Question

Write the features that distinguish between the two

a. Plasma and Serum

b. Open and closed circulatory system

c. Sino-atrial node and Atrio-ventricular node

Answer 1

a. Plasma and Serum

Definition

• Plasma is a clear and yellowish fluid part of the blood.
• Serum is the liquid part of the blood after coagulation and is unable to clot.

Constituents

• Plasma is considered as the medium of blood in which RBCs , WBC and blood platelets are suspended.
• Serum contains proteins, electrolytes, antibodies, antigens and hormones. Plasma without fibrinogen and corpuscles is called serum.

b. Open and closed circulatory system

Criteria Blood flow

• Open circulatory system: In the open circulatory system blood is pumped by heart into a cavity called haemocoel and all the organs and tissues come in direct contact with the blood i.e. the organs and tissues get bathed in the pool of blood.
• Closed circulatory system:In a closed circulatory system, blood flows through a network of vessels.Organs and tissues never come in direct contact with the blood.

Blood vessels

• Open circulatory system: No blood vessels are present.
• Closed circulatory system: Elastic and muscular blood vessels are present.These are arteries and veins.

Exchange of materials

• Open circulatory system: Exchange of materials is direct between blood and tissue cells
• Closed circulatory system:Exchange of materials is indirect between blood and tissue cells with the help of tissue fluid.

Examples

• Open circulatory system: It is present in Arthropods and Mollusks.
• Closed circulatory system: It is present in Annelids and Vertebrates.

c. Sino-atrial node and Atrio-ventricular node

Criteria location

• Sino-atrial node: It is located in the wall of the right auricle near the superior vena cava.
• Atrio-ventricular node: It is located in the wall between the right auricle and right ventricle.

Centre of control

• Sino-atrial node : Cardiovascular centre present in the medulla oblongata controls the S.A. node.
• Atrio-ventricular node: cardiovascular impulses or action potential generated by the S.A. node controls the functioning of the atrio-ventricular node

Function

• Sino-atrial node: It has a property of self excitation and is called the pacemaker of the heart.It spontaneously generates a wave of contraction which spreads to auricles and ventricles.
• Atrio-ventricular node: It does not show the property of self excitation.It passes the wave of contraction generated from the auricles to the ventricles.