DAV Class 8 Science Chapter 1 Notes – The Cell Its Structure and Functions

These DAV Class 8 Science Notes and DAV Class 8 Science Chapter 1 Notes – The Cell Its Structure and Functions act as excellent revision resources, particularly in preparation for board exams.

The Cell Its Structure and Functions Class 8 DAV Notes

→ Cell: The basic structural and functional unit of living organisms is called cell.

→ Discovery of Cell: Robert Hooke was the first scientist who observed thin slices of cork with the help of his self-designed microscope. He observed honeycomb-like structure and called the compartments as cell.

→ Celi Number: Some organisms are composed of a single cell. These are called unicellular organisms. Some organisms are composed of more than one cell. These are called multicellular organisms.

→ Cell Shape: The shape of cells differs in different organisms, as well as in different organs of the same organism. A cell may be oval, spherical, cuboidal, fibre-like or polygonal. The shape of a cell is influenced by its location and the function it serves.

→ Cell Size: The size of cells varies from 0.1 micron to 170 mm. Mycoplasma is a unicellular organism which is 0.1 micron in size. An egg of ostrich is the largest known living cell and is 170 mm in diameter.

→ Parts of a Cell: A cell is composed of protoplasm which is surrounded by a cell membrane. The protoplasm consists of cytoplasm and nucleus. There are a number of cell organelles in the cytoplasm and nucleus.

→ Cell Membrane: All living cells are bound by a thin membrane called plasma membrane or cell membrane. The cell membrane provides protection to the contents of the cell and controls the entry and exit of various substances as per a cell’s requirement.

DAV Class 8 Science Chapter 1 Notes - The Cell Its Structure and Functions

→ Cell Wall: In plants, fungi and bacteria, the cell is surrounded by a cell wall in addition of the cell membrane also. Cell wall provides additional rigidity to the cell.

→ Cytoplasm: The part of the protoplasm which lies between the cell membrane and nucleus is called cytoplasm. It acts like a matrix for various cell organelles. It is made up of carbohydrates, proteins, fats, minerals, vitamins and water.

→ Nucleus: The nucleus lies in the centre of the cell. It controls all the activities of the cell. The protoplasm of the nucleus is called nucleoplasm. Nucleus is surrounded by a nuclear membrane. The nucleus has thread-like network called chromatin. The chromatin network is composed of chromosomes which become visible during cell division. Chromosomes are responsible for inheritance of characters.

→ Plastids: These are found in plant cells only. They are large and capsule-shaped. Plastids are in many colours. The green coloured plastids are called chloropiasts. Photosynthesis happens in chloroplast. Plastids are responsible for imparting colour to a plant part.

→ Mitochondria: Mitochondria are capsule-shaped structures. Cellular respiration takes place in mitochondria and energy is generated. Due to this, mitochondria are also called the powerhouse of the cell.

→ Endoplasmic Reticulum: It is a network of tube-like structures. It provides a skeletal framework to the cell and also facilitates transportation of substances.

→ Golgi Complex: These are sac-like structures stacked over one another. They store materials which are produced by cells. Due to this, Golgi complex is also called the store house of the cell.

→ Vacuole: These are fluid filled spaces inside cells. Vacuoles are very large in plant cells. Excess water and waste products are held in vacuoles. Food vacuoles are present in Amoeba.

→ Ribosomes: These are tiny granules which lie scattered in the cytoplasm. Ribosomes help in protein synthesis.

→ Cilia and Flagella: Some cells have special structures on them for locomotion. Paramecium has cilia, while Euglena has flagella.

DAV Class 8 Science Chapter 1 Notes - The Cell Its Structure and Functions

Levels of Organisation in Organisms

→ Cellular Level: This level of organization is found in unicellular and in some simple multicellular organisms. In such organisms, a single cell is responsible for all life functions.

→ Tissue Level: This level of organization is found in some simple multicellular organisms in which a group of cells, i.e. tissue is responsible for all life functions.

→ Organ Level: Organisms; like hookworm and roundworm show organ level of organization.

→ Organ System Level: Many organs group together to form an organ system. Complex organisms show organ system level of organization.

→ Organism: An organism is an independent entity which can live on its own.

→ Cell : The basic structural and functional unit of living beings.

→ Cytology : The branch of biology in which we study about cells.

→ Protoplasm : The jelly like substance inside the cell.

→ Cytoplasm : The protoplasm which is present between cell membrane and nuclear membrane.

→ Nucleoplasm : The protoplasm which is present inside the nucleus.

→ Chromosomes : Rod-like stwctures inside nucleus which are responsible for transmission of genetic traits.

Comparison between plant cell and animal cell

Cell components Plant cell Animal cell
Cell wall Present Absent
Cell membrane Present Present
Plastids Present Absent
Mitochondria Present Present
Nucleus Present Present
Vacuoles Large in size and more in number Small in size and may be absent