This is Online Notes on Chapter = 5 ( THE FUNDAMENTAL UNIT OF LIFE) Part 3 for preparation of CBSE BOARD Examination, NTSE etc.
Cell Wall:
• It is the outermost covering of the plant cells.
• It is absent in animal cells.
• Cell wall is rigid, strong, thick, porous and non-living structure. It is made up of cellulose and hemicelluloses. Cell walls of two adjacent cells are joined by a layer called middle lamellae.
Functions of Cell Wall :
(a) It provides definite shape to the cell.
(b) It provides strength to the cell.
(c) It is permeable and allows entry of molecules of different sizes.
(d) It has the characteristics of repair and regeneration.
Nucleus:
•Nucleus is the most important cell organelle which directs and controls all its cellular activities.
• It is called as ‘Headquarter of the cell’.
• It was discovered by Robert Brown in 1831.
• In Eukaryotes, a well-defined nucleus is present while in Prokaryotes, a well-defined nucleus is absent.
• Prokaryotes contain a primitive nucleus.
• It has double layered covering called as nuclear membrane.
• Nuclear membrane has pores which regulate the movement of materials in & out of the cell.
• Besides nuclear membrane, nucleus also contains nucleolus and
chromatin material and the substance filled inside the nucleus is nucleolus.
• Chromosomes or chromatin material consists of DNA which stores and transmits hereditary information for the cell to function, grow and reproduce.
Functions of Nucleus :
(a) It controls all the metabolic activities of the cell and regulates the cell cycle.
(b) It helps in transmission of hereditary characters from parents to
off springs.
Cytoplasm:
• Cytoplasm was discovered by Kolliker in 1862.
• It is the site of both biosynthetic and catabolic pathways.
• It can be divided into two parts :
(i) Cytosol : Aqueous soluble part contains various fibrous proteins
forming cytoskeleton.
(ii) Cell organelles : Living part of the cells having definite shape,
structure and function bounded by plasma membrane.
Endoplasmic Reticulum:
• It is the network of membranes present in the cytoplasm.
• It was discovered by Porter, Claude and Fullam.
• These are present in all cells except prokaryotes and mammalian
erythrocytes.
Functions of ER :
(a) It is the only organelle which can move within a cell so it serves
as a channel for the transport of materials between various regions of cytoplasm and between cytoplasm and nucleus.
(b) It also functions as a cytoplasmic framework to provide space for some of the biochemical activities. It forms endoskeleton of cell.
(c) It helps in synthesis of fats, steroids, cholesterol etc.
(d) SER plays a crucial role in detoxification of drugs and poisonous by-products.
Golgi Apparatus:
Golgi apparatus consists of a system of membrane bounded vesicles arranged parallel to each other in stacks called Cisternae along with some large and spherical vacuoles. It was discovered by Camilo Golgi. In plants Golgi membrane is bounded. It is single membrane bounded. It is absent in prokaryotes, mammalian
RBC’s & sieve cells.
Functions of Golgi apparatus :
(a) It helps in formation of lipids.
(b) It helps in formation of middle lamellae.
(c) It is secretary in nature.
(d) It helps in melanin synthesis.
(e) Lipids and proteins synthesized in endoplasmic reticulum are
packed at Golgi complex. They provide the site for assembly of
new membrane material.
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