7
25) As a patch of scraped skin heals, the cells fill in the injured area but do not grow beyond that.
This is an example of
A) density-independent inhibition.
B) density-dependent inhibition.
C) anchorage independence.
D) growth factor inhibition.
26) Which of the following is probably the main factor responsible for the phenomenon of
density-dependent inhibition?
A) a local accumulation of growth-inhibiting factors
B) cells’ innate ability to “sense” when the organ of which they are a part has no need for
additional cells
C) a local deficiency of nutrients
D) physical contact of cell-surface proteins between adjacent cells
27) Mature human nerve cells and muscle cells
A) become cancerous more easily than other cell types.
B) continue to divide throughout their lifetime.
C) are permanently in a state of nondivision.
D) cease dividing after a predetermined number of cell generations.
28) Which of the following statements regarding the cell cycle control system is false?
A) The cell cycle control system receives messages from outside the cell that influence cell
division.
B) The cell cycle control system triggers and controls major events in the cell cycle.
C) The cell cycle control system includes three key checkpoints to complete a cell cycle.
D) The cell cycle control system operates independently of the growth factors.