Cell Structure

Question 1

How does a light microscope work?

Answer 1

A light microscope is composed of two lenses
- Objective lens - which is placed near specimen + magnifies image
- Eyepiece lens - magnifies the image again

Question 2

How to prepare a dry mount?

Answer 2

• Solid specimens are cut into thin slices using a sharp blade
• Place specimen on centre of the slide
• Add a cover slip over the sample

Question 3

How to prepare a wet mount?

Answer 3

• Place specimen on the slide
• Add a drop of water to the sample
• Place cover slip at an angle and gently place down onto the sample

Question 4

How to prepare a squash slide?

Answer 4

• Prepare a wet mount
• Use a lens tissue to gently press down on cover slip

Question 5

How to prepare smear slides?

Answer 5

• Use edge of slide to smear the sample
• Creating a thin, even coating on another slide
• Place cover slip over the sample

Question 6

What is differential staining?

Answer 6

This is a staining technique which is used to distinguish between two types of organisms
- Also used to differentiate between organelles

Question 7

What does Methylene blue + Crystal violet stain?

Answer 7

• They are +ve charges dyes
• Attracted to negatively charged materials in the cytoplasm

Question 8

What does Nigroson + Congo red stain?

Answer 8

• They are -ve charged dyes
• Repel -ve charged cytosol
• Dyes stay on outside, leaving cells unstained
• Negative stain technique

Question 9

What is the purpose of the Gram-stain technique?

Answer 9

• Separate bacteria into Gram-positive + Gram-negative

Question 10

How does the Gram-stain technique work?

Answer 10

• Add Crystal violet to sample on a slide
• Add iodine
• Wash slide with alcohol
• Gram-positive retain the stain - appear blue/purple under microscope
• Gram-negative bacteria have thinner walls + therefore lose the stain
• Add Safranin dye (Counterstain) - Gram-negative bacteria turn red

Question 11

Define Magnification

Answer 11

How many times larger the image is compared to the actual size of the object

Question 12

Define Resolution

Answer 12

Ability to see individual objects as separate entities

Question 13

Magnification calculation

Answer 13

Magnification = image size / actual size

Question 14

How to calibrate a light microscope?

Answer 14

• Line up the stage micrometer and the eyepiece graticule
• Each division on stage micrometer is 0.1mm
• Calculate the size of one division on the eyepiece graticule
• Calculate depending on number of divisions

Question 15

What is a Transmission electron microscope (TEM)

Answer 15

• Electron microscope
• Beam of electrons
• Max Resolution is 0.5nm
• Max Magnification is > x1000000
• 2D image formed
• B+W

Question 16

What is a Scanning electron microscope (SEM)?

Answer 16

• Electron microscope
• Beam of electrons - knocks electrons off the specimen
• Max Resolution is 3-10nm
• Max Magnification is ~ x500000
• 3D image formed
• B+W

Question 17

What is a Laser scanning confocal microscope?

Answer 17

• Laser beams (using a fluorescent dye)
• 3D
• Observe depth
• Coloured image produced
• Max Resolution is 200nm
• Max Magnification is x2000

Question 18

Advantages of a light microscope

Answer 18

Inexpensive
Portable
Simple sample preparation
Vacuum not required
Specimens can be living or dead

Question 19

Disadvantages of a light microscope

Answer 19

Low Resolution
Low Magnification

Question 20

Advantages of an electron microscope

Answer 20

High Magnification
High Resolution

Question 21

Disadvantages of an electron microscope

Answer 21

Expensive
Not easily portable
Complex sample preparation
Vacuum Required
Specimens are not living