The respiratory systems of birds are very efficient at providing oxygen to the blood, which is necessary for birds to expend the energy necessary to fly. What feature of the bird respiratory system makes it more efficient than the respiratory systems of other animals?

A. a one-way air flow through the lungs and airways
B. a two-way air flow through the lungs and airways
C. bubble-like alveoli for gas exchange in the lungs
D. many tracheal tubes that connect the lungs to the skin

the right answer is a. skin cells forming from sunlight.

the liver is an organ endowed with a fantastic ability to regenerate

. thus, if a hepatectomy (ablation) of 70% of the hepatic mass is performed in the rat, there is complete recovery in 7 to 10 days.

prokaryotes are beings that have existed since the existence of life on earth, and do not come from another realm.

ribosomes are organelles that exist naturally in eukaryotes, either in free form or attached to the endoplasmic reticulum.

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