Microscopy Flashcards
Learn all about the fist chapter in the basic components of the living system- module 2
What was the first type of microscope to be developed and when?
light microscope (16th-17th century)
in the mid-19th century what did scientists have access to?
microscopes with a high enough level of magnification to allow then to see individual cells
What does cell theory state?
- both plant and animal tissue is composed of cells
- cells are the basic unit of all life
- cells only develop from existing cells
What contribution did the Romans have with the development of the light microscope?
late in the Roman Empire the Romans began to develop and experiment with glass. They noted how objects looked bigger when viewed through pieces of glass that were thicker in the middle than at the edges.
How did two Dutch spectacle makers contribute to the development of the microscope?
They invented the telescope (which is the opposite of a microscope) after experimenting with multiple glass lenses in a tube in late 15th century.
How did Galileo contribute to the development of the microscope and when?
Galileo Galilei in 1609 developed the first true microscope (compound microscope), and this instrument was the first to be given the name ‘microscope’.
What is the cell theory a good example of?
How scientific theories change over time as new evidence is gained and knowledge increases
when was the cell first observed?
1665
How was the cell first observed?
Robert Hooke, an English scientist, observed the structure of thinly sliced cork using an early light microscope of his own creation. What he saw was dead plant tissue which consisted of only the cell wall. Hooke believed that they looked like ‘cells’ with not a lot going on inside.
https://youtu.be/4OpBylwH9DU?t=157
when was the first living cell observed?
1674-1683
How was the first living cell observed?
A Dutch biologist named Anton van leeuwenhoek developed a technique of creating powerful glass lenses and used his own microscopes to observe samples of pond water. what he saw were bacteria and protoctista, however he named them ‘animalcules’ (‘little animals’). we now know them as microorganisms. Hooke later observed red blood cells, sperm cells and muscle fibres for the first time.
https://youtu.be/4OpBylwH9DU?t=91
when was the evidence for the origin of new plant cells made?
1832
who created evidence for the origin of new plant cells? and how?
A Belgium botanist named Barthélemy Dumortier was the first to observe cell division in plants providing evidence against the common theories of the time.
What were the theories of the origin of new cells before 1832
- New cells arise from within old cells
- Cells formed spontaneously from non-cellular material
was cell division as the origin of new cells a theory that was excepted quickly?
No, it took several years for this theory to be excepted.
when was the Nucleus first observed?
1833
How was the Nucleus first observed?
An English botanist named Robert Brown was the first to describe the Nucleus of a plant cell.
When was the birth of the universal cell theory?
1837-1838
What was the birth of the universal cell theory
A German botanist named Matthias Schleidon proposed that all plant tissues are made of cells. A Czech scientist named Jan Purkyne was the first to use a microtome to make ultra-thin slices of tissue for microscopic examination. From his research he concluded that not only are animals composed of cells but the “basic cellular tissue is similar to that of plants. A German psychologist named Theodor Schwann made a similar observation and cleared that “all living things are composed of cells and cell products”. Schwann was credited with the ‘birth’ of cell theory.
https://youtu.be/4OpBylwH9DU?t=238
When was there evidence for the origin of new animal species?
1844(1855)
What was the evidence for the origin of new animal cells?
A Polish/German biologist named Robert Remark was the first to observe cell division in animal cells, disporving the theory that new cells spawned from within old cells. However, he was not believed at the time and a decade later a German biologist named Rudolf Virchow published these findings as his own a decade later.
How was spontaneous generation disproved?
Louis Pasteur disproved the theory of spontaneous generation of cells by demonstrating that bacteria would only grow in a sterile nutrient broth after it had been exposed to the air.
How does a light microscope work?
A compound light microscope has two lenses (the objective lens, which is placed near the specimen, and the eyepiece lens, which is how you view the specimen). The objective lens produces a magnified image (the magnification can be changed between objective lenses), which is magnified again by the eyepiece lens. This set up enables for higher magnification and reduces chromatic aberration than that in a simple light microscope. Light microscopes require light; this is often provided by a light underneath the sample. However, opaque specimen can be alluminated from above with some microscopes.
Draw and label a compound light microscope
Check page 10
What part of the cell is often transparent?
Cytosol (aqueous interior)
What do stains increase?
Contrast between the organelles within the cell, as different components absorb stains to different degrees.
How do you prepare a specimen slide for staining?
The specimen is placed on a slide and allowed to air dry. It is then heat-fixed by passing through a flame. The specimen will adhere to the slide, allowing it to absorb stains.
Describe crystal violet and methylene blue dyes
They are positively charged dyes, which means that they are attracted to negatively charged materials in the cytoplasm. This enables staining of cell components.
Describe nigrosin and congo red dyes
They are negatively charged dyes that are repelled by the negatively charged cytosol. These dyes stay outside the cells, leaving the cell unstained, which then stands out against the stained background. This is called a negative stain technique.
What can differential staining be used for?
It is used to distinguish between two types of organisms that would otherwise be hard to identify. It can also differentiate between two different organelles of a single organism within a tissue sample.
What are gram-positive bacteria?
Gram-positive bacteria have thicker cell walls, which retain the stain when applied. Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through a microscope. These bacteria are easily harmed by penicillin, which inhibits the formation of cell walls. They appear appear purple or blue under the microscope.
What are gram-negative bacteria?
Gram-negative bacteria are a group of bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation because of there thin cell walls. They have to be counterstained using safranin dye, which makes them red under the microscope. These type of bacteria are not susceptible to penicillin.
What are mycobacterium?
A genus of Actinobacteria. The Greek prefix myco- means “fungus,” alluding to the way mycobacteria have been observed to grow in a mold-like fashion on the surface of cultures.
What are the 4 stages of preparing a slide?
- Fixing
- Sectioning
- Staining
- Mounting
What does ‘sectioning’ involve?
Specimens are dehydrated with alcohols and then placed in a mould with wax or resin to form a hard block. This can then be sliced thinly with a knife called a microtome (Greek mikros, meaning “small”, and temnein, meaning “to cut”).
What must be carried out before any practicals are started?
A risk assessment
Why must a risk assessment be conducted?
Many of the stains used in the preparation of slides are toxic or irritant.
What are the eleven rules for a good scientific drawing?
- Include a title
- State magnification
- use a sharp pencil for drawings and labels
- use white, unlined paper
- Use as much of the paper as possible for the drawing
- draw smooth, continuous lines
- do not shade
- draw clearly defined structures
- ensure proportions are correct
- label lines should not cross or have arrow heads
- label lines should be parallel with the top of the page and should be drawn with a ruler.
