FUNDAMENTAL UNIT OF LIFE CLASS 9 SCIENCE CHAPTER 5 PART 2 BIOLOGY CBSE NCERT KVS , BIOLOGY CLASS 9
Main topics covered in this part of CBSE Class 9 Science, The Fundamental Unit of Life: Chapter Notes, are:
Definition of Cell
Shape and Size of Cell
Types of Cell
Structure of Cell
Cell Organelles
Difference Between Animal Cell and Plant Cell
Cell
It is the structural and functional unit of life.
Cell is termed as the structural unit of life as it provides structure to our body.
Cell is considered as the functional unit of life as all the functions of the body take place at cell level.
Discovery of cell:
Discovered by Robert Hooke in 1665.
Robert Brown in 1831 discovered the nucleus in the cell.
Cell theory states that:
All living organisms are composed of cells.
Cell is the fundamental unit of life.
All new cells come from pre-existing cells.
Types of Organisms on the Basis of Number of Cells
There are two kinds of organisms on the basis of cells:
(i) Unicellular Organisms: The organisms that are made up of single cell and may constitute a whole organism, are named as unicellular organisms.
For example: Amoeba, Paramecium, bacteria, etc.
(ii) Multicellular Organisms: The organisms which are composed of a collection of cells that assume function in a coordinated manner, with different cells specialized to perform particular tasks in the body, are named as multicellular organisms.
For example: Plants, human beings, animals, etc.
hape and Size of Cells
Cells vary in shape and size. They may be oval, spherical, rectangular, spindle shaped, or totally irregular like the nerve cell.
The size of cell also varies in different organisms. Most of the cells are microscopic in size like red blood cells (RBC) while some cells are fairly large like nerve cells.
Types of Cells
The cells can be categorized in two types:
1. Prokaryotic Cell 2. Eukaryotic Cell
1. Prokaryotic cell
Prokaryotic cells are cells in which true nucleus is absent. They are primitive and incomplete cells. Prokaryotes are always unicellular organisms. For example, archaebacteria, bacteria, blue green algae are all prokaryotes.
2. Eukaryotic Cell
Eukaryobc cells are the cells in which true nucleus is present. They are advanced and complete cells. Eukaryotes include all living organisms (both unicellular and multicellular organisms) except bactera and blue green algae.
Structure of Cell
Cell is generally composed of three basic components:
(i) Cell wall and cell membrane
(ii) Nucleus
(iii) Cytoplasm
(i) Cell membrane or Plasma membrane:
Plasma membrane is the covering of the cell that separates the contents of the cell from its external environment.
It is a living part of the cell and is present in cells of plants, animals and microorganisms.
It is very thin, delicate, elastic and selectively permeable membrane.
It is composed of lipid and protein.
(ii) Cell wall:
cell wall is non-living, thick and freely permeable covering made up of cellulose.
It is present in eukaryotic plant cells and in prokaryotic cells.
Functions:
It determines the shape and rigidity to the plant cell.
It protects the plasma membrane.
It prevents desiccation or dryness in cell.
It helps in the transport of varous substances in and out of the cel
(iii) Nucleus:
Nucleus is dense and spherical organelle.
Nucleus is bounded by two membranes, both forming nuclear envelope. Nuclear envelope contains many pores known as nuclear pores.
The fluid which present inside the nucleus is called nucleoplasm.
Nucleus contains chromosomes and chromosomes contain genes which are the centres of genetic information.
Functions:
Nucleus controls all the metabolic activities of the cell.
It regulates the cell cycle.
Nucleus is the storehouse of genes.It is concerned with the transmission of hereditary traits from the parent to offspring.
Function:
As it is selectively permeable membrane, it allows the flow of limited substances in and out of the cell.
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MATTER IN OUR SURROUNDING CLASS 9
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CLASS 10 PHYSICS
REFLECTION AND REFRACTION OF LIGHT
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CLASS 10 BIOLOGY
LIFE PROCESS
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