chapter 2- Basic components of living systems

Question 1

max resolutions?

Answer 1

light microscope= 0.2um
TEM=0.0005um
SEM=0.003um- 0.01um
lower resolution= better image quality

Question 2

Max magnification

Answer 2

light microscope= x1500
TEM= more x1,000,000
SEM= less than x1,000,000
higher magnification the better

Question 3

how does staining enable cell components to become visible?

Answer 3

• resolution is limited by wavelength of light as it passes through the sample
• most cell structures have low contrast and do not absorb light
• stains increase contrast as different cell components take up the stain by different amounts

Question 4

Give examples of stains

Answer 4

• Crystal violet/ methylene blue= positively charged dye, attracted to negatively charged materials in the cytoplasm, stains RNA/DNA.
• Nigrosin/ Congo red= negatively charged dye, repels negatively charged cytosol. These dyes stay outside of the cell, leaving the cell unstained so it can stand out against a stained background.

Question 5

units of measurement

Answer 5

1000nm= 1um
1000um= 1mm
1000mm= 1m
10mm=1cm

Question 6

what are the 4 different ways a specimen can be prepared for light microscopy?

Answer 6

• dry mount
• wet mount
• squash slides
• smear slides

Question 7

stages involved in the production of slidesz

Answer 7

• fixing= used to preserve the specimen
• sectioning= specimens are dehydrated with alcohols then placed in a mould with wax, which can be thinly sliced
• staining= specimens are treated with multiple stains to show different structures
• mounting= specimens are secured to a microscope slide with a cover slip on top

Question 8

describe the acid- fast technique

Answer 8

• carbolfuchsin dye is carried into specific cells
• the cells are then washed with a dilute acid alcohol solution
• bacteria will retain the carbolfuchsin dye which is bright red
• other bacteria will lose stain and appear blue

Question 9

what is the acid fast technique used for?

Answer 9

• used to differentiate species of mycobacterium from other bacteria.

Question 10

describe the gram stain technique.

Answer 10

• crystal violet is added to the bacterial specimen on the 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/ purple
• the gram negative bacteria have thinner cell walls, and therefore lose the stain. so they are stained with a counter stain (e.g. safranin dye), which will make the bacteria appear red.

Question 11

what is the gram stain technique used for?

Answer 11

• used to separate bacteria into 2 groups, gram positive and gram negative bacteria.