Massachusetts Comprehensive Assessment System (MCAS) Biology Practice Test

What is the primary source of energy utilized by plants in the process of making sugar?

1. Water

2. Light energy

3. Carbon dioxide

4. Soil nutrients

The correct answer is: Light energy

The primary source of energy utilized by plants in the process of making sugar is light energy. During photosynthesis, plants capture light energy from the sun, using chlorophyll in their chloroplasts to convert it into chemical energy. This light energy drives the chemical reactions that combine carbon dioxide and water to form glucose, a type of sugar that plants use as a source of energy and as a building block for growth. While water and carbon dioxide are essential raw materials in this process, they do not provide the energy needed for the chemical reactions to take place. Soil nutrients support plant health and growth but do not directly contribute energy in the sugar-making process. Thus, the correct answer focuses on the critical role of light energy in enabling plants to synthesize sugars through photosynthesis.