biology holiday homework
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BIOLOGY HOLIDAY HOMEWORK
BIOLOGY HOLIDAY HOME WORK THE FUNDAMENTAL UNIT OF LIFE1
In 1665 Robert Hooke examined the slice of cork by self designed microscope .Cork is a substance which comes from bark of tree.By microscope cork resembled the structure of a honey comb consisting of many little compartments.This was very important invention in the history of science that living things appear to consist of separate small units.The word cell use to describe this unit in biology .HISTORY
In1839 Purkinje discovered some fluid substance in the cell termed protoplasm.In 1940 with the discovery of electron microscope complex structure of cell and various organelles could understand.
CELLAll organisms around us are made up of cells.Some organisms are made up of single cell called unicellular organism .e.g. Amoeba.Many cells grouped together in a single body and perform various functions called multicellular organisms .Some organisms have different kinds of cells with different shape and size. Each living cell has a capacity to perform certain basic function . That are characteristics of all living forms .All living cell perform this basic function.As we know there is a division of labour in multicellular organism such as human being , means different part of our body perform different part of our body perform different functions .A single cell also perform different functions with the help of its component which is known as cell organelles .These organelles together constitute the basic unit called the cell.
STRUCTURE OF A CELL A cell have 3 features Plasma membrane NucleusCytoplasmPlasma membraneCell membrane is the outer most covering of the cell that separate the content of the from its external environment .
Structure The plasma membrane is flexible made up of organic molecules Lipid ProteinWe can observe the structure of plasma only through an electron microscope .The flexibility of cell membrane also enable the cell to engulf the food and other material from its external environment . This process is known as endocytosis. Ex :- Amoeba enquires its food through this process.
Cell wallIn plants cells addition to the plasma membrane another rigid outer covering called the cell wall.Structure This is made up of complex substance cellulose . It provide strength to plant. FunctionsCell walls permit the cell of plant , fungi and bacteria to with stand very dilute external media without bursting .It take water by osmosis.
Function of plasma membrane Separation of content of cell.Permit the entry and exit of material .Prevent movement of some other material called selectively permeable membrane .Some substance like carbon dioxide , oxygen can move across the cell membrane by a process called diffusion. In diffusion substance move from a region of high concentration to low concentration.
Use of diffusion waste product can excrete out by the cell like carbon dioxide , Respiration.Movement of water through semi permeable membrane is called osmosis.Use of osmosis Transportation of water Transportation of dissolve substance Transportation of nutritious substance Transportation/excretion of waste productExamples of osmosis unicellular fresh water organism and most plant cell absorb water by plant root.Use of diffusion waste product can excrete out by the cell like carbon dioxide , Respiration.Movement of water through semi permeable membrane is called osmosis.Use of osmosis Transportation of water Transportation of dissolve substance Transportation of nutritious substance Transportation/excretion of waste productExamples of osmosis unicellular fresh water organism and most plant cell absorb water by plant root.
NUCLEUSNucleus is a darkly coloured spherical or oval dot like structure near the Centre of each cell.StructureDouble layer covering of nucleus Nuclear membrane.Functions of nuclear membrane porous and transfer the material from nucleus to cytoplasm.
Chromosomes are rod shapely structure. Parts of chromosomes DNA and protein. DNA genes and chromatin .Function of Nucleus cellular reproductionTypes of nucleus Organisms with poorly defined nuclear membrane is known as prokaryotes .Organisms with well defined nuclear membrane is known as eukaryotes.
NUCLEUSCYTOPLASMThe cytoplasm is the fluid content inside the plasma membrane. It contains many specialized cell organelles .
CELL ORGNELLESLarge and complex cells of multicellular organism need a lot of chemical activities to support their complicated structure and functions.To perform these activities membrane bounded little structures are present called organelles, this is the feature of eukaryotic cellThese organelles are visible only with electron microscope.
TYPES OF CELLThese organelles are :Endoplasmic reticulumGolgi apparatusLysosomesMitochondriaPlastids Vacuoles ENDOPLASMIC RETICULUM (ER)It is a large network of membrane bound tubes and sheets.
Structure Long tubules and round or oval vesicles. TypeRough Endoplasmic Reticulum (RER)Looking rough under microscope because it contains particles called ribosomes attached to its surface. Ribosomes : sight of protein manufacturer depending on need.Smooth Endoplasmic Reticulum (SER) Size of SER Varies in size Smooth in different cells and forms network system.
Functions Of Endoplasmic ReticulumTransport of material like protein within the cell organs .Providing a surface framework for some biochemical activities of cell.Detoxifying many poison and drugs .GOLGI APPARATUS It was discovered by Camilo Golgi by his name is called Golgi Apparatus .
Structure Membrane bounded vesicles arrange approximately parallel to each other called cistern.It is also connected with the membrane of ER so its also complex cellular membrane system. FunctionsStorageModificationsPackaging of products in vesicles Formation of lysosomes LYSOSOMESIt is known as waste disposal system of the cell .Helps to keep the cell clean by digesting any foreign material like bacteria or food.It contains powerful digestive enzymes which help to digest foreign materials . It is also known as suicide bags of a cell. StructureMembrane bound sacs, filled with objective enzymes.
MITOCHONDRIAMitochondria are known as power house of the cell.It release energy for various chemical activities. StructureIt have 2 membrane covering outer membrane is very porous while inner one is deeply folded .These folds create a large surface area for formation of ATP.
FunctionsATP is Adenosine triphosphate .It produce energy so it is known as the energy currency of the cell.It is a organelle of sense because it produce DNA PLASTIDSPlastids are present only in plant cells. Types Chromoplast coloured plastidsgreen , yellow etc. Leucoplast white or colourless plastids .
StructureThe internal organization of the plastids consist of numerous membrane layers embedded in a material called the stroma. FunctionsIt contains pigment chlorophyll known as chromoplast and leucoplast .Chloroplast contain pigment chlorophyll used for photosynthesis , it is found in the chromoplast.Leucoplast is used for storage.Plastids work like mitochondria because its own DNA and Ribosomes VACUOLESVacuoles are storage sac for solid or liquid contents.In plant cells there is very large central vacuole , providing rigidity to cell.
CONCLUSIONCells have a basic structural organization with the help of membrane and organelles.Cells perform functions like respiration, obtaining nutrition, forming new proteins and cleaning of waste materials etc.Thus cell is the fundamental structural and functional unit of life.PRESENTED BY Paridhi Gouri PatelCLASS 9th