Question

Which of the following is true of diffusion and osmosis? (A) \(\quad\) Diffusion and osmosis rely on the electrochemical gradient of only the compound of interest. (B) \(\quad\) Diffusion and osmosis rely on the electrochemical gradient of all compounds in a cell. (C) Diffusion and osmosis will proceed in the same direction if there is only one solute. (D) \(\quad\) Diffusion and osmosis cannot occur simultaneously.

Short answer

Option (C) is correct because diffusion and osmosis will move in the same direction with one solute.

Step-by-step solution

Identify the definitions

Define the terms 'diffusion' and 'osmosis'. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration, while osmosis is the movement of water molecules through a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Analyze each option

Evaluate each option in the context of diffusion and osmosis: (A) Incorrect because diffusion relies on the concentration gradient of the compound of interest, while osmosis relies on the concentration gradient of water. (B) Incorrect because both processes rely on their specific gradients, not on the overall electrochemical gradient of all compounds. (C) Correct because if there is only one solute, diffusion and osmosis will move in the same direction to balance the concentration of that solute. (D) Incorrect as diffusion and osmosis can occur simultaneously in biological systems.

Select the correct answer

Based on the analysis, option (C) is the correct answer because diffusion and osmosis will proceed in the same direction if there is only one solute.

Key concepts

Diffusion

Diffusion is a fundamental process in which molecules move from an area of higher concentration to an area of lower concentration. It is driven by the kinetic energy of the molecules. Over time, the molecules spread out to evenly distribute themselves in a given space. The net movement stops once equilibrium is reached, meaning the molecules are evenly distributed, but individual molecules may still move around. Diffusion is crucial in many biological processes, such as the exchange of gases in the lungs and the distribution of nutrients and waste products in cells.

Some key points about diffusion include:

• It involves the movement of solutes
• No energy input (ATP) is required
• It can occur in gases, liquids, and solids
• Factors affecting diffusion rates include temperature, pressure, and the concentration gradient

Osmosis

Osmosis is a specific type of diffusion that involves the movement of water molecules through a semi-permeable membrane. In osmosis, water moves from an area of lower solute concentration (hypotonic) to an area of higher solute concentration (hypertonic) to equalize the solute concentrations on both sides of the membrane. Osmosis is vital for maintaining cell turgor pressure, which is the pressure of the cell contents against the cell wall in plants. This process also affects how cells interact with their surrounding environment.

Important aspects of osmosis include:

• It specifically involves the movement of water
• A semi-permeable membrane is required for osmosis to occur
• Osmosis can create osmotic pressure, which can affect cell stability and function
• It is essential in many physiological processes, such as nutrient absorption and waste removal

Concentration Gradient

A concentration gradient refers to the difference in the concentration of a substance between two areas. It is one of the key driving forces behind diffusion and osmosis. Molecules move down their concentration gradient, from a region of higher concentration to a region of lower concentration, until equilibrium is reached. This movement is due to the molecules' natural kinetic energy. Concentration gradients are crucial for various cellular processes, including the generation of energy in cellular respiration and photosynthesis.

Essential points about concentration gradients include:

• They represent the difference in concentration of a substance between two areas
• They drive the movement of molecules in diffusion and osmosis
• Gradients can be influenced by factors like temperature and pressure
• They play a role in the transport of ions and other substances across cell membranes

Semi-Permeable Membrane

A semi-permeable membrane is a type of biological or synthetic barrier that allows certain molecules or ions to pass through it while blocking others. This selective permeability is essential for processes like osmosis and the selective transport of substances into and out of cells. Cell membranes are typically semi-permeable, permitting the passage of water and some solutes, but restricting larger molecules and ions. This selectivity helps maintain the internal environment of the cell and allows cells to carry out essential functions.

Key characteristics of semi-permeable membranes include:

• They allow selective passage of molecules
• They are critical for maintaining cellular homeostasis
• They are composed of a lipid bilayer with embedded proteins
• They facilitate processes such as nutrient uptake, waste removal, and cell signaling