Cell – The Basic Unit of Life
1. Definition
Cell is the basic unit of life. It is usually referred as “building blocks” of life (plants or
animals) and is made up of proteins.
Remember: Living organisms
Unicellular Multicellular
Made up of Made up of two Note: Unicellular
only one cell or more cells organisms exist in both
eukaryotic and
prokaryotic forms.
Example: Amoeba, Example: Human, Trees,
Escherichia coli (E. coli), Elephants, Jelly Fish
yeast
Cells are too small that it can only be seen using a microscope.
Cells was first introduced in 1665 by Robert Hooke, an English botanist – after he had
examined thin slices of cork from the bark of a tree.
A human body is made up of approximately 60 000 billion cells.
2. Structure of the cell
The cell is made up of a mass of living matter called protoplasm.
The protoplasm:
is a complex jelly-like substance where many chemical reactions occur to keep the
cell alive;
exists in two distinct forms, namely, the liquid state or the semi-liquid state (jelly-
like);
is a mixture of several compounds, namely water (70% - 90%), mineral salts and
organic compounds (such as carbohydrates, proteins and fats).
, The composition of the protoplasm varies from plant to plant and animal to animal.
For example, the protoplasm of brain cells differs from that of the muscle cells.
The protoplasm of a cell is made of:
1. Nucleus
2. Cytoplasm
3. Cell surface membrane (also known as plasma membrane)
A. Nucleus – (controls the normal cell activities)
The nucleus is a tiny, rounded and dark staining body, located within the cytoplasm of the
cell.
The nucleus is made up of the nucleoplasm (small spherical mass of denser protoplasm)
which is surrounded by the nuclear envelope.
The nucleus consists of:
1. Chromatin (a network of thread-like structures that contain hereditary materials
which functions by controlling all the activities of a cell).
For instance, during the process of cell division, these long thread-like structures (chromatin)
condense to become highly coiled structures called chromosomes.
2. Nucleolus (spherical shape) – plays a part in the building up of proteins (protein
synthesis)
3. Nuclear envelope – separates the content of the nucleus from the cytoplasm.
Functions of the nucleus:
Cell reproduction
Controls all the activity of the cell
Repair of worn-out parts
Note: Cells who lack nucleus (for instance, red blood cells) have a short lifespan and are not
able to reproduce.
B. Cytoplasm
The cytoplasm is the part of the protoplasm which surrounds the nucleus.
It is usually the larger part of the cell and is the place where most biochemical reactions
occur.
Within the cytoplasm are found some important organelles (highly organized structure found
within a cell) like the:
i. Mitochondria (in singular: mitochondrion)
1. Definition
Cell is the basic unit of life. It is usually referred as “building blocks” of life (plants or
animals) and is made up of proteins.
Remember: Living organisms
Unicellular Multicellular
Made up of Made up of two Note: Unicellular
only one cell or more cells organisms exist in both
eukaryotic and
prokaryotic forms.
Example: Amoeba, Example: Human, Trees,
Escherichia coli (E. coli), Elephants, Jelly Fish
yeast
Cells are too small that it can only be seen using a microscope.
Cells was first introduced in 1665 by Robert Hooke, an English botanist – after he had
examined thin slices of cork from the bark of a tree.
A human body is made up of approximately 60 000 billion cells.
2. Structure of the cell
The cell is made up of a mass of living matter called protoplasm.
The protoplasm:
is a complex jelly-like substance where many chemical reactions occur to keep the
cell alive;
exists in two distinct forms, namely, the liquid state or the semi-liquid state (jelly-
like);
is a mixture of several compounds, namely water (70% - 90%), mineral salts and
organic compounds (such as carbohydrates, proteins and fats).
, The composition of the protoplasm varies from plant to plant and animal to animal.
For example, the protoplasm of brain cells differs from that of the muscle cells.
The protoplasm of a cell is made of:
1. Nucleus
2. Cytoplasm
3. Cell surface membrane (also known as plasma membrane)
A. Nucleus – (controls the normal cell activities)
The nucleus is a tiny, rounded and dark staining body, located within the cytoplasm of the
cell.
The nucleus is made up of the nucleoplasm (small spherical mass of denser protoplasm)
which is surrounded by the nuclear envelope.
The nucleus consists of:
1. Chromatin (a network of thread-like structures that contain hereditary materials
which functions by controlling all the activities of a cell).
For instance, during the process of cell division, these long thread-like structures (chromatin)
condense to become highly coiled structures called chromosomes.
2. Nucleolus (spherical shape) – plays a part in the building up of proteins (protein
synthesis)
3. Nuclear envelope – separates the content of the nucleus from the cytoplasm.
Functions of the nucleus:
Cell reproduction
Controls all the activity of the cell
Repair of worn-out parts
Note: Cells who lack nucleus (for instance, red blood cells) have a short lifespan and are not
able to reproduce.
B. Cytoplasm
The cytoplasm is the part of the protoplasm which surrounds the nucleus.
It is usually the larger part of the cell and is the place where most biochemical reactions
occur.
Within the cytoplasm are found some important organelles (highly organized structure found
within a cell) like the:
i. Mitochondria (in singular: mitochondrion)
