Question 2
(a) Give two reagents each which are used to test for the following food substances.
Food substance |
Two test reagents |
|---|---|
Reducing sugar |
|
Protein |
|
Fats and oil |
[6 marks]
(b)
Complete the table below on the location of production of enzymes and site of action in the human body for the following digestive enzymes.
Digestive enzyme |
Location of production of enzyme |
Site of action |
|---|---|---|
Maltase |
||
Lipase |
||
Sucrase |
||
Amylase |
[8 marks]
(c)
(i) Explain briefly the procedure for destarching a leaf. [2 marks]
(ii) What happens to the starch after destarching a leaf? [1 mark]
(d)
In testing for starch in a green leaf, why is the leaf:
(i) boiled in water;
(ii) put in warm alcohol;
(iii) put in warm water? [3 marks]
Observation
Candidates lost marks to the poor spellings of reagents and also lack of knowledge about the reagent to be used to conduct food test on the food substances.
Poor spelling of structures like ileum being spelt as ‘iluem’, ‘ileum’ made them lose marks.
Poor knowledge and spelling of the location of production of enzymes and sites of action of the listed enzymes made the candidates lose the marks allotted the questions.
In question c (i), instead of procedure for destarching a leaf, candidates were explaining the procedure of testing for starch in a leaf.
In questions d (i), (ii) and (iii), many candidates could not correctly state the reasons a green leaf is boiled in water, put in warm alcohol and put in warm water when testing for starch in a green leaf.
Reagents used for food test
(a) Explanation of osmosis
Food substance |
Test reagents |
|---|---|
Reducing sugar |
Benedict's solution;Fehling's solutions |
Protein |
Millon's reagent;Biuret test/mixture of sodium hydroxide & copper (II) sulphate;Xanthoproteic test/reagent/conc.nitric acid and ammonia solution. |
Fats and oil |
Sudan(III);Osmic acid; Ethanol. |
Note: Spellings must be correct to score.
(b)
(i) Table
Digestive enzyme |
Location of production of enzyme |
Site of action |
|---|---|---|
Maltase |
Small Intestine |
Ileum/small Intestine |
Lipase |
Pancreas/small intestine/ileum |
Duodenum/ileum/small intestine |
Sucrase |
Small intestine/ileum |
Ileum/small intestine |
Amylase |
Pancreas/Mouth/ salivary gland |
Duodenum/mouth |
Note: Spellings must be correct to score.
(c)
(i) Procedure for destarching a leaf
The potted plant/leaf exposed to sunlight; is left in darkness/in a cupboard/leaves are wrapped in aluminium foils; for 2 or 3 days.
(ii) Fate of starch after destarching a leaf
The starch in the leaf will be changed to sugar/glucose/hydrolysed; and carried away/translocated from the leaf to other parts of the plant.
(d) In testing for starch in a green leaf, reasons for:
(i) boiling in water
To kill the leaf/cells in leaf /burst the starch grains.
(ii) putting in warm alcohol
To remove chlorophyll/decolourize the leaf;
(iii) putting in warm water
To soften the leaf/ loosen the cells/wash off the alcohol.