Class 9 cells notes .Fundamental unit of life class 9 Notes.
Class 9 cells notes.
Table of Content
Fundamental unit of life class 9 Notes.
Class 9 cells notes.
Fundamental unit of life class 9 Notes.
Class 9 cells notes.
Cell
1. All living forms are microscopic units called as 'cells'.
2. A cell is the basic structural and
functional unit of all life forms.
3. Study of structure and composition of cell as 'Cytology.
4. Cell was first observed by 'Robert Hooke' in a dead cork slice in the year 1665. He described about this in his book Micrographic'.
Cell Theory
Two biologists, Schleiden and Schwann' gave the Cell theory' which was later on expanded by Rudolf Virchow'. Cell theory states that
(a) All plants and animals are composed of cells.
(b) Cell is the basic unit of life.
(c) All cells arise from pre-existing cells.
(ii) Viruses are the exceptions of cell theory.
Types of Cell and Organism
(i) On the basis of number of cells organisms can be categorized as
(a) Unicellular Organisms These are organisms which made up of single cell only. This single cell performs all the vital body functions of an organism. e.g., Amoeba.
(b) Multicellular Organisms These are the organisms which made up of numerous cells. These cells then combine to form an organ and group of organs performing different functions forms an organ system which further forms an organism. e.g., plants and animals.
(ii) On the basis of type of organization, cells are two types
(a) Prokaryotic Cells These are primitive and incomplete cells. They have less developed nucleus without nuclear membrane and nucleolus. e.g., Bacteria.
(b) Eukaryotic Cells These are well developed cells. They have advanced nucleus with unclear membrane and nucleolus. e.g., Plants and animals.
Cell Shape
(i) Cells are of variable shapes and sizes. Their shape is according to the function.
(ii) Generally cells are spherical but they may be elon gated (nerve cell), branched (pigmented), dis- coidal (RBC), spindle shaped (muscle cell), etc.
Cell Size
(i) Size of cell is variable depending upon the type of organism. Some are microscopic while some are visible with naked eyes. Their size may vary from 0.2 >m to18 cm.
(ii) Size of a typical cell in a multicellular organism ranges from 20-30 mn.
(iii) The largest cell is ostrich egg(15 cm in dia with shell and 8 cm in dia without shell).
(iv) The longest cell is nerve cell.(upto 1m or more)
(v) Smallest cells so far known are PPLOS, e.g., mycoplasma (0.1 >m in dia). (vi) Human egg is 0.1 mm in dia.
Components of Cell
(1) There is an occurrence of division of labour within a cell as they all got certain specific components called 'cell organelles each of them perform a specific function.
(ii) The three basic components of all the cells are (a) Plasma membrane (b) Nucleus (e) Cytoplasm.
Cell Membrane
Cell membrane is also called as plasma membrane or plasma lemma.
(i) It is the limiting boundary of each cell
which separates the cytoplasm from its
surroundings.
(ii) It is found in both plant as well as animal
cells.
(iii) It is the outer most covering of a cell in case of animals and lies below the cell wall in case of plants.
(iv) It is made up of proteins and lipids, where pro- teins are sandwiched between bilayer of lipids.
(v) Plasma membrane is selectively permeable in nature. It allows or permits the entry and exit of some materials in and out of the cell.
(vi) It is flexible and can be folded, broken and reunited.
(vii) It regulates the movement of molecules inside and outside the cell.
(viii) It helps in maintaining the distinct composi- tion of the cell.
Cell Wall
It is the outermost covering of the plant cells. (i) It is absent in animal cells.
(ii) It is rigid, strong, thick, porous and non-living structure. It is made up of cellulose and hemicelluloses.
(iii) Cell walls of two adjacent cells are joined by a layer called middle lamellae. It is made up of calcium and magnesium pectate.
(iv) It provides definite shape to the cell.
(v) It provides strength to the cell.
(vi) It is permeable and allows entry of molecules of different sizes.
(vii) It has the characteristics of repair and regeneration.
Nucleus
It is the most important cell organelle whi directs and controls all its cellular activities.
(i) It is called as headquarter of the cell.
(ii) In eukaryotes, a well-defined nudes
present in well-defined nucleus is absent.
(iii) Prokaryotes contain a primitive nucleus.
4) It has double layered covering called as nuclear membrane.
(v) Nuclear membrane has pores, which regulate the movement of materials of materials in and out of the cell.
(vi) Chromosomes or chromatin material consists of DNA, which stores and transmits hereditary information for the cell to function, grow and reproduce .
(vii) Nucleus controls all the metabolic activities of the cell and regulates the cell cycle.
(viii) It helps in transmission of hereditary characters from parents to off spring
Cytoplasm
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.
(i) It was discovered by Porter, Claude and Fullam.
(ii) These are present in all cells excep prokaryotes erythrocytes. and mammalian.
(iii) They are made up of three components.
Golgi Apparatus
° It consists of a system of membrane bounded vesicles arranged parallel to each other in stacks called cisternae along with some large
and spherical vacuoles.
(i) It was discove I by Camilo Golgi.
(ii) In plants Golgi membrane bounded. (iii) It is single membrane bounded.
(iv) It is absent in prokaryotes, mammalian RBC's and sieve cells.
Functions
(a) It helps in formation of lipids.
(b) It helps in formation of middle lamellae.
(c) It helps in melanin synthesis.
(d) Lipids and proteins synthesized in endoplasmic reticulum are packed at Golgi complex. They provide the site for
assembly of new membrane material.
Mitochondria
It is a rod-shaped structure found in cytoplasm of all eukaryotic cells except mammalian RBCs. These are also absent in prokaryotes.
(i) It was first seen by Kolliker in insect cells.
(ii) Maximum mitochondria are found in metabolically active cells.
(iii) It is also called as 'Power House of the Cell' or the 'Storage Battery'.
Functions of Mitochondria
(i) Its main function is to produce and store
the energy in the form of ATP
(ii) It is the site of Kreb cycle of respiration.
(iii) Oxysome contains enzymes for ATP production.
(iv) Matrix contains enzymes for Kreb cycle.
Ribosomes
These are the sites of protein synthesis.
All structural and functional proteins (enzymes) coded by the nuclear DNA, are synthesized upon cytoplasmic ribosomes. The DNA codes are transcripted into messenger RNA (mRNA) molecules in the chromosomes
of the nucleus.
Plastid
It is double membranous discoidal structure, found only in plant cells.
1) Term plastic was given by Haeckel.
(ii) Chloroplast was discount by AV Leeuwenhoek and named by Schimper.
(iii) Besides being discoidal of rhombic in plant cells they occur in variable shapes like in algae they can be 'U' shaped, spiral, coiled, ribbon shaped, etc.
Vacuoles
These are membrane bounded regions in the cytoplasm containing water and other substances.
(i) They are bounded by a single membrane called tonoplast.
(ii) In animal cells, vacuoles are smaller in size and numerous while in plant cells a single large vacuole is found, which occupies about 90% of the volume of cell.
Functions of Vacuole
(i) It helps in maintaining osmotic pressure in a cell.
(ii) It stores toxic metabolic products of plant
cell.
(iii) It contains various coloured pigments like anthocyanins.
Lysosomes
These are tiny sac-like granules containing
enzymes of intracellular digestion.
(i) They are bounded by a single membrane. (ii) They occur in animal cells and a few plant
cells.
(iii) They do not have a definite shape or size. (iv) They contain hydrolyzing enzymes called
acid hydrolyses.
Functions of Lysosomes
(a) They help in digesting foreign materials and worm out cells.
(b) During disturbances in cellular metabolism i.e. in case of cell damage lysosomes burst and their enzymes are released into the cytoplasm and they digest their own cell so they are also called as 'Suicidal Bags'.
Peroxisomes
These structures were first described from liver and kidney cells by Rodhin (1954).
(i) In plant cells, they were first observed in
germinating seeds by Tolbert(1969).
(ii) The term 'peroxisomes' was first used by
de Duve and also called as uricosomes. or
(iii) Peroxysomes ovoid granular are structures, limited by a single unit membrane and have a diameter of 0.5 to >m.
(iv) They contain important enzymes as oxidases (peroxide producing enzyme), peroxidases and catalases (which breakdown toxic peroxides to water and oxygen).
Fundamental unit of life class 9 Notes.
Fundamental unit of life class 9 Notes.
Class 9 cells notes.
Class 9 cells notes.
Class 9 cells notes.
Class 9 cells notes.
Class 9 cells notes.
Fundamental_unit_of_life_class_9_Notes.
Fundamental_unit_of_life_class_9_Notes.
Fundamental unit of life class 9 Notes.
Fundamental unit of life class 9 Notes.
Fundamental unit of life class 9 Notes.
Class 9 cells notes.
Class 9 cells notes.
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