topic 2 - cell division (investigating mitosis)

Question 1

what’s the first step to using a root tip to observe mitosis

Answer 1

cut 1cm from the tip from a growing root - it needs to be the tip as that’s where growth occurs (so that’s where mitosis takes place)

Question 2

what’s the second step to using a root tip to observe mitosis

Answer 2

prepare a boiling tube containing 1M hydrochloric acid and put it in a water bath at 60C

Question 3

what’s the third step to using a root tip to observe mitosis

Answer 3

transfer the root tip into the boiling tube and incubate for about 5 minutes

Question 4

what’s the fourth step to using a root tip to observe mitosis

Answer 4

use a pipette to rinse the root tip well with cold water - leave the tip to dry on a paper towel

Question 5

what’s the fifth step to using a root tip to observe mitosis

Answer 5

place the root tip on a microscope slide and cut 2mm from the very tip of it - get rid of the rest

Question 6

what’s the sixth step to using a root tip to observe mitosis

Answer 6

use a mounted needle to break the tip open and spread the cells out thinly

Question 7

what’s the seventh step to using a root tip to observe mitosis

Answer 7

add a few drops of stain and leave it for a few minutes - the stain will make the chromosomes easier to see under a microscope

Question 8

what’s the eighth step to using a root tip to observe mitosis

Answer 8

place a cover slip over the cells and push down firmly to squash the tissue - this will make the tissue thinner and allow light to pass through it - don’t smear the cover slip sideways

Question 9

what’s the ninth step to using a root tip to observe mitosis

Answer 9

now you can look at all the stages of mitosis under an optical microscope

Question 10

what’s the first step of using an optical microscope to observe your prepared root cell

Answer 10

start by clipping the slide you’ve prepared onto the stage

Question 11

what’s the second step of using an optical microscope to observe your prepared root cell

Answer 11

select the lowest powered objective lens

Question 12

what’s the third step of using an optical microscope to observe your prepared root cell

Answer 12

use the coarse adjustment knob to bring the stage up to just below the objective lens

Question 13

what’s the fourth step of using an optical microscope to observe your prepared root cell

Answer 13

look down the eyepiece (which contains the ocular lens) - use the coarse adjustment knob to move the stage downwards, away from the objective lens until the image is roughly in focus

Question 14

what’s the fifth step of using an optical microscope to observe your prepared root cell

Answer 14

adjust the focus with the fine adjustment knob, until you get a clear image of what’s on the slide

Question 15

what’s the sixth step of using an optical microscope to observe your prepared root cell

Answer 15

if you need to see the slide with greater magnification, swap to a higher powered objective lens and refocus

Question 16

how do you calculate the mitotic index

Answer 16

number of cells with visible chromosomes ÷ total number of cells observed

Question 17

what is the mitotic index

Answer 17

the proportion of cells undergoing mitosis

Question 18

what does the mitotic index let you know

Answer 18

how quickly the tissue if growing and if there’s anything weird going on

Question 19

what does it mean if a plant has a high mitotic index

Answer 19

a plant root tip is constantly growing so you’d expect a high mitotic index - in other tissue samples a high mitotic index could mean that tissue repair is taking place or that there’s cancerous growth in tissues

Question 19

what is a stage micrometre

Answer 19

a microscope slide with an accurate scale and it used to work out the value of the divisions on the eyepiece graticule at a particular magnification

Question 19

what equipment do you use to calculate the size of cells

Answer 19

graticule and micrometre

Question 19

where is the stage micrometre placed on

Answer 19

the stage

Question 19

where is the eyepiece graticule fitted onto

Answer 19

the eyepiece

Question 19

how do you calculate the actual size

Answer 19

size of image ÷ magnification

Question 19

what are artifacts

Answer 19

things you can see down the microscope that aren’t part of the cell or specimen that you’re looking at

Question 19

what are four examples of artifacts

Answer 19

(1) dust
(2) air bubbles
(3) fingerprints
(4) inaccuracies caused by squashing and staining your sample

Question 19

where are artefacts especially common, why

Answer 19

in electric micrographs because specimens need a lot of preparation before you can view them under an electric microscope

Question 20

if an object could be seen with one preparation technique but not another, what is it likely to be

Answer 20

an artefact rather than an organelle