cell structure chpt. 7. microscopes simple microscope uses single lens max magnification x400 uses...
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Cell StructureChpt. 7
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Microscopes
Simple Microscope• uses single lens• max magnification x400• uses light
Compound Microscope• microscope used in our labs.• max magnification
x1000
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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.
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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
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Compound MicroscopeParts of the Microscope
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Compound MicroscopeParts 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
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Compound MicroscopeMagnification
Total Magnification:
magnifying power of the eyepiece lens x
the magnifying power of the objective lens
Example:
Eyepiece lens = 10XObjective lens = 4X
Total magnification = 10 x 4= 40X
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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
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Cell Structure seen using the Light Microscope
Animal CellCytoplasm:• 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.
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Cell Structure seen using the Light Microscope
Plant CellCell Wall: - made of cellulose - function: supportCell Membrane: - pressed close to cell wallVacuoles: - contain cell sap - function:
strength shape
store materialsChloroplasts: - photosynthesis
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Electron MicroscopeAllow cell structure to be seen in greater detail
- ultrastructure
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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
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Images from Electron Microscope
Bacteria
Cytoplasm
Platelet
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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.
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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.
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Organelles
• Cells contain a variety of internal structures called ORGANELLES.
• An organelle is a cell component that PERFORMS SPECIFIC FUNCTIONS FOR THE CELL
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Organelles we need to know
•Cell membrane•Nucleus
•Mitochondria•Chloroplast•Ribosomes•DNA
•Cell Wall•Vacuole•Nucleolus
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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.
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Cell (Plasma) Membrane
Cell Membrane: composed of phospholipids and proteins.
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Cell (Plasma) Membrane
Phospholipids:• contain a water-loving phosphate group and a water-hating lipid group.
• arranged into double layers - bilayers
Phosphate(Water loving)
Lipid (Water Hating)
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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
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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.
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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.
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Ultra Structure of the Nucleus
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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).
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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.
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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
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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
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Cytoplasm Organelles
Mitochondria
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Cytoplasm OrganellesMitochondria
• Found in all cells except bacteria.
• Supply energy to the cell – sites of respiration:
Lots of mitochondria Lots of energy
Few mitochondria 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.
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Cytoplasm OrganellesMitochondria
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.
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Cytoplasm OrganellesChloroplasts (Plants Only)
• Found in plant cells only.• Green structures in which photosynthesis takes place.• Contain the green pigment chlorophyll.
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Cytoplasm OrganellesUltrastructure of the Chloroplast
The thylakoids contain the chlorophyll which traps the sun’s energy
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Cytoplasm OrganellesRibosomes
• 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.
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Cytoplasm OrganellesVacuoles
• 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
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Cell Wall
• Found in plant cells only
• Made of cellulose
• Very strong and contributes the following to the cell:
- strength- protection- shape
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Ultra Structure of an Animal Cell
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Ultra Structure of a Plant Cell
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Differences between Plant and Animal Cells
Plant Cells Animal Cells
Have cell walls No cell walls
Contain chloroplasts Do not contain chloroplasts
Contain chlorophyll Do not contain chlorophyll
Have large vacuoles Have small (if any) vacuoles
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Prokaryotic and Eukaryotic Cells
Living things can be placed into special categories depending on the complexity and
structure of their cells.
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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.
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Eukaryotic CellsHave 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.