Nutrition

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					                                                              Nutrition

Nutrition   10.4   KS3      The human diet includes carbohydrates, proteins and fats.
                            The digestive system breaks down food and absorbs it into the bloodstream.
                            The digestive system includes the gullet, stomach, liver, pancreas, small intestine and large
                            intestine.
                   FT       Starch (a carbohydrate), proteins and fats are insoluble. They are broken down into soluble
                   and      substances so that they can be absorbed into the bloodstream in the wall of the small
                   HT       intestine. In the large intestine much of the water is absorbed into the bloodstream. The
                            indigestible food which remains makes up the bulk of the faeces. Faeces leave the body via
                            the anus.
                            The breakdown of large molecules into smaller molecules is speeded up (catalysed) by
                            enzymes.
                            The enzyme amylase is produced in the salivary glands, the pancreas and the small intestine.
                            This enzyme catalyses the breakdown of starch into sugars.
                            Protease enzymes are produced by the stomach, the pancreas and the small intestine. These
                            enzymes catalyse the breakdown of protein into amino acids.
                            Lipase enzymes are produced by the pancreas and small intestine. These enzymes catalyse
                            the breakdown of lipids (fats and oils) into fatty acids and glycerol.
                            The stomach also produces hydrochloric acid. The acid kills most of the bacteria taken in
                            with food. The enzymes in the stomach work most effectively in these acid conditions.
                            The liver produces bile which is stored in the gall bladder before being released into the
                            small intestine. Bile neutralises the acid that was added to food in the stomach. This
                            provides alkaline conditions in which enzymes in the small intestine work most effectively.
                            Bile also emulsifies fats (breaks large drops of fats into smaller droplets). This increases the
                            surface area of fats for lipase enzymes to act upon.


                            HUMAN NUTRITION
Constituents of a healthy diet
All living things need the following materials to build up their bodies and to function properly:
1. Carbohydrates
2. Proteins
3. Fats (lipids)
4. Vitamins
5. Minerals
6. Water
7. Animals also need fibre (roughage)

1.   Carbohydrates are in the form of sugars or starch. They are found in the following foods:
     Potatoes, bread, cereals, pasta, rice, cakes, biscuits, fruit, sweets and chocolate.
     They provide us with energy when the energy is needed quickly.
2.   Proteins are found in meat, fish, egg white, cheese, milk, and pulses (beans and peas).
     They are used in the body for growth and repair of tissues.
3.   Fats (lipids) are found in egg yolk, whole, unskimmed milk, cheese, butter, margarine, and fatty meat.
     They provide us with a store of energy – producing material.
     They are also used to make cell membranes and for insulation to stop heat loss through the body surface.
4.   Vitamins form a group of substances needed only in very small amounts for normal health.
5.   Minerals are also substances needed in very small amounts.
6.   Water makes up about 70% of most tissues. Cytoplasm in cells consists mostly of water. Water is also needed to
     transport dissolved materials around the body. It is found in drinks, fruit and vegetables.
7.   Fibre (roughage) is needed to help the movement of food through the intestine. It is found in wholemeal bread,
     brown rice, bran, fruit and vegetables.

A balanced diet is a diet that contains the correct amount of each of the seven main constituents.
The RDA is the Recommended Daily Allowance of a particular nutrient.

We can find out whether the food which we are going to eat contains carbohydrate, protein or fat by carrying out
food tests.
                                         FOOD TESTS
                                                Safety:
1.   Carbohydrates                              Eye Protection must be worn

     a)   Simple sugars
          Before starting the tests, prepare a boiling water bath:
                   Half fill a large beaker or a metal can with tap water.
                   Place the beaker or can on a gauze on a tripod.
                   Heat the water with a Bunsen Burner until the water boils.
          If the food sample is dry, dissolve a little of the food sample in some cold water.
          Put about1cm3 of this solution in a clean test tube.
          Using the dropping bottle, add about 1 cm3 of Benedict’s Reagent to the test tube..
          Put the test tube into a boiling water bath.
          If there is a simple sugar present, a red-brown precipitate will appear.
          If there is no sugar present, the solution will remain blue and clear.
     b)   Starch
          If the food sample is dry, dissolve a little of the food sample in some cold water.
          Put about1cm3 of this solution in a clean test tube.
          Using the dropping bottle, add a few drops of iodine solution to the test tube.
          If starch is present, the yellow iodine solution will turn blue-black.
          If there is no starch present, the solution will remain yellow.

2.   Proteins – the Biuret Test

          If the food sample is dry, dissolve a little of the food sample in some cold water.
          Put about1cm3 of this solution in a clean test tube.
          Using the dropping bottle, add about 1cm3 of sodium hydroxide solution to the test tube.
          Using the dropping bottle, add about 2 drops of very dilute copper sulphate solution to the test
          tube. The solution in the test tube should now be pale blue.
          If there is protein present, the pale blue colour will change to violet.
          If there is no protein present, the solution will remain pale blue.

3.   Fats (lipids)

     a)   The grease paper test
          Rub some of the food sample onto a piece of filter paper.
          If fat is present, a translucent patch appears on the filter paper. (Translucent means that light
          will shine through it when you hold it up to a window.)
          If no fat is present, this patch will not appear.

     b)   The emulsion test
          Put a little of the sample in a clean test tube.
          Using the dropping bottle, add about 1cm3 of ethanol or propanol to the test tube.
          Shake thoroughly.
          If fat is present, the solution will form an emulsion and turn cloudy.
          If there is no fat present, you should not see this emulsion.
                   INVESTIGATING THE ENERGY VALUES OF SEEDS
MATERIALS AND APPARATUS
Peanuts                                        Thermometer
Maize seeds                                    10 ml measuring cylinder
Castor oil seeds                               Bunsen burner
Mounted needle                                 Retort stand and clamp
Boiling tube                                   Access to a top-loading balance

BACKGROUND INFORMATION
When foods are burnt heat is given out. If this heat is used to warm a known mass of water, temperature rise can be used to calculate
the energy content of the food. If the mass of food is known, we can calculate energy value per gram and compare energy values of
different foods as units of energy output per gram of material.

METHOD
1. Copy out a results table like the one following.

2.   Pour exactly 20 cm3 of water into a boiling-tube clamped to a retort stand.

3.   Measure and record the temperature of the water.

4.   Weigh a peanut, record its mass in the results table, then impale it on the end of a mounted needle.

5.   Ignite the peanut in the bunsen flame, then direct the flame from the burning peanut under the boiling-tube of water.

6.   When the peanut stops burning, measure the temperature of the water, and record this temperature in the results table. Calculate
     the temperature rise and record this in the results table.

7.   Carry out the same procedure (2 – 6) for two other peanuts, then work out and record the average mass of the peanuts and the
     average rise in temperature.

8.   If there is time, repeat stages 2 – 7 for each of the other two species of seeds, recording all results and calculations in the results
     table.

         In the following calculations, show all your working.

9.   Use the following formula to calculate the amount of energy released from peanuts (using the average temperature rise of the
     water).
                           Energy released (joules) = mass of water x temperature rise x 4.2
                           (remember 1cm3 of water has a mass of 1g, so the mass of the water is 20g)
                           NB: You use the mass of water in the calculation, not the mass of the peanut.
         This answer gives the energy in joules.

10. Convert energy in joules to kilojoules .1kJ = 1000 joules, so divide your answer by 1000.

11. Calculate the average mass of the peanuts.
    The answer in (10) gives the total kilojoules given out per peanut.
    Calculate the energy given out per gram of peanut by dividing your answer in (10) by the average mass of the peanuts.
    This is the energy value of the peanut. Record it in the table.

12. If you had time to burn other seeds, repeat the calculations for the other seeds.

RESULTS
Complete your results table from the data you have collected (see table overleaf).

CONCLUSIONS
1. State, with reasons supported from your results, which of the seed species is the most energy-rich.

2.   Which two constituents of a healthy diet are likely to be present in these nuts and seeds, remembering that they burn to produce
     energy?
RESULTS TABLE




                                                     TEMPERATURE                                  ENERGY
                  MASS    VOLUME         MASS                            TEMP        ENERGY
                                                     OF WATER (OC)                                 VALUE
      SEED         OF       OF            OF                             RISE         GIVEN
                                                                                                  OF SEED
                  SEED     WATER         WATER       START     FINISH     (OC)        OUT (j)
                                                                                                   (Kj/ g)
     Peanut 1                 20             20
     Peanut 2                 20             20
     Peanut 3                 20             20
     average                  20             20
     Maize 1                  20             20
     Maize 2                  20             20
     Maize 3                  20             20

     average                  20             20
     Castor oil
                              20             20
         1
     Castor oil
                              20             20
         2
     Castor oil
                              20             20
         3
     average                  20             20



EVALUATION

1.    How well did you think this experiment worked?

2.    What difficulties did you encounter?

3.    How did you solve them?

4.    How did your results compare with the results of other groups?

5.    What safety precautions were necessary in this investigation?

6.    What was the independent variable in the experiment? (The one you changed.)

7.    What was the dependent variable in the experiment? (The one you calculated.)

8.    Which should be the controlled variables? (The ones you kept the same.)

9.    Which of the controlled variables did you not control properly?

10. How could you improve the investigation to try to make sure that all the controlled variables were properly controlled?

11. How could you improve the investigation to make your answers more accurate?
                                               DIGESTION
The food you eat may contain carbohydrate in the form of starch or sugars, protein and fat.
Starch, proteins and fats are large, insoluble molecules, so they cannot be absorbed into the blood stream.
The chemicals that any part of your body needs are carried to that part of the body by the blood.
Therefore, it is necessary to change the large, insoluble molecules into small, soluble molecules, so that these
molecules can be absorbed into the bloodstream.

DIGESTION IS THE BREAKING DOWN OF LARGE, COMPLEX, INSOLUBLE MOLECULES
INTO SMALL, SIMPLE, SOLUBLE MOLECULES, WHICH CAN BE ABSORBED BY THE BODY.

The process of digestion takes place in the digestive system, and there are two types of breakdown:
1. Mechanical Breakdown
   A physical process. It is the first stage of digestion and is mainly carried out by the teeth and tongue.
2. Chemical Breakdown
   A chemical process. It is the second stage of digestion and is carried out by enzymes.
   Enzymes speed up (catalyse) chemical processes. Enzymes are biological catalysts.
   The chemical breakdown is also assisted by acid in the stomach and by bile produced in the livet.

N.B.

Some chemicals do not need to be digested as they are already small enough to be absorbed directly e.g.
minerals, vitamins, water.


                               Digestion of food in the digestive system
1. Mouth

Food is taken into the mouth (INGESTED) and broken down into smaller pieces by the teeth
(MASTICATION). It is mixed with saliva, which is a secretion from the salivary glands and rolled into a
small, soft ball ready to be swallowed. Saliva contains MUCUS (to help lubricate the food) and an enzyme
called salivary amylase, which breaks down the starch into sugars.

2. Oesophagus (gullet)

The food ball is swallowed and slips over the epiglottis, which prevents food from entering the trachea
(windpipe). Muscles in the oesophagus contract rhythmically and force the food down to the stomach. This
rhythmic contraction is called peristalsis.

3. Stomach

Food enters the stomach through a ring of muscle. It remains in the stomach for up to 8 hours, depending on
what was eaten e.g. Rice = 1 hour, Sardines in oil = 8 hours. The stomach walls contract, mixing the food with
the GASTRIC JUICE which is produced by the stomach. Gastric juice contains an enzyme called
PROTEASE which breaks down proteins into amino acids. Gastric juice also contains hydrochloric acid
which kills bacteria.
The enzymes in the stomach work most effectively in acid conditions.

4. Small intestine

The liquid contents of the stomach pass into the small intestine.
The small intestine receives three types of secretions:

a) Secretions from the pancreas through the pancreatic duct (Pancreatic juice).
   The pancreatic juice contains three important enzymes:
      i) amylase (catalyses the break down of starch into sugars)
      ii) lipase (catalyses the break down of lipids [fats and oils] into fatty acids and glycerol)
      iii) protease (catalyses the break down of proteins into amino acids)
b) Secretion from the gall bladder through the bile duct.
   This secretion is called bile.
   Bile is made in the liver, stored in the gall bladder and enters the small intestine through the bile duct.
   Bile has two functions:
      i) Bile is alkaline, so neutralises the acid that was added to the food in the stomach.
           It provides slightly alkaline conditions in which the enzymes in the small intestine work most
           effectively.
      ii) Bile emulsifies fats (breaks large droplets into small droplets). Many small droplets have a larger
           total surface area than a few large droplets. Bile therefore increases the surface area of fats so that
           the lipase enzymes can work more effectively.
c) Secretions from the wall of the small intestine.
   The small intestine produces the three enzymes: amylase, lipase and protease.

When the enzymes have done their work in the small intestine, the soluble products of digestion are absorbed
through the walls of the small intestine into the blood stream.
The soluble products are:
              Sugars (from starch)
              Fatty acids and glycerol (from fats)
              Amino acids (from proteins)
These products of digestion can be absorbed quickly because:
       a)     The small intestine is long – increases surface area
       b)     There are lots of villi in the walls of the small intestine – increases surface area
       c)     There is a good blood supply around the walls of the small intestine.

5. Large intestine

The material which enters the large intestine consists of mostly water and indigestible substances.
The water is absorbed through the walls of the large intestine.

6. Rectum and anus
   The indigestible material that remains makes up the bulk of the faeces.
   The rectum temporarily stores faeces before it leaves the body through the anus.

N.B.

The APPENDIX is a small, blindly ending tube attached to the beginning of the colon. It is important for
cellulose digestion in herbivores, but in man it serves no useful purpose and it can become inflamed and /or
burst (APPENDICITIS). It is sometimes removed surgically.
                                                        TEETH

Your teeth are very important, since they start off the digestion process.

                                               Look after them!
Tooth decay and gum disease

Tooth decay is the most common disease affecting British school children – an average 14 year old will have 7 teeth
affected by decay; about 40% of British adults have lost all their teeth and have false ones.

Tooth decay (DENTAL CARIES)

It is warm and moist inside your mouth and there will probably be bits of food stuck between your teeth. Bacteria find it
a good place to live. They mix with saliva and food and stick to your teeth and gums forming a yellow – white material
called PLAQUE. The remains of food in your mouth often contain sugar. The bacteria in the plaque use sugar as food
and produce acids as waste products. These acids attack the tooth‟s enamel and cause tiny holes (LESIONS). If these
are left untreated they can develop into larger holes called CAVITIES, which reach into the dentine. At this stage a
filling can save the tooth. If treatment is not given, the bacteria can get into the pulp cavity causing pain and abscesses,
which may result in removal of the tooth.

Prevention

1.   Eat less sugary foods and drinks.
2.   Use a good toothbrush and change it every 2 – 3 months.
3.   Use the correct technique for brushing and brush regularly.
4.   Use fluoride toothpaste because it hardens enamel.
5.   Never eat sweets between meals (or eat them all together and then brush your teeth).
6.   Visit your dentist every 6 months.

N.B.

                 SUGAR           +          PLAQUE           =             ACIDS

                 ACIDS           +          TEETH            =             DECAY

Gum disease

This is more serious than tooth decay because it is less painful and so people are less aware of it. More teeth are lost
through gum disorders than through tooth decay.
Healthy gums look and feel good i.e. pale pink in colour, have a matt surface, a firm consistency and their edges should
be finely tapered. They should never bleed when probed by the dentist or during routine brushing.
Plaque can build up on the teeth and tends to collect around and under the edges of the gum. This causes inflammation,
swelling and bleeding (GINGIVITIS). If the bacterial attack is allowed t continue over a period of time, the toxins
produced will eventually destroy the periodontal fibres. The gum will recede and pull away from the tooth forming a
„pocket‟. As the pockets deepen, the tooth will become loose and may fall out (PERIODONAL DISEASE). If plaque is
left on the teeth, it will eventually harden and provide a larger area for more plaque or pockets to develop, so speeding
up the rate of decay. The dentist must remove this CALCULUS.
                     MAKING A MODEL OF THE DIGESTIVE SYSTEM

You will need:
2 boiling-tubes                      4% starch solution
2 lengths of Visking tubing          2% diastase (amylase) solution mixed with starch solution
(starch/amylase mixture)
2 paper-clips                        Iodine solution for starch test
2 lengths of cotton                  Benedict‟s solution for sugar test
test-tube rack                       2 test-tubes
dropping pipette                     water bath – if your teacher tells you to use one

Diagram
Your teacher will show you how to set up the apparatus.
Draw a labelled diagram of the set up in this space




Method
1. Soak each length of Visking tubing in water to soften it, then tie a knot at one end. (This may have already
   been done for you.)
2. Add to one of the Visking tubing bags you have made about 8 cm3 of starch solution, which represents
   the food to be digested in the model. Call this model A.
3. Tie the end of the Visking tubing bag with the cotton thread, and rinse the outside of the Visking tubing
   with tap water. Then suspend the bag in a boiling-tube of distilled water.
4. Call the second Visking tubing bag model B, and add to it about 8 cm3 of starch/amylase mixture. As
   before, tie the end of the bag with cotton and suspend the bag in a boiling-tube containing distilled water.
5. Test both sets of distilled water in tubes A and B immediately for starch and sugar, carrying out the iodine
   test for starch and the Benedict‟s test for sugar. Record the result of each test in the results table.
6. Leave each set of apparatus for 15 minutes. You may be told to put the models in a water bath.
7. After 15 minutes, test the distilled water in each boiling-tube for starch and sugar. Record your results in
   the results table.
Results

Insert a tick or a cross to indicate presence or absence of starch or sugar.

                                                     A                         B
                       Test
                                            Starch       Sugar       Starch        Sugar
          Test on water at start
          Test on water after 15 mins


Conclusions

1. Can starch pass through the Visking tubing?


2. What does the amylase do to the starch?


3. Can sugar pass through the Visking tubing?


4. Can starch break down by itself?


5. What does the Visking tubing in this model represent?


Summary

The Visking tubing in tube A contained starch solution only.
Starch consists of large molecules, which are too big to move through the semi-permeable membrane of the
Visking tubing.
There is nothing inside the Visking tubing that can break down the starch, so the only molecules that can pass
through the semi-permeable membrane are water molecukes.

The Visking tubing in tube B contained a mixture of starch and amylase.
Amylase is an enzyme that catalyses the breakdown of starch into small sugar molecules.
Sugar molecules are small enough to pass through the semi-permeable membrane of the Visking tubing.
After about 15 minutes, the amylase has broken down some of the starch inside the Visking tubing, and the
sugar molecules have diffused through the semi-permeable membrane.
Therefore, the sugar test on the water outside the Visking tubing in B is positive.
                                         DIGESTION QUESTIONS
1. What is the function of an enzyme in the digestive system?

   ______________________________________________________________________________________

2. The main enzyme present in the secretion from the salivary
   glands of human beings is                                                   _________________________

3. Name the substance produced when the enzyme in saliva has done its job. _________________________

4. What substance must have been present in the food in the mouth
   In order to produce the breakdown product named in (3)?                     _________________________

5. The stomach contains an enzyme which catalyses the breakdown of
   proteins. Name this enzyme.                                                 _________________________

6. When proteins are digested in the digestive system, the proteins
   are broken down into                                                        _________________________


7. An enzyme in pancreatic juice changes starch into sugar; this enzyme is called   ____________________


8. The pancreas produces two other important digestive enzymes. Name them:

                  _____________________              and        _________________________

9. Which of the two enzymes named in (7) catalyses the break down of fats? _________________________

10. Name the substances produced when fats are broken down.

                  _____________________              and        ________________________

11. The three main types of digestive enzyme are produced in the pancreas
    and one other area of the digestive system.
    Name the other area that produces all three enzymes.                       _________________________


12. Apart from enzymes, secretions from the stomach contain another
    substance that is important in digestion. Name this substance.             _________________________

13. The acid in the stomach has two important functions.
    These are:
                  (i)________________________________________________________________________

                  (ii) _______________________________________________________________________


14. Before release into the small intestine, bile is stored in the             _________________________


15. Bile is made in the                                                        ________________________
16. Bile “emulsifies” fats. Explain what this means.


   _____________________________________________________________________________________


17. After the fats have been emulsified, the enzymes that break down fats can work more efficiently.
    Explain why.

   _____________________________________________________________________________________


18. Bile also neutralises the contents of the small intestine, because it is an alkaline substance.
    Why are the contents of the small intestine so acidic that they have to be neutralised?

   _____________________________________________________________________________________


19. Suggest a pH at which the enzymes produced by the small intestine might work best. _______________



20. Suggest a pH at which the enzymes produced by the stomach might work best.                  _______________


21. A sample of food was tested to find out whether it contained sugars, starch, protein or fats.
    The result of the tests was as follows:
         Benedicts test                 Reddish brown precipitate
         Protein test (Biuret)          Very pale blue solution
         Emulsion test                  The solution remained clear

   a)    Did the food contain fat?                                                              ______________


   b)    Did the food contain sugar?                                                            ______________


   c)    Did the food contain protein?                                                          ______________
                                    Further digestion questions

1.   Two experiments were set up as in fig. 1.




                                                  Fig.1

   At the start the water in each was tested for starch and sugar. None was detected.
   After a period of time the water was tested again. All that could be detected was sugar in B.
Which, of the following conclusions is NOT correct?
A) Starch can be changed to sugar
B) Sugar can pass through visking tubing
C) Starch is unable to pass through the tubing
D) The warmth of the water had caused the starch to change to sugar
E) The saliva had caused the change in the starch

2.   Refer again to fig.1. The visking tubing in this experiment is meant to represent the gut. Which of the
     following is the most important principle this experiment shows?
A)   The gut is tubular
B)   The wall of the gut is permeable but not to all molecules
C)   The wall of the gut is permeable
D)   The gut is composed of many regions
E)   The wall of the gut is impermeable to starch

3.   Three test tubes were set up as follows:
     X   Milk plus pancreatic juice plus bile
     Y   Milk plus pancreatic juice plus water
     Z   Milk plus boiled pancreatic juice plus bile

After being kept in a warm place for some time, tubes X,Y and Z were tested for the presence of fatty
acids. The results were:-
 Tube X – rich in fatty acids
 Tube Y– fatty acids but not as much as tube 1
 Tube Z – no fatty acids

Which of the following conclusions cannot be drawn from these results?
A) Bile if essential for pancreatic juice to work
B) Pancreatic juice contains an enzyme
C) The enzyme transforms fats to fatty acids
D) The action of the enzyme can take place in water
E) Boiling the juice prevents it from working
4.   Amylases are produced in the :-
A)   Salivary glands, pancreas and small intestine
B)   Pancreas only
C)   Salivary gland only
D)   Stomach and pancreas
E)   Pancreas and gall bladder

5.    The enzyme pepsin (stomach protease) from a human works best in conditions that are:
A)   strongly acid
B)   slightly acid
C)   about neutral
D)   slightly alkaline
E)   strongly alkaline

6.    An enzyme is best described as :
A)   any substance produced by the human body which is destroyed by heat
B)   a chemical messenger
C)   a chemical only produced in the alimentary canal of animals
D)   a protein which speeds up the rate of chemical reactions
E)   any chemical which turns starch into reducing sugars

7.    Which of the following statements is NOT TRUE? All enzymes:
A)   are made of protein
B)   are unchanged after reaction
C)   are unaffected by heat
D)   speed up chemical reactions
                              HUMAN DIGESTIVE SYSTEM – COMPREHENSION

1. List in order, starting with the mouth and ending with the anus, the parts of the digestive system.




2. Name three glands, which secrete into the digestive system.




3. Which part of the digestive system brings about mastication?




4. a) Name the organ which produces bile



    b) Name the organ which stores bile.




5. Name three parts of the digestive system where starch digestion takes place.




6. Name two secretions which the small intestine receives.




7. a) Which part of the digestive system is concerned with the absorption of the products of digestion?



    b) Describe how the surface area of this part is increased.
8. What does the mouth do?




9. What does the stomach do?




10. What two things does bile do?




11. Which part of the digestive system is concerned with water absorption?




12. Name the blindly ending sac found in the human digestive system which has no known function.




13. What is the function of the rectum?
                                                ENZYMES
Enzymes are biological catalysts.
Catalysts speed up the rate of a reaction.
Enzymes speed up the rate of reactions in the body.
Many of the reactions in the body could happen faster at very high temperatures – but the body would
probably vaporise!
Enzymes are therefore vital for all the chemical reactions in the body.

PROPERTIES OF ENZYMES
1. Like catalysts, they speed up reactions.
2. They can be used over and over again – they do not get used up in the chemical reactions
3. They are made of protein.
4. They are specific – i.e. unlike catalysts, they will only speed up one particular chemical reaction.
5. The activity of enzymes if affected by temperature.
6. The activity of enzymes is affected by pH.
7. Enzymes are denatured i.e. destroyed at high temperatures and at extreme pH values.

Effect of pH
Enzymes have an optimum pH at which they work fastest.
The optimum pH for many is pH 7, but some enzymes work best in alkaline conditions, and others work best
in acidic conditions. Some examples are shown in the following table:



               Enzyme                        Source                    Optimum pH
                Pepsin                        Stomach                   1.5 – 2.5
              Peroxidase                   Plant roots                  2.5 – 3.0
                Zymase                        Yeast                     4.5 – 6.5
                Amylase                       Pancreas                  6.0 – 7.0
                Trypsin                       Pancreas                  8.0 – 9.0

The graph below show the effect of pH on the rate of activity of pepsin and trypsin,
Pepsin is found in the stomach (where HCl is also produced).
Trypsin is found in the small intestine (where bile is also present).




Effect of temperature
As temperature rises from 0oC to about 35oC, the rate of activity of an enzyme doubles for every 10o rise.
Above 40oC, denaturation starts, and above 60oC, the enzyme is completely denatured – i.e. completely
destroyed, so it cannot work.
At low temperatures, enzymes work slowly or not at all.
Most enzymes work at their fastest rate between 35oC and 40o C.
The graph below shows the effect of temperature on the rate of activity of an enzyme.
                        ENZYMES – COMPREHENSION QUESTIONS
1. Why are enzymes referred to as biological catalysts?


2. Give two similarities between enzymes and catalysts.

           (i)


           (ii)


3. Give two differences between enzymes and catalysts.

           (i)

           (ii)

4. Give four properties of an enzyme.

           (i)

           (ii)

           (iii)

           (iv)


5. Why are enzymes, as opposed to chemical catalysts, so important to living things?



6. What is meant by the term „denatured‟?



7. Give two conditions in which an enzyme is likely to be denatured.

           (i)

           (ii)



8. A sample of an enzyme was cooled to 100C for 30 minutes (Sample A).
   A second sample of the same enzyme was not cooled. It was kept at 37oC (Sample B).
   Both samples of the enzyme were then used and the rate of activity for each sample was determined.
   The temperature of the substrate (the substance which the enzyme works on) was maintained at 10oC for
   sample A and 37oC for sample B.
    a) What is the independent variable in this investigation?
    b) What is the dependent variable in this investigation?


    c) Give three variables which would have to be controlled to make this a fair test.

           (i)

           (ii)

           (iii)


    d) Which sample would have the higher rate of activity?



    e) Explain your answer to d), in terms of what you know about the properties of enzymes.




9. The same enzyme as that in question 8 was boiled for 30 minutes and then cooled to 37oC.
   The rate of activity of this sample was then determined.
    a) What would be the rate of activity for this sample of enzyme?


    b) What has happened to the enzyme?


    c) Is there any way in which you might be able to restore the activity of this enzyme?
MEASURING THE RATE AT WHICH THE ENZYME DIASTASE BREAKS DOWN STARCH

Materials and apparatus
1% starch solution                       Spotting tile
1% diastase solution                     Glass rod
2 x 5 ml pipettes                        Stop-watch
Test-tube and test-tube rack

Background information
Diastase is a plant amylase enzyme which breaks down starch to sugar. When starch is present, when tested
with iodine solution, it turns a blue-black colour. If starch is not present, i.e. it has been broken down to sugar,
when tested with iodine solution, no blue-black colour will be produced (the only colour which will be seen
will be the brown colour of the iodine). If we time how long it takes for starch to be completely broken down
(no blue-black colour), we have the rate at which the enzyme works.

Method
1. Put spots of iodine in the hollows of the dimple tray.
2. With one of the pipettes put 3 ml of starch solution into the test-tube.
3. With the other pipette add 3 ml of diastase solution to the 3 ml of starch in the test-tube, and start the stop-
   watch immediately.
4. After 20 seconds, using the glass rod, transfer some of the starch/diastase mixture to one of the iodine
   spots and mix.
5. At 20 second intervals continue transferring samples of starch/diastase mixture to iodine spots until you do
   not get a reaction. When this happens stop the watch and record the time for starch breakdown.
6. Express the rate of breakdown as 1/time x 1000.

Precautions
1. After each time you transfer the mixture to an iodine spot, clean the glass rod with a paper towel.
2. If the time for breakdown is very quick, you may take samples at 10 second intervals. If the reaction is
   slow, extend the time intervals between sampling.

Results
Record your own results and those of 9 other people in a table like the one below.

              NAME OF PERSON                   TIME FOR             RATE OF REACTION
                                              BREAKDOWN               ( 1/time x 1000)
                                                (seconds)




                   AVERAGE



Conclusions and evaluations
1. From your experiment, what was the rate of the reaction for diastase?

2. In the class, were results similar?

3. If not, suggest why there were differences.

                                                    TURN OVER
4. List any variables which you can think of which could have affected the rate at which diastase breaks
   down starch.

5. How many of these variables were controlled?

6. How were they controlled?

7. For variables not controlled, suggest how they ought to have been controlled.

8. Why was the glass rod wiped clean after each time it was used?

9. What safety precautions need to be taken during this experiment?

Write up
Write up this experiment carefully in your own words. In your conclusions and evaluation, refer to the 9
questions asked.

Take care with the account of this work, it is going to be followed up by a Sc. 1 investigation, where some of
the techniques, etc, learnt here will be used.
   Investigating the effect of a Protease Enzyme on the breaking down of the
       gelatin coating on camera film – the effect of pH and temperature
Materials and Apparatus
2% pepsin solution
2M HCl
film strip
test-tube and test-tube rack
water bath at 37oC

Introduction
Pepsin is an enzyme released from the lining of the mammalian stomach. It attacks proteins, releasing
peptides. Camera film consists of a gelatin (a protein) layer upon a plastic base material. Developed exposed
film is black and so clearly visible. When pepsin digests black camera film the colour is lost and the film
appears clear. This investigation will consider the effect upon this enzyme of:
                1. acid (low pH)
                2. temperature
                3. boiling

Method
Set up 5 test tubes with contents as follows:
1. 5 ml pepsin solution + 2 ml HCl + film strip
2. 5 ml pepsin solution + 2 ml HCl + film strip
3. 5 ml boiled pepsin solution + 2 ml HCl + film strip
4. 5 ml pepsin solution + 2 ml NaHCO3 + film strip
5. 5 ml water + 2 ml HCl + film strip

Tube 1 should be left at room temperature.
Tubes 2 to 5 are to be kept in a water bath at about 37oC.
Inspect each tube at 1 minute intervals, with shaking.

Results
Construct a table to show at a glance the contents of each tube and the result in each case.

Conclusion and Development
Write your conclusions -
How did the temperature and the acid affect the digestion?
Was the pepsin necessary?
What further investigations could be done?
How could this experiment be improved?
   Investigating the effect of a Protease Enzyme on the breaking down of the
      gelatin coating on camera film – the effect of pH and denaturisation

Introduction:
Pepsin is a protease enzyme which is produced in the stomach.
It breaks down proteins.

Camera film has a chemical on it which turns black when exposed to light,
This chemical is held on the camera film by a layer of gelatin, which is a protein.

The protease is able to break down this gelatin layer, and when it does so, the black chemical falls off the film,
so the film appears cclear.
If the enzyme works quickly, the time taken to turn clear is short.

This investigation will look at:       (i) how pH affects the speed of action of the enzyme
                                       (ii) how boiling affects the speed of action of the enzyme.


Method:

Set up 4 test tubes as follows.

               NB Do not add the film strip until you have everything else in the tube.
               Prepare all the tubes and then add a film strip to each tube at the same time.

               1.   5cm3 of pepsin solution + 2cm3 of dilute HCl + film strip.
               2.   5cm3 of boiled pepsin solution + 2cm3 dilute HCl + film strip.
               3.   5cm3 of pepsin solution + 2cm3 of NaHCO3 + film strip.
               4.   5cm3 of water + 2cm3 of dilute HCl + film strip.

As soon as you add the film strip, start timing.

Put all the tubes in a water bath at 35oC.

Check the tubes every minute to see whether the black has disappeared. If you cannot find anything in the test
tube, it means that the black has come off – the clear film is in there somewhere!

Record the time at which the black has disappeared.


Results:

Record your results in a suitable table.


Conclusion:

What can you conclude about: (i) The effect of boiling on the enzyme – what has happened to the enzyme?
          (ii)      The effect of pH on the enzyme?
           THE ACTION OF TRYPSIN ON CASEIN (MILK PROTEIN)

INTRODUCTION:
Casein is a white protein. A white opaque (unable to see through it) suspension of Marvel milk in water loses
its opaqueness and becomes translucent (able to see through it) after hydrolysis by Trypsin.



METHOD:
   1. Set up four test tubes as shown below. Do not forget to label each tube.

        no alkali             add two drops of 1% sodium hydroxide to B, C and D
    A                       B                    C                    D




                2cm3                   2cm3                    2cm3                  2cm3
               trypsin                 water                   trypsin              boiled & cooled trypsin


                                      10cm3 casein

        Place all four tubes in a beaker of warm water at 35oC for 10 – 15 minutes and then record your
        observations in rough, i.e. time taken to go clear. (Do not let the temperature rise above 35oC.)

   2. Whilst waiting for your results, write up this experiment. (Title, diagram and method)

   3. Record you observations in a results table.

   4. After recording your observations, clear away the apparatus and answer the following questions in
      complete sentences.

           a) In which test tubes did the trypsin have an effect on the casein?

           b) Under which conditions does trypsin work best, alkaline or neutral.

           c) Did the trypsin work after it had been boiled?

           d) Why was tube B set up?

           e) What do tubes (i) A, (ii) C and (iii) D tell you about the action of trypsin?

           f) What type of substance is trypsin, where would you expect to find it in the body? (You may use
              your text book to find out.)
                    THE EFFECT OF PH ON ENZYME ACTIVITY
A carefully designed experiment was conducted to investigate the effect of varying pH on the activity of an
enzyme found in a „Biological Washing Powder‟.

The rate of breakdown of a substrate (cooked eggwhite) was measured at different pH. The results were
recorded in a table. At each pH the rate given is the average of two observations. The quantity of enzyme used
was the same in all cases and the temperature of the whole investigation was carefully controlled at 37oC.

The results were as follows:

                      pH                            Rate (arbitrary units)

                      2.0                           0.1
                      4.2                           0.6
                      5.8                           2.3
                      7.6                           4.2
                      8.4                           4.7
                     10.0                           2.9
                     11.0                           0.2


   a) Plot these results on the axes given.

   b) What was the optimum pH for the activity of this enzyme?

   c) Name another enzyme with a different pH optimum to this one that would also digest egg white.

   d) Why was the temperature maintained at 37oC?

   e) Why were two readings made for each pH?

   f) What factor other than temperature and amount of enzyme would also have been kept constant if this
      were a well designed experiment?

				
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