2. Understanding Cells
Cells
•Living organismsaremadeup of 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, aBritish Scientist, wasthefirst person
to study cells. Thefigurebelow showssomecork cells
observed through amicroscopeby him.
Cork cells as seen by Robert Hooke

4. Using a microscope
•Cellsarevery tiny
and cannot beseen
with thenaked eye.
•Cellsof living
organismscan be
observed using a
microscope.
A Microscope

5. Functions of the different 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 hold the 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 way to 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 thespecimen on 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 of a 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 animal cells
•Generally, each animal cell ismadeup of cell
membraneand protoplasm (which consistsof
cytoplasm and nucleus.)
An animal cell

11. •Animal cellsdo not havecell wallsor chloroplasts.
•Thereisgreat variety of formsand functionsamong
animal cells. Thefigurebelow showssomeexamplesof
animal cells
Paramecium Red blood cell
Nerve cell

12. Structure of plant cells
•Thefigurebelow showsthegeneral structureof aplant
cell.
A plant cell

13. •Thebasic structureof plant cellsissimilar 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 vary in their shapes,
sizes, structures and functions.
Epidermal cell in the
root
Palisade
cells
Guard cells
Examples of plant cells

15. The function of cell 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 Cell wall
Cytoplasm

17. Structure Present in Function
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.

18. Nucleus Chloroplast
Vacuole

19. Comparison between animal cell and plant cells
SimilaritiesSimilarities
Animal cells Plant cells
•Have cell membrane
•Able to carry out
activities to life
•Have protoplasm

20. DifferencesDifferences
Animal cells Plant cells
•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
centre of the
cells
•Glycogen
granules
•Maybe to one
side of the cells
•Starch
granules
Position of
nucleus
Food
storage