The Cell
The basic unit of life
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Contents
The Light
Microscope
Electron Microscope
The Cell
Cell Ultrastructure
Cell membrane
The Cell Wall
Mitochondria
Plastids
Ribosomes
Vacuoles
Slides of cell types
Prokaryotic or
Eukaryotic?
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The Light Microscope
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Microscope
• Light microscope
• Light microscope: it focuses light with a
combination of objective lens and an
eyepiece to a maximum magnification of
1500
• The parts of a light microscope include:
• The stage, to hold the slide
• The light source
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Microscope cont’d
• The diaphragm, to adjust the
brightness of the light
• The eyepiece
• The objective lens
• The total magnification is found by
multiplying the magnification of the
eyepiece with that of the objective lens.
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Transmitting Electron Microscope
(TEM)
• Electron microscope: a microscope
that magnifies up to 500,000 times
by passing beams of electrons
through the specimen
• A TEM is much more powerful than
a light microscope. It reveals the
ultrastructure of cells because its
resolving power is about 1 nm.
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Scanning Electron Microscope (SEM)
• Photographs reflected electros from
surfaces and reveals 3D structures.
• It has less detail than a TEM but can
be used on slightly larger specimens
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The Cell
• Cell: the basic unit of life.
• Cells consist of plasma membrane,
cytoplasm, and nucleus (if present).
• Outside the plasma membrane there
may be a cell wall e.g. plant, fungal
and bacterial cells.
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There are two kinds of cell
• prokaryotic cells, e.g. bacteria, do not
have a true nucleus
• eukaryotic cells do have a nucleus.
Eukaryotic cells may also have
mitochondria and chloroplasts.
Plant cells differ from animal cells in
having
• A cell wall
• A large vacuole
• Chloroplasts.
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Prokaryotic Cells
Possess nuclear material
Do not have a membrane surrounding
this genetic material
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Prokaryotic cells – mixed bacteria
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Eukaryotic Cells
Possess a true nucleus
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Eukaryotic cells - amoeba
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More eukaryotic cells
Paramaecium
Spirogyra
Euglena
Chlamydamonas
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Cell Ultrastructure
• Cell ultrastructure:
the cell organisation that is visible
under the electron microscope.
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Cell ultrastructure
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Cell Components
Cell wall
Cytoplasm
Nucleus
Vacuole
Chloroplast
Cell membrane
Mitochondria
Nuclear pores
Ribosome
DNA
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Cell Membrane Structure 2D
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Cell membrane structure 3D
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Phospholipid
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Phospholipid
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Cell Membrane
• Is not solid and is self-sealing if broken
open, i.e. it is a fluid, moving barrier.
• Forms a bilayer around the perimeter of
the cell
• The heads of the lipid molecules are
hydrophilic – attracted to water
• The tails of the molecules are
hydrophobic – repel water
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Cell Membrane cont’d
• Large protein molecules float freely
within the bilayer
• Carbohydrate molecules are often fixed
to proteins and lipids on the outer side
of the membrane
• These glycoproteins and glycolipids are
involved in making contact with other
cells and in cell protection
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Functions of cell membrane
•
•
•
•
Allow diffusion of gases
Allow the passage of water by osmosis
Allow the transmission of light
Actively move specific chemicals from
one side to the other
• Defend the cell against attack
• Generate nerve impulses (as in nerve
cells)
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The Cell Wall
• Lies outside the cell membrane
• Composed of tiny microfibrils of
cellulose and other polysaccharides
• Very strong – contributes to strength,
protection and shape of the cell
• Fully permeable
• Adjacent plant cells glued together by
calcium pectate – the middle lamella
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Mitochondrion structure
• Power house of cell
• Produces ATP
• Used during
respiration
• 2 or 3 per skin cell
800 per muscle cell
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Plastids
Three types
• Chloroplasts (green
- chlorophyll) –
photosynthesis
• Chromoplasts
(coloured) – petal
colour
• Leucoplasts
(colourless) – starch
storage e.g. potato
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Ribosomes
• Thousands found in the cytoplasm of
every cell
• Made from protein and RNA
• Enzymes and proteins made here –
DNA in the nucleus sends mRNA to the
ribosomes with instructions for protein
synthesis
• A single strand of mRNA often passes
over several ribosomes
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Vacuoles
• Plant cells have permanent vacuoles
• Fluid filled spaces surrounded by a
membrane (the tonoplast)
• Contain cell sap – a mixture of food,
minerals, pigments and water
• Animal cells have smaller, temporary
vacuoles sometimes called vesicles
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Examples of Animal Cells
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Examples of Plant cells
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Drawing of a Root cell - TEM
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Prokaryotic? or Eukaryotic?
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Prokaryotic cells
• Bacteria differ from plants, animal and
fungi in the type of cell they possess
• Bacteria have prokaryotic cells –
perhaps the type of cell that first
appeared millions of years ago
• Do not have a definite nucleus and have
fewer organelles
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Eukaryotic cells
• Plants, animals and fungi possess
eukaryotic cells
• A more advanced cell type
• Have a definite nucleus, bounded by a
nuclear membrane, and many
organelles
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Prokaryotic Cells V Eukaryotic Cells
• No distinct nucleus
• No nuclear membrane
• Single, circular
chromosome of DNA
• Have ribosomes
• No mitochondria
• No plastids
• Cell wall contains protein
• Small cell size 1 – 10 µm
• Distinct nucleus
• Nucleus bounded by a
nuclear membrane
• Many chromosomes of
DNA
• Have ribosomes
• Have mitochondria
• Have plastids
• Cell wall contains
cellulose or chitin
• Larger cell size 10 – 100
µm
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Generalised Animal Cell
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Generalised Plant Cell
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END
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