Practical 9.2 Investigation of the effect of light intensity on gas exchange in plants

Summary

This experiment demonstrates how light exposure affects the process of photosynthesis in plants. The setup involves four boiling tubes labeled A to D, each containing 10 cubic centimeters of hydrogen carbonate indicator. A green leaf is placed in each of tubes B to D, with varying light conditions: bright light, wrapped in muslin, or wrapped in aluminum foil. After five hours, the tubes are unwrapped, and the changes in the hydrogen carbonate indicator are recorded to observe the impact of light on photosynthesis.

Takeaways

• 😀 Label four boiling tubes A to D.
• 😀 Add 10 cubic centimeters of hydrogen carbonate indicator into each tube.
• 😀 Tie three freshly picked green leaves with threads and place one leaf into each of tubes B to D.
• 😀 Stopper the tubes after placing the leaves inside.
• 😀 Wrap tubes B and C with muslin, and tube D with aluminum foil, to create different light conditions.
• 😀 Leave the setup under bright light for about five hours.
• 😀 Remove the wrappings from the tubes after the time period.
• 😀 Observe changes in the hydrogen carbonate indicator.
• 😀 Record the results of the experiment in a table.
• 😀 The setup is designed to investigate the effect of light on the leaves' ability to influence the hydrogen carbonate indicator.

Q & A

What is the purpose of labeling the boiling tubes A to D?

Labeling the tubes ensures that each experimental condition can be identified clearly and compared accurately after observations are made.

Why is hydrogen carbonate indicator added to each boiling tube?

Hydrogen carbonate indicator is used to detect changes in carbon dioxide concentration, which helps determine whether photosynthesis or respiration is occurring in each tube.

Why are freshly picked green leaves placed in tubes B to D?

Freshly picked leaves are placed in the tubes to observe how their metabolic processes, such as photosynthesis and respiration, affect CO₂ levels in different light conditions.

What is the purpose of stoppering the tubes?

Stoppering the tubes creates a closed environment, allowing any changes in CO₂ concentration to be attributed solely to the processes inside the tube.

Why is Tube C wrapped with muslin?

Muslin allows light to pass through but reduces its intensity, enabling observation of leaf activity under partial or diffused light.

Why is Tube D wrapped with aluminum foil?

Aluminum foil blocks light completely, allowing the experiment to show how leaves behave in complete darkness, where photosynthesis cannot occur.

Why is the setup placed under bright light for five hours?

Bright light provides the ideal conditions for photosynthesis to take place, allowing noticeable changes in CO₂ levels depending on the tube’s setup.

What changes does the hydrogen carbonate indicator show?

The indicator changes color based on CO₂ concentration: yellow for high CO₂, red for atmospheric levels, and purple for low CO₂.

What result is expected in Tube B, which contains a leaf and full light?

Tube B is expected to turn purple, indicating reduced CO₂ levels due to active photosynthesis.

What result is expected in Tube D, which is wrapped in aluminum foil?

Tube D is expected to turn yellow because the leaf respires in darkness, increasing CO₂ concentration.

Why is a control tube (Tube A) used with no leaf inside?

Tube A provides a baseline for comparison, showing how the indicator behaves when no biological processes are affecting CO₂ levels.

What is the final step in the experiment according to the script?

The final step is to observe the color changes in the indicator and record the results in a table.