Carry on vs Carry out

• Carry on : to continue doing something/ to continue moving on.( Example. Carry on until you're exhausted.)

  • Carry out: to complete a task / to fulfil a task you once promised (Example. You must carry out the promise / the investigation.)

It is a coincidence that in your examples they carry out the same sense ; so you may carry on such practice.

In this sentence, what's being carried out, or on, is a plant's life cycle.
By its nature, this has a beginning, a middle, and an end;
and restarts to do the same over again.

So there is one series that the plant can complete, and this allows carry out:

• With enough light, plants carry out a normal life cycle.
  (i.e, with enough light, plants can sprout, grow, and reproduce)

But plants do reproduce, and they occur in groups with different cycles,
so there is also a continuity that allows the use of carry on.

• With enough light, plants carry on a normal life cycle.
  (i.e, with enough light, plant life continues)

Since we're talking about plants here, this is not exactly a coincidence.
The distinction between carry on and carry out is designed for active
verb phrases with agent subjects, not metaphors of evolution.