Question

'Cell are the basic structural unit of living organisms'. explain.

Answer 1

$\textbf{CELLS}$

→ Cells are the $\underline{structural}$ and $\underline{functional}$ unit of life of living organisms.

All living organisms are made up of cell. That's why cell is known as structural unit of life.

A single cell can perform all life functions with the help of it's components. Therefore it is known as functional unit of life.

→ Robert Hooke first discovered the cell in 1665. 

He prepared a thin slice of cork and observed it under self made microscope. He saw some box like structures which he named as cell.

→ Anton Von Leeuwenhoek first saw the living cell and also first describe the living cell. 

→ Cells can replicate independently.

→ It contain hereditary information due to presence of nucleus or nucleoid.

→ All organisms are made up of cells. Organisms with single cells are known as unicellular organisms. And organisms with multiple cells are known as multicellular organisms. 

→ Cells size ranges from 1 - 100 μm.

→ Mycoplasmas, is the shortest cell (0.3 μm) and ostrich egg and nerve cells are the largest cell. 

→ Cells are in different shapes. Their shape vary with their function. They may be cuboid, thread like, disc like etc.

→ Cells are of two types namely; Eukaryotic and Prokayotic cells.

a) Eukaryotic cells :- 

≈ These are generally large in size.

≈ Nuclear region is well defined and surrounded by a nuclear membrane.

≈ These are multicellular.

≈ Single chromosome are present.

≈ Member bound cell organelles are present such as mitochondria, endoplasmic reticulum, golgi appartus etc.

≈ DNA is linear.

≈ Cell divides by binary fission and budding.

≈ Ex :- Human beings, plants etc.

b) Prokayotic cells :-

≈ These are smaller in size.

≈ Nuclear region is not well defined and not surrounded by a nuclear membrane.

≈ These are unicellular.

≈ More than one chromosomes are present in it.

≈ Membrane bound cell organelles are absent such as mitochondria, endoplasmic reticulum, golgi appartus etc.

≈ DNA is circular.

≈ Cell divides by mitosis and meiosis.

≈ Ex :- Bacteria, blue-green algae etc.

° Animal cell :-

≈ Cell wall absent.

≈ Centrosome present.

≈ Vacuoles are small and many.

° Plant Cell :-

≈ Cell wall present.

≈ Centrosome absent.

≈ Vacuole is large and single.
__________________________________

Answer 2

Answer:

Similarly , organs combine to form body . Thus they are termed as the basis structural unit of every living organisms.