Class 8th / Biology / Chapter - Cell Structure and Function // Notes
Some facts
1. The basic structural and functional units of all the organs of the living organisms is call 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 microscope.
4. Cells exhibit a variety of shapes and size.
5. Number of cells also varies from organism to organism.
6. Organism made of more than one cell are called multicellular organisms while organisms made up of single cell are called unicellular organism .
7. A single - celled organisms are Amoeba , Paramecium , Protozoa , Protista , Diatoms
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 message . thereby helping to control and coordinate the working of different parts of the body .
10. The smallest cell is 0.1 to 0.5 micrometer 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 tissue .
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 shapes and rigidity to these cell.
16. The jelly - like substance between the nucleus and the cell membrane is called cytoplasm . Various components or organelles , like mitochondria , ribosomes etc. are present in cytoplasm .
17. The central dense round body in the centre is called nucleus .
or , The smaller spherical body in the nucleus is called nucleolus.
18. The membrane which separates nucleus from the cytoplasm is called the nuclear membrane.
19. Cells without well - organised nucleus , like lacking nuclear membrane are called prokaryotic cells.
20. Chromosomes are the thread - like structures which carry genes and help in inheritance or transfer of characters from the parents to the offspring.
21. Plant cells differ from animal cell in having a central large vacuole , cell wall and plastids.
22. The blank - looking structures in the cytoplasm are called vacuole.
23. Plastids are the coloured organelles , that are found in plant cells only .
24. Green coloured plastids are called chloroplasts.
Some 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 called plasma membrane or Cytoplasmic membrane.
• Cell wall :- The hard and rigid covering of plasma membrane which are found in plants cells only is called Cell wall .
• Chloroplasts :- The green coloured plastids having chlorophull , which is essential for photosynthesis is called chloroplasts .
• Chromosomes :- The thread like structure 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.
• Organ :- The group of tissue , which are specialised to perform specific functions is called organ .
• Organelle : - One of the smaller component of cell is known as organelle.
• Plastids :- The coloured organelles , that are found in plant cells only are called plastids .
• White Blood Cell :- It is the component of blood cells .It is an example of a single cell which can change its shape.
• Vacuoles :- Vacuoles are the empty or blank looking structure in the Cytoplasm .
