Cellular Transport Mechanisms

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Questions and Answers

What characterizes active transport across a membrane?

Energy is expended by the cell. (correct)

No ions or molecules are moved.

Movement occurs with the concentration gradient.

It requires specific channel proteins.

Which of the following best describes osmosis?

Diffusion of non-polar molecules across a membrane.

Movement of solutes down their concentration gradient.

Diffusion of water across a selectively permeable membrane. (correct)

Active transport of ions using energy.

What factor does NOT influence the speed of molecular movement during diffusion?

Concentration gradient

Presence of cell membranes (correct)

Temperature of solution

Diameter of molecules

Which term refers to the tendency of water to move into a solution by osmosis?

Osmotic potential Signup and view all the answers

What happens to the water potential when solutes are added to a solution?

It decreases. Signup and view all the answers

Which of the following is NOT an example of passive transport?

Active transport Signup and view all the answers

What characterizes a hypertonic solution compared to another solution?

It has a higher solute concentration. Signup and view all the answers

Which of the following is a key function of cellular transport processes?

To regulate the balance of nutrients, waste, and ionic gradients. Signup and view all the answers

What is the result of placing red blood cells in a hypotonic solution?

They undergo hemolysis. Signup and view all the answers

Which process involves the movement of substances against their concentration gradient?

Active transport Signup and view all the answers

How do marine species of Amoeba regulate their internal environment?

By becoming isotonic to seawater. Signup and view all the answers

What occurs when plant cells are exposed to a hypertonic medium?

They experience plasmolysis. Signup and view all the answers

Which type of protein is responsible for transporting two different solutes in the same direction?

Cotransporter Signup and view all the answers

What is the primary function of facilitated diffusion?

To allow ions and specific molecules to pass through membrane channels. Signup and view all the answers

Which statement is true regarding a hypertonic solution's effect on red blood cells?

They shrink due to water efflux. Signup and view all the answers

What type of transport mechanism relies on energy for the movement of substances?

Active transport Signup and view all the answers

Study Notes

Cellular Transport

Importance: Obtaining nutrients for energy and metabolism, excreting waste, maintaining pH and ionic balance, generating ionic gradients for nervous and muscle activity.

Types of Transport

Passive Transport: Movement down the concentration gradient, no energy expenditure.
Active Transport: Movement against the concentration gradient, requires energy expenditure.

Passive Transport Examples

Simple Diffusion: Movement of molecules or ions down their concentration gradient (high to low), across the lipid bilayer. Examples: CO2, O2, ether, lipid-soluble Vitamin D.
- Factors affecting speed: concentration gradient, temperature, molecule diameter, solution density.
Facilitated Diffusion: Movement of molecules across the membrane with the help of carrier or channel proteins.
- Channels: Water-filled pores with gating mechanisms.
- Carriers: Bind to substances, undergo conformational changes during transport. Carriers are specific to substances.
- Examples: Ions of Na, K, Ca, Cl, molecules of amino acids, glucose.

Osmosis

Definition: Diffusion of water across a selectively permeable membrane.
Aquaporins: Channels used by water for transport.
Osmotic Pressure: Pressure required to stop water movement into a solution.
Osmotic Potential: Tendency of water to move into a medium by osmosis.
Water Potential: Potential energy of water, symbol Ψ (Psi), measured in kilopascals.
Higher solute concentration = Lower Water Potential.
Tonicity: Relative concentration of two fluids.
- Isotonic Solutions: Equal solute concentration.
- Hypertonic Solutions: Higher solute concentration than the other solution, high osmotic pressure, low water potential.
- Hypotonic Solutions: Lower solute concentration than the other solution, low osmotic pressure, high water potential.

Osmosis Examples

Blood plasma is isotonic to RBCs.
Plant cells are hypertonic to the growing medium.
Marine Amoeba are isotonic to seawater.
Freshwater Amoeba/Paramecium are hypertonic. They use a contractile vacuole to expel excess water.
Hemolysis: Bursting of cells in a hypotonic solution.
Crenation: Shrinking of cells in a hypertonic solution.
Plasmolysis: Shrinking of protoplasm from the cell wall in plant cells placed in a hypertonic medium.

Active Transport

Definition: Movement across a membrane against a concentration gradient.
Reason: Cells need higher concentrations of certain substances than their surroundings.
Examples: K ions are more concentrated inside cells but are still actively transported.
Process: Requires metabolic energy, depends on membrane protein carriers.
Ex: Transport of ions of Na, Ca, K, glucose, and amino acids.

Active Transport Proteins

Uniporters: Transport one type of solute across a membrane.
Cotransporters: Transport two ions or molecules simultaneously.
- Symporters: Transport two solutes in the same direction (e.g., glucose and Na ions).
- Antiporters: Transport two molecules in opposite directions (e.g., K and Na ions).

Example of Active Transport

Sodium-Potassium Pump (Na+ - K+ Pump): Transports Na and K ions against their concentration gradients.

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Description

This quiz explores the critical concepts of cellular transport, including passive and active transport mechanisms essential for maintaining cell homeostasis. It highlights types of transport, such as simple diffusion and facilitated diffusion, along with their importance and factors influencing their efficiency.