The Fundamental Unit of Life CBSE Notes for Class 9
In the year 1665, Robert Hooke observed cork under a self-designed microscope. Cork is a part of the bark of the tree and when the cork was examined, Hooke found that it resembled honeycomb. The boxes of cork were known for ‘Cell’ which is given by Robert Hooke. The cell is a Latin word that means little room. After that, the field of biology got a new term called ‘Cell’ and became important in the history of science till now. To know more about the Fundamental Units of life, read the given information below.
Cell
All living organisms are made up of cells in this world. Also, some organisms are single organisms that live on their own. The cell is the basic unit of life. All animals and plants are made up of cells that are included in the cell theory that is presented by Schleiden and Schwann. Organisms such as Bacteria, Amoeba, Paramecium, and Chlamydomonas are unicellular organisms. On the basis of the specific functions of cells, the size and shape of the cell depend. The basic structure which forms an organism is referred to as cells.
Important to Know
- Robert Hooke was the first person who discovered cells in 1665.
- In 1831, the nucleus of a cell was discovered by Robert Brown.
- Purkinje coined the term ‘Protoplasm in 1839.
Unicellular organisms
Those organisms that are composed of a single cell are called as Unicellular organisms. E.g. Bacteria, Amoeba, Paramoecium etc.
Multicellular organisms
Those organisms that are composed of many cells are called as Multicellular Organisms. E.g. Plants, Animals Fungi, etc.
Prokaryotic cells
In the chapter of fundamental units of life, two types of cells are categorized. When a true nucleus is absent in the cell then it is known as a Prokaryotic cell. Prokaryotic cell-containing organisms are unicellular organisms.
Eukaryotic cells
When a true nucleus is present in the cell then it is known as the Eukaryotic cell. The Eukaryotic cell-containing organisms are multicellular organisms. Additionally, they consist of membrane-bound organelle, nucleus, and Mitochondria.
Difference between Animal and Plant Cell
Animal Cell |
Plant Cell |
The cell wall and chloroplast are absent in the animal cell.
Animal cells contain a nucleus at the centre. The small vacuoles or no vacuoles are present in the animal cell. |
The cell wall and chloroplast are present in the plant cell. Plant cells contain a nucleus at the periphery. The large vacuoles are present in the plant cell. |
Plant cell
Cell Composition
Some special components are present in the cell to function which is called Organelles. Every cell has a nucleus, plasma membrane or cell membrane, and cytoplasm which help cells to function accordingly.
1.) Plasma Membrane or Cell Membrane of Cell
A cell membrane or Plasma membrane is an outer membrane and the content of the cell is separated by this part. This is a selectively permeable membrane that allows few materials to enter and exit the cell. The Fluid mosaic model is the best when it comes to describing the cell membrane or plasma membrane structure.
Diffusion
From the region of high concentration to the region of low concentration when molecules move, it is called diffusion. It is an important process that exchanges gaseous between the cell and the cell environment. In the diffusion process, oxygen or carbon dioxide moves across the plasma or cell membrane. Both carbon dioxide and oxygen are examples of the Diffusion process.
Osmosis
When the water moves across the semi-permeable membrane then it is called osmosis.
Hypotonic Solutions
The cell can forcefully gain water if the surrounding has a higher water concentration and it happens through the osmosis process which is known as Hypotonic Solutions.
Isotonic Solutions
Across the cell membrane, when there will be no net movement of water between medium and cell then it is known as Isotonic Solutions.
Hypertonic Solutions
When the cell will lose water due to a lower concentration of water in the medium then the concentrated solution is called a Hypertonic Solution.
2.) Cell wall of Cell
The cell wall is a rigid outer covering of plant cells that is present outside the plasma membrane. The cell is an important differentiable character between plant and animal cells. The cell wall of the plant is made up of cellulose and helps to give structural strength to the plant.
Plasmolysis
The contraction of cell contents away from the cell wall due to water loss in plant cells, this phenomenon is known as Plasmolysis.
3.) Nucleus of cell
- In the cell, the nucleus consists of genetic material. The nucleus is present in the Eukaryotic cell as an organelle.
- Nuclear membrane is a double-layered covering that covers the nucleus. A rod-shaped chromosome is also present in the nucleus which is composed of proteins and specific molecules of deoxyribonucleic acid or DNA.
- The metabolic activities of cellular components and genetic characteristics are under the control of the nucleus.
- Genes are the functional segments of DNA and DNA possesses the information which is important for organizing cells.
- Organisms which do not contain a nuclear membrane are known as Prokaryotes.And, the organisms which contain nuclear membranes are known as Eukaryotes.
4.) Cytoplasm of Cell
A jelly-like, thick structure in which the nucleus is absent but the rest of the cell organelles are present and is enclosed by a cell membrane is referred to as Cytoplasm. The cytosol is another name for cytoplasm. The cytoplasm is mainly composed of water, proteins, and salts.
5.) Organelles in a cell
The cytoplasm of a cell contains many organelles which perform different functions of the cell. With the help of an electron microscope, few organelles can be viewed. The endoplasmic reticulum, Golgi complex, Smooth ER, Rough ER, Plastids, Mitochondria, Lysosomes, and Vacuoles are the organelles of cells.
ER or Endoplasmic Reticulum
A large network of membrane-bound tubes and sheets is also referred to as the Endoplasmic Reticulum. The plasma structure mainly resembles the ER membrane. The Endoplasmic Reticulum is divided into two types i.e. Smooth Endoplasmic Reticulum and Rough Endoplasmic Reticulum.
1.) Smooth Endoplasmic Reticulum or SER
In the cell, the fat molecules are manufactured by smooth Endoplasmic Reticulum. The detoxification of poisonous molecules and lipid metabolism include SER. Smooth ER does not take part in the photosynthesis process because of the absence of ribosomes.
2.) Rough Endoplasmic Reticulum or RER
The Ribosomes are mainly present in rough ER which are composed of proteins and nucleic acids. The sites of the rough endoplasmic reticulum are involved in protein synthesis. The folding of proteins also involves rough ER.
Golgi Apparatus
The formation of the lysosome involves the Golgi apparatus. Also, the Golgi apparatus is known for the post office of cells. The products of vesicles are packaged and modified by the Golgi apparatus.
Lysosome
The potent enzymes are present in lysosomes which are helpful in digesting the cell. The lysosomes are also known as suicide bags of the cell.
Mitochondria
Mitochondria is a semi-autonomous organelle and are also called the powerhouse of the cell. They form their own proteins as well as generate Adenosine Triphosphate or ATP.
Plastids
Only plant cells contain plastids and plastids contain their own DNA and Ribosomes. Plastids are divided into two types, which are chloroplasts and leucoplasts. Chloroplasts are colored plastids and leucoplasts are white or colourless plastids.
Vacuoles
The liquid and solid contents are stored in these vacuoles which are storage sacs. Small vacuoles are present in animal cells and plant cells contain large vacuoles. The cells have rigidity and turbidity due to these vacuoles.
6.) Cell division
Different cells are formed in organisms for different functions and the process of making new cells is known as Cell division. Mitosis and Meiosis are the two types of cell division.
Frequently Asked Questions on class 9 CBSE notes for Fundamental Units of Life
What is ‘Cell Division’?
To grow, reproduce, and replace old cells, generating new cells is important for organisms. And, the process through which the new cells are produced is called Cell division.
Why is a solution described as ‘isotonic’?
When the solution and mole concentration will be the same then the solution is said to be an isotonic solution.
In the cell, where does protein synthesis take place?
In the cell, protein synthesis mainly takes place in ribosomes.
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