_________ are circular and biconcave for easy passage through blood capillaries and to transport oxygen.
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. Red blood cells (RBCs) .
Red blood cells (RBCs), also known as erythrocytes, are circular and biconcave in shape. This unique structure increases their surface area-to-volume ratio, which facilitates efficient gas exchange, especially the absorption and release of oxygen. The biconcave shape also provides flexibility, allowing RBCs to squeeze through even the narrowest capillaries without rupturing. These cells contain the protein hemoglobin, which binds to oxygen in the lungs and delivers it to tissues throughout the body. The absence of a nucleus in mature RBCs provides more space for hemoglobin, enhancing their oxygen-carrying capacity. Thus, their shape is crucial for their function.
Other Options:
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Guard cells – Found in plant leaves, they regulate gas exchange and transpiration, not involved in blood transport.
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Nerve cells – Have a long, branched structure for transmitting nerve signals, not for transporting oxygen.
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White blood cells – Irregular in shape and involved in immune defense, not primarily in oxygen transport.