The rate of photosynthesis
A pondweed experiment: counting oxygen bubbles to see how light intensity and temperature change the rate of photosynthesis, and what a limiting factor is. With Vietnamese subtitles. A “Check yourself” section with typed questions is below the video on the site.
Practice
- Check yourself: The rate of photosynthesis – Type the missing words, put the steps in order and write a short answer. No multiple choice: you have to remember it. Vietnamese help for every question.
Transcript
To measure the rate of photosynthesis, we use a water plant, such as pondweed. It makes bubbles of oxygen. We count the bubbles in one minute. More bubbles means a faster rate.
We use a lamp as the light source. We change the light intensity by moving the lamp closer or further away. A beaker of water absorbs the heat, so the temperature stays the same.
When the lamp is close, the light is bright, and we count many bubbles. When the lamp is far away, the light is dim, and there are fewer bubbles.
On a graph, the rate increases with light intensity, and then it levels off. At this point, something else is limiting the rate, such as carbon dioxide or temperature. We call this a limiting factor.
Temperature also changes the rate. We use water baths at different temperatures, and we keep the light the same. As the temperature rises, the rate increases, because the enzymes work faster.
Above about forty degrees Celsius, the enzymes are denatured. The rate falls quickly, and the bubbles stop.
Remember. Count the oxygen bubbles. More bubbles means a faster rate. Brighter light speeds up photosynthesis, until another factor is limiting. A warmer temperature speeds it up, until the enzymes are denatured.
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