2.1 Microscopy

Question 1

cell theory

Answer 1

Both plant and animal tissue is composed of cells

cells are the basic unit of all life

cells only develop from existing cells

Question 2

Galileo Galilei

Answer 2

1609
Said to have developed the first true or compound microscope
His instrument was the first to be given the name ‘microscope/

First type of microscopes developed in 16th to 17th century.

Question 3

Robert hooke

Answer 3

Cells first observed
coined the term cell for the structure he saw

1665

Question 4

Anton von Leeuwenhoek

Answer 4

First living cells observed
First to observe bacteria and protoctista
went on to observe red blood cell, sperm cell and muscle fibres

1674-1683

Question 5

Barthelemy Dumortier

Answer 5

Evidence for theorigin of new plant cells
first to observe cell division in plants

1832

Question 6

Robert brown

Answer 6

nucleus of a plant first observed

1833

Question 7

Theoder Schwann

Answer 7

the birth of universal theory
“all living things are composed of cells and cell products”

1837-38

Question 8

Robert Remak

Answer 8

evidence of the origin of new animal cells
first to observe cell division in animals

Question 9

Louis Pasteur

Answer 9

spontaneous geration disproved
demonstrating that bacteria would only ggrow in a sterile nutrient broth after it had been exposed to air

Question 10

How a light microscope works

Answer 10

A compound light microscope has 2 lenses
1) objective (placed near the specimen)
2) eyepiece (through which the specimen is viewed)

the objective lens produces a magnfied image which is further magnified by the eyepiece lens.

allows for higher magnification

illumination is usually provided by a light underneath the sample
opaque specimens can be illuminated from above with some microscopes

Question 11

dry mount

Answer 11

Solid specimens are viewed whole or cut into very thin slices (sectioning).

Specimen is placed on the centre of the slide.

Cover slip is placed over the sample.

E.g. hair, pollen, dust,insect parts.

Sectioned: muscle tissue, plants.

Question 12

wet mount

Answer 12

Specimen is suspended in a liquid (water or an immersion oil).
Cover slip is placed on from an angle.

E.g. aquatic samples and other living organisms can be viewed.

Question 13

smear slide

Answer 13

Edge of slide is used to smear the sample,
Creating a thin, even coating on another slide.
Cover slip is placed on top.

E.g. sample of blood.

Question 14

squash slide

Answer 14

Wet mount is first prepared.
Lens tissue is used to gently press down cover slip (may cause damage to specimen).
Press down using a slide.

E.g. soft sample: root tip squashes.

Question 15

why do we use staining

Answer 15

Staining increases contrast

Differentiate between organelle

And cells.

Question 16

preparing a slide for staining

Answer 16

Sample is placed on slide
Allow to air dry
Heat fixed by passing through flame
Specimen would adhere to slide
Will then take up stains.

Question 17

negative stain technique

Answer 17

Positive

Dyes: Crystal violet and methylene blue

Attracted to negatively charged part of the cytoplasm

Negative

Dyes: Nigrosin and congo red

Repelled by negatively charged cytosol.

Leaves cells unstained compared to stained background, providing clear contrast.

Question 18

differential staining

Answer 18

Able to distinguish between :

• 2 types of organisms that are hard to identify

= different organelles of a single organism within a tissue sample.

Question 19

gram stain technique

Answer 19

Used to separate bacteria into two groups.

Gram positive bacteria and gram negative bacteria.

1. Crystal violet is first applied to a bacterial specimen.
2. Then iodine, which fixes the die.
3. The slide is then washed with alcohol.

Gram positive bacteria: retain the crystal violet stain and will appear blue or purple under a microscope.

Gram negative bacteria: have thinner cell walls and therefore lose the stain.

4. They are then stained with safranin dye, which is a counterstain

These bacteria will then appear red.

Gram positive bacteria: susceptible to the antibiotic penicillin, which inhibits the formation of cell walls.

Gram negative bacteria: much thinner cell walls that are not susceptible to penicillin.

Question 20

definition:
- fixing
- staining
- sectioning
- mounting

Answer 20

Fixing - chemicals are used to preserve specimens in as near natural state as possible

Staining- specimens are often treated with many stains to show different structures.

Sectioning - specimens are dehydrated with alcohols

placed in a mould with wax/resin to form a hard block

sliced thinly using a knife

Mounting - the specimens are then secured to a microscope slide and a cover slip is placed on top

Question 21

acid fast tecnhique

Answer 21

Used to differentiate between species of Mycobacterium from other bacteria.

1. A lipid solvent is used to carry carbolfuchsin dye into the cells being studied.
2. The cells are then washed with dilute acid-alcohol solution.

Mycobacterium:

• are not affected by the acid-alcohol
• retain the carbolfuchsin dye
• which is bright red.

Other bacteria:

• lose the stain
• are exposed to a methylene blue stain
• which is blue.

Question 22

Good scientific drawing

Answer 22

Include a title of what the specimen is
State the magnification of the drawing
Use a sharp pencil on plain white paper
Draw smooth continuous lines
Do not shade
Clearly label all structures
Ensure proportions are correct
Label lines should be drawn with a ruler, should not cross and have no heads

Question 23

end of 2.1