The primary mechanism of energy storage in plants is through the synthesis of starch, a polysaccharide composed of glucose units. Starch is primarily stored in specialized plant tissues such as roots, seeds, and leaves. During photosynthesis, plants convert sunlight into chemical energy, producing glucose, which can be linked together to form starch for long-term energy storage. When energy is needed, plants can break down starch into glucose, facilitating metabolic processes and growth.