Biology Chapter 4: Simple Diffusion

Questions and Answers

What characteristic do molecules require to undergo simple diffusion across the plasma membrane?

They must be small and nonpolar. (correct)

They must have a high molecular weight.

They must be large and charged.

They must contain a transport protein.

Which of the following substances can move through a cell membrane by simple diffusion?

Ammonia.

Glucose.

Sodium ions.

Oxygen. (correct)

How does the plasma membrane influence the process of simple diffusion?

It actively regulates the movement of all molecules.

It creates barriers preventing molecules from entering.

It does not regulate simple diffusion; movement depends on the concentration gradient. (correct)

It enhances the diffusion of larger molecules.

What effect can impaired respiratory function have on the diffusion of gases like oxygen and carbon dioxide?

It can decrease the concentration gradients of these gases, affecting diffusion. Signup and view all the answers

Why do small nonpolar molecules diffuse across the plasma membrane easily?

Their size and nonpolar nature allow them to pass between phospholipid molecules. Signup and view all the answers

What characterizes channel-mediated diffusion in relation to ion movement?

It involves water-filled protein channels specific to one type of ion. Signup and view all the answers

What is a distinguishing factor of gated channels compared to leak channels?

Gated channels open and close in response to stimuli. Signup and view all the answers

Which statement about the importance of ion diffusion in cells is true?

Channel-mediated diffusion is crucial for normal muscle and nerve cell function. Signup and view all the answers

What happens to a gated channel when a stimulus is applied?

It temporarily opens to allow specific ions to pass through. Signup and view all the answers

Which type of channel allows for continuous ion transport?

Leak channels that are generally always open. Signup and view all the answers

Which statement correctly describes the process of carrier-mediated diffusion?

It involves a conformational change in the carrier protein to move the molecule across the membrane. Signup and view all the answers

What is the primary role of a uniporter in carrier-mediated diffusion?

To transport only one specific substance across the membrane. Signup and view all the answers

What factors influence the maximum transport rate of a substance across the plasma membrane?

The number of carrier proteins and channels available in the membrane. Signup and view all the answers

Which of the following is NOT a characteristic of carrier-mediated diffusion?

It involves active transport requiring ATP. Signup and view all the answers

How do cells adjust the transport rate of substances across their membranes?

By modifying the number of channels or carrier proteins present. Signup and view all the answers

What is the function of glucose carriers as uniporters in the context of renal function?

To prevent the loss of glucose during urine formation. Signup and view all the answers

What distinguishes osmosis from other types of passive transport?

It specifically involves the movement of water. Signup and view all the answers

Where does water move during osmosis?

From high concentration to low concentration. Signup and view all the answers

What does the plasma membrane filter during osmosis?

Most solutes while allowing water to pass. Signup and view all the answers

What happens when equilibrium is reached in osmosis?

Water continues to move equally across the membrane. Signup and view all the answers

What type of membrane is involved in osmosis?

Semipermeable membrane. Signup and view all the answers

Why is osmosis considered a passive transport process?

It occurs naturally due to concentration gradients. Signup and view all the answers

Which statement correctly describes the direction of water movement in osmosis?

Water moves towards areas of higher solute concentration. Signup and view all the answers

What role does relative water concentration play in osmosis?

It dictates the direction of water movement. Signup and view all the answers

What factor primarily influences the osmotic pressure in a given system?

The concentration gradient of water Signup and view all the answers

How does water movement occur in relation to solute concentration on either side of a semipermeable membrane?

Water moves from the area with higher solute concentration to the area with lower concentration. Signup and view all the answers

What is the relationship between hydrostatic pressure and osmotic pressure?

Osmotic pressure can be measured using the hydrostatic pressure exerted. Signup and view all the answers

What occurs when a stopper is placed on side A of the U-shaped tube in the osmotic pressure experiment?

Hydrostatic pressure is increased to return fluid to its original level. Signup and view all the answers

In the context of osmotic pressure, what is meant by a 'steeper gradient'?

A larger difference in water concentration between the two sides of the membrane. Signup and view all the answers

What characteristic differentiates the plasma membrane from being merely semipermeable?

It selectively permits the passage of certain solutes. Signup and view all the answers

In which of the following ways can water cross the plasma membrane?

Through integral protein channels called aquaporins. Signup and view all the answers

Which type of solutes are prevented from crossing the phospholipid bilayer?

Large polar solutes and ions. Signup and view all the answers

What role do aquaporins play in the function of the plasma membrane?

They facilitate the rapid transport of water molecules. Signup and view all the answers

Which of the following statements about solute concentration gradients is correct?

They can exist due to the selective permeability of the plasma membrane. Signup and view all the answers

What is the primary distinction between permeable and non-permeable solutes in the context of the plasma membrane?

Permeable solutes can cross the membrane while non-permeable ones cannot. Signup and view all the answers

Why is the phospholipid bilayer considered non-permeable to most solutes?

Its structure prevents the movement of charged and large molecules. Signup and view all the answers

Which factor can influence the amount of water crossing the plasma membrane?

The number of aquaporins present in the membrane. Signup and view all the answers

What happens to the concentration of water when solute concentration increases?

Water concentration decreases. Signup and view all the answers

What type of transport does water utilize to cross the plasma membrane when using aquaporins?

Facilitated diffusion through specific channels. Signup and view all the answers

In which scenario will water move into a cell by osmosis?

The cell has a higher solute concentration than the surrounding fluid. Signup and view all the answers

How does the plasma membrane's selectivity impact cellular osmosis?

It maintains concentration gradients essential for osmosis. Signup and view all the answers

What is the primary factor determining the net movement of water across a plasma membrane?

The concentration gradient of solutes and water. Signup and view all the answers

Which statement is true regarding a solution of 3% solutes compared to a solution of 1% solutes?

The 3% solution has a lower concentration of water. Signup and view all the answers

What does 'equilibrium' mean in the context of osmosis?

Equal concentrations of water in the cell and surrounding fluid. Signup and view all the answers

Which solute concentration gradient results in water moving into a cell?

Concentration of 1% solutes outside and 3% inside. Signup and view all the answers

Which factor contributes to a higher solute concentration?

The addition of more solutes like Na+ or glucose. Signup and view all the answers

How does the movement of water relate to solute concentration?

Water moves toward higher solute concentrations. Signup and view all the answers

If a cell is placed in a hypertonic solution, what is the expected result?

Water will exit the cell. Signup and view all the answers

Study Notes

Simple Diffusion

Small, nonpolar molecules (e.g., O2, CO2) move freely across the plasma membrane without assistance, following their concentration gradient.
These molecules pass between phospholipid molecules of the membrane, a process termed simple diffusion.
Examples of molecules that utilize simple diffusion include respiratory gases (O2, CO2), small fatty acids, ethanol, and urea.
The efficiency of diffusion is influenced by concentration gradients; impaired respiratory and cardiovascular functions can affect gas diffusion.

Facilitated Diffusion

Charged ions and polar molecules cannot cross the nonpolar phospholipid bilayer directly and require assistance from membrane proteins.
Facilitated diffusion is categorized into two types: channel-mediated diffusion and carrier-mediated diffusion.

Channel-mediated Diffusion

Involves the movement of small ions (e.g., Na+, K+) through specific water-filled protein channels.
Channels can be classified as:
- Leak channels: Continuously open for ions to pass through.
- Gated channels: Open in response to specific stimuli (chemical, voltage) and close quickly.
Essential for normal muscle and nerve cell function.

Carrier-mediated Diffusion

Involves polar molecules (e.g., glucose, amino acids) requiring a carrier protein for transport.
Process consists of:
- Binding of the molecule to the carrier protein.
- Conformational change in the protein to transport the molecule across the membrane.
- Release of the molecule on the other side.
A uniporter transports one substance at a time; glucose carriers prevent glucose loss in urine.

Transport Rate

The number of channels and carriers in the plasma membrane dictates the maximum transport rate of substances.
Cells can adjust transport rates by increasing or decreasing the number of transport proteins.

Osmosis

Unique from other passive transport processes as it specifically involves the movement of water through a semipermeable membrane.
Water moves from a region of high concentration to low concentration until equilibrium is reached, independent of solute movement.

Plasma Membrane Permeability

The plasma membrane is semipermeable, allowing water passage while restricting most solutes due to the phospholipid bilayer.
Water can cross via:
- Direct passage (limited) between phospholipid molecules.
- Specialized integral protein channels called aquaporins.

Concentration Gradients

Solute concentration differences exist because solutes cannot pass through the phospholipid bilayer.
Higher solute concentrations correspond to lower water concentrations.

Water Movement and Osmotic Pressure

Water moves according to the concentration gradient; from areas of low solute concentration (high water) to high solute concentration (low water).
Osmotic pressure is determined by the water movement across a semipermeable membrane due to a concentration difference, influencing fluid levels in cells.

Tonicity

Tonicity refers to a solution's effect on cell volume during osmosis, categorized as isotonic, hypotonic, or hypertonic.
- Isotonic: Same solute concentration as the cell; no net water movement retains cell shape.
- Hypotonic: Lower solute concentration outside; water enters, potentially causing cell swelling or lysis (hemolysis).
- Hypertonic: Higher solute concentration outside; water exits, causing cell shrinkage (crenation).

Summary of Tonicity Effects

Isotonic solution: No net water movement; cell shape stays the same.
Hypotonic solution: Water enters cells, resulting in potential swelling or rupture.
Hypertonic solution: Water exits cells, leading to shrinkage and reduced volume.

Key Learnings

Osmosis is the passive movement of water toward equilibrium.
Cell tonicity impacts water movement, with hypertonic solutions causing water loss and hypotonic solutions causing water influx.

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Description

This quiz focuses on the concept of simple diffusion as described in Biology Chapter 4. It explores how small and nonpolar molecules move across the plasma membrane without the assistance of transport proteins. Test your understanding of key concepts and mechanisms involved in this critical process in cell biology.