PSLE Science 2025 – 400 Free Practice Questions to Pass the Exam

The carbon cycle describes the movement of carbon among different reservoirs on Earth, which include the atmosphere, oceans, soil, and living organisms. Photosynthesis, respiration, and decomposition are all integral processes in this cycle.

Photosynthesis is how plants and certain organisms convert carbon dioxide from the atmosphere into organic matter, using sunlight as energy. This process is fundamental to the carbon cycle as it transforms carbon into a form that can be consumed by living organisms.

Respiration occurs in animals and plants when they convert organic matter back into carbon dioxide, returning it to the atmosphere. This process is essential for releasing energy stored in organic compounds and is another key part of the carbon cycle.

Decomposition involves the breakdown of dead organic material by decomposers such as fungi and bacteria, which release carbon back into the soil and atmosphere as carbon dioxide. This recycling of matter ensures that carbon is continuously cycled through the ecosystem.

On the other hand, evaporation does not play a role in the carbon cycle. It pertains to the water cycle, where water changes from liquid to vapor and moves into the atmosphere. Thus, it does not contribute to the movement of carbon within Earth’s systems, making it the correct answer for the component that is not part of the carbon cycle.