What is a serving size? How is it determined? Are they the same for every food?

A serving size is the amount of food that you should eat. It’s determined by how nutritional a food is. If it is healthy and has less calories, it’s serving size would be larger than if it was unhealthy will more calories. Serving sizes are not the same for every food because each food has its own nutritional values and calories.

Covalent bond is the correct answer

Although i don't know what is the simulated system, starfish are predators that eat mostly  microalgae,  snails, sponges, bivalves, mussels and other small marine animals. removing starfish from any system would definitely increase this animals that they prey.