What is true about hemoglobin

Options

A. It is a dipeptide and present in red blood corpuscles in blood warm
B. It is present in the dissolved state in blood plasma in earthworm
C. It is a dipeptide in mammals and localized in red blood corpuscles
D. It is present in the dissolved state in blood plasma in scorpions

Explanation

### Step-by-Step Solution:

1. **Understanding Hemoglobin**: Hemoglobin is a protein found in red blood cells (RBCs) that is essential for transporting oxygen throughout the body.

2. **Structure of Hemoglobin**: Hemoglobin is not a dipeptide; rather, it is a polypeptide. A dipeptide consists of two amino acids, while a polypeptide is made up of multiple amino acids. Hemoglobin is composed of four polypeptide chains: two alpha chains and two beta chains.

3. **Function of Hemoglobin**: The primary function of hemoglobin is to bind oxygen in the lungs and release it in the tissues. This is crucial for cellular respiration and energy production in the body.

4. **Presence in Organisms**: Hemoglobin is primarily found in vertebrates, including humans. In contrast, some invertebrates, such as earthworms, do not have hemoglobin in their RBCs; instead, they have it dissolved in their blood plasma.

5. **Comparison with Other Proteins**: While hemoglobin is a well-known oxygen-carrying protein, other organisms may use different proteins for similar functions. For example, scorpions use hemocyanin, which is a larger protein than hemoglobin and contains copper instead of iron.

6. **Correct Statement**: The statement that is true about hemoglobin is that it is present in red blood cells and helps bind oxygen. The incorrect statements regarding it being a dipeptide or being present in a dissolved state in blood plasma (in the case of vertebrates) can be eliminated.

### Conclusion:
The correct statement about hemoglobin is that it is a polypeptide present in red blood cells and is essential for oxygen transport.

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