Microscope Aberrations and Focusing

Play an AI-generated podcast conversation about this lesson

Who is credited with being the first person known to have observed living microbes?

Robert Hooke

Alexander Fleming

Antonie van Leeuwenhoek (correct)

Louis Pasteur

What did Antonie van Leeuwenhoek observe in tooth tartar and feces?

Viruses

Protozoa

Bacteria (correct)

Fungi

Why did Antonie van Leeuwenhoek keep his microscopes and method of observing 'animalcules' to himself?

Because he wanted to sell his microscopes

To protect his homemade microscopes (correct)

Because he was too busy to share his knowledge

To prevent others from learning about microbes

Where can directions for making a replica of van Leeuwenhoek's microscope be found?

In a biology textbook Signup and view all the answers

What is the primary purpose of Exercises 1 and 2 in the context of the text?

To familiarize students with the compound light microscope Signup and view all the answers

What is emphasized as a critical part of any science in the context of the text?

Simple observation Signup and view all the answers

What is the most logical way to eliminate chromatic aberrations?

Using a light source of one wavelength Signup and view all the answers

What is the cause of spherical aberration in a microscope lens?

Curvature of the lens, resulting in multiple focal points Signup and view all the answers

What is the purpose of using filters, usually blue, in a microscope?

Minimizing chromatic aberration Signup and view all the answers

What should be done before using the oil immersion lens in a microscope?

Focus with low power first Signup and view all the answers

How can spherical aberrations be minimized in a microscope?

Using a series of lenses resulting in essentially a flat optical system Signup and view all the answers

What is the purpose of using the iris diaphragm in a microscope?

To minimize chromatic aberration Signup and view all the answers

What should be done to achieve good contrast when using the low-power lens in a microscope?

Keep the iris diaphragm barely open Signup and view all the answers

What is the most effective method of eliminating chromatic aberrations in a microscope?

Using a light source of one wavelength Signup and view all the answers

What should be done after use to maintain the microscope?

Remove the slide, wipe oil off it, put the dust cover on the microscope, and return it to the designated area Signup and view all the answers

What is recommended to avoid eyestrain when using a microscope?

Observe with both eyes open Signup and view all the answers

Why is it important to carry the microscope with both hands?

To avoid tilt and ensure comfortable use Signup and view all the answers

What is the function of the coarse-adjustment knob in a microscope?

Moves the lenses or the stage longer distances for focusing with the low-power objectives Signup and view all the answers

In a compound microscope, what is the function of the oil immersion lens?

Has the highest magnification and must be used with immersion oil Signup and view all the answers

What is the total magnification of an object when using an ocular lens with a magnification of 10* and an objective lens with a magnification of 40*?

600* Signup and view all the answers

What is resolving power in microscopy?

The ability of a lens to reveal fine detail or two points distinctly separated Signup and view all the answers

Which part of the microscope controls the amount of light entering the condenser?

Iris diaphragm Signup and view all the answers

What is the function of the ocular lens in a microscope?

Remagnifies the image formed by the objective lens Signup and view all the answers

In a compound light microscope, what is used for focusing with the high-power and oil immersion lenses?

Fine-adjustment knob Signup and view all the answers

What is the purpose of immersion oil in microscopy?

To minimize light loss and focus very close to the slide Signup and view all the answers

What is numerical aperture (N.A.) in microscopy?

The maximum angle of light entering the objective lens and on the refractive index of the material between the lens and the slide Signup and view all the answers

What does resolving power in microscopy depend on?

Wavelength of light used and numerical aperture Signup and view all the answers

What is used to adjust current to lamp in a compound microscope?

Iris diaphragm Signup and view all the answers

What is the purpose of the exercise described in the text?

To practice using different microscope objectives Signup and view all the answers

What is the advantage of having parfocal microscope objectives?

It allows for easier focusing when switching between objectives Signup and view all the answers

Which objective focuses closest to the slide when it is in focus?

Low-power objective Signup and view all the answers

What would occur if water were accidentally used in place of immersion oil?

The image would appear darker and less clear Signup and view all the answers

Which controls on the microscope affect the amount of light reaching the ocular lens?

Iris diaphragm and condenser adjustment knob Signup and view all the answers

What are the advantages of the low-power objective over the oil immersion objective for viewing fungi or algae?

Ability to observe larger field of view Signup and view all the answers

In what situation would microorganisms become apparent when switching to 1000* magnification?

When looking for microorganisms in a tissue sample from a lung biopsy Signup and view all the answers

What is the purpose of moving the high-dry lens out of position and placing a drop of immersion oil on the slide?

To prepare for observing prokaryotes Signup and view all the answers

What does increased magnification do to the depth of field?

It decreases the depth of field at higher magnifications. Signup and view all the answers

What are two ways in which you can enhance the resolving power?

Increasing numerical aperture and using shorter wavelength light. Signup and view all the answers

What would occur if one Bacillus cell measures 2 μm long, how many Bacillus cells could fit end-to-end across a field which has a diameter of 2 mm under low power?

One hundred Bacillus cells could fit end-to-end across the field. Signup and view all the answers

What is the purpose of handling the coverslip carefully by its edges when preparing a wet-mount slide?

To prevent the introduction of air bubbles into the sample Signup and view all the answers

What is the main difference between Brownian movement and true motility in microorganisms?

Brownian movement is caused by the movement of water molecules, while true motility is self-propelled movement Signup and view all the answers

What is the advantage of using a hanging-drop slide over a wet-mount slide for observing motile microorganisms?

It reduces evaporation of the suspended drop of fluid Signup and view all the answers

What is one reason why direct examination of living microorganisms is very useful?

It provides information about size, shape, and movement of microorganisms Signup and view all the answers

What effect does alcohol or Gram’s iodine have on motile microorganisms in a wet-mount slide?

It stops their movement completely Signup and view all the answers

What technique would be most effective for observing bacteria in a wet-mount slide?

Use high-dry lens (40x to 45x) and increase the light Signup and view all the answers

What should be done before discarding slides and coverslips in the disinfectant jar?

Wipe the oil from the objective lens with lens paper Signup and view all the answers

What is the purpose of placing a ring of petroleum jelly around the edge of a coverslip in the hanging-drop procedure?

To reduce evaporation of the suspended drop of fluid Signup and view all the answers

What is the significance of using brightfield microscopy to observe unstained microorganisms in wet mounts and hanging drop slides?

It enables observation without altering the natural characteristics of microorganisms Signup and view all the answers

What does motility look like in microorganisms as compared to Brownian movement?

It looks more rapid and directed than Brownian movement Signup and view all the answers

What type of microscope lens should be used to observe bacteria in a wet-mount slide?

High-dry lens (40x to 45x) and high light intensity Signup and view all the answers

What is one advantage of using a petroleum jelly seal in the hanging-drop procedure?

It reduces evaporation of the suspended drop of fluid Signup and view all the answers

What type of microorganism is most likely to be observed in a wet mount of urine if flagellated, nucleated cells are seen?

Protozoan Signup and view all the answers

In a fixed, stained slide, when cells are not visible until the oil immersion objective is used, what type of microorganism is most likely?

Bacterium Signup and view all the answers

In a wet mount of scrapings, if long filaments composed of many cells are observed, which type of microorganism is most likely?

Alga Signup and view all the answers

When observing microorganisms through a microscope, which optical system is used to ensure adequate light for viewing?

Condenser Signup and view all the answers

What was the invention by Zacharias Janssen that paved the way for the examination of microorganisms?

Simple microscope Signup and view all the answers

What type of microscope is used most often to show dark objects in a bright field when observing microorganisms?

Brightfield compound microscope Signup and view all the answers

What is the purpose of the condenser’s iris diaphragm in a compound microscope?

To control the amount of light entering the condenser Signup and view all the answers

What part of the microscope holds the objective lenses and allows for easy switching between different magnifications?

Revolving nosepiece Signup and view all the answers

What did Antoni van Leeuwenhoek use to observe microorganisms that were too small to be seen with the naked eye?