Observe the population growth curve and answer the questions given below:
[Graph with labels $\frac{dN}{dt}=rN$, $\frac{dN}{dt}=rN(\frac{K-N}{K})$, A, B, K]
(a) State the conditions under which growth curve 'A' and growth curve 'B' plotted in the graph are possible.
(b) Mention what does 'K' in the graph represent.