Teacher`s Instructions

Transcription

Teacher’s Instructions
The following instructions are to aid the teachers who are preparing equipment for the practicals, and to
highlight important safety issues for particular practicals.
Unit 1
Practical 5
Sodium hydroxide is caustic. Avoid contact with skin and eyes. Flush with water if contact occurs.
The solutions must be made up just prior to use. Solutions for flasks A and B:
for 1 litre:
1000 mL water
10 g sodium hydroxide
10 g glucose
1 mL 1% methylene blue. (Slowly dissolve 0.15 g methylene blue in 10 mL of ethyl alcohol.)
Flask A should be half filled and stoppered. Flask B should be filled to the top with no air space below the
stopper.
Unit 3
Practicals 1, 16 and 17
Solution A
Solution B
Solution C
Solution D
Solution E
Add 240 g manganese sulfate (MnSO4.4H2O) to 500 mL water (keeps indefinitely).
Add 350 g potassium hydroxide (KOH) to 500 mL water. Add 75 g potassium iodide (KI)
(keeps indefinitely).
Concentrated sulfuric acid
Mix 2 g starch with 10 mL water to form a paste. Add to 100 mL of boiling water. Continue
to boil for 2–3 minutes while stirring (keeps 2–3 days).
Add 3.1 g sodium thiosulphate (Na2S2O3) to 1000 mL water (keeps 1–2 weeks).
Unit 5
Practical 4
This practical has been split into three sections, as time does not usually allow all three sections to be done
in one practical session. Also there is a computer simulation, ‘Enzyme Lab’, that gives an excellent
T E AC H E R I N S T RU C T I O N S
demonstration of the principles involved in this practical. If the teacher feels that section 1 is too difficult as
it is it can be done under separate headings:
Section 1
Demonstration of the action of an enzyme.
Section 2
The effect of pH on enzyme action.
Section 3
The optimum temperature for enzyme action.
Five solutions of fresh hydrogen peroxide (3%) are required for this practical. The pH should be adjusted by
the addition of drops of either dilute hydrochloric acid or dilute sodium hydroxide. Test the pH of the
solution after the addition of each drop using a pH meter or universal pH indicator paper. It is suggested that
the following pH values are used: 1, 3, 5, 7, 9 and 11. It is better to have these solutions prepared before the
practical.
Alternatives for Section 1—Demonstration of the action of
an enzyme
1. Comparison of an inorganic and organic catalyst. Use tubes A, B and D.
2. Increasing the surface area of the liver to allow more of the enzyme to come in contact with the substrate.
Use tubes A, C, D and E.
3. Does changing the amount of substrate available change the reaction rate and/or the time taken for the
reaction? Use tubes A, D and E.
4. Enzymes are denatured by being heated at 45oC. Use tubes A, D and F.
5. An extension of section 1D could be to freeze liver and then use a 1 cm × 1 cm cube to illustrate that
freezing does not denature enzymes.
6. An extension of section 1B and C: does changing the amount of enzyme available change the reaction
rate/or the time taken for the reaction? Use tubes A, D and another tube that contains two or three 1 cm
× 1 cm cubes of liver.
The following section is an extension experiment for section 1 of this practical.
Demonstration of the action of an enzyme—
extension
The enzyme catalase breaks down hydrogen peroxide into water and oxygen. Hydrogen peroxide is a highly
active chemical formed continually as a by-product of chemical reactions in living cells. It is very toxic to
living cells, and if the cells did not immediately break it down, it would destroy them.
Aim
1. To demonstrate that catalase, the enzyme that is necessary for the speedy break down of hydrogen
peroxide, is present in all plant and animal tissue.
Theoretical basis
The basis of jelly crystals is the protein, gelatin. This protein is found in the horns and hooves of animals.
Pineapples are one of the best sources of the protease bromelain (bromelase), which is an enzyme that aids
in the breakdown of large protein molecules to amino acids. Gelatin dissolves in hot water and on cooling a
chemical reaction causes the jelly to set. Bromelase affects the protein gelatin, and jelly in contact with this
enzyme will not set.
Requirements
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test-tubes
jelly crystals
boiled fresh pineapple that has been allowed to cool
distilled water
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test tube rack
fresh pineapple juice
measuring pipettes and cylinders
Method
1. Prepare and label the following 3 test tubes as indicated below. After each tube has been set up observe
what is occurring and record your results in a table. Assess the amount of setting of the jelly as:
–
= not set
+
= some evidence of setting
++
= moderate setting
+ + + = definitely set (a qualitative assessment)
It may be necessary to extend the qualitative assessment of – = no reaction, + = slight reaction, + + =
moderate reaction and + + + = very reactive to a ten point scale as the reaction rate can vary with the
samples chosen as well as their age and previous storage.
a. Tube A
b. Tube B
c. Tube C
5 mL of double strength jelly plus 5 mL of distilled water
5 mL of double strength jelly plus 5 mL of fresh pineapple juice
5 mL of double strength jelly plus 5 mL of cooled boiled pineapple juice
Unit 6
Practical 10
Mineral nutrient solutions
The following salts are dissolved in 1 litre distilled water. Each solution is diluted (1 part solution : 10 parts
distilled water) for the experiment.
Complete nutrient solution
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0.25 g calcium sulfate
0.25 g magnesium sulfate
0.70 g potassium nitrate
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0.25 g calcium phosphate
0.08 g sodium chloride
0.005 g iron III chloride
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0.71 g sodium phosphate
Calcium deficient
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0.20 g potassium sulfate
Iron deficient
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0.16 g calcium nitrate
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Nitrogen deficient
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0.52 g potassium chloride
Phosphorus deficient
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Sulfur deficient
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0.16 g calcium chloride
0.21 g magnesium chloride
Magnesium deficient
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0.17 g potassium sulfate
Potassium deficient
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0.59 g sodium sulfate
Unit 6
Practical 12
All caution instructions involved in the use of potting mix must be strictly adhered to and gloves and
masks must be used.
1. Wheat, oats or barley seed can be used for this practical.
2. They can be grown beforehand in small separate pots and this would eliminate the first three instructions
of ‘Preparing for the practical’.
3. The first leaves should not have broken through the coleoptile.
4. The length of time for germination and growth to this point will depend on the time of year, the type of
seeds and conditions in which they are grown
5. The use of the box is optional; the experiment will work on a window ledge provided the main source of
light is only from one direction.
Unit 6
Practical 13
All caution instructions involved in the use of potting mix must be strictly adhered to and gloves and
masks must be used.
1. Bean plants for this practical can be:
a. those used in a previous practical
b. grown beforehand in separate pots
c. purchased from a nursery.
2. If growth lights are not available then a sunny window ledge can be used.
Unit 7
Practical 3
Solutions to karyotypes
Figure T.1 Answer for the normal individual A = male
Figure T.2 Answer for the normal individual B = female
Figure T.3 Answer for the abnormal individual A = Down syndrome (male)
Figure T.4 Answer for the abnormal individual B = Turner syndrome (female)
Figure T.5 Answer for the abnormal individual C = Klinefelter syndrome (male)

Teacher`s Instructions

Transcription

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