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A level Biology - Module 2 > 2.1 - Microscopy (2.1.1) > Flashcards

2.1 - Microscopy (2.1.1) Flashcards

1
Q

What 3 things does ‘cell theory’ state?

A
  • Both plant and animal tissue is composed of cells
  • Cells are the basic unit of all life
  • Cells only develop from existing cells
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2
Q

When was the first cell observed?

A

1665

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3
Q

Which English scientist observed the first cells?

A

Robert Hooke

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4
Q

Which Dutch biologist observed the first living cells?

A

Anton van Leeuwenhoek

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5
Q

When did the evidence for the origin of new plant cells arise?

A

1832

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6
Q

When was the first nucleus observed?

A

1833

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7
Q

Who observed the first nucleus?

A

Robert Brown

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8
Q

When did the birth of a universal cell theory arise?

A

1837 - 1838

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9
Q

Which German scientist proposed that all plant tissues are composed of cells?

A

Matthias Schleiden

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10
Q

Which Czech scientist was the first to use a microtome to make ultra thin slices of tissue for microscopic examination?

A

Jan Purkyně

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11
Q

Based on his observations, what did Jan Purkyně propose?

A

That not only are animals composed of cells but also that the “basic cellular tissue is clearly analogous to that of plants”

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12
Q

Which German physiologist is credited with the ‘birth’ of cell theory?

A

Theodor Schwann

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13
Q

What did Theodor Schwann, a German physiologist, declare?

A

“all living things are composed of cells and cell products”

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14
Q

Which Polish/German biologist was the first to observe cell division in animal cells, disproving the existing theory that new cells originate from within old cells?

A

Robert Remak

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15
Q

When did the evidence for the origin of new animal cells arise?

A

1844 (1855)

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16
Q

Which German biologist published Robert Remak’s findings as his own in 1855?

A

Rudolf Virchow

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17
Q

Who disproved the theory of spontaneous generation of cells?

A

Louis Pasteur

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18
Q

When did Louis Pasteur disprove the theory of spontaneous generation of cells?

A

1860

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19
Q

How did Louise Pasteur disprove the theory of spontaneous generation of cells?

A

By demonstrating that bacteria would only grow in a sterile nutrient broth after it had been exposed to the air

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20
Q

What are the two lenses of a compound light microscope?

A

The objective lens and an eyepiece lens

21
Q

In a compound light microscope, what does the objective/eyepiece lens configuration allow for?

A

Much higher magnification and reduced chromatic aberration than that in a simple light microscope

22
Q

What is chromatic aberration?

A

Chromatic aberration, also known as color fringing, is a color distortion that creates an outline of unwanted color along the edges of objects in a photograph

23
Q

Describe how a dry mount is prepared

A

Solid specimens are viewed whole or cut into very thin slices with a sharp blade, this is called sectioning. The specimen is placed on the centre of the slide and a cover slip is placed over the sample.

24
Q

Describe how a wet mount is prepared

A

Specimens are suspended in a liquid such as water or an immersion oil. A cover slip is placed on from an angle, as shown.

25
Q

What are some examples of things that can be prepared as a dry mount? (3)

A
  • Hair
  • Pollen
  • Dust
26
Q

What are some examples of things that can be prepared as a wet mount? (2)

A
  • Aquatic samples
  • Other living organisms
27
Q

Describe how a squash slide is prepared

A

A wet mount is first prepared, then a lens tissue is used to gently press down the cover slip. Depending on the material, potential damage to a cover slip can be avoided by squashing a sample between two microscope slides.

28
Q

What is using squash slides a good technique for?

A

Soft samples

29
Q

What is an example of something that can be prepared using a squash slide?

A

Root tip squashes - they’re used to look at cell division

30
Q

Describe how a smear slide is prepared

A

The edge of a slide is used to smear the sample, creating a thin, even coating on another slide. A cover slip is then placed over the sample.

31
Q

What is an example of a smear slide?

A

A sample of blood

32
Q

In basic light microscopy the sample is illuminated from below with white light and observed from above. What type of microscopy is this?

A

Brightfield microscopy

33
Q

In basic microscopy the sample is illuminated from below with white light and observed from above. The whole sample is illuminated. What type of microscopy is this?

A

Wide-field microscopy

34
Q

What is resolution limited by?

A

The wavelength of light and diffraction of light as it passes through the sample

35
Q

What is diffraction?

A

Diffraction is the bending of light as it passes close to the edge of an object

36
Q

What is the cytosol of cells?

A

The aqueous interior

37
Q

How do stains on cells increase contrast?

A

Different components within a cell take up stains to different degrees. The increase in contrast allows components to become visible so they can be identified.

38
Q

How do you prepare a sample for staining?

A

It is first placed on a slide and allowed to air dry. This is then heat-fixed by passing through a flame. The specimen will adhere to the microscope slide and will then take up stains.

39
Q

What stain is used to stain the nuclei of white blood cells to the colour purple?

A

Wright’s stain (a mixture of eosin red and methylene blue dyes)

40
Q

How do dyes like crystal violet or methylene blue lead to the staining of cell components?

A

Crystal violet or methylene blue are positively charged dyes, which are attracted to negatively charged materials in cytoplasm leading to staining of cell components.

41
Q

How are dyes like nigrosin or Congo red used as a negative stain technique?

A

Dyes such as nigrosin or Congo red are negatively charged and are repelled by the negatively charged cytosol. These dyes stay outside cells, leaving the cells unstained, which then stand out against the stained background. This is a negative stain technique.

42
Q

What is the purpose of differential staining?

A

Differential staining can distinguish between two types of organisms that would otherwise be hard to identify. It can also differentiate between different organelles of a single organism within a tissue sample.

43
Q

Describe the gram stain technique in full detail

A

Gram stain technique is used to separate bacteria into two groups, Gram - positive bacteria and Gram - negative bacteria. Crystal violet is first applied to a bacterial specimen on a slide, then iodine, which fixes the dye. The slide is then washed with alcohol. The Gram-positive bacteria retain the crystal violet stain and will appear blue or purple under a microscope. Gram - negative bacteria have thinner cell walls and therefore lose the stain. They are then stained with safranin dye, which is called a counterstain. These bacteria will then appear red. Gram-positive bacteria are susceptible to the antibiotic penicillin, which inhibits the formation of cell walls. Gram-negative bacteria have much thinner cell walls that are not susceptible to penicillin.

44
Q

Describe the Acid-fast technique in detail

A

The Acid-fast technique is used to differentiate species of Mycobacterium from other bacteria. A lipid solvent is used to carry carbolfuchsin dye into the cells being studied. The cells are then washed with a dilute acid-alcohol solution. Mycobacterium are not affected by the acid-alcohol and retain the carbolfuchsin stain, which is bright red. Other bacteria lose the stain and are exposed to a methylene blue stain, which is blue.

45
Q

In the acid-fast technique, what dye is carried into the cells being studied?

A

Carbolfuchsin dye

46
Q

You will often look at slides that have been pre-prepared. Describe the 4 stages that are in this preparation process.

A
  • Fixing: chemicals like formaldehyde are used to preserve specimens in as near-natural a state as possible.
  • Sectioning: 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.
  • Staining: specimens are often treated with multiple stains to show different structures.
  • Mounting: the specimens are then secured to a microscope slide and a cover slip placed on top.
47
Q

Many of the stains used in the preparation of slides are toxic or irritants. What does this mean for the user?

A

A risk assessment must be carried out before any practical is started to identify any procedures involved that may result in harm.

48
Q

Describe all the safety measures that are put in place for the use of stains (that are toxic or irritants) (4)

A
  • A risk assessment must be carried out before any practical is started to identify any procedures involved that may result in harm.
  • CLEAPSS (Consortium of Local Education Authorities for the Provision of Science Services) is the organisation that provides support for the practical work carried out in schools. One of the main areas covered is health and safety, including risk assessment. Advice and support is provided to all types of educational establishments and their employees about all aspects of practical work such as the use of chemicals or living organisms, laboratory design, and even where to obtain the right equipment.
  • CLEAPSS provide student safety sheets that identify specific risks, advise on the measures to be taken to reduce these risks and the action to be taken in any emergency.
  • In fact, in schools many of the microscopy slides that are used are bought ready-prepared and pre-stained, not only because of the harmful nature of the stains but also because of the long complex process needed to produce high quality sections
49
Q

What are the 11 rules to follow when producing good scientific drawings?

A
  • 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 and should not have arrow heads
  • Label lines should be parallel to the top of the page and drawn with a ruler

A level Biology - Module 2 (10 decks)

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