18. What is the function of the cell surface's carbohydrate layer? (A) Energy storage (B) DNA replication (C) Protein transport (D) Cell-cell recognition (E) Nutrient absorption

25. Both excitatory and inhibitory neurons form junctions with muscles. By what mechanism do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential? (A) By closing Na⁺ channels (B) By preventing the secretion of excitatory neurotransmitters (C) By opening K⁺ channels (D) By opening Cl⁻ channels (E) By blocking voltage-gated Ca²⁺ channels

18. What is the function of the cell surface's carbohydrate layer?
(A) Energy storage
(B) DNA replication
(C) Protein transport
(D) Cell-cell recognition
(E) Nutrient absorption

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