Microscopes (DR)

Question 1

Cell theory timeline

Answer 1

1665: Cell first observed
-thinly sliced cork, observed dead cell walls -HOOKE
1674-1683: First living cells observed -LEEUWENHOEK
-bacteria and protoctista (RBC, sperm cells, muscle fibers)
1832: Evidence for new plant cells -DUMORTIER
-observed cell division
1833: Nucleus observed -BROWN
1837-38: Birth of universal cell theory -SCHLEIDEN
-all living things are made of cells and cell products
1844 (1855): Observe cell division in animal cells
-however was published a decade later -REMAK
1860: Spontaneous generation disproved
-bacteria ONLY grew when in nutrient broth and allowed air -PASTEUR

Question 2

DEFINITION
Cell theory

Answer 2

Cell theory states that all living organisms are made of cells, cells are the basic unit of life, and all cells arise from pre-existing cells

Question 3

Light Microscopes

Answer 3

-easily transportable
-easy to use
-can observe living OR dead organisms
-relatively cheap

TOTAL Magnification X2000 (relatively low)
TOTAL Resolution 2µm

Question 4

Laser Scanning Confocal Microscope
(type of light microscope)

Answer 4

-moves a single laser across a specimen (point illumination) causing flourescence from components labelled with a dye.
(flourescence is the absorption and re-radiation of light)
-> the emitted light is filtered through pinhole apertures so any unwanted light does not cause blurring. and light waves will have the same focal plane and focus point.
-> the beamsplitter is dichroic mirror (different colours from different angles) which only reflects 1 wavelength from the laser but allows others from the sample to pass through.

-a laser is used instead of light for more illumination
-very thin sections of specimens used so very high resolution images are obtained
2D image: the laser is moved across the specimen
3D image: produced by creating images at different focal planes
-non invasive

! used in diagnosis of diseases of the eye and in endoscopic procedures
! development of new drugs as molecules interacting within cells can be viewed
! future uses include virtual biopsies of suspected skin cancer

Question 5

GFP
Green flourescent protein

Answer 5

-a stain isolated from a jellyfish that fluoresces under UV light
-used to identify proteins and their use in cells using different colours and genetic binding.

Question 6

DEFINITION
Resolution

Answer 6

the ability to distinguish between 2 points clearly
-if a microscope can clearly distinguish between the 2 points it has a higher resolution

Question 7

DEFINITION
Magnification

Answer 7

the number of times larger an image is than the actual object

Question 8

Acetic Orcein
(stain)

Answer 8

Binds to DNA/RNA and fixes the cell
-stops mitosis
stains DARK RED

Question 9

Eosin
(stain)

Answer 9

Stains cytoplasm RED

Question 10

Iodine
(stain)

Answer 10

Stains starch BLUE/BLACK

Question 11

Methylene Blue
(stain)

Answer 11

Stains DNA/RNA BLUE

Question 12

Type of sample prep:
Dry mount

Answer 12

A thin slice or whole organism is viewed with just the cover slip on top
e.g viewing a hair sample

Question 13

Type of sample prep:
Wet mount

Answer 13

Water or immersion oil is added to the specimen before lowering the coverslip with a mounting needle
-this prevents air bubbles
e.g aquatic organisms

Question 14

Type of sample prep:
Smear sample

Answer 14

smear a sample of the specimen using the edge of another slide
e.g a blood smear

Question 15

Type of sample prep:
Squash slide

Answer 15

1) Prepare a wet mount
2) gently press down the coverslip to squash the sample (ensuring it is a thin layer)
-this enables light to pass through and generate an image
e.g root tip squash sample to view cells with chromosomes at different stages of mitosis

Question 16

Advantages of staining a sample (4)

Answer 16

-see more detail
-increase contrast
-allows you to identify different cells
-identify different cellular components like organelles

Question 17

Artifacts

Answer 17

-a visible structural detail from the processing of the specimen
e.g an air bubble
An ‘actual structure’ is part of the cell ultrastructure

! Mesosomes (inner foldings of bacterial cell membranes) are now though to be artifacts of the specific chemical preparation!