Huxley defined protoplasm as "physical basis of life" because it is the fundamental substance in all organisms. Protoplasm is endowed with life and as protoplasm does cell ceases to function and dies.

Phagocytosis: It is the process of intake of large sized solid food particles by cell. It is also called as cell eating process.

Pinocytosis: It is the process of large sized liquid nutrients by cell. It is also called as cell drinking process.

Exocytosis: It is the process of expelling large sized materials outside the cell. It is also called as cell vomiting process.

The two types of proteins in fluid mosaic model are:

I) Extrinsic or peripheral proteins : They are the proteins that lie outside the outer and inner surface of Phospholipid bilayer.

ii) Intrinsic or internal proteins: They are partially or completely embedded over Phospholipid bilayer

Plasmodesmata are the gaps formed during the development of primary and secondary cell wall. They are important as they act as a cytoplasmic bridges or junctions between two adjacent cells and help in transfer of materials.

If the passage of substances across the selectively permeable plasma membrane requires the energy then it is called active transport.The energy required for active transport is obtained from ATP in the cell. For eg: Salt intake by plants take place through active transport.

Mitochondria and Plastids are the two semi-autonomous cell organelles.

They are called semi-autonomous cell organelles because they have got all the requirements for the synthesis of proteins and enzymes for their functioning like:

I) 70S type of ribosomes

ii)Self replicating DNA molecules which can form RNA

iii) ATP molecules to provide energy.

However, they are not fully autonomous and some activities are performed by nuclear DNA.

The small tennis racket like structure present in the cristae in the inner membrane of mitochondria are called F₁ particles. They are also called elementary particles or oxysomes.

In the head of F1 particles, enzyme ATPase or ATP synthase is present which controls the synthesis of ATP, so these are the functional unit of mitochondria Al's called as ATP particles

Cell inculsions are non living, metabolically inactive substances present in cytoplasm. They are also called as deutoplasmic bodies or ergastic bodies. For eg: Carbohydrates, proteins, essential oils, latex, mineral crystals, cellulose, inulin, fats, oils, pigment, enzymes etc. They may also be produced as a by product of various metabolic activities inside the cell.

The streaming movement of cytoplasm within the eukaryotic cell is called Cyclosis.

Cyclosis is important because of following reasons:

• It helps in movement of cell organelles and cell inculsions.
• It helps in distribution of materials inside the cell.
• It helps in formation of pseudopodia in Amoeba and leucocytes.

Generally, cell wall is composed of cellulose which is one of its strongest layer. However, decomposition of additional amount of lignin on the cellulose forms the secondary cell wall which is primarily responsible for providing the rigidity to the cell. Hence, lignin is the chemical that gives rigidity to the cell wall.