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.
→ 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.
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 |