Rates Of Photosynthesis - GCSE Science Required Practical

Summary

This video demonstrates a practical experiment on photosynthesis, focusing on how light intensity affects the rate of the process. Using pondweed in a sodium hydrogen carbonate solution, the experiment measures oxygen production by counting bubbles from the plant's stem. The independent variable is light intensity, adjusted by changing the distance between the pondweed and a light source. The process is repeated at various distances, and an alternative method to collect and measure oxygen is also introduced. The aim is to understand photosynthesis rates and confirm oxygen production using a glowing splint test.

Takeaways

• 🌱 Photosynthesis is a biological process where green plants use carbon dioxide, water, and light energy to produce glucose and oxygen.
• 💡 The practical experiment investigates how light intensity affects the rate of photosynthesis in pondweed.
• 🌊 The experiment uses an aquatic plant (pondweed) placed in sodium hydrogen carbonate solution to promote photosynthesis.
• ✂️ The stem of the pondweed is cut underwater to allow oxygen bubbles to be produced and counted as a measure of the photosynthesis rate.
• 📏 Light intensity is the independent variable and is changed by varying the distance between the light source and the pondweed.
• 🔦 Using an LED light source is preferable to minimize heat, as temperature can also affect the rate of photosynthesis.
• ⏱ The rate of photosynthesis is measured by counting the number of oxygen bubbles produced in one minute.
• 📉 As the distance from the light source increases, the number of oxygen bubbles decreases, indicating a lower rate of photosynthesis.
• 🧪 An alternative method collects the oxygen in a tube, allowing for the volume of gas to be measured or tested with a glowing splint to confirm it's oxygen.
• ⚖️ The bubble counting method assumes all bubbles are of the same size, which could introduce measurement errors, making the collection method more accurate.

Q & A

What is the main biological process being discussed in the script?

The main biological process discussed is photosynthesis, where green plants use carbon dioxide and water in the presence of light energy to produce glucose and oxygen.

What plant is used in the experiment to demonstrate photosynthesis?

The plant used in the experiment is a common aquatic plant called pond weed, which is easily available from pet shops or garden centers.

What role does sodium hydrogen carbonate play in the experiment?

Sodium hydrogen carbonate is added to the water in the boiling tube to encourage the pond weed to photosynthesize by providing a source of carbon dioxide.

How is the rate of photosynthesis measured in the experiment?

The rate of photosynthesis is measured by counting the number of oxygen bubbles produced from the cut stem of the pond weed over one minute.

What is the independent variable in this experiment?

The independent variable in the experiment is light intensity, which is adjusted by changing the distance between the pond weed and the light source.

Why is it recommended to use an LED light source for this experiment?

An LED light source is recommended because it emits less heat, ensuring that only light intensity is changed without affecting the temperature, which could also impact the rate of photosynthesis.

What is the purpose of cutting the pond weed's stem underwater?

The pond weed's stem is cut underwater to ensure a steady release of oxygen bubbles from the cut end, which can then be easily counted to measure the photosynthesis rate.

What is the effect of increasing the distance between the light source and the pond weed?

As the distance between the light source and the pond weed increases, the number of oxygen bubbles produced decreases, indicating a lower rate of photosynthesis.

What is an alternative method mentioned for measuring the rate of photosynthesis more accurately?

An alternative method involves collecting the oxygen gas produced under a glass funnel in a beaker and measuring its volume using a boiling tube, providing a more accurate measure of oxygen production.

How can the gas collected during the experiment be confirmed as oxygen?

The gas collected during the experiment can be confirmed as oxygen by performing the glowing splint test, where the gas relights a glowing splint, indicating it is oxygen.