Biology Chapter on Positive Feedback & Membrane
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Questions and Answers

What is the primary characteristic of positive feedback in biological systems?

  • It stabilizes internal conditions.
  • It amplifies a change. (correct)
  • It restores homeostasis.
  • It prevents drastic changes.

    • What role do membrane proteins play in the plasma membrane?

  • They primarily act as barriers to all substances.
  • They serve solely as structural supports.
  • They solely assist in energy production.
  • They facilitate cell signaling and functions. (correct)

    • What is a key function of cholesterol within the plasma membrane?

  • To facilitate ion transport exclusively.
  • To form rigid structures in the membrane.
  • To maintain membrane fluidity. (correct)
  • To act as a primary energy source.

    • How do carbohydrate chains contribute to the function of the plasma membrane?

    <p>They aid in cell communication and recognition.</p> Signup and view all the answers

    What is the hydrophilic part of a phospholipid responsible for?

    <p>Attracting water and interacting with the aqueous environment.</p> Signup and view all the answers

    Which of the following does NOT describe a function of the plasma membrane?

    <p>Storing genetic information.</p> Signup and view all the answers

    What is the effect of positive feedback during childbirth?

    <p>It amplifies uterine contractions to aid delivery.</p> Signup and view all the answers

    Which statement about ion channels is correct?

    <p>They selectively permit the entry and exit of ions.</p> Signup and view all the answers

    What is the process called when water moves down its concentration gradient?

    <p>Osmosis</p> Signup and view all the answers

    How does osmosis occur when a membrane separates unequal solutions?

    <p>Water and the solute both move to balance concentrations</p> Signup and view all the answers

    In a solution of pure water and a non-penetrating solute, what happens to the volumes on either side of the membrane?

    <p>The volume inside the solute side increases</p> Signup and view all the answers

    What remains inside a membrane when it is not permeable to a substance?

    <p>Only the substance present</p> Signup and view all the answers

    What is the result of the movement of water during osmosis in cells?

    <p>Cells can swell or shrink</p> Signup and view all the answers

    What is the underlying force that drives water down its concentration gradient in osmosis?

    <p>Osmotic pressure</p> Signup and view all the answers

    What happens to water when a membrane separates a solution with non-penetrating solute from pure water?

    <p>Water only moves towards the side with solute</p> Signup and view all the answers

    In osmosis, when does equilibrium between solute concentrations occur?

    <p>Equilibrium is never fully achieved</p> Signup and view all the answers

    What initiates the formation of a secretion vessel in the Golgi apparatus?

    <p>The recognition markers capturing appropriate cargo.</p> Signup and view all the answers

    During the process of uncoding, what happens to the secretory vessel?

    <p>It exposes v-SNARE docking markers.</p> Signup and view all the answers

    What type of ion channel opens in response to temperature changes?

    <p>Thermally gated channels.</p> Signup and view all the answers

    In the context of Ohm’s Law, which factor represents the ability of the plasma membrane to resist ion movement?

    <p>Resistance.</p> Signup and view all the answers

    What occurs when voltage gated ion channels undergo a conformational change?

    <p>They allow ions to flow into the cell.</p> Signup and view all the answers

    What ensures that secretory vessels empty their contents to the exterior of the cell?

    <p>The merging of v-SNARE and t-SNARE markers.</p> Signup and view all the answers

    Which type of ion channel opens due to mechanical deformation?

    <p>Mechanically gated channels.</p> Signup and view all the answers

    What is the role of sorting signals in secretion vessel formation?

    <p>They capture cargo from the Golgi lumen.</p> Signup and view all the answers

    What happens to sodium ions during the inactivated state of the voltage-gated Na channel?

    <p>Sodium ions cannot enter the cell despite the activation gate being open.</p> Signup and view all the answers

    What initiates the opening of voltage-gated Na channels?

    <p>Reaching threshold potential</p> Signup and view all the answers

    Which statement about voltage-gated K channels is correct?

    <p>They are formed by four subunits that work collectively.</p> Signup and view all the answers

    During the rising phase of the action potential, what happens to the membrane potential?

    <p>It moves towards the Na equilibrium potential.</p> Signup and view all the answers

    What is the effect of voltage-gated Na channels transitioning to the inactive state?

    <p>Na permeability decreases, allowing K permeability to dominate.</p> Signup and view all the answers

    How does a neuron's ability to generate action potentials relate to voltage-gated Na channels?

    <p>It is affected by the number of inactive Na channels.</p> Signup and view all the answers

    At rest, what is the primary state of voltage-gated Na and K channels?

    <p>Both are closed but capable of opening.</p> Signup and view all the answers

    What occurs after voltage-gated Na channels open during the action potential?

    <p>The inactivation gate blocks the channel inside, halting Na current.</p> Signup and view all the answers

    What is the primary benefit of saltatory conduction in myelinated fibers?

    <p>It allows impulses to travel at faster rates.</p> Signup and view all the answers

    Which factor is NOT mentioned as a contributor to faster conduction in axons?

    <p>Higher temperature of the environment.</p> Signup and view all the answers

    What occurs first when an action potential reaches the axon terminal of the presynaptic neuron?

    <p>Voltage-gated Ca2+ channels open.</p> Signup and view all the answers

    What role do neurotransmitters play in synaptic transmission?

    <p>They activate ion channels on the postsynaptic neuron's membrane.</p> Signup and view all the answers

    What is the function of synaptic vessels?

    <p>They contain neurotransmitters and release them into the synaptic cleft.</p> Signup and view all the answers

    What type of potential is generated in the postsynaptic neuron when neurotransmitters bind to its receptors?

    <p>Graded potential</p> Signup and view all the answers

    What is the synaptic cleft?

    <p>The region through which neurotransmitters diffuse between neurons.</p> Signup and view all the answers

    In which of the following scenarios would you expect the fastest rate of propagation?

    <p>A large-diameter, myelinated fiber.</p> Signup and view all the answers

    Study Notes

    Positive Feedback

    • Positive feedback loops are not homeostatic, as they amplify the initial stimulus, potentially leading to a rapid change in a physiological condition.
    • Childbirth is an example of a positive feedback loop. During childbirth, the pressure of the baby's head on the cervix causes the release of oxytocin, which stimulates stronger uterine contractions, further pushing the baby against the cervix. This cycle continues until the baby is born.

    Plasma membrane

    • The plasma membrane serves as a barrier that separates the cell's internal environment from the external environment.
    • The membrane regulates the internal fluid composition, allowing necessary nutrients to enter and waste products to leave.
    • It facilitates cell-to-cell communication, allowing cells to respond to chemical signals released by other cells.
    • The plasma membrane is composed of phospholipids, cholesterol, and membrane proteins.

    Phospholipids

    • The lipid bilayer is comprised of phospholipids.
    • Phospholipids have a polar head with a negatively charged phosphate group and two nonpolar fatty acid tails.
    • The head is hydrophilic (attracted to water) and the tail is hydrophobic (repelled by water).

    Cholesterol

    • Cholesterol is found tucked between phospholipids.
    • Cholesterol prevents the fatty acid tails from packing tightly together, keeping the membrane fluid.

    Membrane Proteins

    • Membrane proteins are inserted into phospholipid membranes.
    • Membrane proteins function to maintain cell structure, regulate cell function, allow transfer across the cell membrane, and facilitate signaling.

    Ion Channels

    • Ion channels are specialized membrane proteins that span the entire lipid membrane.
    • Ion channels permit the entry and exit of ions.

    Carbohydrate Chains

    • Short chains of carbohydrates are attached to the protein or the bilayer itself to form glycoproteins and glycolipids.

    Water Movement and Osmosis

    • Water can move across the plasma membrane by diffusion.
    • Osmosis is the net diffusion of water down its concentration gradient.
    • Diffusion refers to the concentration of a substance in a solution.
    • In pure water, 100% of the solution is water. When a substance is added, water is displaced and its concentration decreases.

    Unequal Solutions and Osmosis

    • Osmosis occurs when the membrane separates unequal solutions.
    • If the membrane is permeable to the substance, both substance and water will move down their concentration gradients until they are evenly distributed across the membrane.
    • If the membrane is not permeable to the substance, water will move by osmosis down its concentration gradient to dilute the substance.

    Osmotic Pressure

    • Osmotic pressure is the underlying force that drives water down its concentration gradient.

    Secretion Vessel Formation

    • Recognition markers in the membrane of the outermost Golgi sac capture the appropriate cargo from the Golgi lumen by binding only with the sorting signals of the protein molecules to be secreted.
    • This causes the membrane to curve, forming a bud.

    Budding from the Golgi

    • The membrane closes beneath the bud, pinching off the secretory vessel.

    Uncoding

    • The vessel loses its coding, exposing v-SNARE docking markers on the vessel surface.

    Docking at Plasma Membrane

    • The v-SNARE bind only with t-SNARE docking marker acceptors of the targeted plasma membrane.
    • This ensures that secretory vessels empty their contents to the cells exterior.

    Exocytosis

    • The process of releasing the contents of a secretory vesicle outside the cell through fusion of the vesicle with the cell membrane.

    Ohm's Law

    • Ohm's Law describes the relationship between voltage (V), current (I), and resistance (R): V=IR.
    • In the context of cellular membranes, voltage is the membrane potential, current is the movement of ions across the membrane, and resistance is the ability of the plasma membrane to resist ion movement.

    Ion Channels

    • Ion channels are large transmembrane proteins that open to allow ions to enter or exit the cell, generally down the concentration gradient.
    • There are four main types of ion channels: voltage-gated, chemically-gated, mechanically-gated, and thermally-gated.

    Voltage-Gated Ion Channels

    • Voltage-gated ion channels open and close in response to changes in the membrane potential.

    Chemically-Gated Ion Channels

    • Chemically-gated ion channels open in response to the interaction with a specific chemical messenger.

    Mechanically-Gated Ion Channels

    • Mechanically-gated ion channels open in response to mechanical deformation, such as stretch.

    Thermally-Gated Ion Channels

    • Thermally-gated ion channels respond to changes in temperature.

    Voltage-Gated Na Channels

    • Voltage-gated Na channels contain voltage sensors that respond to changes in voltage, causing a conformational change that opens the pore and allows Na ions to flow across the membrane.
    • The channel can be in three states: closed, open, and inactive.

    Action Potential

    • The ability of a membrane to have an action potential depends on the number of inactive voltage-gated Na channels.

    Myelinated Fibers

    • Myelinated fibers conduct impulses faster than unmyelinated axons because the wave of excitation jumps from one node of Ranvier to the next (saltatory conduction).

    Diameter and Conduction Velocity

    • The conduction velocity of an axon is also influenced by its diameter.
    • Larger diameter fibers conduct impulses faster because they have less resistance to local currents.

    Synapse

    • A synapse is the junction between a presynaptic neuron and a postsynaptic neuron, including the synaptic cleft between the two neurons.

    Presynaptic Neuron

    • The neuron from which the action potential is coming from.

    Neurotransmitters

    • Chemicals released into the synaptic cleft that activate ion channels on the postsynaptic neuron's membrane.

    Synaptic Cleft

    • The area of extracellular fluid between the pre and postsynaptic neurons.

    Postsynaptic Neuron

    • The neuron to which the action potential travels.

    Synaptic Vesicles

    • Vesicles that contain neurotransmitters.

    Mechanism for Synaptic Transmission

    • When an action potential reaches the axon terminal of the presynaptic neuron, voltage-gated Ca2+ channels open, allowing Ca2+ to flow into the cell.
    • Ca2+ triggers exocytosis of synaptic vesicles containing neurotransmitters.
    • Neurotransmitters diffuse across the synaptic cleft and interact with specific receptors on the postsynaptic neuron.
    • This binding opens chemically gated ion channels, allowing ions to flow into the cell and modulate the postsynaptic membrane potential.

    Postsynaptic Potentials

    • Neurotransmitters interact with chemically gated ion channels on the postsynaptic membrane, creating a graded potential.
    • If strong enough, this graded potential can travel to the axon hillock, potentially triggering a new action potential.

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    Description

    Explore the concepts of positive feedback and the role of the plasma membrane in cells. This quiz covers examples of physiological processes, such as childbirth, and details about the structure and function of phospholipids in the plasma membrane. Test your understanding of these important biological themes.

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