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Cell Structure
Chpt. 7
Microscopes
Simple Microscope
• uses single lens
• max magnification
x400
• uses light
Compound Microscope
• microscope used in our
labs.
• max magnification
x1000
Compound Microscope
• Has two magnifying lens:
- the Eyepiece Lens is the lens that you look
through.
- the Objective lens is the lens that is
immediately above the specimen.
Compound Microscope
The Objective Lens:
• There are three objective lenses:
- the scanning lens with the 4X label
- the low power lens with the 10X label
- the high power lens with the 40X label
Compound Microscope
Parts of the Microscope
Compound Microscope
Parts of the Microscope
Part
Function
Lenses
Magnification
Stage
To place the slide on
Clips
Hold the slide in place
Diaphragm
To control the amount of light
Coarse Focus Knob
To focus the image
Fine Focus Knob
To precisely focus the image
Light
To supply light to the object
Compound Microscope
Magnification
Total Magnification:
magnifying power of the eyepiece lens
x
the magnifying power of the objective lens
Example:
Eyepiece lens = 10X
Objective lens = 4X
Total magnification = 10 x 4= 40X
Cell Structure seen using the
Light Microscope
Robert Hooke
Robert Hooke looked at thin
slices of cork under a microscope.
He thought the spaces he saw
reminded him of Monks Cells –
Hence the name cells
Cell Structure seen using the
Light Microscope
Animal Cell
Cytoplasm:
• living material
outside the nucleus.
• most reactions take
place in cytoplasm.
Protoplasm:
• comprises all the
living parts of the cell
e.g. Nucleus and
surrounding cytoplasm.
Cell Structure seen using the Light
Microscope
Plant Cell
Cell Wall:
- made of cellulose
- function: support
Cell Membrane:
- pressed close to cell
wall
Vacuoles:
- contain cell sap
- function:
strength
shape
store materials
Chloroplasts:
- photosynthesis
Electron Microscope
Allow cell structure to be seen in greater detail
- ultrastructure
Electron Microscope
•Uses Electrons instead of light
•Electrons have much lower wavelength than light –
image is shown on a screen or as a photograph
•Resolution is much better
•Magnification is much greater
Images from Electron Microscope
Bacteria
Platelet
Cytoplasm
Electron Microscope
2 Types
Transmission Electron
Microscope (TEM)
• beam of electrons sent
through thin section of
the sample and shows
the INTERNAL
structure
Scanning Electron
Microscope (SEM)
• beam of electrons provides
a surface view.
Cells
- All living things are composed of one or more
cells.
- Cells are the basic units of structure and function
in an organism.
- Cells come only from reproduction of existing
cells.
Organelles
• Cells contain a variety of internal structures
called ORGANELLES.
• An organelle is a cell component that
PERFORMS SPECIFIC FUNCTIONS FOR
THE CELL
Organelles we need to know
•Cell membrane
•Nucleus
•Mitochondria
•Chloroplast
•Ribosomes
•DNA
•Cell Wall
•Vacuole
•Nucleolus
Animal Cells
Animal Cells contain the following structures
Cell Membranes
Mitochondria
Nucleus
Cytoplasm
Only the cell membrane, the cytoplasm and the
nucleus can be seen under the light microscope.
Cell (Plasma) Membrane
Cell Membrane: composed of phospholipids and
proteins.
Cell (Plasma) Membrane
Phospholipids:
• contain a water-loving phosphate group and a
water-hating lipid group.
Phosphate
(Water loving)
Lipid
(Water Hating)
• arranged into double layers - bilayers
Cell (Plasma) Membrane
Proteins:
• completely or partially embedded in
phospholipid bilayer.
The phospholipids and proteins are in
constant motion.
Therefore membranes are thought of as
fluids
Functions of Cell Membrane
•
Separate the cell organelles and cytoplasm
from the outside.
•
Semi permeable – controls what enters and
leaves the cell.
•
Membranes give some support to the cell.
•
Membranes recognise molecules that touch
them.
Nucleus
• A large organelle near the center of the cell is
the NUCLEUS.
• It contains the cell's genetic information.
• It is the control centre of the cell.
Ultra Structure of the Nucleus
What’s in the Nucleus???
Double Membrane: nucleus is surrounded by a
double membrane with nuclear pores.
Nuclear Pores: allows the controlled entry and
exit of molecules in and out of the nucleus e.g.
- allow a type of RNA called mRNA to pass
in and out of the nucleus.
Nucleolus:
• contains RNA, DNA and protein.
• is responsible for making ribosomes which
are made up of RNA (Ribonucleic acid).
What’s in the Nucleus???
Chromosomes:
• nucleus contains strands of DNA which are
arranged into structures called Chromosomes.
• genes are located randomly along
chromosomes:
genes = units of inheritance
• when cell is not dividing the chromosomes form
a mass of threads called chromatin.
Functions of Nucleus
• directs growth, development and activities of
the cell.
• makes replicas of DNA for new cells
• carries out cell division
• instructs the formation of enzymes and
hormones
Cytoplasm
• liquid in a cell that surrounds the nucleus
• small bodies called organelles are
suspended in the cytoplasm:
1. Mitochondria
2. Chloroplasts
3. Ribosomes
4. Vacuoles
Cytoplasm Organelles
Mitochondria
Cytoplasm Organelles
Mitochondria
• Found in all cells except bacteria.
• Supply energy to the cell – sites of respiration:
Lots of mitochondria
Few mitochondria
Lots of energy
Less energy
• Consist of a smooth outer membrane and a
folded inner membrane.
• It is on the inner membrane, especially the
infoldings, that energy is released. Therefore
the more infoldings the more energy produced.
Cytoplasm Organelles
Mitochondria
Inactive mitochondria:
- have a decrease in infoldings and as a result a
decrease in the energy released.
Active mitochondria:
- have a increase in infoldings and as a result
an increase in the energy released.
Cytoplasm Organelles
Chloroplasts (Plants Only)
• Found in plant cells only.
• Green structures in which photosynthesis
takes place.
• Contain the green pigment chlorophyll.
Cytoplasm Organelles
Ultrastructure of the Chloroplast
The thylakoids contain the chlorophyll
which traps the sun’s energy
Cytoplasm Organelles
Ribosomes
• Found in all cells
• Tiny, bead – like structures
• Made up of ribonucleic acid (RNA) and
proteins.
• Function:
- to make proteins by combining a sequence of
amino acids.
Cytoplasm Organelles
Vacuoles
• Vacuoles are membrane-bound sacs within
the cytoplasm of a cell.
• Vacuoles provide structural support, as well
as serving functions such as storage, waste
disposal, protection, and growth.
• Plant cells have large vacuoles
Cell Wall
• Found in plant cells only
• Made of cellulose
• Very strong and
contributes the following
to the cell:
- strength
- protection
- shape
Ultra Structure of an Animal Cell
Ultra Structure of a Plant Cell
Differences between Plant and
Animal Cells
Plant Cells
Animal Cells
Have cell walls
No cell walls
Contain chloroplasts
Do not contain
chloroplasts
Do not contain
chlorophyll
Have small (if any)
vacuoles
Contain chlorophyll
Have large vacuoles
Prokaryotic and Eukaryotic Cells
Living things can be placed into special
categories depending on the complexity and
structure of their cells.
Prokaryotic Cells
Do not have a nucleus or membrane enclosed
organelles.
• They are single celled organisms e.g. Bacteria
• Their DNA is found as circular loops found in the
cytoplasm.
• Do not have mitochondria or chloroplasts.
• Respiration and photosynthesis is carried out on
infolding of the plasma membrane.
Eukaryotic Cells
Have a nucleus and cell organelles, all of
which are enclosed by membranes
• More advanced than prokaryotic cells.
• Larger than prokaryotic cells.
• Plant and animal cells are examples of
eukaryotic cells.