NCERT Class 8 Cell-structure and function

1. CELL-STRUCTURE AND
FUNCTION

2. Catalogue
● Discovery of the cell
● The cell
● Shape of cells
● Size of cells
● Cell functions
● Parts of cells
● Eukaryotic and Prokaryotic cells
● Comparison of animal and plant cells

3. Discovery of the cell
1. Robert Hooke (1665) - observed dead cork (wood bark)and discovered cells
2. Anton Van Leeuwenhoek (1700) invented the compound microscope, observed living
cells (saliva & blood) ,and discovered algae
3. Matthias Schleiden- discovered that all plants and every part of them are made up of
cells, discovered the cell nucleus
4. Theodor Schwann (1807-1893)-discovered that all animals and every part of them are
made up of cells, independently announced that yeast is a living organism.
5. Rudolf Virchow (1858) -best known for his theory Omnis cellula e cellula every cell
originates from another existing cell like it. "), first to recognize leukemia cells

4. 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.Human body has trillions of cells which vary
in shapes and sizes.A single-celled organism performs all the
necessary functions that multicellular organisms perform.
1.Organisms made up of many cells are called multicellular
organisms. Eg: a tree, an elephant.
2.Organisms made up of only one cell are called unicellular
organisms. Eg: amoeba, paramecium.

5. 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.

6. 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).

7. Cell Functions
Each living organism is made up of organs.Each organ
performs different functions.Each organ is further made
up of smaller parts called tissues.A tissue is a group of
smaller cells performing a specific function.

8. Eukaryotic and Prokaryotic cells
● Cells having well organised nucleus with a nuclear
membrane are called eukaryotic cells.All organisms
other than bacteria and blue green algae are called
eukaryotes.
● Cells having nuclear material without nuclear membrane
are called prokaryotic cells.The organism with these
type of cells are called prokaryotes.Example-
bacteria,blue green algae.

9. Parts of cells
1.Cell membrane-The cytoplasm and nucleus are enclosed within the
cell membrane, also called the plasma membrane. The membrane
separates cells from one another and also the cell from the
surrounding medium. The plasma membrane is porous and allows the
movement of substances or materials both inward and outward.
2.Cell wall- In addition to the cell membrane, there is an outer
thick layer in cells of plants called cell wall. This additional
layer surrounding the cell membrane is required by the plants for
protection. Plant cells need protection against variations in
temperature, high wind speed, atmospheric moisture, etc. They are
exposed to these variations because they cannot move.

10. 3.Cytoplasm-It is the jelly-like substance present between the
cell membrane and the nucleus. Various other components, or
organelles, of cells are present in the cytoplasm. These are
mitochondria, golgi bodies, ribosomes, etc.
4.Nucleus-It is an important component of the living cell. It is
generally spherical and located in the centre of the cell.
Nucleus is separated from the cytoplasm by a membrane called the
nuclear membrane. This membrane is also porous and allows the
movement of materials between the cytoplasm and the inside of
the nucleus.With a microscope of higher magnification, we can
see a smaller spherical body in the nucleus. It is called the
nucleolus. In addition, nucleus contains thread-like structures
called chromosomes. These carry genes and help in inheritance or
transfer of characters from the parents to the offspring. The
chromosomes can be seen only when the cell divides.

11. Nucleus, in addition to its role in inheritance, acts as
control centre of the activities of the cell. The entire
content of a living cell is known as protoplasm. It includes
the cytoplasm and the nucleus. Protoplasm is called the
living substance of the cell.
5. Vacuoles-Vacuoles are blank looking structures in the
cytoplasm. Vacuoles are large in size in plant cells and
small in size in animal cells.
6.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.

12. Comparison of Plant cell and Animal cell

13. Thank You