The diagram on the left shows the Marginal Cost curve. Why does it slope downwards and then upwards?
If the marginal cost is rising then surely the cost of supply is rising so why do firms supply more if the price rises as the marginal cost is clearly rising?

Marginal cost

The cost of the first item is the same as the average total cost.
Marginal cost is the cost of the last unit.
Surely this means that the two curves - ATC and MC - must start in the same place?