Biology 1401: Chapter 5 Membranes

When a cell has the same concentration of dissolved molecules as its outside environment, it is in an isotonic condition. In an isotonic solution, there is no net movement of water across the cell membrane, as the concentration of solutes inside and outside the cell is balanced. This means that the cell maintains its shape and size without gaining or losing water.

Osmosis is the movement of water molecules from an area of lower solute concentration to an area of higher solute concentration through a semi-permeable membrane. The semi-permeable membrane allows the passage of water molecules but restricts the movement of solute particles. Therefore, osmosis can only occur if water travels through the semi-permeable membrane. The other options mentioned, such as the cell wall, vacuole, ER, and cytoskeleton, are not directly involved in the process of osmosis.

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Diffusion is the movement of substances from regions of higher concentration to regions of lower concentration. It occurs passively, without the need for energy input. Active transport, on the other hand, requires energy to move substances against their concentration gradient. Osmosis is a specific type of diffusion that refers to the movement of water molecules across a selectively permeable membrane. Pumping and exocytosis are processes that involve the active movement of substances across cell membranes. Therefore, the correct answer is diffusion.

During a single sodium-potassium pump cycle, ATP is used up to transport 3 sodium ions out of the cell and 2 potassium ions into the cell. This pump is responsible for maintaining the concentration gradients of sodium and potassium across the cell membrane, as it moves sodium ions against their concentration gradient and potassium ions with their concentration gradient. This active transport process is essential for various cellular functions, including nerve impulse transmission and muscle contraction.

Cholesterol is an important component of the plasma membrane and plays a crucial role in maintaining its fluidity. It helps to regulate the fluidity of the membrane by preventing it from becoming too rigid or too fluid. This is important for the proper functioning of the membrane, as it allows for the movement of molecules and ions across the membrane, as well as the interaction of proteins within the membrane. Cholesterol also helps to stabilize the membrane and protect it from damage. Therefore, the correct answer is maintain fluidity.

Diffusion is the process by which molecules move from areas of high concentration to areas of lower concentration until an equilibrium is reached. This occurs due to the random motion of molecules, where they move freely and collide with each other. As a result of these collisions, molecules tend to spread out and distribute evenly throughout a given space. This movement continues until the concentration of molecules becomes equal in all areas, which is known as equilibrium. Therefore, the correct answer is that molecules must move from areas of high concentration to areas of lesser concentration until an equilibrium is reached.

The plasma membrane is composed of a thin sheet of phosphate lipid that is embedded with proteins. These proteins play a crucial role in various cellular processes such as transport of molecules, cell signaling, and cell adhesion. They also act as receptors for hormones and other signaling molecules. Additionally, some proteins in the plasma membrane form channels that allow the passage of specific ions and molecules. Therefore, proteins are an essential component of the plasma membrane and are responsible for its structure and function.

Hormones are not found as membrane proteins because they are signaling molecules that are secreted by glands into the bloodstream to target distant cells. They travel through the bloodstream and bind to specific receptors on the surface of target cells, initiating a cellular response. Unlike membrane proteins, hormones are not directly embedded in the cell membrane but rather act as signaling molecules that interact with membrane proteins and initiate intracellular signaling pathways.

When two solutions have unequal concentrations of a solute, the solution with the lower concentration is called hypotonic. In a hypotonic solution, there is a higher concentration of water molecules outside the cell compared to inside the cell. This causes water to move into the cell through the process of osmosis, leading to cell swelling or bursting.

The plasma membrane is responsible for various functions in a cell, including selective transport of molecules, reception of information, and expression of cellular identity. However, synthesis of DNA is not a function of the plasma membrane. DNA synthesis occurs in the nucleus of the cell, where the DNA is replicated during cell division. The plasma membrane does not play a direct role in this process.

If the function of transport proteins is blocked, the process that will be blocked is active transport. Active transport is the movement of substances across a cell membrane against their concentration gradient, requiring the use of energy. Since the chemical added blocks the function of transport proteins, it will prevent the active transport of substances across the membrane. Osmosis, diffusion, phagocytosis, and pinocytosis are not dependent on transport proteins and will not be affected by the chemical.

A hypotonic solution has a lower solute concentration compared to the inside of the blood cells. When blood cells are placed in a hypotonic solution, water molecules move into the cells through osmosis. This causes the cells to swell and potentially burst, leading to blood cell lysis.

The correct answer is "Only the saturated fatty acids are always present." This statement is not true because membrane phospholipids can contain both saturated and unsaturated fatty acids. Unsaturated fatty acids have double bonds in their carbon chains, which can introduce kinks and increase fluidity in the membrane. Therefore, the presence of unsaturated fatty acids in membrane phospholipids is essential for maintaining the fluidity and flexibility of the membrane.

Facilitated diffusion is a process by which molecules move across a cell membrane with the help of specific carrier molecules. These carrier molecules are specific to the molecule being transported, meaning they can only bind to and transport a particular molecule. The direction of movement in facilitated diffusion is always with the concentration gradient, meaning molecules move from an area of higher concentration to an area of lower concentration. This is because the carrier molecules facilitate the movement of molecules down their concentration gradient, requiring no energy input.

Active transport is the correct answer because it involves the movement of solutes across a membrane against their concentration gradient, which requires the expenditure of energy. This energy is provided by ATP, a molecule that stores and releases chemical energy. Protein carriers are used in active transport to transport the solutes across the membrane. Osmosis is the movement of water molecules across a membrane, diffusion is the movement of solutes from an area of high concentration to an area of low concentration, facilitated transport is the movement of solutes across a membrane with the help of specific proteins, and exocytosis is the process of releasing molecules from a cell by fusion of vesicles with the cell membrane.

The Fluid Mosaic Model proposed by Singer and Nicolson in 1972 suggested that the cell membrane is made up of a phospholipid bilayer with globular proteins embedded within the bilayer. This means that the proteins are not just attached to the surface of the membrane, but are actually inserted into the lipid bilayer. This model also implies that the membrane is fluid, allowing for movement of the lipids and proteins within it.

Active transport is the process of moving molecules or ions 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 carrier molecules, such as proteins, to transport the molecules or ions across the membrane. Additionally, active transport also requires the input of energy in the form of ATP. Therefore, active transport is the type of transport that is specific, requires specific carrier molecules, and energy.

Hydrogen bonding of water holding the membrane together does not influence membrane fluidity because it is a separate mechanism that helps stabilize the structure of the membrane. Membrane fluidity is primarily influenced by temperature, the addition of cholesterol, and the introduction of double bonds into fatty acids. A decrease in temperature decreases fluidity, while an increase in temperature increases fluidity. The addition of cholesterol helps regulate fluidity by reducing it at high temperatures and increasing it at low temperatures. The introduction of double bonds into fatty acids increases fluidity by creating kinks in the fatty acid chains.

In bacteria, fungi, and plants, the high internal pressure generated by osmosis is counteracted by the mechanical strength of their cell walls. The cell walls provide a rigid structure that prevents the cells from bursting under osmotic pressure. The cell walls act as a protective barrier and help maintain the shape and integrity of the cells. This is why cell walls are the correct answer in this context.

When a selectively permeable membrane is present, only water molecules can pass through it, while larger molecules like glucose cannot. In this case, the artificial cell contains a 5M solution of glucose, which means that the concentration of glucose inside the cell is higher than in the surrounding beaker of water. As a result, water molecules will move from an area of lower concentration (the beaker) to an area of higher concentration (the cell) through osmosis. Therefore, the observation that is expected to be seen is that water moves into the cell.

Carbohydrate chains are marker molecules found on the outer surface of the plasma membrane that help identify the cell-type. These chains, also known as glycoproteins or glycolipids, are composed of sugar molecules attached to proteins or lipids. They play a crucial role in cell recognition and communication, allowing cells to interact with each other and with their environment. ATP, amino acids, nucleotides, and inorganic ions are important molecules in cellular processes, but they do not serve as marker molecules on the plasma membrane.

The correct answer is "conformation." The explanation for this is that the actual transport of protons by the proton pump is facilitated by a transmembrane protein. This protein undergoes a change in its conformation, or shape, which allows it to transport the protons across the membrane. The change in conformation is crucial for the protein's function as a proton pump, as it enables the protein to bind to and transport the protons effectively.

The fluid nature of the membranes is attributed to a lateral movement of phospholipid molecules. Phospholipids are the main components of cell membranes and they have a hydrophilic (water-loving) head and hydrophobic (water-repelling) tail. This structure allows them to form a bilayer, with the hydrophilic heads facing outward towards the aqueous environment and the hydrophobic tails facing inward. The phospholipid molecules can move laterally within the membrane, which gives the membrane its fluidity. This fluidity is important for various cellular processes, such as the movement of proteins and other molecules within the membrane.

Coupled transport refers to the process by which two or more substances are transported across a cell membrane simultaneously, using the energy from one substance moving down its concentration gradient to power the movement of another substance against its concentration gradient. In the case of the accumulation of amino acids and sugars in animal cells, coupled transport allows these molecules to be taken up against their concentration gradients, with the energy provided by the movement of ions such as sodium or hydrogen. This process is essential for the uptake of nutrients and maintaining cellular homeostasis.

In this experiment, the artificial cell has a selectively permeable membrane that only allows water to pass through. The concentration of glucose inside the cell is lower (5M) compared to the concentration outside the cell (10M). According to the principle of osmosis, water will move from an area of lower solute concentration (inside the cell) to an area of higher solute concentration (outside the cell) to equalize the solute concentrations. Therefore, water will move out of the cell, resulting in a decrease in cell weight.

Aquaporins are not a component of an animal cell membrane. Aquaporins are specialized proteins that function as water channels, allowing for the movement of water molecules across cell membranes. While phospholipids, polynucleotides, glycolipids, and cholesterol are all components of the animal cell membrane, aquaporins are not.

The sodium-potassium pump is a membrane protein responsible for maintaining the concentration of sodium and potassium ions inside and outside of the cell. It works by binding three sodium ions on the cytoplasmic side of the protein, which are then translocated out of the cell. Simultaneously, two potassium ions are transported into the cell. ATP binds to the protein, causing it to become phosphorylated and release ADP. The correct answer states that phosphate facilitates potassium ion binding to the transport protein, which is not a part of the sodium-potassium pump process.

The cell's plasma membrane mediates its transactions with the environment, including ingesting food, returning waste, responding to chemical cues, and passing messages to other cells. However, directing the synthesis of various food-digesting proteins is not a transaction that is mediated by the plasma membrane. This process occurs within the cell's cytoplasm and is regulated by the cell's genetic material and intracellular machinery.

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