A2.2.2 - Cells & the Microscope

Question 1

Types of microscopes

Answer 1

• Light microscopes: Light passes through specimens
• Electron microscopes (EMs): Electrons passes through specimens
  → Provides greatest magnification (100,000x) & resolution
• Compound microscopes

Question 2

Parts of microscope

Answer 2

(On physical flashcard)

Question 3

Diff. between light & electron microscopes

Answer 3

• Light Microscopes:
  → Inexpensive to purchase & operate
  → Less complex & easy preparation
  → Living/dead samples
  → Magnifies up to 2,000x
• EMs:
  → Expensive to “”
  → Very complex & lengthy preparation
  → Dead samples
  → Magnifies over 500,000x

Question 4

Decreasing order of sizes for cells

Answer 4

• Organelles
• Bacteria (some may be as big as organelles)
• Viruses
• Membranes
• Molecules

Question 5

How to create temporary mounts (wet mounts)?

Answer 5

1. Transfer sample onto the glass slide
2. Add a small drop of stain/water onto specimen
3. Gently lower the cover slip at an angle onto specimen to avoid bubbles
   → If there is too much water, cover slide can move around
   → Use tissue to dry the edge of the cover slip (will draw out some water)
4. Push out the bubble if necessary with a tool (i.e. eraser end of a pencil)

Question 6

What are stains?

Answer 6

Chemical solution applied to samples to make certain areas of the cell more visible

Question 7

Types of stains

Answer 7

Plant cells → Iodine
* Binds to starch
→ Starch: brown/blue-black
→ Glycogen: red
Animal cells → Methylene Blue
* Binds to nucleus & DNA(?)
Bacteria → Gram staining
* Divides cells into 2 types: gram-pos. & gram-neg.
→ Gram-positive: purple
→ Gram-negative: pink

Question 8

Diff. between eyepiece graticules & stage micrometer (IB focuses on eyepiece graticules)

Answer 8

• Eyepiece graticules: A finer scale/ruler than stage micrometer
  → 1 graticule division = 5 µm
  → 20 graticule divisions = 100 µm
• Stage micrometer: Only measures by 100 µm (= 0.1mm)

Question 9

Unit conversions

Answer 9

• nm → µm → mm → m
  → ÷1000
• m → mm → µm → nm
  → x1000

Question 10

Magnification calculations

Answer 10

Magnification = (image size) / (actual size)
→ convert units to mm or µm

Question 11

OPTIONAL - Field of View (FOV) equation (A2.2.2 slide 13 & 22)

Answer 11

(diameter (LP)) × (Magnification of LP objective) / (Magnification of HP obj.) = diameter (HP)

Question 12

Guidelines for drawing cell structures (A2.2.1-2: Interactive 1)

Answer 12

• Certain features should be left out depending on the magnifications (i.e. 400x → no ribosomes)
• No shading
• Fill the space w the drawing if necessary (when given a microscope FOV)
• Gap in the cell membrane
• Lines should point directly at the thing being labelled
  → Have to be straight lines
  → No lines crossing over each other