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IGCSE Biology Extended4.1.3—Food testsTopic Practice

4.1.3—Food tests

• Describe the use of: (a) iodine solution test for starch (b) Benedict’s solution test for reducing sugars (c) biuret test for proteins (d) ethanol emulsion test for fats and oils (e) DCPIP test for vitamin C

Question 7

[Maximum number: 1]

The data show the concentrations of sugar and starch in an onion.

Table

The onion is tested with Benedict's solution and iodine solution.

Which set of results is correct?

Benedict's

solution

iodine

solution

blue

blue-black

blue

brown

brick red

blue-black

brick red

brown

Question 7

[Maximum number: 1]

The data show the concentrations of sugar and starch in an onion.

Table

The onion is tested with Benedict's solution and iodine solution.

Which set of results is correct?

Benedict's

solution

iodine

solution

blue

blue-black

blue

brown

brick red

blue-black

brick red

brown

Question 7

[Maximum number: 1]

Which row is correct for a positive food test for vitamin C?

colour of the
food test reagent
at the start

heat required

final colour of the
food test reagent

colourless

yes

purple

blue

no

colourless

colourless

no

blue

blue

yes

orange

Question 7

[Maximum number: 1]

Which substance is used to test a food for vitamin C?

A

Benedict's solution

B

DCPIP

C

ethanol

D

iodine solution

Question 7

[Maximum number: 1]

The data show the concentrations of sugar and starch in an onion.

Table

The onion is tested with Benedict's solution and iodine solution.

Which set of results is correct?

Benedict's solution

iodine solution

blue

blue-black

blue

brown

brick red

blue-black

brick red

brown

Question 7

[Maximum number: 1]

The table shows the results of food tests carried out on a fruit.

Table

What did the fruit contain?

A

fat and reducing sugar

B

fat and starch

C

protein and reducing sugar

D

protein and starch

Question 8

[Maximum number: 1]

When a food substance is tested with iodine solution, which colour shows the presence of starch?

A

blue-black

B

brown

C

orange

D

purple

Question 8

[Maximum number: 1]

Four solutions were tested to see whether they contained protein, starch or glucose.
The colours of the solutions after the tests are recorded in the table.
Which solution contained protein and glucose but not starch?

biuret test

iodine test

Benedict's test

blue

brown

orange

blue

blue-black

blue

purple

brown

orange

purple

blue-black

blue

Question 8

[Maximum number: 1]

Which food-testing solution shows a positive result when it turns from blue to purple?

A

Benedict's solution

B

biuret solution

C

ethanol

D

iodine solution

Question 8

[Maximum number: 1]

What is the colour change shown by Benedict's solution when heated with a reducing sugar?

A

blue to purple

B

blue to red

C

brown to blue-black

D

red to yellow

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