AP Biology Chapter 7 About Membranes

Being selectively permeable means that only certain substances are allowed to cross a barrier or membrane, while others are not. This process is essential for maintaining homeostasis in cells and organisms, as it allows the regulation of what enters and exits a cell or organ. Selective permeability ensures that necessary molecules, such as nutrients and oxygen, can enter while harmful substances and waste products are prevented from crossing. This mechanism is crucial for the proper functioning of biological systems.

If a solution is isotonic, it means that the concentration of solutes (other things) is equal to the concentration of water. In other words, there is an equal balance between the amount of solutes and the amount of water in the solution.

The equation Psi S = -iCRT is known as the van't Hoff equation, which relates the change in entropy of a reaction (ΔS) to the temperature (T), the gas constant (R), the molar concentration (C), and the ionication constant (i). In this equation, T represents the temperature in Kelvin. Therefore, the correct answer is Temperature in Kelvin.

Osmosis is the process of diffusion of water across a selectively permeable membrane. It occurs when there is a difference in solute concentration on either side of the membrane, causing water molecules to move from an area of lower solute concentration to an area of higher solute concentration. This movement of water helps to equalize the concentration of solutes on both sides of the membrane. Therefore, the correct answer is "Diffusion of water."

If an animal cell is placed in an isotonic solution, it means that the concentration of solutes inside and outside the cell is the same. In this case, there will be no net movement of water into or out of the cell. As a result, the cell will maintain its normal shape and size, and it will be able to carry out its normal functions. Therefore, the cell will live in an isotonic solution.

Co-transport refers to the process in which two substances are simultaneously transported across a cell membrane. This can occur through various mechanisms such as symport, where both substances are transported in the same direction, or antiport, where the substances are transported in opposite directions. In co-transport, the movement of one substance is coupled with the movement of another, allowing for the efficient uptake or secretion of multiple molecules by cells.

The hypertonic part of the solution refers to the part that has the highest concentration of solutes or other substances compared to the solvent. In this case, the correct answer "Least water, most other thing" indicates that the solution has a higher concentration of solutes or other substances and a lower concentration of water. This means that the solution is hypertonic, as it has a higher osmotic pressure compared to the surrounding environment.

The correct answer is "Ionication constant." In the given equation, Psi S = -iCRT, "i" represents the ionication constant. This constant is used to calculate the effect of ions on colligative properties, such as boiling point elevation and freezing point depression. It is a dimensionless quantity that represents the number of ions produced when a compound dissociates in a solution.

The fluid-mosaic model is the current model of cell membranes. This model describes the structure of the cell membrane as a fluid lipid bilayer with embedded proteins. The lipid bilayer is composed of phospholipids, which are arranged in a fluid-like manner, allowing for flexibility and movement of molecules within the membrane. The proteins embedded in the lipid bilayer are diverse and have various functions, such as transport, signaling, and structural support. This model emphasizes the dynamic nature of cell membranes and the mosaic-like arrangement of lipids and proteins.

Diffusion is the process by which molecules move from an area of high concentration to an area of low concentration. This movement occurs passively, meaning that it does not require any energy input. Therefore, the correct answer is "High to low concentration, passive transport."

The hypotonic part of a solution refers to the portion of the solution that has a lower concentration of solutes compared to another solution. In this case, the correct answer is "Most water, least other thing." This means that the hypotonic part of the solution contains a higher proportion of water and a lower concentration of other substances or solutes.

The correct answer is "-iCRT". This is because the question asks for "Psi S", and the negative sign indicates that it is the negative value of iCRT.

Aquaporins are proteins that facilitate the movement of water across membranes. These proteins form channels in the membrane, allowing water molecules to pass through. They are found in various cells and tissues throughout the body and play a crucial role in maintaining water balance and regulating water movement in and out of cells. Lipids called aquaporins and proteins called hydroglycins are not correct explanations as they do not exist or have the same function as aquaporins.

When an animal cell is placed in a hypotonic solution, it means that the solution has a lower concentration of solutes compared to the cell's cytoplasm. As a result, water will move into the cell through osmosis, causing the cell to swell and potentially burst. This process is known as lysis. Since bursting can cause the cell to lose its structural integrity and essential components, the cell will not be able to survive and will eventually die. Therefore, the correct answer is that the cell will lyse (burst) and die.

Active transport is a process in which substances are transported across a cell membrane against their concentration gradient, from an area of lower concentration to an area of higher concentration. This process requires the use of ATP (adenosine triphosphate) as an energy source to pump the substances against the concentration gradient.

Psi P stands for pressure potential, which is typically zero. Pressure potential refers to the physical pressure exerted on water in a plant cell. In most cases, this pressure is negligible or zero, hence the term "usually zero". Pressure potential plays a role in determining the movement of water within plants, particularly in the process of water uptake and transport.

When an animal cell is placed in a hypertonic solution, the solution has a higher concentration of solutes compared to the cell. This causes water to move out of the cell through osmosis, resulting in the cell losing water and shrinking. As a result, the cell will shrivel and eventually die due to the loss of water and the inability to maintain its normal shape and function.

Receptor-mediated endocytosis is a process in which cells take in small amounts of specific substances that are selected by protein receptors. This process is highly regulated and allows cells to selectively internalize molecules such as hormones, enzymes, and nutrients. It is different from other forms of endocytosis because it involves the binding of specific ligands to receptors on the cell surface, triggering the formation of specialized vesicles that transport the selected substances into the cell. This mechanism ensures that only necessary molecules are taken up by the cell, maintaining homeostasis and regulating various cellular processes.

Non-polar substances can easily cross the membrane by going straight through the bilayer. The lipid bilayer is composed of a double layer of phospholipids, which have hydrophobic tails that repel water. Since non-polar substances are also hydrophobic, they can pass through the hydrophobic interior of the bilayer without the need for any additional transport proteins or channels. This allows non-polar substances to diffuse freely across the membrane.

Ionic substances cannot easily cross the lipid bilayer of a membrane due to their charge. Instead, they rely on protein channels or transporters to facilitate their movement across the membrane. These proteins create a passageway for the ions to move through, allowing them to cross the membrane. Therefore, the correct answer is "By going through the protein."

The correct answer is Gas constant (0.0831). In the equation Psi S = -iCRT, R represents the gas constant. The gas constant is a constant value that relates the properties of a gas to the amount of the gas present and the temperature. In this equation, R is used to calculate the osmotic pressure (Psi S) of a solution.

Psi S stands for solute potential. Solute potential is a measure of the effect of solute concentration on the movement of water molecules. It represents the tendency of water to move from a region of lower solute concentration to a region of higher solute concentration. A higher solute concentration leads to a lower solute potential, which in turn reduces the water potential.

Phagocytosis is the process by which cells engulf and ingest large chunks of material. This can include solid particles or even whole cells. The correct answer, A and B, is accurate because phagocytosis can be described as "cell eating" and involves taking large chunks of material into a cell at one time.

Embedded proteins have multiple functions in a cell. They are involved in the transport of polar substances across the membrane, which is important for maintaining cellular homeostasis. They also exhibit enzyme activity and sequencing, playing a crucial role in various metabolic processes within the cell. Embedded proteins are involved in signal transduction and cell communication, allowing cells to respond to external stimuli. They are also involved in cell-to-cell regulation, forming intercellular junctions such as tight and gap junctions. Additionally, embedded proteins help attach the extracellular matrix (ECM) to the cell. Therefore, all of the mentioned functions are performed by embedded proteins.

Pinocytosis is the process of "cell drinking" where small chunks of stuff, usually liquid, are taken into a cell at one time. The correct answer is C and D because both options describe pinocytosis accurately. "Cell eating" refers to phagocytosis, which is a different process where large chunks of stuff are taken into a cell at one time.

The fluid part of the fluid-mosaic model refers to the ability of the phospholipids in the cell membrane to move laterally or side to side. This means that the phospholipids can freely move within the membrane, allowing for flexibility and dynamic changes in the structure of the membrane. This fluidity is important for various cellular processes such as membrane fusion, cell signaling, and the movement of molecules across the membrane.

The term "mosaic" in the fluid-mosaic model refers to the arrangement of proteins within the phospholipid bilayer. Proteins are embedded in the phospholipid bilayer, creating a mosaic-like pattern. This means that the proteins are not uniformly distributed, but rather scattered throughout the lipid bilayer. This arrangement allows for various functions and roles of the proteins within the cell membrane, such as transport, signaling, and structural support.

To convert a temperature from Celsius to Kelvin, you need to add 273 to the Celsius value. This is because the Kelvin scale starts at absolute zero, which is -273.15 degrees Celsius. Therefore, to convert Celsius to Kelvin, you simply add 273 to the Celsius value.

When a plant cell is placed in a hypotonic solution, the concentration of solutes outside the cell is lower than inside the cell. As a result, water moves into the cell through osmosis, causing the cell to swell and become turgid or stiff. This is a normal response for plant cells and allows them to maintain their shape and carry out essential functions. Therefore, the plant cell will survive in a hypotonic solution.

Exocytosis is a type of bulk transport that involves the release of substances from the cell by fusing vesicles containing the substances with the cell membrane, allowing the contents to be expelled outside of the cell. Therefore, options A and C are correct as they both describe exocytosis accurately.

When a plant cell is placed in an isotonic solution, the concentration of solutes inside and outside the cell is the same. This means that there is no net movement of water into or out of the cell. As a result, the cell becomes flaccid or limp because there is no pressure exerted on the cell wall. However, the cell can still carry out its normal functions and survive in this state.

Endocytosis is the process of bringing substances into the cell through the formation of vesicles. It is a type of bulk transport where the cell engulfs molecules or particles from the external environment by forming a pocket in the cell membrane. This pocket then pinches off to form a vesicle, which is then transported into the cell's cytoplasm. Therefore, the correct answer is B and C, as endocytosis involves bringing stuff into the cell and is a type of bulk transport.

C in the equation Psi S = -iCRT represents molar concentration. The equation is known as the van 't Hoff factor equation, which relates the osmotic pressure (Psi S) to the molar concentration (C), temperature (T), gas constant (R), and the van 't Hoff factor (i). The molar concentration refers to the amount of a solute present in a given volume of solution and is measured in moles per liter (mol/L).

When a plant cell is placed in a hypertonic solution, the concentration of solutes outside the cell is higher than inside the cell. This causes water to move out of the cell, resulting in the cell membrane detaching from the cell wall. This process is known as plasmolysis. As a result, the cell becomes dehydrated and shrinks, leading to its death. Therefore, the correct answer is "it plasmolyzes and dies."

Facilitated diffusion refers to the process of molecules or ions moving across a cell membrane with the help of specific transport proteins. These proteins create channels or pores that allow the passage of certain substances that cannot freely diffuse through the phospholipid bilayer of the membrane. Therefore, the correct answer is "The diffusion of a substance through a protein pore."

Psi stands for water potential. Water potential is the measure of the potential energy of water in a system, and it determines the direction and rate of water movement. It takes into account factors such as pressure potential and solute potential. Pressure potential is usually zero, while solute potential is determined by the concentration of solutes in the water. Therefore, water potential is the most comprehensive term to encompass all the factors that influence water movement.

Cholesterol and unsaturated fatty acids can increase fluidity in membranes. Cholesterol is a lipid molecule that helps maintain the fluidity of the cell membrane by preventing the fatty acid chains from packing too closely together. Unsaturated fatty acids, on the other hand, have double bonds in their carbon chains, which introduce kinks and prevent tight packing, thus increasing membrane fluidity. Saturated fatty acids, in contrast, have no double bonds and tend to pack tightly, decreasing membrane fluidity. Glucose, a sugar molecule, does not have an effect on membrane fluidity.

Co-transport is useful when pumped out H+ ions are used to transport sucrose into the cell. This process involves the movement of both H+ ions and sucrose molecules across the cell membrane using a co-transport protein. The H+ ions are pumped out of the cell, creating a concentration gradient. This gradient is then used to drive the transport of sucrose molecules into the cell. The sucrose molecules bind to the co-transport protein, which also transports H+ ions. As the H+ ions move down their concentration gradient, they carry the sucrose molecules with them into the cell. This mechanism allows the cell to efficiently uptake sucrose for energy or other cellular processes.

The formula for water potential is Psi = Psi P + Psi S. This equation represents the total water potential (Psi) as the sum of the pressure potential (Psi P) and the solute potential (Psi S). The pressure potential is a measure of the physical pressure exerted on the water, while the solute potential is a measure of the effect of solute concentration on the water potential. By adding these two components together, we can determine the overall water potential.

Pressure potential refers to the amount of pressure that must be applied to prevent the movement of water. This is because water naturally moves from an area of higher pressure potential to an area of lower pressure potential. Therefore, to stop water from moving, an equal or greater amount of pressure must be applied.

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