USA Biology Olympiad (USABO) Practice Exam

Which of the following statements is invalid regarding a glass bottle containing plants and animals sealed for three months?

1. No energy has entered the bottle from the outside

2. The plants are not using photosynthesis

3. The animals are relying solely on the plants for oxygen

4. The carbon dioxide level increased significantly

The correct answer is: No energy has entered the bottle from the outside

The statement that "no energy has entered the bottle from the outside" is considered the invalid one because in any closed system that includes plants, light energy from the sun can still penetrate through transparent materials like glass. This energy facilitates photosynthesis in plants, allowing them to convert solar energy into chemical energy, generating oxygen as a byproduct. Even though the system is sealed for three months, provided there is sunlight, the plants can utilize that energy, contradicting the assertion that no energy has entered the bottle. Other options present logical outcomes based on the scenario. If the plants are in a closed environment and receiving sunlight, they would still engage in photosynthesis. However, if conditions are limited, such as reduced light or nutrients, their activity could be affected, leading to alternative scenarios put forth in the other statements. The animals relying solely on the plants for oxygen makes sense in this closed system, where the plants are the primary source of oxygen production through photosynthesis. The increase in carbon dioxide levels is also plausible as animal respiration can produce carbon dioxide, which may accumulate due to a lack of sufficient photosynthetic activity or limited ability of plants to process what's available in a sealed environment. Hence, they reflect the expected biological interactions within the closed system.