CELL IS FUNDAMENTAL STRUCTURAL and FUNCTIONAL UNIT OF LIFE.
This means that structure of every living organism is made up of cell and the cell carry out various functions.
DISCOVERY OF CELL
Robert Hooke discovered cell
Leeuwenhoek discovered living cell.
Robert Brown discovered nucleus.
Purkinje called the fluid part of cell as Protoplasm.
Schwan and Schleiden gave cell theory.
Virchow expanded cell theory.
Cells are of different shapes
Cells are of different shape and size to perform specific function and their different shapes helps them to perform these functions.
EXAMPLE:
Nerve cells are Elongated in shape for transmission of signal.
Red Blood Cells are Disc shaped to increase surface area.
Stomata are Dumbbell shaped for exchange of gases.
Cells, the Repetitive unites together form a tissue, tissue unite to form organ, and organs will form organ system.
CELL ==> TISSUE ==> ORGAN ==> ORGAN SYSTEM
Organisms can be Unicellular or Multicellular.
In some Organisms only one cell constitutes the whole organism as in Amoeba, Paramecium and Bacteria, they are called as Unicellular Organism.
Uni= Means single.
Cellular= Means Cell.
In other organisms, cells group together in a single body and assume different functions in it to form various body parts, they are called as Multicellular Organism.
Multi= Means many.
Cellular= Means Cell.
Example: Fungi, Plants and Animals.
HOW DO LIVING ORGANISMS PERFORM CERTAIN BASIC FUNCTIONS?
There is DIVISION of LABOUR in Unicellular and Multicellular organisms that helps them to perform basic functions.
In Multicellular organisms
Different parts of the body perform different functions like:
Heart: Pumping of Blood
Stomach: Digestion of Food
Brain: Transmission of Signals
Cell has got certain specific components within it known as cell organelles.
Each kind of cell organelle performs a special function, such as making new material in the cell, clearing up the waste material from the cell.
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.
In Unicellular organisms.
Only one cell constitutes the whole organism, so the cell components called as organelles take up their respective function like digestion, excretion, transportation etc.
STRUCTURAL ORGANISATION OF CELL
TYPES OF CELLS
Plant Cell:
In addition to the plasma membrane, have another rigid outer covering called the cell wall.
Made up of Cellulose. Cellulose is a complex substance and provides structural strength to plants.
Animal Cell: They do not have cell wall.
Fungal Cell: They have cell wall made up of Chitin.
A Cell is made up of three common features: Plasma Membrane, Cytoplasm and Cell organelles.
1. PLASMA MEMBRANE OR CELL MEMBRANE
Cell membrane is the outermost covering of the cell.
It is thin, flexible, delicate and Selectively Permeable.
The plasma membrane allows or permits the entry and exit of some materials in and out of the cell. It also prevents movement of some other materials. The cell membrane, therefore, is called a selectively permeable membrane.
1.1 Movement of substances into cell
Movement of substances into cell takes place by:
1. Diffusion
2. Osmosis
3.Endocytosis
4.Active transport
DIFFUSION:
The spontaneous movement of a substance from a region of high concentration to a region where its concentration is low is called as Diffusion.
Diffusion involves movement of various substance like gases and solids.
Example: Movement of gases: Carbon Dioxide and Oxygen.
How do substances like carbon dioxide (CO2) and water (H2O) move in and out of the cell? (NCERT Exemplar)
Movement of Carbon Dioxide
Carbon Dioxide is cellular waste and requires to be excreted out by the cell.
CO2 exits the cell by the process of diffusion.
It accumulates in high concentrations inside the cell.
In the cell’s external environment, the concentration of CO2 is low as compared to that inside the cell.
As soon as there is a difference of concentration of CO2 inside and outside a cell, CO2 moves out of the cell, from a region of high concentration to a region of low concentration outside the cell by the process of diffusion.
Movement of oxygen:
Oxygen is needed for cellular respiration, so O2 enters the cell by the process of diffusion.
The concentration of oxygen is high outside the cell.
When the concentration of oxygen is low inside the cell, the oxygen moves in the cell from region of lower concentration by process of diffusion.
OSMOSIS:
The movement of water molecules through a selectively permeable membrane is called osmosis.
The movement of water across the plasma membrane is also affected by the amount of substance dissolved in water called as Solute.
Osmosis is the net diffusion of water across a selectively permeable membrane from a lower solute concentration toward a higher solute concentration.
Osmosis is a special case of diffusion through a selectively permeable membrane.
What would happen if cell placed in solutions of different concentrations:
1.If the cell is placed in Hypotonic Solution
Means the solution in which cell is placed is dilute.
If the medium surrounding cell has higher water concentration than the cell
The cell will gain water by osmosis.
So, when a cell is placed in Hypotonic solution, it swells.
2.If the cell is placed in Hypotonic Solution
If the medium surrounding cell has lower water concentration than the cell.
Means the solution is very concentrated solution.
The cell will lose water by osmosis. water moves out of the cell.
So, when a cell is placed in Hypertonic solution, it shrinks.
3.If the cell is placed in Isotonic Solution
If the medium has exactly the same water concentration as the cell, Such a solution is known as an isotonic solution.
There will be no net movement of water across the cell membrane.
The cell will stay the same size, there is no overall movement of water.
Example of Osmosis:
Absorption of water by plant roots is also an example of osmosis.
Unicellular freshwater organisms and most plant cells tend to gain water through osmosis.
So, diffusion is important in exchange of gases and water in the life of a cell.
In additions to this, the cell also obtains nutrition from its environment.
ACTIVE TRANSPORT:
Different molecules move in and out of the cell through a type of transport requiring use of energy called as Active transport.
Small molecules are transported by diffusion, osmosis and active transport but What about large molecules?
ENDOCYTOSIS:
The process of engulfing of substance inside cell is called as Endocytosis.
The flexibility of the cell membrane also enables the cell to engulf in food and other material from its external environment.
Such processes are known as endocytosis.
Example: Amoeba acquires its food through such processes.
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