Describe double circulation in human beings. Why is it necessary?
In double circulation there is complete segregation of oxygenated and deoxygenated blood. Because of this the blood passes twice through the heart in one cycle of circulation hence the name double circulation. This is necessary for optimum oxygen utilization as humans are warm blooded animals and need extra energy to maintain their body temperature. 33. What are the differences between the transport of materials in xylem and phloem? Answer: Transport in xylem: The transport in xylem is from roots to upwards and takes place in only one direction. This is a kind of passive transport as no energy is required. Through xylem only water and minerals are transported. Transport in phloem: The transport in phloem is bidirectional and food and some other products are transported. The transport in phloem is an active transport as it requires energy. 34. Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.
