Michaelmas week 1

Question 1

Draw a basic microscope

Answer 1

(see notes for diagram)

Question 2

What are 8 steps to setting up a microscope?

Answer 2

1) Focus on object on slide
2) close field iris until edge encroaches on field of view
3) Move condenser-focus control until edge is as sharp as possible
4) centre condenser with screws
5) open field iris until the edge is at the edge of your field of view
6) Remove eyepiece
7) Adjust condenser-iris until diameter is 2/3 diameter of field OR for 100x objective open fully and replace the eyepiece
8) Adjust the image brightness

Question 3

What stains do you use to view DNA and RNA?

Answer 3

Methyl green –> DNA, stains green-blue

Pryonin –> RNA, stains pink

Question 4

What is wrong with these stains?

Answer 4

They do not preserve general structure and it isn’t possible to make out the boundaries between cells

Question 5

Define spatial resolving power

Answer 5

The smallest separation at which 2 objects can be distinguished

Question 6

What is the actual spatial resolving power? (equation and meaning)
What is a typical NA value

Answer 6

d=0.61 lambda/ NA
Lambda and d both in MICROmetres
NA : Numerical aperture of objective lens, given on barrel of objective, typically 0.5 micrometres
Measure of range of angles from which a lens can adapt light

Question 7

Lambda in visible light ranges…

Answer 7

From 400-750 nm

Question 8

The actual spatial resolving power for a 100x objective is close to…

Answer 8

The theoretical max resolving power of a light microscope

Question 9

Draw out the principles in the microscope set up

Answer 9

(see notes for diagram)

Question 10

In setting up what do you want on the same optic axis?

Answer 10

3 lenses and 2 irises

Question 11

What defines the optic axis?

Answer 11

The relative positions of the eyepiece and objective lens (position slightly different for each objective when it swings in)
The condenser lens and 2 irises must be aligned with the optic axis and and size of irises adjusted for max resolution

Question 12

What is chara?

Answer 12

An alga with branchlets made from a single row of large cells arising from the central axis
(see notes for diagram)

Question 13

How long are chara cells?

Answer 13

Up to several cm

Question 14

Why do cells show cytoplasmic streaming?

Answer 14

They are large and the cytoplasm is sparse and spread out so diffusion is too slow

Question 15

What is average cytoplasmic streaming conduction velocity?

Answer 15

30 micrometres per second

Question 16

How does cytoplasmic streaming work?

Answer 16

Myosin moves over actin filaments that lay along chloroplasts
Different directions achieved because filaments lie in different directions along different parts of the cell
This is the fastest known myosin –> mammalian myosin is 1-5 micrometres per second

Question 17

What is the chara indifference zone?

Answer 17

Area between 2 sections where cytoplasmic streaming occurs
In one section chloroplasts move up and in the other they move down
(see notes for diagram)