Week 8 Reactions of Life
Task 1 Observation and description of the organs of the Allium cepa
Left Page
Botanical Drawing of a longitudinal section of a Spring Onion with main organs labelled.
(This is an example of a botanical drawing. These three spring onions each have a flower.)
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Right Page
Longitudinal section of the Allium cepaCarefully and neatly cut a longitudinal section to reveal the anatomy of the plant. Draw, identify and label the following organs;
Explain the function of each of these organs in relation to the life process of photosynthesis. Explain the function of each of these organs in relation to the life process of respiration. |
Task 2 Chemical tests to identify some of the carbohydrates produced by plants.
Background
Carbohydrates (sugars and starch) can be detected by the use of an indicator, which is a chemical that produces a characteristic colour when a particular substance is present.
The positive test for glucose is that it turns "brick red when heated with Benedict's Solution.
The positive test for starch is that it turns black when Iodine Solution is added.
Aim: To test the green leaves of the spring onion for glucose and the white stem bases and roots for starch.
Method:
1. In a mortar and pestle grind the green leaf of the spring onion.
Scrape the paste into a test tube. Add two droppers full of Benedict's Solution.
GENTLY heat the mixture.
Note any colour change.
2. In a mortar and pestle grind the white parts of the spring onion.
Scrape the paste into a test tube. Add a few drops of Iodine Solution.
Note any colour change.
SAFETY: Always wear safety goggles when working with chemicals.
Carbohydrates (sugars and starch) can be detected by the use of an indicator, which is a chemical that produces a characteristic colour when a particular substance is present.
The positive test for glucose is that it turns "brick red when heated with Benedict's Solution.
The positive test for starch is that it turns black when Iodine Solution is added.
Aim: To test the green leaves of the spring onion for glucose and the white stem bases and roots for starch.
Method:
1. In a mortar and pestle grind the green leaf of the spring onion.
Scrape the paste into a test tube. Add two droppers full of Benedict's Solution.
GENTLY heat the mixture.
Note any colour change.
2. In a mortar and pestle grind the white parts of the spring onion.
Scrape the paste into a test tube. Add a few drops of Iodine Solution.
Note any colour change.
SAFETY: Always wear safety goggles when working with chemicals.
Results: Record the colour changes in a suitable fashion.
Conclusion: Discuss the results in terms of glucose and starch.
Conclusion: Discuss the results in terms of glucose and starch.
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The image below shows samples of;
- Top row Right to Left: roots, crushed roots, yellow iodine solution, blackish iodine and crushed roots, indicating starch.
- Top row Left to Right: green leaves, blue Benedict's solution, brick-red Benedict's solution and crushed leaves , indicating glucose.