Characterized by both differentiation and growth, is the characteristic of life that explains increased size and functional complexity.

Development

Explanation:

Growth refers to an increase in size and mass of the organisms and occurs through increase in number of cells and cell enlargement. The newly formed cells are specialized to perform specific functions.

For the purpose, these cells undergo some structural changes to suit their designated functions and the process is known as differentiation. For example, specific stem cells in bone marrow divide to produce daughter cells which in turn undergo structural changes such as loss of nucleus and differentiate as mature red blood cells.  

Growth and differentiation are two components of development which in turn makes one of the unified and basic features of living beings.  

that scientist would be robert hooke

cells spend most of their time in interphase