RP2 - using optical microscopes and preparation of temporary mounts

Question 1

describe how temporary mounts of plant tissue are made

Answer 1

• thin slice/section of plant tissue
• put slide in water/stain
• add cover slip

Question 2

describe how scientist could use temporary mounts of leaves to determine mean number of chloroplasts in mesophyll cells of a leaf

Answer 2

• select large number of cells
• count number of chloroplasts
• divide number of chloroplasts by number of cells

Question 3

a student cut thin sections of tissue to view with an optical microscope. explain why it is important that the sections were thin.

Answer 3

• allows light through
• a few layers of cells can be viewed

Question 4

when the student was making microscope slides they were told to ensure they did not move the coverslip sideways. explain why.

Answer 4

to not damage chromosomes/to prevent cells rolling on top of each other

Question 5

mitosis is important in life of organism. give 2 reasons why

Answer 5

• growth
• replace cells
• genetically identical cells
• asexual reproduction

Question 6

explain why the biologist chose to examine 200 cells

Answer 6

ensures representative sample

Question 7

explain why student only used 5mm from tip of onion root

Answer 7

where mitosis occurs/fits under cover slip

Question 8

explain why student pressed firmly on cover slip

Answer 8

thin layer/spread out cells allows light to pass through

Question 9

what is the name given to division of cytoplasm during cell cycle

Answer 9

cytokenisis

Question 10

describe and explain what student should have done when counting cells to make sure mitotic index obtained for root tip was accurate

Answer 10

• examine large number of cells
• to ensure representative sample
  OR
• repeat count
• to ensure correct figures
  OR
• only count whole cells
• to standardise counting

Question 11

explain why root tips are used

Answer 11

where mitosis occurs

Question 12

explain why a stain is used

Answer 12

to make chromosomes visible

Question 13

explain why root tip was firmly squashed

Answer 13

to let light through thin layer

Question 14

a different set of results was obtained when the count was repeated on another occasion with a different garlic root tip. give 2 reasons for difference in results

Answer 14

any 2 from
- type of garlic
- time of day
- chance
- temperature

Question 15

how to calculate mitotic index

Answer 15

mitotic index = number of cells with visible chromosomes ÷ total number of cells x 100