Advanced Placement (AP) Biology Practice Exam

What is a growth factor?

1. A protein that inhibits cell division

2. A protein necessary for cell growth and development

3. A type of carbohydrate for energy

4. A molecule that promotes apoptosis

The correct answer is: A protein necessary for cell growth and development

A growth factor is defined as a protein that is essential for cell growth and development. These proteins play crucial roles in signaling pathways that stimulate cellular processes such as division, survival, and differentiation. Growth factors bind to specific receptors on the surface of target cells, triggering intracellular signaling cascades that lead to various biological responses, including increased cell proliferation and enhancement of cellular functions. Growth factors are critical in many physiological processes, including embryonic development, tissue repair, and immune responses. They help regulate vital activities in both normal and pathological conditions, such as wound healing and cancer progression. Their presence can dramatically influence how cells behave in multicellular organisms. The other options represent different biological concepts: proteins that inhibit cell division are known as inhibitors or tumor suppressors; carbohydrates are primarily energy sources, not growth factors; and molecules promoting apoptosis are involved in programmed cell death, which is distinct from the growth-promoting functions of growth factors.