do processes access cpu and memory by system calls to the kernel?

If I am correct, processes access devices by system calls to the kernel.

CPU and memory are also devices.

1. when a process starts to run, does it get cpu and memory by system calls to the kernel?


2. When a process runs concurrently with other processes, the kernel schedules their running in an interleaving way. Does the process also call system calls to the kernel, when it give up cpu and memory to a different process and when it regain them back?


3. when a process finishes running, does it release cpu and memory also by system calls to the kernel?