Question

Assertion: Open circulatory system is found in most arthropods.
Reason: Arthropods contain haemolymph which directly bathes internal tissues and organs.
A. If both the assertion and reason are true and reason is the correct explanation of the assertion.
B. If both the assertion and reason are true but the reason is not a correct explanation of the assertion.
C. If the assertion is true but the reason is false.
D. If both the assertion and reason are false.

Answer 1

Hint: Haemolymph is a colorless fluid plasma with the haemolymph cells known as haemocytes. Haemolymph in invertebrates is similar to the blood in vertebrates.

Complete Answer:
The open circulatory system refers to the circulatory system where the blood is not enclosed within the arteries and veins and flows directly through the cavities which bathe the internal tissue and organs. Arthropods show an open circulatory system where the poorly developed blood vessels are found in an open space known as Haemocoel.

Haemocoel also contains all the visceral organs of Arthropods. Arthropods include insects like honeybees, silkworms and vectors like anopheles mosquitoes, Culex mosquitoes, pests like locusta and living fossil like king crab, etc

Option(A): The assertion and reason both are true and the reason is the correct explanation of the assertion, Therefore this is the correct option.

Additional Information:
- Mollusks are not Arthropods but they also show a Hemolymphatic circulatory system.
- Haemocyte cells play a great role in the immune system of the Arthropods.
- Heart of Arthropoda shows an opening called Ostia through which hemolymph flow takes place.

Note: Haemolymph contains haemocyanin which is a copper-based protein that gives a blue color to the haemolymph when it is oxygenated, when it is not oxygenated it loses blue color and appears greyish. It does not have a red color blood-like appearance because they lack an iron-based protein called haemoglobin.