2.1 Microscopy

Question 1

When were light microscopes first developed?

Answer 1

16th-17th century

Question 2

Describe cell theory (3 things)

Answer 2

1. both plant and animal tissues are made from cells
2. cells are the basic unit of all life
3. cells only develop from existing cells

Question 3

Cell theory timeline - Robert Hooke

Answer 3

1665 = Robert Hooke - thinly sliced cork, observed ‘cells’

Question 4

Cell theory timeline - Anton van Leeuwenhoek

Answer 4

1674-83 = Anton van Leeuwenhoek developed powerful glass lenses, first to observe microorganisms and red blood cells, sperm cells and muscle fibres

Question 5

Cell theory timeline - Dumortier

Answer 5

1832 = Dumortier observed cell division in plants, took years for theory to be accepted

Question 6

Cell theory timeline = Robert Brown

Answer 6

1833 = Robert Brown first to observe plant nucleus

Question 7

Cell theory timeline = Schleiden, Purkyne and Schwann

Answer 7

1837-38 = Schleiden proposed all plant tissues are made of cells
Purkyne was first to use a microtome to cut thin samples, proposed both animals and plants are made of cells
Schwann declared all living things are made of cells + their products (birth of cell theory)

Question 8

Cell theory timeline - Remak

Answer 8

1844-55 = Remak observed cell division in animals, findings copied and published by Virchow in 1855 as his own

Question 9

Cell theory timeline - Pasteur

Answer 9

1860 = Pasteur disproved theory of spontaneous generation of cells by showing that bacteria only grow in a sterile nutrient broth after being exposed to air

Question 10

Why wasn’t cell theory fully developed before the mid-19th century?

Answer 10

Magnification of microscopes was not developed enough (high enough) to view cells in enough detail, theories not believed for many years

Question 11

Name the two lenses on a compound light microscope

Answer 11

Objective lens and eyepiece lens

Question 12

Describe the process of a dry mount

Answer 12

solid specimen, viewed whole or cut thinly, placed on slide with cover slip on top

Question 13

Examples of dry mounting

Answer 13

E.g. pollen, hair, muscle tissue, plants

Question 14

Describe the process of a wet mount

Answer 14

specimens suspended in liquid (water or oil), cover slip placed at an angle

Question 15

Examples of a wet mount

Answer 15

E.g. aquatic samples, other living organisms

Question 16

Process of squash slides

Answer 16

wet mount prepped first, lens tissue used to push down cover slip, good technique for soft samples
take care so cover slip isn’t broken

Question 17

Examples of a squash mount

Answer 17

E.g. root tips - for viewing cell division

Question 18

Process of a smear slide

Answer 18

edge of slide used to smear sample to create a thin, even coating on another slide

Question 19

Examples of smear slides

Answer 19

E.g. blood samples - good to view cells

Question 20

Why do scientists use stains?

Answer 20

Increases visibility , creates contrast between different organelles as they take up dye by differing amounts, can distinguish between different variations of organism e.g. bacteria

Question 21

Crystal violet and methylene blue stains

Answer 21

Positively charged dyes which are attracted to negatively charged materials in cytoplasm which leads to staining of cell compounds

Question 22

Nigrosin and Congo Red stains

Answer 22

negatively charged dyes and are repelled by negatively charged cytosol so stay outside of cells so they stand out against stained background

Question 23

Differential staining

Answer 23

can distinguish between 2 organisms that are difficult to identify or can differentiate between organelles of a single organism

Question 24

Gram stain technique - what does it do

Answer 24

used to separate bacteria into 2 groups - gram positive and gram negative

Question 25

Gram stain technique - process

Answer 25

crystal violet dye added to specimen, then iodine which fixes the dye, washed with alcohol then a safranin dye is added to stain the negative bacteria which lost the blue stain

Question 26

Gram stain technique - results if gram positive bacteria are present

Answer 26

Retain dye so appear blue/purple

Question 27

Gram stain technique - results if gram negative bacteria are present

Answer 27

Thinner walls so lose the stain, then stained with a counter stain called safranin dye which makes them appear red

Question 28

Gram positive bacteria + penicillin

Answer 28

Gram positive bacteria are susceptible to penicillin

Question 29

Gram negative bacteria and penicillin

Answer 29

Gram negative bacteria have thinner cell walls so aren’t susceptible to penicillin

Question 30

What is Acid-fast technique used to test for

Answer 30

used to differentiate species of Mycobacterium from other bacteria using a lipid solvent

Question 31

Acid fast technique method

Answer 31

solvent used to carry carbolfuchsin dye into cells
cells are washed with a dilute acid-alcohol solution
then stained with a counter stain (methylene blue)

Question 32

acid fast expected results

Answer 32

Mycobacterium aren’t affected by the acid-alcohol so retain the stain which is bright red
other bacteria lose the stain and are exposed to a methylene blue stain - turning them blue

Question 33

Stages of slide prep - fixing

Answer 33

chemicals such as formldehyde are used to preserve specimens in a near-natural state

Question 34

Stages of slide prep - sectioning

Answer 34

specimens are dehydrated with alcohols, placed in a mold with wax/resin to form a hard block which can then be sliced using a microtome knife

Question 35

Stages of slide prep- why are specimens treated with multiple stains

Answer 35

specimens are often treated with multiple stains to show different structures

Question 36

Stages of slide prep - mounting

Answer 36

specimens are secured to slide with a cover slip

Question 37

Precautions around stains

Answer 37

Gloves, goggles, wash hands, clean surfaces, disinfect
Some stains are toxic or irritants so precautions must be taken