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Carbon dioxide levels in the atmosphere have become the subject of international concern in recent years, as demonstrated by the United Nations Climate Change Conference held in Paris in December 2015 - Leaving Cert Agricultural Science - Question d - 2016
Question d
Carbon dioxide levels in the atmosphere have become the subject of international concern in recent years, as demonstrated by the United Nations Climate Change Confer... show full transcript
Worked Solution & Example Answer:Carbon dioxide levels in the atmosphere have become the subject of international concern in recent years, as demonstrated by the United Nations Climate Change Conference held in Paris in December 2015 - Leaving Cert Agricultural Science - Question d - 2016
Step 1
What happens to carbon dioxide during photosynthesis in green plants?
Answer
During photosynthesis, carbon dioxide (CO₂) is absorbed by green plants from the atmosphere. It undergoes a series of chemical reactions in the presence of sunlight and chlorophyll, ultimately resulting in the production of glucose (sugar) and oxygen as by-products. The overall equation for photosynthesis can be represented as:
ightarrow ext{C}_6 ext{H}_{12} ext{O}_6 + 6 ext{O}_2$$ This equation shows that six molecules of carbon dioxide react with six molecules of water to form one molecule of glucose and six molecules of oxygen.Step 2
Step 3
Describe, with the aid of a labelled diagram, a laboratory experiment to show that carbon dioxide is needed for photosynthesis.
Answer
To demonstrate that carbon dioxide is required for photosynthesis, the following experiment can be conducted:
Diagram: The diagram should show a potted plant (A), a plastic bag, a dish containing soda lime (B), and a setup indicating that plant B is placed in a dark environment.
Labels: The labels for the diagram should include:
- Plant
- Plastic bag
- Rubber band
- Dish
- Soda lime
Method:
- Take two potted plants, label them A and B.
- Place plant A under light source and place plant B in a dark environment for about 48 hours.
- Remove plant A and B, ensuring to cover the soda lime dish with a plastic bag by using a rubber band.
- Allow both plants to absorb carbon dioxide from the atmosphere; plant A will have light while plant B will be deprived of carbon dioxide.
- After about two hours, heat leaf samples from both plants in boiling alcohol for 10 minutes to kill them.
- Rinse the leaves with warm water to soften them, and then cover with iodine to test for the presence of starch.
Result:
- For plant A, if starch is present, the iodine will turn blue-black.
- For plant B, there should be no change in color, indicating absence of starch.
Conclusion: This experiment shows that carbon dioxide is essential for photosynthesis, as plant B did not undergo photosynthesis in the absence of CO₂.