protons, neutrons, and electrons
The answer to your question is:
<span>Facilitated diffusion</span>
Answer:
Oxygen levels are generally thought to have increased dramatically about 2.3 billion years ago. Photosynthesis by ancient bacteria may have produced oxygen before this time. ... In addition, early plants and algae began to release oxygen at a faster rate. Oxygen levels then showed a dramatic increase.
The answer is D homeostasis. For A, hemoglobin is a protein exists in blood and can bring oxygen. For B, photosynthesis is a process of converting CO2 to glucose using the energy of light. It occurs in chloroplast. For C, hypothesis means suppose.