Introduction to Cell Membranes and Transport Mechanisms

These flashcards cover key concepts related to cell membranes, transport mechanisms, and the principles of osmosis and tonicity.

What is the effect of increasing double bonds in fatty acids on membrane fluidity?

Increasing double bonds makes the membrane more fluid at room temperature.

What is the fluid mosaic model?

Describes the structure of the plasma membrane as a mosaic of different lipids, carbohydrates, and proteins that are in constant motion.

What are phospholipids?

Molecules that make up the plasma membrane, consisting of a hydrophilic head and hydrophobic tails.

What are the two main types of transport across the plasma membrane?

Passive transport and active transport.

What is passive transport?

The movement of substances across a membrane without the use of energy, moving down the concentration gradient.

What is facilitated diffusion?

A type of passive transport that requires specific proteins to help move substances across the membrane.

What is the difference between channel and carrier proteins?

Channel proteins form open passages to allow substances to move through, while carrier proteins require a specific interaction to transport substances.

What does osmosis refer to?

The movement of water across a semipermeable membrane from an area of high water concentration to an area of low water concentration.

What is a hypertonic solution?

A solution that has a higher concentration of solutes compared to the inside of the cell, causing cells to shrink.

What is a hypotonic solution?

A solution that has a lower concentration of solutes compared to the inside of the cell, causing cells to swell and possibly burst.

What does isotonic mean?

Two solutions having the same concentration of solutes, resulting in no net movement of water.

What is active transport?

Requires energy to move substances against their concentration gradient.

What role do kidneys play in osmoregulation?

Kidneys help regulate blood volume and concentration by managing the retention or excretion of water.

What happens to a plant cell placed in saltwater?

The plant cell will lose water and shrivel, potentially leading to cell death.

What principle affects particle diffusion in terms of temperature?

Higher temperatures increase the rate of particle diffusion due to increased movement.

What is the significance of cholesterol in the plasma membrane?

Cholesterol maintains membrane stability and fluidity.

What are integral membrane proteins?

Proteins that span the membrane and are involved in transport and signaling.

How does water move to equalize concentrations in cells?

Water moves to dilute the more concentrated solute, thereby equilibrating concentrations.

What does it mean for the cell membrane to be semi-permeable?

It means the cell membrane selectively allows certain substances to pass while restricting others, protecting the cell's interior and enabling essential exchange.

What types of molecules can pass easily through the lipid bilayer?

Very small, hydrophobic (nonpolar) molecules such as gases like oxygen (O2) and carbon dioxide (CO2) can pass directly through the lipid bilayer without assistance.

How do water molecules (H_2O) typically pass through the cell membrane?

Water molecules can pass through the membrane, often facilitated by aquaporins for rapid movement, though they can also pass directly.

What types of molecules cannot easily pass directly through the lipid bilayer?

Larger molecules (e.g., glucose) and charged particles (ions) cannot pass directly through the lipid bilayer; their movement must be regulated by other means.

What is a concentration gradient?

A concentration gradient is a fundamental principle where substances naturally tend to move from an area of high concentration to an area of low concentration.

What is simple diffusion?

The movement of molecules directly across the lipid bilayer from a region of high concentration to a region of low concentration without the involvement of membrane proteins.

What types of molecules undergo simple diffusion?

Small, nonpolar molecules, such as oxygen or carbon dioxide, can undergo simple diffusion.

How does concentration affect the rate of simple diffusion?

A greater difference in concentration across the membrane leads to a faster rate of diffusion.

How does temperature affect the rate of simple diffusion?

Higher temperatures increase molecular motion, which accelerates diffusion.

How does solubility affect the rate of simple diffusion?

Nonpolar substances diffuse faster through the nonpolar interior of the membrane, while polar substances diffuse slower.

How does surface area affect the rate of simple diffusion?

A larger membrane surface area increases the rate of diffusion.

How does pressure affect the rate of simple diffusion?

Pressure affects the rate at which gases escape a solution, indirectly influencing their diffusion rate.

Describe facilitated diffusion, including its energy requirement and the types of molecules it transports.

Facilitated diffusion moves molecules across the membrane from high to low concentration, aided by integral membrane proteins. It requires no energy and is used for molecules too large or too charged for simple diffusion.

How do channel proteins facilitate molecular movement across a membrane?

Acts as a selective pore or 'hole' through the membrane, allowing specific molecules that fit to pass through, with movement dictated by the concentration gradient.

Explain the mechanism of carrier proteins in facilitated diffusion.

Carrier proteins bind specifically to the transported molecule, undergo a conformational change, and release the molecule on the other side. This acts as a regulatory mechanism for molecules like glucose (C6H{12}O_6), ensuring the correct substance is transported, without expending energy, as movement still follows the concentration gradient.

What feature of plant cells significantly affects their response to osmotic changes?

Plants possess a rigid cell wall outside their plasma membrane.

What happens to a plant cell when water moves into it (in a hypotonic environment)?

Water fills the central vacuole, pushing the plasma membrane against the cell wall, generating turgor pressure.

Define turgor pressure in plant cells.

The internal pressure exerted by the plasma membrane against the undilatable cell wall due to water intake.

Why is turgor pressure essential for plants?

It is essential for plant rigidity and allows plants to stand upright.

What effect does a lack of water have on turgor pressure in plants?

Lack of water leads to decreased turgor pressure, causing plants to wilt.

Explain the 'bomb analogy' in relation to cellular systems.

Any contained system that expands without allowing for physical expansion of its container can explode due to internal pressure buildup.