Class 9 Science Chapter 5 The Fundamental Unit Of Life Notes

9 Class Science Chapter 5 The Fundamental Unit Of Life Notes

Textbook	NCERT
Class	Class 9
Subject	Science
Chapter	Chapter 5
Chapter Name	The Fundamental Unit Of Life
Category	Class 9 Science Notes
Medium	English

Class 9 Science Chapter 5 The Fundamental Unit Of Life Notes. here we will be learn about Cell , Cell Theory , Type of Cells , Type of Organism , Cell Shape , Cell Size , Cell Wall , Nucleus , Cytoplasm , Endoplasmic Reticulum etc.

Class 9 Science Chapter 5 The Fundamental Unit Of Life Notes

Chapter - 5

The Fundamental Unit Of Life

Cell :-

All living forms are composed of microscopic units called as ‘Cells’.
A cell is the basic structural and functional unit of all life forms.
Study of structure and composition of cell is called Cytology’.

Discovery of Cell :-

Cell was first discovered and observed by Robert Hooke in a thin dead slice of cork in the year 1665.

First free living cell was discovered by A. V. Leeuwenhoek. in 1674.

Cell Formation :-

Protoplasm is an aggregate of various chemicals such as water, ions, salts and other organic molecules like proteins, carbohydrates, fats, nucleic acids, vitamins etc. along with cell organelles & nucleus that constitute a cell. It exists in sol-gel states.

Cell Theory :-

Two biologists, Schleiden and Schwann (1838) gave the Cell theory which states that :-

All plants and animals are composed of cells.
Cell is the basic unit of life.
All cell arise from pre-existing cells.

Viruses are the exceptions of cell theory.

Type of Cells :-

On the Basis of Type of Organization Cells are of two kind :-

Prokaryotic Cells
Eukaryotic Cells

Prokaryotic Cells :-

Very minute in size. ( 1 to 10⁻⁶ m )
Nuclear region (nucleoid) not surrounded by a nuclear membreane.
Always Unicellular
Single Chromosome present.
Nucleolus absent.
Cell division by fission or budding
Membrane bound cell organelles are absent.
Ex. Bacteria

Eukaryotic Cells :-

Fairly large in size. ( 5-100 μm )
Nuclear material surrounded by a nuclear membrance.
May be unicellular or multicellular.
More than one chromosome present.
Nucleolus present.
Cell division by mitosis or meiosis.
Membrane bound cell organelles are present.
Ex. All Plants, Animals, Amoeba etc.

Difference between Animal cell and Plant cell :-

Plant Cell	Animal Cell
Contain chloroplasts for phtosynthesis.	No chloroplasts
Have a cell wall to maintain structure and rigidity.	No cell wall
Usually do not contain lysosomes and Peroxisomes.	May Contain cilia and/or flagella
Cells are square and rigid or geometric shaped. Limited movement.	Cells are fluidic and flexible, many shapes.
Have one large central vacuole.	Cells can move around. Has small or no vacuoles. Have lysosome

Type of Organism :-

Organism are of Two Type :-

Unicellular organism
Multicellular organism

Unicellular Organism :- These organisms are single celled which perform all the functions. Example :- Amoeba, paramecium, bacteria.

Multicellular Organism :- Many cells grouped together to perform different function in the body and also form various body parts. Example :- fungi, plants, animals.

Cell Shape :-

Cells are of variable shapes and sizes. That varies is according to their function position. Generally cells are spherical but they may be elongated (nerve cell). branched (pigmented), discoidal (RBC). Spindle- shaped (muscle cell) etc.

Cell Size :-

Size of cell is variable depending upon the its position & function Some are microscopic while some are visible with naked eyes. Their size may vary from 0.2 um to 18 cm.

Size of typical cell in a multicellular organism ranges from 2-120 micron.
The largest cell is ostrich egg (15 cm long 13cm wide & weight 1.4 kg)
The longest cell is nerve cell (upto 1m).
Smallest cells so far known are PPLOS e.g., mycoplasma

Components of Cell :-

There is an occurrence of division of labour within a Eukaryotic cell as they all got certain specific components called ‘Cell organelles’. Each of them perform a specific function.

The three basic components of all the cells are :-

Plasma membrane
Nucleus
Cytoplasm

Cell Membrane/Plasma Membrance :-

Plasma membrane is selectively permeable in nature, means it allows or permits the entry and exit of some materials in and out of the cell.

Cell membrane is also called plasma membrane or plasma lemma.

Properties of Plasma membrane :-

It is the limiting boundary of each cell which separates cytoplasm from its surroundings.
It is found in both plant as well as animal cells.
It is the outermost covering of a cell in case of animals and lies below the cell wall in case of plants.
As per the liquid model of plasma membrane. It is made up of proteins and lipids where proteins are sandwiched between bilayer of lipids.
Singer and Nicholson gave the fluid mosaic model or liquid – bilayer model of plasma membrane.
It is flexible and can be folded, broken and reunited.

Functions of Plasma Membrane :-

It regulates the movement of molecules inside and outside the cell.
It helps in maintaining the distinct composition of the cell.

Transportation of molecules across the Plasma Membrane :-

This can be done by following ways :-

Diffusion :-

Movement of solutes or ions from a region of higher concentration to a region of lower concentration is called as diffusion. It does not require energy therefore, it is called as passive transport.

Osmosis :-

The movement of solvent or water from its higher concentration (solvent) to lower concentration (solvent) through a semipermeable membrane is called as osmosis.

Osmosis can also be called as ‘Diffusion of solvents’.

Endomosis :- Movement of solvent into the cell is called Endomosis.
Exosmosis :- Movement of solvent outside the cell is called Exomosis.

Cell Wall :-

It is the outermost covering of the plant cells and cells of fungi.
It is absent in animal cells.

Cell wall is rigid, strong, thick porous and non-living structure. In plant it is made up of cellulose and hemicelluloses. In fungi it is primarily made up of Chitin. Cell walls of two adjacent cells are joined by a layer called middle lamellae and microscopic channels called plasmodesmata for transport.

Functions of Cell Wall :-

It provides definite shape, structure, support and protection to the cell.
It provides strength to the cell.
It is permeable and allows entry of molecules of different sizes & thus control intercellular Transport.

Nucleus :-

Nucleus is the most important cell organelle which directs and controls all its cellular activities.
It is called as ‘Headquarter of the cell’/controller of cell.
It was discovered by Robert Brown in 1831.
In Eukaryotes, a well-defined nucleus is present while in Prokaryotes, a well- defined nucleus is absent.
Prokaryotes contain a primitive nucleus called Nucleoid.
It has double layered covering called as nuclear membrane.
Nuclear membrane has pores which regulate the movement of materials in & out of the Nucleus.
Besides nuclear membrane, nucleus also contains nucleolus and chromatin material. Chromatin is made up of DNA and Protein, that ultimatly condense and forms chromosome.
Chromosomes or chromatin material consists of DNA which stores and transmits hereditary information for the cell to function, grow and reproduce.

Functions of Nucleus :-

It controls all the metabolic activities cell and regulates the cell cycle.
It helps in transmission of hereditary characters from parents to their offsprings.

Cytoplasm :-

Cytoplasm was discovered by Kolliker in 1862. It is the site of both biosynthetic and catabolic pathways (Metabolic activities)

It can be divided into two parts :-

Cytosol :- Aqueous soluble part contain various fibrous proteins forming cytoskeleton. It contain about 90% water, 7% Protein 2% carbohydrates & 1% etc.

Cell organelles :- Living part of the cells having definite shape, structure and function bounded by plasma membrane. There are single membrane bound, double membrane bound and non membrane bound Cell organelles.

Endoplasmic Reticulum :-

It is the network of membrane bound tubules and sheet present in the cytoplasm. It was discovered by Porter, Claude and Fullam. These are present in all cells except prokaryotes and mammaliam erythrocytes.

Endoplasmic reticulum is of two types :-

Smooth ER :-

Made of tubules mainly.
Helps in steroid, lipids and Polysaccharide synthesis.
Ribosomes are absent.

Rough ER :-

Made of Cisternae and vesicles.
Helps in protein synthesis.
Contains ribosome on its surface.

Function of ER :-

It is the only organelle which serves as a channel for the transport of materials between various regions ofcytoplasm and between cytoplasm and nucleus.
It also functions as a cytoplasmic framework to provide surface for some of the biochemical activities. It forms endoskeleton of cell.
It helps in synthesis of fats, protien, steroids, cholesterol etc.
SER plays a crucial role in detoxification of drugs and poisonous by products.
Membrane biogenesis: Protein & Lipids produced by ER are used to produce cell membrane.

Golgi apparatus :-

Golgi apparatus consists of a system of membrane bounded fluid filled vesicles arranged parallel to each other in stacks called Cisternae along with some large and spherical vesicles. It was discovered by Camillo Golgi. It is absent in prokaryotes, mammalian RBC’s & sieve cells.

Functions of Golgi apparatus :-

Its function include the storage, modification, Packaging & secretion of products in vesicles.
It involved in the formation of lysosomes.
It is secretary in nature.
It helps in melanin synthesis.
It also involved in the synthesis of cell wall & plasma membrane.

Mitochondria :-

It is a rod shaped structure found in cytoplasm of all eukaryotic cells except mammalian RBC’s.

These are also absent in prokaryotes.
It was first seen by Kolliker in insect cells in 1880.
It is also called as ‘Power House of the Cell’ or the ‘Storage Battery’.
It is double membranous structure where outer membrane has specific proteins while inner membrane is folded inside to form chambers called Cristae.
Mitochondria has its own DNA & Ribosomes

Functions of Mitochondria :-

Its main function is to produce, store and release the energy in the form of ATP (Adenosine Triphosphate) The energy currency of the cell.
It is the site for cellular respiration (Kreb cycle) in which ATPare produced.

Ribosomes :-

Ribosomes are the sites of protein synthesis.

All structural and functional proteins (enzymes) coded by the nuclear DNA are synthesized upon cytoplasmic ribosomes. The DNA codes are transcripted into messenger RNA (MRNA) molecules, Which comes out of the Nucleolus and translated (Protein synthesis) by ribosomes attached to RER in the form of proteins.

Functions of Ribosomes :-

Ribosomes are the main site of protein synthesis. Synthesized proteins is transported by endoplasmic reticulum.

Plastids :-

It is double membranous, discoidal structure, found mainly in algae and plant cells.

Besides being discoidal or rhombic in plant cells, they occur in variable shapes like in (algae.) They can be ‘U’- shaped, spiral, coiled, ribbon- shaped etc.

Vacuoles :-

These are membrane bounded regions in the cytoplasm containing water and other substances.
They are bounded by a single membrane called Tonoplast.
In animal cells vacuoles are absent or smaller in size. In plant cells a single large vacuole is found which occupies about 90% of the volume of cell.

Functions of Vacuoles :-

It helps in maintaining osmotic pressure in a cell & stores toxic metabolic products (Waste product, water, sugar, protein etc.) of plant cell.

Lysosome (Suicidal Bag) :-

They are tiny membrane bound cell organelle containing powerful digestive enzymes for intracellular digestion.
Lysosome absent in RBC’s
Lysosomes are synthesised by golgi body & enzymes present in it are synthesised by RER.

Functions :-

Their main function is phagy (digestion). Means they breakdown worn out cell parts.
They are kind of waste disposal system of the cell.
They help in digesting foreign materials like invading viruses and bacteria in the cell.

Suicidal Bag :-

During disturbances in cellular metabolism (i.e., in case of cell damage), lysosomes burst and their enzymes are released into the cytoplasm which digest their own cell. So they are also called ‘Suicidal Bags’.

Cell Division :-

New cells are formed in organisms in order to grow, to replace old, dead and injured cells, and to form gametes required for reproduction. The process by which new cells are made is called cell division. The are two main types of cell division:

Mitosis :- The process of cell division by which most of the cells divide for growth is called mitosis. In this process, each cell called mother cell divides to form two identical daughter cells. The daughter cells have the same number of chromosomes as mother cell. It helps in growth and repair of tissues in organisms.

Meiosis :- Specific cells of reproductive organs or tissues in animals and plants divide to form gametes, which after fertilisation give rise to offspring. They divide by a different process called meiosis which involves two consecutive divisions. When a cell divides by meiosis it produces four new cells instead of just two. The new cells have only half the number of chromosomes than that of the mother cells.