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Understanding cells 2.1 101 1
Cells are the basic unit of living organisms. They come in various sizes and shapes. Robert Hooke first observed cells using a microscope. A microscope uses lenses and light to magnify cells, which are too small to be seen with the naked eye. Cells contain a cell membrane, cytoplasm, and usually a nucleus. Plant cells also contain a cell wall and often chloroplasts. The structures of cells allow them to carry out functions necessary for life.
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Understanding cells 2.1 101 1
- 2. Understanding Cells Cells •Living organismsaremadeupof oneor morecells. •Cellsarethemost basic unit of organismswhich can function on their own. Cellscarry out lifeprocessessuch asrespiration, division, excretion and growth. •Cellsarethebuilding blocksof an organism. •Cellswork together to keep an organism alive. •Cellsof living thingsexist in many sizesand shapes. They can beround, oval, long, short, with tail and so on.
- 3. •Robert Hooke, aBritishScientist, wasthefirst person to study cells. Thefigurebelow showssomecork cells observed through amicroscopeby him. Cork cells as seen by Robert Hooke
- 4. Using a microscope •Cellsareverytiny and cannot beseen with thenaked eye. •Cellsof living organismscan be observed using a microscope. A Microscope
- 5. Functions of thedifferent parts of microscope Parts of a microscope Functions Eye piece •To magnify theimageof thespecimen Objective lens •To magnify thespecimen Body tube •To hold theeyepieceat afixed distanceaway from theobjectivelens Coarse focus knob •To raiseor lower thebody tubegently for sharp focusing. Arm and base •For holding and supporting themicroscope
- 6. Clip To holdthe slide on the stage in position Stage To put theslideon. Diaphragm To control theamount of light entering thelens. Mirror To direct reflected light towardsthediaphragm. Condenser To concentratelight from themirror onto thespecimen
- 7. The correct wayto use a compound light microscope a. Placethemicroscopeon aflat surfacein awell- lighted area. b. Position thelow power objectivelensabovethehole of thestage. c. Raisethecondenser ashigh asit can go and open the irisof thediaphragm fully. d. Look through theeyepieceand adjust themirror to obtain abright field of view.
- 8. e. Placeaslidewith thespecimenon thestageand hold it in placewith theclip. f. Lower theobjectivelensusing thecoarsefocusknob until it isadjust abovetheslide. g. Look through theeyepiece. Turn thecoarsefocus knob counter – clockwiseuntil theobject isin focus. h. If necessary, changeto ahigh power objectivelens. i. Adjust thefinefocusknob until asharp imageis obtained.
- 9. General structure ofa cell •A typical cell ismadeup of cell membranewhich containsaliving substancecalled protoplasm. a.Protoplasm consistsof anucleusand cytoplasm. b.Thenucleusisaspherical in shapeand surrounded by a nucleusmembrane. c.Cytoplasm isacolourlessjelly – likematerial surrounded by cell membrane. d.Thecell membraneisathin film which ispartially permeableto thesurrounding substances.
- 10. Structure of animalcells •Generally, each animal cell ismadeup of cell membraneand protoplasm (which consistsof cytoplasm and nucleus.) An animal cell
- 11. •Animal cellsdo nothavecell wallsor chloroplasts. •Thereisgreat variety of formsand functionsamong animal cells. Thefigurebelow showssomeexamplesof animal cells Paramecium Red blood cell Nerve cell
- 12. Structure of plantcells •Thefigurebelow showsthegeneral structureof aplant cell. A plant cell
- 13. •Thebasic structureof plantcellsissimilar to that of animal cellsin having acell membrane, cytoplasm and a nucleus. •All plant cellshaveacell wall which givesthem an almost fixed shape. •Plant cellsoften haveonelargevacuole, whereas animal cellsusually havemany small ones. •Most plant cellsthat areunder thelight contain chloroplastswhich aregreen in colour.
- 14. •Plant cells varyin their shapes, sizes, structures and functions. Epidermal cell in the root Palisade cells Guard cells Examples of plant cells
- 15. The function ofcell structures Structure Present in Function Cell membrane All cells •Enclosethecytoplasm. •Controlsthemovement of materialsin and out of cells. Cell wall ( anon – living layer of cellulose) Plant cell only •Supportsand giveshapeto the cells Cytoplasm ( jelly – like substance) All cells •Thisiswherechemical reactions takeplaceinsidethecell. •Storesdissolved material
- 16. Cell membrane Cellwall Cytoplasm
- 17. Structure Present inFunction Nucleus Almost all cells (maturered blood cellsdo not have nuclei) •Controlsall cellular activities Chloroplast (contain green pigmentscalled chlorophyll) Most plant cells that areunder light •Chlorophyll absorbslight for photosynthesisto producefood and oxygen. Vacuole(cell sap) Most plant cells and someanimal cells •Holdsuseful substancesand wastes. •Supportstheplant when it isfull of water.
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- 19. Comparison between animalcell and plant cells SimilaritiesSimilarities Animal cells Plant cells •Have cell membrane •Able to carry out activities to life •Have protoplasm
- 20. DifferencesDifferences Animal cells Plantcells •Generally smaller •Usually irregular and may vary during life •No cell wall •No chloroplast •With a small or no vacuoles •Generally bigger •Fixed by cell wall •Have a cell wall •Many plant cell under light have chloroplasts •Often have a large vacuole Size Shape Contents
- 21. •Usually at the centreof the cells •Glycogen granules •Maybe to one side of the cells •Starch granules Position of nucleus Food storage