Exoskeleton
Exoskeleton is a evolutionary innovation. This is operated by muscles attached to it and acts as an armor. Other than support this is an adaptive mechanism to provide protection against predators. In vertebrates, it is considered as the dermal bone that developed via membranous ossification. Fishes retained their exoskeleton in the form of their scales. However, in some organisms terrestrial evolution allows the loss of exoskeleton and formed a more mobile endoskeleton,
C because oxygen was a byproduct of photosynthesis and proved to be EXTREMELY important in the atmosphere.
Prokaryotic cells because they don't have a nuclei.
Answer:
C. levels of specific hormones
Sample Response:
Bacteria are helpful because they produce oxygen, which our bodies need to breathe, and they help us to digest the food we eat. Bacteria are also helpful because they are used in medicine to help us overcome disease. Bacteria are harmful because they can cause tooth decay and illnesses that can be either common or quite serious.
This is a sample response, so it's 100% correct. Peace!
