During reduction, PGA reacts with ATP and NADPH. What does ATP contribute to the reaction?

The Answer is Electrons

ATP also is known as adenosine triphosphate, refers to a molecule found in the cells of all the living species. It is considered to be very essential as it helps in transporting the energy that plays an essential role in all the cellular metabolic activities.  The mentioned reaction is the second step of the Calvin cycle, also termed as reduction step. During the process, the electrons from NADPH and ATP are transferred to 3-PGA, which further gets reduced to produce G3P or glyceraldehyde-3-phosphate. Thus, ATP is providing electrons in the mentioned reaction.  

your body is trying to warm itself up. or more precisely, sensors in your skin send messages to your brain to generate heat to your body.