-membrane bound organelles found in all cells both eukaryotic as well as prokaryotic cell. Within the cell, ribosomes are found not only in the cytoplasm but also within the two organelles - chloroplasts (in plants) and mitochondria and on rough ER.

Animal cells contain another non-membrane bound organelle called centriole which helps in cell division.

SIZE AND SHAPE OF CELL:

SIZE:

• Cell differ greartly in size, shape and activites.
• Mycoplasma (Smallest cells) only 0.3 μm in length.
• Bacteria = 3 to 5 μm.
• Largest isolated single cell = egg of an ostrich.
• Human red blood cell = 70.μm in dia meter.
• Nerve cell = longest cell. 

SHAPE :

• The shape of the cell may vary with the function they perform.
• They may be disc-like, poygonal, columnar, thread like or even irregular.

fig : Different size and shape of cell