The document goes in great detail about the ib biology SL and HL topics; Water, Origin of cells, cell structure, virsues, carbohydrates and lipids, organelles and compartementalization, diversity of organisms, membranes, cell specialization, stem cells etc. It's almost 200 pages of the topics descr...
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Microscopes
Light vs Electron microscopes
Light microscopes Electron microscopes
Inexpensive Expensive
Simple specimen prep Preparations of specimens is very complex
Smaller Bigger
Magnifies up to x2000 Magnifies up to x500 000
Specimens can be dead or alive Specimens have to be dead
Can’t see viruses Can see viruses
Converting units
,Most cells are measured in micrometers. Parts of cells are measured in nanometers.
Formula for magnification
,Electron microscopes
• Electron microscopes use beams of electrons instead of light. Electron beams have a much
shorter wavelength, providing a much greater resolving power.
• Resolving power is the ability of a lens to distinguish between 2 lines.
• There are 2 different types of electron microscopes.
Transmission electron microscope
• It produced 2d images.
• A beam of electrons is transmitted through a specimen and focused to produce an image.
• Similar to light microscopy.
• It only produced black and white.
• Has excellent resolution (resolving power of 0.5 nm).
• It has magnification of up to 500,000.
Scanning electron microscope
• A beam of electrons is sent across the surface of a specimen and the reflecton electron are
collected.
• They produce 3d images. Therefore, their resolution and magnification is less powerful than
the 2d image producing microscopes.
• Has good resolution (resolving power of 3-10).
• It has magnification of up to 100,000.
Artifacts
• They are part of the preparation process but not actually part of the specimen.
• They can be found in light microscopy too. Bubbles trapped under the cover slip are
artifacts.
• Artifacts are inevitable in electron microscopy. Experience allows scientists to distinguish
between artifacts and actual structures.
Freeze frature
• Freez fracture is a process of preparing a sample for electron microscopy.
• The process is very simple.
• The specimen is rapidly frozen and then physically broken apart. This reveals a plan through
a sample.
• This technique was vital in the understanding of the structure of the cell membrane.
Cryogenic electron microscopy
, • This method has been revolutionary in understanding the structure of viruses and other
cellular proteins.
• Specimens are frozen in ice using very low temperatures and 3d computer aided structures
are created.
Microscopy skills
• How to focus the microscope on a sample: Place your sample on the stage (3) and turn on
the LED light (2). Look through the eyepieces (4) and move the focus knob (1) until the
image comes into focus. Adjust the distance between the eyepieces (4) until you can see the
sample clearly with both eyes simultaneously (you should see the sample in 3D).
• How to make a temporary wet mount and stain a microscopic sample: Collect a thin slice of
your sample and place it on a clean, dry slide. Place one drop of water over your sample.
Place the coverslip at a 45-degree angle with one edge touching the water and let go.
• How to measure the field of view diameter of a microscope under low power: To determine
the diameter of your field of view, place a transparent metric ruler under the low power (LP)
objective of a microscope. Focus the microscope on the scale of the ruler and measure the
diameter of the field of vision in millimeters.
• How to calculate the field of view diameter of a microscope under medium or high power:
Diameter of the field of view (mm) = F / M, where F is the number of field of view (FOV) of
the eyepiece, and M is the magnification.
• Quantitative vs qualitive observation: Quantitative observations involve measuring or
counting something and expressing the result in numerical form, while qualitative
observations involve describing something in non-numerical terms, such as its appearance,
texture, or color.
• Resolution and magnification: Magnification is the enlargement of an image; resolution is
the ability to tell two objects apart.
• Benefit of using fluorescent stains to visualize cell structures: Fluorescent staining can
provide high-resolution images with great specificity, allowing researchers to study the
spatial distribution, interactions, and dynamics of different cellular components in living or
fixed samples.
• Process of visualizing specific proteins in cells using immunofluorescence technology:
Immunofluorescence is a technique that uses a fluorescence microscope to visualize the
distribution and/or localization of a target molecule in a biological sample.
• Process of producing images of cell surfaces using freeze-fracture electron microscopy:
There are four key steps in making a standard freeze-fracture replica: i) rapid freezing of the
specimen, ii) fracturing it at low temperature (-100°C or lower), iii) making the replica of the
newly exposed frozen surface by vacuum-deposition of platinum and carbon; and iv)
cleaning the replica using bleach or acids to remove the biological material. The replica, with
no biological material remaining, is finally mounted on a grid for examination in the electron
microscope.
• Process of visualizing specific proteins using cryogenic electron microscopy: Cryo-
electron tomography, a cryo-electron microscopy (cryo-EM) technique, provides 3D
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