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Which of the following substances can move across the cell membrane by diffusion?
Oxygen
Nucleic acid
Proteins
Starch
Oxygen
Oxygen moves across the cell membrane primarily by simple passive diffusion. Due to its small, non-polar molecular nature, it can freely pass through the hydrophobic lipid bilayer of the cell membrane along its concentration gradient without the expenditure of cellular energy (ATP).
Oxygen moves across the cell membrane primarily by simple passive diffusion. Due to its small, non-polar molecular nature, it can freely pass through the hydrophobic lipid bilayer of the cell membrane along its concentration gradient without the expenditure of cellular energy (ATP).
Just like the smell of perfume spreading out evenly across a room from a concentrated spray without anyone pushing it, oxygen molecules naturally drift from areas of high concentration (like the lungs or blood capillaries) into cells where concentration is lower.
Remember 'SMALL' for simple diffusion: Small, Non-polar, Lipid-soluble molecules Always Leak (diffuse) freely.
J = -D dxdCтАЛ тАФ Fick's first law of diffusion describing passive molecular flux
Simple diffusion is the net passive movement of particles (molecules or ions) from a region of higher concentration to a region of lower concentration. Because oxygen (O2тАЛ) is small and uncharged, it dissolves easily in the hydrophobic core of the phospholipid bilayer, allowing it to rapidly cross the membrane directly.
Oxygen (O2тАЛ) and Carbon dioxide (CO2тАЛ) move across the cell membrane by simple diffusion.
Diffusion is a passive process requiring no cellular energy (ATP).
Large or charged molecules (such as nucleic acids, proteins, and starch) cannot pass freely and require specialized transport mechanisms or endocytosis.
Does not consume cellular energy (ATP).
Enables rapid exchange of respiratory gases essential for cellular respiration.
Only effective over short distances and for small, non-polar molecules.
Gas exchange in alveoli of lungs and tissues in human physiology.
Absorption of dissolved oxygen by unicellular organisms from their surrounding water.
Nucleic acids, proteins, and starch are large macromolecules that are impermeable to the lipid bilayer via simple diffusion.
Option A (Oxygen) is the correct choice as it is a small, uncharged gas molecule capable of simple diffusion.
A is correct тАФ Oxygen moves across the cell membrane by simple diffusion along its concentration gradient without requiring metabolic energy.
In competitive exams, remember that small non-polar molecules (O2тАЛ, CO2тАЛ, N2тАЛ) and lipid-soluble substances pass via simple diffusion, whereas ions and large polar molecules (glucose, amino acids) require facilitated diffusion or active transport.
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