Final answer:
The substance formed from photosynthesis that serves as an energy source for cellular respiration is glucose. It is option b. Glucose.
Step-by-step explanation:
Photosynthesis takes carbon in from the atmosphere and uses it to form glucose, the energy source for all plants and animals to use in cellular respiration.
The correct answer to the question is option b. Glucose. This process can be summarized in the equation: carbon dioxide + water → glucose + oxygen, in the presence of sunlight. While oxygen is released as a byproduct, glucose is the main product of photosynthesis that acts as a source of energy for plants and is vital for cellular respiration in both plants and animals.