Observation under the microscope
Cells cannot be seen with the naked eye: you need an instrument that magnifies them hundreds of times. The optical microscope is the basic tool of any biology laboratory, and using it well does not come automatically: it has its steps and its tricks.
Parts of the microscope
When you place a transparent piece of onion skin under the microscope, you discover a grid of tiny compartments that are invisible to the naked eye, but to see them clearly you need to hold the glass, light it and focus it: which parts work together to make this magnification possible, and how do they coordinate?
In the light microscope diagram, there are three parts labelled with "?". Write the name of each one and explain its function.
In the light microscope diagram, there are three parts labelled with "?". Write the name of each one and explain its function.
Name the two parts of the microscope that contain lenses and explain where you look through and where the specimen is placed.
Name the two parts of the microscope that contain lenses and explain where you look through and where the specimen is placed.
Explain what the microscope slide and the coverslip are and what each one is used for when preparing a specimen.
Explain what the microscope slide and the coverslip are and what each one is used for when preparing a specimen.
Total magnification
A microscope has an eyepiece lens of $10\times$ and objective lenses of $4\times$, $10\times$, and $40\times$. Calculate the total magnification achieved with each…
A microscope has an eyepiece lens of $10\times$ and objective lenses of $4\times$, $10\times$, and $40\times$. Calculate the total magnification achieved with each objective lens, and explain which one you should always start observing with and why.
A microscope has an eyepiece lens of $10\times$ and an objective lens of $20\times$. Calculate the total magnification. If you switch to a $40\times$ objective lens,…
A microscope has an eyepiece lens of $10\times$ and an objective lens of $20\times$. Calculate the total magnification. If you switch to a $40\times$ objective lens, explain what happens to the size of the image, to the area of the specimen you manage to see, and to the amount of light.
Preparing a specimen
Put the steps for preparing an onion cell sample in order: (a) cover with the coverslip taking care to avoid air bubbles, (b) place a thin layer of onion on the…
Put the steps for preparing an onion cell sample in order: (a) cover with the coverslip taking care to avoid air bubbles, (b) place a thin layer of onion on the microscope slide, (c) add a drop of iodine solution (lugol) to stain, (d) remove excess liquid with filter paper.
Why are many samples stained before observing them under a microscope? Give an example of a stain used in the school laboratory.
Why are many samples stained before observing them under a microscope? Give an example of a stain used in the school laboratory.
To observe something under the light microscope it must be cut into very thin sections. Explain why the specimen must let light through and what happens if it is too…
To observe something under the light microscope it must be cut into very thin sections. Explain why the specimen must let light through and what happens if it is too thick.
Focusing correctly
Why must you focus first using the lowest power objective lens and reserve the fine focus knob for higher power objective lenses? Explain what might happen if you use…
Why must you focus first using the lowest power objective lens and reserve the fine focus knob for higher power objective lenses? Explain what might happen if you use the coarse focus knob with the $40\times$ objective lens.
You have focused a cell with the $10\times$ objective lens and switch to the $40\times$ one: the image is left slightly blurry and darker. Explain which focus knob you…
You have focused a cell with the $10\times$ objective lens and switch to the $40\times$ one: the image is left slightly blurry and darker. Explain which focus knob you must use to refocus (and which one you must not touch) and which lighting adjustment can improve the image.