Why is the supply curve in perfect competition equal to the Marginal Cost curve.?

Question

i jsut don't quite understand how it all connects. I understand that in perfect competition the price is the same I just don't understand how supply works with it all.

Answer 1

In perfect competition, there are no fixed costs or barriers to entry, and no one can make excess profits.
Without any barriers to entry or fixed costs, as the marginal cost curve goes down, supply increases as more suppliers enter the market and squeeze out all of the excess profits.
So no one ever makes any excess profits or excess losses, since suppliers can move in and out of markets costlessly.