When the warrants are not in the money, they are only a speculation on the future value of the stock;
When they are in the money they have an intrinsic value - If PTA was 50 cents and the B warrant allowed you to buy the stock at 35 the intrinsic value would be your spread, 15 cents.
Hence the warrant would probably trade around a range of its intrinsic value. Of course for the same $ invested a warrant will give you leverage / higher rate of return than a stock (and corresponding risk)
For example, a 5 cent gain on a 15 cent warrant to 20 cents would be a ROR of 33% vs. a 5 cent gain on a 50 cent stock which would be 10%.
Hence - Bigger gain potential on Warrants (for the same $ invested) but also bigger risk and in the case of PTA less liquidity.
Best thing to do with them is buy them when they are really cheap and have a longer term to expiry. Just like anything.