The stages of secondary succession are similar to those of primary succession; however, primary succession always begins on a barren surface, whereas secondary succession begins in environments that already possess soil.
Secondary succession occurs when the severity of disturbance is insufficient to remove all the existing vegetation and soil from a site. Many different kinds of disturbances, such as fire, flooding, windstorms, and human activities (e.g., logging of forests) can initiate secondary succession.
The stages of secondary succession are similar to those of primary succession; however, primary succession always begins on a barren surface, whereas secondary succession begins in environments that already possess soil.
Apoptosis also plays a key role in human development. For instance, as we saw in the introduction, your hand started out as a paddle-like block of tissue when you were an embryo. The block was “carved” into fingers by apoptosis of the cells in between the developing fingers.
B is referring to cell theory, which basically states that all living things are made of cells and all cells come from other cells withe the exception of the first life forms.
