Which of these substances need proteins to transport across cell membrane
**Core Concept**
The question tests the understanding of **cell membrane transport mechanisms**, specifically focusing on the role of proteins in facilitating the movement of substances across the cell membrane. This involves knowledge of **passive transport** (diffusion, osmosis) and **active transport** mechanisms.
**Why the Correct Answer is Right**
Since the correct answer options are not provided, a general explanation is given. Substances that are large, charged, or polar require **protein-mediated transport** to cross the cell membrane. This can involve **channel proteins** for ions or **carrier proteins** for larger molecules, utilizing energy for **active transport** against concentration gradients.
**Why Each Wrong Option is Incorrect**
**Option A:** Without specific details, generally, small non-polar molecules can diffuse directly through the lipid bilayer without needing proteins.
**Option B:** Similar to Option A, the lack of specifics makes it hard to determine, but typically, ions and large molecules are those that require protein transport.
**Option C:** This option's correctness depends on the substance in question, but often, proteins are needed for the transport of large or charged molecules.
**Option D:** Like the other options, without specifics, it's challenging to assess, but usually, protein transport is necessary for substances that cannot pass through the lipid bilayer.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **oxygen** and **carbon dioxide** can diffuse directly through the cell membrane without the need for proteins, while **glucose** typically requires **facilitated diffusion** via **glucose transporters**.
**Correct Answer:** Not provided due to missing answer choices.