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The Fundamental Units of Life Notes for Class 9

The Fundamental Units of Life Notes:

The fundamental unit of life notes for class 9

Are you searching for biology notes of class 9 for revision? You are at right place. In this section, we have provided you with the fundamental units of life notes for class 9. These CBSE notes include cell theory, plant and animal cells, diffusion, osmosis, Hypotonic and hypertonic solutions, plasma and cell membrane, cell wall, nucleus, nucleoid, cytoplasm, endoplasmic reticulum, Golgi bodies, Lysosomes, Mitochondria, plastids and vacuoles.

Introduction to the cells:

  • All organisms on this earth are made up of cells.
  • Cells are the smallest structural and functional units of life. It is the primary unit of life.
  • It was discovered by Robert Hooke in early 1665.
  • The nucleus of the cell was discovered by Robert Brown in 1831.
  • Protoplasm was termed by Purkinje for fluid present in the cell.
  • A cell can exist independently as a whole organism and can carry out all the functions which are necessary for a living being. As unicellular organisms like amoeba exists and perform all the metabolic activities.

Read all the important topics orderly in the fundamental units of life notes to revise in a better way.

The cell Theory:

The cell theory given by two biologists Schleiden, Schwann and Virchow, states that:

  • All living organisms are composed of cells.
  • Cells are the fundamental units of life.
  • New cells are generated from the pre-existing cells.

Classification of Organisms:

On the basis of number of cells present in organisms, they are classified into two categories:

  1. Unicellular organisms
  2. Multicellular organisms

Explanation as per the fundamental units of life notes:

  1. Unicellular organisms: The organisms which are made up of single cells and perform all the essential activities of life is said to be unicellular organisms. Amoeba, Paramecium and some bacteria are some examples of unicellular organisms.
  2. Multicellular organisms: The organisms which are made up of a group of cells and perform different function to sustain the life of organism is called multicellular organisms. Plants, animals, fungi etc. are some examples of multicellular organisms.

Physical appearance of cells:

  • Different cells performing different functions have variable shape and size.
  • Cells may be spherical, oval, rectangular, or totally irregular like the nerve cell.
  • Every type of cell consist of cell organelle which perform different functions.
  • Average size of cells lies between 0.5 to 20 μ.

Types of cells:

There are mainly two types of cells in living organisms, they are:

  1. Prokaryotes
  2. Eukaryotes

Difference between Prokaryotes and Eukaryotes are:



In this type of cells nuclear membrane is absent.

This type of cells have nuclear membrane.

Size of cell lies between (1-10 mm).

Size of cell is lies between (5-100 mm).

Single chromosome is there.

Single or multiple chromosomes are there.

There is no nucleolus.

Nucleolus is there.

Always possess asexual reproduction.

Both Sexual, as well as asexual reproduction, takes place.

Always Unicellular.

In most cases, multicellular.

These lack membrane-bound cell organelles.

Membrane bound cell organelles are present in mitochondria.

There are no Centrioles.

Only animal cells possess Centriole.

Cell division takes place by binary fission.

Cell division takes place by Mitosis or Meiosis.

Bacteria, Blue-green algae are examples of prokaryotes.

Fungi, Plant cells etc. are examples of eukaryotes.

Difference table are very useful when you read the fundamental units of life notes.

Structure of Cell:

A cell is mainly composed of these basic parts:

  1. Cell membrane
  2. Cell wall
  3. Nucleus
  4. Cytoplasm

Read here in the fundamental units of life notes, the full criterion of structure of cells.

Cell membrane or plasma membrane:

  • It is the outer thin, delicate and elastic covering of the cell which separates internal components of the cell from the external environment.
  • It is present in cells of plants, animals and microorganisms and is a living part of the cell.
  • Plasma membrane are made up of lipids and proteins.

Properties of plasma membrane:

  • These membranes are flexible which enables cell to take in food and other materials from outside.
  • This process is said to be Through this process Amoeba acquires its food.

Functions of plasma membrane:

  • Plasma membrane controls the entry as well as exit of materials in the cell.
  • It also checks the movement of non-useful components in the cell. That is why it is also called selectively permeable membrane.

You will study in deatil in higher section of the fundamental units of life notes.

Cell wall:

  • In plant cells, there is another hard outer covering along with plasma membrane said to be cell wall.
  • It is over and outside the plasma membrane.
  • The cell wall of plants are composed of cellulose.
  • Cellulose is a complex substance and provides strength to plants.
  • Cell walls are present in Eukaryotic plant cells as well as Prokaryotic cells

Function of cell walls:

  • Cell walls define the shape and rigidity to the plant cell.
  • It protects the plasma membrane as it covers the membrane.
  • Cell walls prevents the dryness in the cell.
  • It also helps in transport of materials inside and outside the cells.
  • It helps the cell to withstand the changes in surrounding medium upto a greater extent.


  • Nucleus controls all the activities of the cell.
  • It is regarded as the brain of the cell.
  • Pores present in the nuclear membrane allows material transference are called nuclear pores.
  • When the cell is about to divide, a rod shaped structure is seen which clarifies the presence of chromosomes in the nucleus.
  • The fluid which present in the nucleus is called Nucleoid.

Functions of nucleus:

  • It controls all metabolic activities of the cell.
  • It has main role in cellular reproduction.
  • Nucleus directs chemical activities inside the cell.
  • Thus regulates the cell cycle.
  • It is also the storehouse of genes.
  • Genes transfers hereditary traits from the parent to offspring.

Revise the fundamental units of life notes as per NCERT pattern regularly.


  • The jelly like fluid material present inside the plasma membrane is said to be cytoplasm.
  • Many cell organelle are present in it which provides specific function to the cell.

Functions of cytoplasm:

  • Cytoplasm contains enzymes which are responsible for breaking down waste.
  • It is also responsible for providing the shape of the cell.
  • It also helps in exchange of substances between the organelles.
  • Cytoplasm stores important chemicals such as amino acid, glucose, vitamins and iron etc.

The fundamental units of life notes is mainly for CBSE students.

Common Terminology in cells:

  • Plasmolysis: The phenomenon by which a living plant cell loses water through osmosis and the contents inside the cell contracts is known as plasmolysis.
  • Nucleoid: Due to absence of nuclear membrane in some organisms like bacteria, the nuclear region may not be defined or poorly defined. These non-defined region containing nucleic acid is called nucleoid.
  • Diffusion: when there is spontaneous movement of materials from higher concentration region to lower concentration then it is called Carbon dioxide and oxygen diffuses through cell membrane.
  • Osmosis: The movement of water from higher concentration to lower concentration through semi permeable membrane is said to be osmosis. Plant cell obtain water through osmosis.
  • Hypertonic solution: The solution having a higher osmotic concentration than the surrounding medium. Example: larger amount of salts dissolved in it.
  • Hypotonic Solution: The solution having lower osmotic concentration than the surrounding medium. Example: lesser amount of salts.
  • Isotonic Solution: The solution having same osmotic concentration as that of the surrounding medium.

These are the important terminology of the fundamental units of life notes.

Cell Organelle:

To keep the cells alive and functional, different part of the cell carries different functions. These parts are said to be cell organelle.

Different cell organelle are:

Endoplasmic Reticulum (ER):

  • The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets.
  • Its appearance is like long tubules or round or oblong bags (vesicles).
  • It is not present in prokaryotic cells and matured RBCs of mammals.
  • The endoplasmic reticulum is very much similar to the plasma membrane.
  • Its constituents are also same i.e. lipids and proteins.

Types of Endoplasmic reticulum:

In the fundamental units of life notes we will read about two types of endoplasmic reticulum.

  1. Rough Endoplasmic reticulum (RER) – Ribosomes attached to its surface for manufacture of protein.
  2. Smooth Endoplasmic Reticulum (SER) – It helps in manufacture of fat molecules or lipids which is much important for cell function.

Functions of Endoplasmic reticulum:

  • It provides internal support to cell.
  • It is also involved in transport of various substances from nuclear membrane to plasma membrane or vice versa.
  • Endoplasmic reticulum also provides surface for biochemical activities of the cell.
  • Rough Endoplasmic Reticulum helps in synthesis and transportation of proteins.
  • Soft Endoplasmic Reticulum helps in synthesis and transportation of lipids.
  • These proteins and lipids help in building cell membrane also function as enzymes and hormones.
  • In vertebrates, Soft ER detoxifies many chemicals and drugs which are harmful for their body.

Wisely read and learn the fundamental units of life notes for class 9.

Golgi Apparatus (bodies)

  • It is a system of membrane bound vesicles which is filled with fluid, and vacuoles.
  • It has also closed sacks (cisternae) which are arranged approximately parallel to each other.

Function of Golgi apparatus:

  • It carries material which is synthesized near ER to various places inside and outside the cell.
  • It stores, modifies and packages the products in vesicles.
  • Lysosomes formation also involves Golgi bodies.

Moreover, the functions and differences are clear in the fundamental units of life notes

Lysosomes (suicidal bags):

  • Lysosomes are membrane-bound spherical sac like structure filled with digestive enzymes (made by soft ER).
  • Mostly they are found in eukaryotic cells.
  • It acts as a waste disposal system.

Function of Lysosomes:

  • It breaks down the foreign external material entering the cell.
  • Protects cell from harmful bacteria and viruses.
  • It keeps the cell clean.
  • During abnormal metabolism, as cell damages, then lysosomes burst and digest their own cell. So they are also called suicidal bags of the cell.

Biology study material is included in the fundamental units of life notes.


  • Mitochondria are very small rod shaped organelle.
  • It is the powerhouse of the cell.
  • It has two membrane covering. (outer is smooth and porous whereas inner membrane has number of folds called cristae)
  • The outer folds provides a large surface area for ATP generating reactions.
  • Mitochondria are not present in bacteria and RBC of mammals.
  • It contains its own DNA and ribosomes.

Functions of Mitochondria:

  • It is the site for cellular respiration.
  • It provides energy for all the important activities of the living cells needed for life.
  • During reactions the stored energy releases in the form of ATP. So mitochondria is also called “powerhouse of the cell”.
  • Mitochondria itself makes some of its proteins.

The complete CBSE material is available with the fundamental units of life notes.


  • These are present in almost every plant cells.
  • It is also a two membrane bound organelle.
  • It is of spherical in shape.
  • Mitochondria also have their own DNA and Ribosomes.

For exams take a look at the fundamental units of life notes.

Types of plastids:

  1. Chloroplasts: Green colored plastids containing chlorophyll.
  2. Chromoplasts: Colored plastids (other than green color).
  3. Leucoplasts: Colorless plastids.

Function of plastids:

  • Chloroplasts are involved in the process of photosynthesis.
  • The main role of chromoplast is to provide various colors to flowers to attract insects for pollination.
  • Leucoplasts has the main role in the storage of food in the form of starch, proteins etc.


  • These are the storage part of solid or liquid materials.
  • Small sized vacuoles are there in animal cells whereas in plant cells there are large vacuoles.
  • Almost 90% of the volume of cell is occupied by vacuoles in mature plant cells.
  • Many other organelles, including nucleus shift towards plasma membrane due to its size. Read the fundamental units of life notes throughout for better learnings.

Function of vacuoles:

  • They maintain osmotic pressure in a cell.
  • Vacuoles provide rigidity to the plant cells.
  • Vacuoles also acts as the storage of important chemicals as amino acids, organic acids, sugars etc.
  • Food vacuole of amoeba contains food what it has consumed.
  • Vacuoles in some unicellular organisms helps to remove excess of water from cell.

All the differences are mentioned in the fundamental units of life notes. Here difference between plants and animal cells are given.

Difference between plant cells and animal cells:

Plant cells

Animal cells

Have cell walls.

Do not have cell walls

Have Plastids

Do not have plastids

Large vacuoles are there

If vacuoles are there then it is of small size.

Centriole and centrosome are not there.

Centrosome are there with two or more centrioles.

Cells contain Golgi bodies (dictyosome).

It also contain Golgi bodies

The fundamental units of life notes is committed to give you detailed analysis of CBSE NCERT curriculum. CBSE notes will help you for better score. We have provided all the important discussions in the fundamental units of life notes. 

FAQ’s on The Fundamental Units of Life Notes:

What are Living Organisms Made Up of?

Living organisms are made up of cells which are the building blocks of the body. It was discovered by Robert Hooke. Moreover, you have already read in the fundamental units of life notes.

What is a Cell Made Up of? or What is the Structural Organisation of a Cell?

Cell is made up of different components they are cell wall, cell membrane, nucleus and cytoplasm.

What would happen if the plasma membrane ruptures or breaks down?

If the plasma membrane ruptures or breakdown then the cell will lose its ability to exchange material from its surrounding by diffusion or osmosis. Thereafter the cell will die as protoplasmic material will be disappeared.

Which organelle is known as the powerhouse of the cell? Why?

Mitochondria is called the powerhouse of the cell because they carry out the process of cellular aerobic respiration and generate much amount of energy molecules (ATP or Adenosine Triphosphate) for cell operation.

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