Biology Cell Membrane Functions

Questions and Answers

What is the function of a transport protein?

allow solute molecules to enter the cell.

Which of these cannot rapidly pass directly through the phospholipids of the plasma membrane?

Water (correct)

Hydrogen ion (correct)

Oxygen

Glucose (correct)

What is the function of cholesterol?

helps to stabilize the structure of the plasma membrane (phospholipids)

Which of the following best describes the structure of a biological membrane?

two layers of phospholipids with proteins either crossing the layers or on the surface of the layers Signup and view all the answers

The fluid mosaic model of the membrane proposed that membranes ________.

consist of protein molecules embedded in a fluid bilayer of phospholipids. Signup and view all the answers

A primary function of cholesterol in the plasma membranes of some animals is to ________.

enable the membrane to stay fluid more easily when the temperature drops. Signup and view all the answers

An integral membrane protein would have to be ________.

amphipathic, with at least one hydrophobic region. Signup and view all the answers

How do unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

The double bonds form kinks in the fatty acid tails that prevent adjacent lipids from packing tightly together. Signup and view all the answers

In facilitated diffusion, what is the role of the transport protein?

Transport proteins provide a hydrophilic route for the solute to cross the membrane. Signup and view all the answers

Which of the following is a characteristic feature of a carrier protein in a plasma membrane?

It exhibits a specificity for a particular type of molecule. Signup and view all the answers

Water passes quickly through cell membranes because _______.

it moves through aquaporin channel proteins. Signup and view all the answers

Which of the following factors does not affect membrane permeability?

The polarity of membrane phospholipids Signup and view all the answers

How can a lipid be distinguished from a sugar?

Lipids are mostly nonpolar. Signup and view all the answers

True or false? Osmosis is a type of diffusion.

True Signup and view all the answers

What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?

Amphipathic nature Signup and view all the answers

Which of the following particles could diffuse easily through a cell membrane?

Oxygen (O2) Signup and view all the answers

True or false? The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate group.

True Signup and view all the answers

If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?

Hypotonic Signup and view all the answers

What name is given to the process by which water crosses a selectively permeable membrane?

osmosis Signup and view all the answers

What kind of solution is a cell in if there is a greater concentration of solute outside of the cell?

Hypertonic Signup and view all the answers

You know that a cell is in a(n) _ solution because the cell _.

hypotonic...swelled Signup and view all the answers

You know that this cell is in a(n) _ solution because it _.

hypertonic...lost water Signup and view all the answers

Submerging a red blood cell in a hypertonic solution will result in _______.

the cell wall shriveling. Signup and view all the answers

A patient has had a serious accident and lost a lot of blood. In an attempt to replenish body fluids, distilled water equal to the volume of blood lost is transferred directly into one of his veins. What will be the most probable result of this transfusion?

The patient's red blood cells will swell because the blood fluid has become hypotonic compared to the cells. Signup and view all the answers

A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. Indicate whether crenation, hemolysis, or neither will occur in Solution A: 3.21% (m/v) NaCl; Solution B: 1.65% (m/v) glucose; Solution C: distilled H2O; Solution D: 6.97% (m/v) glucose; Solution E: 5.0% (m/v) glucose and 0.9% (m/v) NaCl.

Crenation: A, D, E; Hemolysis: B, C Signup and view all the answers

Which of the following statements is TRUE with regard to this animation of active transport?

Both sodium and potassium ions are transported against their concentration gradients. Signup and view all the answers

Active and passive transport of solutes across a membrane typically differ in which of the following ways?

Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy. Signup and view all the answers

The movement of glucose into a cell against a concentration gradient is most likely to be accomplished by which of the following?

cotransport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis Signup and view all the answers

What is the voltage across a membrane called?

membrane potential Signup and view all the answers

The sodium-potassium pump is called an electrogenic pump because it _______.

contributes to the membrane potential. Signup and view all the answers

Which of the following would increase the electrochemical gradient across a membrane?

a proton pump Signup and view all the answers

Endocytosis moves materials _ a cell via _.

into...membranous vesicles Signup and view all the answers

You can recognize the process of pinocytosis when _______.

the cell is engulfing extracellular fluid Signup and view all the answers

A white blood cell engulfing a bacterium is an example of _______.

phagocytosis Signup and view all the answers

Which of the following correctly describes some aspect of exocytosis or endocytosis?

Exocytosis and endocytosis change the surface area of the plasma membrane. Signup and view all the answers

The difference between pinocytosis and receptor-mediated endocytosis is that _______.

pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis is highly selective. Signup and view all the answers

A signal transduction pathway is initiated when a _______ binds to a receptor.

signal molecule Signup and view all the answers

A signal molecule is also known as a(n) _______.

ligand Signup and view all the answers

Which of these is the second of the three stages of cell signaling?

Transduction Signup and view all the answers

Which of the following is a substance that acts at a long distance from the site at which it is secreted?

hormone Signup and view all the answers

Why are there often so many steps between the original signal event and the cell's response?

Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses. Signup and view all the answers

Which of the following sequences is/are correct?

All of the above Signup and view all the answers

Immediately following binding of a growth factor, an activated receptor would most likely stimulate ________.

activation of a protein kinase. Signup and view all the answers

Following activation of a receptor, which sequence below represents the correct order in which components will be involved in a signaling pathway that utilizes the second messenger cAMP?

G protein → adenyl cyclase → cAMP → protein kinase Signup and view all the answers

Which of the following enzymes adds a phosphate group to target proteins?

kinase Signup and view all the answers

Which of the following is least likely to be important in holding the components of a biological membrane together?

Covalent interactions between the phospholipid and protein components of the membrane Signup and view all the answers

Which of the following factors would tend to increase membrane fluidity?

A greater proportion of unsaturated phospholipids Signup and view all the answers

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because __________.

they amplify the original signal manifold Signup and view all the answers

Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect ONLY target cells because __________.

intracellular receptors are present only in target cells Signup and view all the answers

Which of the following molecular movements is due to diffusion or osmosis?

When a plant cell is placed in concentrated salt water, water moves out of the cell. Signup and view all the answers

Which statement is correct?

The contents of a red blood cell are hyperosmotic to distilled water. A solution of seawater is hypertonic. Signup and view all the answers

Select the correct statement about osmosis.

Osmosis is the diffusion of water molecules across a selectively permeable membrane. Signup and view all the answers

What are the functions of signal transduction pathways?

Signal transduction pathways convert a signal on a cell's surface to a specific cellular response. Signal transduction pathways allow different types of cells to respond differently to the same signal molecule. Signal transduction pathways amplify the effect of a signal molecule. Signup and view all the answers

Select the statement that correctly distinguishes between relay proteins and second messengers in signal transduction pathways.

Signal transduction pathways are multistep pathways that include relay proteins and small, nonprotein, water-soluble molecules or ions called second messengers. Signup and view all the answers

Study Notes

Transport Proteins and Membrane Structure

Transport proteins facilitate the movement of solute molecules into cells.
Certain substances, such as water, glucose, and hydrogen ions, cannot pass through phospholipids of the plasma membrane rapidly.
Cholesterol stabilizes the structure of phospholipid membranes and maintains fluidity under varying temperatures.

Fluid Mosaic Model

Biological membranes consist of two layers of phospholipids, incorporated with proteins that span or are attached to the membrane surface.
The fluid mosaic model describes membranes as protein molecules embedded in a fluid bilayer.

Membrane Permeability and Transport

Integral membrane proteins are amphipathic, featuring both hydrophilic and hydrophobic regions.
Unsaturated fatty acids introduce kinks in lipid tails, enhancing membrane fluidity at lower temperatures.
Facilitated diffusion involves transport proteins creating hydrophilic pathways for solute movement.

Osmosis and Tonicity

Osmosis refers to the diffusion of water through selectively permeable membranes, facilitating the movement of water in relation to solute concentration.
A hypotonic solution has a lower solute concentration than a cell, leading to swelling due to water influx.
A hypertonic solution causes cells to lose water and shrink (crenation).
Isotonic solutions prevent osmotic imbalance, maintaining cell shape and size.

Active Transport and Signaling Pathways

Active transport, such as the sodium-potassium pump, requires ATP energy to move ions against their concentration gradients.
Signal transduction pathways initiate responses when a ligand binds to a receptor, triggering a cascade of intracellular reactions.
Each step in a signaling cascade amplifies the signal for greater cellular response.

Types of Endocytosis and Exocytosis

Endocytosis transports materials into cells through vesicles, while exocytosis expels materials, altering membrane surface area.
Pinocytosis is the non-selective uptake of fluids, while phagocytosis specifically involves engulfing larger particles, such as bacteria.

Signal Transduction and Hormones

Hormones act as long-distance signaling molecules, affecting only target cells equipped with specific receptors.
Kinases add phosphate groups to target proteins, playing a critical role in transduction pathways.
Phosphorylation cascades amplify signals after receptor activation.

Key Definitions and Concepts

Membrane potential refers to the voltage across a cell membrane, crucial for cellular function.
Lipid-soluble molecules can cross membranes but affect only target cells with specific receptors.
Diffusion movement includes the behavior of water in hypertonic environments, highlighting the dynamics of osmosis.
Relay proteins and second messengers work together within signaling pathways to relay signals from receptors to effectors.

Membrane Composition and Functionality

Membranes rely on non-covalent interactions to maintain structure, emphasizing lipid and protein dynamics.
Increasing the proportion of unsaturated phospholipids enhances membrane fluidity, crucial for many cellular processes.

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Description

Test your knowledge on the functions and components of the cell membrane with this quiz. From transport proteins to the role of cholesterol, assess your understanding of how molecules interact with the plasma membrane. Perfect for students studying cellular biology!