Cell Biology - Cell Division and Culturing 26-32

Question 1

what are chromosomes
3 points

Answer 1

1) coiled up lengths of DNA molecules
2) each carries a large number of genes
3) different genes control the development of different characteristics

Question 2

where are chromosomes found

Answer 2

in the cell nucleus

Question 3

how many copies of each chromosome do body cells normally contain

Answer 3

body cells normally have 2 copies of of each chromosome - one from the ‘mother’ one from the ‘father’

Question 4

how many chromosomes do body cells normally contain

Answer 4

there are 23 pairs of chromosomes in a body cell so 46 altogether

Question 5

what is the function of the cell cycle

Answer 5

it makes cells for growth, development and repair

Question 6

what is the cell cycle
4 points

Answer 6

1) body cells in multicellular organisms divide to produce new cells
2) the stage of the cycle when cells divide is called mitosis
3) mitosis is used to grow or replace cells that have been damaged
4) the end of the cycle results in 2 new cells identical to the original cell

Question 7

what are the 2 stages of the cell cycle
2 points

Answer 7

1) growth and DNA replication
2) mitosis

Question 8

describe the growth can DNA replication stage of the cell cycle
5 points

Answer 8

1) in a cell that’s not dividing the DNA is all spread out in long strings
2) before it divides the cell has to grow and increase the amount of subcellular structures
3) it then duplicates its DNA so there is one copy for each new cell
4) the DNA is copied and forms X shaped chromosomes
5) each arm of the chromosome is an exact duplicate of the other

Question 9

draw a picture of growth and DNA replication

Answer 9

pg 27 of bio book

Question 10

describe the phases of mitosis
6 points

Answer 10

1) chromosomes line up at the centre of the cell
2) the cell fibres pull them apart
3) the 2 arms of each chromosome goes to the opposite ends of the cell
4) membranes form around each of these sets of chromosomes
5) these become the nuclei of the 2 new cells
6) lastly the cytoplasm and cell membrane divide producing 2 new daughter cells

Question 11

what is the result of mitosis
3 points

Answer 11

1) one parent cell produces 2 new daughter cells
2) the daughter cells contain exactly the same DNA they’re identical
3) they also have the exact same DNA as the parent cell

Question 12

how do prokaryotic cells replicate

Answer 12

by binary fission

Question 13

describe the steps of binary fission
4 points

Answer 13

1) the circular DNA and plasmids replicate
2) the cell gets bigger and the circular DNA strands move to opposite poles of the cells
3) the cytoplasm begins to divide and new cell walls begin to form
4) the cytoplasm divides and 2 new daughter cells are produced

Question 14

what is the result of binary fission
2 points

Answer 14

1) each daughter cell has one copy of the circular DNA
2) but can have a variable number of copies of the plasmids

Question 15

what is the mean division time

Answer 15

the average amount of time it takes for one bacterial cell to divide into 2

Question 16

what can the mean division time tell you
2 points

Answer 16

1) you can work out how many times a bacterial cell has divided in a certain amount of time
2) so the number of cells it has produced in that time

Question 17

how can you calculate the number of bacteria in a population e.g. mean division time is 30mins, how many cells after 2.5 hours
4 points

Answer 17

1) make sure both times are the same units - 2.5hr = 150 mins
2) divide the total time that the bacteria are producing cells by the mean division time - 150/30 = 5
3) this gives you the number of divisions - 5 divisions
4) then do 2 to the power of how ever many divisions - 2^5 = 32 cells

Question 18

give 2 things that help to maximise the rate of binary fission

Answer 18

the right conditions e.g. a warm environment and lots of nutrients

Question 19

what are bacteria grown in

Answer 19

a culture medium

Question 20

what is a culture medium
2 points

Answer 20

1) it can be a nutrient broth solution or solid agar jelly
2) they contain the carbohydrates, mineral, proteins and vitamins they need to grow

Question 21

how do you grown bacteria on an agar plate
3 points

Answer 21

1) hot agar jelly is poured into shallow round plastic dishes called petri dishes to make the agar plate
2) when the jelly is cooled and set inoculating loops can be used to transfer microorganisms to the culture medium
3) microorganisms then multiply

Question 22

what’s an alternative to an inoculating loop

Answer 22

a sterile dropping pipette and spreader to get an even covering

Question 23

what temperature are microorganisms grown at in a school and in industry
2 points

Answer 23

1) not above 25’c because harmful pathogens are more likely to grow above this temp
2) in industry they use higher temps so they grow faster

Question 24

how can you avoid unwanted microorganisms contaminating you results
4 points

Answer 24

1) petri dish and culture medium must me sterilised by heating to a high temperature to kill them
2) inoculating loop should be sterilised by passing it through a hot flame
3) after transferring the bacteria the lid of the petri dish should be lightly taped on to stop micorg from the air
4) petri dish should be stored upside down to stop drops of condensation from falling on agar jelly

Question 25

how can you investigate the effect of antibiotics on bacterial growth
5 points

Answer 25

1) place paper discs soaked in different types (or concentrations) of antibiotics on an agar plate that has an even covering of bacteria
2) leave some space between the discs
3) the antibiotics should diffuse into the agar jelly
4) leave the plate for 48 hours at 25’c

Question 26

describe the results when you investigate the effect of antibiotics on bacterial growth
3 points

Answer 26

1) antibiotic resistant bacteria will continue to grow around the paper discs
2) non-resistant strains will die leaving a clear area called the inhibition zone
3) the larger the inhibition zone the more effective the antibiotic against the bacteria

Question 27

what control can you use when you investigate the effect of antibiotics on bacterial growth
2 points

Answer 27

1) paper disc soaked in sterile water
2) to make sure any difference between the growth of bacteria is due to the effect of the antibiotic alone

Question 28

how can you compare the effectiveness of different antibiotics on bacteria
3 points

Answer 28

1) calculating the sizes of the inhibition zones
2) use a ruler through the petri dish- don’t open
3) you can also use this to measure the area of a colony