Answer:
4 Charles Darwin was not able to explain the variation
Answer:
The correct answer is 4.ecosystem.
Explanation:
An ecosystem is a system, that is, a set of elements that interact with each other, in which such elements are: physical environment, living beings and their interactions (predator-prey, parasite-host, competition, symbiosis, pollination, distribution of seeds , etc.) The interrelation between living beings (competition, parasitism, etc.) occurs through cycles of matter and energy flows on which the functioning of the entire ecosystem depends.
B, hormones that serve as chemical messengers im not 100% sure though
The answer is The Doppler Effect. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.
Answer:
lungs:
The blood first enters the right atrium.
The blood then flows through the tricuspid valve into the right ventricle.
When the heart beats, the ventricle pushes blood through the pulmonic valve into the pulmonary artery.
The pulmonary artery carries blood to the lungs where it “picks up” oxygen.
It then leaves the lungs to return to the heart through the pulmonary vein.
The blood enters the left atrium.
It drops through the mitral valve into the left ventricle.
The left ventricle then pumps blood through the aortic valve and into the aorta. The aorta is the artery that feeds the rest of the body through a system of blood vessels.
Blood returns to the heart from the body via two large blood vessels called the superior vena cava and the inferior vena cava. This blood carries little oxygen, as it is returning from the body where oxygen was used.
The vena cavas pump blood into the right atrium and the cycle begins all over again.