This document provides information about cell structure and function in a science class for 8th grade students. It defines key terms like cell, unicellular and multicellular organisms. It describes some of the first observations of cells under a microscope. The summary also outlines the basic components of cells, including the plasma membrane, nucleus, cytoplasm, and cell wall in plant cells. It provides examples of unicellular organisms like yeast and bacteria, as well as multicellular organisms like plants and animals. Finally, it describes the functions of the main cell structures like the plasma membrane, nucleus, and cell wall.

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

2. 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.

3. 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

4. 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

5. Some Unicellular Organisms
Amoeba Chlamydomona
Paramecium

6. 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

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

8. 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.

9. Various Cells from the Human Body

10. 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

11. 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

12. 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

13. 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

14. 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

15. Thank you