Final answer:
Sugar cannot easily pass through the cell membrane due to its size and polarity, requiring transport proteins, whereas oxygen can pass freely by simple diffusion.
Step-by-step explanation:
Sugar has a harder time passing through a cell membrane than a gas like oxygen because of the differences in the properties of these molecules. Sugar molecules are larger and typically have polar characteristics, making it difficult for them to pass through the lipid bilayer of the cell membrane. Gases such as oxygen (O2) and carbon dioxide (CO2), however, are small and nonpolar, which allows them to move freely across cell membranes by simple diffusion.
Oxygen diffuses into cells from areas of higher concentration to lower concentration without the need for energy, a process known as passive transport. In contrast, sugars cannot pass directly through the cell membrane because they are polar molecules and their size requires transport proteins to help them enter or exit the cell. These substances need a form of facilitated diffusion or active transport to move across the plasma membrane.