Under development of the brain.
The valves are responsible for preventing blood from flowing in the wrong direction, they are present in the veins, and the arteries don't need them because the aorta (biggest artery) pumps or in other words pushes it with such a force that no other force can change its direction, in the veins there is no structure present for pumping them as a result we have got valves so that they go in one direction...... the meaning of the word valve is to allow in one direction
Because bacteria mutates that's why we have a new flu vaccine every year , because strains of DNA in the bacteria change all the time.
<span>Some sources stated that in the North Atlantic, the rate of movement is only about 1 cm (about 0.4 in) per year, while in the Pacific it amounts to more than 4 cm (almost 2 in) annually, while two others said the plates, in general, traveled from 5 to 10 cm/yr.</span>
