You have a large, healthy philodendron that you carelessly leave in total darkness while you are away on vacation. You are surprised to find that it is still alive when you return. What has the plant been using for an energy source while in the dark?

• A. Even though it cannot carry out the light reactions, the plant can still produce sugars because the Calvin cycle does not require light.
• B. Even though the plant received no visible light, it was able to use the short-wave part of the electromagnetic spectrum (gamma rays and X-rays) to carry out photosynthesis.
• C. When light energy is not available, plants can derive energy from inorganic molecules.
• D. None of the listed responses is correct.
• E. While it did have access to light, the plant stored energy in the form of sugars or starch, and it was able to derive energy from the stored molecules during your vacation.

Answer: (E)

Verified step by step guidance

1. Understand that plants typically rely on photosynthesis to produce energy, which requires light. However, in the absence of light, they must use stored energy.
2. Recall that plants store energy in the form of carbohydrates, such as sugars and starch, during periods when light is available.
3. Recognize that in the absence of light, the plant cannot perform the light-dependent reactions of photosynthesis, but it can still utilize stored carbohydrates.
4. Consider that the plant uses cellular respiration to break down these stored carbohydrates into usable energy (ATP) in the absence of light.
5. Conclude that the plant survived in darkness by metabolizing its stored energy reserves, such as sugars or starch, through cellular respiration.