Practical work

Grade 10

Life Sciences

Session 1

Strand: Life at the molecular, cellular and tissue level

Index

1

1 Food test for starch 3

2 Food test for glucose 6

3 Food test for lipids 10

4 Food test for proteins 11

5 Enzymes: 5.1 Investigation to test the working of a “biological” washing powder

5.2 Action and denaturation of the enzyme bromelain

15

18

6 Microscopic work: Wet mount of plant and animal tissues

20

7 Investigate diffusion 23

8 Investigate osmosis 26

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1. Food test for starchAim: To find out if starch is present in the given types of food.

Apparatus/Chemicals:

1. Ten medium sized test – tubes (preferably ±10 cm tall or a test plate (white).2. Scalpel or razor blade 3. Dropper

4. Materials: Small amounts of different food stuffs (preferably the ones easily available to you (what learners use everyday), e.g. Carrot, rice, grapes, onion, potato, tomato, sweet potato, peanut, small pieces of pumpkin, egg white.

5. Reagent: Freshly prepared iodine solution.

(Iodine solution freshly prepared by mixing equal amounts of iodine crystals (I2) ½ a spatula) and potassium iodine (KI). Dissolve this mixture in 20ml of water. Put this iodine solution in an amber bottle so that you may use it even in future.

Method:

Cut a small piece from each of your food stuffs and put each piece in a separate cell of your test plate or test tube.

For your control put half a spatula-full of starch powder in one of the cells of your test plate/test tube.

Use the dropper to put one drop of the iodine solution on each of the types of food. Leave the experiment for 30 seconds without disturbing the test plate/test tubes. Observe the results: Observe the colour of each type of food and compare it to the

colour change of starch after adding iodine solution.Precautions:

1. Do not leave the bottle containing iodine open because iodine (I2) sublimes (changes from solid to vapour once exposed to air).

2. Make sure that the iodine solution is not exposed to direct sunlight; hence you are instructed to keep it in an amber bottle.

3. Make sure that there is no spill over of the liquid from any of the test plate cells.

4. Avoid touching iodine crystals and iodine solution with your bare hands.5. Do not include any processed food among the type of food you are testing.

Examples: processed food; bread, yoghurt, cakes, viennas etc.

Complete the table below by doing the following .Write the name of the type of food you are testing in the space provided. If the colour changes, like that of starch write (+); if the colour shows slight change, write (±). If the there is no colour change write (-) in the appropriate spaces.

Observation:

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Observation Results

Original colour and name of food

Colour change when iodine solution is added

(+) (±) or (-)

A lot of starch present

A bit of starch present

No starch present

1 White starch Blue black + Starch present

- -

2

3

4

5

6

7

8

9

10

Questions:

Answer the following questions in response to what you observed:

(a) What do your results indicate in terms of which food contains a lot of, some, and no starch respectively?

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_________________________________________________________________(b) Starch provides the body with a lot of energy and if taken in excess it is converted to

fat in the body. Which types of food from your list should be taken by a busy athlete? Give a reason for your answer.

________________________________________________________________(c) Write down the names of the food from your list that would make a good diet for a

diabetic person. Give a reason for your answer.

__________________________________________________________________(d) Suggest the food on your list, that you would advise a person who would like to loose

weight to include in his or her diet.

__________________________________________________________________

Conclusion:

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

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2. Food test for glucoseActivity 1.

Aim: To demonstrate the presence of glucose.

Apparatus/Chemicals:

2 test tubes 1 beaker A burner Glucose solution Sucrose solution Benedict’s solution

Precautions:

Ensure that it is safe to use a flame. When boiling ensure that the mouth of the test tubes points away from people. Use a test tube holder and wear goggles.

Method:

Half fill the beaker with water and boil it. Label test tubes as A and B Quarter fill test tube A with the glucose solution. Quarter fill test tube B with the sucrose solution. A few drops of Benedict’s solution are added to each test tube. Observe and record the colour in the table below. Place the test tubes into the boiling water bath, lower the flame. Wait for 5 minutes then observe and record the colour of the solutions.

Observation:

Observation table:

Test tube A Test tube BColour of solution before heating

Colour of solution after heating

Conclusion:

On heating the change of colour from blue to green to yellow and orange/ brick red indicates the presence of glucose.

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Activity 2.

Aim: To demonstrate the presence of glucose in different solutions.

Apparatus:

4 test tubes 1 beaker A burner Glucose solution Albumen solution Starch solution Water Benedict’s solution Crayons

Precautions:

Ensure that it is safe to use a flame. When boiling ensure that the mouth of the test tubes points away from people. Use a test tube holder and wear goggles.

Method:

(a) Half fill a beaker with tap water and place it on a tripod and gauze. Heat the water with a Bunsen burner. While waiting for the water to boil, carry on with instructions (b) to (d).

(b) Label four test-tubes 1-4.

1% starch solution into tube 1

10% glucose solution into tube 2

(c) Put 20 mm (depth) of

1% albumen solution into tube 3

water into tube 4

(d) To each tube add about 10 mm Benedict's solution.

(e) Place the test-tubes in the beaker of hot water as illustrated below, and adjust the flame to keep the water just boiling.

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Heat the test tubes in a water bath

(f) After about 5 minutes, turn out the flame. Place the four tubes in a test-tube rack and compare the colours. Record the results in the table and match the final colours as nearly as possible with crayons.

Observation:

Solution Colour change on heating with Benedict’s reagent

Final colour (crayon)

1 1% starch

2 10% glucose

3 1% albumen

4 water

Discussion:

I. What colour changes took place when Benedict's solution was added to each liquid?

____________________________________________________________________

____________________________________________________________________

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2. The solutions selected for testing are examples of three of the principal chemical substances found in cells: glucose, starch, protein (albumen). With which of these food materials did Benedict's solution give a decisive change on heating?

___________________________________

3. Apart from the colour, what change took place in the consistency of the Benedict's solution?

_____________________________________________________________________

4. Do your results indicate that any sugar (e.g. sucrose, fructose and maltose) will give the same colour as glucose did when tested with Benedict's solution? Give a reason for your answer.

_____________________________________________________________________

5. Do your results allow you to say that (a) no protein will give a colour change when heated with Benedict's solution; (b) albumen never reacts with Benedict's solution to give a colour change?

_____________________________________________________________________

6. Can you predict that glucose will always give the same result with Benedict's solution as it did in your experiment?

_____________________________________________________________________

7. Why was water included in the test?

_____________________________________________________________________

Conclusion:

_____________________________________________________________________

_____________________________________________________________________

Discussion - answers

I. No colour change should occur in the cold.

2. The only 'decisive' change, i.e. a red/orange colour, is with the glucose solution. The 1% starch may give a cloudy green colour.

3. Students may have observed the change from a clear solution to a suspension or precipitate.

4. Glucose is an example of a sugar and not 'sugars' in general. Fructose and maltose will react with Benedict’s solution but sucrose will not.

5. Neither of the generalizations are admissible from the results of this single experiment.

6. Such a prediction is not justified from the results of a single experiment.

7. Although failure to give a red precipitate with albumen and starch provides a control, it could be argued that Benedict's solution always gives a red precipitate on boiling and that this change is inhibited by albumen and starch but not sugar. Water acts as a control against this hypothesis.

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3. Food test for lipids

Aim: To develop a test for determining whether or not fats and oils are present.

Apparatus/chemicals:

Ethanol (ether)

Cooking oil

2 small test tubes

Filter paper (or blotting paper)/brown paper/news paper

Method:

1. Add 5ml of ethanol (or ether) to each of the two small test tubes.2. Add two to three drops of cooking oil in one of the test tubes. Shake thoroughly until

the oil dissolves.3. Put a drop of the oil in ethanol solution on a piece of filter paper (or blotting paper).

Mark the position of the drop. This is your experiment.4. Put a drop of pure ethanol (or ether) on another piece of filter paper. Mark the

position of the drop. This is your control.5. Leave the filter papers out to dry for a few minutes.

Results

Note that in the experiment, a grease stain is left behind. In the control no such stain is created.

Conclusion

Since only fats and oils leave behind a grease spot stain on filter paper, the test can be used to determine whether or not an unknown substance contains fats and oils.

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4.Food test for proteinsTEST FOR PROTEINS USING MILLONS REAGENT

Aim: To show if proteins are present or absent in a biological compound.

Apparatus/Chemicals:

Two test tubes Two beakers Millon’s Reagent Water Spatula Medicine droppers Egg white Starch Water bath (90˚ C)

NB. Millon’s reagent is poisonous and should be handled with care.

Method:

1. Mix some egg white with water in a beaker. Stir the contents using a spatula.2. Quarter fill test tube T1 with the egg white solution and test tube T2 with a starch

solution.3. Using a medicine dropper add 2-3 drops of Millon’s Reagent to test tube T1 and to

test tube T2. Gently agitate both the test tubes to mix the contents.4. Place both test tubes in a water bath of 90̊ C for a few minutes.5. Note the colour change in the test tubes.

Observations/Results

NB. 1. Starch in water is white. 2. Egg white, boiled, changes from a sol to a gel state.

3. Egg white, unboiled, is in a sol state. 4. Egg white in water is translucent.

After heating the following is observed:

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Starch solution

TEST TUBE T1(PROTEIN) TEST TUBE T 2(STARCH)

Colour changes

Change of state

Discussion/Questions

Millon's reagent is an analytical reagent used to detect the presence of soluble proteins. A few drops of the reagent are added to the test solution, which is then heated gently. A reddish-brown coloration or precipitate indicates the presence of tyrosine residue which occurs in nearly all proteins.

Millon's test is not specific for proteins (it actually detects phenolic compounds), and so must be confirmed by other tests for proteins such as the biuret test.

The reagent is made by dissolving metallic mercury in nitric acid and diluting with water.

1. Why was egg white used? __________________________________________

2. Name the protein present in egg white.________________________________

3. What are the monomers that make up proteins called? ____________________

4. State one precaution you should undertake when working with Millon’s Reagent.

_________________________________________________________________

_________________________________________________________________

Conclusion:

When a protein is present, the colour_______________ indicates a positive test, e.g. test tube T1.

When a protein is absent, the colour ________________ indicates a negative test, e.g. test tube T2.

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TEST FOR PROTEINS USING THE BIURET TEST

Aim: To show if proteins are present or absent in a biological compound.

Apparatus/Chemicals:

Two test tubes Two beakers Water Spatula Medicine droppers Egg white Starch

NB. The biuret test is made by mixing a 10% sodium hydroxide solution with a few drops of

1 % copper sulphate solution.

Method:

1. Mix some egg white with water in a beaker. Stir the contents using a spatula.2. Quarter fill test tube T1 with the egg white solution and test tube T2 with starch

solution.3. Using a medicine dropper add 2-3 drops of biuret solution to test tube T1 and to test

tube T2. Gently agitate both the test tubes to mix the contents.4. Note the colour change in the test tubes.

Observation/Results

TEST TUBE T1 (PROTEIN) TEST TUBE T2 (STARCH)

Colour changes

Discussion:

Buiret solution is a blue liquid that changes to purple when proteins are present and to pink in the presence of short chains of polypeptides. The copper atom of the biuret solution reacts with the peptide bonds to cause the colour change.

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Starch solution

Conclusion:

When a protein is present, the colour_______________ indicates a positive test, e.g. test tube T1.

When a protein is absent, the colour ________________ indicates a negative test, e.g. test tube T2

EXTENTION ACTIVITY

Use the protein test on small samples of food materials, e.g. crushed beans, crushed apple, milk, boiled rice, etc. Indicate the results obtained with a tick (√) to show a positive test and a cross (X) to indicate a negative test in the table below.

Food sample Positive test Negative testCrushed beansCrushed appleMilkBoiled riceCheese

1. Compile a list of foods containing proteins after carrying out this test on common

household foods.

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5.Enzymes: 5.1 Investigation to test the working of a

“biological” washing powderHave you heard or seen advertisements for washing powders that claim the powders contain enzymes that can remove specific stains? Are the claims of the manufacturers true? Let’s see ...

Our bodies use food to give us energy. Some foods, like proteins such as gelatine and starch, need to be broken down before our bodies can use them. The units, or molecules that make up proteins and starches are large, but they again are made up of smaller units. This breaking down of the larger units into smaller ones is called digestion. Our bodies use enzymes to burn the foods (or digest them) for their energy.

The enzymes which help in digestion are specialists. An enzyme which would digest a protein will not digest starch, nor would a starch-digesting enzyme break down proteins.

ACTIVITY 1

Hole in the jelly

Aim: To see how an enzyme can break down proteins, and at the same time see if the claims of manufacturers of washing powders are true.

Apparatus:

Two small plastic dishes Gelatine

Agar

An ordinary washing powder

A biological washing powder

Method:

1. Read the instructions on the packets carefully and prepare two dishes of clear jelly, one of gelatine, and the other of agar.

2. On each jelly, put a small pinch of an ordinary powder detergent, and of a so-called biological washing powder.

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Observations/Results:

Discussion:

The biological powder is supposed to contain an enzyme which 'removes difficult stains like egg, gravy and blood'. These contain proteins.

If this is a true claim, we would expect to find the gelatine (a protein) dissolved away under the 'biological' washing powder, but not under the ordinary powder.

The agar (not a protein) should not be dissolved by either. The jelly might soften a little for many reasons, but do not be misled by this. Look for a great hole in the jelly.

Conclusion:

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

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If there is a hole in the gelatine under the biological washing powder, but not one under the ordinary washing powder, then the claims of the manufacturer are true.

ACTIVITY 2

Get rid of the yolk

Aim: To see how an enzyme can break down proteins, and at the same time see if the claims of manufacturers of washing powders are true.

Apparatus:

Two eggs Two glasses

Biological washing powder

Ordinary washing powder

Method:

1. Boil two standard eggs together, and push two teaspoons into the yolks so that there is some yolk left on the spoons.

2. Dissolve equal amounts of ordinary and 'biological' detergents in two separate glasses of water, and leave a yolk-stained spoon in each glass.

3. Note the changes after some time.

Observations/Results:

Discussion:

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After some time the spoon in the ordinary detergent still has yolk on, but the yolk on the other spoon has been digested by the 'biological' detergent. This will happen if the 'biological' detergent really contains enzymes that break down the proteins in egg yolk.

Conclusion:

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

5.2 Action and denaturation of the enzyme bromelain

Aim: To investigate the effect of the enzyme bromelain (protease) on gelatine (protein) at different temperatures.

Apparatus: 10g powdered gelatine 1 slice fresh pineapple(skin removed) 500 ml measuring cylinder 300 ml cold water 250 ml glass beaker 150 ml boiling water Bunsen burner,tripod and gauze mat 3 petri or shallow dishes ( same size) Knife and saucer

Method:1. Dissolve the gelatine powder in 150 ml boiling water and gently stir until all the

gelatine has completely dissolved.2. Add 300 ml of cold water to the gelatine mixture.3. Pour equal quantities of gelatine mixture into each petri dish.4. Place the petri dishes in the refrigerator for three hours to allow for the gelatine to

set.5. Cut the fresh pineapple into equal halves.6. Boil one half of the pineapple piece in a beaker of water above the Bunsen burner

and cook until the pineapple piece is soft.7. Remove the piece of pineapple from the beaker and allow cooling on a saucer.8. Remove petri dishes from refrigerator.9. Place the raw piece of pineapple in the first gelatine dish and the cooked piece on

the second gelatine dish. The third gelatine dish serves as a CONTROL.

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10. Place the dishes in a cool place for 24 hours.11. Examine the dishes every few hours and note any changes in the gelatine texture.

N.B. Gelatine is a protein derived from skin and bones. When gelatine powder is dissolved in hot water and is cooled down it forms a semi- solid gel. It is used in cooking and available at most supermarkets

TIPS: Ensured that the boiled pineapple is cool before placing it on the gelatine otherwise the gelatine will melts and the results of the investigation will be altered.If powdered gelatine is not available, use a packet of flavoured jelly.

Results:

Dish Texture of the gelatineWith fresh pineapple

Control

With boiled pineapple

Discussion:_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

Conclusion:

The protease enzyme in the fresh pineapple broke down the protein in the gelatine. The gelatine liquefied from a solid state. The boiled pineapple had no effect on the gelatine; the gelatine in the dish remained as solid as the gelatine in the control dish. Boiling the pineapple denatured the enzyme bromelain.

APPLICATION:

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6. Microscopic work: Wet mount of plant and animal tissues

Aim: Observing plant and animal cells using a light microscope.

PART A: Plant cells (Onion skin wet mount)

Apparatus: Onion Scalpel or knife Forceps Dropper or straw Water Microscope slide Dissecting needle Cover slip Tissue paper

Method: Peel the delicate transparent tissue from the inner surface of a piece of onion

using forceps. Make a wet mount by placing the tissue, unwrinkled, in a small drop of water

on a glass slide. Add one small drop of iodine stain to the tissue and cover with a cover slip. Examine the onion cells at low power, focus as necessary. Examine next the cells at medium and high power.

Observation/Results:

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Prepare a diagram of onion skin tissue showing three to four cells. Label the structures you can identify from the microscope. (Don’t forget to calculate the magnification)

Questions:

(a) Describe the shape of the cells._________________________________________________________________

(b) What cell structures and organelles can you see?_________________________________________________________________

(c) Why are no chloroplasts evident?_________________________________________________________________

PART B: Animal cells (Human cheek cell wet mount)

Apparatus: Compound microscope 2 microscope slides 2 cover slips 1 % Methylene blue stain Sterile toothpick Beaker of water

Method: Place a drop of water on a clean microscope slide. Gently scrape the inside of

your cheek with the blunt end of a clean toothpick and stir the material on the toothpick in the drop of water on the slide.

Add one drop of methylene blue stain to the microscope slide and then add a cover slip.

Focus and examine the microscope slide under low power before moving to the higher magnifications.

Observations/Results:

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Prepare a diagram showing 3 – 4 cells of the cheek and label structures you can identify. (Don’t forget to calculate the magnification)

Questions:

(a) What are the shapes of the cells?

___________________________________________________________________ (b) What cell structures can you identify?

___________________________________________________________________ (c) Would the cells normally be attached to one another? Explain.

__________________________________________________________________ ___________________________________________________________________

(d) Some of the cells may be folded or wrinkled. What does this indicate to you about the thickness of the cells?___________________________________________________________________ ___________________________________________________________________

(e) Explain how these cells differ from the plant cells viewed previously.

__________________________________________________________________

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7. Investigate diffusionExperiment 1: Diffusion in Gases

Aim: To investigate diffusion in gases

Apparatus:

Air freshener/ Perfume Classroom with learners

Method:

Stand at the corner of the room and spray the fragrance liberally. Tell the learners to raise their right hands as soon as they can smell the

fragrance.

Observation/results:

Discuss what you/learners observe

_________________________________________________________________________________________________________________________________________________

Which learners will smell the fragrance last?

_______________________________________________________________________

Discussion /Questions:

Define diffusion

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__________________________________________________________________________________________________________________________________________________________________________________________________________________________

Explain with reasons 3 factors affecting rate of diffusion

__________________________________________________________________________________________________________________________________________________________________________________________________________________________

Diffusion is a passive /active movement. ____________

Explain the statement.______________________________________________________

Conclusion:

____________________________________________________________________________________________________________________________________________________________________________________________________________________________

Experiment 2: Diffusion in Liquids

Aim: To investigate diffusion in liquids

Apparatus:

clear drinking water

glass beaker

potassium permanganate

Method:

Carefully drop a lump of K2MnO4 into a glass with clear drinking water.

Observation/Results

Draw what you observe after 30 min Draw what you observe after 24 hrs

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Beaker

Clear Water

Potassium Permanganate

Discussion/Questions:

Discuss your observation at 30min

__________________________________________________________________________________________________________________________________________________________________________________________________________________________

Discuss your observation after 24 hours

__________________________________________________________________________________________________________________________________________________________________________________________________________________________

Explain what would happen if hot water is used instead of cold water and why.

_________________________________________________________________________

What precaution would you exercise for the experiment to work properly?

_________________________________________________________________________

Conclusion:

_________________________________________________________________________________________________________________________________________________

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8. Investigate osmosis

Aim: To illustrate osmosis in plant tissue.

Apparatus/Chemicals

Two beakers

Two peeled potatoes

Concentrated sugar solution

Knife/potato peeler

Method

1. Peel two potatoes carefully.

2. Cut the base of each potato flat to ensure that the potato is able to stand on its own

3. Hollow out each of the potatoes to form thin-walled cups.

a. A thinner wall will ensure faster results

b. Be careful not to perforate the walls of the potato.

4. Prepare a 20% sugar solution and pour this solution halfway into the hollow of one of

the potatoes (see diagram). This will be your experiment.

5. Put the potato into a beaker with tap water. (see diagram)

6. Pour tap water halfway into the hollow of the other potato. (see diagram). This will be

your control.

7. Put the potato into a beaker with tap water. (see diagram)

8. It is important that the level inside the cup is the same as the liquid level on the

outside.

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9. Allow the apparatus to stand overnight.

Diagram to indicate the setup of the experiment.

Experiment Control

Results

1. Observe the levels in each set of apparatus.

a. What happened to the level of the sugar solution inside the hollow potato in

the experiment?

_________________________________________________

b. What happened to the level of the tap water inside the hollow potato in the

control? ____________________________________________________

2. In the space provided below draw the results that you observe in the experiment and in

the control. Label your diagram.

Experiment Control

Discussion

1. Give the function of a differentially permeable membrane.

___________________________________________________________________

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beaker

potato

sugar solution

tap water

2. How did the differentially permeable membrane functioned in the experiment?

_________________________________________________________

Conclusion

Water moved from a ____________ water potential through a _______________________

membrane to a _______________ water potential.

ANSWER SHEET

Results

1. Observe the levels in each set of apparatus.

c. What happened to the level of the sugar solution inside the hollow potato in

the experiment? __The sugar solution was raised/ became

higher__________

d. What happened to the level of the tap water inside the hollow potato in the

control? ___The level of the tap water stayed the same.______________

2. In the space provided below draw the results that you observe in the experiment

and in the control. Label your diagram.

Experiment Control

Discussion

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sugar solution

beaker

tap water

potato

1.Give the function of a differentially permeable membrane. A permeable membrane

only allow water molecules to pass through._______

2.How did the differentially permeable membrane functioned in the experiment?_____It

only allowed water molecules to pass through, the sugar molecules were too big.

Therefore water moved into the potato through osmosis._

Conclusion

Water moved from a _high__ water potential through a __differentially permeable__

membrane to a __low__ water potential.

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