Cellular Organization

• A cell is the structural and functional unit of all life forms. • All living organisms, whether plants or animals, are made up of microscopic units called cells. • The cell occupies the same central position in biology as the atom in the physical sciences. • Organisms may be broadly classified into two kinds: – Unicellular – Multi-cellularIt was the British botanist Robert Hooke who, in 1665, while examining a slice of bottle cork under a microscope, found its structure resembling the box-like living quarters of the monks in a monastery, and coined the word “cells”

Cellular Organization

Some Facts about Cells • • The word cell is derived from the Latin word “cellula” which means “a little room” • • • It was the British botanist Robert Hooke who, in 1665, while examining a slice of bottle cork under a microscope, structure resembling living quarters of the monks in a monastery, and coined the word “cells” found the its box-like

Cellular Organization

Some Facts about Cells • • The Dutch scientist A.V. in 1674, Leeuwenhoek, the minute discovered forms of life such as bacteria and single celled animals in a drop of water • • In 1831, Robert Brown discovered the nucleus in the cell • • In the year 1838, Matthias Schleiden, a German botanist, first proposed the idea that all plants consist of cells

Cellular Organization

Some Facts about Cells • • In 1839, Theodor Schwann, another German botanist, asserted that all plants and animals are made up of cells • • J.E. Purkinje, in 1839, used the term protoplasm to describe the juicy, slimy gelatinous contents of the cell • • In 1885, Rudolf Virchow expressed that all cells arise from pre-existing cells

Cellular Organization

Some Facts about Cells • • In 1940, two German Scientists, Ruska and Knoll, invented the electron microscope • • Man is estimated to have about 100 trillion (1014 ) cells in number • • The cells that make up our body are so small that you could fit over 200 of them on the full stop at the end of this sentence.

Cellular Organization

Cells: An Introduction • • A cell is the structural and functional unit of all life forms. • • All living organisms, whether plants or animals, are made up of microscopic units called cells. • • The cell occupies the same central position in biology as the atom in the physical sciences. • • Organisms may be broadly classified into two kinds: • – Unicellular • – Multi-cellular

Cellular Organization

Cells: An Introduction • • All living beings, plants and animals, start their life with a single cell. • • Some organisms exist as a single cell and carry out the various metabolic life processes such as assimilation, respiration, reproduction, excretion, etc., that are essential for their survival. • • These are known as unicellular organisms. • • Example: Yeast, bacteria, chlamydomonas, amoeba

Cellular Organization

Some Unicellular Organisms Amoeba Paramecium Chlamydomona

Cellular Organization

Cells: An Introduction • • Some cells divide and give rise to organisms with more than one cell, these organisms are termed as multi- cellular. • • Example: animals, humans, most plants

Cellular Organization

Some Multi-cellular Organisms Cells from the cheek

Cellular Organization

Structure of a Cell • • Cells vary in shape and size. They may be oval, spherical, rectangular, polygonal, spindle shaped, star shaped, rod-shaped or totally irregular like the nerve cell. • • The diversity in cells is in accordance with the role or function it has to perform as part of the tissue or organ system. • • In general, there is no typical shape for cells.

Cellular Organization

Various Cells from the Human Body

Cellular Organization

Structure of a Cell • • Each cell has got certain specific components within it known as cell organelles, each of which performs a special function • • A cell is able to live and perform all its functions because of these organelles • • These organelles together constitute the basic unit called the cell • All cells have the same organelles, no matter what their function is or what organism they are found in

Cellular Organization

Structure of a Cell • • There are three features in almost every cell: • – Plasma Membrane • – Nucleus • – Cytoplasm • • All activities inside the cell and interactions of the cell with its environment are possible due to these features

Cellular Organization

Plasma Membrane or Cell Membrane • • Cell membrane is present in both plant and animal cells. • • It is living, elastic and made of proteins and lipids (fats). • • Its function is to provide a mechanical barrier for the protection of the inner cell contents and to regulate the movement of molecules in and out of the cell. • • It is called a selectively permeable membrane

Cellular Organization

Cell Wall • • The cell wall is present only in plant cells and lies outside the plasma membrane • • It is made up of a complex polysaccharide (carbohydrate) called cellulose. • • Its function is to give strength and rigidity to the cell. It is non-living. • • Cell walls permit the cells of plants, fungi and bacteria to withstand hypotonic external media without bursting

Cellular Organization

Nucleus • • This is a prominent, spherical or oval structure found at the centre of the cell. • • It is the controlling centre of all cell activities and has been described as the brain of the cell. • • It regulates all metabolic and hereditary activities of the cell • • It also plays a central role in cellular reproduction - the process by which a single cell divides and forms two new cells

Cellular Organization

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26.03.2017