Question

density - dependent inhibition is explained by which of the following statements?
as cells become more numerous, they begin to squeeze against each other, restricting their size and ability to produce growth factors.
as cells become more numerous, the level of waste products increases, eventually slowing down metabolism.
as cells become more numerous, the protein kinases they produce begin to compete with each other, such that the proteins produced by one cell essentially cancel those produced by its neighbor.
as cells become more numerous, the cell surface proteins of adjacent cells bind to each other and send signals that inhibit cell division.

Explanation:

Density - dependent inhibition is a phenomenon in cell biology. When cells reach a certain density, cell - cell contact (mediated by cell surface proteins) occurs. These cell - surface protein - protein interactions send signals that inhibit further cell division.

• Option A: Restricting size and growth factor production is not the key mechanism of density - dependent inhibition.
• Option B: Waste product accumulation is more related to general cell environment deterioration rather than the specific cell - cell contact - mediated density - dependent inhibition.
• Option C: Protein kinase competition is not the basis of density - dependent inhibition.
• Option D: Cell surface proteins binding and sending inhibitory signals for cell division is the correct description of density - dependent inhibition.

Answer:

D. As cells become more numerous, the cell surface proteins of adjacent cells bind to each other and send signals that inhibit cell division.