Incomplete Double Circulation System in Toad and Lizard

To understand why the correct answer is option 'D' (Toad and lizard), let's first discuss what a double circulation system is.

Double circulation is a circulatory system found in some animals, including mammals and birds, where blood is pumped twice through the heart in one complete circuit of the body. It consists of two separate circuits: the pulmonary circuit and the systemic circuit.

1. Pulmonary Circuit:
- In this circuit, blood is pumped from the heart to the lungs (or gills) for oxygenation and returns to the heart.
- The heart pumps deoxygenated blood from the right atrium to the right ventricle, which then pumps it to the lungs.
- In the lungs, the blood gets oxygenated and returns to the heart, entering the left atrium.

2. Systemic Circuit:
- In this circuit, oxygenated blood is pumped from the heart to the rest of the body and returns to the heart.
- The oxygenated blood in the left atrium is pumped to the left ventricle, which then pumps it to the rest of the body.
- After delivering oxygen to the tissues, the blood returns to the heart, entering the right atrium.

Now, let's analyze the given options:

a) Frog and crocodile:
- Both frogs and crocodiles have a complete double circulation system.
- They have a four-chambered heart, which allows separation of oxygenated and deoxygenated blood.

b) Shark and whale:
- Sharks and whales have an incomplete double circulation system.
- They have a two-chambered heart, with one atrium and one ventricle.
- The mixing of oxygenated and deoxygenated blood occurs in their heart, which reduces the efficiency of oxygen delivery to the tissues.

c) Lizard and pigeon:
- Pigeons have a complete double circulation system.
- They have a four-chambered heart similar to mammals and birds.
- Lizards, on the other hand, have an incomplete double circulation system.
- They have a three-chambered heart, consisting of two atria and one ventricle.
- The ventricle in lizards has a partial septum, which allows some mixing of oxygenated and deoxygenated blood.

d) Toad and lizard:
- Toads have an incomplete double circulation system.
- They have a three-chambered heart, similar to lizards.
- The ventricle in toads also has a partial septum, allowing some mixing of oxygenated and deoxygenated blood.

Therefore, the correct answer is option 'D' (Toad and lizard) as both toads and lizards have an incomplete double circulation system with a three-chambered heart and a partial septum in the ventricle.

Incomplete Double Circulation System- Incomplete double circulation is a type of circulatory system where the blood passes through the heart twice during one complete circulation, but the oxygenated and deoxygenated blood gets partially mixed in the heart.- This type of circulation is common in reptiles (except crocodiles) and amphibians.Answer Explanation- Option A (Frog and crocodile): Frog has an incomplete double circulation system, but crocodile has a complete double circulation system.- Option B (Shark and whale): Shark has a single circulation system, while whale has a complete double circulation system.- Option C (Lizard and pigeon): Lizard has an incomplete double circulation system, but pigeon has a complete double circulation system.- Option D (Toad and lizard): Both toad and lizard have an incomplete double circulation system.Therefore, the correct answer is Option D (Toad and lizard).