The Fundamental Unit of Life Class 9 Notes

The Fundamental Unit of Life Class 9 Notes – In 1665, Robert Hooke discovered the cellular structure of cork while examining a thin slice of it through a self-made microscope. He saw that the cork was made up of many small compartments, similar to the structure of a honeycomb. Hooke referred to these compartments as “cells”. The cell term derived from the Latin word for “little room”.

There are two main categories of cells: plant cells and animal cells.

The Fundamental Unit of Life Class 9 Notes

What is cell?

The fundamental building block of life and the structural and functional unit of every living thing is the cell. It is the smallest component of an organism capable of carrying out all vital functions. All living things, from simple single-celled creatures to complex multicellular ones like plants and animals, are made up of cells. There are different types of cells muscle cell, blood cells, nerve cell, ovum, bone cell, sperm and fat cell.

types of cell

Cellular respiration

Cellular respiration helps to transformation of the energy stored in food into a form usable by cells. During this process, glucose is taken in by the cells and transformed into energy in the mitochondria through a sequence of chemical processes. Cells utilise this energy to carry out a variety of tasks.

Structural Organisation of a Cell?

Cells Plasma membrane or Cell membrane

The cell membrane, sometimes referred to as the plasma membrane, is a slender membrane that surrounds the cell and divides its inside from its external environment. It is made up of a lipid bilayer and many proteins that combine to form a selectively permeable barrier that permits some substances to enter or exit the cell while blocking the passage of others.

Cell membrane have a several important functions

  1. Membrane help to maintenance of cell shape and structure
  2. Cell membrane is involved to transmitting signals between cells
  3. The cell membrane helps to protect the cell from its surroundings, providing a barrier against harmful substances.
  4. Cell membrane helps to break down nutrients.

Cell Wall

Plant cells have a rigid outer covering called the cell wall in addition to the plasma membrane. The cell wall is located outside the plasma membrane and is made up mainly of cellulose, a complex substance that gives plants structural strength. When a living plant cell loses water through osmosis, the contents of the cell shrink and move away from the cell wall, a phenomenon known as plasmolysis.


Nuclear membrane refers to the two-layered coating that surrounds the nucleus. The nuclear membrane has pores that enable material to move from the nucleus’ inside to its exterior, or to the cytoplasm. Only when the cell is prepared to divide do the chromosomes, which are rod-shaped structures, become visible in the nucleus.


A gel-like substance called cytoplasm fills a cell’s interior and is encased by the cell membrane. It includes the cytoskeleton and other cytoplasmic inclusions in addition to the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes, which are all cellular organelles.

The maintenance of cell structure, the movement of materials inside the cell, and the control of metabolic activities are all cellular processes that depend on the cytoplasm. Additionally, it facilitates the mobility of organelles and other cellular parts.

Cell Organelles

Every single cell has a membrane separating the interior from the external world. Use small, membrane-bound organelles in multicellular organisms to carry out various chemical tasks. These vital organelles, which can only be seen under a strong microscope, include the nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, and plastids.

animal cell
Animal cell

i) Endoplasmic Reticulum

The ER is a complex network of membrane-bound tubes and sheets within the cytoplasm of a cell. There are two types of ER: rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). The RER is covered in ribosomes, which are involved in protein synthesis, while the SER helps in the production of lipids needed for cell function. Some of these proteins and lipids contribute to the construction of the cell membrane and others function as enzymes or hormones.

endoplasmic reticulum
Endoplasmic Reticulum, Plant Cell

ii) Golgi Apparatus

The Golgi Apparatus is often referred to as the cell’s post office, as it processes and sends out proteins to different parts of the cell or to other cells.

iii) Lysosomes

Lysosomes are known as the cell’s garbage disposals because they have strong enzymes that can break down cellular waste and unwanted material. They also act as the cell’s defense mechanism by destroying invading foreign substances.

iv) Mitochondria

Mitochondria are referred to as the energy factories of the cell as they produce ATP through a process called the electron transport chain. They possess their own DNA known as mtDNA, making them somewhat self-governing organelles, able to create their own proteins.

v) Plastids

Plastids are a type of cell organelle found in plant cells, which are specialized structures with specific functions. There are various types of plastids including chloroplasts, leucoplasts and chromoplasts, each containing different pigments. Chloroplasts are involved in photosynthesis and contain chlorophyll, while leucoplasts store starch, oil and protein granules. Chromoplasts contain pigments that give color to flowers and fruits. Plastids have their own DNA and ribosomes, and can produce their own proteins.

vi) Vacuoles

Vacuoles are huge sacs that are either filled with air or water and assist give cells shape. In contrast to animal cells, where they are either completely absent or very tiny, they are frequently seen in plant cells.

Cell Division

The process through which a single cell splits into two or more daughter cells is known as cell division. This process is essential for the development of organisms as well as the growth and repair of tissues. The two primary processes of cell division are meiosis and mitosis. Meiosis is the process by which cells split into four genetically unique daughter cells, whereas mitosis is the process by which a single cell divides into two identical daughter cells. Depending on the requirements of the organism, these daughter cells can subsequently differentiate into specialised cells like muscle cells, nerve cells, or skin cells.


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