Cell (The function and structural unit of life) Class-8th
1. The Cell –
Its Structure
And Functions
[In Detail]
1May 29, 2015
2. The Discovery Of A Cell
Cells emerged on Earth at least 3.5 billion
years ago. In 1655, the English scientist
Robert Hooke made an observation that
would change basic biological theory and
research forever. While examining a dried
section of cork tree with a crude light
microscope, he observed small chambers and
named them as cells.
After 175 years, research led to the
formation of the cell theory. In its modern
form, this theorem has four basic parts:
I. 1. The cell is the basic structural and
functional unit of life; all organisms are
composed of cells.
II. 2. All cells are produced by the division of
pre-existing cells. Each cell contains genetic
material that is passed down during this
process.
III. 3. All basic chemical and physiological
functions are carried out inside of cells.
IV. 4. The activities of cells depends on the
activities of subcellular structures within the
cell.
What is a Cell ?
The cell (from Latin cella, meaning “small
room”)is the basic structural, functional and
biological unit of all known living organisms.
Cells are the smallest unit of life that
can reproduce independently, and are often
called the "building blocks of life". The study of
cells is called cell biology. 2
3. Variation In Cell Number, Shape And Size In
Living Organisms
Cell Number
Human body has trillions of cells which vary in
shapes and sizes. Different groups of cells
perform a variety of functions. living organisms
can be classified into two categories-
a) Organisms made of more than one cell are
called multicellular organisms. For example,
human beings ,animals etc.
b) The single-celled organisms are called
unicellular organisms. For example, amoeba,
euglena etc.
The both type organism can performs all the
necessary functions for their existence.
Cell Shape
Generally, cells are round, spherical or elongated.
Some cells are long and pointed at both ends.
They exhibit spindle shape . Cells sometimes are
quite long. Some are branched like the nerve cell
or a neuron.
Cell Size
Cell vary in size. The smallest cell is PPLO(Pleuro
pneumonia-like organism)and is about 0.1µm in
diameter. The ostrich egg is the largest cell with
1,70,000µm in diameter.
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4. Part Of The Cell
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Cell
Membrane
• Cell Wall
Cytoplasm
Nucleus
• Nucleoplasm
• Chromosomes
• DNA
5. Cell Membrane
The cell membrane (also known as the plasma membrane or cytoplasmic
membrane) is a biological membrane that separates the interior of
all cells from the outside environment. It also surrounds the inner gel-like
material called protoplasm. It controls the entry and the exit of substance
according to the requirements of the cell.
The cell wall is a tough, flexible but sometimes fairly rigid layer that
surrounds plant cells. It is located outside the cell membrane and provides
plant cells with structural support and protection.
Cytoplasm
The cytoplasm comprises cytosol – the gel-like substance enclosed within
the cell membrane – and the organelles – the cell's internal sub-structures.
All of the contents of the cells are contained within the cytoplasm. The
cytoplasm is made up of carbohydrates, proteins, fats, minerals vitamins and
about 80% water and usually colourless.
In plants, movements of the cytoplasm around vacuoles are known
as cytoplasmic streaming.
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6. Nucleus
The nucleus is the most important
part of the cell as it controls the
functions and activities of the cell. It
is lies in the centre of the cell but it
also occupy peripheral positions.
The nucleus is bound by a nuclear
membrane. The protoplasm present
in the nucleus is called nucleoplasm.
It has a thread-like network called
chromatin. When the cell divides it
condenses to form, a thread-like
structure called chromosomes. The
number of chromosomes in human
beings is 46(23 pairs of
chromosomes).
Chromosomes contain genetic
material, organized as multiple long
linear DNA (deoxyribonucleic
acid)molecules in complex with a
large variety of proteins.
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8. Plastids
The plastid is a major organelle found in
the cells of plants and algae. Plastids are the
site of manufacture. They often contain
pigments used in photosynthesis, and the types
of pigments present can change or determine
the cell's colour.
Mitochondrion
The mitochondrion (plural mitochondria) is
a membrane-bound organelle. These are rod
shape or spherical structures. These structures
are described as "cellular power plants"
because they generate most of the cell's supply
of adenosine triphosphate (ATP).
Endoplasmic Reticulum
The endoplasmic reticulum (ER) is a type
of organelle in the cells that forms an
interconnected network of flattened. There
are two types of endoplasmic reticulum, rough
endoplasmic reticulum (RER) and smooth
endoplasmic reticulum (SER). It works as
skeletal framework for the cell.
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9. Golgi Apparatus
The Golgi apparatus, also known as
the Golgi complex is an organelle found in
the cells. It was identified in 1897 by the
Italian physician Camillo Golgi. The Golgi
apparatus packages proteins inside the
cell before they are sent to their
destination; it is important in the
processing of proteins for secretion.
Vacuole
A vacuole is a membrane-
bound organelle which is present in all
types cells. Vacuoles are essentially
enclosed compartments which are filled
with water containing inorganic and
organic molecules. The organelle has no
basic shape or size; its structure varies
according to the needs of the cell.
Ribosomes
The ribosome is a large and complex
molecular machine, found within all living
cells, that help in protein synthesis.
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10. Some of the cells have small organelles
on their cell membrane, which help them
in transportation and collection of food.
Two of them are-
Flagellum
A flagellum is a lash-like appendage that
protrudes from the cell body of
certain cells like Euglena. The primary
role of the flagellum is locomotion but it
also often has function as a
sensory organelle, being sensitive to
chemicals and temperatures outside the
cell.
Cilium
A cilium is an organelle found
in unicellular cells like Paramecium. Cilia
are slender protuberances that project
from the much larger cell body.
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11. Sr.
no.
Part of a Cell Plant Cells Animal Cells
1. Cell Membrane Present Present
2. Nucleus & Nucleus Membrane Present Present
3. Cytoplasm Present Present
4. Cell Wall Present Absent
5. Plastids Present Absent
6. Vacuole Present (Large in size) Present (Small in size)
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13. 13
The basic unit of structure and
function in living things.
Made up of cells that are similar in structure and
function and which work together to perform a
specific activity.
Made up of tissues that work together to
perform a specific activity.
Groups of two or more tissues that work
together to perform a specific function for
the organism.
Entire living things that can
carry out all basic life
processes.
![The Cell –
Its Structure
And Functions
[In Detail]
1May 29, 2015](https://image.slidesharecdn.com/group1presentationoncellscience-150529084242-lva1-app6892/85/Cell-The-function-and-structural-unit-of-life-Class-8th-1-320.jpg)
