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#Chapter 26: Biology Practicals

##26.1 Introduction to Biology Practicals

###26.1.1 Format

The format of the Biology practical exam was revised in 2011 to keep up with the 2007 updated syllabus. As such, there will be no further Alternative to Practical exams, pending approval from the Ministry of Education. Prior to 2011, there were 3 questions in the Biology practical. Question 1 was required and the student could choose to answer either Question 2 or 3.

As of now, the Biology practical has 2 questions and students must answer both. Question 1 can come from any of the following topics: Nutrition, Movement, Transport of Living Things, Respiration, Reproduction, Coordination, Regulation or Growth. Question 2 is on Classification of Living Things. Each question is worth 25 marks, and students have 21 hours to complete the exam.

###Biology 1 Theory Format

The theory portion of the Biology exam comprises 100 marks, while the practical carries 50 marks. A student’s final grade for Biology is thus found by taking her total marks from both exams out of 150.

The theory exam for Biology contains 13 questions over 3 sections. Section A has 2 questions worth 10 marks each. Section B has 8 short answer questions, each having two items. This section weighs a total of 60 marks, and the mark allocation for individual questions is indicated at the end of each question. Section C has 3 long answer/essay questions, though students only need to answer 1 of them. The answer must be comprehensive and include as many points as possible. It is worth 20 marks.

Note This information is current as of the time of publication of this manual. Updated information may be obtained by contacting the Ministry of Education.

###26.1.2 Notes for Teachers

###NECTA Advance Instructions

There are two sets of advance instructions. One set of advance instruction are given to teachers at least one month before the date of the exam. These instructions contain the list of specimen, apparatus, and other materials required for setting up the Biology practical questions. The instructions also suggest how many specimen to acquire for each candidate or group of candidates. It is imperative that the collection and storage of specimen for the practical be kept confidential.

The second set of instructions should be given 24 hours before the time of the practical. It includes how to label each specimen and which materials should be given to each candidate (or shared among candidates).

Usually if the instructions include a scalpel of some sort, this means students will be required to do some form of dissection. In most cases, the dissection is of a maize seed or bean to show whether is it a monocotyledon or dicotyledon. If the advance instructions include any form of glass apparatus or test tubes, there will most likely be a question on food tests.

###26.1.3 Common Practicals

**Food Tests** test a food solution for starch, sugars, fats, and protein

**Classification** name and classify specimens, then answer questions about their characteristics

**Respiration** use lime water to test air from the lungs for carbon dioxide

**Transport** investigate osmosis by placing leaf petioles or pieces of raw potato in solutions of different solute concentrations

**Photosynthesis** 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

**Movement** name bones and answer questions about their structure and position in the body

*Note* These are the most common practicals, but they are not necessarily the only practicals that can occur on the national exam. Food tests and Classification are by far the most common, but there are many eligible topics. Be sure to regularly look through Biology Past Papers (p. 162) to get an idea of the kind of questions that can occur.

##26.2 Food Tests

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

This section contains the following:

- Preparation of Chemical Solutions
- Preparation of Food Solutions
- Performing the Food Tests
- Examination Room
- Student Report
- Sample Food Test Practical

###26.2.1 Preparation of Chemical Solutions

Always make sure the chemicals work before performing the food tests with students.

**Benedict’s Solution**

This solution can be bought at a chemical store already prepared or you can make it yourself.

**Using Sodium Carbonate:**

- Add about 1 L of water to a plastic bottle.
- Add 5 spoons of sodium carbonate (NaCO3).
- Add 3 spoons of citric acid.
- Add one spoon of copper sulphate.

**Using Bicarbonate of Soda:**

- Add 1 L of water to a cooking pot.
- Add a box (70 g) of bicarbonate of soda.
- Boil the mixture for 5-10 minutes. This makes sodium carbonate.
- Let cool and transfer to a plastic water bottle.
- Add 3 spoons of citric acid.
- Add one spoon of copper sulphate. Cap and shake to mix.

Label as: BENEDICT’S SOLUTION FOR FOOD TESTS
The solution may be stored in any plastic or glass bottle and will keep indefinitely.

**Copper (II) Sulphate**

- Add one spoon of copper (II) sulphate to a 1.5 L bottle.
- Add 1 L of water and shake until chemicals are fully dissolved.

Label as: 1% COPPER (II) SULPHATE SOLUTION FOR FOOD TESTS
The solution may be stored in any plastic or glass bottle and will keep indefinitely.

**Iodine Solution**

Make sure to use iodine tincture from a pharmacy. The tincture must not contain ethanol/alcohol/spirit.

- Add 1 part iodine tincture to 10 parts water. Example: In a 500 mL bottle, add 40 mL iodine tincture, then and 400 mL of water.
- Cap the bottle and shake.

Label as: IODINE SOLUTION FOR FOOD TESTS
The solution may be stored in any plastic or glass bottle and will keep indefinitely.

**Dilute NaOH**

- Using a PLASTIC teaspoon, add one level teaspoon of NaOH to a 500 mL water bottle. Caustic soda (NaOH) reacts with metal. DO NOT TOUCH.
SAFETY NOTE: Prepare about 100 mL of citric acid or ethanoic acid solution to neutralize sodium hydroxide spills on skin or lab tables. One spoon of citric acid in 100 mL of water is suitable. Ethanoic acid solutions are sold in stores as vinegar.
- Add 250 mL of water.
SAFETY NOTE: This reaction can cause the solution to become very warm. Avoid chemical burns by wearing gloves.
- Cap well and shake. This makes 1 M sodium hydroxide solution.

Label as: 1 M SODIUM HYDROXIDE SOLUTION FOR FOOD TESTS (CORROSIVE)
The solution will react with carbon dioxide in the air if not well sealed. Do not store in glass bottles with glass stoppers as these will stick. The solution may be stored in plastic bottles indefinitely.

**Dilute Acid**

Your school may have dilute hydrochloric acid or you may have to make it yourself.

**Using Hydrochloric Acid (HCl):**

- Add 1 part HCl to 9 parts water. Example: In a 1.5 L water bottle, add 900 mL of water, then add 100 mL of HCl.
- Shake well.

**Using Citric Acid:**

- Add500mLofwatertoa1or1.5Lwaterbottle.
- Add 5 spoons of citric acid.
- Cap well and shake. This makes 0.5 M citric acid.

Label as: 0.5 M CITRIC ACID FOR FOOD TESTS
The solution may be stored in any plastic or glass bottle and will keep indefinitely.

**Sudan III Solution**

Using Sudan III solution takes a long time to show results. It may be replaced by iodine tincture solution for the lipids test.

- Combine 0.5 g of Sudan III powder with 100 mL of 70% ethanol solution (30 mL water and 70 mL ethanol).
- Place the solution in a warm water bath to help the Sudan III dissolve.
- Filter to remove any remaining solid.

Label as: SUDAN III SOLUTION FOR FOOD TESTS
The solution may be stored in any plastic or glass bottle and will keep indefinitely.

###26.2.2 Preparation of Food Solutions

For the NECTA and mock exams you may have to set up the food test solutions. The instructions will tell you which ones you’ll need to prepare in order to make ‘Solution X.’ Solution X consists of a mixture of at least 3 of the different food substances and is given to each student in at least 3 test tubes. Make sure food solutions are well-dissolved and colorless so that students don’t know what is in the mixture. You don’t need to measure the ingredients, but make sure to test the solutions before the practical.

**Reducing sugar**

Use glucose powder and dissolve in water. Make sure the substance is fully dissolved so that students don’t know what is in the mixture.

**Non-reducing sugar**

Use sugar and dissolve in water. Make sure the substance is fully dissolved so that students don’t know what is in the mixture.

**Lipids**

Mix sunflower oil with water. Shake immediately before use. Sunflower oil is best since it is liquid at room temperature.

**Protein**

Mix an egg white with water.

**Starch**

Save the water you use to boil potatoes, rice, or pasta. Make sure to remove the bits of food. You can also just mix flour in water, but it would be obvious.

###26.2.3 Performing the Food Tests

**Reducing Sugars Test**

- Add a small amount of Benedict’s solution to the food solution.
- Boil the solution and allow it to cool. Observe the colour changes from blue to green, yellow, then deep orange/brick red precipitate if reducing sugars are present.

Always do the reducing sugars test first because a non-reducing sugar will always test positive for a reducing sugar.

**Non-reducing Sugars Test**

- Add a small amount of dilute acid (HCl) to the solution.
- Boil the solution for about 30 seconds and allow it to cool.
- Add a small amount of NaOH to the solution and shake.
- Add a small amount of Benedict’s solution and boil.
- Allow the solution to cool and observe as the solution changes from green to yellow, then to deep orange/brick red precipitate if non-reducing sugars are present.

**Lipids Test**

- Add a small amount of Sudan III or iodine solution to the food solution and shake.
- A red ring will form at the top of the test tube if lipids are present.

Using Sudan III colours the whole solution red whether it contains lipids or not. Use iodine solution to get a more distinct result.

**Protein Test**

- Add an equal amount of sodium hydroxide (NaOH) to the solution and shake.
- Add a small amount of copper (II) sulphate to the solution and shake.
- Observe the solution turn violet/purple in colour if protein is present.

**Starch Test**

- Add a small amount of iodine solution to the food solution.
- Observe the solution turn blue-black in colour if starch is present.

###26.2.4 Examination Room

The NECTA practical exam is done in the school’s lab or any other suitable room. Heat sources (jiko, etc.) should be spread evenly in the exam room so that students don’t have to go far to heat their test tubes; this also cuts down on cheating. Spread students out and distribute supplies as you see fit.

**Each student gets:**

- 3 or more test tubes (to carry out 5 tests)
- A beaker containing Solution X
- A test tube rack (or a cut out water bottle with sand to hold the tubes)

*Note* Students may share the racks, but shouldn’t share the cut out bottles

**Each station should have:**

- Copper II sulphate
- Water
- Dilute acid (HCl, etc.)
- Dilute base (sodium hydroxide)
- Iodine solution
- Sudan III solution (can be replaced by iodine solution)
- Benedict’s solution

###26.2.5 Student Report

Food test data is recorded in a table containing four columns: Test for, Procedure, Observation and Inference.Students should write the Procedure using the passive voice in the past tense. For example, “A small amount of Benedict’s solution was added to the solution. Then the solution was boiled and allowed to cool.”

In the Observation column, the student should write what they observed using the past tense and passive voice. For example, “A violet colour was observed.”

In the Inferences column, the students should write what they saw in the past tense and passive voice. For example, “Reducing sugars were not (or were) present.” 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.

An example of a completed food test results table is given below. Assume the solution contains proteins, reducing sugars, non-reducing sugars and starch.

| **Food Tested** | **Procedure** | **Observation** | **Inference**|
| --------------- | ------------- | --------------- | -------------|
| Lipids | A few drops of Sudan III solution (or iodine solution) were added to solution X. The solution was shaken and allowed to stand.| A red ring did not form at the surface.| Lipids were not present. |
| Proteins | An equal amount of NaOH was added to solution X and shaken. A few drops of copper (II) sulphate were added to solution X and shaken again. | A violet colour was observed. | Proteins were present.|
| Reducing sugars | A small amount of Benedict’s so- lution was added to solution X. The solution was heated and al- lowed to cool. | A brick red precipitate was observed.| Reducing sugars were present. |
| Non-reducing sugars | A small amount of dilute acid was added to solution X. The so- lution was heated and allowed to cool. Then a small amount of NaOH solution was added, and the solution was shaken. Finally, a small amount of Benedict’s so- lution was added. The solution was boiled and let cool. | The solution changed from green to yellow, then to a deep orange/brick red precipitate. | Non-reducing sugars were present. |
| Starch | A few drops of iodine solution were added to solution X and shaken. | A blue-black colour was observed. | Starch was present. |


###26.2.6 Sample Food Test Practical

**You have been provided with solution B.**

1. Identify the food substances present in solution B by using the reagents provided. Tabulate your work as shown in the following Table:

| **Food Tested** | **Procedure** | **Observation** | **Inference** |
| --------------- | ------------- | --------------- | ------------- |
| | | | |
| | | | |
![26-1-student-report.png](images/26-1-student-report.png)

###26.2.6 Sample Food Test Practical

**You have been provided with solution B.**

1. Identify the food substances present in solution B by using the reagents provided. Tabulate your work as shown in the following Table:

![26-2-table-food-test.png](images/26-2-table-food-test.png)


2. For each food substance identified in Question 1,

(i) Name two common sources.

(ii) State their role in the body of human being.


3. The digestion of one of the identified food substance in Question 1 starts in the mouth.

(i) Name this food substance.

(ii) Identify the enzyme responsible for its digestion in the mouth.


4. The digestive system of human being has several parts.

(i) Name the part of digestive system in which most of digestion and absorption of food takes place.

(ii) Explain how the named part in 4(i) is adapted for absorption of digested food substances.


**Additional Food Test Questions:** See Biology Past Papers (p. 162) for additional food test questions.

##26.3 Classification

The classification practical requires students to identify specimens of animals, plants, and fungi. The students must write the common name, kingdom, phylum, and sometimes class of each specimen. They also answer questions about the characteristics and uses of the specimens.
This section contains the following:

- Common specimens
- Where to find specimens
- Storage of specimens
- Sample practical with solutions
- Additional classification questions

###26.3.1 Common Specimens

- **Fungi:** Mushroom, yeast, bread mold
- **Plants:** Fern, moss, bean plant, bean seed, maize plant, maize seed, pine tree, cactus, sugar cane, Irish potato, cypress tree, acacia tree, hibiscus leaf, cassava
- **Animals:** Millipede, centipede, grasshopper, lizard, tilapia (fish), scorpion, frog, tapeworm, liver fluke, cockroach, spider

###26.3.2 Where to Find Specimens

- Start collecting specimens several months before the NECTA exams, as some specimens can be hard to find in the dry season.
- Ask your students to bring specimens! Students are especially good at finding insects and other animals. You can even find primary school children to gather insects such as grasshopper and millipedes.
- Ferns, hibiscus, pines, and cypresses are used in landscaping. Try looking near nice hotelis or guestis. Ferns should have sori (sporangia) on the underside of their leaves.
- Moss often grows near water tanks and in shady corners of courtyards. It is hard to find in the dry season.
- Sugarcane, Irish potato, cassava, tilapia, bean seeds, and maize seeds can be found at the market. Yeast is available at shops.
- Mushrooms are hard to find in the dry season. However, they are available at grocery stores in large cities, and you may be able to find dried mushrooms at the market. You can also collect mushrooms in the rainy season and dry them yourself.
- Tapeworms and liver flukes may be acquired from butchers. Find out where livestock is slaughtered and ask the butchers to look for worms (minyoo). Liver flukes are found in the bile ducts inside the liver, while tapeworms are found in the intestines. You can also try going to a livestock fair/market (mnada) or talking to the local meat inspector (mkaguzi wa nyama).
- Grow your own bread mold. Just put some bread in a plastic bag and leave it in a warm place. But do it ahead of time – it can take two weeks to obtain bread mold with visible sporangia.


###26.3.3 Storage of Specimens

- Insects and mushrooms can be dried and stored in jars. However, they become brittle and break easily.
- A 10% solution of formaldehyde is the best way of storing specimens. Formaldehyde is often sold as a 40% solution. It should be stored in glass jars and out of the sun. Check specimens periodically for evaporation. Formaldehyde works because it is toxic; handle carefully.
- In a pinch, a 70% solution of ethanol can also be used to store insects, lizards, and worms. However, specimens sometimes decay in ethanol.

###26.3.4 Sample Classification Practical

**You have been provided with specimens L, M, N, O, and P.**

1. Identify the specimens by their common names.
2. Classify each specimen to the phylum level.
3. Further classification:
3.1. Write the classes of specimens L and M.
3.2. List two observable differences between specimens L and M.
4. Explain why specimen P cannot grow taller.
5. Write down two distinctive characteristics of the phylum to which specimen O belongs.
6. Reproduction:
6.1. List the modes of reproduction in specimens M and N.
6.2. What are two differences between these modes of reproduction?

###26.3.5 Sample Practical Solutions

1. Common names of specimens:
- L: maize plant
- M: bean plant
- N: yeast
- O: millipede
- P: moss

2. Classifaction by kingdom and phylum:

| Specimen | Kingdom | Phylum |
| -------- | ------- | ------ |
| L (Maize) | Plantae | Angiospermophyta |
| M (Bean) | Plantae | Angiospermophyta |
| N (Yeast) | Fungi | Ascomycota |
| O (Millipede) | Animalia | Arthropoda |
| P (moss) | Plantae | Bryophyta |

3. Further classification:
- Specimen L (maize plant): Class Monocotyledonae
- Specimen M (bean plant): Class Dicotyledonae
- Observable differences:

| Specimen | Vein structure | Root structure |
| -------- | -------------- | -------------- |
| L (maize) | Parallel veins | Fibrous roots |
| M (bean plant) | Net veins | Tap roots |

_The answers to this question should be differences between monocots and dicots that the student can see by observing the plants with their naked eyes. Hence answers such as “vascular bundles in a ring” are not correct._

4. Specimen P (moss) cannot grow taller because it has no xylem and phloem. If it grew taller, it would not be able to transport food and water throughout the plant.

5. Characteristics of phylum Arthropoda:
- jointed legs
- segmented body
- exoskeleton made of chitin
6. Reproduction
6.1. Specimen M (bean plant) reproduces by sexual reproduction. Specimen N (yeast) reproduces by asexual reproduction.

| Method | Genetic variation | Parents | Gametes |
| ------ | ----------------- | ------- | ------- |
| Asexual reproduction | There is NO genetic variation between offspring | Requires only one parent | No gametes are involved |
| Sexual reproduction | There IS genetic variation between offspring | Usually requires two parents | Involves fusion of two gametes |

###26.3.6 Additional Classification Questions
- Identify specimen X, Y, and Z by their common names.
- Classify specimens X, Y, and Z to the class level. (This means write the kingdom, phylum, and class.)
- Write the observable features of specimen X.
- List three observable differences/similarities between specimens X and Y.
- State the economic importance of specimen X.
- What characteristics are common among specimens X and Y?
- Why are specimens X and Y placed in different classes/phyla/kingdoms?
- Why are specimens X and Y classified under the same class/phylum/kingdom?
- What distinctive features place specimen X in its respective kingdom/phylum/class?
- How is specimen X adapted to its way of life?
- Suggest possible habitats for specimens X and Y.
- Which specimen is a primary producer/parasite/decomposer?
- For mushroom, yeast, bread mold, grasshopper, moss, tilapia, liver fluke, and tapeworm: Draw and label a diagram of specimen X.
- For tilapia: Draw a big and well-labeled diagram showing a lateral view of specimen X.

For maize and bean:

- Mention the type of pollination in specimen X [wind pollinated or insect pollinated].
- How is specimen X adapted to this type of pollination?
- Mention the type of germination [hypogeal or epigeal] in specimen X.

For bean seed:

- List three observable features of specimen X and state their biological importance.
- Split specimen X into two natural halves. Draw and label the half containing the embryo.

For fern:

- Observe the underside of the leaves of specimen X
- What is the name of the structures you have observed?
- Give the function of the structures named above.
- Draw specimen X and show the structures named above.

##26.4 Respiration

The purpose of this practical is to investigate the properties of air exhaled from the lungs. This section contains the following:

- Limewater (properties and preparation)
- Apparatus
- Cautions and advice when using traditional materials
- Sample practical with solutions

###26.4.1 Limewater

Limewater is a saturated solution of calcium hydroxide. It is used to test for carbon dioxide. When carbon dioxide is bubbled through limewater, the solution becomes cloudy. This is due to the precipitation of calcium carbonate by the reaction:

CO\(_2\)(g) + Ca(OH)\(_2\)(aq) → CaCO\(_3\)(s)

Limewater can be prepared from either calcium hydroxide or calcium oxide. Calcium oxide reacts with water to form calcium hydroxide, so either way you end up with a calcium hydroxide solution. Calcium oxide is the primary component in cement. Calcium hydroxide is available from building supply shops as chokaa.

To prepare lime water, add three spoons of fresh chokaa or cement to a bottle of water. Shake vigorously and then let stand until the suspended solids precipitate. Decant the clear solution. Chokaa produces a solution much faster than cement.

The exact mass of calcium hydroxide or calcium oxide used is not important. Just check whether some calcium hydroxide remains undissolved at the end – a sign that you have made a saturated solution. Test limewater by blowing air into a sample with a straw. It should become cloudy. If it does not, then the concentration of Ca(OH)2 is too low.

###26.4.2 Apparatus
Many books call for delivery tubes, test tubes, and stoppers. These are totally unnecessary. Add the limewater to any small clear container and blow into it with a straw.

###26.4.3 Cautions and Advice When Using Traditional Materials

If you use a delivery tube and pass it through a rubber stopper, do not use a single-holed stopper. This is what the pictures on NECTA practicals suggest, but it is a terrible idea. A single-holed stopper has no space for air to escape. So when a student blows air into the solution, the pressure in the test tube increases. The high pressure air then pushes limewater up the straw into the student’s mouth. Alternatively, the student blows the stopper out of the test tube. If you use a stopper, use a double-holed stopper so that the extra air has a place to escape.

Is a glass delivery tube stuck in a rubber stopper? Do not pull hard on it. Just soak the stopper in warm water for a few minutes. The rubber will soften and the tube will come out.

Are your test tubes and delivery tubes cloudy after the practical? Clean them with dilute acid. This will dissolve any calcium carbonate that has been deposited on the glass.

###26.4.4 Sample Respiration Practical

You have been provided with Solution B in a test tube. Use a delivery tube to breathe (exhale) into the solution until its color changes. (See diagram below.)

1. What is the aim of this experiment?
2. What is Solution B?
2.1. What changes did you observe after breathing into Solution B?
2.2. What can you conclude from these changes?
3. Breathe out over the palm of your hand. What do you observe?
4. Breathe out over a mirror. What do you observe?
5. Using your observations in the three experiments above, list three properties of exhaled air.
6. Explain why exhaled air is different from inhaled air. Where do the substances you identified in exhaled air come from?

###26.4.5 Sample Practical Solutions
1. The aim of this experiment is to test exhaled air for carbon dioxide.
2. Solution B is limewater.
- Solution B became cloudy (or milky).
- Conclusion: exhaled air contains carbon dioxide.
3. Air breathed out over the palm of the hand is warm.
4. Droplets of water condense on the mirror.
5. Conclusions:
- exhaled air contains carbon dioxide
- exhaled air contains water
- exhaled air is warm
6. Exhaled air contains the waste products of aerobic respiration. The carbon dioxide and water in exhaled air are products of respiration.

##26.5 Transport
The purpose of this practical is to investigate osmosis by observing the changes in a leaf petiole placed in a hypotonic solution (water) and a hypertonic solution (water containing salt or sugar). This section contains the following:

- Materials
- Sample practical with solutions
- Additional questions

###26.5.1 Materials

The petiole is the stalk which attaches a leaf to a branch. The papaya leaf petioles in this practical should be soft petioles from young leaves, not stiff petioles from older leaves. Cut the petioles into pieces, and give each student two pieces of about 6 cm in length. Cylinders cut from a raw potato may be used instead of petioles. The hypertonic solution may be made with by mixing either salt or sugar with water. The hypotonic solution is tap water.

###26.5.2 Sample Transport Practical

**Instructions**

You have been provided with two pieces of a papaya leaf petiole, Solution A, and Solution B.
Use a razor blade to split the pieces of petiole longitudinally, up to a half of their length. You should have four strips at one end of each petiole, while the other end remains intact.
Place one petiole in solution A, and place the other petiole in solution B. Let the petiole sit for about
ten minutes, then touch them to feel their hardness or softness.
Draw a sketch of each petiole after sitting in its respective solution for ten minutes. Record your observations and explanations about the petioles in the table below.

| Solution | Observation | Explanation |
| -------- | ----------- | ----------- |
| A | | |
| B | | |

**Questions**

1. What was the aim of this experiment?
2. What was the biological process demonstrated by this experiment?
3. What is the importance of this process to plants?
4. Which solution contained:
-pure water
-a high concentration of solutes
5. What happened to the cells of the petioles in each solution? Illustrate your answer.
6. What would happen to the cells of the petioles in solution A if their cell walls were removed?

###26.5.3 Sample Practical Solutions
(Assume Solution A is pure water, and Solution B is a concentrated solution of water and salt.)

| Solution | Observation | Explanation |
| -------- | ----------- | ----------- |
| A | The petiole became hard (turgid) | Water diffused into the petiole cells |
| B | The petiole became soft (flaccid) | Water diffused out of the petiole cells |

**Answers to the questions**

1. The aim of the experiment was to investigate the effect of osmosis on plant cells.
2. The experiment demonstrated osmosis.
3. Importance of osmosis in plants:
3.1. Water enters plant cells by osmosis so that they become turgid. Turgor helps support the plant and hold it upright.
3.2. Water diffuses into the xylem from the soil via osmosis.
4. Solution identification
4.1. Pure water: Solution A.
4.2. High concentration of solutes: Solution B
5. [Illustrations]
6. The petiole cells would burst in Solution A if their cell walls were removed.

###26.5.4 Additional Questions

You can extend this experiment by giving students two pieces of meat in addition to the petioles. The piece of meat placed in pure water should expand and become soft due to the cells bursting. The piece placed in salt water should shrink and become hard due to water diffusing out of the cells. This experiment helps to teach the different effects of osmosis on plant and animal cells.

If your school has a good microscope, try observing plant cells under the microscope after letting them sit in hypotonic and hypertonic solutions.
You can add critical thinking questions to the practical that require the student to use their knowledge of osmosis. For example:

- Why does a freshwater fish die if it is placed in salt water?
- Why do merchants spray vegetables with water in the market?
- You can die if a doctor injects pure water into your bloodstream. Why?

##26.6 Photosynthesis
The purpose of this practical is to prove that chlorophyll is required for photosynthesis. This is done by using iodine to test a variegated leaf for starch. The parts of the leaf containing chlorophyll are expected to contain starch, while the parts lacking chlorophyll are expected to lack starch. This section contains the following:

- Procedure
- Cautions
- Materials and where to find them
- Sample practical with solutions
- Additional practicals

###26.6.1 Procedure
1. Use iodine tincture from the pharmacy without dilution.
2. Prepare hot water bathes. The water should be boiling.
3. While the water gets hot, send the students to gather small leaves. The best have no waxy coating and are varigated (have sections without green).
4. The leaves should be boiled in the hot water bath for one minute.
5. Each group should then move its leaf into their test tube and cover it with methylated spirit.
6. Each group should then heat their test tube in a water bath. Over time, the leaf should decolorize and the methylated spirit will turn bight green. The chlorophyll has been extracted and moved to the spirit. A well chosen leaf should turn completely white, although this does not always happen.
7. After decolorization, dips the leaves briefly in the hot water.
8. For leaves that turn white, students should test them for starch with drops of iodine solution.

###26.6.2 Cautions
Ethanol is flammable! It should never be heated directly on a flame. Use a hot water bath – place a test tube or beaker of ethanol in a beaker or bowl of hot water and let it heat slowly. The boiling point of ethanol is lower than the boiling point of water, so it will start boiling before the water. If the ethanol does catch fire, cover the burning test tube with a petri dish or other non-flammable container to extinguish the flame.

###26.6.3 Materials and Where to Find Them
- Variegated leaf: this is a leaf that contains chlorophyll in some parts, but not in others. Often variegated leaves are green and white or green and red. Look at the flower beds around the school and at the teachers’ houses – they often contain variegated leaves. Test the leaves before the practical, as some kinds are too waxy to be decolorized by ethanol. Also, check for chlorophyll by looking at the underside of the leaves; the leaves you use have at least a small section of white on their undersides, signifying a lack of chlorophyll.
- Source of heat: anything that boils water – Motopoa is best, followed by kerosene and charcoal
- Ethanol: use the least expensive strong ethanol available; this is probably methylated spirits unless your village specializes in high proof gongo.

###26.6.4 Sample Photosynthsis Practical

**You have been provided with specimen G.**

1. Identify specimen G.
2. Make a sketch showing the color pattern of specimen G. Carry out the following experiment:
2.1. Place specimen G in boiling water for one minute.
2.2. Boil specimen G in ethanol using a hot water bath. Do not heat the ethanol directly on a flame.
2.3. Remove specimen G from the ethanol. Dip it in hot water.
2.4. Spread specimen G on a white tile and drip iodine solution onto it. Use enough iodine to cover the entire specimen.
2.5. Make a sketch showing the color pattern of specimen G at the end of the experiment.
3. What was the aim of this experiment?
4. Why was specimen G
4.1. Boiled in water for one minute
4.2. Boiled in ethanol
4.3. Dipped in hot water at the end of the experiment
5. What was the purpose of the iodine solution?
6. Why was the ethanol heated using a hot water bath?
7. What can you conclude from this experiment? Why?

###26.6.5 Sample Practical Solutions
1. Specimen G is a variegated leaf.
2. Drawing: See diagram above.
3. The aim of this experiment was to investigate whether chlorophyll is required for photosynthesis.
4. Specimen G was:
4.1. boiled in water to kill the cells and stop all metabolic processes.
4.2. boiled in ethanol to decolorize it (to remove the chlorophyll).
4.3. dipped in hot water to remove the ethanol. (If ethanol is left on the leaf it will become hard and brittle.)
5. The purpose of the iodine solution was to test for starch.
6. The ethanol was heated using a hot water bath because ethanol is flammable.
7. The experiment shows that chlorophyll is required for photosynthesis. We know this because the parts of the leaf containing chlorophyll also contained starch, which is a product of photosynthesis. Thus, the parts of the leaf containing chlorophyll performed photosynthesis. The parts of the leaf lacking chlorophyll lacked starch. Hence, these parts of the leaf did not perform photosynthesis.

###26.6.6 Additional Practicals

**To test if light is required for photosynthesis:**

Take a live plant, and leave it in the dark for 24 hours to destarch all leaves. Then, cover some of its leaves with cardboard or aluminum foil, while leaving others uncovered. Let the plant sit in bright light for several hours. Give each group of students one leaf that was covered in cardboard, and one leaf that was uncovered. Have them use the procedure above to test for starch. They should find that the covered leaf contains no starch, while the uncovered leaf contains starch.

A cool variation on this experiment is to cover leaves with pieces of cardboard that have letters or pictures cut out of them. The area where the cardboard is cut out will perform photosynthesis and produce starch. When the students do a starch test, a blue-black letter or picture will appear on the leaf.

**To prove that oxygen is a product of photosynthesis:**

This experiment requires a water plant. Basically, place a live water plant under water*, then cover it with an inverted funnel. Place an upside-down test tube filled with water on top of the funnel. Let the plant sit in bright light until the water in the test tube is displaced and the test tube fills with gas. Use a glowing splint to test the gas – if it is oxygen, it will relight the splint.

**Note:** some books suggest putting sodium bicarbonate (baking soda) in the water.