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 The cell is the structural and functional unit of all
living organisms.
 Robert hooke was the first scientist who look at cells
under a microscope by viewing and describing the box –
like structures of cork.
Researches had formulated the cell theory that has
three principles:
All organisms are composed of one or more cells.
The cell is the basic functional unit of living organisms.
All cells arise by division of pre-existing cells
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All cells share four structural features:
Plasma membrane
 Delineate the border of the cell
 Function in regulate the passage of
materials into and out of the cell.
Plasma
membrane
Deoxyribonucleic acid (DNA)
 Function as the genetic instructions for the
cell.
Genetic
material
DNA
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Plasma
membrane
 Ribosomes
 Function as a site of
Ribosome
protein synthesis
 Cytoplasm
 Components enclosed by
the plasma membrane by
which the rest of
organelles are floating.
Cytoplasm
Genetic
material
DNA
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Cells vary in:
 Size
 Function
 Organization
With respect to internal organization there are two
major types of cells according to the presence of
nucleus.
Nucleus is the spherical organelle within the
cytoplasm, which contain the genetic materials
(DNA) and controls cell metabolism and division.
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Prokaryotic (before the nucleus)
Eukaryotic (true nucleus)
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Prokaryotic
Eukaryotic
Unicellular
 unicellular ex. Protists
 multicellular ex. Animal, plants
and fungi
Small cell size (0.5 – 5 µm)
Don’t have organized nucleus
surrounded by nuclear membrane
and the DNA found free in the
cytoplasm
Large cell size (5 – 200 µm)
Have organized nucleus enclosed
by a nuclear membrane, the DNA
found within the nucleus
Don’t have membrane bound
organelles
Have membrane bound organelles
ex. mitochondria
In this lab. We will examine a
prepared slides of different
bacterial cell shapes
In this lab. We will examine and
describe cells of humans (animals)
and onions (plants)
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Basic shapes of bacterial cells
1. Spheres (cocci)
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2. Rods (bacilli)
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3. Spirals
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Human cheek epithelial cells
The cells that line the inner check (inside the mouth) called epithelial cells,
easily removed by:
1. With a clean toothpick, gently scrape the inside of your cheek
several times.
2. Roll the scraping into a drop of water on a clean microscope
slide.
3. Add a small drop of methylene blue.
4. Cover with coverslip gently.
5. Discard the used toothpick.
6. Examine under microscope and notice:
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•The cell appear as pentagons
•The cells are flat
•The nucleus will be blue
•The cytoplasm will stain light blue
•The cell membrane
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Onion epidermal cells
Prepare a wet mount of onion epidermal tissue according to the steps
Cut an onion bulb into quarters.
Remove one of the fleshy scale leaves
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Fold the leaf backward to produce a ragged
piece of epidermis.
Peel back a small piece of epidermis.
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Spread the epidermis in a drop of water on a slide
Add a small drop of Lugol’s solution, gently cover it by cover slip to avoid
air bubbles
Observe under microscope and notice
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•The shape of onion cells
•The nucleus
•The cell wall
•Cytoplasm
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Plant cell
Cell wall
Cell membrane
Ribosome
Smooth ER
Golgi apparatus
Chloroplast
Nucleus
Rough ER
Large central vacuole
Mitochondrion
Cytoplasm
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Animal cell
Lysosome
Mitochondrion
Golgi apparatus
Rough ER
Nucleus
Smooth ER
Cell membrane
Cytoplasm
Ribosome
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Animal cells compared with plant cells
Plant cell
Animal cell
Chloroplast
-
Cell wall
-
Central vacuole
-
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