Blood Plasma 

Blood Serum

It is the fluid without blood corpuscles. 

It is faint yellow in colour.

It has fibrinogen and other clotting  materials.

It takes part in blood clotting. 

It is liquid without clotting elements.

It is pale yellow.

It does not have fibrinogen and other clotting materials.

It does not take part in blood clotting.

Open Circulatory System

Closed Circulatory System

Open circulation occurs in arthropods and molluscs.

The blood is not completely enclosed within vessels, the heart pumps blood through arteries into large cavities or sinuses, where it mixes with the interstitial fluid and bathes the cells of the body.

Circulation is slower in an open system, because some of the blood pooled in sinuses and, the heart is unable to build up enough pressure to make the blood flow rapidly.

Respiratory pigment,if present, is dissolved in the plasma, no red corpuscles are present.

It occurs in annelids (earthworms), some molluscs and all vertebrates.

In closed circulatory system, materials move between the blood and interstitial fluid through thin walls capillaries.

Blood flows at a high pressure in a closed circulatory system.

Respiratory pigment is present which may be dissolved in the plasma but is usually contained red blood corpuscles.

SA Node

AV Node

It is the small mass of specialised muscle cells in the wall of right atrium near the opening of vena cava.

It initiates and maintains the heart beat.

It is situated in the fibrous ring between the right atrium and ventricle of the heart.

It is the pathway through, which electrical impulses can pass.