Final answer:
The abnormal development of cells is called dysplasia. It can manifest as hypoplasia, abnormal growth patterns, and discoloration in the case of plant viral diseases. Critical periods during fetal development and differentiation in embryonic development are crucial for proper tissue and organ formation.
Step-by-step explanation:
The abnormal development of cells within tissues or organs is referred to as dysplasia. This condition implies an alteration in the size, shape, and organization of mature cells. Upon observing a light micrograph of the cells of a plant root affected by a viral disease, one may notice symptoms including hypoplasia (underdevelopment of a tissue or organ), abnormal growth patterns such as malformed stems, leaves, or fruits, and discoloration. During embryonic development, a stage known as differentiation occurs when unique cell layers develop into specific groups of tissues or organs. The time when specific parts or organs of a fetus develop is known as the critical period. Concerning cancer, this condition represents cells escaping regulatory signals leading to unchecked growth and the potential for invasion into adjacent tissues, as noted by changes in cell size, nucleus size, and organization in the tissue.