AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
If oxygenated and deoxygenated blood mix, the oxygen concentration delivered to body tissues would decrease, reducing the efficiency of energy release — which is essential for warm-blooded mammals with high energy needs.
The examiner wants you to state the consequence of mixing: reduced oxygen supply to body cells, lowering metabolic efficiency. The key phrase from the textbook is "highly efficient supply of oxygen to the body." Mentioning that mammals have high energy needs adds the biological reason, which strengthens a 1-mark answer.