(7) A certain type of bacteria divides every two hours (each bacterium splits into two, and the time required for division is negligible). At the start of the study, there are two bacteria, and they continue to divide throughout the study. The total number of bacteria $y$ is a function of the study time $t$, denoted as $y=f(t)$.
(1) Write the domain and range of the function $y=f(t)$;
(2) In the given coordinate system, draw the graph of $y=f(t)(0 \leqslant t<6)$;
(3) Write the total number of bacteria when the study has been ongoing for $n$ hours $(n \geqslant 0, n \in \mathbf{Z})$ (expressed as a formula involving $n$).
(7) (1) $y=f(t)$ has a domain of $t \in[0,+\infty)$, and a range

of $\left\{y \mid y=2^{n}, n \in \mathbf{N}^{*}\right\}$
(2) For $0 \leqslant t<6$, it is a piecewise function $y=\left\{\begin{array}{ll}2, & 0 \leqslant t<2, \\ 4, & 2 \leqslant t<4 \text {, graph } \\ 8, & 4 \leqslant t<6 .\end{array}\right.$
(3) $y=\left\{\begin{array}{ll}2^{\frac{n}{2}+1}, & n \text { is even, } \\ 2^{\frac{n-1}{2}+1}, & n \text { is odd }\end{array}\right.$