Animal cells combine to form tissues, organs, and organ systems that allow organisms to carry out life functions. Adaptations like panting in dogs and long necks in giraffes allow animals to obtain food, regulate internal conditions, and move in their environments. All animals must obtain food, either by eating plants as herbivores, meat as carnivores, or both as omnivores. Humans are omnivores. Animals reproduce both sexually through fertilization of egg and sperm cells that combine traits from both parents, and asexually through single organisms splitting to form identical new organisms.