Biology - An Illustrated Guide to Science (794127), страница 4
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It is used forintracellular transport. Ribosomes,usually found on the roughendoplasmic reticulum, synthesizeprotein.● The Gogli body is involved with thecreation of the endoplasmic reticulumand in the secretion of somesubstances from the cell. It is thepackaging center of the cell.● Lysosomes contain digestive enzymes.●ribosomeGolgibodycentriolesnucleusnuclearenvelopenuclearporenucleoluschromatinlysosomemitochondrionOther structuresThe nucleus controls the cell.
It isseparated from the cytoplasm by thenuclear envelope. The nucleuscontains the nucleolus, which containsthe DNA templates for ribosomal RNA,and chromatin, the substances fromwhich chromosomes are made.Openings in the cell's nuclearenvelope, called nuclear pores, allowthe exchange of materials between thenucleus and the cytoplasm.● Mitochondria are the site of aerobicrespiration, which gives the cellenergy. The mitrochondrion issometimes referred to as the“powerhouse” of the cell.● Pinocytotic vesicles contain solublemolecules from outside the cell.● Centrioles, found only in animal cells,help the cell to divide.●© Diagram Visual Information Ltd.roughendoplasmicreticulum22UNITYKey wordschloroplastendoplasmicreticulumGolgi bodygranumlysosomemitochondrionplasmamembraneribosomePlant cell:electron microscopePlant cellcell wallPlant and animal cells●Many of the structures found in animalcells are also present in plant cells.However, plant cells do not containcentrioles.plasmamembranecytoplasmMembrane structuresThe plant cell uses a doublelayered membrane to buildmany structures: the plasmamembrane, Golgi body, lysosomes,and endoplasmic reticulum.
Thesemembrane-based structures carry outexactly the same functions in plantsand animals (see page 23).● The plasma membrane in plants hasthe same double-layered structure as ithas in animals but is further supportedby a cell wall. The cell wall is a toughcellulose-rich structure that surroundsthe plant cell. The plasma membraneis not attached to the cell wall, butwhen a plant cell is fully filled withwater, the membrane is pressedtight against the cell wall.●nucleusnuclear envelopenuclear porenucleolusmitochondrionsmoothendoplasmicreticulumribosomeroughendoplasmicreticulumOther structuresPlant cells have a large centralvacuole enclosed by thetonoplast.● The nucleus controls the cell.● Mitochondria are the site ofaerobic respiration, whichgives the cell energy bybreaking down glucose.● Ribosomes, usuallyfound on the roughendoplasmic reticulum,make protein.chromatin© Diagram Visual Information Ltd.●vacuolegranumtonoplast(vacuole membrane)ChloroplastsChloroplasts are only found in greenplants.
They are green-colored bodiesthat carry out photosynthesis to makesugar for the plant.● The grana in the chloroplasts containthe photosynthetic pigments.●Golgi bodycell wall ofneighboring cell23Cell substructureUNITYKey wordsCell contentschlorophyllchloroplastcytoplasmendoplasmicreticulumGolgi bodycelllysosomemitochondrionorganelleplasmamembraneribosomePlasma membrane●organellescytoplasmplasma membraneAll cells are surrounded by a plasma(cell) membrane, which separates andprotects the cell and controlsmovement in and out of it. The plasmamembrane is composed of unitmembrane, a two-layered structurewith proteins on the outer surfacesand hydrophobic (water insoluble) fatmolecules on the inside.Cytoplasm●Inside the plasma membrane,cytoplasm takes up most of the cellvolume.
It maintains the shape andconsistency of the cell and storeschemical substances needed for life.The cytoplasm is also the site of vitalmetabolic reactions such as proteinsynthesis.OrganellesSuspended in the cytoplasm areorganelles, specialized structures thatcarry out particular functions.● The nucleus contains the cell’s geneticmaterial.● Chloroplasts are concerned withphotosynthesis and containchlorophyll.● Lysosomes are membrane-boundvacuoles containing digestive enzymes.● Ribosomes are involved in proteinsynthesis and are sometimes attachedin groups to the endoplasmicreticulum (ER) to produce rough ER.● Many plant cells also contain a largevacuole that stores waste.● The endoplasmic reticulum is anetwork of unit membranes runningthroughout the cell.● The Golgi body is an area of the ERparticularly concerned with secretoryfunctions.● Mitochondria carry out respirationand are surrounded by a plasmamembrane, as are chloroplasts.ribosomechloroplastnucleuslysosomeGolgi bodyroughendoplasmicreticulummitochondrion© Diagram Visual Information Ltd.●24UNITYKey wordslipidplasmamembraneproteinPlasma membrane:structureMembrane structurehydrophobicregions ofproteinsProtein-lipid mixAll membranes in the cell are made ofthe same basic structure.
This is calledthe unit membrane and consists oftwo main chemicals: proteins(glycoproteins, etc.) and lipids(glycolipids, etc.).● Lipids are organic molecules that areinsoluble in water.● The main lipid components of plasmamembranes are phospholipids—molecules composed of glycerol,phosphate, and fatty acid residues—and heads with different chemicalproperties (see bottom diagram). Thetails are hydrophobic (water insoluble)fatty acid residues that face the centerof the membrane. The heads, whichare hydrophilic (water soluble), formthe surface.●glycolipidoutside cellinside cellhydrophilicregions ofproteinslipid bilayerexternallayerglycoproteinphospholipidhydrophilicheadhydrophobictailhydrophilic channelinternallayerThree-dimensional model of membrane structureglycoproteinlipid bilayerMembrane structurePhospholipids form wide, thinbilayers.
In between thesephospholipids are membrane proteinsfloating like icebergs in a sea of lipid.● Some proteins reach completelyacross the lipid molecules. Othersprotrude above the lipid layer onone side but only get halfwaythrough the fat layer in the middleof the membrane.● Many of the protein molecules arenot fixed—they can drift around inthe lipid sea.
This fluidity isessential for the proper function ofproteins in the membranes.●Double membranes© Diagram Visual Information Ltd.●A unit membrane consists of one lipidlayer with protein found on each side.However, the membranes in cells aremade of two unit membranes laid ontop of each other.hydrophilic headhydrophobic tailphospholipidhydrophobic tailhydrophilic headmembraneproteins25Plasma membrane:osmosisOsmosisUNITYKey wordsconcentrationgradientosmosispermeabilityplasmamembraneRed blood cellplaced in waterplasma membranesemipermeablemembranesoluteSemipermeablemembranesThe plasma membrane is semipermeable. It lets small molecules likewater pass very easily but holds backlarger solute molecules like proteins.● Water can diffuse through asemipermeable membrane almost asif it were not there. Water alwaysmoves from areas of highconcentration to areas of lowconcentration.● If two areas are separated by asemipermeable membrane and thereis a higher concentration of water onone side, water moves through toequalize the concentration on bothsides.
This type of water movement iscalled osmosis.●outside cellinside cellplasmamembranewatermoleculepore inmembranearrow indicatingmovement ofwatersolute moleculein cell cytoplasmmembraneRed blood cell takesin water and bursts.Concentration gradientThe difference in concentration of asubstance between two areas is calleda concentration gradient.● The movement of materials along aconcentration gradient depends onthe size of the gradient and thepermeability of the space betweenthem.● High concentration gradients givefaster movements. Lower permeabilityslows down movement.● The concentration of water within acell is lower than the outside when itis placed in de-ionized water.
This isbecause some of the space inside thecell is taken up by other chemicals(sugars, proteins, fats etc.). Waterrushes in to equalize theconcentrations, which makes the cellswell and burst.●© Diagram Visual Information Ltd.Model showing osmosis acrossred blood cell membrane26UNITYKey wordsabsorptionactive transportadenosinetriphosphateconcentrationgradientpassivetransportPlasma membrane:active transportActive transportoutside cellActive or passive?Passive transport occurs whenparticles move down aconcentration—from areas of highconcentration to areas of lowconcentration. Passive transport doesnot require any energy input by thecell.
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