The fundamental unit of life class 9 CBSE notes - chapter-5 New St. Mery English School

 What is cell?

Ans:- Cell is a fundamental unit of life because every life is dependent on it. It is a building block of life because millions of cells combined together to constitute an organism. It is also called structural unit of life because it gives shape to the body. It is also called functional unit of life because it performs all the functions that a living organism do.

What are unicellular organisms?

Ans:- Those organisms that are made of only one cell are called unicellular organisms.

Ex:- amoeba,  

What are multicellular organisms?

Ans:- Those organisms that are made of more than one cells are called multicellular organisms.

Ex:- trees, animals 

Discovery of cell

Cell was first discovered by Robert hook in 1665. He discovered it while he was examining a thin slice of cork under the microscope made by him. The cork is obtained from the bark of tree. Robert Hooke saw that the structure of cork is same as the structure of a honeycomb consisting of many little compartments. He named these little compartments cell.

the words cell is derived from Latin words which means small room.

Leeuwenhoek discovered free living cells in pond water in 1674.

Robert Brown discovered Nucleus of a cell in 1831.

Purkinje discovered Protoplasm in 1839.

Cell Theory

Cell theory was presented by two biologists, Schleiden( शिल्डन ) in 1838 and Schwann ( श्वान ) in 1839 

In this theory they proposed that

1- All the plants and animals are composed of cells

2- The basic unit of life is cell.

This cell theory latterly expended by Virchow (वारकाओ ) in 1855.

He said that Cells arise from pre-existing cells. 

Cell Membrane / Plasma Membrane

Cell Membrane is the outer most covering of the cell that  separates the contents of the cell from external environment. It allows the entry and exit of some materials in and out of the cell. It also prevents movement of some other materials.

Why Cell Membrane is also called selectively permeable membrane?

Ans:- Cell Membrane is also called selectively permeable membrane because It allows the entry and exit of some materials in and out of the cell. It also prevents movement of some other materials.

Characteristics of Cell Membrane

The characteristics of cell membrane are

1- It is thin , elastic and flexible

2- It is living

3- It is the outer most covering of a cell

4- It holds the content of cell

5- It provides a definite shape of a living organism\

6- It facilitates movement of some materials because it is selectively permeable

7- It is made up of organic molecules that is lipids and proteins.

8- It it flexible therefor it helps the cell to engulf

What are cellular activities ?

Ans:- cells are living organisms. they do all the functions like digestion, respiration, making proteins, making carbohydrates etc that is done by a living organism. All the activities that is done by a cell to survive are called cellular activities.

Movement across Cell Membrane

Diffusion

What is Diffusion?

A spontaneous movement of molecules from a region of high concentration to lower concentration is called diffusion.

The rate of diffusion is greatest in gas, lowest in liquid and very lowest in solid.

gases > liquids > solids

Some substances that showed diffusion are ions, molecules, carbon dioxide, oxygen, water etc

What is diffusion in cell?

Ans:- Due to cellular activities, carbon dioxide is produced in a cell. The concentration of carbon dioxide in a cell is greater than the concentration of carbon dioxide in external environment. due to high concentration, the carbon dioxide formed in cell flows towards the external environment. This is called the diffusion in cell. 

carbon dioxide leaves the cell through diffusion

osmosis

What is solution?

Ans:- A homogeneous mixture of two or more components in which one is solvent and others are solute is called solution.

Solute + solvent = solution

How many types of solution?

There are three types of solution

1- hypertonic solution

2- hypotonic solution

3- Isotonic solution

What is hypertonic solution?

Ans:- Those solutions in which solute is more than solvent is called hypertonic solution.

What is hypotonic solution?

Ans:- Those solutions in which solute is less than solvent is called hypotonic solution.

What is isotonic solution?

Ans:- Those solutions in which solute is equal to the solvent is called isotonic solution.

What happens when we drop a raisin in plain water and a raisin in water in which sugar is dissolved

What happens when a cell is in hypertonic environment? 

Ans- When a cell is in hypertonic environment than the liquid present in cell move towards the hypertonic environment. 

What happens when a cell is in hypotonic environment? 

Ans- When a cell is in hypotonic environment than the liquid present in hypotonic environment  move towards the cell. 

What happens when a cell is in isotonic condition? 

Ans- When a cell is in isotonic condition than the liquid does not show movement.

What is endosmosis?

Ans- The movement of water into the cell from the environment is called endosmosis. Hypotonic is the example of endosmosis. 

What is exosmosis? 

Ans- The movement of water into the surrounding from the cell is called exosmosis. Hypertonic is the example of exosmosis. 

What is osmosis? 

The movement of water from higher concentration to lower concentration is called osmosis. 

Cell absorbs Water through osmosis.  No energy is required for the osmosis in cell.  The process of osmosis lasts upto equilibrium state. 

What is plasmolysis? 

Ans- The process by which living plant cell shrinkage  due to exosmosis is called plasmolysis. 

What is plasmolysid cell? 

Ans- The cell that is shrinkage due to exosmosis is called plasmolysid cell. 

Call Wall 

How many types of cell? 

There are two types of cell. 

1- plant cell- cell that is present in plant is called plant cell 

2- animal cell - cell that is present in animal is called animal cell. 

Characteristics of cell wall

1- cell wall is only present in plant cell. 

2- cell wall is non living.

3- Cell wall is freely permeable.

4- cell wall determines shape of cell

5- cell wall protects the contents of cell.

6- cell wall is made up of cellulose. cellulose is made up of carbohydrate.

7- cell wall provides strength to the cell.

8- cell wall provides turgidity to the cell so that the cell does not rapture due to endosmosis

Write some difference between cell membrane and cell wall

Cell membrane	Cell wall
1-It is found in both plant and animal cell	1-It is found in plant cell only
2-It is the outer most covering in animal cell but inner to the cell wall in plant cell.	2- It lies outside of the plant cell
3-It is living	3-It is non living
4-It is flexible	4-It is rigid
5-It is selectively permeable	5- It is permeable and allow every thing to go into the cell.
6-it is made up of lipids and proteins	6-It is made up of cellulose
7-It holds inner content of cell	7-It provides protection and strength to the cell
8-It control passage of materials	8-It does not control passage of materials

Nucleus

Nucleus is a cellular component that is centrally located in a cell. It is also the largest cell structure. 

There are two components of nucleus

1- Nuclear Envelope

2- Nucleoplasm

Characteristics of nuclear Envelope

1- It is composed of two nuclear membranes.

2- It covers the nucleus.

3- It separates nucleus from cytoplasm.

4- Nuclear envelop have pores, These pores are called nuclear pores.

5- It permit the materials to transfer between nucleoplasm and cytoplasm.

Characteristics of Nucleoplasm

1- It is liquid ground substance of a nucleus

2- It is covered by Nuclear Envelope.

Nucleoplasm is made of two substance

1- Nucleolus

2- Chromatin material

Nucleolus

It is one or more in number in Nucleoplasm. Nucleolus also form ribosomes. These ribosomes help the cell to form protein. A cell need protein to work.

Chromatin material

Chromatin materials are thread like structures which are Entangled to each other. During cell division, chromatin material gets organised into chromosomes.

Chromosomes

Chromosomes are thread like structure that have definite shape. They are visible during cell division. Chromosomes are made of two types of components that is DNA ( Deoxyribonucleic acid ) and Histones proteins

1- DNA ( Deoxyribonucleic acid )

 Chromosomes consist DNA and DNA consists genes . These genes are transferred from parents to children. The nature of parents and children are similar due to genes. Genes carry genetic information from one generation to other. So we can say that DNA is responsible to transfer genetic information from one generation to other.  Genes are the functional segment of DNA.  

Cytoplasm

Cytoplasm is a cellular component that is found between plasma membrane and nuclear envelope. Cytoplasm is made up of aqueous substance called cytosol. In cytosol, cell organelles are present.

Eukaryotic cell

Eu means true and karyotic means nucleus.

Those cells that have true nucleus are called Eukaryotic cell

Prokaryotic cell

Pro means before or primitive. 

Prokaryotic cell is The earliest known cell on earth. It lacks a distinct nucleus and other organelles due to the absence of internal membranes. 

Bacteria is the best known Prokaryotic organism. 

Difference between prokaryotic cell and eukaryotic cell

Prokaryotic Cell	Eukaryotic Cell
The size of Prokaryotic Cell is 1-10 µm ( micro meter)	The size of Eukaryotic Cell is 5-100 µm micro meter
The nucleus is absent in prokaryotic cell	The nucleus is present in Eukaryotic Cell
The nucleolus is absent in Prokaryotic Cell	The nucleolus is present in Eukaryotic Cell
Cell organelles is absent in Prokaryotic Cell	Cell organelles is present in Eukaryotic Cell
There is a single chromosome in prokaryotic cell	There is more than one chromosome in eukaryotic cell

 

Cell organelles

What are cell organelles?

Ans:- The cellular components of cell that is responsible for different function in a cell like providing shape and support, locomotion, reproduction, digestion, synthesis in protein etc are called cell organelles. They are membrane bounded organelles. They are present in cell to support complex activity of cell.

How many types of cell organelles in a cell on the basis of presence or absence of membrane

There are three types of cell organelles in a cell on the basis of presence or absence of membrane. 

1- organelles without membrane - cell wall, ribosomes and cytoskeleton are some organelles that do not have membrane. They are present both in the prokaryotic and the eukaryotic cell.

2- Single membrane -bound organelles - vacuole, lysosome, golgi apparatus, endoplasmic reticulum are Single membrane -bound organelles. They are present only in eukaryotic cell. 

3- double membrane -bound organelles - nucleus, mitochondria, and chloroplast are double membrane -bound organelles. They are present only in eukaryotic cell. 

Vacuoles

What is vacuoles

Vacuoles is the Single membrane -bound organelles. They are used to store something that is either solid or liquid so that its other name is storage sac. It is present in both plant cell and animal cell.

Difference between vacuoles in animal cell and vacuoles in plant cell

Vacuoles in animal cell	Vacuoles in plant cell
It is smaller in size	It is large and distinct.
It is temporary and it get extinct when it is not functioning in cell	It is permanent
It stores glucose, glycogen, and protein	It stores cell sap like amino acids, sugars and organic acid
	Plant cell vacuoles Provide  turgidity and rigidity
	Central vacuoles of Some Plant may occupy 50 – 90 % of cell volume

   

Endoplasmic reticulum

Endoplasmic reticulum is a Single membrane bound organelle. It has definite shape because it is bounded by membrane. It is a large network of tubes and sheets. Endoplasmic reticulum is sin in three forms in a cell.

1- long tubules

2- vesicles वेसिकल्स  ( oblong bags ) (The meaning of oblong bag is stretched bag )

3- cisternae ( closed, fluid filled sacs )

Endoplasmic reticulum is attached through nucleus from one side and through plasma membrane from another side.

How many types of Endoplasmic reticulum ?

There are two types of Endoplasmic reticulum.

1- Rough Endoplasmic reticulum - The part of Endoplasmic Reticulum where the Ribosomes present on surface. Due to presence of Ribosomes, their surface appears rough. This part of Endoplasmic reticulum is called Rough Endoplasmic Reticulum. Ribosomes synthesis protein. Cisternae has ribosomes, hence it is Rough Endoplasmic Reticulum.

2- Smooth Endoplasmic reticulum - The part of Endoplasmic Reticulum where the Ribosomes absent on surface. Due to absence of Ribosomes, their surface appears smooth . This part of Endoplasmic reticulum is called smooth Endoplasmic Reticulum. Long Tubules do not have Ribosomes, hence it is smooth Endoplasmic Reticulum.

Functions of Endoplasmic reticulum

1- RER ( Rough Endoplasmic reticulum )  synthesize proteins.

2- SER ( Smooth Endoplasmic reticulum ) manufactures fat molecules.

3- ER ( Endoplasmic reticulum ) shows Membrane biogenesis. It  form Plasma membrane

( genesis means generate ) 

4- Protein and lipids (Fat molecules ) act as hormones and enzymes.

5- ER ( Endoplasmic reticulum ) forms network system.

6- Er helps to transport materials between cytoplasm and nucleus.

7- ER ( Endoplasmic reticulum ) detoxify poisons and drugs.

8- ER ( Endoplasmic reticulum ) form a cytoplasmic framework for biochemical activities

Golgi apparatus : Cell organelles

Golgi apparatus is first described by camillo golgi.

Golgi apparatus is a cell organelles that consists a system of membrane bound that is vesicles, cisternae, and vacuoles. in Golgi apparatus cisternae arranged parallely to each other just like stacks called cisterns. Golgi apparatus is present as network near nucleus in animal cell. Golgi apparatus is present as freely distributed submits in plant cell that is called dictyosomes in plant cell.

Golgi apparatus has two faces.

1- Cis face- It is present towards the nucleus in a cell

2- Trans- It is present towards the plasma membrane in a cell

Golgi apparatus is first described by Camillo Golgi.

Function of Golgi apparatus

Golgi apparatus nucleus के द्वारा बनाये गए किसी भी प्रोडक्ट को Cis की सहायता से store करता है , उसके बाद उसमे मॉडिफाई करता है। मॉडिफाई के बाद फिर उसका पैकिंग कर जहाँ भी भेजना होता है , उस स्थान पर भेज देता है। 

1- Golgi apparatus stores, modified and packages the products.

2-Golgi apparatus converts simple sugar into complex sugar.

3- Golgi apparatus involved in the formation of lysosomes.

Lysosomes - Cell organelles 

Lysosomes is a single membrane bound organelle. It is spherical in shape and a sac like structure.It is filled with digestive enzymes. This digestive enzymes stored in lysosomes is made by Rough Endoplasmic reticulum. This enzymes break down the complex substances into simpler substances. Lysosomes is a kind of waste disposal system of a cell. It helps to clean cell by digesting foreign material like bacteria, food and viruses. It also helps in digestion of worn out cell organelle. It is also known as suicide bags of a cell. When a cell gets damaged, lysosomes may brust and enzymes digest their own cell.

Plastids - Cell organelles

Plastids are membrane bound organals. They are present in most plant cell. They are absent in animal cells. Plastids have own DNA and Ribosomes. 

How many types of plastids?

Ans:- There are two types of plastids.

1- Chromoplasts ( coloured plastids )

2- Leucoplasts ( white and colourless plastids )

What are chromoplasts?

Ans:- Chromoplasts are coloured plastids. It has coloured pigments. chloroplasts is a type of chromoplasts that carry green pigments called chlorophyll. Chlorophyll that is present in chlorolasts provide green colour to the plant. Chloroplasts also contain yellow and orange pigments.

What is leucoplasts?

Ans:- Leucoplasts are colourless plastids. It has no coloured pigments. It stores food like starch, oils and protein granules.

Structure of chloroplast  

Just as the matrix of cell is cytoplasm and the matrix of nucleus is neucloplasm, same as the matrix of chloroplast is called stroma. The disk like structures present in stroma that is arranged like stack. one disk like structure is called thylakoid but the stack of disks is called granum. A group of stacks is called granna. All the granna are connected by a structure called stroma lemele. The chlorophyll is present on the surface of thylakoid as dot like structure. 

Function of chlorophyll

1-The colour of chlorophyll is green. The colour of leaves and small stems are green due to chlorophyll. 

2- Plants perform photosynthesis with the help of chlorophyll.

Function of chromoplasts

Chromoplasts have colour pigments. These pigments provide colour to flowers and fruits.

Cell devision

The process of division of cells into new new cells is called cell devision.

Reasons of division of cells

There are three reasons of division of cells.

1- Cell division performs in a living organism for growth of organisms.

2- Cell division performs in a living organism for replace old, dead and injured cells.

3- Cell division performs in a living organism for gamete formation

Gamete formation

There are 46 chromosomes in a human cell. but the sperm formed by the male reproductive system has 23 chromosomes and the eggs formed by the female reproductive system has 23 chromosomes. When the sperm and egg fuse together they form cell. now this cell has 46 chromosomes. These sperms and eggs are called gametes.

What is diploid cell?

Ans:- cell that has two chromosomes is called diploid cell.

What is haploid cell?

Ans:- The cell that has one chromosome is called haploid cell.

What is the meaning of DNA replication?

Ans:- making photo copy of DNA is called DNA replication.

Types of cell division

There are two types of cell division

1- mitosis

2- meiosis

Mitosis

A cell that has two chromosome is called diploid cell. These chromosomes has DNA. The cell replicate its DNA and make its chromosomes double. Now the new formed cell has four chromosomes. Now this cell divides itself into two new cells. Now each new formed cells has two chrosomes. This type of cell division is called mitosis.

The number of chromosomes of parent cell and daughters cells are same in mitosis. Only one time the cell division perform in mitosis

Meiosis

A cell that has two chromosome is called diploid cell. These chromosomes has DNA. The cell replicate its DNA and make its chromosomes double. Now the new formed cell has four chromosomes. Now this cell divides itself into two new cells. Now each new formed cells has two chrosomes. Now these formed daughter cells divide themselves into two cells. Now the number of daughter cells are four and each daughter cells has one chromosomes. this type of cell divison is called meiosis.

In meiosis the number of chromosomes present in daughter cell is half from its parents cell.  In meosis the cell division completed in two steps.

Gamete formation is performed by the help of meiosis.

Difference between mitosis and meiosis

Mitosis	Meiosis
In mitosis, only one cell division occurs.	In meiosis, two cell divisions occur.
In mitosis, two daughter cells are formed.	In meiosis, four daughter cells are formed
In mitosis, the daughter cells are diploid cells.	In meiosis, the daughter cells are haploid cells.
In mitosis, the daughter cells are identical.	In meiosis, the daughter cells are different.
Mitosis occurs for growth and repair of tissues.	Meiosis occurs for gamete formation.