AP Biology Ch 5 Outline Quiz Test

Explanation
The fluid-mosaic model is the current theory that best describes the structure of the plasma membrane. This model suggests that the membrane is composed of a fluid phospholipid bilayer with embedded proteins, resembling a mosaic pattern. The fluidity of the membrane allows for the movement of molecules and proteins within it, while the mosaic nature refers to the diverse arrangement of lipids and proteins. This model explains the dynamic and flexible nature of the plasma membrane and how it functions in controlling the movement of substances in and out of the cell.

Explanation
The correct answer is "all of the above" because whether a molecule can cross the plasma membrane depends on multiple factors. The size of the molecule is important as smaller molecules can pass through more easily. The shape of the molecule also plays a role, as certain shapes may hinder or facilitate movement across the membrane. The chemical properties of the molecule, such as its polarity or hydrophobicity, can affect its ability to interact with the lipid bilayer of the membrane. Additionally, the charge of the molecule can influence its interaction with charged components of the membrane. Therefore, all of these factors are considered when determining if a molecule can cross the plasma membrane.

Explanation
Pinocytosis is a type of endocytosis, which is the process by which cells take in molecules or particles from their external environment by engulfing them into a vesicle. In pinocytosis, the cell takes in fluid droplets or small solute molecules by forming small vesicles around them. This process does not require energy input and is therefore considered a form of passive transport. Facilitated transport, active transport, cotransport, and exocytosis are all different processes that involve the movement of molecules across cell membranes, but they are not specifically related to the process of pinocytosis.

Explanation
The lipid portion of a plasma membrane is composed of phospholipids, which have a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail. These phospholipids are arranged in a bilayer, with the hydrophilic heads facing outward towards the watery environment and the hydrophobic tails facing inward, away from water. This arrangement allows the lipid portion of the membrane to behave like a fluid, with the phospholipids able to move and slide past each other. At the temperature of the human body, which is around 37 degrees Celsius, the lipid portion of the plasma membrane is in a fluid state, similar to the consistency of olive oil. Therefore, the statement is true.

Explanation
The statement is false because not all cells contain the same kinds of proteins in the same relative locations. Different types of cells have different protein compositions and distributions based on their specific functions and structures. For example, muscle cells have proteins like actin and myosin that enable muscle contraction, while nerve cells have proteins like neurotransmitters that facilitate communication between neurons. Additionally, proteins can be localized to specific organelles within a cell, such as the mitochondria or the nucleus, further highlighting the variability in protein distribution among different cell types.

Explanation
Cells placed in an isotonic environment will not die as they will maintain a stable balance of solute concentration inside and outside the cell. In an isotonic environment, the concentration of solutes outside the cell is the same as inside the cell, resulting in no net movement of water across the cell membrane. As a result, the cells will not swell or burst and will be able to function normally.

Explanation
Carrier proteins play a crucial role in active transport, which is the movement of molecules against their concentration gradient. These proteins bind to specific molecules or ions and undergo a conformational change to transport them across the cell membrane. This process requires energy to be expended, usually in the form of ATP. Therefore, carrier proteins are indeed necessary for active transport to occur.

Explanation
The statement is true because the sodium-potassium pump is a vital mechanism in maintaining the cell's electrochemical gradient. It uses energy from ATP to actively transport sodium ions out of the cell and potassium ions into the cell. This process is crucial for various cellular functions, such as nerve impulse transmission and maintaining proper cell volume.

Explanation
Phagocytosis is the process by which a white blood cell or an amoeba engulfs bacteria. This process involves the cell extending its membrane around the bacteria, forming a vacuole that is then transported to the cell's interior for digestion. Therefore, the statement is true.

Explanation
Receptors play a crucial role in the movement of certain materials across the plasma membrane. They can bind to specific molecules or ions and trigger a response within the cell, leading to the transport of these substances across the membrane. This process is essential for various cellular functions such as signal transduction, nutrient uptake, and hormone regulation. Therefore, it is accurate to say that receptors are involved in the movement of some materials across the plasma membrane.