Name the organ which is located in the chest cavity with its lower tip slightly tilted towards the left.

Veins have valves which allow blood to flow only in one direction. Arteries do not have valves. Yet the blood flows in one direction only. Can you explain why?

What is the special feature present in a human heart which does not allow mixing of blood when oxygen-rich and carbon dioxide-rich blood reach the heart?

Look at Figure 11.1. Draw another figure of the same set-up as would be observed after a few hours.

Arrange the following statements in the correct order in which they occur during the formation and removal of urine in human beings.

(a) Ureters carry urine to the urinary bladder.

(b) Wastes dissolved in water is filtered out as urine in the kidneys.

(c) Urine stored in the urinary bladder is passed out through the urinary opening at the end of the urethra.

(d) Blood containing useful and harmful substances reaches the kidneys for filtration.

(e) Useful substances are absorbed back into the blood.