GCSE Biology Revision "Required Practical 6: Photosynthesis"

Summary

This video demonstrates a practical experiment to investigate how light intensity affects the rate of photosynthesis. By using an LED light source and sodium hydrogen carbonate solution, students can observe oxygen production from pondweed, which occurs due to photosynthesis. The experiment involves varying the light distance and measuring oxygen output. The inverse square law is explained, showing how increasing the distance from the light reduces the light intensity, thus lowering the rate of photosynthesis. The video also addresses practical issues like bubble counting, suggesting using a measuring cylinder for more accurate results.

Takeaways

• 😀 The experiment investigates the effect of light intensity on the rate of photosynthesis.
• 😀 A 10 cm distance from the LED light source is initially set for the experiment.
• 😀 LED lights are used to minimize heat, preventing temperature fluctuations that could impact results.
• 😀 If using a regular light bulb, a beaker of water is placed between the light and the boiling tube to absorb excess heat.
• 😀 Sodium hydrogen carbonate solution is used to release carbon dioxide, which is required for photosynthesis.
• 😀 Pond weed is placed in the boiling tube, and oxygen bubbles are observed as a result of photosynthesis.
• 😀 The number of oxygen bubbles produced is counted in one-minute intervals, with the process repeated for accuracy.
• 😀 To solve the problem of counting bubbles too quickly, the volume of oxygen produced can be measured instead of counting bubbles.
• 😀 A measuring cylinder is used to capture and measure the volume of oxygen produced by the pond weed.
• 😀 The experiment is repeated at different distances: 10 cm, 20 cm, 30 cm, and 40 cm from the light source.
• 😀 The results show that as the distance from the light source doubles, the number of oxygen bubbles per minute decreases by a factor of four, demonstrating the inverse square law.
• 😀 The inverse square law explains how light intensity decreases as the distance from the light source increases, impacting the rate of photosynthesis.

Q & A

What is the purpose of this experiment?

The purpose of this experiment is to investigate the effect of light intensity on the rate of photosynthesis.

Why is an LED light source used in this experiment?

An LED light source is used because it does not release much heat, which could otherwise affect the temperature of the experiment.

What is the function of the sodium hydrogen carbonate solution in this experiment?

The sodium hydrogen carbonate solution releases carbon dioxide, which is needed for photosynthesis to occur.

How is the rate of photosynthesis measured in this experiment?

The rate of photosynthesis is measured by counting the number of bubbles produced by the pondweed in one minute, which represent oxygen being released.

What are the two main problems encountered in this practical?

The two main problems are that the number of bubbles can be too fast to count accurately, and the bubbles are not always the same size.

How can the issues with counting bubbles be solved?

The issues can be solved by measuring the volume of oxygen produced instead of counting the bubbles, using a measuring cylinder to collect and measure the oxygen.

What does the graph of the experiment show?

The graph shows that as the distance from the light source increases, the rate of photosynthesis (measured by oxygen production) decreases.

What is the inverse square law, and how does it relate to this experiment?

The inverse square law states that if the distance from the light source is doubled, the light intensity decreases by a factor of four. This leads to a reduction in the rate of photosynthesis and oxygen production.

What happens to the number of oxygen bubbles when the distance is doubled from 10 cm to 20 cm?

When the distance is doubled from 10 cm to 20 cm, the number of oxygen bubbles produced per minute falls by a factor of four.

What is the key observation related to the inverse square law in this experiment?

The key observation is that the number of oxygen bubbles per minute decreases by a factor of four each time the distance from the light source is doubled (e.g., 10 cm to 20 cm, 20 cm to 40 cm).