Exercise helps memory and thinking through both direct and indirect means. The benefits of exercise come directly from its ability to reduce insulin resistance, reduce inflammation, and stimulate the release of growth factors-chemicals in the brain that affect the health of brain cells, the growth of new blood vessels in the brain, and even the abundance and survival of new brain cells. (Harvart Health Letter, May 2014)
There's some evidence that exercise alone protects the brain. One study of people in their seventies published in Neurology showed that those who exercised the most had the least brain shrinkage and fewer whire matter brain lesions, which can be signs of dementia. People who engaged in mental acitivities had more brain shrinkage and white matter brain lesions. (Godman, 2013)
Students who have regular physical activities were more enthusiastic, alert and calm during exams. You all need that kind of attitude to gain focus especially when you are studying, reviewing notes, and the most important is when you're taking examinations.
To give your best, you have to work it out and workout! literally.