They rarely tact with any other elements
The digestion of the food in humans begins in the mouth. In the mouth, the salivary amylase enzyme digests and breaks down a small amount of the starch present in the food. The digestion process begins right in the mouth. and continues till the intestine. The carbohydrates (starch) are the ones whose digestion starts in the mouth.
Hence, the blanks can be filled with 'mouth and amylase' respectively.
Overproduction - An organism gives birth to too many children
Genetic Variation - The offspring each have genetic differences in appearance, behavior, etc
Struggle to Survive - Offspring must fight in order to gain essential resources (food, water, mates, etc)
Successful Reproduction - Organism produces offspring with beneficial adaptations that aid in survival
