I honestly think it is D. Impulses.
Answer:
Walls are thin.
Inner surface is moist.
Tissues are filled with blood vessels.
Exposed to air
Explanation:
Answer:
restrict population growth
Answer:
Cyanobacteria were photosynthetic and slowly changed the earth's atmosphere from CO2 rich to O2 rich. Photosynthetic cyanobacteria evolved by 3.5 billion years ago and greatly modified earth's atmosphere.