Biochemical Tests

Question 1

Name the reagent to test for sugars

Answer 1

Benedict’s reagent

Question 2

Describe the method for testing reducing sugars

Answer 2

1.add excess Benedict’s reagent to the sample
2. Heat in water bath (above 80)

Question 3

Describe the method for testing non reducing sugars

Answer 3

1. Add. Dilute hydrochloric acid and heat in water bath (breaks bonds and produce monosaccharide)
2. Add an alkali to neutralise
3. Add excess Benedict’s reagent
4. Heat in water bath (above 80)

Question 4

Positive test results for reducing sugar

Answer 4

Green > yellow > orange > brick red

Question 5

Quantitative measurement for a reducing sugar

Answer 5

1. Filter solution and weigh precipitate
2. Remove the precipitate and use a colorimeter to measure the absorbable of remaining Benedict’s solution

Question 6

Describe the test for starch

Answer 6

Add iodine to sample if starch is present the iodine will turn from brown/ yellow to blue/ black this is only a qualitative result

Question 7

Name the test for proteins

Answer 7

Biuret reagent

Question 8

Describe the method for testing proteins

Answer 8

1. Add excess biuret reagent to sample
2. Shake and leave at room temperature

Question 9

What is a positive test Result

Answer 9

If amino acids are present a purple precipitate forms. This is a qualitative chromatography can be used to identify amino acids in mixture

Question 10

Name the test from lipids

Answer 10

Milky white emulsion. This is only a a

Question 11

Describe the method for testing lipids

Answer 11

1. Add ethanol to sample
2. Add water to sample and shake for a minute

Question 12

Describe the positive test result for lipids

Answer 12

Milky white emulsion. This is only a qualitative test