Class IXth (Biology Notes)
Chapter-5 (The Fundamental Unit Of Life)
A) Cell - Cell is the smallest structural and functional unit of life. It is called structural unit as
all living organism are made up of cells and functional unit as it is the smallest structure
capable of performing basic life processes.
Two postulates of the cell theory are-
1. All organisms are made up of cells.
2. All cells exist from pre- existing cells.
B) Who discovered cell-It was discovered by Robert Hooke in 1665.Other discoveries about
cell are:
a) Robert Brown –Nucleus of the cell in 1831
b) Anton Van Leeuwenhoek – Free living cells in pond water (bacteria) in 1674
c) Purkinje – Fluid substance of cell (Protoplasm) in 1839
d) J.E.Virchow- Expanded cell theory (all cells arise from pre-existing cells) in 1855
e) M.J. Schleiden and T. Schwann – Gave cell theory (cell is basic unit of life) in 1838-39
f) The discovery of electron microscope in 1940 helped to understand complex structure of
cell and its organelles.
C) What are cell organelles- Each cell has got certain basic components within it known as cell
organelles. Each kind of cell organelle performs a special function that is why a cell is able
to live and perform all its function in any organism. These organelles are suspended in the
cytoplasm.
D) Basic components of cell- Plasma membrane, Nucleus and cytoplasm.
E) PLASMA MEMBRANE:
a) It is the outermost layer of animal cell.
b) It gives shape to the cell and provides mechanical support and protection to the inner
contents of the cell.
c) It is protective covering of the cell.
d) It is called selectively permeable membrane as it allows the entry and exit of some
materials in and out of the cell.
e) It is highly flexible, living membrane made up of organic molecules- proteins and lipids.
F) What is difference between diffusion and osmosis-
1
, DIFFUSION OSMOSIS
1. The process of movement of 1. The process of movement of
molecules from a region of water molecules from region of
higher concentration to lower higher concentration to lower
concentration to spread concentration through semi-
uniformly in given space. permeable membrane.
2. It is seen in solids, liquids and 2. It is seen only in liquids.
gases.
3. It helps in exchange of gases 3. It helps in absorption of water by
like CO2 and O2 between cell as plant cells and unicellular
well as its external environment. organisms.
4. 4.
G) What happens when we put an animal cell into a solution of salt or sugar?
** Solute + Solvent ---------- SOLUTION
Three things can happen-
a) Higher water concentration than a cell in surrounding medium i.e. the solution is dilute-
forms hypotonic solution-Cell gains water and swells up (becomes turgid)-process is
Endosmosis.
b) Lower concentration of water than a cell in surrounding medium i.e. the solution is
concentrated-forms Hypertonic solution- Cell loses water and shrinks (plasmolysed i.e.
becomes flaccid)-process is Exosmosis.
c) Same concentration inside and outside the cell-forms Isotonic solution- No change and
remains normal cell.
Conclusion: Osmosis is special kind of diffusion through plasma membrane which can be
affected by the amount of substance dissolved in water.
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Chapter-5 (The Fundamental Unit Of Life)
A) Cell - Cell is the smallest structural and functional unit of life. It is called structural unit as
all living organism are made up of cells and functional unit as it is the smallest structure
capable of performing basic life processes.
Two postulates of the cell theory are-
1. All organisms are made up of cells.
2. All cells exist from pre- existing cells.
B) Who discovered cell-It was discovered by Robert Hooke in 1665.Other discoveries about
cell are:
a) Robert Brown –Nucleus of the cell in 1831
b) Anton Van Leeuwenhoek – Free living cells in pond water (bacteria) in 1674
c) Purkinje – Fluid substance of cell (Protoplasm) in 1839
d) J.E.Virchow- Expanded cell theory (all cells arise from pre-existing cells) in 1855
e) M.J. Schleiden and T. Schwann – Gave cell theory (cell is basic unit of life) in 1838-39
f) The discovery of electron microscope in 1940 helped to understand complex structure of
cell and its organelles.
C) What are cell organelles- Each cell has got certain basic components within it known as cell
organelles. Each kind of cell organelle performs a special function that is why a cell is able
to live and perform all its function in any organism. These organelles are suspended in the
cytoplasm.
D) Basic components of cell- Plasma membrane, Nucleus and cytoplasm.
E) PLASMA MEMBRANE:
a) It is the outermost layer of animal cell.
b) It gives shape to the cell and provides mechanical support and protection to the inner
contents of the cell.
c) It is protective covering of the cell.
d) It is called selectively permeable membrane as it allows the entry and exit of some
materials in and out of the cell.
e) It is highly flexible, living membrane made up of organic molecules- proteins and lipids.
F) What is difference between diffusion and osmosis-
1
, DIFFUSION OSMOSIS
1. The process of movement of 1. The process of movement of
molecules from a region of water molecules from region of
higher concentration to lower higher concentration to lower
concentration to spread concentration through semi-
uniformly in given space. permeable membrane.
2. It is seen in solids, liquids and 2. It is seen only in liquids.
gases.
3. It helps in exchange of gases 3. It helps in absorption of water by
like CO2 and O2 between cell as plant cells and unicellular
well as its external environment. organisms.
4. 4.
G) What happens when we put an animal cell into a solution of salt or sugar?
** Solute + Solvent ---------- SOLUTION
Three things can happen-
a) Higher water concentration than a cell in surrounding medium i.e. the solution is dilute-
forms hypotonic solution-Cell gains water and swells up (becomes turgid)-process is
Endosmosis.
b) Lower concentration of water than a cell in surrounding medium i.e. the solution is
concentrated-forms Hypertonic solution- Cell loses water and shrinks (plasmolysed i.e.
becomes flaccid)-process is Exosmosis.
c) Same concentration inside and outside the cell-forms Isotonic solution- No change and
remains normal cell.
Conclusion: Osmosis is special kind of diffusion through plasma membrane which can be
affected by the amount of substance dissolved in water.
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