Question

based on the full description of cell - surface receptor function, which sequence of events is the most accurate analysis of signal transduction? ligand passes through plasma membrane > nuclear receptor is activated > transcription factor enters the cytoplasm. receptor changes shape > ligand binds to receptor > g - protein is activated > second messenger is created. ligand binds to enzyme>second messenger is released > receptor changes shape>gene is regulated. ligand binds to receptor > receptor undergoes conformational change > g - protein/kinase is activated > second messenger initiates internal change. what is the most accurate description of the helper t cells role in b cell activation? it acts as a final signal, releasing cytokines to confirm the threat and tell the b cell to become a plasma cell. it directly destroys the pathogen by engulfing it. it produces the antibodies that will flag the pathogen for destruction. it becomes a memory cell before the b cell is fully activated

Explanation:

For the first question, in cell - surface receptor - mediated signal transduction, a ligand first binds to the receptor, causing a conformational change in the receptor. This can activate a G - protein or kinase, which then leads to the production of a second messenger that initiates internal cellular changes. For the second question, helper T cells release cytokines to signal B cells to differentiate into plasma cells during the immune response.
For the first question, the first option is incorrect as ligands for cell - surface receptors do not pass through the plasma membrane to activate nuclear receptors in this context. The second option has the wrong order of events (receptor shape change occurs after ligand binding). The third option has an incorrect starting point (ligand binds to receptor, not enzyme first).
For the second question, helper T cells do not directly destroy pathogens by engulfing them (that's phagocytes' role), do not produce antibodies (B cells/plasma cells do), and do not become memory cells to directly activate B cells.

Answer:

1. Ligand binds to receptor > Receptor undergoes conformational change >G - protein/kinase is activated >Second messenger initiates internal change.
2. It acts as a final signal, releasing cytokines to confirm the threat and tell the B cell to become a plasma cell.