Home BIOLOGY Food Test Biology​​ Practical Questions And Answers 

Food Test Biology​​ Practical Questions And Answers 

995
0
Food Test Biology​​ Practical Questions And Answers

Food Test Biology​​ Practical Questions And Answers

BIOLOGY PRACTICAL O’LEVEL FOOD TESTS  | Food Test Biology​​ Practical | Food Test Biology​​ Practical | Food Test Questions With Answers

Format

Until 2008, NECTA biology practicals contained three questions. Question 1 was required, and was a food test. Students then chose to answer either question 2 or question 3.

One of these questions was usually classification. The format changed in 2008. Now, the practical contains two questions, and both are required.

Food test and classification remain the most common questions, but sometimes only one of these two topics is on a given exam.

The second question may cover one of a variety of topics, including respiration, transport, coordination, photosynthesis, and movement.

Each question is worth 25 marks.

Common Practicals

<> Food test:​​ students must test a solution for starch, sugars, fats, and protein

<> Classification:​​ students must name and classify specimens, then answer questions about their characteristics

<> Respiration:​​ students use lime water to test air from the lungs for carbon dioxide

<> Transport:​​ students investigate osmosis by placing leaf petioles or pieces of raw potato in solutions of different solute concentrations

<> Photosynthesis:​​ students test a variegated leaf for starch to prove that chlorophyll is necessary for photosynthesis

<>Coordination:​​ students look at themselves in the mirror and answer questions about the sense organs they see

Note:​​ These are the most common practicals, but they are not necessarily the only practicals that can occur on the national exam. Biology practicals frequently change, and it is possible that a given exam will contain a new kind of question. Look through past NECTA practicals yourself to get an idea of the kind of questions that can occur

Food​​ Tests

In this practical, students test a solution of unknown food substances for starch, protein, reducing sugars, non- reducing sugars, and fats/oils. They record their procedure, observation, and conclusions, then answer questions about nutrition and the digestive system.

This section contains the following:

<> How to carry out food tests

<> How to write a report

<> Sample practical with solutions

How to Carry Out Food​​ Tests

Starch

Add a few drops of iodine to the solution and shake well. A blue-black color forms if starch is present

Lipids

Add a few drops of iodine to the solution and shake well. A red ring will form at the top of the test tube is lipids are present.

You can also have your students do the grease spot test { rub a drop of solution onto a piece of paper, and let dry. A translucent spot forms if fat is present. This test is great for its simplicity, but is not used on national exams.

Protein (Biuret​​ test)

Add a few drops of 1 M NaOH to the solution and shake well. Then add a few drops of 1% CuSO4 solution and shake. A violet color forms if protein is present. Sometimes the color takes a minute or two to appear.

Some textbooks may recommend using Millon’s reagent to test for protein.

This reagent contains mercury, which is extremely poisonous and should never be handled by students.

The purple colour from a positive test is the result of a complex between four nitrogen atoms and the copper (II) ion. Specifically, these nitrogen atoms are all part of peptide bonds. These peptide bonds are adjacent on a protein, either two from one protein and two from another, or two from one part of a protein and two from another part of the same protein.

Reducing​​ sugar

Place some food solution in a test tube, and add an equal volume of Benedict’s solution. Heat to boiling, then let cool. A brick red or orange precipitate forms if a reducing sugar is present.

Benedict’s solution contains aqueous copper (II) sulphate, sodium carbonate, and sodium citrate. The citrate ions in Benedict’s solution complex the copper (II) ions to prevent the formation of insoluble copper (II) carbonate.

In the presence of a reducing sugar, however, the copper (II) ions are reduced to copper (I) ions which form a brick red precipitate of copper (I) oxide. The oxygen in the copper (I) oxide come from hydroxide; the purpose of the sodium carbonate is to provide this hydroxide by creating an alkaline environment.

Normally, sugar molecules form five or six member rings and have no reducing properties. In water, however, the rings of some sugar molecules can open to form a linear structure, often with an aldehyde group at one end. These aldehyde groups react with copper (II) to reduce it to copper

Sugars that do not have an aldehyde group in the linear structure or that are not able to open are not able to reduce copper (II) ions and are thus called non-reducing sugars. Students do not need to understand this chemistry for their exam, but they may ask about what is happening in the​​ reaction.

Non-reducing​​ sugar

Do the test for a reducing sugar using Benedict’s solution. Notice that no reaction occurs. Add a few drops of citric acid solution to the solution, then heat to boiling. Let solution cool. Add a few drops of 1 M NaOH, and shake well.

Then, add some Benedict’s solution (equal in volume to the liquid in the test tube). Boil the solution, and let it cool. A brick red or orange precipitate forms if a non-reducing sugar is present.

This experiment will also test positive for all reducing sugars. Therefore it is important to first perform the test for reducing sugars before considering this test. If the test for reducing sugars is positive, there is no reason to perform the test for non-reducing sugars – the conclusion will be invalid.

Non-reducing sugars are a misnomer, that is, their name is incorrect. This test does not test for any sugar that is not reducing. Rather, this is a test for any molecule made of multiple reducing sugars bound together, such as sucrose or starch.

See also  Privatization With Its Advantages and Disadvantages

When these polysaccharides are heated in the presence of acid, they hydrolyse and release monosaccharides. The presence of these monosaccharides is then identified with Benedict’s solution.

The purpose of the sodium hydroxide is to neutralize the citric acid added for hydrolysis. If the citric acid is not hydrolysed, it will react with the sodium carbonate in Benedict’s solution, possibly making the solution ineffective.

How to Write a​​ Report

Food test data is reported in a table containing four columns: test for, procedure, observation, and inference. With the exception of the `test for’ column, data should be reported in full sentences written in past tense.

The procedure should also be in passive voice. No, this is not the way professional scientists write. However, students here must use passive voice to get marks on the national exam.

Note that every column is worth marks on the exam. Even if students fail to do the food tests correctly, they can still get marks for writing what they are testing for and what the procedure should be.

See the sample practical below for an example of a report.

Sample Food Test Practical​​s

Practical 01

You have been provided with Solution K. Carry out food test experiments to identify the food substances present in the solution.

Record your experimental work as shown in the table​​ below.

Suggest two natural food substances from which solution K might have been​​ prepared.

What is the function of each of the food substances in solution K to human​​ beings?

For each food substance identified, name the enzyme and end product of digestion taking place in​​ the:

  • Stomach
  • Duodenum

What deficiency diseases are caused by a lack of the identified food​​ substances?

Solution

(Assume Solution K contains protein and​​ starch.)

The results were as​​ follows

Solution K could have been prepared from egg and maize. (Note: Any non-processed food containing protein or starch is correct​​ here.)

Starch provides energy to the body. Proteins are used in growth and tissue​​ repair.

A deficiency of protein causes kwashiorkor. A deficiency of starch causes marasmus.

Practical​​ 02

You are provided with food sample A. By using scientific procedures, taste what sample A contained.

TABLE OF RESULTS
FOOD TASTED
PROCEDURES
OBSERVATION
INFERENCE

STARCH

A small portion of food solution A was kept in a test tube then a few drops of iodine solution were added

and was shaken.

REDUCING SUGAR

A small portion of food solution A was kept in a test tube then an equal amount of Benedict’s solution was

added and the mixture was heated to boil.

PROTEIN

A small portion of food solution A was kept in a test tube then a few drops of​​ Na OH​​ and​​ Cu SO​​ 4​​ solution

was added and shaken.

NON- REDUCING SUGAR

A small portion of food solution A was kept in a test tube then a few drops of dill​​ HCl​​ was added heated and then cooled then a few drops of​​ Na OH​​ was added and equal amount of Benedicts solution was

added and the mixture was heated to boil.

FATSTOLS

A small portion of food solution A was kept in a test tube then few drops of sudden III solution were

added and were shaken strongly and leave it to settle.

Solution

By using the table​​ below

TABLE OF​​ RESULTS
FOOD
TASTED
PROCEDURES
OBSERVATION
INFERENCE

STARCH

A small portion of food solution A was kept in a test

tube then a few drops of iodine solution were added and was shaken.

The colour of solution A

changed from white to black

Starch is present

REDUCING SUGAR

A small portion of food solution A was kept in a test

tube then an equal amount of Benedict’s solution was added and the mixture was heated to boil.

Series of colour change

from blue to green to yellow to Orange PPts

Food solution A

contained reducing sugar

PROTEIN

A small portion of food solution A was kept in a test tube then a few drops of​​ Na OH​​ and​​ Cu SO4​​ solution

was added and shaken.

Food sample A retained light blue colour of

Cu S04

Protein is absent

NON- REDUCING SUGAR

A small portion of food solution A was kept in a test tube then a few drops of dill​​ HCl​​ was added heated and then cooled then a few drops of​​ Na OH​​ was added and equal amount of Benedicts solution was

added and the mixture was heated to boil.

Food solution A retained blue colour of Benedict’s solution

Non-reducing sugar is absent

FATS/OILS

A small portion of food solution A was kept in a test tube then few drops of sudden III solution were​​ added

and were shaken strongly and leave it to settle.

Food solution A retained red colour of Sudan III

solution

Fats. Oils is absent

Hence

The food solution A contained

  • Reducing​​ sugar
  • Starch

Practical​​ 03

From the samples

  • Sample​​ A…………………….
  • Sample​​ B…………………….
TABLE OF RESULTS

FOOD TEST

PROCEDURES

OBSERVATION

INFERENCE

Starch

A small portion of food solution A and B were kept in two different test tubes then few drops of iodine solution were added to each test tube and were shaken

Reducing sugar

A small portion of food solution A and B were kept in two different test tubes then on equal amount of Benedicts solution was added in each test tube and the mixture of each was heated to boil.

Non-reducing sugar

A small portion of food solution A and B were kept in two different test tubes then a few drops of dill​​ HCl​​ were added; heated and then cooled; then a few drops of​​ NaOH​​ were added and equal amount of benedicts solution were addled and the mixture were heated to boil for all solution A and​​ B.

Protein

A small portion of food solution A and B were kept in two different test tubes then a few drops of​​ NaOH​​ and​​ CuS04​​ solution were added to both solution and shaken

Lipids​​ (​​ Fat and Oil)

A small protein of food solution A and B were kept in two different test tubes then a few drops of Sudan III solution were added and were shaken:​​ strongly and leave to settle to both two test tubes

Solution

From the samples

TABLE OF RESULTS

FOOD TEST

PROCEDURES

OBSERVATION

INFERENCE

Starch

A small portion of food solution A and B were kept in two different test tubes then few drops of iodine solution were added to each test tube and were

shaken

Food sample A and B solutions rationed brownish yellow color of iodine

Starch was absent in both sample A and B

Reducing sugar

A small portion of food solution A and B were kept in two different test tubes then on equal amount of Benedicts solution was added in each test tube and the mixture of each was heated to boil.

Series of colors change from blue to green to yellow to change PPts (Brick red PPts) to both food solution A and B

Reducing sugar is present to both food samples

Non-reducing sugar

A small portion of food solution A and B were kept in two different test tubes then a few drops of dill​​ HCl​​ were added; heated and then cooled; then a few drops of​​ NaOH​​ were added and equal amount of benedicts solution were addled and the mixture were heated to boil for

all solution A and B.

Both solution A and B rationed black color of Benedict its solution

Non-reducing sugar to both sample food A and B

Protein

A small portion of food solution A and B were kept in two different test tubes then a few drops of​​ NaOH​​ and​​ CuS04​​ solution were added to both

solution and shaken

Food solution A and B rationed; light blue color of​​ CuS04

Protein is absent in all food sample A and B

Lipids​​ (​​ Fat and Oil)

A small protein of food solution A and B were kept in two different test tubes then a few drops of Sudan III solution were added and were shaken:​​ strongly and leave to settle to both two

test tubes

Food solution A and B rationed red color of Sudan III solution

Lipids is absent in all food sample A and B

Practical​​ 04

You are provided with solution S

  • Carry out experiments to identify the food substances present in solution​​ S
  • Record your experimental work as shown in table 1​​ below Table​​ 1

Test for

Procedure

Observations

Inference

  • Solution S​​ contains…………………….
  • Suggest one storage organ in a plant from which solution S might have been​​ prepared.
  • For each food substance identified in (a) (ii) above, name its end product(s) of​​ digestion.
  • Which of the identified food substance is mostly needed by small​​ children?

Solution

i)​​ Experimental work to identify food substance(s) present in solution​​ S.

TEST FOR
PROCEDURE
OBSERVATION
INFERENCE

Starch

To 2 cm3​​ of a sample solution S, few drops of iodine solution was​​ added.

Yellow- brown​​ color​​ was observed i.e. iodine color​​ was

retained.

Starch was​​ absent.

Reducing​​ sugar

To 2 cm3​​ of a sample solution S, equal volume of Benedict’s solution was added and boiled for​​ few

minutes.

The blue color of Benedict’s​​ retained​​ (observed).

Reducing sugar was not present

Non reducing​​ sugar

To 2 cm3​​ of a sample solution S, few drops of​​ Hcl​​ solution was added and heated followed by cooling. After cooling few drops of NaoH/NaHC03​​ were added, followed by​​ Benedicts

solution + boiling

The blue – color​​ of

Benedict’s solution was retained

(observed.)

No reducing sugar was not present

Protein

To 2 cm3​​ a sample solutions, few drops of sodium hydroxide solution was added followed by addition 1% copper II sulphate solution drop​​ vise

white shaking

Purple color​​ was​​ formed

Protein was​​ present.

Lipids (Fats and​​ oil)

To 2 cm3​​ a sample solution s, few drops of Sudan III​​ dye​​ solution was added followed by addition of few mills of distilled water and then the mixture was shaken Vigorously and left to​​ stand

for about 5min.

Red stained food droplets were found​​ at​​ the upper layer of the test tube

Lipid (oil) was​​ present

(ii)​​ Solution S contains protein and lipid (oil).

Storage organ in a plant from which solution S might have been prepared might be root tuber (bulb – like tuber (which is ground​​ nut

Protein end product of digestion was amino​​ acid(s)

Lipid (Fat and) oil end product of digestion was Fatty acids and glycerol.

Food substance in solution S identified which is mostly needed by small children is​​ protein.

Practical 05

In a practical lesson, a candidates has been provided with a sweet potato and a ginger.

Explain how the candidates should prepare these organs for investigation of stored foods and suggest the experiment (s) he/she would carry out and his her​​ observations

Record the information as shown in the table​​ below

Test for

Producer

Observation

Inference

(i)​​ State the nature of the stored food substances identified in each storage​​ organ.

(ii)​​ Name the plant from which each storage organ develops.

Solution
a) Preparation for sweet
  1. Clean your sweet potatoes under normal tap running​​ water
  2. Peel off your sweet potatoes using normal kitchen​​ knife
  3. Cut it into small slices or pieces using kitchen​​ knife
  4. Grind it either by using mortar and pestle or blender​​ machine.
  5. Slurry or porridge of sweet potato is now read for laboratory food test –​​ procedures.
(b) Preparation for a ginger
  1. Clean your ginger preferably under normal running tap​​ water.
  2. Peel off your ginger using normal kitchen​​ knife.
  3. Cut into small slices or pieces using kitchen​​ knife
  4. Grind it by using either mortar and pestle or blender​​ machine
  5. Slurry or porridge of ginger is now ready for laboratory food test​​ procedures.

TEST FOR

PROCEDURE

OBSERVATION

INFERENCE

Starch

To 2mls of a sample (potato slurry), a few drop of iodine solution was​​ added.

Blue – black coloration was​​ observed

Indicates​​ that

starch was present in the sample.

Reducing​​ sugar

To 2cm3​​ of a sample in a test tube, equal volume of Benedict’s solution was added and the mixture was shaken. The mixture was then boiled for about 2-5​​ min.

The series of color changes was then observed from blue to green, yellow, orange and finally – brick​​ -red

coloration

This shows that reducing sugar was present in​​ the​​ food sample (sweet potato)

Non reducing sugar

To 2 cm3​​ of a food sample in a test tube, 1 cm3​​ of​​ HCl was added to the sample and the mixture was then boiled for about one minute. After cooling the mixture, sodium hydrogen carbonate solution was then added to the mixture. Equal volume of Benedict’s solution​​ was

added into the mixture and boiled again.

The series of color changes was observed from blue to green, yellow, orange and finally brick – red​​ coloration.

Non reducing sugar was​​ present

Protein

To 2 cm3​​ of potato sample in a test tube, a​​ little

solution of NaOH was added, followed by solution of Copper II Sulphate drop wise

Purple color​​ was​​ observed

Protein​​ was​​ present

Lipids​​ (fats​​ &​​ oil)

To 2 cm3​​ of sweet potato sample, a little amount of water was placed, followed by addition of few drops of Sudan III dye solution and then, the mixture was shaken. After five (5 min) the observation was​​ done.

There was no any food droplets trapped by the Sudan III solution at the upper part (top) of the test tube.

Lipids​​ was​​ absent

(i)​​ The nature of the stored food substances identified in each storage​​ organ.

In sweet potato: (as storage organ)

Starch found in sweet potato remain as it is i.e. is stored as​​ starch.

Both reducing sugar and non reducing sugar found in potato are stored in from of starch since the storage​​ of glucose in plants is​​ starch.

Protein found in sweet potato are stored in form of amino​​ acids

In ginger (as a storage organ

Starch found in sweet potato is stored as starch (it remains as it​​ was).

Reducing sugar and non reducing sugar are both stored as starch since the storage of glucose is plants is​​ starch.

Protein however small is it; it is stored in form of amino​​ acids.

The plant part from which each storage organ​​ develops

For sweet potato was root​​ tuber

For ginger is a rhizome (modified plant​​ stem.)

Practical​​ 06

From two students of Salma Kikwete secondary school were asked to carry out an experiment by their biology teacher the experiment was conducted as follows

Three test tubes labeled A, B and C were set as shown in figure 4 below. Each of the three test tubes contained 1 ml saliva and 1 ml water. The three test tubes wee heated in water bath at different temperature for 30​​ minutes.

Another set of three test tubes also labeled A, B, and C each containing 1 mil starch solution was heated for the same duration in water bath as shown in figure 5​​ below.

The contents of the test tubes in the corresponding water bath of figure 4 and figure 5 was mixed and​​ heated further for 30​​ minutes.

The contents of each test tube was then tested for starch using iodine solution Study the above procedures carefully and then answer the following​​ questions

1. What was the aim of the​​ experiment?

2. Why was it necessary to heat the tubes for 30 minutes before mixing their​​ contents?

3. State the colour change you would expect in each test tube after adding iodine​​ solution

4. Account for the expected​​ observations

Solution

The aim​​ of the experiment was to find out the effect of temperature on salivary amylases or to study the effect of temperature on enzyme salivary amylase) activity

It was necessary to heat the tubes for 30 minutes before mixing their content in order to obtain optimal temperature for enzymes (salivary amylase) to work​​ properly.

After adding iodine solution, the following color change were​​ observed

Test tube labeled A: in this case, blue- black colouration was​​ observed

Test tube labeled B: in this case, yellowish -brown colouration was observed Test tube labeled C: blue – black colouration was observed as well.

Accounting for the expected​​ observations.

For the test tube labeled A blue- black colouration was observed to indicate that starch is still present because the temperature 5 is not suitable temperature for the enzyme to act on substrate​​ (starch)

For the test tube labeled B, the colour of iodine (yellowish – brown) was retained because all the substrate (starch) has been reduced into simple sugar by the action of enzymes (salivary amylase) due to the availability of​​ favourable or suitable temperature for such enzyme to act on the​​ substrate

For test tube labeled C, blue – black colouration was observed to indicate; substrate (starch) was still present because the temperature 7 is not optimal temperature for the enzymes (salivary- amylase) to act on substrate​​ (starch).

YOU MUST ALSO READ

BIOLOGY PRACTICAL O’LEVEL​​​​ CLASSIFICATION I KINGDOM FUNGI 

BIOLOGY PRACTICAL O’ LEVEL ​​​​ CLASSIFICATION II KINGDOM PLANTAE

BIOLOGY PRACTICAL O’ LEVEL ​​​​ CLASSIFICATION III KINGDOM ANIMALIA

LEAVE A REPLY

Please enter your comment!
Please enter your name here