Exam Questions Unit 3

Question 1

Explain why the results of an experiment might have been affected if the variable temperature had not been controlled. (3)

Answer 1

• temperature has an effect on enzyme activity
• if temperature changes, the enzyme activity changes
• so the experiment is not valid

Question 2

What axis are the independant and dependant variables drawn on a graph? (2)

Answer 2

• independant= horixontal x axis

- dependant= vertical y axis

Question 3

Devise a method that can be used to make a valid comparison of the tensile strength of fibres from the same plant, treated with different concentrations of sodium hydroxide solution (6)

Answer 3

• take the same age, mass and part of the plant extract
• temperature must be controlled
• the size of mass must be controlled
• masses must be added until fibre breaks and measure the mass that breaks the fibre
• repeat and find the mean
• make sure the masses dont fall on your feet (safety procedure)

Question 4

name two variables that should be controlled in beetroot experiment (2)

Answer 4

• storage conditions

- age of beetroots

Question 5

Name an inorganic ion needed for the synthesis of amino acids

Answer 5

nitrate ions

Question 6

Name an inorganic ion needed for the synthesis of chlorphyll

Answer 6

magnesium ions

Question 7

Name an inorganic ion needed for the synthesis of the middle lamella

Answer 7

calcium ions

Question 8

Explain what standard deviations indicate about the results of a given investiation (2)

Answer 8

• if the standard deviations do not overlap, it shows that the difference between the means is significant
• the results are less reliable

Question 9

Why would root tips be be placed in acetic orcein in a water bath at 55 ~C and left for five minutes?

Answer 9

to stain/die/colour the chromosomes

Question 10

Why would a slide be viewed first using low power and then high power of a microscope?

Answer 10

to locate and then magnify the cells

Question 11

Explain why the mitotic index is affected by pH? (4)

Answer 11

• enzymes are involved
• enzymes are proteins
• at pH below or above the optimum, the active site is not the right shape, the enzyme denatures and the bonds holding the shape change
• enzyme substrate complexes do not form

Question 12

How could the area of a zone of inhibition be determined? (2)

Answer 12

• measure the diameter or radius of the zone

- apply area pi X r2

Question 13

suggest why agar plates would be kept at 5~C before they were incubated

Answer 13

to stop the growth of bacteria