1. How would you explain that energy in animals' food was once energy

Explanation: That energy inanimals food, used for body repair, growth, motion. It maintain body warmth, once energy from the sun.

The energy released from food was once energy from the sun that was captured by plants in the chemical process that forms plant matter (from air and water). Food provides animals with the materials they need for body repair and growth and the energy they need to maintain body warmth and for motion.