Question

The important feature of a four chambered heart is/are:
A. The left half is completely separated from the right by a septa.
B. Prevents oxygenated and deoxygenated blood from mixing.
C. Allows a highly efficient supply of oxygenated blood to all parts of the body.
D. All of the above.

Answer 1

The four chambers in the heart are there to meet the needs of the complex body in which they are present. Simple organisms have 2 or 3 chambered hearts but in the case of higher organisms 4 chambered hearts are present which is divided by walls in which blood is safely collected without intermixing.

Complete answer:
First heart-like organ is said to appear around 500 million years ago and since then it has undergone many changes as a part of evolution. Primitive structure of the heart was a single layered tube like structure that can expand and contract in an open circulatory system. This single layered tube like structure has evolved into a more powerful double layered four chambered heart. Four chambered hearts can load and unload large volumes of blood in a closed and valved circulatory system being the centre of the circulatory system. Its primary aim is to pump blood through the pulmonary and systemic network of blood vessels that are laid throughout the body.
A four chambered heart is divided into right and left half with the help of septa, these halves are further divided into upper and lower chambers. The upper chambers are known as atria and the lower chambers are known as ventricles. The upper chambers (atria) are divided into left and right atrium with the help of interatrial septum and the lower chambers (ventricles) are divided into left and right by interventricular septum. The atrium and ventricle are separated with the atrio-ventricular septum. Each septa has openings by which the chambers on the same sides are connected. Right atrium and right ventricle have a tricuspid valve in the atrio-ventricular septum and the left side atrium and ventricle have a bicuspid valve. These valves allow the flow of blood only in one direction that is from atria to ventricle and from them to pulmonary aorta and not in the opposite direction. The chambers prevent the intermixing of blood as the right atrium receives deoxygenated blood from the body organs except the lungs and the left atrium oxygenated blood from the lungs which is further passed on to the body.
Thus, the right option is D.

Additional information:
- Tube like heart (found in Tunicates) which was the primitive heart evolved to two chambered heart with one atria and one ventricle (found in Gnathostome fishes), three chambered heart with two atria and one ventricle (found in amphibians) and finally four chambered heart with two atria and two ventricle.
- The walls of the ventricles are thicker than that of atria.
- Entire heart is made of cardiac muscles.

Note: All the higher organisms including birds, amphibians like crocodiles and other terrestrial animals including humans have evolved the four chambered heart due to the increased requirement of oxygen by the large bodies which can be met only by such structure of heart which can continuously pump oxygen to the complete body.