microscopes and gram staining

Question 1

what is gram staining

Answer 1

the method of staining bacteria to identify them by differentiating between the two main cell wall types

Question 2

what is the method for Gram staining ?

Answer 2

add the purple crystal violet to the sample ( this stains all the types of bacteria )
then add iodine to darken the stain
add alcohol ( this would break down the stain in the gram negative bacteria as it only has a thin layer of peptidoglycan in the cell wall so the alcohol dissolves this )
then add a different coloured stain - normally safranin - to colour the gram negative bacteria as it is now colourless
observe the bacteria under the microscope and the gram positive bacteria has the darker purple stain

Question 3

what type of bacteria do most antibiotics work on ?

Answer 3

gram positive bacteria because the antibiotics break up the many crosslinks between the peptidoglycan in the cell wall . therefore the cell wall is weakened so when osmotic changes occur , the cell lyses

Question 4

what are the three main microscope types ?

Answer 4

Light microscope
Scanning electron microscope
Transmission electron microscope

Question 5

advantages of a light microscope

Answer 5

can work with living organsims
cheap
can be used in the field without electricity

Question 6

disadvantages of a light microscope

Answer 6

lack of resolution at a higher magnification so you cant see detail within the cell

Question 7

advantages of an electron microscope

Answer 7

very high resolution so subcellular structures can be seen in way more detail

Question 8

disadvantages of an electron microscope

Answer 8

a vacuum is needed therefore specimen cant be living
specimens are embedded in plastic so cant be manipulated under the microscope
delicate structures may be destroyed
specimen needs to be stained by toxic metals
artefacts are sometimes seen

Question 9

why can a beam of electrons be used in an electron microscope

Answer 9

they behave like waves and can be easily produced

Question 10

why do electron microscopes contain a vacuum ?

Answer 10

because the air molecules would scatter beam of electrons if no vacuum

Question 11

difference between transmission and scanning electron microscope

Answer 11

TEM works like a light microscopes transmitting the beam of electrons through the specimen and focusing them to form a film - the short wavelength allows for a high resolution
SEM scans a fine beam of elecrons onto the surface of the specimen and collects the electrons scattered by the surface ( electrons don’t pass through specimen )