Core Practicals

Question 1

Core practical 1: investigating the initial rate of reaction
describe how to make up 0.2%, 0.4%, 0.6%, 0.8% dilutions of trypsin solution

Answer 1

-for the 0.2% solution: take 2cm3 of 1% trypsin solution and add 8cm3 of distilled water
-for the 0.4%: mix 4cm3 of trypsin solution and 6cm3 of distilled water
-for the 0.6%: mix 6cm3 of trypsin solution and 4cm3 of distilled water
-for the 0.8%: mix 8cm3 of trypsin solution and 2cm3 of distilled water

Question 2

Core practical 1: investigating the initial rate of reaction
describe how to use a colorimeter to measure the absorbance of different concentrations of trypsin solution

Answer 2

-mix 2cm3 of 1% trypsin solution and 2cm3 of distilled water and use this as a reference cuvette to set the colorimeter absorbance to 0
-add 2cm3 of milk suspension and 2cm3 of 0.2% trypsin solution to another cuvette
-mix and quickly place into the colorimeter
-measure the initial absorbance and again at 15 second intervals for 5 minutes
-repeat for each dilution

Question 3

core practical 3:

Answer 3

-fill a small bottle with hydrochloric acid, put it in a water bath for 5 minutes, put the garlic clove in the acid and place in the hot water bath for another 5 minutes - make sure roots are submerged
-rinse the acid off the roots and cut several root tips
-put the root tips in a vial containing acetic orcein

Question 4

Core practical 8: using a potometer
explain precautions that need to be taken when setting up a potometer before it can be used to measure the water uptake of a leaf
(2 marks)

Answer 4

-cut the shoot underwater
-so no air enters the xylem

-seal using petroleum jelly
-so that no air leaks into the system

-move the air bubble to 0
-so that water lost can be accurately measured

Question 5

Core practical 8: using a potometer
explain why water uptake of the leafy shoot may not be the same as the water transpired
(2 marks)

Answer 5

-not all water taken up by the shoot is lost in transpiration
-because some water is used for photosynthesis

Question 6

Core practical 8: using a potometer
state one way in which the temperature could be increased without affecting the validity of the investigation

Answer 6

change the temperature of the room using a heater