Question

question ① an important factor in the function of the immune system is the ability to line all external surfaces of the body (digestive, skin, respiratory, and reproductive) with secure cell junctions. this prevents pathogens from entering the body. given this, which of the following is true? answer most critical to the cell junction is the gap junction. connexons, composed of transmembrane proteins, hold cells together. desmosomes, on their own, provide an impermeable seal between cells. epithelia are the only cells that are likely to use all three cell junction types (tight junctions, desmosomes, and gap junctions). i dont know yet

Explanation:

• Analyze each option:
• Option 1: Gap junctions are for communication, not the most critical for cell - cell adhesion in barrier function, so incorrect.
• Option 2: Connexons are part of gap junctions (for communication), not for holding cells together. Cell adhesion molecules or structures like desmosomes (with cadherins) or tight junctions (with claudins/occludins) hold cells together. Wait, no—wait, maybe a mistake here. Wait, actually, the correct concept: Tight junctions form an impermeable seal, desmosomes anchor cells together, gap junctions allow communication. But the option "Connexons, composed of transmembrane proteins, hold cells together" is incorrect because connexons are for gap junctions (communication). Wait, maybe I misread. Wait, the correct answer should be re - evaluated. Wait, let's re - check:
• Tight junctions (not desmosomes alone) provide the impermeable seal (so option 3 is wrong).
• Epithelia use tight junctions, desmosomes, and sometimes gap junctions, but are they the only ones? No, some other cell types in tissues with cell - cell contact might use them too, but among the options, let's re - check the second option. Wait, maybe the original analysis was wrong. Wait, connexons are made of connexin proteins (transmembrane), and gap junctions (with connexons) allow communication, not holding cells together. So maybe the correct option is the one about epithelia? Wait, no—wait, the problem is about cell junctions in the immune system's barrier function (lining external surfaces). Epithelial cells (like in skin, digestive, respiratory, reproductive) use tight junctions (seal), desmosomes (adhesion), and gap junctions (communication). Other cell types may not use all three. So "Epithelia are the only cells that are likely to use all three cell junction types (tight junctions, desmosomes, and gap junctions)" is a more accurate statement. Wait, but let's check each option again:
• Option 1: Gap junctions are not the most critical for cell junction in barrier function (tight junctions are for sealing), so wrong.
• Option 2: Connexons (gap junctions) are for communication, not holding cells together. Desmosomes (with cadherins) hold cells together, so this is wrong.
• Option 3: Desmosomes anchor cells, tight junctions provide the impermeable seal. So desmosomes alone don't provide an impermeable seal, wrong.
• Option 4: Epithelial cells (which line the external surfaces mentioned: digestive, skin, respiratory, reproductive) are the main cells that use tight junctions (seal against pathogens), desmosomes (adhesion), and gap junctions (communication between cells). Other cell types (like in connective tissue) don't typically use all three. So this is correct.

Answer:

1. Epithelia are the only cells that are likely to use all three cell junction types (tight junctions, desmosomes, and gap junctions).