Physics: Wavelength and Magnification Concepts

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Questions and Answers

A wavelength of 390 nm corresponds to ______.

violets

As wavelength decreases, energy ______.

increases

The ability to enlarge objects is known as ______.

magnification

The ability to show detail in an image is referred to as ______.

resolving power Signup and view all the answers

The refractive index is defined as the ______ ability of a medium.

light-bending Signup and view all the answers

Using immersion oil can increase the refractive index from ______ to 1.5.

1.0 Signup and view all the answers

Electron waves are ______ shorter than the waves of visible light.

100,000X Signup and view all the answers

Electron microscopy can achieve magnification of ______ to 1500X.

1000 Signup and view all the answers

Ethidium bromide stains unhealthy cells in the final stages of ______.

apoptosis Signup and view all the answers

Osmium tetroxide is used in optical microscopy to stain lipids ______.

black Signup and view all the answers

Fuchsin stain is commonly used to stain ______.

collagen Signup and view all the answers

Hematoxylin is a nuclear stain that, with a mordant, stains nuclei ______ or brown.

blue-violet Signup and view all the answers

Differential-interference-contrast is an optical microscopy technique used to enhance the contrast in unstained, transparent ______.

samples Signup and view all the answers

Hoechst stains are used to stain ______ in living cells.

DNA Signup and view all the answers

Fluorescence microscopy combines the magnifying properties of light microscopy with visualization of ______.

fluorescence Signup and view all the answers

Wet mount preparation allows examination of characteristics of ______ cells.

live Signup and view all the answers

Scanning electron microscopy (SEM) produces a ______ image.

3D Signup and view all the answers

Transmission electron microscopy (TEM) produces a ______ image.

2D Signup and view all the answers

Permanent fixation is used for ______ specimens.

dead Signup and view all the answers

Cell staining is a technique used to better visualize ______ and cell components under a microscope.

cells Signup and view all the answers

All cells share basic features like plasma membrane, cytosol, and ______.

DNA Signup and view all the answers

Cells may be stained to highlight metabolic ______ or to differentiate between live and dead cells.

processes Signup and view all the answers

Most stains can be used on fixed, or non-living cells, while only some can be used on ______ cells.

living Signup and view all the answers

Cells may be enumerated by staining cells to determine ______ in an environment of interest.

biomass Signup and view all the answers

Cytosol is a jelly-like fluid located inside the ______ membrane.

plasma Signup and view all the answers

The ______ includes the cytosol and all the organelles other than the nucleus.

cytoplasm Signup and view all the answers

Protein synthesis takes place on the ______.

ribosomes Signup and view all the answers

DNA is the genetic material contained in one or more ______.

chromosomes Signup and view all the answers

The mixture obtained after rupturing the cell membrane is referred to as the ______.

homogenate Signup and view all the answers

In differential centrifugation, the separation of cellular organelles is based on their ______ rate.

sedimentation Signup and view all the answers

A neuron is an example of a ______ shaped cell.

long Signup and view all the answers

Cells can only grow to a certain size due to their surface area to ______ ratio.

volume Signup and view all the answers

The protobionts are the evolutionary precursors of ______ cells.

prokaryotic Signup and view all the answers

According to the Endosymbiosis Theory, ______ and plastids are thought to have originated from small prokaryotes.

mitochondria Signup and view all the answers

An endosymbiont is a cell that lives within a ______ cell.

host Signup and view all the answers

The oldest fossils of ______ cells date back 2.1 billion years.

eukaryotic Signup and view all the answers

The hypothesis of endosymbiosis proposes that mitochondria and ______ were once independent prokaryotes.

plastids Signup and view all the answers

Key evidence for the endosymbiotic origin of mitochondria includes similarities in inner membrane structures and ______.

functions Signup and view all the answers

The process of becoming more interdependent leads to the host and endosymbionts evolving into a ______ organism.

single Signup and view all the answers

According to the Endosymbiosis Theory, large cells ______ small cells to form organelles.

engulfed Signup and view all the answers

Study Notes

Wavelength and Energy

Violet light has a wavelength of 390 nm.
Green light has a wavelength of 550 nm.
Red light has a wavelength of 750 nm.
As the wavelength of light decreases, the energy of the light increases.

Magnification & Resolution

Magnification is the ability to enlarge objects.
Resolving power is the ability to show detail.

Enhancing Resolving Power

Resolving power can be enhanced by increasing the numerical aperture.
Numerical aperture can be increased by:
- Altering the sub-stage condenser to increase the angle of light incidence.
- Widening the cone of light to allow more light to pass through the lens.
- Increasing the refractive index through specialised lenses or immersion oil.
The refractive index is the light-bending ability of a medium. Water has a refractive index of 1.0 and oil has a refractive index of 1.5.

Refractive Index: Path of Light Through Different Mediums

Through air:
- Smaller angle of incidence.
- Angle of refraction bends away from the normal line (larger angle of refraction).
- Smaller refractive index (RI) value.
- Smaller numerical aperture (NA).
Through Oil:
- Large angle of incidence.
- Angle of refraction approaches the normal line (smaller angle of refraction).
- Larger refractive index (RI) value.
- Larger numerical aperture (NA).

Effect of Magnification

High magnification can produce an image that is too large to fit within the field of view.
High magnification can decrease the resolving power.

Resolution: Light Microscopy

With light microscopy, resolution levels are between 100-200 nm (0.1-0.2 µm).
The magnification range for light microscopy is 1000-1500X.

Resolution: Electron Microscopy

Electron microscopy uses a beam of electrons to form an image.
Electron waves are 100,000 times shorter than the waves of visible light.
Electron microscopy has significantly higher resolution.

Electron Microscopy: Resolution and Magnification

Resolution for electron microscopy is between 0.1-2 nm.
Magnification for electron microscopy ranges from 1000X to 400-500,000X.

Techniques of Microscopy

Differential Interference Contrast (Nomarski)

A technique used to enhance contrast in unstained, transparent samples.
Small phase changes in light rays are transformed into brightness or light intensity differences.

Fluorescence Microscopy

Combines magnification with visualizing fluorescence.
Requires a powerful light source, specialized filters, and fluorescently labelled samples.

Scanning Electron Microscopy (SEM)

Produces a 3D image.
Uses a focused beam of electrons to scan the surface of a sample.

Transmission Electron Microscopy (TEM)

Produces a 2D image.
Uses a beam of electrons that are transmitted through the sample.

Cell Staining

Cell staining is a technique used to enhance visualization of cells and their components under a microscope.
Different stains can target specific cell components.
Some stains are used on fixed (non-living) cells, some are used on living cells, and some are used on both.

Why Stain Cells?

To enhance visualization.
To highlight metabolic processes.
To differentiate between live and dead cells in a sample.
To enumerate cells to determine biomass in an environment.

Example Stains

Sudan Black: accumulates in intracellular lipid globules, staining them red – used on living cells.
Ethidium bromide: stains unhealthy cells red-orange – used on living cells.
Osmium tetroxide: stains lipids black – used in optical microscopy.
Fuchsin: stains collagen, smooth muscle, or mitochondria.
Hematoxylin: stains nuclei blue-violet or brown.
Hoechst stains: both 33258 and 33342 stain DNA in living cells.
Rhodamine: a fluorescent stain used on proteins in fluorescence microscopy.
Safranin: stains nuclei and colours collagen yellow.

Preparation of Samples

Wet Mount

Allows examination of characteristics of live cells: motility, shape, and arrangement.
Allows for immediate observation.
Can be stained or unstained.
Example: blood smear.

Dry Mount

Made by drying and heating a film of a specimen.
Allows for repeated observations.
Only used with dead specimens.
Can be stained.
Example: prepared slide for pathology and biological research.

Microscope Field of View

The field of view is the circular area that you can see when looking through a microscope.
The size of the field of view changes depending on the magnification of the objective lens.

Measuring Field of View

It is necessary to measure the field of view to determine the size of objects in the microscopy field of view.
The field of view can be measured by observing a ruler under the microscope.

Size of Cells

It is necessary to measure the field of view because cells come in a variety of sizes.
Cell size depends on the function the cell performs.
Cell shapes can also vary significantly:
- Neurons are long.
- Parenchyma cells are equidimensional.
- Cell membranes are flexible.
- Cell walls are rigid.

The Cytoskeleton

The cytoskeleton is a network of protein-based fibers.
The cytoskeleton is responsible for:
- Cell shape and support.
- Cell movement.
- Organelle movement.
The cytoskeleton is composed of three types of protein filaments:
- Microtubules: 25 nm in diameter, made of tubulin dimers.
- Microfilaments: 7 nm in diameter, made of actin subunits.
- Intermediate Filaments: 8–12 nm in diameter, made of fibrous subunits (keratins coiled together).

Significance of Cell Size

The maximum size a cell can grow to is limited by its surface area to volume ratio.
As a cell grows, its volume increases faster than its surface area.
This means that the cell's surface area eventually becomes too small to support the metabolic needs of the growing cell.

Origin of Life

Scientists believe that life originated from a "primordial soup" of organic molecules on early Earth.
The conditions on early Earth—such as the presence of volcanic activity, lightning, and the absence of a protective ozone layer—would have provided the energy needed for these molecules to form.
Protobionts are thought to be the evolutionary precursors of prokaryotic cells.
Protobionts may have originated as microspheres enclosed by lipidic membranes.

Endosymbiosis Theory

The endosymbiosis theory proposed by Lynn Margulis explains the origin of eukaryotic cells.
This theory states that mitochondria and plastids (chloroplasts and related organelles) were once free-living prokaryotic cells that were engulfed by larger cells.
These engulfed cells were not digested, but instead began to live within the host cell.
Over time, the engulfed cells and the host cells became dependent on each other, eventually evolving into a single organism.

Evidence Supporting Endosymbiosis

Mitochondria and plastids have their own DNA and ribosomes.
The DNA and ribosomes of mitochondria and plastids are more similar to prokaryotic DNA and ribosomes than to eukaryotic DNA and ribosomes.
Mitochondria and plastids divide independently of the host cell.

Basic Features of All Cells

Plasma membrane: A selective barrier that encloses the cell (in plant and bacteria cells, it’s called a cell wall).
Cytosol: A jelly-like fluid that supports organelles and other cellular components.
Cytoplasm: The cytosol and all of the organelles, excluding the nucleus.
Ribosomes: Organelles where protein synthesis takes place.
DNA: The genetic material contained in one or more chromosomes.

Differential Centrifugation

Differential centrifugation is a technique used to separate cell organelles based on their size and density.
First, the cell membrane is ruptured to release the cell's components using a homogenizer.
The resulting mixture is called a homogenate.
The homogenate is centrifuged at increasing speeds and time intervals.
This separates the components of the cell by density and size. The most dense organelles sediment first.

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Description

This quiz covers key topics related to the wavelength and energy of light, magnification, and the resolving power of optical instruments. You will explore how modifying settings like numerical aperture and refractive index can enhance visibility and detail in microscopy. Test your understanding of these fundamental concepts in physics!