Question

Write notes on cell theory.

Answer 1

Cell theory:Cells are the basic units of structures and function in all living thingsAll living things are composed of cellsNew cells are produced from pre-existing cells Cells are small. This is important because they need a high surface area-to-volume ratio.Volume decides the amount of chemical activity occurring in a cellSurface Area decides the amount of substances or particles that can pass through the cell boundary Major Parts of the cell: Plasma MembraneMade up of a phospholipid bilayerPlasma membranes are selectively permeable barriersSubstances that can freely pass through:Small, uncharged, polar moleculesWater through water channels called aquaporinsHydrophobic moleculesO2Allows the cells to maintain constant internal environmentMembrane contain proteinsIntegral membrane proteinsPeripheral membrane proteinsPlasma membranes are also important for receiving signals and communication NucleusContains the DNANucleus is where DNA replication occursSite of the genetic control of the cell activitiesProteins, called histones, and DNA are combined to formchromatinThe nucleus is surrounded by the nuclear envelopeNuclear pores direct the passage of moleculesUsually the largest organelle RibosomesRibosomes are where protein synthesis occursAppear in both prokaryotes and eukaryotesIn eukaryotes:They are attached to the rough ERLocated in the cytoplasmAlso found inside the mitochondria and chloroplasts Endoplasmic ReticulumRough ERRibosomes are presentSmooth ERHas no ribosomesInvolved in the synthesis of lipids and steroidsInvolved in the breakdown of toxins, drugs or pesticidesInvolved in the hydrolysis of glycogen Golgi ApparatusGolgi Apparatus modifies and packages proteins received from the ER into vesiclesCis regionReceives vesicles coming from the endoplasmic reticulumTrans regionVesicles will bud off from the Golgi apparatus and onto the plasma membrane LysosomesLysosomes are vesicles that orginate from the Golgi apparatusLysosomes contain digestive enzymes MitochondriaCarry out cellular respiration ChloroplastsCarry out photosynthesis PeroxisomesBreak down substances such as hydrogen peroxide CytoskeletonSupports and maintains the cellular shapePositions the organellesAllows for some types of movementThree parts:MicrofilamentsIntermediate filamentsMicrotubules  Cilia and FlagellaImportant for motilityCiliaShort and many presentExample: can sweep away debris and other particles from the respiratory tractFlagellaLong and whip-likeUsually one or two presentExample: can propel sperm Cell WallProvide support for the cellCan be found in bacteria, fungi, plants and other types of organisms  CentriolesCentrioles are involved in the formation of mitotic spindle VacuolesUsed as storageStore waste products, starch, pigments or even toxic compoundsCan provide structural support for plant cellsIf the central vacuole was filled, then they exert pressure on the cell walls.This pressure is also known as turgor   There are differences between the plant and animal cells 
For example:
Typically, cell walls, chloroplasts and the central vacuoles are present in plant cells and absent in animal cells.End of notes on cell theory and cell parts.

Answer 2

Answer-

⭐ In 1838, Matthias Schleiden studied various types of plants and found that plants are composed of cells which forms the tissues of the plant.

⭐At around the same time, in another year, in 1839, Theodore Schwann studied various animals and found that they are composed of cell membrane called plasma membrane.

⭐Schleiden and Schwann together formulated the cell theory.

⭐However, it did not explain as to how new cells were formed.

⭐Rudolf Virchow in 1855 first explained that cells divide and new cells are formed from pre-existing cells.

⭐Cell theory is defined as:

● All cells are composed of cells and its products.

●New cells are formed from pre-existing cells.