Lesson 2: Understanding cells


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Living organisms are made up of one or more cells.•Cells are the most basic unit of organisms which canfunction on their own. Cells carry out life processes suchas respiration, division, excretion and growth.•Cells are the building blocks of an organism.•

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Lesson 2: Understanding cells

  1. 1. Understanding CellsCells•Living organisms are made up of one or more cells.•Cells are the most basic unit of organisms which canfunction on their own. Cells carry out life processes suchas respiration, division, excretion and growth.•Cells are the building blocks of an organism.•Cells work together to keep an organism alive.•Cells of living things exist in many sizes and shapes.They can be round, oval, long, short, with tail and so on.
  2. 2. •Robert Hooke, a British Scientist, was the first personto study cells. The figure below shows some cork cellsobserved through a microscope by him.Cork cells as seen by Robert Hooke
  3. 3. Using a microscope•Cells are very tinyand cannot be seenwith the naked eye.•Cells of livingorganisms can beobserved using amicroscope. A Microscope
  4. 4. Functions of the different parts of microscopeParts of a FunctionsmicroscopeEye piece •To magnify the image of the specimenObjective lens •To magnify the specimenBody tube •To hold the eye piece at a fixed distance away from the objective lensCoarse focus knob •To raise or lower the body tube gently for sharp focusing.Arm and base •For holding and supporting the microscope
  5. 5. Clip T hold the slide on the stage in position oStage To put the slide on.Diaphragm To control the amount of light entering the lens.Mirror To direct reflected light towards the diaphragm.Condenser To concentrate light from the mirror onto the specimen
  6. 6. The correct way to use a compound light microscopea. Place the microscope on a flat surface in a well- lighted area.b. Position the low power objective lens above the hole of the stage.c. Raise the condenser as high as it can go and open the iris of the diaphragm fully.d. Look through the eye piece and adjust the mirror to obtain a bright field of view.
  7. 7. e. Place a slide with the specimen on the stage and hold it in place with the clip.f. Lower the objective lens using the coarse focus knob until it is adjust above the slide.g. Look through the eye piece. Turn the coarse focus knob counter – clockwise until the object is in focus.h. If necessary, change to a high power objective lens.i. Adjust the fine focus knob until a sharp image is obtained.
  8. 8. General structure of a cell•A typical cell is made up of cell membrane whichcontains a living substance called protoplasm.a.Protoplasm consists of a nucleus and cytoplasm.b.The nucleus is a spherical in shape and surrounded by anucleus membrane.c.Cytoplasm is a colourless jelly – like materialsurrounded by cell membrane.d.The cell membrane is a thin film which is partiallypermeable to the surrounding substances.
  9. 9. Structure of animal cells•Generally, each animal cell is made up of cellmembrane and protoplasm (which consists ofcytoplasm and nucleus.) An animal cell
  10. 10. •Animal cells do not have cell walls or chloroplasts.•There is great variety of forms and functions amonganimal cells. The figure below shows some examples ofanimal cells Paramecium Red blood cell Nerve cell
  11. 11. Structure of plant cells•The figure below shows the general structure of a plantcell. A plant cell
  12. 12. •The basic structure of plant cells is similar to that ofanimal cells in having a cell membrane, cytoplasm and anucleus.•All plant cells have a cell wall which gives them analmost fixed shape.•Plant cells often have one large vacuole, whereasanimal cells usually have many small ones.•Most plant cells that are under the light containchloroplasts which are green in colour.
  13. 13. •Plant cells vary in their shapes, sizes, structures and functions.Palisade Guard cellscells Epidermal cell in the root Examples of plant cells
  14. 14. The function of cell structuresStructure Present in FunctionCell membrane All cells •Enclose the cytoplasm. •Controls the movement of materials in and out of cells.Cell wall ( a non – Plant cell only •Supports and give shape to theliving layer of cellscellulose)Cytoplasm ( jelly – like All cells •This is where chemical reactionssubstance) take place inside the cell. •Stores dissolved material
  15. 15. Cell membrane Cell wall Cytoplasm
  16. 16. Structure Present in FunctionNucleus Almost all cells •Controls all cellular activities (mature red blood cells do not have nuclei)Chloroplast (contain Most plant cells •Chlorophyll absorbs light forgreen pigments called that are under light photosynthesis to produce foodchlorophyll) and oxygen.Vacuole (cell sap) Most plant cells •Holds useful substances and and some animal wastes. cells •Supports the plant when it is full of water.
  17. 17. Nucleus Chloroplast Vacuole
  18. 18. Comparison between animal cell and plant cells Similarities Similarities Animal cells Plant cells•Have cell membrane •Have protoplasm •Able to carry out activities to life
  19. 19. Differences Differences Animal cells Plant cells•Generally smaller Size •Generally bigger•Usually irregular •Fixed by cell wall Shapeand may vary duringlife •Have a cell wall •Many plant cell under•No cell wall light have chloroplasts•No chloroplast Contents •Often have a large•With a small or no vacuolevacuoles
  20. 20. •Usually at the •Maybe to one Position ofcentre of the side of the cells nucleuscells•Glycogen •Starch Foodgranules granules storage