Unit 4 Target 5: Cell Membrane Transport Quiz

Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. This occurs because molecules are in constant random motion and tend to spread out to achieve a more uniform distribution. Diffusion can occur in gases, liquids, and solids, but in this case, the question specifies that it takes place only through a lipid bilayer membrane. This is because the lipid bilayer is selectively permeable, allowing only certain molecules to pass through it via diffusion.

Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. Over time, this movement of molecules will continue until the concentration is equal on both sides of a membrane. Therefore, the correct answer is that the concentration of many types of substances eventually becomes balanced on both sides of a membrane.

Active transport is the correct answer because it is the only means of particle transport that requires input of energy from the cell. Active transport is a process in which particles are transported across a cell membrane against their concentration gradient, meaning from an area of lower concentration to an area of higher concentration. This requires the cell to expend energy in the form of ATP to move the particles against the concentration gradient. Osmosis, diffusion, and facilitated diffusion do not require energy input from the cell.

Exocytosis is the process by which a cell releases proteins or other molecules into the extracellular space. It involves the fusion of vesicles, which contain the proteins, with the cell membrane, allowing the contents to be released outside the cell. This is the correct answer because exocytosis specifically refers to the transport of molecules out of the cell, which is the scenario described in the question. Osmosis is the movement of water across a selectively permeable membrane, facilitated diffusion is the passive transport of molecules across a membrane with the help of transport proteins, and endocytosis is the process by which cells internalize substances by engulfing them into vesicles.

The process shown in the illustration is diffusion. Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. In this process, particles move down their concentration gradient, without the need for energy or a transport protein. Osmosis is the diffusion of water molecules across a selectively permeable membrane, facilitated diffusion involves the use of transport proteins, and active transport requires energy to move particles against their concentration gradient. Therefore, the correct answer is diffusion.

Osmosis is the correct answer because it refers to the diffusion of water across a selectively permeable membrane. In osmosis, water molecules move from an area of lower solute concentration to an area of higher solute concentration, in order to equalize the concentration on both sides of the membrane. Osmosis is a passive process and does not require energy. Osmotic pressure, facilitated diffusion, and active transport are all different processes that do not specifically involve the diffusion of water molecules.

The molecules move into the cell through the channel protein because facilitated diffusion refers to the passive movement of molecules across a cell membrane with the help of specific transport proteins. In this case, the channel protein serves as a pathway or channel for the molecules to move through, allowing them to enter the cell. The phospholipid bilayer, on the other hand, does not directly facilitate the movement of molecules but rather forms the structure of the cell membrane.

Diffusion does not expend energy because it is a passive process that occurs naturally due to the random movement of particles. It involves the movement of molecules or ions from an area of high concentration to an area of low concentration, until equilibrium is reached. Unlike active transport, which requires the use of energy to move substances against their concentration gradient, diffusion does not require any external energy source. Therefore, diffusion is the only option listed that does not expend energy.

Exocytosis is the process by which a cell releases substances from the cell interior to the extracellular space. In the case of a sodium ion exiting a cell, exocytosis would involve the fusion of vesicles containing the sodium ions with the plasma membrane, allowing the ions to be expelled outside the cell. This process requires energy and is typically used for larger molecules or substances that are actively transported out of the cell. Facilitated diffusion, osmosis, and active transport are not suitable explanations for the exit of a sodium ion through the plasma membrane.

Facilitated diffusion is the process by which sugar molecules can enter cells. This process involves the use of specific protein channels or carriers that help transport the sugar molecules across the cell membrane, from an area of higher concentration to an area of lower concentration. Unlike active transport processes such as ion pumps or exocytosis, facilitated diffusion does not require energy expenditure by the cell. Osmosis, on the other hand, is the movement of water molecules across a semi-permeable membrane, not sugar molecules. Therefore, facilitated diffusion is the most appropriate process for the entry of sugar molecules into cells.

Endocytosis is the process by which large molecules are transported into the cell. It involves the formation of a vesicle from the cell membrane, which engulfs the molecules and brings them into the cell. This process is used for the uptake of macromolecules, such as proteins or nucleic acids, that are too large to pass through the membrane by diffusion. Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration, and it does not specifically involve the transport of large molecules. Exocytosis is the opposite process, where vesicles fuse with the cell membrane to release molecules outside the cell. Lipid carriers are not directly involved in the transport of large molecules into the cell.

When a red blood cell is placed in pure water, water molecules will move from an area of lower solute concentration (pure water) to an area of higher solute concentration (cytoplasm of red blood cell) through a process called osmosis. The cytoplasm of red blood cells has a higher concentration of Na+ than pure water, creating a concentration gradient that drives the movement of water molecules into the cell. Therefore, the net flow of water molecules is into the red blood cell by osmosis.

Facilitated diffusion is a passive transport process that allows the movement of substances across a cell membrane with the help of carrier proteins. It does not require energy input, as it relies on the concentration gradient to drive the movement of molecules. The other three characteristics mentioned are correct. However, the statement "It moves substances against a concentration gradient" is incorrect. Facilitated diffusion only occurs down the concentration gradient, moving substances from an area of high concentration to an area of low concentration.

The sodium-potassium pump is a vital mechanism in maintaining the resting potential of cells. It actively transports three sodium ions out of the cell for every two potassium ions it brings in. This results in a net movement of potassium into the cell, making the correct answer "potassium into the cell."