The Fundamental Unit OF Life CBSE Class 9 Notes

A summary and notes for revision are provided here for CBSE Class 9 Science Chapter 5, The Fundamental Unit of Life. In this article, you will find CBSE Key Notes, Images, and Diagrams of the entire chapter titled, The Fundamental Unit of Life that is taught in Class 9. Your next step, after studying the chapter thoroughly, is to memorize the notes.

We have compiled all the CBSE Class 9 notes for Chapter 5, The Fundamental Unit of Life in one place.

This CBSE Class 9 Chapter 5 Notes guide students through the concepts of the chapter, The Fundamental Unit of Life, and the importance of life and evolution over billions of years. Students are able to comprehend the topics covered in the CBSE Class 9 Notes Science Chapter 5 Notes. The revision notes provided here can help students prepare for their exams.

Cells are the fundamental unit of life. What makes a cell such an important structural and functional component of life?

This is because a cell is a small and specialized living entity that is responsible for carrying out a number of functions. An overview of cells and their characteristics is presented in the chapter – The Fundamental Unit of Life of Class 9. 

CBSE Class 9 Science Chapter Notes: The Fundamental Unit of Life

Cell: History & Features

  • History

The building blocks of all living things are said to be cells. The role cells play in the existence and sustenance of life on earth cannot be overstated.

The term ‘cell’ was introduced in 1665 by a scientist named Robert Hooke. Under his compound microscope, he examined a slice of cork. His observations changed the entire history of science. As he examined the cock slice under his microscope, he noticed thousands of small blocks that resembled honeycomb.

There was nothing else but cells. Cells were discovered as a result, which is the fundamental unit of life on earth.

  • Features

There are numerous types of cells in our bodies. The function of each cell in the body is integral to its overall health. The following are some characteristics of a cell:

  1. The simplest and smallest building blocks of life are cells.
  2. In a single organism, cells can be of different shapes and sizes.
  3. Each active cell performs a specific function. Among these functions are respiration, reproduction, growth, and many others.
  4. According to Cell Theory, every cell originates from a pre-existing cell. In other words, it means that a single cell divides into multiple cells as it grows.
  5. All cells are capable of dividing and forming new ones.

Cellular Respiration: Definition

In a cell, cellular respiration is the process by which energy is released from the mitochondria. As we eat, glucose is absorbed by our cells and utilized for energy production. Energy is received by the body through ATP.

Types oF Organisms

There are a wide variety of cell types in nature. Living cells in an organism fall into two broad categories:

  • Unicellular Organisms- In Biology, these are organisms that are more than just a single cell. The majority of these organisms are made up of prokaryotic cells, which do not have membrane-bound organelles or nuclei. The majority of microorganisms, such as bacteria, consist of just one cell.
  • Multicellular Organisms- Organisms with multiple cells are more complex and structured than organisms with a single cell. Multicellular organisms possess better structure and shape than unicellular organisms. A multicellular organism is made up of eukaryotic cells. These cells have membrane-bound organelles and a nucleus with a nuclear membrane.

Types oF Cells

The structural organization of the cell is determined by the arrangements of the structures inside the cell. Based on the above criteria, there are two main types of cells:

  • Prokaryotic Cells
  • Eukaryotic Cells

Difference between Prokaryotic Cells and Eukaryotic Cells

Prokaryotic CellsEukaryotic Cells
There is no nuclear membrane in the cells of organism. There is a nuclear membrane in the cells of organism. 
Nucleolus is absentNucleolus is present
Single chromosomes Single or multiple chromosomes
Reproduction is always asexualReproduction is both sexual and asexual
Always unicellularMostly multicellular
Centriole is absentCentriole is only present in animal cells
Membrane bound cell organelles are absentMembrane bound cell organelles are present
Cell division happens by binary fissionCell division happens by mitosis or meiosis
Example: Bacteria, Blue/Green AlgaeExample: Fungi, Plant and Animal Cell

Difference between Plant Cell and Animal Cell

Plant CellAnimal Cell
Cell wall is presentCell wall is absent
Plastids are presentPlastids are absent
Centrioles are absentCentrioles are present
Large-sized Vacuoles are presentVacuoles are absent
Golgi bodies are presentGolgi bodies are present and known as Dictyosome
Centrosome is absentCentrosome is present 

Cell Organelles

Cells contain several organelles within their cytoplasm. Every cell organelle looks and performs differently. Listed below are the different cell organelles and their functions:

  • Plasma Membrane- Cell Membrane or Plasma Membrane is referred to as the outermost covering of a cell. This structure provides shape and protection to the cell and all the cell organelles present inside it. Plasma Membranes permit only certain substances to pass through them. In other words, it suggests that the membrane of the cell is selectively permeable.
  • Diffusion- Diffusion is a natural phenomenon that is associated with the Cell Membrane. It happens when the molecules move across a Cell Membrane. Generally, these molecules flow from high concentration regions to low concentration regions. Gases like Carbon Dioxide and Oxygen move across the Plasma Membrane through the phenomena known as Diffusion.
  • Osmosis- Osmosis is identified as the passage of water molecules through a Semipermeable Membrane. In Osmosis, the water molecules move across a semipermeable membrane from a concentration region of low solute to a concentration region of high solute. It means if the surroundings of a cell have more water than the inside, the water molecules will flow from the surroundings to the inside of the cell and vice versa.
  • Cell Wall-  The Cell Wall is a structure that is unfamiliar to only Plant Cells. It means that the Animal Cells do not have a Cell Wall. The presence of a Cell Wall is a major difference between a Plant Cell and an Animal Cell. A Cell Wall is composed of Cellulose or other Biomolecules depending on the organism.

The main function of a Cell Wall is to provide rigidity and protection to a Plant Cell.

  • Nucleus- The Nucleus is the storage centre for all the genetic material inside a cell and that is why it is also known as the brain of a cell. The Nucleus is surrounded by a layer called a Nuclear Membrane. It covers the Nucleus that contains Chromatin fibres and Proteins. 

Chromatin fibres form Chromosomes during Cell Division. The Nucleus plays an important role in the initiation and completion of a Cell Cycle (Meiosis or Mitosis).

  • Cytoplasm- Cytoplasm is a fluid-like substance which is found throughout the surface of a cell. The Cytoplasm consists of all the organelles of a cell. The Cytoplasm also plays an integral role in the formation of a cell’s structure, just as the Cell Membrane does. In the cytoplasm, various cell organelles can be found.

Cytoplasm, however, is a place where various biochemical reactions are carried out, including glycolysis. 

  • Endoplasmic Reticulum-  The Endoplasmic Reticulum is a structure that is formed as a continuation of the Nuclear Membrane.

There are two varieties of the endoplasmic reticulum.

  1. Smooth Endoplasmic Reticulum (SER) – SER is distinguished by the absence of Ribosomes found on the surface of the Endoplasmic Reticulum. Despite not being a part of protein synthesis, they contribute to the production of lipid and fat molecules.
  2. Rough Endoplasmic Reticulum (RER) – RER has ribosomes on their surface and hence appear to be rough. The ribosomes are involved in Protein Synthesis. Thus, the Rough Endoplasmic Reticulum participates in the modification and folding of proteins.
  • Golgi Apparatus- This Cell Organelle appears as an arrangement of membranous vesicles placed parallel to each other. This structure is involved in the retention and transportation of complex molecules across the Cytoplasm.
  • Lysosomes- Lysosomes are the Cell Organelle that is responsible for maintaining the purity and cleanliness of the cell. It is why they are called ‘Suicide Bags’. They are referred to as the cell’s waste disposal system because they aid in cell cleaning by digesting debris and other outdated Cell Organelles. As a result of powerful enzymes, they can break down large organic materials.
  • Mitochondria- Mitochondria are a Cell Organelle that is responsible for generating energy; this is why it is known as the ‘Powerhouse of the Cell’. The glucose found in our food is further refined inside a cell to generate energy from it in the form of ATP.

Mitochondria are membrane-bound Cell Organelle that has their own genetic material.

  • Plastids- This is a term used for Cell Organelles that are present in Plant Cells only. Plastids refer to Chloroplasts and Chromoplasts. Chlorophyll is found in cell structures called chloroplasts. Thus, it is involved in Photosynthesis. 

Plant parts such as flowers, leaves, and fruits get their color from Chromoplasts.

  • Vacuoles- There are storage vesicles placed inside the cell, which are known as Vacuoles. As a result of these vacuoles containing solid or liquid materials, the cell is indirectly able to maintain its shape. 

Animal cells have smaller vacuoles, whereas plant cells have large Vacuoles.

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