Which of the following has a three-chambered heart?

It has been found that people living in very high mountains have many more red corpuscles in their blood than people living in plains. Which one of the following best accounts for this phenomenon?

The phloem tissue in plants is responsible for the transport of :

In which of the following are the largest amounts of nitrogen excreted from a mammalian body ?

Which one of the following has cytoplasm but no nucleus :