Kaplan Nursing Entrance Practice Exam

Which of the following reactions is typically endothermic?

1. Freezing water

2. Burning wood

3. Photosynthesis

4. Condensation of steam

The correct answer is: Photosynthesis

Photosynthesis is considered an endothermic reaction because it requires the absorption of energy in the form of sunlight to convert carbon dioxide and water into glucose and oxygen. During this process, plants capture solar energy, which is necessary for driving the chemical reactions that occur. This energy is stored in the chemical bonds of the glucose molecule, making photosynthesis an essential process for life on Earth, as it not only provides energy for the plants themselves but also forms the basis of the food chain for other organisms. In contrast, the other options involve processes that release energy. For instance, freezing water involves the release of heat as water transitions from a liquid to a solid state, making it exothermic. Burning wood is a combustion reaction that releases energy in the form of heat and light, also an exothermic process. Condensation of steam similarly releases heat as water vapor transforms into liquid water. Thus, among the given options, photosynthesis is unique in that it requires an input of energy, firmly categorizing it as an endothermic reaction.