The buying and selling in the market place basically affects the value of bitcoin. Others may include the popularity of the product and its stability.
Well, there can be many reason that can influence or affect bitcoin's value. Among all the news I think the investors who invest without the patience and sell them in low rate, makes a great affect on the price. The price of bitcoin is based on the supply and demand relationship. If the demand is high then the price of new bitcoin can increase. But when demand drops, the price of bitcoin will decrease. But the most important thing is the news