Chapter: The Fundamental Unit of Life (Notes) - Based on NCERT - Class 9 PDF Download

1. Cell - Cell is the basic structural and fundamental unit of life. It was discovered by Robert Hooke.
2. Protoplasm - The term 'protoplasm' was coined by Purkinji. It is the colourless material comprising the living part of a cell, including the cytoplasm, nucleus, and other organelles.
3. Plasma membrane (or cell membrane)- It is the outermost covering of the cell that separates the contents of the cell from its external environment.
4. Diffusion- The spontaneous movement of a substance from the region of high concentration to the region where it's concentration is low is called diffusion
5. Osmosis- It is the passage of water from a region of high water concentration through a semi permeable membrane to the region of low water concentration. Osmosis is a special case of diffusion through a selectively permeable membrane. Absorption of water by plant roots is also an example of osmosis.
6. Cell theory- The 'cell theory' was presented by 'Schleiden' and 'Schwan' and further expanded by 'Virchow'. It's postulates are as follows- 
(i)  All organisms are made of cells.
(ii) Cells are the structural and functional units of life.
(iii) All cells arise from pre - existing cells only.
7. Types of Solutions-

8. Cell wall- It is present in plant cells. It lies outside the plasma membrane. It is composed of cellulose. Cell wall provides strength to plants. It prevents the plant from bursting when kept in Hypotonic solution.
9. Plasmolysis- The shrinkage or contraction of protoplasm away from the plasma membrane (cell wall) when the cell is kept in Hypertonic solution.
10. Nucleus-
▪️Structure- The nucleus has a double layered membrane called nuclear membrane. Nuclear pores are present on the nuclear membrane which allow the transfer of materials from the nucleus to the cytoplasm. It contains chromosomes which further contains DNA (Deoxyribo Nucleic Acid) that contain genes (functional segments of DNA). DNA is present as a part of chromatin material which is visible as the entangled mass of thread- like structures.
▪️ Function- (i) Cellular reproduction
(ii) Inheritance of features from parents to the next generation.
11. Endoplasmic Reticulum (ER)- It is a large network of membrane bound tubes and sheets. There are two types of Endoplasmic Reticulum-
(i) RER (Rough Endoplasmic Reticulum)
(ii) SER (Smooth Endoplasmic Reticulum)
▪️ Function- (i) RER manufacturers proteins.
(ii) SER helps in the manufacture of days or lipids.
(iii) ER helps in transport of materials between the regions of the cytoplasm or between cytoplasm and the nucleus.
(iv) SER of liver of vertebrates helps in detoxification.
12. Membrane biogenesis- Building up of cell membrane by lipids and proteins is called Membrane Biogenesis.
13. Golgi apparatus - It was first described by Camillo Golgi.
▪️ Structure- It consists of membrane bound vesicles parallel to each other in stacks called cisterns.
▪️Function- (i) Packaging and dispatching of materials synthesized near ER to various targets in/out of the cell.
(ii) Storage, modification and packaging of products in vesicles.
(iii) Making complex sugars from simple sugars in some cases.
(iv) Formation of lysosomes.
14. Lysosomes- 
▪️ Structure- Lysosomes are membrane bound sacs filled with digestive enzymes made by RER.
▪️ Functions- (i) They keep the cell clean by digesting any foreign material and worn out cell organalles.
(ii) They serve as intercellular digestive system, hence called digestive bags.
(iii) During disturbance in metabolism, they may burst and the enzymes digest their own cell. Therefore, they are known as the "suicidal bags" of a cell.
15. Mitochondria- It is also known as the powerhouse of the cell.
▪️ Structure- Mitochondria has a double layered membrane. The outer membrane is porous and the inner membrane is deeply folded.
▪️ Functions- (i) They release energy in the form of ATP (Adenosine Triphosphate).
(ii) They have their own DNA and ribosomes.
(iii) They are able to make some of their own proteins.
16. Plastids- They are present only in plant cells. There are three types of plastids-
(i) Chromoplasts (They are coloured depending on the pigment they contain)
(ii)Chloroplasts (They are green in colour)
(iii)Leucoplasts (They are white in colour)
▪️Functions- (i) Chloroplasts are important for photosynthesis.
(ii) Leucoplasts store materials like starch, oils and protein granules 
(iii) Chromoplasts are coloured pigments which are responsible for giving colour.
(iv) They have their own DNA and ribosomes.
17. Vacuoles- 
▪️ Structure- They are of small size in animal cells and large size in plant cells.
▪️ Functions- (i) They provide turgidity and rigidity to the cells.
(ii) They store substances like Amino acids, sugars, various organic acids and some proteins.
(iii) In amoeba, the food vacuole contains the food items that the amoeba has consumed.
(iv) It expells excess water and wastes from the cell in unicellular organisms.