The Fundamental Unit of Life – Cell Class 9 Science

The Fundamental Unit of Life – Cell Biology Class 9

 

Cell is an important chapter when it comes to Biology Class 9 as it the basic unit of life and form the basis of biology as well. So, here in this article, you will get to know about Chapter 6 of NCERT Biology Class 9 Science which is going to help you in understanding the topic and its related terms and aspects at a glance. You can also consider this article for the Cell Biology notes of the fundamental unit of life – NCERT Biology Class 9. Here is the Table of Contents:

1. What is Cell?

2. What are the Characteristics of a Cell?

3. What are the functions of cells?

4. Who discovered Cell?

5. What is Cell theory?

6. What are the types of a cell?

7. Differentiation between Prokaryotic and Eukaryotic cells

8. Cell structure – Cell membrane, Nucleus, Cell wall and Cytoplasm

9. Cell Organelles – Golgi Apparatus, Endoplasmic Reticulum, Mitochondria, Lysosomes, Vacuoles, and Plastids

 

Let’s start with the definition of cell:

 

What is a Cell?

 

A cell is basically the structural and fundamental unit of life. If we were to break an organism to the cellular level, the smallest independent component that we would find is known as the cell. Cells are structural unit of all living beings as they provide structure to the body. They come in different shapes and sizes, just like bricks of the buildings. Based on a number of cells, all organisms are divided as unicellular (single cells) and multicellular (many cells).

 

What are the Characteristics of Cell?

 

1. Cells provide structure and support to the body of an organism.

2. Every cell has one nucleus and membrane-bound organelles in the cytoplasm.

3. The nucleus (major organelle) holds genetic information necessary for reproduction and cell growth.

4. Mitochondria are mainly responsible for the energy transactions vital for the survival of the cell.

5. Lysosomes digest unwanted materials in the cell.

6. Endoplasmic reticulum plays a significant role in the internal organisation of the cell by synthesising selective molecules and processing.

 

Now let’s understand why cell is important and what function do a cell perform in an organism:

What are the Functions of Cell?

 

A cell performs these major functions essential for the growth and development of an organism. Important functions of cell are as follows:

 

1.     Provides Support and Structure:  All organisms are made up of cells that provides the structural basis of all the organisms. The cell wall and the cell membrane are the main components that function to provide support and structure to the organism.

 

2.     Facilitate Growth: Cells facilitate growth by mitosis. In mitosis, the parent cell divides into the daughter cells. Thus, the cells multiply and facilitate the growth in an organism.

 

3.     Allows Transport of Substances: Various nutrients are imported by the cells to carry out various chemical processes going on inside the cells. The waste produced by the chemical processes is eliminated from the cells by active and passive transport.

 

4.     Produce and Provide Energy: Cells require energy to carry out various chemical processes. This energy is produced by the cells by process called photosynthesis in plants and respiration in animals.

 

5.     Aids in Reproduction: A cell aids in reproduction through the processes called mitosis and meiosis. Mitosis is termed as the asexual reproduction where the parent cell divides to form daughter cells. Meiosis causes the daughter cells to be genetically different from the parent cells.

 

Who discovered the Cell?

 

Discovery of cells is one of the remarkable advancements in the field of science. It helped us to learn that all the organisms are made up of cells, and these cells help in carrying out various life processes. The study of cells from its basic structure to the functions of every cell organelle is called Cell Biology.

 

Robert Hooke discovered the cell in 1665. He observed a piece of bottle cork under a compound microscope and noticed minuscule structures that reminded him of small rooms. Consequently, he named these “rooms” as cells.

 

Later AntonVan Leeuwenhoek observed cells under compound microscope with higher magnification. This time, he had noted that the cells exhibited some form of movement (motility). As a result, Leeuwenhoek concluded that these microscopic entities were “alive.”

 

In 1883, Robert Brown, a Scottish botanist, provided the very first insights into the cell structure. He was able to describe the nucleus present in the cells of orchids.

 

What is Cell Theory?

 

Cell Theory was proposed by the German scientists, Theodor Schwann, Matthias Schleiden, and Rudolf Virchow which states that:

 

1. All living species on Earth are composed of cells.

2. A cell is the basic unit of life.

3. All cells arise from pre-existing cells.

 

What are the Types of Cells?

 

Based on cellular structure, the cells are dived into two types, viz., Prokaryotic Cell and Eukaryotic Cell.

 

Here is the differentiation between the Prokaryotic and Eukaryotic Cell:

 

PROKARYOTIC CELL	EUKARYOTIC CELL
1  Prokaryotic cells are cells with no nucleus. Instead, some prokaryotes have nucleoid which is a region within the cell where the genetic material is freely suspended.	1  Eukaryotic cells are characterised by a true nucleus.
2  The cell size ranges from 0.1 to 0.5 µm in diameter.	2  The size of the cells ranges between 10–100 µm in diameter.
3  They all are single-celled microorganisms like archaea, bacteria, and cyanobacteria.	3  This broad category involves plants, fungi, protozoans, and animals.
4  Prokaryotes reproduce by binary fission, a form of sexual reproduction.	4  They reproduce sexually as well as asexually.

Cell Structure:

 

The cell structure comprises of components which perform functions essential to carry out life’s processes.

 

1.     Cell Membrane:

The cell membrane is the outer covering of a cell in which all other organelles are enclosed. It is also called the plasma membrane. It forms the wall-like structure between two cells as well as between the cell and its surroundings. By structure, it is a porous membrane (with pores) which permit the movement of selective substances in and out of the cell.

Major functions of cell membrane are –

i. The cell membrane supports and protects the cell.

ii. It controls the movement of substances in and out of the cells.

iii. It separates the cell from the external environment.

 

2.     Cell Wall:

The cell wall is present exclusively in plant cells. The cell wall is the most prominent part of the plant’s cell structure which is made up of cellulose, hemicellulose and pectin. The cell wall is also the outermost layer of plant cells. Major functions of cell wall are –

i. It protects the plasma membrane and other cellular components.

ii. It is a rigid and stiff structure surrounding the cell membrane.

iii. It provides shape and support to the cells and protects them from mechanical shocks and injuries.

 

3.     Cytoplasm:

The cytoplasm is a thick, clear, jelly-like substance present inside the cell membrane. Major functions of cytoplasm are –

i. Most of the chemical reactions within a cell take place in this cytoplasm.

ii. The cell organelles are suspended in this cytoplasm.

 

4.     Nucleus:

Nucleus has highly extended, elaborate nucleoprotein fibers called chromatin, nuclear matrix, and nucleoli. The nucleus protects the DNA  and is an integral component of a plant’s cell structure. Major functions of nucleus are –

i. The nucleus contains the hereditary material of the cell, the DNA.

ii. It sends signals to the cells to grow, mature, divide and die.

iii. The nucleus is surrounded by the nuclear envelope that separates the DNA from the rest of the cell.

 

5.     Cell Organelles:

Cells comprise several cell organelles that perform specialised functions to carry out life processes. Every organelle has a specific structure. The different cell organelles, along with its principal functions, are as follows:

 

1. Endoplasmic Reticulum (ER): they are the tubular structure scattered in the cytoplasm.

a). Rough endoplasmic reticulum (RER) bears ribosomes on its surface. They are involved in protein synthesis and secretion.

b). Smooth endoplasmic reticulum (SER) does not bear ribosomes on its surface. They are involved in lipid synthesis and steroidal hormones.

 

2. Golgi apparatus: they consist of many flat, disc-shaped sacs or cisternae stacked parallel to each other. Golgi apparatus performs the function of packaging of materials and its transportation.

 

3. Lysosomes: the suicidal bags. They are membrane-bound vesicular structures which are rich in hydrolytic enzymes- lipase, protease, and carbohydrates active at acidic PH. These enzymes are capable of digesting carbohydrates, proteins, lipids, and nucleic acids.

 

4. Vacuoles: they are membrane-bound space found in cytoplasm containing water, sap and excretory product. They are bound by single membrane. They are responsible for formation of contractile vacuole and food vacuole in many organisms.

 

5. Mitochondria: the powerhouse of the cell. They are the double membrane-bound structure with the outer membrane and inner membrane dividing its lumen in two compartments. Mitochondria are sites for aerobic respiration and they produce cellular energy in form of ATP.

 

6. Plastids: they are found only in plant cells and in Euglenoids. There are different types of plastids –

 

i. Chloroplast contains chlorophyll that traps solar energy for photosynthesis.

ii. Chromoplast provides yellow, orange and red colours to different parts of plants.

iii. Leucoplasts are colourless plastids that store food, amyloplasts (carbohydrates), elaioplasts (oils) and aleuroplasts (proteins).

 

7. Centrosome: it is an organelle containing two cylindrical structures called centrioles. Central part of centriole is called hub and peripheral fibrils are called spokes. Every chromosome has a primary constriction or the centromere, on the sides of which disc-shaped kinetochores are present.

Conclusion:

 

We can conclude that cells are the structural and functional unit of life. This is because they are responsible for providing structure to the organisms and performs several functions necessary for carrying out life’s processes.

Browse the video Introduction to Cell

 

Takshila learning is offering Animated course for NCERT Class k-10 for all subjects and CBSE Online Classes for NCERT Class 11 & 12 for Commerce and Science that are completely bases on the latest syllabus of CBSE Board so that you can study independently with utmost ease at your own pace without the need of any external help from tutor or parents. Our School Online Courses includes NCERT guide/solutions, Notes, Videos, Study Material, Sample question papers based on CBSE pattern.

For more details, call @ 8800999280 / 8800999283 / 8800999284 or fill the form for any other details:

 

 

Tag – Characteristics of a Cell /  the functions of Cell /  discovered Cell / Cell theory / Types of cell / Differentiation between Prokaryotic and Eukaryotic cells / Cell structure / Cell Organelles