What macromolecule made by plants is burned in the mitochondria?

The answer is glucose.

During the process of photosynthesis, using the energy of Sunlight, carbon dioxide and water are converted to glucose and oxygen. This process takes place in the green leaves of plants, in which pigment chlorophyll absorb energy Sunlight which is then converted into chemical energy necessary for the production of glucose. Glucose now enters aerobic respiration, which consists of several stages. First, in glycolysis, glucose in the cytoplasm is broken down to pyruvate which is then transferred to mitochondria during link reaction. Once in mitochondria, it is used in Krebs cycle and electron transport chain reactions and as a result energy, in the form of ATP, is produced.