IX A Science Fundamental unit of life (Summary of the topic taught as on 07/06/2021)
Cells as a Structural and Functional Unit of Life
Cells form the basic structure of an organism and a collection of similar cells that perform an organized function form a Tissue. Each tissue serves a particular purpose and can be combined with other tissues to form organs. These carry out essential life processes like metabolism, growth, reproduction, etc. in unicellular and multicellular organisms. Here are some examples of tissues and organs in plants and animals:
| Category | Tissues | Organs |
| Plants | Phloem, Xylem, Protective, etc. | Leaves, Roots, Stems, etc |
| Animals | Connective, Muscular, Nervous, etc | Heart, Liver, Kidney, etc |
Types of Cells
Regardless of the complexity as well as type of organism, cells are mainly divided into two categories. Mentioned below is a distinction between the 2 major types of cells in our fundamental unit of life class 9 notes-
Prokaryotic Cells
Cells in which a true nucleus is absent are called Prokaryotic Cells. Since they do not contain any membrane-bound organelle, these are always unicellular organisms, such as Bacteria, Blue-Green Algae, Amoeba, etc.
Eukaryotic Cells
Cells that have a true nucleus are called Eukaryotic Cells. These are complete cells that contain a nucleus, mitochondria, and another membrane-bound organelle. These are always multicellular organisms like animals, plants, fungi, etc.
Structure of a Cell
Whether prokaryotic or eukaryotic, the cells have a similar structure upto some extent. A variety of key features of the cell are same. A cell is essentially made up of 4 main components:
- Cell Wall and Cell Membrane
- Nucleus
- Cytoplasm
- Cell Organelle
Cell Membrane and Plasma Membrane
It is a biological membrane that separates a cell’s contents from its outside surrounding or external environment.
Properties:
- Thin-walled, elastic, and semi-permeable
- Made up of proteins and lipids
- It is a living component of the cell
Functions:
- Protects the contents of the cell from its external environment
- Its semi-permeable allows only selective materials to flow in and out of the cell
Cell wall
The next important topic in our fundamental unit of life class 9 notes is the Cell Wall. It is a structural layer just outside the plasma membrane.
Properties:
- Flexible, tough, or rigid in some cells
- Non-living and freely permeable
- Made up of cellulose
Functions:
- Protects the cell membrane
- It is majorly responsible for maintaining the shape and size of the cell
- Prevents the cell from becoming flaccid and from drying out.
Nucleus
Nucleus refers to an organelle that is found in eukaryotic cells and contains the genetic material of a cell.
Properties:
- It is spherical in shape and is enclosed in a nuclear membrane (also known as the nuclear envelope)
- Contains a type of protoplasm called nucleoplasm in which the nucleus is suspended
- The nucleus contains chromosomes that are made up of proteins and specific molecules of deoxyribonucleic acid or DNA. Chromosomes are, therefore, the carriers of an organism’s genetic information
Functions:
- Regulates the cell cycle and is responsible for cell division, protein synthesis, growth, etc.
- Controls the metabolic activity of cellular components
- Controls the genetic characteristics of an organism
- Stores hereditary materials in the form of DNA
