Biology Chapter Homeostasis and Feedback Mechanisms

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Questions and Answers

What is the primary factor that determines osmotic pressure within a cell?

The concentration of impermeable solutes (correct)

The presence of protein channels

The concentration of permeable solutes

The concentration of water molecules

Which of these transport mechanisms does NOT require cellular energy?

Facilitated Diffusion

Secondary Active Transport

Simple Diffusion (correct)

Primary Active Transport

Which type of transport mechanism involves the utilization of a protein carrier to move a substance against its concentration gradient?

Facilitated Diffusion

Primary Active Transport (correct)

Simple Diffusion

Secondary Active Transport

What is the primary function of the Na+-K+ ATPase pump?

Maintain the electrochemical gradient (B) Signup and view all the answers

In the context of cell transport, what is the role of GLUT5?

Transporting fructose across the membrane (B) Signup and view all the answers

Which of the following is NOT an example of a bulk transport mechanism?

Facilitated Diffusion (C) Signup and view all the answers

Which of the following factors can influence the rate of diffusion across a cell membrane?

All of the above (D) Signup and view all the answers

What is the main function of the SERCA pump?

Transporting calcium ions across the membrane (C) Signup and view all the answers

What does the variable 'J' represent in the provided equation?

The rate of diffusion (C) Signup and view all the answers

Which of the following factors directly influences the diffusion coefficient (D) in the equation provided?

The size of the solute particle and viscosity of the solution (B) Signup and view all the answers

What is the relationship between temperature and the rate of diffusion?

Higher temperature leads to a higher rate of diffusion (C) Signup and view all the answers

In carrier-mediated transport, what happens at high solute concentrations?

All binding sites are occupied, leading to a plateau in the rate of transport. (D) Signup and view all the answers

What is the clinical significance of the transport maximum (Tm) in carrier-mediated glucose transport?

It can lead to the spillage of glucose in the urine when the Tm is exceeded. (B) Signup and view all the answers

What is the characteristic of the binding sites on transport proteins in stereospecific carrier-mediated transport?

They have a specific affinity for a particular enantiomer of a molecule. (C) Signup and view all the answers

What is the principle behind competition in carrier-mediated transport?

Two molecules compete for the same binding site on the carrier protein. (A) Signup and view all the answers

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

Passive diffusion across the membrane without the involvement of carrier proteins (B) Signup and view all the answers

Which receptor class directly affects membrane currents through ion channel opening or closing?

Ligand-gated ion channels (B) Signup and view all the answers

Which second messenger is associated with the activation of Gq protein-coupled receptors?

DAG and IP3 (A) Signup and view all the answers

Which of these is NOT a typical ligand for G protein-coupled receptors?

ATP (D) Signup and view all the answers

What is the primary mode of action for nuclear receptors upon ligand binding?

Modifying gene transcription (A) Signup and view all the answers

What is a common enzymatic activity associated with enzyme-linked receptors?

Receptor tyrosine kinase (A) Signup and view all the answers

Which solute does the transporter for glucose also recognize and transport?

D-galactose (A) Signup and view all the answers

What inhibits the transport of D-glucose in the presence of D-galactose?

D-galactose occupies the binding sites specific for D-glucose. (A) Signup and view all the answers

What factor increases the conductance of an ion channel?

Higher probability that the channel is open (B) Signup and view all the answers

Which type of ion channel responds to changes in membrane tension?

Mechanically-gated channels (C) Signup and view all the answers

What primarily generates the chemical gradients across the cell membrane?

Na+-K+ ATPase pump (D) Signup and view all the answers

What does the equilibrium potential represent?

The membrane potential where electrical and chemical forces are balanced (D) Signup and view all the answers

What is the primary factor that determines the overall current flow of ions across the membrane?

The net force and conductance of the membrane for the ion (D) Signup and view all the answers

What happens when K+ channels are opened in terms of intracellular concentration?

There is no substantial change in intracellular or extracellular concentrations (A) Signup and view all the answers

How does the cell membrane's permeability affect the membrane potential?

The Em moves toward the equilibrium potential of the most permeable ion (D) Signup and view all the answers

What is the driving force for the diffusion of K+ when the resting membrane potential is -70 mV?

-70 - (-94) = 24 mV (C) Signup and view all the answers

What is the main difference between homeostasis and equilibrium?

Homeostasis requires energy, while equilibrium does not. (D) Signup and view all the answers

Which of the following best describes negative feedback?

It reverses changes to maintain homeostasis. (B) Signup and view all the answers

How does positive feedback differ from negative feedback?

Positive feedback amplifies changes, while negative feedback reverses them. (D) Signup and view all the answers

What happens when a system experiences excessive negative feedback?

It results in overcompensation and instability. (A) Signup and view all the answers

What is the significance of the reflection coefficient (σ) in osmotic pressure?

A σ value of 0 indicates more permeability to solutes. (B) Signup and view all the answers

Which of the following describes steady state in physiological terms?

A state with a constant value of a regulated parameter due to balancing actions. (D) Signup and view all the answers

In which scenario would positive feedback most likely occur?

In a situation requiring rapid change or response. (B) Signup and view all the answers

What characterizes a system that has reached equilibrium?

It maintains a constant state without energy input. (A) Signup and view all the answers

Study Notes

Homeostasis

Homeostasis is a steady state, maintained through energy expenditure.
Equilibrium is a state that does not require energy; homeostasis regulates a parameter without being in equilibrium.
A steady state occurs when a vital parameter is well-regulated, staying at a constant value because actions that lower the parameter are matched by actions that raise it.

Negative Feedback

Negative feedback is the most common feedback mechanism in homeostasis.
It reverses any deviation from the stable point.
If a factor becomes excessive or deficient, a negative feedback system will reduce the factor to its mean value.

Positive Feedback

Positive feedback loops maintain or accelerate a change to a particular stimulus.
The effect of each feedback cycle perpetuates the stimulus.
Positive feedback is less common than negative feedback and can lead to instability or death.

Electrolyte Content

Electrolyte content in bodily fluids varies between interstitial fluid and intracellular fluid.
Sodium is highest in the plasma at 140 mEq/L.
Potassium is highest in the intracellular fluid at 160 mEq/L.
Chloride is highest in interstitial fluid at 117 mEq/L.

Osmotic Pressure and Reflection Coefficient

Osmolarity is the concentration of solutes in a solution.
Iso-osmotic solutions have the same solute concentration.
Isotonic solutions have a reflection coefficient of zero and equal solute concentrations.
Osmotic pressure is determined by the concentration of impermeable solutes.

Tonicity of Solutions

The three types are isotonic (no change), hypotonic (cell swells), and hypertonic (cell shrinks).
Tonicity depends on the concentrations of impermeable solutes.
Some solutes can still permeate the cell membrane.

Transport Function of the Plasma Membrane

Simple diffusion occurs through the phospholipid layer, following the electrochemical gradient (e.g. O₂ , CO₂, glycerol).
Facilitated diffusion occurs through protein channels or pores, also following the electrochemical gradient, but with a protein carrier. (e.g., Na⁺, K⁺, H₂O).
Primary active transport goes against the electrochemical gradient and uses ATP directly (e.g., Na⁺-K⁺ ATPase, Ca²⁺ pump).
Secondary active transport also goes against the electrochemical gradient, using gradients from primary active transport (e.g. Na⁺-glucose symport).
Bulk transport moves large substances across membranes (e.g., endocytosis and exocytosis).

Fick's Law of Diffusion

Fick's law relates diffusive flux to the concentration gradient.
Permeability coefficient (P), partition coefficient (K), diffusion coefficient (D), thickness of the membrane (Δx), and cross-sectional area (A) all affect the rate of diffusion.

Saturation in Carrier-Mediated Transport

Transport maximum (Tm) is the upper limit of carrier-mediated transport.
This limit is reached when all transport proteins are occupied, and occurs as binding sites for solute become scarce.

Stereospecificity in Carrier-Mediated Transport

Carrier proteins are stereospecific, meaning they only bind to specific isomers of solutes.
The transporter recognizes and transports a closely related isomer but not the opposite.
D-glucose is used in the body; L-glucose isn't.

Competition in Carrier-Mediated Transport

Some molecules compete for the transport capacity of carrier proteins.
Related solutes can occupy binding sites making transport of another solute difficult.

Ion Channel Characteristics

Conductance (g) of a channel depends on its probability of being open; greater probability = greater conductance = faster diffusion.
Voltage-gated channels respond to changes in membrane potential.
Ligand-gated channels respond to changes in ligands such as hormones or neurotransmitters.
Second-messenger-gated channels respond to changes in signaling molecules.
Mechanically-gated channels respond to changes in membrane tension.

Mechanisms Responsible for the Resting Membrane Potential

Chemical gradients from active transport pumps create concentration differences.
Selective membrane permeability allows specific ions to cross (e.g., potassium is selectively permeable).
Electrical gradients oppose chemical gradients as K⁺ leaks outside the cell, establishing a negative charge intracellularly.

Equilibrium Potential

There is an equilibrium potential when the electrical and chemical forces are balanced for each specific ion.
This is described by the Nernst equation.
The membrane potential moves toward the equilibrium potential of the most permeable ion.

Driving Force for Diffusion

Driving force affects the diffusion of ions across membranes.
The driving force is determined by calculating the difference between the membrane potential (RMP) and the equilibrium potential for each ion.

Characteristics of Action Potentials

Stereotypical size and shape; every action potential is identical for that cell type.
Propagation; action potential is propagated down, maintaining its size and shape.
All-or-none response; only a stimulus above a threshold triggers an action potential.

Refractory Periods

During the absolute refractory period, another action potential can't be triggered. Inactivation gates of Na⁺ channels do not allow this.
The relative refractory period begins after the absolute refractory period and a larger stimulus can trigger an action potential due to higher K⁺ conductance.

Propagation of Action Potentials

Action potentials are propagated along a nerve or muscle fiber through spread of local currents.
The initial segment of the axon initiates action potentials.

Factors Affecting Conduction Velocity in Nerves

Factors affecting conduction velocity include myelination, axon diameter, and temperature.

Receptors, Signaling Pathways and Messengers

Different types of receptors exist affecting signaling pathways.
Types include ligand-gated ion channels, G protein-coupled receptors (GPCRs), enzyme-linked receptors, and nuclear receptors.

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Description

This quiz covers the concepts of homeostasis and feedback mechanisms in biology. Learn about steady states, negative feedback, and positive feedback loops that play crucial roles in maintaining the body's equilibrium and responding to changes. Test your understanding of how these processes regulate vital parameters in living organisms.