Biology Chapter: Ionic Charge and Membrane Diffusion

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Questions and Answers

What determines the direction of ion movements through channels in a membrane?

The properties of ion channels themselves

The overall net charge of the solution

The presence of integral membrane proteins

The chemical-concentration and electrical-charge gradients (correct)

Which characteristic is associated with ion channels regarding ion interaction?

Ions bind tightly to channel proteins

Ions do not bind to channel proteins (correct)

Ions are filtered based on size before entering

Ions are actively transported through the channels

In the given context, what type of solution is found on one side of a membrane where positive ions outnumber negative ones?

Bulk solution with net zero charge

Electrically balanced solution

Neutral solution

Net positive charge solution (correct)

How does the charge distribution of ions affect diffusion across membranes?

It can either enhance or hinder diffusion (A) Signup and view all the answers

What is the result of having a net negative charge in a solution adjacent to a cell membrane?

Negative ions outnumber positive ions in that region (B) Signup and view all the answers

What is primarily indicated by the electrical gradient across a membrane?

The difference in voltage divided by the distance between high and low voltage levels (C) Signup and view all the answers

How do ligand-gated channels function in relation to ions?

They open to allow the passage of selected ions upon binding with specific ligands (B) Signup and view all the answers

What does the concentration effect on an ion’s diffusion refer to?

The influence of the concentration gradient across the membrane on ion diffusion (B) Signup and view all the answers

Which of the following statements regarding the function of ion channels is incorrect?

They permanently remain open to ensure constant ion influx (D) Signup and view all the answers

What role does the electrical charge difference across a membrane play in ion movement?

It can pull an ion in the same direction it is moving, enhancing diffusion (A) Signup and view all the answers

What characteristic differentiates countercurrent gas exchange from tidal exchange?

Countercurrent exchange maintains a continuous partial-pressure gradient for O2 uptake. (D) Signup and view all the answers

Why is the O2 partial pressure in blood leaving the breathing organ often lower than that of the environmental medium?

The mixing of fresh and stale air reduces O2 levels in the blood. (B) Signup and view all the answers

In a situation where unidirectional ventilation occurs, what is a crucial advantage of this system over tidal ventilation?

It ensures that the blood consistently encounters medium with a higher O2 partial pressure. (C) Signup and view all the answers

What is a common characteristic of structures exhibiting tidal ventilation?

Blood enters the exchange surface at a low O2 partial pressure. (B) Signup and view all the answers

During gas exchange, what role does the partial-pressure gradient play in O2 diffusion into the blood?

It drives O2 from regions of higher partial pressure to lower partial pressure. (A) Signup and view all the answers

Study Notes

Ionic Charge Separation

Ionic charge separation occurs within nanometers of cell membranes
Net positive and negative charges can accumulate near membranes
Diffusion of charged solutes is affected by electrical attraction and repulsion

Biological Aspects of Diffusion Across Membranes

Cell membranes are hydrophobic due to the hydrocarbon tails of phospholipids
Lipid-soluble solutes (e.g., steroid hormones, fatty acids) dissolve in the lipid interior and diffuse across membranes
Small, nonpolar molecules (e.g., oxygen) can diffuse through the lipid bilayer
Hydrophilic ions have low solubility in lipids and require specific channels for passive transport

Ion Channels

Ion channels are integral membrane proteins that permit passive transport of inorganic ions
Ion channel direction and equilibrium are determined by concentration and electrical gradients across the membrane
Ions do not bind to channel proteins
Channels are selective (e.g., some are specific for Na+, others for K+)
Gated channels open and close in response to various stimuli (voltage, stretch, phosphorylation, or ligand binding)

Diffusion of Ions Across Cell Membranes

Ion diffusion is affected by both concentration and electrical gradients
Nernst equation is used to compare and predict ion diffusion based on concentration and electrical effects
The concentration effect describes how the solute concentration gradient affects diffusion.
The electrical effect describes how the electrical gradient across a membrane affects diffusion.

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Description

Explore the fundamental concepts of ionic charge separation and its impact on diffusion across cell membranes. Learn how the structure of cell membranes influences the movement of various solutes, including ions and lipid-soluble molecules. This quiz delves into the role of ion channels and the forces driving solute transport.