Plasmodesmata are numerous channels that pass between cell walls of adjacent plant cells and connect their cytoplasm thereby enabling materials to be transported from cell to cell and thus throughout the plant.
A gene that makes the body cells to divide in an uncontrolled manner is called an oncogene. An oncogene is responsible for the development of tumors due to disturbed regulation of cell division. The gene src makes the cells to enter the process of cell division in response to the growth factors.
However, the mutant src gene does not require the presence of growth factors and signals the cells to enter the process of cell division even in the absence of the growth factors. Since the mutant src gene causes uncontrolled cell division, it represents an oncogene.
More individuals are produced each generation that can survive. Phenotypic variation exists among individuals and the variation is heritable. Those individuals with heritable traits better suited to the environment will survive.