Ontario Grade 9 Science Practice Exam 2025 – Complete Study Resource

The transformation of chemical energy in food into usable energy occurs through cellular respiration. This biochemical process takes place in the cells of living organisms, where glucose and oxygen are broken down to produce energy in the form of adenosine triphosphate (ATP). During cellular respiration, cells convert the stored energy in food (particularly carbohydrates) into a form that they can use to power various cellular functions. This process is vital for maintaining life, as it supplies the necessary energy for growth, repair, and maintenance of cellular activities.

Photosynthesis, on the other hand, is the process by which plants and some other organisms convert light energy into chemical energy stored in glucose. While related, it occurs in the chloroplasts of plant cells and is not the process that transforms the energy in food into usable energy.

Combustion refers to the chemical reaction that occurs when substances react rapidly with oxygen, releasing heat and light, and does not involve the biological conversion of food into energy.

Fermentation is an anaerobic process that also converts sugar into energy, but it does not fully break down glucose and produces by-products such as alcohol or lactic acid rather than ATP as efficiently as cellular respiration does. Therefore, while fermentation contributes to energy production, it is not the