An example of mitosis at work is a leaf

Leaf is a non-reproductive organ of the plant that grows in size through a process of mitosis. In Mitosis the new cells produced have identical genetic information unlike in the case of meiosis in which the daughter cells are not identical to the parent cells instead they are a random combination of both due to exchange of genes thorough crossover.

Plants form tissues to perform a complex function. In this case a leaf is a combination of multiple tissues that work together to support the function of photosynthesis. The meristem in plants is the type of tissues with undifferentiated cells. These cells in the leaves divide only by mitosis i.e. each cell made is a replica of the other. However, the process of differentiation transforms the cells into specialized cells with diverse functions such as palisade parenchyma to perform photosynthesis and guard cells to aid in the process of transpiration.  

the generally accepted parts of modern cell theory include: all known living things are made up of one or more cells. all living cells arise from pre-existing cells by division. the cell is the fundamental unit of structure and function in all living organisms.