cells unit 1 aqa biology

1. EPITHELIAL CELLS
EPITHELIAL CELLS IN THE SMALL INTESTINE ARE ADAPTED TPO ABSORB FOOD EFFICIENTLY:
• The wallsof the small intestine have lots of finger-like villi toincrease surface area
• The cellson the surface of the villi have microvilli to increase surface area evenmore
• They also have lots of mitochondria- to provide energyfor the transport of digestedfoodmoleculesinto
the cell
THE MICROVILLI
 The brush borderof the microvilli providesaverylarge surface areafordigestedfoodmoleculestopass
through-makingabsorptionmore rapid
THE NUCLEUS
 The largestorganellle inthe cell
 The nucleuscontainschromosomesmade of DNA
 Each gene on a chromosome isa code the cell can read to make a specificproteinthe cell hastoproduce
 A dense partof the nucleuscalledthe nucleolusmakesribosomes
 The nucleushasa membrane (the phospholipidbilayer)whichisjoinedinplacestothe endoplasmic
reticulum
 Poresinthe membrane allowthe RNA toleave the nucleustoenterthe cytoplasm, where the proteinsare
assembled
 The nucleusalsocontainschromatin
 Chromatinismade fromproteinsandDNA (DNA controlsthe cell`sactivities)
MITOCHONDRIA
 Are foundinlivingplantandanimal cell
 Mitochondriaare usuallyoval-shaped

2.  Theyhave a double membrane
 The innerone isfoldedtoformstructurescalledcristae- thisallowsthe membranetoholdmore enzymes
 The outer membrane controlswhatcanenterandleave the mitochondrion-
 The gap betweenthe innerandoutermembrane iscalledthe intermembrane space
 inside isthe matrix,whichcontainsenzymesinvolvedin respiration
 the mitochondriaisthe site of aerobicrespiration
 it producesATP - a commonenergysource inthe cell
 ATP isusedforactive transport
 Mitochondriaare foundinlarge numbersincellsthatare veryactive and require alotof energy
RIBOSOMES
 A ribosome isaverysmall organelle thatfloatsfree inthe cytoplasmoris
attachedto the rough endoplasmicreticulum
 Ribosomesare maidmainlyof RNA andproducedinthe nucleolus
 Theirjobis to attach to mRNA moleculesasproteinsare made
 Some ribosomesare free floating- thesemake proteinsforuse inthe cell
 Othersare attachedto the endoplasmicreticulum- thesemake proteinstobe
transportedoutof the cell
ENDOPLASMIC RETICULUM
 Flattenedtubesspreadingoutfromthe nuclearmembrane
 There are twotypesof endoplasmicreticulum
 The smoothER isa systemof membranesenclosingafluid-filledspace
 The smoothER synthesisesandprocesseslipids
 The rough ER is similartothe smoothER but iscoveredinribosomes
 The rough ER foldsand processesproteinsthathave beenmade atthe ribosomes

3. GOLGIAPPARATUS
 Thisis a group of fluid-filledsacs
 It processesandpackagesproteins(made inthe ER) andnew lipids
 It then formsbubblesaroundthemcalledvesicles
 The vesiclestransportthe proteintoanotherpartof the cell,orto the edge of the cell where theyfuse with
the plasmamembrane,secretingthe protein
 The Golgi also makeslysosomes
 The appearanceof theGolgi is constantly changing asmaterialcomesin oneside of the ER and is lost from
the otheras completed vesicles bud off
LYSOSOMES
 Thisis a roundorganelle surroundedbyamembrane,withnoclearinternal structure
 Lysosomescontaindigestiveenzymes
 These are keptseparate fromthe cytoplasmbythe surroundingmembrane,andcanbe usedto digest
invadingcellsortobreakdownworn outcomponentsof the cell
 The body usesthisprocesstobreakdownexcessmuscle inthe uterusafterbirth,andto destroymilk-
producingtissue inthe breastsaftera babyhas beenweaned