<span>Mammals require an extensive respiratory surface because we have high energy requirements.Unlike fishes, reptiles and amphibians, we are warm blooded and maintain a constant body temperature, and this does take energy.Compared to reptiles we use more oxygen because we need it to convert food into body heat. We are also more active than most reptiles. Birds don't need as much respiratory surface as you would expect because their lungs have one way flow so every breath has the full amount of oxygen as fresh air. Our lungs are mostly filled with "used" air which is lower in oxygen content.</span>
Monotremes are the animals which belong to the group of mammals. There are only five species of monotremes known today which are found in New Guinea and Australia.
The monotremes differ from other mammals which is that they lay eggs instead of giving birth to the young ones. This shows that these mammals are closely related to the reptiles and amphibians and are thus the primitive mammals.
Why are enzymes necessary for all biochemical reactions?<span>Therefore, the rate of most biochemical reactions must be increased by a catalyst. A catalyst is a chemical that speeds up chemical reactions. In organisms, catalysts are called enzymes. Like other catalysts, enzymes are not reactants in the reactions they control.