CBSE Class 8 Science Notes Chapter 8 Cell Structure and Function
Cell Structure and Function Class 8 Notes Understanding the Lesson
1. The basic structural and functional units of all the organs of the living organisms is called cell.
2. Cells were first discovered by Robert Hooke in 1665.
3. Cells of living organisms could be observed only after the discovery of improved microscopes.
4. Cells exhibit a variety of shapes and sizes.
5. Number of cells also varies from organism to organism.
6. Organisms made of more than one cell are called multicellular organisms while organisms made up of single cell are called unicellular organisms.
7. A single-celled organism, e.g., Amoeba captures and digests food, respires, excretes, grows and reproduces. Similar functions in multicellular organisms are carried out by groups of specialised cells forming different tissues.
8. A white blood cell (WBC) in human blood is an example of a single cell which can change its shape.
9. The nerve cell receives and transfers messages, thereby helping to control and coordinate the working of different parts of the body.
10. The smallest cell is 0.1 to 0.5 micrometre in bacteria. The largest cell measuring 170 mm x 130 mm, is the egg of an ostrich.
11. Each organ is further made up of smaller parts called tissues.
12. A tissue is a group of similar cells performing a specific function.
13. The basic components of a cell are cell membrane, cytoplasm and nucleus.
14. Cell membrane is also called plasma membrane or cytoplasmic membrane. The cell membrane separates cells from one another and also the cell from the surrounding medium. It is porous and allows the movement of substances or materials both inward and outward.
15. Cell wall is an additional covering over the cell membrane in plant cells. It gives shape and rigidity to these cells.
16. The jelly-like substance between the nucleus and the cell membrane is called cytoplasm. Various components or organelles, like mitochondria, golgi bodies, ribosomes, etc., are present in cytoplasm.
17. The central dense round body in the centre is called the nucleus.
18. The membrane which separates nucleus from the cytoplasm is called the nuclear membrane.
19. Cells without well-organised nucleus, i.e., lacking nuclear membrane, are called prokaryotic cells.
20. The smaller spherical body in the nucleus is called the nucleolus.
21. Chromosomes are the thread-like structures which carry genes and help in inheritance or transfer of characters from the parents to the offspring.
22. Plant cell differs from animal cell in having a central large vacuole, cell wall and plastids.
23. The blank-looking structures in the cytoplasm are called vacuole.
24. Plastids are the coloured organelles, that are found in plant cells only.
25. Green coloured plastids are called chloroplasts.
Class 8 Science Chapter 8 Notes Important Terms
Cell: Cell is the basic structural and functional unit of all living organisms.
Cell membrane: The membrane around the cell is called cell membrane. It is also called plasma membrane or cytoplasmic membrane.
Cell wall: The hard and rigid covering of plasma membrane which are found in plant cells only is called cell wall.
Chloroplasts: The green coloured plastids having chlorophyll, which is essential for photosynthesis is called chloroplasts.
Chromosomes: The thread like structures found in the nucleus which carry genes are called chromosomes.
Eukaryotes: Organisms which have eukaryotic cells, i.e., which contains a well developed nucleus are called eukaryotes.
Gene: Genes are located in chromosomes. It is a unit of inheritance in living organisms.
Multicellular: The category of organism like plants and animals which contains a large number of cells are called multicellular organisms.
Nuclear membrane: Nuclear membrane separates nucleus from cytoplasm.
Nucleolus: The smaller, spherical and dense body inside the nucleus is called nucleolus.
Nucleus: The denser region of the cell that may be present at the centre of the cell is called nucleus.
Organ: The group of tissues, which are specialised to perform specific functions is called organ.
Organelle: One of the smaller component of cell is known as organelle.
Plasma membrane: The other name of cell membrane is plasma membrane. It is a membrane around the cell.
Plastids: The coloured organelles, that are found in plant cells only are called plastids.
Prokaryotes: The organisms which have prokaryotic cells, i.e., lack true nucleus are called prokaryotes, e.g., bacteria and blue green algae.
Protoplasm: The viscous fluid inside the cell which provides living nature to it is called protoplasm.
Pseudopodia: The temporary projections protruding out of the body of Amoeba for locomotion and taking food. These appear and disappear as Amoeba moves.
Tissue: A group of similar cells performing a specific function is called tissue.
Unicellular: The category of organisms containing single cell are called unicellular organisms.
Vacuoles: Vacuoles are the empty or blank looking structures in the cytoplasm.
White Blood Cell (WBC): It is the component of blood cells. It is an example of a single cell which can change its shape.