Download CHAPTER - 8 CELL * STRUCTURE AND FUNCTIONS

CHAPTER - 8
CELL – STRUCTURE AND
FUNCTIONS
Javed Anwar@MSc.MPhil.BEd
1) Discovery of the cell
In 1965 Robert Hooke observed slices of cork
from the bark of a tree under a simple magnifying
glass. He noticed small boxes or compartments in
the cork slice. The boxes were separated from
each other by a wall or partition. He named each
box as a Cell.The cells which Hooke observed
were actually dead cells of plants.
Javed Anwar@MSc.MPhil.BEd
2) The Cell
Cells are the basic structural units of living organisms.
Some organisms are made up of a single cell and some are
made up of many cells.
The number of cells in a tall tree or an animal like an
elephant or human being are billions and trillions of cells.
Organisms made up of many cells are called multicellular
organisms. Eg: a tree, an elephant.
Organisms made up of only one cell are called unicellular
organisms. Eg: amoeba, paramaecium.
Javed Anwar@MSc.MPhil.BEd
3) Shape of cells
Cells are of different shapes.
Some cells keep changing their shape. Eg : amoeba,
white blood cells in human beings.
Some cells are spherical, round, elongated, spindle
shaped, or branched.
Javed Anwar@MSc.MPhil.BEd
4) Size of cells
Cells in living organisms are of different sizes.They may be as
small as millionth of a meter (micrometre or micron) or large as a
few centimetres.
The smallest cell is the cell of bacteria (0.1 to 0.5 micrometre).
The largest cell is the egg of an ostrich (17cm x 13cm).
Javed Anwar@MSc.MPhil.BEd
Onion peel cells as seen under a microscope
Javed Anwar@MSc.MPhil.BEd
Human cheek cells as seen under a microscope
Javed Anwar@MSc.MPhil.BEd
Structure of a plant cell
Javed Anwar@MSc.MPhil.BEd
Structure of an animal cell
vacuole
Javed Anwar@MSc.MPhil.BEd
Structure of an animal cell
Javed Anwar@MSc.MPhil.BEd
5) Parts of a cell :The main parts of a cell are cell membrane (plasma
membrane), cytoplasm and nucleus.
The cell membrane gives shape to the cell, protects the inner
parts of the cell and allows movement of materials in and out of
the cell. In plant cells the cell membrane is covered by another
thick covering called cell wall.
The cytoplasm is a jelly like substance between the cell
membrane ad nucleus. It contains other components (organells)
like mitochondria, golgi bodies, ribosomes, vacuoles etc.
The nucleus is a spherical body generally found in the centre of
the cell. It has a membrane called nuclear membrane. It has a
smaller spherical body called nucleolus and thread like structures
called chromosomes.The chromosomes carry genes which
transfer characters from the parents to the off springs.
Vacuoles are blank looking structures in the cytoplasm.
Vacuoles are large in size in plant cells and small in size in animal
cells.
Plant cells have several small coloured bodies in the cytoplasm
called plastids.The green coloured plastids are called chloroplasts.
They contain chlorophyll which helps in photosynthesis.
Javed Anwar@MSc.MPhil.BEd
Structure of an animal cell and a plant cell
Vacoule
Javed Anwar@MSc.MPhil.BEd
Comparison of Plant cell and Animal cell
Javed Anwar@MSc.MPhil.BEd
Comparison of Plant cell and Animal
SN.
Part
cell
Plant cell
Animal cell
1
Cell membrane
Present
Present
2
Cell wall
Present
Absent
3
Nucleus
Present
Present
4
Nuclear membrane
Present
Present
5
Cytoplasm
Present
Present
6
Plastids
Present
Absent
7
Vacuole
Present
(smaller in size
Present
(larger in size)
Javed Anwar@MSc.MPhil.BEd
You don't always get what you wish for;
you get what you work for.
Javed Anwar@MSc.MPhil.BEd