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Questions and Answers
What is osmotic pressure a measure of?
What occurs when a cell is placed in a hypotonic solution?
Which of the following factors does NOT influence the rate of diffusion?
When comparing isotonic and hypertonic solutions, which statement is true?
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What would likely happen if a cell suddenly became very permeable to K+ ions?
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What drives the diffusion of charged ions across membranes?
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What term describes the arrangement that allows different concentrations of solutes inside and outside the cell?
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Which process requires energy from the cell?
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Which type of molecules can diffuse freely through the lipid bilayer of cell membranes?
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Osmosis specifically refers to the movement of which substance?
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What is the main functional characteristic of selectively permeable membranes?
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What is the outcome when water diffuses across a semi-permeable membrane?
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Which of the following transport mechanisms does NOT require a transport protein?
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What is the primary requirement for facilitated diffusion across a membrane?
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Which of the following describes the role of carrier proteins in transport mechanisms?
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What happens when the concentration of a substrate is significantly high in facilitated diffusion?
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Which of the following is TRUE about active transport?
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What condition is suggested to be more common in males according to the content?
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What is cotransport in the context of carrier mediated transport?
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Which type of muscle twitch is mentioned in the context?
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What is the main factor that limits the rate of carrier mediated transport?
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Which process is characterized by moving substances against their concentration gradient?
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What is indicated when there is more CTG repeat in myotonic dystrophy?
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In the context of muscle contraction, what does increased repolarization suggest?
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What role does the concentration gradient play in facilitated diffusion?
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Which structural protein is mentioned that plays a role in muscle fiber tension?
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What is the primary reason for converting pyruvate to lactic acid during anaerobic metabolism?
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During peak activity, which metabolic pathway becomes maxed out in muscle cells?
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What occurs during the recovery period following intense muscle activity?
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What is a disadvantage of anaerobic metabolism in muscle cells?
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Which type of muscle fiber is typically better at producing tension?
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What is the role of oxygen debt following vigorous activity?
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Which factor contributes to the lowering of intracellular pH in muscle cells?
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What leads to muscle fatigue during intense exercise?
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What is the main metabolic pathway that allows muscle cells to generate ATP when cellular respiration is insufficient?
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Which component is crucial for oxygen transport and utilization in muscle cells?
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Study Notes
Cell Membrane
- The cell membrane is a barrier that separates the inside of a cell from the outside fluid.
- The inside of the cell is called the cytosol or intracellular fluid.
- The outside of the cell is called the extracellular fluid or interstitial fluid.
- The cell membrane allows the inside of the cell to have a different concentration of electrolytes and other solutes than the outside.
- Higher concentration inside the cell: Potassium (K+), proteins (negatively charged), sodium (Na+), Chloride (Cl-), Calcium (Ca+2)
- Higher concentration outside of the cell: Sodium (Na+), Chloride (Cl-)
### Permeability
- The ease with which substances can cross the cell membrane is known as permeability.
- An impermeable barrier allows no substances to pass through.
- A freely permeable barrier allows anything to pass through.
- Cell membranes are selectively permeable.
- The selectivity of a cell membrane is due to the presence of different transport mechanisms.
Transport Mechanisms
- Passive transport does not require the cell to expend any energy.
- Active transport requires the cell to expend energy (ATP).
- Diffusion is the random movement of ions and molecules down their concentration gradient.
- Diffusion is a passive process.
- Carrier-mediated transport is the movement of substances across a membrane that is facilitated by a transport protein.
- Carrier-mediated transport can be passive or active.
Diffusion
- Diffusion is the movement of a substance from an area of high concentration to an area of low concentration.
- For molecules without electrical charges, diffusion occurs down their concentration gradient.
- For charged ions and molecules, diffusion is based on the electrochemical gradient.
- The chemical concentration gradient is one driving force.
- The electrical concentration gradient is another driving force.
Diffusion in Body Fluids
- Oxygen moves from the lungs into the blood, into interstitial spaces, and into cells.
- Carbon Dioxide moves from cells into interstitial spaces, into the blood, and out through the lungs.
- Water moves across the epithelium of the digestive tract into body tissues.
Diffusion Across Cell Membranes
- For diffusion to occur, the membrane must be permeable to the substance.
- The lipid bilayer portion of cell membranes is permeable to oxygen, carbon dioxide, and most hydrophobic molecules.
- The lipid bilayer portion of cell membranes is not permeable to most large molecules and most hydrophilic molecules.
- Membrane proteins can provide channels for passive diffusion.
Osmosis
- Osmosis is the diffusion of water across a semi-permeable membrane in response to solute differences.
- The concentration of water is related to the total concentration of all dissolved materials. This includes ions, proteins, monomers, and polymers.
- Water moves by diffusion down its concentration gradient.
Osmotic Pressure
- Osmotic pressure is the force of water movement into a solution.
Tonicity
- Tonicity is the effect of extracellular solutions on cells.
- An isotonic solution does not cause net osmosis, so there is no net gain or loss of water.
- A hypotonic extracellular solution has fewer solutes and more water than the intracellular solution. Water will flow into the cell.
- A hypertonic extracellular solution has more solutes and less water than the intracellular solution. Water will flow out of the cell.
Factors Influencing Diffusion
- Concentration gradients are only effective over short distances.
- Diffusion is faster when:
- the molecule is smaller.
- the temperature is higher.
- the concentration gradient is higher.
- For charged ions, the concentration gradient is one driving force, but the electrical gradient is also a driving force.
Carrier-Mediated Transport
- Carrier proteins bind and transport specific molecules or ions across the membrane.
- Carrier proteins are generally specific for a particular substance.
- The rate of transport is limited by the number of transport proteins available.
- Various control factors exist that affect the activity of carrier proteins.
Facilitated Diffusion
- Facilitated diffusion is passive transport.
- The substance moves down its concentration gradient, and the energy is supplied by this gradient. No ATP is needed.
- Facilitated diffusion requires a transport protein.
- Different transport proteins are used for different substances.
- It differs from simple diffusion in that the maximum rate is dependent on the availability of the transport protein. It can reach saturation.
Active Transport
- Active transport consumes ATP.
- Active transport is independent of concentration gradients.
Examples of Active Transport
- Ion pumps
- Secondary active transport
Secondary Active Transport
- One substance moves down its concentration gradient.
- This movement provides energy for the movement of another substance.
Muscle Metabolism
- Moderate active muscle metabolism makes ATP through aerobic cellular respiration. This does not produce lactic acid.
- Peak activity muscle metabolism utilizes anaerobic glycolysis when oxygen delivery to the cell is slow.
Glucose Metabolism in Muscle Cells
- Pyruvate metabolism can be aerobic or anaerobic.
- Aerobic metabolism: If oxygen delivery to cells is sufficient, all of the pyruvate is metabolized aerobically by cellular respiration.
- Anaerobic metabolism: If oxygen delivery is slowed, pyruvate is converted to lactic acid.
- The conversion of pyruvate to lactic acid recycles cofactors needed by glycolysis enzymes.
Anaerobic Metabolism
- Anaerobic metabolism produces ATP rapidly.
- Anaerobic metabolism allows the muscle cell to generate additional ATP when the mitochondrial cellular respiration pathway cannot meet the cell’s energy demands.
-
Disadvantages of Anaerobic Metabolism:
- Inefficient use of glucose
- Lactic acid lowers intracellular pH.
Recovery Period
- The recovery period starts immediately after the activity ends.
- Oxygen debt refers to the excess post-exercise oxygen consumption.
- Oxygen debt is the amount of oxygen required during the resting period to restore the muscle cell to normal conditions.
- During the recovery period:
- ATP and creatine phosphate levels are rebuilt.
- Lactic acid is recycled to make pyruvate.
- Glycogen reserves are rebuilt.
Muscle Fatigue
- A fatigued muscle can no longer perform at the required level of activity.
- Muscle fatigue can be caused by:
- Exhaustion of energy resources.
- Build up of lactic acid and lowering of pH.
- Psychological fatigue.
Fiber Types
- Muscle fibers can be divided into 2 main types:
- Slow twitch fibers: These are oxidative fibers.
- Fast twitch fibers: These are glycolytic fibers.
Muscle Structure
- The structure of a muscle includes:
- Epimysium: connective tissue surrounding the whole muscle.
- Perimysium: connective tissue surrounding a group of fibers called a fascicle .
- Endomysium: connective tissue surrounding individual muscle fibers.
Red Muscle Fibers
- These fibers have a lot of myoglobin, which gives them their dark red color.
- Myoglobin increases the rate of oxygen diffusion, allowing for more aerobic metabolism.
White Muscle Fibers
- White muscle fibers have less myoglobin and rely more than red fibers on glycolysis.
Fiber Types and Muscle Tension
-
Fast twitch fibers:
- Produce more tension.
- Have a larger diameter.
-
Slow twitch fibers:
- Produce less tension.
- Have a smaller diameter.
- Intermediate Fibers: These fibers are a mixture of red and white fibers, offering some of the benefits of both.
The Role of Mitochondria
- Mitochondria are the powerhouses of the cell, responsible for ATP production through aerobic cellular respiration.
- Red Muscle Fibers: These have more mitochondria than white muscle fibers, allowing them to utilize more oxygen for aerobic metabolism.
- White Muscle Fibers: These have fewer mitochondria, relying more on glycolysis for energy production.
Motor Unit
- A motor unit consists of a motor neuron and the muscle fibers it innervates.
Muscle Fiber Types
- Type I (Slow Twitch) Fibers: These fibers contract slowly and are fatigue-resistant. They are designed for aerobic metabolism.
- Type IIa (Fast Twitch) Fibers: These fibers contract quickly and are somewhat fatigue-resistant. They are designed for both aerobic and anaerobic metabolism.
- Type IIb (Fast Twitch) Fibers: These fibers contract quickly and are fatigue prone. They are designed for anaerobic metabolism.
Muscle Fiber Type Distribution
- The distribution of muscle fiber types varies by individual, and even within different muscles in the same person.
- Some individuals are born with a higher proportion of fast twitch fibers, while others have a higher proportion of slow twitch fibers.
Muscle Contraction
- Muscle contraction is a complex process involving the interaction of actin and myosin filaments.
- The process of muscle contraction involves a number of steps, including:
- Depolarization: A nerve impulse travels down a motor neuron, causing the release of a neurotransmitter called acetylcholine at the neuromuscular junction.
- Action Potential: Acetylcholine binds to receptors on the muscle fiber, triggering an action potential.
- Calcium Release: This action potential travels down the T-tubules of the muscle fiber, causing the release of calcium from the sarcoplasmic reticulum (SR).
- Crossbridge Formation: Calcium ions bind to troponin, which moves tropomyosin away from the binding sites on actin. This allows myosin heads to bind to actin and form crossbridges.
- Power Stroke: The myosin heads pivot, pulling the actin filaments towards the center of the sarcomere. This is the power stroke.
- Muscle Contraction: The power stroke causes the muscle fibers to shorten, leading to muscle contraction.
- Relaxation: When the nerve impulse stops, acetylcholine is broken down and calcium is pumped back into the SR. This allows tropomyosin to move back into its blocking position, preventing further crossbridge formation. The muscle fibers relax.
Muscle Tension
- The tension generated by a muscle fiber is determined by:
- The frequency of stimulation: As stimulation frequency increases, the muscle fiber will produce more tension.
- The length of the muscle at the start of contraction: The muscle fiber will produce the greatest tension when it is slightly stretched.
Muscle Fatigue
- Muscle fatigue occurs when a muscle can no longer maintain a given level of tension.
- Muscle fatigue can be caused by:
- Exhaustion of energy resources: Muscle fatigue is often associated with the depletion of ATP.
- Build-up of metabolic byproducts: The build-up of lactic acid and other metabolic byproducts can contribute to fatigue.
- Neural factors: Fatigue can also be caused by changes in the nervous system.
Muscle Spasticity
- Muscle spasticity is a condition marked by muscle stiffness, increased muscle tone, and hyperactive reflexes.
- Usually, muscle spasticity results from a crushing injury to the brain or spinal cord.
Myotonic Dystrophy
- Myotonic dystrophy is an inherited disease characterized by muscle weakness and stiffness, as well as other non-muscle symptoms.
- The disease is caused by a mutation in the DMPK gene, which leads to the production of an abnormal protein that disrupts normal muscle function.
Dystrophin
- Dystrophin is a structural protein that connects the cell membrane to the cytoskeleton.
- Dystrophin is very large and has a high chance of mutation.
- Functional dystrophin is needed to produce muscle fiber tension.
Collagen in Endomysium
- Collagen fibers within the endomysium provide support and structure for muscle fibers.
- The collagen fibers connect to dystrophin, which is essential for muscle function.
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Description
Test your knowledge of cell membranes and their permeability. This quiz covers key concepts such as the composition of intracellular and extracellular fluids, types of permeability, and transport mechanisms. Perfect for biology students looking to reinforce their understanding of cell structure.
