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Question Video: Comparing the Production and Use of Carbon Dioxide in Plants and Humans Biology

In humans, carbon dioxide produced by respiration is considered a waste product. Why is the same not completely true for plants?

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Video Transcript

In humans, carbon dioxide produced by respiration is considered a waste product. Why is the same not completely true for plants? (A) This is incorrect, as carbon dioxide is always a waste product. (B) Plants can store carbon dioxide in their vacuoles to provide structural support. (C) Plants can use carbon dioxide as a reactant in photosynthesis to produce glucose. Or (D) plants use carbon dioxide as a source of energy for life processes.

Let’s remove the answer options for now and remind ourselves about respiration in humans and plants. Animals and plants both need energy for their life processes. And they get this energy by carrying out cellular respiration to break down sugars. If we look at the equation for cellular respiration, we can see that it’s the chemical reaction in which glucose and oxygen are converted into carbon dioxide and water, and energy is released.

Firstly, where do these organisms get the glucose and oxygen from? Animals, like us humans, consume carbohydrates in our food, which are then broken down into glucose by enzymes in our digestive system. To get the oxygen we need, we breathe air containing around 21 percent oxygen into our lungs. Plants, on the other hand, cannot eat or breathe, but they do carry out another chemical reaction which humans cannot. This is called photosynthesis. And it’s where water and carbon dioxide are converted into glucose and oxygen using light energy. Glucose and oxygen produced by photosynthesis can then be used for cellular respiration in plants.

Secondly, what do humans and plants do with the products of cellular respiration? While the water and energy are useful to animal cells, they have no need for carbon dioxide. So it is breathed out of the lungs to remove it from the body. This is why carbon dioxide is considered a waste product in humans. However, as we’ve seen, plants can use some of the carbon dioxide produced during cellular respiration as a reactant for photosynthesis. So carbon dioxide cannot be considered a waste product in plants.

We have therefore determined that the correct answer is (C). It is not completely true that carbon dioxide is a waste product in plants because plants can use carbon dioxide as a reactant in photosynthesis to produce glucose.

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