Heart rate is controlled by the two branches of the autonomic (involuntary) nervous system. The sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). The sympathetic nervous system (SNS) releases the hormones (catecholamines - epinephrine and norepinephrine) to accelerate the heart rate. The parasympathetic nervous system (PNS) releases the hormone acetylcholine to slow the heart rate. Such factors as stress, caffeine, and excitement may temporarily accelerate your heart rate, while meditating or taking slow, deep breaths may help to slow your heart rate.
To breathe, they use the <span>the carbon dioxide. Carbon dioxide is the main element which help the organisms to breathe.</span>
<span>The answer is A because it is true that these three stages consist the aerobic respiration.</span>
i think the correct answer is B considering that the channels are not always open for the protons to freely diffuse through the inner membrane.
