Limiting Factors of Photosynthesis

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  • 0:03 Photosynthesis
  • 0:33 Limiting Factors
  • 3:05 So What About Water?
  • 3:44 Interaction of Factors
  • 4:16 Lesson Summary
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Lesson Transcript
Instructor: Lauren Posey

Lauren has taught intermediate reading in an English Language Institute, and she has her Master's degree in Linguistics.

In this lesson, you'll learn about the major factors that can limit the rate of photosynthesis: carbon dioxide level, light intensity, and temperature. Test what you learned with the quiz following the lesson.

Photosynthesis

When people are low on energy, our bodies tell us that we're hungry, and we eat to gain energy. But what if, instead of reaching for a granola bar, you went outside and turned your face up to the sun to recharge? If that were true, you would be like the vast majority of plants on Earth, which gain energy through a process known as photosynthesis. In photosynthesis, organisms use light energy to transform carbon dioxide and water into glucose that they can use as fuel to grow and live.

Limiting Factors

There are a number of factors that interact to make the process of photosynthesis work. Any one of these could become a limiting factor. This means that the factor directly affects the rate of photosynthesis on its own, regardless of the level of the other factors. The major limiting factors for photosynthesis are light intensity, temperature, and carbon dioxide levels.

Light Intensity

Since photosynthesis cannot begin without light, it is the first limiting factor. Plants use chlorophyll, usually found in their leaves, to absorb sunlight. The light energy from the sun is what fuels the reactions that transform carbon dioxide and water into glucose and oxygen. Without light, photosynthesis is impossible.

As sunlight hits more of the chlorophyll molecules, the rate of photosynthesis increases. At a certain light level, the rate tends to stop increasing due to a different limiting factor. At extremely high light levels, the rate might even decrease as the chlorophyll molecules become damaged. This level varies from plant to plant, which is why some plants need to be kept in the shade, whereas others do perfectly well in direct sunlight.

Temperature

Living organisms use enzymes, protein molecules, to assist in carrying out the reactions necessary to bind and store glucose. The rate at which these enzymes work is affected by temperature, which makes temperature another major limiting factor.

The optimal temperature is between 10-20 degrees C (50-68 degrees F), though this can vary widely depending on the plant type. At very low temperatures, the enzymes cannot function properly, and so the rate of photosynthesis decreases. The same is true at high temperatures.

At extremely high temperatures (above 40 degrees C/104 degrees F) the enzymes can even become denatured or damaged, which sharply decreases the rate of photosynthesis. As you can see, too much or too little of many factors in the photosynthesis process can be a major problem!

Carbon Dioxide Concentration

Another limiting factor is carbon dioxide concentration. Carbon dioxide and water are what the plant converts into glucose, and so without enough carbon dioxide, the process cannot occur.

As levels of carbon dioxide increase, the rates of photosynthesis also increase. This only goes up to a certain point, when the plant has reached its maximum rate of photosynthesis. Unlike some of the other factors, an excess of carbon dioxide does not negatively affect the plant: it simply reaches a point where it cannot process the molecule any faster.

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