Answer:
The valves The heart has four valves - one for each chamber of the heart. The valves keep blood moving through the heart in the right direction.
Explanation:
it is right hope this helps
Oxygen,carbon,nitrogen and hydrogen hope this helps
It could be underneath a glacier.
Answer:
endosymbiosis.
Explanation:
By the beginning of the 20th century, researchers thought that plastids and mitochondria could come from bacteria. These would have been ingested by primitive cells and live within them in symbiosis.
