question_answer 3)

Write short notes on the following. (a) Cytoplasm (b) Nucleus of a cell  

Answer:

(a) Cytoplasm : The cytoplasm is a jelly-like substance present between the cell membrane and the nucleus. Various components, or cell organelles such as mitochondria, endoplasmic reticulum, Golgi body, lysosome, plastids, etc. are present in the cytoplasm. It is made up of carbohydrates, proteins and water. All life functions such as synthesis of substance, secretion of substance, digestion of substance to generate energy etc. take place in cytoplasm. (b) Nucleus of a cell: The nucleus is centrally located, and is the major functional centre of the cell. It may be spherical or oval in shape. It is surrounded by an envelope known as the nuclear membrane. Fores, present at intervals, have the effect of perforating the envelope. The liquid present in the nucleus is known as nucleoplasm and is enclosed by a nuclear membrane. It is the nuclear pores that make possible the exchange of materials between cytoplasm and nucleoplasm. The nucleoplasm contains the nucleolus and chromatin material. The nucleolus helps in protein synthesis. This is where ribosome formation takes place. Chromatin material is thin, thread-like mass of chromosome material. It is composed of the genetic substance known as DNA, which has a major role to play in heredity, since it transmits information from one generation to the next. The functions of nucleus are to control all metabolic activities of the cell, take part in cell division and transmit hereditary characters from one generation to the next.