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Cells, Cell Structure and Functions – CBSE NCERT Science

Published: 4 years ago

Category: Education, General Knowledge

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“Cells, Cell Structure and Functions – CBSE NCERT Science”

Cells, Cell Structure and Functions (CBSE NCERT Science lesson) by Soma Mukhopadhyay and Rupal Chopra for SuccessCDs Videos. ( http://videos.successcds.net )

What is a cell?

Cell is the basic structural and functional unit of life. It is the smallest unit of life and is often called the building block of life.

DISCOVERY
The cell was discovered by Robert Hooke in 1665. He examined (under a coarse, compound microscope) very thin slices of cork and saw a multitude of tiny pores that he remarked looked like the walled compartments and named them cells.

Matthias Jakob Schleiden and Theodore Schwann proposed cell theory in 1839 which states that all plants and animals are made up of cells and cell is a basic unit of life.

M.J. Schleiden Theodore Schwann

Types of Organisms

Unicellular Organisms : They are formed of one cell. E.g. amoeba ,etc.
Multicellular Organisms : They are formed of many cells. E.g. humans ,etc.

Structure of Animal cell

Structure of Plant cell

Components of a cell
Cell membrane :

It is the outermost elastic covering of the cell.
It is made up of lipids and proteins.
It protects the cell from injury and allows osmosis.
It is selectively permeable and allows endocytosis.
Membrane has carrier proteins for active transport.

Components of a cell
Cell wall:

It is a rigid, semi-elastic, protective and permeable covering present outside the cell membrane only in plant cells.

It is made up of cellulose, hemicellulose and pectin.

It gives strength to plants and prevents cell from bursting.

Components of a cell
Nucleus :

It is made up of four parts:- nuclear membrane, nucleoplasm, nucleolus and chromatin material.
It controls all cell functions and brings about cell differentiation.
DNA of chromosome transfers the hereditary characters from parents to off springs.

Components of a cell
Cytoplasm :

It is a jelly like, semi-fluid substance.
It is present between cell membrane and nucleus.
Various cell organelles are present in it.

Cell organelles
These are tiny sub-cellular structures specialized to perform specific functions and hence are very important as they carry out important functions.

They various cell organelles and their functions are:-
Endoplasmic Reticulum(E.R)

Golgi Apparatus(GA)
They are membrane bound vesicles arranged parallel to each other in tiny sacs called cisternae.
It helps in formation of cell wall, cell membrane and lysosomes.
Complex sugars may be made from simple sugars in GA.

Lysosomes
They are small vesicles covered by single membrane and contain digestive enzymes.
They are known as the suicide bags of the cell.
They destroy foreign particles and remove dead and worn out cells.

Mitochondria
These are rod shaped covered by double membrane.
It is the site for respiration.
It provides energy in the form of Adenosine triphosphate for various chemical activities hence it is called power house of cell.

Plastids
There are present only in plant cells and are of two types: Leucoplast and Chromoplast.
Green coloured plastids called chloroplast contain chlorophyll and are important for photosynthesis.
Chromoplast give colour to flowers and fruits.
Leucoplast store starch, oil and proteins.

Ribosomes

Vacuole
Animal cells have small sized vacuoles while plant cells have very large vacuoles.
They are covered by single membrane called tonoplast.
Turgidity and rigidity of plant cell is due to cell sap.

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