Cytoplasm contains 65-96% water. Plant cells contain 75% water, 20% carbohydrates, 2% protein, 2% mineral salts and 1% fat. Animal cells contain 67% water, 15% protein, 13% fat, 4% mineral salts and 1% sugar. Contains calcium, magnesium, potassium, sodium etc.

1. Cytoplasm is alive, slightly transparent, colorless, colloidal, viscous and elastic.
2. Various organs and substances are spread evenly in it.
3. It has flow resisting power as it is sticky adhesive.

The word Cytoplasm is formed from the Greek words cyto meaning cell and plasma meaning formed. The protoplasmic part of the cell surrounded by the cell membrane located outside the nucleus is called cytoplasm. Organelles and non-living matter in the cytoplasm are collectively called trophoplasm. It is now called the cytosol. The outer denser and less granular region of the cytosol is called ectoplasm and the inner less dense region is called endoplasm. The translucent, granular, homogeneous and colloidal fluid of the cytoplasm is called cytomatics or hyaloplasm. If the cytoplasm is like a thin membrane around the cell, it is called tonoplasm. Organelles that contain cytoplasm are called cytoplasmic organelles. American biochemist H. A. Lardy coined the term cytosol in 1965.

1. Shape giving: Cell membrane gives specific shape to each cell. Animal cells only have a plasma membrane, but plant cells have a cell wall outside the plasma membrane. Because of this, the cell membrane plays a key role in giving the specific shape of the animal cell.
2. Protection of living parts: The plasma membrane always covers the living protoplasm of the cell and protects it from external heat, pressure and injury.
3. Food intake: It takes in solid food by the process of phagocytosis and liquid food by the process of pinocytosis.
4. Organelle formation: It helps in the formation of some essential organelles of the cell like mitochondria, chloroplasts, Golgibodies, nuclear membrane etc.
5. As a chemical fast: cell membrane contains numerous consumer molecules. These consumer molecules maintain contact with the external environment. The plasma membrane collects information from the external environment chemically with the help of antigens, neurotransmitters, hormones etc.
6. Chemical secretion: It secretes enzymes and antigens for cells.
7. Physiological functions: Plasma membrane participates in respiration and other physiological functions in living organisms.
8. Conduction of impulses: It transports nerve impulses from outside to inside and from one cell to another.
9. Transport: Amino acids, glucose, ions etc. enter the cell through the plasma membrane. On the other hand, the carbon dioxide, ammonia, uric acid etc. created in the cells go out.
10. Absorption barrier: It acts as a barrier between the extracellular and intracellular medium.
11. Molecular motility: It regulates the molecular motility of the cell.
12. Energy production: Bacterial cell membrane folds to form mesosomes. Mesosomes undergo maturation and produce energy.
13. Growth and Movement: It helps in cell bonding, growth and movement.
14. As Antigen: In some cases cell membrane acts as antigen.
15. Enzyme content: There are 30 types of enzymes in the cell membrane. The most important enzymes are transport ATPases enzymes. This enzyme transports a variety of ions.
16. Basis: Cell membrane acts as a base for various information.
17. Receptors: act as receptors for hormones, neurotransmitters, mediated endocytosis, insulin etc.
18. Synthesis: Cell membrane synthesizes different types of large molecules.

1. Microvilli: Projections on the walls of the absorptive ducts in animals are called microvilli. Each cell in the intestine and nephron contains about 3000 microvilli. It increases the absorption surface.
2. Pinocytic vesicle: The cavity containing liquid food particles created from the cell membrane is called pinocytic vesicle. The process by which pinocytic vesicles are formed is called pinocytosis.
3. Phagocytic vesicle: The cavity containing solid food particles formed from cell membrane is called phagocytic vesicle. The process by which phagocytic vesicles are formed is called phagocytosis. White blood cells contain phagocytic vesicles.
4. Desmosome: When the cell membrane of two closely adjacent cells transforms and forms a leaf-like structure, it is called a desmosome. Desmosomes are accompanied by tonofibril fibers. It keeps the two cells firmly attached.
5. Tight junction: The cell membrane of two closely adjacent cells forming a tight junction is called a tight junction. No matter can move through this zone. Neurons in the brain have tight junctions.
6. Pseudopodia: The extension formed outside the cell membrane during phagocytosis is called pseudopodia. It participates in food intake and locomotion.
7. Invagination: Cell membrane folds to form numerous tubular structures. This is called intussusception.

1. Cell membrane contains 60-80% protein.
2. Cell membrane contains 20-40% lipids. Lecithin is the major phospholipid.
3. In some cases polysaccharides are 4-5%.
4. About 75% of the dry weight of the cell membrane is lipid.
5. Some contain RNA (onion cells).
6. Contains a small amount of water and salt.

In 1972, scientists Singer and Nicholson proposed the widely accepted fluid-mosaic model of cell membrane structure. It is also called iceberg or iceberg model.
Cell membranes contain five types of phospholipids. Lecithin, cephalin, glycolipid, glycophosphotide and phosphotidic acid. Phospholipids are arranged in two layers. Each lipid molecule has two parts. head and tail Lipid molecules are always moving, shaking and bouncing around each other. This type of movement is called flip flop movement. Flip flop movement causes the cell membrane to behave like a liquid when the layers change.
There are three types of proteins in the cell membrane. Peripheral proteins, intrinsic proteins and intermembrane proteins. At the edges of the lipid layer are the peripheral proteins, the intrinsic proteins are embedded inside, and the intermembrane proteins span from one end to the other. Proteins take energy from ATP to change their conformation.
Protein molecules are scattered between phospholipids in the cell membrane. Because of this, the protein molecules look like a mosaic when viewed from the surface of the cell membrane. To explain this situation in one word, the cell membrane model is called fluid mosaic model. Hence, the fluid mosaic model nomenclature has been meaningful and accurate.

In 1972 scientists S. J. Singer and G. L. Nicholson described the most widely accepted model of cell membrane structure called the fluid-mosaic model. In this model, protein molecules in the lipid layer are compared to icebergs floating in the ocean. This is called the iceberg model. Cell membrane structure is discussed according to fluid-mosaic model

1. Phospholipid: There are five types of phospholipids in the cell membrane. Lecithin, cephalin, glycolipid, glycophosphotide and phosphotidic acid. Phospholipids are arranged in two layers. Each layer is composed of numerous lipid molecules. Each lipid molecule has two parts. head and tail The large outer part is called the head. It is spherical or oval and composed of phosphates. It is polar and hydrophilic. The two fine filament-like parts attached to the head are called tails. It is composed of fatty acids. The tail is non-polar and hydrophobic. Between the head and the tail is the gyserol. Lipid molecules are always moving, shaking and bouncing around each other. This type of movement is called flip flop movement. As the flip flop motion changes the space between the two layers, the membrane feels like a fluid.
2. Protein: There are three types of proteins in the plasma membrane. These are-

(i) Peripheral protein: The protein located at the edge of the lipid layer is called peripheral protein. It looks round. It is enzyme in nature. It remains attached to the cytoskeleton. Adenylate cyclase produces cyclin AMP from ATP by the action of the membrane bound enzyme Adenylate cyclase.

(ii) Integral protein: The protein that is embedded inside the lipid layer is called integral protein. It looks oval. Acts as a carrier and transports essential substances. It maintains cell-to-cell adhesion.

(iii) Inter membrane protein: The protein that extends from one end of the lipid layer to the other end is called intermembrane protein. It is the largest protein. It takes energy from ATP to change its conformation. As a result, a hole is created through it. Essential substances move through these pores. It acts as a receptor for hormones, neurotransmitters, mediated endocytosis, insulin etc. Various molecules, ions and electrons move through channels, pumps and electron transport chains.

3. Glycocalyx: Carbohydrate chains on the outside of the cell membrane. Carbohydrate chains are attached to lipids to form glycolipids and proteins to form glycoproteins. Glycoproteins and glycolipids together are called glycocalyx or cell coat. It acts as a cell recognizer. It helps in the movement of essential substances.
4. Cholesterol: Cholesterol is a type of steroid. It has an OH group at the head and is hydrophilic. The other part is water repellent. Cholesterol is sandwiched between phospholipid molecules. It is irregularly arranged. Cholesterol is higher in animal cells and lower in plant cells.

Protein molecules are scattered between phospholipids in the cell membrane. Because of this, the protein molecules look like a mosaic when viewed from the surface of the cell membrane. To explain this situation in one word, the cell membrane model has been named fluid mosaic model.

In 1959, scientist Robertson proposed the unit membrane model of cell membrane structure. According to him, the molecular structure of all biological membranes is similar. It consists of three levels. The three levels together are called units or units. It is composed of phospholipid bilayers. Each lipid molecule has two parts. head and tail Molecules are polar and water absorbing (hydrophilic). The tail is non-polar and hydrophobic. Protein is grown in its place. A phospholipid bilayer with proteins is called a unit membrane. Its structure is protein-lipid-protein (P-L-P) with a total thickness of 75 Å. The outer layer is 20 Å thick and the inner layer is 35 Å thick.

In 1935 scientists Danielli & Davson first proposed a precise model of cell membrane structure. It is called sandwich model. According to this model the cell membrane is bi-layered. Each layer consists of protein and lipid sub-layers. The upper and lower layers contain proteins and the middle layer contains lipids.