required practical 4

Question 1

what is the hypothesis for this practical?

Answer 1

that temperature will affect the leakage of pigment from beetroot cells

Question 2

what is the independent variable?

Answer 2

the temperature of the water bath

Question 3

what is the dependent variable?

Answer 3

the absorbance of the solution (measured with a colorimeter)

Question 4

what are the control variables?

Answer 4

volume of distilled water in each test tube, mass of beetroot in each test tube, time the beetroot is left in the water bath, amount of shaking each test tube receives

Question 5

what is the method for the practical?

Answer 5

1. set up water baths at 20, 30, 40, 50 and 60 degrees celsius
2. use a scalpel to cut 12 identical discs of beetroot
3. add 5cm^3 of distilled water to a test tube and put a bung in the opening
4. label the tube with the temperature it will be incubated at
5. repeat for further test tubes at each temperature
6. rinse the beetroot tubes with water and blot with a paper towel
7. as simultaneously as possible, put two discs of beetroot in each test tube, replace the bungs, put each test tube in the correct water bath and start a timer
8. leave the tubes for 5 minutes and follow the shaking protocol
9. remove the tubes from the water baths, pour the water into a clean test tube (labelled appropriately) and throw the beetroot away
10. use a colorimeter to measure the absorbance of each solution (use a distilled water control sample to calibrate it)
11. record the results

Question 6

what is the risk assessment for the practical?

Answer 6

hazard-risk-prevention
scalpel-cuts from sharp object-cut away from fingers, keep scalpel away from edge of desk
broken glass-cuts from shop object-be careful when handling glassware, keep away from edge of desk
hot water-scalding-wear eye protection, use tongs to remove test tubes from water bath, keep water baths in centre of desk

Question 7

what other factors may affect the dependent variable and how will they be controlled?

Answer 7

time the beetroot was in the water bath for - add and remove them at the same time
some pigment may leak out when beetroot is cut - rinse with water and blot with paper towel to remove
beetroot discs could stick together in test tube which would affect diffusion of pigment - shake test tubes
pigment may build up around discs which would reduce concentration gradient and affect diffusion - shake test tubes

Question 8

why does temperature affect cell surface membranes?

Answer 8

high temperatures mean the phospholipid molecules become more fluid and move around more, making the membrane more permeable than at lower temperatures where the phospholipids pack closely together