1.3 Cell Membrane Transport Overview

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Questions and Answers

Which substance is found in higher concentration in extracellular fluid compared to intracellular fluid?

Phosphates

Sodium (correct)

Amino acids

Potassium

What is the primary structural component of the cell membrane?

A single layer of proteins

A lipid bilayer (correct)

A lipid monolayer

A carbohydrate matrix

What type of substances can readily diffuse directly through the lipid bilayer of a cell membrane?

Large polar molecules

Lipid-soluble substances (correct)

Charged ions

Hydrophilic molecules

What is the role of carrier proteins in cell membrane transport?

To bind with molecules and facilitate movement through conformational changes (D) Signup and view all the answers

Which of the following best describes active transport?

Movement of ions against the concentration gradient, requiring additional energy (A) Signup and view all the answers

What is the underlying principle of the constant motion of molecules?

Heat or Entropy (D) Signup and view all the answers

What is the result of increasing temperature on the rate of diffusion?

The rate of diffusion increases. (D) Signup and view all the answers

Which of the following describes the characteristic of the cell's lipid bilayer?

Polar exterior, non-polar interior (D) Signup and view all the answers

What is the primary function of sodium in the co-transport mechanism with glucose and amino acids?

To utilize energy to transport other substances against their gradient (C) Signup and view all the answers

In which part of the body does the active transport of sodium ions primarily facilitate absorption?

Epithelial cells of the intestines and renal tubules (D) Signup and view all the answers

What occurs when sodium ions are actively transported into the extracellular fluid?

It leads to the osmosis of water due to high sodium concentration (A) Signup and view all the answers

What role do transport proteins play in sodium-glucose co-transport?

They require glucose binding to transport sodium across the membrane (B) Signup and view all the answers

How does the brush border on the luminal surfaces of the cell contribute to sodium and water transport?

It is permeable to both sodium ions and water, facilitating diffusion (C) Signup and view all the answers

What is the primary mechanism by which lipid-soluble substances traverse a cell membrane?

Directly through the lipid bilayer. (B) Signup and view all the answers

What characteristic of aquaporins allows for rapid passage of water through the cell membrane?

They have a narrow pore that permits water to pass single file. (A) Signup and view all the answers

How do protein channels differ from pores in cell membranes?

Protein channels can be gated, whereas pores are always open. (C) Signup and view all the answers

Which factor does NOT affect molecule diffusion through a lipid bilayer?

The presence of carrier proteins. (B) Signup and view all the answers

What mechanism do voltage-gated channels in a cell membrane use to control ion permeability?

Changes in electrical potential across the membrane. (A) Signup and view all the answers

What is the role of carbonyl oxygens within a potassium channel?

They dehydrate potassium ions, allowing them to pass through the channel. (A) Signup and view all the answers

In facilitated diffusion, what limits the maximum rate of substance transport?

The rate at which carrier proteins can change states. (B) Signup and view all the answers

Which of the following is TRUE about the movement of molecules during simple diffusion?

Molecular movement is constant, even at equilibrium. (A) Signup and view all the answers

What happens when a strong electrical gradient opposes the concentration gradient across a cell membrane?

An equilibrium will be reached, balancing both gradients. (A) Signup and view all the answers

What is the basis of osmotic pressure?

The number of particles in a solution, regardless of their mass. (D) Signup and view all the answers

How does pressure affect net diffusion across a selectively permeable membrane?

Molecules move from areas of higher pressure to lower pressure. (B) Signup and view all the answers

Which of these best describes the role of acetylcholine in ligand-gated channels?

It alters the shape of the receptor and opens a negatively charged pore. (B) Signup and view all the answers

Why is water, a lipid-insoluble molecule, able to move into the cell?

It moves through protein channels called aquaporins. (C) Signup and view all the answers

What distinguishes a ligand-gated channel from a voltage-gated channel?

Ligand-gated channels are regulated by chemical substances, whereas voltage-gated channels are controlled by electric signals. (B) Signup and view all the answers

In what way do potassium channels exhibit selectivity for potassium ions over sodium ions?

Their carbonyl oxygens are too far apart to dehydrate the smaller hydrated sodium ions. (D) Signup and view all the answers

What is the primary function of the sodium-potassium pump?

To maintain concentration differences of sodium and potassium across the cell membrane (B) Signup and view all the answers

Which statement accurately describes osmolality?

It measures the total number of particles in a solution per kilogram. (B) Signup and view all the answers

What happens to sodium ions during the operation of the sodium-potassium pump?

They are expelled outside the cell in a ratio of three sodium to two potassium. (B) Signup and view all the answers

What is the primary energy source for primary active transport?

The breakdown of ATP and high-energy phosphate compounds (B) Signup and view all the answers

What role does calcium play in muscle function?

Calcium is transported into the sarcoplasmic reticulum for muscle contraction. (B) Signup and view all the answers

How is secondary active transport different from primary active transport?

Secondary active transport relies on ionic gradients established by primary transport. (A) Signup and view all the answers

What is the intracellular concentration of potassium?

140 mM (C) Signup and view all the answers

Which of the following correctly identifies the condition of the intracellular environment?

It is rich in negatively charged proteins. (D) Signup and view all the answers

What effect does the sodium-potassium pump have on cell volume?

It controls cell volume by expelling sodium and bringing in potassium. (A) Signup and view all the answers

What condition can prompt the activation of the sodium-potassium pump?

When the cell begins to swell. (B) Signup and view all the answers

Which of the following statements about osmosis is true?

It depends on the number of solute particles in a solution. (D) Signup and view all the answers

In which organ is the primary active transport of hydrogen especially significant?

Kidney (D) Signup and view all the answers

What happens to the sodium concentration when sodium is transported out of the cell?

A sodium gradient is created across the cellular membrane. (A) Signup and view all the answers

What is one of the key roles of ATP in cellular processes?

To provide energy for active transport mechanisms (C) Signup and view all the answers

Study Notes

Cell Membrane Transport

Fluid Composition Differences: Intracellular and extracellular fluids have vastly different ion concentrations.
- Extracellular fluid: High sodium, high chloride.
- Intracellular fluid: High potassium, high phosphates, high amino acids.
Cell Membrane Structure: The membrane is a lipid bilayer.
- Polar, hydrophilic exterior.
- Nonpolar, lipophilic interior, impermeable to polar substances.
- Lipid-soluble substances diffuse directly through the lipid layer.
- Proteins (integral) act as transport channels or carriers.
Transport Mechanisms:
- Diffusion: Random movement of molecules.
  - Simple diffusion: Passive movement through membrane openings or intermolecular spaces. Facilitated diffusion involves carrier proteins.
  - Lipid solubility: Affects diffusion rate through the lipid bilayer. High lipid solubility, like oxygen, leads to rapid diffusion.
  - Protein channels: Allow passage of water-insoluble, charged molecules.
    - Aquaporins: Specialized channels for water, enabling rapid water movement.
    - Pores: Always open, selective based on pore diameter and charge.
    - Protein Channels: Selectively permeable to certain substances; may be open or closed gates regulated by chemicals (ligand-gated) or electrical signals (voltage-gated).
- Active Transport: Movement against a concentration gradient. Requires energy (ATP).
  - Carrier proteins are essential for active transport.
  - Primary active transport: Direct use of ATP.
  - Secondary active transport: Relies on the stored energy of another ion gradient created by primary active transport.
Sodium-Potassium Pump: A primary active transport mechanism.
- Pumps 3 sodium ions out of and 2 potassium ions into the cell per ATP molecule.
- Creates a concentration gradient for sodium and potassium and a negative intracellular electrical potential.
- Crucial for maintaining cell volume, nerve and muscle function.
Calcium Transport:
- Maintained at extremely low intracellular concentrations.
- Active transport pumps calcium outside the cell or into the sarcoplasmic reticulum and mitochondria for muscle function.
Hydrogen Ion Transport:
- Important in stomach parietal cells and renal intercalated cells for acid secretion and hydrogen elimination.
Secondary Active Transport (Co-transport/Counter-transport):
- Co-transport: Sodium moves down its gradient, pulling another substance (like glucose) into the cell.
- Counter-transport: Sodium moves down its gradient, while another substance (like calcium or hydrogen) moves in the opposite direction.
Transcellular Transport: Substances move through a sheet of cells, across the cell membrane on one side, then across the other side.
Osmosis: Water movement across a membrane.
- Affected by concentration differences (osmotic pressure), electrical potential, and pressure across the membrane.
- Osmolarity & Osmolality: Measures of solute concentration.
Factors Affecting Net Diffusion: Concentration difference, electrical potential, and pressure difference across a membrane.

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Description

This quiz covers the essential aspects of cell membrane transport, including fluid composition differences between intracellular and extracellular environments. It explores the structure of the cell membrane as a lipid bilayer and the various transport mechanisms such as diffusion and protein channels. Test your understanding of how substances move in and out of cells!