The human heart has four chambers - two atria and two ventricles.
1. Right atrium - receives oxygen-poor blood from the body and pumps it to the right ventricle.
2. Right ventricle - pumps oxygen-poor blood to the heart.
3. Left atrium - receive oxygen - rich blood from the lungs.
4. Left ventricle - pumps oxygen rich blood to the body.
The heart is a muscular organ. It is about the size of a closed fist. It is located in the thoracic cavity. It is protected by the rib cage and is the major organ of the circulatory system.
Explanation: the human heart contains 4 chambers -2 atria and 2 ventricle while a fish contains only 2 chambers- 1 auricle and 1 ventricle.
In humans, the right atrium receives deoxygenated blood and transfers it to right ventricle from where it gets transferred to the blood. Left atrium receives the pure blood and transfers it to left ventricle.
A single molecule is the one that is responsible for initiating a signal transduction pathway. The answer in this question is a single molecule. Molecule is defined as an electrically neutral group of two atoms or more held together by a chemical bonds.
