Cell Membrane And Transport MCQ Quiz With Answers

The cell membrane is composed of a phospholipid bilayer, which consists of two layers of phospholipids. These phospholipids have a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail, which arrange themselves in a way that the heads face outward towards the watery environment both inside and outside the cell, while the tails face inward, creating a barrier. In addition to phospholipids, the cell membrane also contains many other organic compounds such as proteins, cholesterol, and carbohydrates, which play various roles in maintaining the structure and function of the membrane.

The sodium-potassium pump is indeed one of the most important membrane pumps in animal cells. It helps maintain the proper balance of sodium and potassium ions inside and outside the cell, which is crucial for various cellular processes such as nerve impulse transmission and muscle contraction. This pump actively transports three sodium ions out of the cell for every two potassium ions it brings in, using ATP as an energy source. This constant pumping action is essential for maintaining the cell's resting membrane potential and overall cell function.

Equilibrium refers to a state in which there is a balance or equal distribution of a substance inside and outside of a cell. In this state, there is no net movement of the substance across the cell membrane, as the concentration is the same on both sides. This is important for the proper functioning of cells, as it allows for the maintenance of homeostasis and the exchange of necessary molecules and ions.

Active transport occurs when energy is needed to move a substance across the cell membrane. This process requires the cell to expend energy in order to transport molecules or ions against their concentration gradient, from an area of lower concentration to an area of higher concentration. This is in contrast to passive transport, where substances move across the cell membrane without the need for energy. Active transport is essential for maintaining proper cell function and allowing the cell to take up necessary nutrients or remove waste products.

The illustration most likely represents a sodium-potassium pump. This is because a sodium-potassium pump is a type of active transport mechanism that moves sodium ions out of a cell and potassium ions into the cell. The pump uses energy from ATP to perform this task, and it helps maintain the electrochemical gradient across the cell membrane. The other options, vesicle moving and sodium-glucose cotransport, do not involve the specific mechanism of a sodium-potassium pump.

The concentration gradient determines how fast a molecule crosses the membrane because it refers to the difference in concentration of a substance on either side of the membrane. This difference creates a driving force for molecules to move from an area of higher concentration to an area of lower concentration, which is known as diffusion. The steeper the concentration gradient, the faster the molecules will move across the membrane through diffusion. Therefore, the concentration gradient directly affects the rate at which molecules can cross the membrane.

Proteins are indeed embedded in the cell membrane. These proteins help with important functions like transporting materials, receiving signals, and supporting the cell’s shape. Some proteins go all the way through the membrane (integral proteins), while others are attached on the surface (peripheral proteins). This structure is part of the fluid mosaic model of the membrane.

The correct answer is simple diffusion, facilitated diffusion, and osmosis. Passive transport refers to the movement of substances across a cell membrane without the use of energy. Simple diffusion involves the movement of molecules from an area of high concentration to an area of low concentration. Facilitated diffusion involves the movement of molecules with the help of transport proteins. Osmosis is the movement of water molecules across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. These three types of passive transport play a crucial role in maintaining the balance of substances within a cell.

Simple diffusion occurs when something moves from a higher concentration to a lower concentration, randomly. This process happens due to the random movement of particles, where they naturally move from an area of high concentration to an area of low concentration until equilibrium is reached. It does not require any external energy or assistance to occur.

The sodium-potassium pump is a vital membrane protein that maintains the concentration gradients of sodium and potassium ions across the cell membrane. It actively transports three sodium ions out of the cell for every two potassium ions it brings in, against their respective concentration gradients. This process requires energy in the form of ATP. Therefore, the statement that the sodium-potassium pump transports both ions against their concentration gradients is true.

The term "Selective permeability" refers to the property of the cell membrane that allows certain substances to enter or exit the cell while restricting others. This means that the cell membrane acts as a selective barrier, controlling the movement of molecules and ions. It only permits the passage of specific substances through various mechanisms such as diffusion, facilitated diffusion, and active transport. Therefore, "selectively permeable" is the best definition for the given word.

Integral/transmembrane proteins are proteins that are embedded within the cell membrane. They span across the lipid bilayer, with parts of the protein exposed on both sides of the membrane. These proteins play crucial roles in transporting molecules and ions across the membrane. Protein channels are specific integral proteins that form pores or channels, allowing the selective passage of molecules or ions. Carrier proteins, on the other hand, bind to specific molecules and undergo conformational changes to transport them across the membrane. Therefore, the correct answer is protein channels and carrier proteins.

Phagocytosis is a process in which cells engulf and internalize solid particles or microorganisms. It is often referred to as "cell eating" because the cell surrounds the particle with its membrane and forms a vesicle called a phagosome. The phagosome then fuses with lysosomes, where the ingested material is broken down and digested. This process is important for immune defense and the removal of debris or pathogens from the body.

Receptor-mediated endocytosis is a process in which the cell membrane folds inward to form protein-coated pits that ultimately form vesicles. This process allows the cell to selectively take in specific molecules or particles from the extracellular environment. The protein-coated pits contain specific receptors that bind to the target molecules, facilitating their internalization into the cell. Therefore, the statement "Receptor-mediated endocytosis is when the cell membrane folds inward to form protein-coated pits that form vesicles" is true.

The nonpolar tails of phospholipids in the bilayer face towards the interior. This is because the nonpolar tails are hydrophobic, meaning they repel water. By facing towards the interior, they are shielded from the surrounding aqueous environment, which is polar and water-filled. This arrangement helps to stabilize the bilayer structure and maintain the integrity of the cell membrane.

The cytoplasm is made up of the liquid cytosol. The cytosol is a gel-like substance that fills the cell and surrounds the organelles. It contains various molecules such as proteins, ions, and nutrients that are essential for cell functions. The cytosol provides a medium for cellular processes to occur and supports the organelles within the cell. It also acts as a transportation system, allowing molecules to move within the cell. Therefore, the liquid cytosol is a major component of the cytoplasm.

Cells maintain homeostasis by controlling what moves across the cell membrane. The cell membrane acts as a selective barrier, allowing certain substances to enter or leave the cell while preventing others from doing so. This control over the movement of molecules and ions is crucial for maintaining the internal environment of the cell and ensuring that the necessary nutrients and molecules are present in the right concentrations. By regulating the movement of substances across the cell membrane, cells are able to maintain the balance and stability required for proper functioning.

Peripheral proteins are attached to the surface of the cell membrane. These proteins are not embedded within the lipid bilayer of the membrane, but rather loosely bound to it through non-covalent interactions. They can be easily detached from the membrane without disrupting its integrity. Peripheral proteins play various roles in cell signaling, transport of molecules across the membrane, and structural support. Their attachment to the cell membrane allows them to interact with other molecules on the cell surface and participate in important cellular processes.

Molecules tend to disperse or spread out evenly in a given space rather than congregate in one area. This tendency is governed by the principle of diffusion, where molecules move from regions of higher concentration to regions of lower concentration until equilibrium is reached.

The pictures depict exocytosis, which is a mode of active transport. Exocytosis is the process by which cells release substances from their cytoplasm into the extracellular space. In exocytosis, vesicles containing the substances fuse with the cell membrane and release their contents outside the cell. This process requires energy and is therefore considered active transport.

Animal cells prefer to be in an isotonic solution because it allows for a balanced exchange of water and solutes between the cell and its environment. In an isotonic solution, the concentration of solutes outside the cell is equal to the concentration inside the cell, resulting in no net movement of water across the cell membrane. This ensures that the cell maintains its shape and normal functioning without losing or gaining excessive amounts of water. Hypertonic solutions have a higher solute concentration than the cell, causing water to leave the cell and potentially leading to cell shrinkage. Hypotonic solutions have a lower solute concentration than the cell, causing water to enter the cell and potentially leading to cell swelling or bursting.

Active transport is a process in which substances are moved across a cell membrane against their concentration gradient, from an area of lower concentration to an area of higher concentration. This movement requires the expenditure of energy in the form of ATP (adenosine triphosphate). Therefore, the statement that active transport requires energy is true.

Sodium ions are usually more concentrated outside of the cell because they are actively pumped out of the cell by the sodium-potassium pump. On the other hand, potassium ions are usually more concentrated inside the cell because they are actively pumped into the cell by the same pump. This concentration gradient is important for various cellular processes, including the generation of electrical signals and the maintenance of cell volume.

This cell represents a hypotonic solution. A hypotonic solution has a lower concentration of solutes compared to the cell. When a cell is placed in a hypotonic solution, water moves into the cell through osmosis, causing the cell to swell and potentially burst.

Cells use the sodium ion concentration to move other substances, such as glucose, across the cell membrane. Sodium ions play a crucial role in the process of active transport, where they create a concentration gradient that allows the movement of other molecules against their concentration gradient. This process is essential for the uptake of nutrients like glucose into the cell, as well as the removal of waste products. By utilizing the sodium ion concentration, cells are able to regulate the movement of substances in and out of the cell, maintaining homeostasis and supporting various cellular functions.

The main purpose of a cell is to maintain homeostasis. Homeostasis refers to the ability of an organism or cell to maintain a stable internal environment despite external changes. Cells regulate various factors such as temperature, pH, and nutrient levels to ensure optimal conditions for their functioning. This balance is crucial for the survival and proper functioning of the cell and the organism as a whole.

The sodium-potassium pump is important because it prevents the inside of the cell from having too many sodium ions pile up. This pump actively transports sodium ions out of the cell and potassium ions into the cell, maintaining the proper balance of these ions. This balance is crucial for various cellular processes, such as maintaining the cell's resting membrane potential and facilitating nerve impulse transmission.

When equilibrium is reached, it means that the rate of molecules moving in one direction is equal to the rate of molecules moving in the opposite direction. However, this does not mean that the molecules will stop moving altogether. Even at equilibrium, the molecules will continue to move, albeit in a random and constant manner. This movement is known as thermal motion and is a fundamental property of matter. Therefore, the statement that substance molecules will not stop moving when equilibrium is reached is true.

The sodium-potassium pump is an active transport mechanism that uses ATP to move three sodium ions out of the cell and two potassium ions into the cell, against their concentration gradients. This action helps maintain the resting membrane potential by ensuring a higher concentration of sodium ions outside the cell and a higher concentration of potassium ions inside the cell, making the inside of the cell more negatively charged relative to the outside. The other options do not accurately describe this process.

The polar head of a phospholipid is made of glycerol. Phospholipids are composed of a hydrophilic (water-loving) head and a hydrophobic (water-repelling) tail. The head group is typically made up of glycerol, which contains hydroxyl (-OH) groups that interact with water molecules. This polar head allows phospholipids to form the outer layer of cell membranes, with the hydrophobic tails oriented towards the interior of the membrane and the polar heads facing the aqueous environment.

Carbohydrates are often attached to integral proteins in a process known as glycosylation. This modification plays a crucial role in various cellular processes, including cell adhesion, signaling, and immune response. By attaching carbohydrates to integral proteins, cells can enhance their functionality and recognition by other cells. Therefore, carbohydrates are the organic compound that is commonly attached to integral proteins.

If the concentrations of molecules are vastly different, they will move quickly. This is because there is a greater concentration gradient, causing molecules to move from an area of high concentration to an area of low concentration more rapidly. On the other hand, if the concentrations are similar, the molecules will move slowly. This is because there is a smaller concentration gradient, resulting in a slower rate of diffusion as molecules have less distance to travel to reach equilibrium.

A hypertonic solution has a lower free water molecule concentration than the cytosol. In other words, the solution has a higher solute concentration compared to the cytosol. This difference in concentration creates an osmotic pressure that causes water to move out of the cytosol and into the hypertonic solution, resulting in cell shrinkage or dehydration.

A pump is a type of carrier protein. Carrier proteins are membrane proteins that facilitate the transport of molecules across cell membranes. They bind to specific molecules, such as ions or small molecules, and undergo conformational changes to transport them across the membrane. Pumps are a specific type of carrier protein that use energy, such as ATP, to actively transport molecules against their concentration gradient.

The correct answer includes the major modes of active transport, which are endocytosis, exocytosis, and pumps. Endocytosis is the process by which cells take in materials from the outside by engulfing them. Exocytosis is the opposite process, where cells release materials to the outside by fusing vesicles with the cell membrane. Pumps are proteins that actively transport molecules across the cell membrane against their concentration gradient. Therefore, these three options are the major modes of active transport.

Vesicles assist substances that are too big to move across the cell membrane with carrier proteins. Vesicles are small, membrane-bound sacs that transport substances within cells. They can fuse with the cell membrane, allowing the substances to be released outside the cell or taken into the cell. This process, known as endocytosis and exocytosis, enables the movement of large molecules or particles across the cell membrane.

Plant cells actually prefer a hypotonic solution, not an isotonic one. In a hypotonic solution, the concentration of solutes outside the cell is lower than inside the cell, causing water to move into the cell through osmosis. This influx of water helps maintain turgor pressure, which is important for plant cell structure and function. In an isotonic solution, the concentration of solutes is equal inside and outside the cell, resulting in no net movement of water.

The specific structure of the cell membrane depends on the function of the cell. Proteins play a crucial role in cell membrane structure and function. They are embedded within the phospholipid bilayer and serve various functions such as transporting molecules across the membrane, acting as receptors for signaling molecules, and providing structural support. Different cells have different protein compositions in their cell membranes, depending on their specific functions and needs. Therefore, certain cells may not require the same types or amounts of proteins as other cells.