Tanvi Ma'am will discuss important MCQs for Chapter 5 - The Fundamental Unit of Life. These MCQs are important for your Term 1 preparation. The MCQs for Chapter 5 - The Fundamental Unit of Life will be covered in two parts. This is the first part.
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Notes:
Chapter 5
The Fundamental Unit Of Life
Class 9 Science | CBSE | NCERT
Revision Notes
Cell and its Discovery
Cell is the structural and functional unit of all living organisms.
In 1665, Robert Hooke first discovered and introduced the term cell.
A cell generally shows Plasma membrane, Nucleus and Cytoplasm.
The size, shape and volume of the cell are related to the specific function that they perform.
Cell Theory
Cell theory was given by Schleidan and Schwann.
It stated that all the plants and animals are composed of cells and the cell is the basic unit of life.
Virchow (1855) Expanded the cell theory by suggesting that all cells arises from pre-existing cells.
Cell wall and Cell Membrane
1. Plasma membrane is a thin, selectively permeable membrane, Covering the cell and is made up of lipids and proteins.
Functions of plasma membrane -
It separates the contents of a cell from its outside environment.
It regulates the flow of substances to and from the cell through diffusion, facilitated diffusion, active transport and endocytosis.
2. Cell wall provides mechanical strength to the. sell it the cell withstand huge changes in the surrounding medium.
3. Cells of plants, fungi and bacteria - Contain both plasma membrane and cell wall. cell wall is rigid, non living an outermost covering, composed mainly of cellulose.
Osmosis
Osmosis is diffusion of water through a selectively permeable membrane.
If a cell is placed in different solutions -
Hypotonic solution - A cell placed in it will gain water.
Hypotonic solution - A cell please in it will lose water, Also known as plasmolysis
Isotonic solution - A cell placed in it neither gain or lose water.
Cell organelles:
1. Nucleus and Chromosome
Is an important, spherical, usually centrally located constituent of the cell and is bounded by a double layer nuclear envelope.
The nucleus of a dividing Cell shows rod shaped chromosomes, made up of DNA and proteins. in and non dividing cell, the chromosome elongate and take the form of thread like chromatin
DNA molecules are responsible for transmitting hereditary information from one generation to the next.
Nucleus controls all metabolic activities of the cell.
2. Cytoplasm
It is the fluid content of the cell, occurring between nucleus and plasma membrane. It stores several vital chemicals and is the site of certain important metabolic Pathways.
Several specialised cell organelle is our present in the cytoplasm. These organelle perform different kinds of metabolic activities and are kept separate from each other.
3. Endoplasmic reticulum(ER)
It Is an extensive, interconnected, membrane bound network of tubes and sheets
Ribosomes Are attached to the surface of a rough endoplasmic reticulum (RER) and are absent in smooth endoplasmic reticulum (SER).
Ribosomes are sites of protein synthesis.
Functions of Endoplasmic reticulum (ER)
It synthesizes important (RER) and lipids(SER).
It provides a pathway for intracellular transport of materials.
SER of liver cells is important for detoxification.
4. Golgi apparatus
Golgi apparatus is a network of stacked, flattened, membrane bound sacs and vesicles.
Golgi apparatus carries out the storage, Modification and Packaging of substances manufactured in the cell and is also involved in lysosome formation.
5. Lysosomes
It is a spherical sac-like structure which contains powerful digestive enzymes and forms the water disposal system of the cell. They are known as “suicidal bags”
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