NCERT Solutions Class 9th Science Chapter – 5 The Fundamental Unit of Life Notes

NCERT Solutions Class 9th Science Chapter – 5 The Fundamental Unit of Life

NCERT Solutions Class 9th Science Chapter – 5 The Fundamental Unit of Life

Chapter – 5

The Fundamental Unit of Life

Notes

Type of Organism

Cell

Cell Theory

Two biologists, Schleiden and Schwann (1838) gave the Cell theory which states that: (i) All plants and animals are composed of cells. (ii) Cell is the basic unit of life. (iii) All cell arise from pre-existing cells. Viruses are the exceptions of cell theory.

Types of Cell & Organism

On the Basis of Type of Oraganization Cells are of two kind Prokaryotic Cells Eukaryotic Cells • Very minute in size. (1 to 10-6 m) • Fairly large in size. (5-100μm) • Nuclear region (nucleoid) not surrounded by a nuclear membreane. • Nuclear material surrounded by a nuclear membrance. • Always Unicellular • May be unicellular or multicellular • Single Chromosome present. • More than one chromosome present. • Nucleolus absent. • Nucleolus present. • Cell division by fission or budding • Cell division by mitosis or meiosis. • Membrane bound cell organelles are absent. • Membrane bound cell organelles are present. Ex. Bacteria Ex. All Plants, Animals, Amoeba etc.

Organism are of Two Type

Cell Shape

Cells are of variable shapes and sizes. That varies is according to their function position. Generally cells are spherical but they may be elongated (nerve cell). branched (pigmented), discoidal (RBC). Spindle-shaped (muscle cell) etc.

Cell Size

Components of Cell

Cell Membrane/Plasma Membrance

(a) Plasma membrane is selectively permeable in nature, means it allows or permits the entry and exit of some materials in and out of the cell. (b) Cell membrane is also called plasma membrane or plasma lemma. (c) It is the limiting boundary of each cell which separates cytoplasm from its surroundings. It is found in both plant as well as animal cells. (d) It is the outermost covering of a cell in case of animals and lies below the cell wall in case of plants. (e) As per the lipid model of plasma membrane. It is made up of proteins and lipids where proteins are sandwiched between bilayer of lipids. (f) Singer and Nicholson gave the fluid mosaic model or lipid bilayer model of plasma membrane. (g) It is flexible and can be folded, broken and reunited.

(i) Functions of Plasma Membrane: (a) It regulates the movement of molecules inside and outside the cell. (b) It helps in maintaining the distinct composition of the cell. (ii) Transportation of molecules across the Plasma Membrane: This can be done by following ways: Diffusion – Movement of solutes or ions from a region of higher concentration to a region of lower concentration is called as diffusion. It does not require energy therefore, it is called as passive transport. Osmosis– The movement of solvent or water from its higher concentration (solvent) to lower concentration (solvent) through a semipermeable membrane is called as osmosis. Or The movement of water a across semipermeable membrane is called as osmosis. Osmosis can also be called as ‘Diffusion of solvents’ Endomosis- Movement of solvent into the cell is called Endomosis. Exosmosis- Movement of solvent outside the cell is called Exomosis.

Types of Solutions on the Basis of Concentration and its effect on cell

(a) Isotonic Solution– When concentration of a solution outside the cell is equal to the concentration of cytoplasm of the cell, it is called as isotonic solution. (b) Hypertonic Solution– When concentration of a solution outside the cell is more than inside of the cell. Due to this, cell loses water and becomes plasmolysed. Plasmolysis– Shrinking of the protoplasm away from the cell wall due to Excessive loss of water (Exosmosis) is called Plasmolysis (c) Hypotonic Solutions– When the concentration of the solutions outside the cell is lesser than that of cytoplasm of cell, due to excessive endosmosis cell swells up and animal cell may bursts.

Cell Wall

It is the outermost covering of the plant cells and cells of fungi. It is absent in animal cells. Cell wall is rigid, strong, thick porous and non-living structure. In plant it is made up of cellulose and hemicelluloses. In fungi it is primarily made up of Chitin. Cell walls of two adjacent cells are joined by a layer called middle lamellae and microscopic channels called plasmodesmata for transport.

Functions of Cell Wall

(a) It provides definite shape, structure, support and protection to the cell. (b) It provides strength to the cell. (c) It is permeable and allows entry of molecules of different sizes & thus control intercellular Transport. • Nucleus is the most important cell organelle which directs and controls all its cellular activities. • It is called as ‘Headquarter of the cell’/controller of cell. • Nucleus 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 called Nucleoid. • It has double layered covering called as nuclear membrane. • Besides nuclear membrane, nucleus also contains nucleolus and chromatin material. Chromatin is made up of DNA (Deoxyribonucleic acid) and Protein, that ultimatly condense and forms chromosome. • Chromosomes or chromatin material consists of DNA which stores and transmits hereditary information for the cell to function, grow and reproduce. •The functional segment of DNA is called Gene.

Functions of Nucleus

(a) It direct and controls all the metabolic activities of the cell and regulates the cell cycle. (b) It helps in transmission of hereditary characters from parents to their offsprings. Cytoplasm is the fluid content enclosed by the plasma membrane. Cytoplasm was discovered by Kolliker in 1862. It is the site of both biosynthetic and catabolic pathways (Metabolic activities) It can be divided into two parts: (i) Cytosol – Aqueous soluble part contain various fibrous proteins forming cytoskeleton. It contain about 90% water, 7% Protein 2% carbohydrates & 1% etc. (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 membrane bound tubules and sheet present in the cytoplasm. • It was discovered by Garnier and structure given by Porter, Claude and fullum. • These are present in all cells except prokaryotes and mammaliam erythrocytes.

Endoplasmic reticulum is of two types

Function of ER

Golgi apparatus

consists of a system of membrane bounded fluid filled vesicles arranged parallel to each other in stacks called Cisternae along with some large and spherical vesicles. It was discovered by Camillo Golgi. It is absent in prokaryotes, mammalian RBC’s & sieve cells.

Functions of Golgi apparatus

(a) Its function include the storage, modification, Packaging & secretion of products in vesicles. (b) It involved in the formation of lysosomes. (c) It is secretary in nature. It helps in melanin synthesis. (d) It also involved in the synthesis of cell wall & plasma membrane. • It is a rod shaped structure found in cytoplasm of all eukaryotic cells except mammalian RBC’s. • These are also absent in prokaryotes. • It was first seen by Kolliker in insect cells in 1880. •It is also called as ‘Power House of the Cell’ or the ‘Storage Battery’. • It is double membranous structure where outer membrane has specific proteins while inner membrane is folded inside to form chambers called Cristae. • Mitochondria has its own DNA & Ribosomes

Functions of Mitochondria

(a) Its main function is to produce, store and release the energy in the form of ATP (Adenosine Triphosphate) The energy currency of the cell. (b) It is the site for cellular respiration (Kreb cycle) in which ATP are produced. Ribosomes 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) (Ribonucleic Acid) molecules, Which comes out of the Nucleolus and translated (Protein synthesis) by ribosomes attached to RER in the form of proteins.

Functions of Ribosomes

Chloroplast have following two parts

(i) Grana- It constitutes the lamellar system. These are found layered on top of each other. These stacks are called Grana. Each granum of the chloroplast is formed by superimposed closed compartments called Thylakoids. Function- They are the sites of light reaction of photosynthesis as they contain photosynthetic pigment chlorophyll, photosynthetic units. (ii) Stroma– It is a granular transparent substance also called as matrix. Grana are embedded in it. Besides Grana they also contain lipid droplets, starch grains, ribosomes etc.   These are membrane bounded regions in the cytoplasm containing water and other substances. They are bounded by a single membrane called Tonoplast. In animal cells vacuoles are absent or smaller in size. In plant cells a single large vacuole is found which occupies about 90% of the volume of cell.

Functions

It helps in maintaining osmotic pressure in a cell & stores toxic metabolic products (Waste product) water, sugar, protein etc. They are tiny single membrane bound cell organelle containing powerful digestive enzymes for intracellular digestion. Lysosome absent in RBC’s Lysosomes are synthesised by golgi body & enzymes present in it are synthesised by RER.

Suicidal Bag

Difference between Plant cell and Animal cell

Plant Cell Animal Cell • Contain chloroplasts for Photosynthesis • No chloroplasts (plastids) • Have a cell wall to maintain structure and rigidity. • No cell wall • Usually do not contain lysosomes and Peroxisomes. • May Contain cilia and/or flagella • Cells are square and rigid or geometric shaped. • Cells are fluidic and flexible, many shapes. • Have one large central vacuole. • Has small or no vacuoles. • Have lysosome

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