Chapter 2.1 - Microscopy and calibration

Question 1

What is resolution?

Answer 1

The ability to distinguish between two separate points that are very close together

Question 2

What is magnification?

Answer 2

The number of times greater an image is than the object

Question 3

How do you calculate magnification?

Answer 3

Image size/Real size

Question 4

How do you convert from cm - mm - μm - nm?

Answer 4

cm - mm = x 10
mm - μm = x 1000
μm - nm = x 1000

Question 5

What is a photomicrograph?

Answer 5

A photograph taken through a microscope

Question 6

What are the four types of sample preparation?

Answer 6

1. Dry mount
2. Wet mount
3. Squash slides
4. Smear slides

Question 7

How can samples be prepared on a dry mount?

Answer 7

• Solid specimens are sectioned(cut into very thin slices with a sharp blade) or viewed whole
• It is placed on the centre of a slide and a coverslip is placed over the sample

Question 8

How can samples be prepared on a wet mount?

Answer 8

• Specimens are suspended in a liquids such as water or an immersion oil
• A coverslip is placed on from an angle

Question 9

How can samples be prepared on squash slides?

Answer 9

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

Question 10

How can samples be prepared on smear slides?

Answer 10

• The edge of a slide is used to smear the sample, creating a thin, even coating on another slide
• A coverslip is placed over the sample

Question 11

How do you calibrate a microscope?

Answer 11

1. Fix the stage micrometer(on the stage) into place on the stage
2. Look through the eyepiece lens to line up the micrometer and eyepiece graticule(inside eyepiece)
3. Count the number of graticule divisions that fit into one micrometer division
4. Use the formula, graticule division = size of one micrometer division / number of graticule divisions, to calculate the size of each graticule division at that magnification

Question 12

What are stains?

Answer 12

Coloured chemicals that bind to molecules in or on the specimen, increasing contrast

Question 13

Why are stains used?

Answer 13

Most of a cell is transparent and so stains bind to certain structures to increase contrast, this allows components to become more visible

Question 14

What is differential staining?

Answer 14

Stains that bind to specific chemicals

Question 15

What is the gram stain technique?

Answer 15

It is a technique used to separate bacteria into two groups, gram-positive and gram-negative bacteria

Question 16

How is the gram stain technique carried out?

Answer 16

• 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 will retain the crystal violet stain and will appear blue/purple
• The gram-negative bacteria have thinner cell walls and will lose the stain, they are stained with safranin dye(counterstain), it then appears 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

Question 17

What does acetic orcein bind to and stain?

Answer 17

It binds to DNA and stains chromosomes dark red

Question 18

What does eosin stain?

Answer 18

It stains cytoplasm pink

Question 19

What does sudan red stain?

Answer 19

It stains lipids red

Question 20

What does iodine in potassium iodide stain?

Answer 20

It stains cellulose walls yellow and starch granules blue/black, but they look violet under the microscope

Question 21

What should biological drawing not include?

Answer 21

• Shading or colouring
• Arrow heads for labels
• Overlapping lines

Question 22

What should biological drawings include?

Answer 22

• Titles
• Magnification/scale
• Draw with a sharp pencil
• Smooth, continuous lines
• Labels