AP Biology Quiz Challenge

1. The current theory of the structure of the plasma membrane is best described by the ____ model.

Sandwich

Fluid-mosaic

Unit membrane

Electrochemical

Unipermeable

The fluid-mosaic model is the accepted theory describing the structure of the plasma membrane. According to this model, the membrane is composed of a double layer of phospholipids with proteins embedded throughout. The "fluid" part refers to the flexibility of the lipid bilayer, allowing lipids and proteins to move sideways within the layer. The "mosaic" part describes the pattern produced by the scattered protein molecules when the membrane is viewed from above. This model explains how the membrane functions in a dynamic and flexible manner, allowing for selective permeability and the fluid movement of substances across the membrane.

Explanation

The fluid-mosaic model is the accepted theory describing the structure of the plasma membrane. According to this model, the membrane is composed of a double layer of phospholipids with proteins embedded throughout. The "fluid" part refers to the flexibility of the lipid bilayer, allowing lipids and proteins to move sideways within the layer. The "mosaic" part describes the pattern produced by the scattered protein molecules when the membrane is viewed from above. This model explains how the membrane functions in a dynamic and flexible manner, allowing for selective permeability and the fluid movement of substances across the membrane.

2. Does a molecule's ability to cross the plasma membrane depend upon its size, shape, chemical properties, and charge?

The size of the molecule.

The shape of the molecule.

The chemical properties of the molecule.

The charge of the molecule.

All of the above.

The ability of a molecule to cross the plasma membrane depends on several factors: its size, shape, chemical properties, and charge. Small, nonpolar molecules can easily pass through the lipid bilayer, while larger or polar molecules require specific transport proteins. The shape of the molecule can affect how it interacts with membrane components and fits through transport channels. Chemical properties, such as hydrophobic or hydrophilic nature, determine how well a molecule can dissolve in the lipid bilayer. Additionally, the charge of a molecule influences its interaction with the membrane's electric field and transport proteins, affecting its ability to cross.

Explanation

The ability of a molecule to cross the plasma membrane depends on several factors: its size, shape, chemical properties, and charge. Small, nonpolar molecules can easily pass through the lipid bilayer, while larger or polar molecules require specific transport proteins. The shape of the molecule can affect how it interacts with membrane components and fits through transport channels. Chemical properties, such as hydrophobic or hydrophilic nature, determine how well a molecule can dissolve in the lipid bilayer. Additionally, the charge of a molecule influences its interaction with the membrane's electric field and transport proteins, affecting its ability to cross.

3. All cells contain the same kinds of proteins in the same relative locations.

True

False

Not all cells contain the same kinds of proteins in the same relative locations. The types and locations of proteins within a cell vary depending on the cell's function, type, and the specific requirements of the organism. For example, muscle cells have abundant contractile proteins like actin and myosin, while nerve cells contain proteins necessary for signal transmission. Additionally, membrane proteins can differ between cell types, contributing to distinct cellular functions such as nutrient uptake, signaling, and cell recognition. This diversity in protein composition and distribution allows for the specialization and efficient functioning of different cell types within an organism.

Explanation

Not all cells contain the same kinds of proteins in the same relative locations. The types and locations of proteins within a cell vary depending on the cell's function, type, and the specific requirements of the organism. For example, muscle cells have abundant contractile proteins like actin and myosin, while nerve cells contain proteins necessary for signal transmission. Additionally, membrane proteins can differ between cell types, contributing to distinct cellular functions such as nutrient uptake, signaling, and cell recognition. This diversity in protein composition and distribution allows for the specialization and efficient functioning of different cell types within an organism.

4. The process by which a white blood cell or an amoeba engulfs bacteria is called phagocytosis.

True

False

Phagocytosis is the process by which cells, such as white blood cells or amoebas, engulf and ingest large particles, including bacteria. During phagocytosis, the cell extends its membrane around the particle to form a phagosome, a vesicle that encloses the ingested material. The phagosome then fuses with a lysosome, where the contents are digested and broken down by enzymes. This process is a crucial part of the immune response in multicellular organisms, allowing cells to remove pathogens and debris. In amoebas, phagocytosis serves as a primary means of obtaining nutrients.

Explanation

Phagocytosis is the process by which cells, such as white blood cells or amoebas, engulf and ingest large particles, including bacteria. During phagocytosis, the cell extends its membrane around the particle to form a phagosome, a vesicle that encloses the ingested material. The phagosome then fuses with a lysosome, where the contents are digested and broken down by enzymes. This process is a crucial part of the immune response in multicellular organisms, allowing cells to remove pathogens and debris. In amoebas, phagocytosis serves as a primary means of obtaining nutrients.

5. Cells placed in an isotonic environment will die as they swell and burst.

True

False

Cells placed in an isotonic environment will neither swell nor burst; they will maintain their normal shape and function. In an isotonic environment, the concentration of solutes outside the cell is equal to the concentration of solutes inside the cell. This balance means there is no net movement of water into or out of the cell, preventing any change in cell volume. This equilibrium allows cells to function properly without the risk of swelling or shrinking, making isotonic solutions ideal for maintaining cell viability and stability in physiological conditions.

Explanation

Cells placed in an isotonic environment will neither swell nor burst; they will maintain their normal shape and function. In an isotonic environment, the concentration of solutes outside the cell is equal to the concentration of solutes inside the cell. This balance means there is no net movement of water into or out of the cell, preventing any change in cell volume. This equilibrium allows cells to function properly without the risk of swelling or shrinking, making isotonic solutions ideal for maintaining cell viability and stability in physiological conditions.

6. In the sodium-potassium pump, sodium is transported out of the cell and potassium is transported into the cell as ATP is broken by a membrane protein.

True

False

The sodium-potassium pump actively transports sodium (Na⁺) out of the cell and potassium (K⁺) into the cell, using energy from the hydrolysis of ATP. This membrane protein, also known as an ATPase, binds three sodium ions inside the cell and transports them out, while simultaneously binding two potassium ions from outside the cell and transporting them in. The energy for this process comes from breaking down one molecule of ATP into ADP and inorganic phosphate. This pump is crucial for maintaining the cell's electrochemical gradient, essential for various cellular processes such as nerve impulse transmission and muscle contraction.

Explanation

The sodium-potassium pump actively transports sodium (Na⁺) out of the cell and potassium (K⁺) into the cell, using energy from the hydrolysis of ATP. This membrane protein, also known as an ATPase, binds three sodium ions inside the cell and transports them out, while simultaneously binding two potassium ions from outside the cell and transporting them in. The energy for this process comes from breaking down one molecule of ATP into ADP and inorganic phosphate. This pump is crucial for maintaining the cell's electrochemical gradient, essential for various cellular processes such as nerve impulse transmission and muscle contraction.

7. Carrier proteins are necessary for active transport to occur.

True

False

Carrier proteins are essential for active transport to occur. Active transport is the process by which cells move molecules against their concentration gradient, from areas of lower concentration to areas of higher concentration. This process requires energy, usually in the form of ATP, and relies on specific carrier proteins embedded in the cell membrane. These carrier proteins bind to the molecules being transported and undergo conformational changes to move the molecules across the membrane. Without carrier proteins, the cell would not be able to perform active transport, which is crucial for maintaining cellular functions and homeostasis.

Explanation

Carrier proteins are essential for active transport to occur. Active transport is the process by which cells move molecules against their concentration gradient, from areas of lower concentration to areas of higher concentration. This process requires energy, usually in the form of ATP, and relies on specific carrier proteins embedded in the cell membrane. These carrier proteins bind to the molecules being transported and undergo conformational changes to move the molecules across the membrane. Without carrier proteins, the cell would not be able to perform active transport, which is crucial for maintaining cellular functions and homeostasis.

8. Receptors are involved in the movement of some materials across the plasma membrane.

True

False

Receptors play a crucial role in the movement of some materials across the plasma membrane. These membrane proteins bind to specific molecules, such as hormones or nutrients, initiating a cellular response. In receptor-mediated endocytosis, receptors on the cell surface bind to target molecules, triggering the formation of a vesicle that transports the bound molecules into the cell. This selective uptake mechanism ensures that cells efficiently capture necessary substances from their environment. Receptors are also involved in signal transduction, where they relay external signals into the cell, affecting various physiological processes and responses.

Explanation

Receptors play a crucial role in the movement of some materials across the plasma membrane. These membrane proteins bind to specific molecules, such as hormones or nutrients, initiating a cellular response. In receptor-mediated endocytosis, receptors on the cell surface bind to target molecules, triggering the formation of a vesicle that transports the bound molecules into the cell. This selective uptake mechanism ensures that cells efficiently capture necessary substances from their environment. Receptors are also involved in signal transduction, where they relay external signals into the cell, affecting various physiological processes and responses.

9. The lipid portion of a plasma membrane acts like a liquid at the temperature of the human body.

True

False

The lipid portion of the plasma membrane does act like a liquid at human body temperature (around 37°C or 98.6°F). This fluidity is due to the unsaturated fatty acid tails in the phospholipids, which prevent the molecules from packing tightly together. This characteristic allows the membrane to be flexible and dynamic, enabling the movement of proteins within the lipid bilayer and allowing for various cellular processes such as membrane fusion, endocytosis, and the proper functioning of membrane proteins. The fluid nature of the membrane is crucial for the cell's ability to adapt to changes and maintain homeostasis.

Explanation

The lipid portion of the plasma membrane does act like a liquid at human body temperature (around 37°C or 98.6°F). This fluidity is due to the unsaturated fatty acid tails in the phospholipids, which prevent the molecules from packing tightly together. This characteristic allows the membrane to be flexible and dynamic, enabling the movement of proteins within the lipid bilayer and allowing for various cellular processes such as membrane fusion, endocytosis, and the proper functioning of membrane proteins. The fluid nature of the membrane is crucial for the cell's ability to adapt to changes and maintain homeostasis.

10. Pinocytosis is an example of:

Facilitated transport.

Active transport.

Cotransport.

Endocytosis.

Exocytosis.

Pinocytosis is a type of endocytosis where the cell engulfs liquid from its surroundings, incorporating the liquid and any dissolved substances into small vesicles. This process involves the cell membrane folding inward to form a pocket, which then pinches off to form an internal vesicle. Pinocytosis is often referred to as "cell drinking" because it involves the intake of extracellular fluids. This mechanism allows cells to take in large quantities of fluids and solutes, which are essential for various cellular functions. Unlike facilitated transport, pinocytosis requires energy, making it an active process.

Explanation

Pinocytosis is a type of endocytosis where the cell engulfs liquid from its surroundings, incorporating the liquid and any dissolved substances into small vesicles. This process involves the cell membrane folding inward to form a pocket, which then pinches off to form an internal vesicle. Pinocytosis is often referred to as "cell drinking" because it involves the intake of extracellular fluids. This mechanism allows cells to take in large quantities of fluids and solutes, which are essential for various cellular functions. Unlike facilitated transport, pinocytosis requires energy, making it an active process.