Why do proteins not pass through plasma membranes?
They contain nitrogen.
They cause emulsification.
The membrane is made of protein.
They are very large molecules.
They bind to the phospholipids.
The Correct Answer is D
Choice A rationale: Proteins contain nitrogen, but this is not the reason why they cannot pass through plasma membranes. Nitrogen is a common element in many organic molecules, including nucleic acids and amino acids, which can cross the membrane under certain conditions.
Choice B rationale: Proteins do not cause emulsification, which is the process of breaking down large fat droplets into smaller ones. Emulsification is facilitated by bile salts, which are amphipathic molecules that have both hydrophilic and hydrophobic regions. Proteins are not amphipathic, and they do not interact with fats in this way.
Choice C rationale: The membrane is made of protein, but this does not prevent proteins from passing through it. The membrane is composed of a phospholipid bilayer with embedded proteins, which can act as channels, carriers, receptors, or enzymes for various substances. Some proteins can cross the membrane by using these transport proteins, or by endocytosis or exocytosis.
Choice D rationale: Proteins are very large molecules, and this is the main reason why they cannot pass through plasma membranes. The size of a molecule determines its permeability across the membrane, and proteins are too big to diffuse through the small gaps between the phospholipids or the pores of the transport proteins. Proteins can only cross the membrane by vesicular transport, which requires energy and specific signals.
Choice E rationale: Proteins do not bind to the phospholipids, which are the main components of the membrane. Phospholipids are also amphipathic molecules, with a hydrophilic head and a hydrophobic tail. Proteins are generally hydrophilic, and they do not associate with the hydrophobic core of the membrane. Proteins can bind to other proteins or carbohydrates on the surface of the membrane, but this does not affect their ability to cross it.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
Choice A rationale: Eukaryotes is incorrect because eukaryotes are organisms that have cells with a nucleus and other membrane-bound organelles, such as animals, plants, fungi, and protists. Some eukaryotes, such as protists, are microscopic and require microscopy to be studied, but others, such as animals and plants, are macroscopic and can be seen with the naked eye.
Choice B rationale: Fungi is incorrect because fungi are a group of eukaryotic organisms that include mushrooms, molds, yeasts, and lichens. Some fungi, such as yeasts and molds, are microscopic and require microscopy to be studied, but others, such as mushrooms and lichens, are macroscopic and can be seen with the naked eye.
Choice C rationale: Prokaryotes is correct because prokaryotes are organisms that have cells without a nucleus or other membrane-bound organelles, such as bacteria and archaea. All prokaryotes are microscopic and require microscopy to be studied. Prokaryotes are the smallest and most abundant living organisms on Earth.
Choice D rationale: Plants is incorrect because plants are a group of eukaryotic organisms that have cells with a cell wall, chloroplasts, and a large central vacuole, such as mosses, ferns, and flowering plants. Some plants, such as mosses and algae, are microscopic and require microscopy to be studied, but others, such as ferns and flowering plants, are macroscopic and can be seen with the naked eye.
Correct Answer is D
Explanation
Choice A rationale: CO2 is not the source of oxygen produced by a plant, but a reactant of the dark reaction. The dark reaction uses CO2 and energy intermediates from the light reaction to produce glucose, a type of sugar. The dark reaction does not release any oxygen¹.
Choice B rationale: C6H12O6 is the chemical formula for glucose, which is the product of the dark reaction. Glucose is synthesized from CO2 and energy intermediates from the light reaction. Glucose does not produce any oxygen, but can be used by the plant for respiration or storage².
Choice C rationale: Glyceraldehyde-3-phosphate is an intermediate molecule in the dark reaction. It is formed from CO2 and energy intermediates from the light reaction, and then converted into glucose. Glyceraldehyde-3-phosphate does not produce any oxygen³.
Choice D rationale: H2O is the source of oxygen produced by a plant. In the light reaction, water is split by the energy from sunlight in photosystem II, releasing electrons, protons, and oxygen. The oxygen is either used for respiration or released into the air⁴.
Choice E rationale: O2 is the product of oxygen produced by a plant, not the source. O2 is released as a by-product of the splitting of water in photosystem II. O2 is either used for respiration or released into the air⁴.
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