Which set of substances requires either channel or transport proteins in order to cross the cell membrane?
A. $N _2, H _2 O , C _6 H _{12} O _6$
B. $H _2 O , NaCl , C _6 H _{12} O _6$
C. $N _2, H _2 O , NH _3$
D. $NaCl , NH _2 CONH _2, O _2$
Answer (1)
Analyze the properties of each substance (size, polarity, charge).
Determine which substances can diffuse directly across the membrane (small, nonpolar).
Identify which substances require channel or transport proteins (large, polar, or charged).
Select the option where all three substances require channel or transport proteins, which is B: H 2 O , N a Cl , C 6 H 12 O 6 .
Explanation
Understanding the Problem We need to determine which set of substances requires either channel or transport proteins to cross the cell membrane. Channel or transport proteins are required for substances that cannot easily diffuse across the lipid bilayer. Small, nonpolar molecules can diffuse directly across the membrane, while large, polar or charged molecules require transport proteins.
Analyzing the Options Let's analyze each option:
A. N 2 , H 2 O , C 6 H 12 O 6 : N 2 is small and nonpolar, so it can diffuse directly. H 2 O is small and polar, and can cross the membrane directly to some extent, but its transport is facilitated by aquaporins (channel proteins). C 6 H 12 O 6 (glucose) is a large polar molecule and requires transport proteins.
B. H 2 O , N a Cl , C 6 H 12 O 6 : H 2 O is small and polar, and can cross the membrane directly to some extent, but its transport is facilitated by aquaporins (channel proteins). N a Cl dissociates into N a + and C l − ions, which are charged and require channel or transport proteins. C 6 H 12 O 6 (glucose) is a large polar molecule and requires transport proteins.
C. N 2 , H 2 O , N H 3 : N 2 is small and nonpolar, so it can diffuse directly. H 2 O is small and polar, and can cross the membrane directly to some extent, but its transport is facilitated by aquaporins (channel proteins). N H 3 (ammonia) is small and polar, and can diffuse across the membrane.
D. N a Cl , N H 2 CON H 2 , O 2 : N a Cl dissociates into N a + and C l − ions, which are charged and require channel or transport proteins. N H 2 CON H 2 (urea) is a small polar molecule that can cross the membrane using transport proteins. O 2 is small and nonpolar, so it can diffuse directly.
Determining the Correct Option Based on the analysis, option B contains substances that all require either channel or transport proteins: H 2 O (aquaporins), N a Cl ( N a + and C l − ions), and C 6 H 12 O 6 (glucose).
Final Answer Therefore, the correct answer is B.
Examples
Understanding how substances cross the cell membrane is crucial in biology and medicine. For example, drug delivery systems often rely on transport proteins to get medication into cells. Similarly, kidney function depends on the ability of channel proteins to regulate the movement of ions and water across cell membranes. This knowledge helps in designing effective treatments and understanding physiological processes.
