from food to maintain a core temperature, in the case of humans that temperature is around 37 degrees Celsius. As the process requires a lot of energy, the animal has to eat more food. This also means that they have to eat a lot to put on weight. A cold blooded animal will use the sun to warm it up, and so all it needs to do is bask, or lie in the sun until it's blood is warm enough for it to move around. As this method requires no effort on the part of the animal, they don't need to eat as much as a mammal does to get warm. When the sun goes down, the cold blooded creatures stop moving around as they cool. The mammals, not dependant on the sun, can hunt at night. The suns energy cannot turn into mass.... but it can give the energy fr the mass to move around and reorganize themselves into different ways. For example the sun powers the reaction where carbon dioxide and water become sugar. These sugars make up the hard parts of plants. THese plants are eaten by larger animals, and may mak up some of their mass... I would recomend picking up a very general book on concepts like thermodyamic law, atomic law and maybe get an idea how the sun actually provides energy for life. as not all of the sun hits plants so cannot be used in photosynthesis to make glucose, some sun misses the