Cell theory , discovery, types, structure

Cell theory, discovery, types, structure

Cell theory, discovery, types, structure

What is Cell –

Cell is the structural and functional unit of living organisms.

Various types of organisms are found in the earth which have variations.

The body of every living being is made up of a microscopic unit called a cell.

Discovery of cell –

Robert Hooke (1665) observed bee hive-like cells while studying a thin layer of bottle cork and named these cells cells.

The word cell is a Latin word which means a little room.

This work was published in the book Micrographia.

Leeuwenhoek (1674) first studied the organization of living cells.

Robert Brown (1833) discovered and named the nucleus.

Cell Theory –

Schleiden and Schwann presented the cell theory.

According to these-

1. From the simplest single-celled organisms to the most complex multicellular animals and plants,

every living being is made up of cells.

2. Each cell can function independently.

3. The cell functions as a unit in the entire organism.

Genetic material is present in it.

Therefore the cell came to be considered as the genetic unit.

4. All cells can be formed only from precursor cells.

5. Various activities taking place in any organism are accomplished due to the biological activities taking place in its constituent cells.

smallest cell – Mycoplasma

largest cell – Egg of Ostrich

longest animal cell – nerve cell

Exception of Cell Theory –

Cell theory is not a theory in the traditional sense but a fact.

Is the cell the structural and functional unit of all living organisms?

Viruses are an exception to this question

because they do not have cells and are completely infectious parasites.

Viruses are non-living in isolated state.

Viruses are primitive micro-organisms that could not reach the state of a cell.

“Virus is primitive organism that has not reached a cellular state”

Types of Cells –

Two types of cells are found in living organisms –

(1) Prokaryotic Cell –

On the basis of cellular structure, it is primitive.

In these cells there is absence of nuclear membrane around the nucleus.

These do not contain developed organelles.

(2) Eukaryotic Cell –

It develops on the basis of cellular composition.

In these cells there is a nuclear membrane around the nucleus.

In these the cellular organs are fully developed.

Cell Structure –

The cell is mainly just a mass of protoplasm surrounded by plasma membrane

which has a nucleus in its middle.

There are cell organelles in the cytoplasm.

In plant cells, cell wall is found around the plasma membrane.

Which is synthesized by the plasma membrane.

A normal cell has three parts

(1) Plasma membrane

(2) Nucleus

(3) Cytoplasm

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Centrosome, definition, function

Cell division

Plasma membrane

Function of Lysosome

Function of Lysosome  –

These were discovered by a scientist named de Duve in 1964.

These are microscopic, round, sac-like structures surrounded by a single membrane.

Enzymes are found inside them.

There are special catalysts found in living organisms which increase the speed of biological processes.

The enzymes found in lysosomes are decomposers and digest various substances.

Some bacteria even digest the organelles of their own cell,

due to which the cell itself gets destroyed.

The useless cells of the body are destroyed in this way.

For this reason lysosome is also called “suicide bag”.

Function of Lysosome-

(1) They consume foreign substances that enter the cell.

(2) They clean the cells by eating dead and old cells.

Mitochondria –

It is a two-layered organelle found in the cytoplasm of eukaryotic cells.

R.B.C. of mammals Mitochondria are not found in.

Generally it is called the power house of the cell because by completely oxidizing the food,

A.T.P. Releases energy in the form of.

ATP in the body Energy is stored in the form of energy,

hence it is called energy currency.

Mitochondria structure –

Mitochondria are structures surrounded by a double membrane.

The cavity of mitochondria surrounded by outer and inner membrane is filled with matrix.

Many processes emerge from the inner membrane and hang in the matrix, which are called cristae.

DNA, ribosomes and enzymes are found in the matrix.

Function-

(1) It is the site of cellular respiration. ATP energy is produced.

(2) Acts as a mediator in the synthesis of amino acids and steroids.

Golgi Body

It is also called Golgi apparatus.

Plant cells are called dictyosomes.

It is found in all eukaryotic cells But RBC.

Is not found in.

Golgi body structure –

Three types of smooth membrane structures are found in it.

(1) Cisternae –

has a structure similar to parallel flat sacs.

(2) Vesicles –

are small round structures.

(3) Vacuoles –

These are large round structures.

Function –

(1) It is the main secretory organ of the cell.

(2) Works to transport substances in and out of the cell.

3) Synthesizes lysosomes and peroxisomes.

(4) Forms complex sugars from simple sugars.

 Lysosome

These were discovered by a scientist named de Duve in 1964.

These are microscopic, round, sac-like structures surrounded by a single membrane.

Enzymes are found inside them.

There are special catalysts found in living organisms which increase the speed of biological processes.

The enzymes found in lysosomes are decomposers and digest various substances.

Some bacteria even digest the organelles of their own cell,

due to which the cell itself gets destroyed.

The useless cells of the body are destroyed in this way.

For this reason lysosome is also called “suicide bag”.

Functions –

(1) They consume foreign substances that enter the cell.

(2) They clean the cells by eating dead and old cells.

Centrosome

Centrosome

This is the organelle located in the cytoplasm near the nucleus

which is made up of two parts –

(1) centroid pericentre and

(2) centroid nucleus.

The perihelion of the star is a colourless, clean circle inside which two microscopic particles called centra are found.

Stellate body is often found in animal cells.

But some of it is also found in plant cells, in fungi and algae.

During cell division the centrosome also gets divided into two parts.

Functions –

(1) To help in cell division (regulation of division).

(2) It helps in the formation of spindle during division of animal cells.

Nucleus

Large, round structures are found in the cytoplasm.

Which is called nucleus.

four of the nucleus

There are parts.

(1) Nuclear membrane –

A two-layered membrane is found around the nucleus.

Which is made of lipo-protein.

(2) Nucleoplasm-

This is a liquid containing chromosome and nucleus.

(3) Nucleolus-

There is a small round structure inside the nucleus which is called nucleolus.

There is no membrane in the nucleus.

(4) Chromatin network –

Forms a thin thread like structure in the nuclear substance which is called nuclear network.

On the occasion of cell division,

these threads separate from each other and shrink and become thick and small,

these are called chromosomes.

Function of Nucleus –

(1) Controls the metabolic activities of the cell.

(2) Controls the cell cycle.

(3) Transmits genetic traits from parents to offspring.

(4) The nucleus synthesizes RNA.

activities

(1) Take a piece of onion, remove its layer, place it on a slide and apply a cover slip.

We observe them with the help of a microscope.

(2) In the laboratory, blood corpuscles are studied under a microscope with the help of a permanent slide of human blood.