microscopes

Question 1

core practical - onion cells
what is the equipment needed?

Answer 1

microscope
toothpicks
cover slips
iodine tincture
pipettes
onion
microscope slides
kitchen knife

Question 2

core practical-onion cells
what are the steps?

Answer 2

slice the onion as thin as possible
clean your microscope slide and cover slip
put the onion on the microscope slide and reposition with a toothpick
add a drop of iodine on the onion
put the cover slip on top of the onion and only add a bit of pressure to push it down

Question 3

how to calculate magnification?

Answer 3

magnification=observed size/actual size

Question 4

exam question-observed size
the nucleus of a cell viewed at x500 magnification has an image size of 2.4mm calculate the real size of nucleus

Answer 4

2.4/500
Ans x 1000
=4.8 micrometre

Question 5

exam question-actual size
a leaf cell is observed at x400 magnification, the size of the image is 2cm calculate the real size of the cell

Answer 5

2/400=5x10^-3
Ans x 1000
=5micrometres

Question 6

exam question-actual size
three adjacent onion cells are viewed under a microscope at x200 magnification the combined image size of all three cells is 75mm
assuming all the cells are the same size calculate the real size of a single onion cell

Answer 6

75/3=25
25/0.125
Ans x 100=125micrometre

Question 7

exam question-observed size
a cell with a length of 0.05mm is observed at x200 magnification calculate the size of the image

Answer 7

200 x 0.05
=10mm

Question 7

core practical-light microscope
what is the equipment needed?

Answer 7

sterile cotton bud
microscope slide
methylene blue stain
distilled water
coverslip
light microscope

Question 8

core practical-light microscope
what are the steps?

Answer 8

use a sterile cotton bud move it over the inside of your mouth
smear the cotton bud over a small area in the centre of a clean microscope slide
allow the smear to air dry
place two drops of 1% methylene blue stain onto the smear and leave for 1 minute
rinse off the excess methylene blue
dry the slide and add a drop of distilled water to the stained smear
cover with coverslip and observe the cheek cell under the microscope use low power first
draw three cheek cells as seen under high power

Question 9

what do electron microscopes use?

Answer 9

electron beams

Question 10

why do electron microscopes use short wavelengths?

Answer 10

so it has better resolving power

Question 11

how can electron beams be focused?

Answer 11

using electromagnetic lenses (electromagnets)

Question 12

what is resolution?

Answer 12

the ability to distinguish clearly between two points

Question 13

what is a light microscopes resolution?

Answer 13

0.2 micrometres or 200 nanometre

Question 14

how does a light microscope produce images?

Answer 14

uses light rays to make the object visible

Question 15

how does a transmission electron microscope produce images?

Answer 15

electrons that pass through strike a detector producing an image

Question 16

how does a scanning electron microscope produce images?

Answer 16

beams of electrons reflect back onto a detector

Question 17

what are the advantages of using a light microscope?

Answer 17

it is cheap and easy to use

Question 18

what are the advantages of using a transmission electron microscope?

Answer 18

gives more detail

Question 19

what are the advantages of using a scanning electron microscope?

Answer 19

has a higher resolution

Question 20

what are the disadvantages of using a light microscope?

Answer 20

lower resolution

Question 21

what are the disadvantages of using a transmission electron microscope?

Answer 21

expensive and requires more training

Question 22

what are the disadvantages of using a scanning electron microscope?

Answer 22

also expensive

Question 23

do specimens have to be dead or alive to be seen under a microscope?

Answer 23

can be both

Question 24

why do you have to stain cells with iodine to see them under a microscope?

Answer 24

because cells are colourless