microscopy

Question 1

magnification definition

Answer 1

how much bigger the image is than the specimen

Question 2

resolution definition

Answer 2

the ability of a microscope to distinguish between 2 points that are close together

Question 3

light microscopes
- max magnification
- resolution
- specimen prep
- image produced

Answer 3

x1500
200nm

specimens can be living/dead, must be thin and transparent

images are 2D and colour

Question 4

scanning electron microscopes
- max magnification
- resolution
- specimen prep
- image produced

Answer 4

x100,000
0.2-10nm

specimen must be dead, dried and coated with metal

image produced are 3D and black + white, colour can be added artificially

Question 5

transmission electron microscopes
- max magnification
- resolution
- specimen prep
- image produced

Answer 5

x500,000
0.02-1nm

specimen must be dead, dried and coated with metal, must be thin slices

image will be 2D and black + white, colour can be added artificially after

Question 6

laser scanning confocal microscopes
- max magnification
- resolution
- specimen prep
- image produced

Answer 6

x2000
200nm

samples can be living or dead

produces 3D images of sample in layers at different depths, fluorescent colours/dyes can be seen

Question 7

how does staining enable cell components to become visible

Answer 7

resolution is limited by wavelength of light and diffraction of light passing through sample
as most cell structures are transparent, images have low contrast as they don’t absorb light
staining increases contrast as different cell components will take up the stain to varying degrees therefore increasing visibility

Question 8

give 2 examples of stains

Answer 8

iodine - a stain commonly used to observe plant cells, yellow-brown colour, black in the presence of starch

methylene blue - positively charged stain so attracted to negatively charged materials in cytoplasm/cell, such as RNA/DNA

Question 9

what is GRAM staining?

Answer 9

a technique used to separate bacteria into 2 groups:

• GRAM positive = blue
  e.g. pneumonia causing bacteria
• GRAM negative = red
  e.g. bubonic plague causing bacteria

Question 10

describe GRAM stain technique

Answer 10

• apply crystal violet to bacterial specimen
• add iodine to fix the dye
• wash slide with ethanol, GRAM positive will retain stain, GRAM negative loses stain (as bacteria has thinner walls)
• GRAM negative is then dyed with safranin which makes them appear red

Question 11

magnification formula

Answer 11

magnification
= image size / actual size

I
A M

Question 12

if given an image + magnification, but no scale bar/actual size - how could you work out the actual size

Answer 12

measure the sides of the image and divide both by magnification
then multiple together to find the area
- be wary of what units to use!

Question 13

if given an image + a scale bar, but no magnification, how could you work out the magnification

Answer 13

measure the scale bar with a ruler, then divide this length by the length the scale bar represents for magnification

Question 14

formula for the volume of a sphere

Answer 14

4/3πr^3

Question 15

give 12 rules for biological drawings

Answer 15

• use a sharp pencil
• no arrow heads
• title
• label lines should be drawn with a ruler
• drawing must take up 50% of the page
• no sketch lines
• no shading
• state magnification
• add a scale bar
• drawing must be to scale
• labels should be drawn outside the diagram
• plain paper should be used