Mitosis is important for processes that involve growth, development, and repair where new cells are needed. In the options provided:
a) A tree growing taller - Mitosis is important for growth. b) A lizard regenerating its tail - Mitosis is important for regeneration. c) A human embryo developing - Mitosis is crucial for development. d) A butterfly laying eggs - This process involves the formation of eggs, which is more about meiosis than mitosis, as meiosis produces gametes.
Thus, the correct answer is d) A butterfly laying eggs.