Question

Distinguish between open circulation and closed circulation.

Answer 1

	Open circulation		Closed circulation
1.	In open circulation, blood is circulated through the body cavities (haemocoels).	1.	In closed circulation, blood circulates the blood vessels and does not come in direct contact with cells and body tissues.
2.	The blood flows with low pressure.	2.	The blood flows with high pressure.
3.	Exchange of material takes place directly between blood and cells or tissues of the body.	3.	Exchange of material between blood and body tissues is through intermediate fluid called lymph.
4.	It usually does not contain any respiratory pigment like haemoglobin so it does not transport respiratory gases	4.	It contains respiratory pigments like haemoglobin for transportation of respiratory gases.
5.	e.g. Arthropods and molluscs	5.	e.g. All vertebrates, higher molluscs and annelids