One of the following can retain a large amount of urea in the blood and tissue fluid-
(a) Mammals including man
(b) Toad, frog, prawn
(c) Sharks, electric ray, sting ray
(d) Alligators, terrapins, turtles

Options

A. Mammals including man
B. Toad, frog, prawn
C. Sharks, electric ray, sting ray
D. Alligators, terrapins, turtles

Answer

To solve the question of which organism can retain a large amount of urea in the blood and tissue fluid, we will analyze each option provided:

**Step 1: Understand Urea Retention**
- Urea is a nitrogenous waste product that is typically excreted by organisms. However, some organisms can retain urea for various physiological reasons, including osmoregulation.

**Step 2: Analyze Option (a) Mammals including man**
- Mammals, including humans, primarily excrete urea through urine and do not retain significant amounts in their blood or tissue fluid. Therefore, this option is not correct.

**Step 3: Analyze Option (b) Toad, frog, prawn**
- Amphibians like toads and frogs, as well as crustaceans like prawns, typically excrete urea and do not retain it in large amounts. Thus, this option is also incorrect.

**Step 4: Analyze Option (c) Sharks, electric ray, sting ray**
- Sharks, electric rays, and stingrays are known to retain a large amount of urea in their blood and tissue fluid. This retention helps them in osmoregulation, allowing them to maintain osmotic balance in their marine environment. This option is correct.

**Step 5: Analyze Option (d) Alligators, terrapins, turtles**
- While reptiles such as alligators, terrapins, and turtles have adaptations for water conservation, they do not retain large amounts of urea in their blood. They excrete nitrogenous waste primarily in the form of uric acid. Therefore, this option is incorrect.

**Conclusion:**
The correct answer is (c) Sharks, electric ray, sting ray, as they can retain a large amount of urea in their blood and tissue fluid.

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