notes of the fundamental unit of life class 9
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The Cell Theory
1. A cell is the structural and functional unit of all living organisms.
2. All the living organisms are made up of cells.
3. Cells are formed from pre-existing cells.
Unicellular Organisms – The organisms that consist of a single cell such as Amoeba.
Multicellular Organisms – The organisms which contain various cells that perform different functions in the organism such as plants fungi and animals
The Shape of the Cell
The shape of the cell may vary depending upon the type of function they perform in an organism.
Plasma Membrane
It is just like an envelope that covers the whole cell. Therefore, a cell gets separated from the external environment because it has a plasma membrane.
The plasma membrane has the capability to decide which materials should enter or leave the cell and which should not. That is why it is also called as a ‘Selectively Permeable Membrane’.
The Fluid Mosaic Model of Plasma Membrane
The Fluid Mosaic model explains the structure of the plasma membrane. According to it, the plasma membrane comprises of 3 components - Lipids, Proteins and Carbohydrates. These components can flow freely and fluidly inside the plasma membrane.
endocytosis
It is a process by which the plasma membrane engulfs food and other materials inside the cell.
Cell Wall
The cell wall is a outer, hard covering of the cell which maintains the shape of the cell.
The cell wall is generally made up of cellulose.
plasmolysis
Plasmolysis is a process in which the contents of the cell that are away from the cell wall shrink or contract when a cell loses water due to Osmosis when it is kept in hypertonic solution.
The Nucleus
Nucleus is a prominent, organelle present in cell which is the controlling centre of all activities of cell.
Chromatin
Chromatin is thread-like material present in a cell. The chromatin organizes itself into chromosomes whenever the cell is about to divide.
Nucleolus
It is called as the Brain of the Nucleus. It comprises of 25% of the volume of the nucleus. It consists of proteins and ribonucleic acids (RNA). It helps in formation of ribosomes which help in formation of proteins inside the cell.
nucleoid
Sometimes cells do not have a well-defined nucleus because they lack a nuclear membrane. Such a nucleus with no definite nuclear boundaries is called a Nucleoid.
prokaryotes
Organisms whose cells do not have a definite cell membrane are called Prokaryotes.
eukaryotes
Organisms whose cells contain a well-defined nuclear membrane are called Eukaryotes.
Cytoplasm
The plasma membrane has a fluid like substance in it which is called the cytoplasm.
The Cell Organelles
In the case of Eukaryotic organisms, the cells contain organelles that have their own membranes apart from the overall cell membrane of the cell.
Endoplasmic Reticulum (ER)
The structure of the ER is quite similar to that of the plasma membrane. It is a network-like structure which consists of membrane-bound tubes and sheets.
Two types of ER –
Rough ER
Smooth ER
Rough ER contains ribosomes that are responsible for the manufacturing of proteins in the cells. They give a rough texture to the cell.
The smooth ER manufactures fats or lipids in the cell which allow the functioning of the cell.
golgi apparatus
It contains vesicles that are arranged parallel in stacks. These stacks are called Cisterns. These vesicles have their own membranes. These membranes are sometimes connected to those of the ER.
Functions of Golgi Apparatus
Golgi apparatus carries materials synthesized by the ER to different parts of the cell. The material is stored and packaged in vesicles.
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fundamental unit of life
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