Practicals

Question 1

How do you test for reducing sugars?

Answer 1

Add Benedictus solution and heat.

Question 2

How do you test for non - reducing sugars?

Answer 2

Add HCl to failed benedicts test and heat.
Add sodium hydroxide until it stops fizzing.
Add more benedicts solution and heat again.

Question 3

What is iodine used to test for?

Answer 3

Starch

Question 4

How do you test for lipids?

Answer 4

• Add ethanol to sample and shake.

- Add water

Question 5

What’s the positive result of a test for lipids?

Answer 5

White cloudy solution.

Question 6

How do you test for proteins?

Answer 6

Biuret test - detects peptide bonds
Add sodium hydroxide to sample
Add dilute copper (II) sulphate solution and mix.

Question 7

What’s the positive and negative result of a biuret test?

Answer 7

Positive - purple

Negative - blue

Question 8

How do you prepare an ultracentrifugation?

Answer 8

Put solution in cold, buffered solution of the same water potential and homogenise.

Question 9

Why is the solution used in ultracentrifugation cold, buffered and the same water potential as the sample?

Answer 9

Cold - reduce enzyme activity
Buffered - pH won’t fluctuate
Same water potential - prevent the cells from bursting or shrinking

Question 10

How do you test for carbohydrates?

Answer 10

Benedicts test

Question 11

How do you prepare the stained squash slide when viewing plant root tips?

Answer 11

• Cut 2cm off the end of a root tip and leave in a watch glass for 10 minutes, covered in ethanoic acid.
• Pour 15cm3 of 1M HCl into a test tube and heat till it gets to 60°C.
• Wash root tips in cold water for 5 mins and then dry and place in HCl tubes for 5 mins and then wash and dry again.
• Place tips on microscope slide and cut each 2mm from the tip, discard the rest.
• Add a small drop of etheneo-orcein stain in the root and leave for 2mins before breaking up the tips and covering them w/ a cover slip.
• Squash with thumb without rolling.

Question 12

How do you make the serial dilutions of a 10% glucose solution when identifying the water potential of a plant tissue?

Answer 12

• Add 9cm3 of distilled water to 4 labeled test tubes.
• Add 1cm3 of the 10% glucose to the first tube and shake.
• Using a clean Pipette and bung, repeat the last step for the 3 remaining tubes, on each occasion, transferring 1cm3 of the most recently diluted glucose solution into the next test tube.

Question 13

How do you devise w standardised test when identifying the water potential of a plant tissue?

Answer 13

• Add Benedicts reagent to each tube and heat.

- Observe the colours formed.

Question 14

How do you prepare the beetroot discs when investigating the permeability of cell surface membranes?

Answer 14

• Use a cork borer to cut cylinders from beetroot and cut them into 3mm long discs on a tile using a scalpel and ruler.
• Remove the pigment by blotting the discs on paper and then soaking then in water, repeat this process until the water is free of pigment.

Question 15

How do you subject the discs to the required temperatures when investigating the permeability of cell surface membranes?

Answer 15

• Add 5cm3 of distilled water to 6 labeled test tubes before putting them each in baths of different temps.
• Add 3 discs to a test tube and start the clock, after 60s shake the tube, carry out the same procedure for the other tubes.

Question 16

How do you test the effect of antimicronial substances on microbial growth using antiseptic techniques?

Answer 16

• Wash hands and disinfect work area.
• Label agar plate w/ bacteria being used, name and date.
• Sterilise neck of culture after removing lid and use Pipette to draw up culture before sterilising culture again.
• Place culture sample on agar w/ lid safely ajar.
• Spread culture across agar and place antibiotic disc on agar.
• Steralise and disinfect all equipment and work area after.
• Tape lid to plate and place it upside down and use a role to measure the diameter of the zone of inhibition in mm.

Question 17

Cohesion tension theory

Answer 17

The theory by which tension is created from transpiration pulling water out the top of the leaf creating a negative pressure in the xylem.