Video Transcript
A diagram linking the processes of photosynthesis and respiration in plants is
provided, with two key molecules removed. Which of the following correctly replaces 1 and 2? (A) 1 oxygen, 2 carbon dioxide; (B) 1 carbon dioxide, 2 oxygen; (C) 1 hydrogen, 2
glucose; or (D) 1 water, 2 hydrogen.
Our question deals with the processes of photosynthesis and cellular respiration. The prefix photo- means light, and synthesis means to create. This reminds us that photosynthesis is how plants, algae, and some protists create
their own food in the presence of light energy.
The process takes place in the plant’s chloroplasts. These special organelles are only found in photosynthetic organisms. Here, the pigment chlorophyll absorbs specific wavelengths of sunlight, allowing
carbon dioxide and water to be converted into glucose and oxygen.
Cellular respiration is a process that breaks down sugars to produce energy. It occurs in organelles called mitochondria, which are found in nearly all eukaryotic
organisms. Plants use a type of respiration called aerobic respiration, in which glucose must be
broken down in the presence of oxygen. The result is the production of energy in the form of ATP and the release of carbon
dioxide and water. Take a look at the basic equations for these two critical processes. What do you notice?
Hopefully, you spotted an interesting feature, namely, that two of the products of
aerobic respiration are actually the reactants of photosynthesis, and vice
versa. Now, let’s take a closer look at the provided diagram to determine the correct answer
to our question.
We first need to figure out the correct molecule to replace the number 1. It needs to be a product of photosynthesis and a reactant of respiration. We’ve just learned that oxygen and glucose are produced during photosynthesis and are
also required for aerobic cellular respiration. Glucose is already filled in on the diagram, so number 1 can be correctly replaced by
oxygen.
To replace the number 2, we need to find a molecule that is a product of respiration
and a reactant of photosynthesis. We know that respiration produces carbon dioxide and water, while photosynthesis
requires these two molecules. Water is already filled in on the diagram, so the number 2 can be correctly replaced
by carbon dioxide.
Therefore, the correct answer is (A). The numbers 1 and 2 in the diagram can be correctly replaced by the key molecules
oxygen and carbon dioxide.
