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School Name : DCS International School
Class : VIII
Sub : General Science
Date : 6-7-2019
Period : 1
Duration : 45 min
Topic : Cell Structure and Function

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 cork ( bark of a plant) under a microscope,
found compartments like structures. They look like honey comb and
they are separated from each other by walls and he called them
��cells��.
? He actually saw dead cells.
? 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.

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:
? �C Unicellular
? �C Multi-cellular

Unicellular Organisms
? 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

Some Unicellular Organisms
Amoeba Chlamydomona
Paramecium

Multicellular Organism
? 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

Onion Peel Cells Cells from the cheek
Some Multi-cellular Organisms

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.

Various Cells from the Human Body

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

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

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

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

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

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Cell structure anmd function

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