Problem 141 - Objective Biology for NEET

Question

Assertion: Blood of insects is colourless. Reason: The blood of insect does not play any role in transport of oxygen.

Step-by-Step Solution

Answer

The assertion and the reason are correct. Insects have a different respiratory system which allows oxygen to be transported directly to the tissues without requiring hemoglobin, which results in their blood being colorless.

Step 1: Understanding Basic Biology

In many animals, including humans, the oxygen-carrying protein hemoglobin gives blood its red color. Insects do not possess hemoglobin; instead, they possess a different type of circulatory system in which oxygen is directly transferred to the body cells.

Step 2: Explore Insect Physiology

Insect's blood, called hemolymph, unlike human's blood, does not need to transport oxygen. They have a different respiratory system, the tracheal system, which carries oxygen directly to their tissues. This hemolymph is primarily responsible for nutrient transport, and it does not have iron-rich hemoglobin, hence it is colorless.

Step 3: Connection and Conclusion

As we have learned, the assertion is correct, insect blood is colorless and the reason given is also correct. The primary function of insect blood does not involve oxygen transportation, hence it lacks the red pigment associated with oxygen carriage in many other animals.

Key Concepts

Hemolymph

Insects have a unique form of blood called hemolymph. Unlike human blood, which is red due to the oxygen-carrying protein known as hemoglobin, insect hemolymph is usually colorless. This is because it doesn't contain hemoglobin or similar proteins that bind to oxygen.

The primary role of hemolymph is to distribute nutrients throughout the insect's body. It also plays a role in removing waste products from the cells and helping in immune responses.

Therefore, hemolymph functions more like a delivery system for nutrients and aids in metabolic waste management rather than oxygen transportation. This is a key difference between insect circulatory systems and those of many other animals, including humans.

Tracheal System

Insects breathe using a specialized respiratory system known as the tracheal system. This system is a network of tubes that allows air to flow directly to and from cells.

Structure of the Tracheal System:

• Tracheae: Large tubes that branch throughout the insect's body.
• Tracheoles: Smaller tubes that extend from the tracheae directly to individual cells.
• Spiracles: Openings on the body surface that allow air to enter and leave.

The tracheal system bypasses the need for a blood-based oxygen transport system. Air enters through the spiracles and travels through tracheae and tracheoles directly to cells. This direct delivery system makes insect respiration incredibly efficient, with oxygen spreading quickly to all necessary areas without needing hemolymph as a carrier.

Oxygen Transport in Insects

Insects do not rely on their blood for oxygen transport, unlike vertebrates. Instead, the tracheal system provides a direct route for oxygen to travel to tissues and cells.

Efficiency of Oxygen Transport:

• Direct oxygen delivery reduces the reliance on circulatory systems.
• Insect muscles and tissues receive oxygen rapidly, supporting their active lifestyles.
• The absence of hemoglobin means less energy is used for transporting oxygen.

This system ensures that even during high activity levels, such as flying, insects receive the oxygen necessary to meet their metabolic demands. This efficiency is one reason insects can thrive in various environments with varying oxygen levels.