What type of molecules are ATP and NADPH considered in photosynthesis?

ATP and NADPH are considered energy carriers in photosynthesis because they serve as vital molecules that store and transport energy produced during the light reactions of photosynthesis to the Calvin cycle, where it is used for synthesizing glucose and other carbohydrates.

ATP, or adenosine triphosphate, releases energy when it loses a phosphate group in a process called hydrolysis, which powers various cellular activities. NADPH, on the other hand, functions as a reducing agent, donating electrons in biochemical reactions. Both ATP and NADPH are crucial for converting light energy into chemical energy, directly facilitating the energy transfer necessary for the biological processes of plants.

In contrast, structural molecules do not play this role; they form part of the plant's cellular structure. Waste products are substances that are not utilized further in the process, while respiratory substrates are primarily organic molecules used in cellular respiration to generate ATP, rather than directly involved in photosynthesis. Thus, highlighting their role as energy carriers emphasizes their importance in the photosynthetic process.