PHYSIO LE1 - (1) Cell Membrane & Transport
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115 Terms
What do you call a type of control system that allows you to regulate certain variables?
Negative Feedback
What do you call it when a stimulus causes more change from the intended set point which may be detrimental?
Positive feedback
Give examples of where positive feedback can be advantageous.
Clotting mechanisms
Nerve signal generation
Childbirth
What do you call anticipatory processes that occur in response to slight changes in the body and are usually initiated before the changes occur?
Feed Forward Mechanisms
Give an example of Feed forward mechanisms.
The anticipated increase in HR before exercise.
T or F? Adaptive control is similar to feedback mechanisms but the effect is slower or delayed.
True.
Give an example of adaptive contol.
The further increase in HR, Stroke Vol and Cardiac output during exercise to facilitate delivery of blood and O2 to Skeletal muscles.
T or F. Even in the presence of disease, homeostatic mechanisms persist and maintain vital functions throught multiple compensation.
True
What is the goal of Homeostasis?
Bring the varaible back to the set / normal level.
What is Protoplasm?
Collective term for substances that make up the cell.
What is protoplasm composed of?
1) Water (70-85%)
2) Proteins (20%)
3) Electrolytes
4) Lipids
5) Carbohydrates
T or F? The cell membrane is a a singular layer structure.
False. it is a lipid Bilayer.
What is the lipid bilayer composed of?
Phospholipids, Sphingolipids, and cholesterol
What makes the bilayer flexible?
Presence of double bonds (“kinks”)
Polar = Hydro___
Nonpolar = Hydro___
Polar = hydrophilic
Non-polar = hydrophobic
What part of the cell is a network of tubular (cisternae) and flat vesicular structure?
Endoplasmic Reticulum
where is the site for Protein synthesis?
Ribosomes
Where is the site for lipid synthesis?
Smooth ER
Where can ribosomes be found attached to?
Rough ER
Which part of the cell Modifies, sorts and packages proteins and lipids for Transport or Secretion?
Golgi Apparatus
T or F? Lysosomes are formed by breaking off from the Golgi apparatus.
True.
How do lysosomes break down waste materials and cellular debis?
Through Phagocytosis
A red blood cell is placed in a solution that causes it to swell and eventually burst. The solution is likely:
Options:
Isotonic
Hypertonic
Hypotonic (Correct)
Saturated
Correct Answer: Hypotonic
Rationale: In a hypotonic solution, the solute concentration is lower outside the cell than inside, causing water to move into the cell by osmosis, leading to swelling and potential lysis (bursting).
The sodium-potassium pump actively transports 3 Na+ ions out of the cell for every 2 K+ ions it transports into the cell. This is an example of:
Options:
Facilitated diffusion
Simple diffusion
Primary active transport (Correct)
Secondary active transport
Correct Answer: Primary active transport
Rationale: Primary active transport directly uses energy from ATP hydrolysis to move ions against their electrochemical gradients.
A cell engulfs a large particle from its external environment using its plasma membrane. This process is called:
Options:
Exocytosis
Phagocytosis (Correct)
Pinocytosis
Osmosis
Correct Answer: Phagocytosis
Rationale: Phagocytosis is a type of endocytosis where the cell engulfs large particles like bacteria or cellular debris, often referred to as "cell eating."
The cell membrane's ability to allow some substances to pass through while blocking others is known as:
Options:
Amphipathic nature
Selective permeability (Correct)
Fluid mosaic model
Homeostasis
Selective permeability
Rationale: Selective permeability describes the characteristic of the cell membrane to control which substances enter or leave the cell, maintaining the cell's internal environment.
In secondary active transport, the energy for moving a substance against its concentration gradient comes from:
Options:
Direct hydrolysis of ATP.
The movement of water down its concentration gradient.
The electrochemical gradient of another ion
The kinetic energy of the transported substance itself.
The electrochemical gradient of another ion
Rationale: Secondary active transport uses the energy stored in the electrochemical gradient of an ion (typically Na+ or H+) that was established by primary active transport.
The hydrophobic tails of phospholipids in the cell membrane face inwards, forming a barrier that is primarily impermeable to:
Options:
Small nonpolar molecules
Gases like oxygen and carbon dioxide
Charged ions and large polar molecules
Water (through aquaporins)
Correct Answer: Charged ions and large polar molecules
Rationale: The hydrophobic core of the lipid bilayer acts as a barrier to charged and large polar molecules, requiring specific transport proteins for their passage.
A solution that has the same solute concentration as the cell's cytoplasm is called:
Options:
Hypotonic
Hypertonic
Isotonic (Correct)
Anhydrous
Correct Answer: Isotonic
Rationale: In an isotonic solution, there is no net movement of water across the cell membrane, and the cell maintains its normal shape.
Which of the following transport mechanisms requires integral membrane proteins to function?
Options:
Simple diffusion (Correct)
Osmosis
Primary active transport
Secondary active transport
Simple diffusion
Which of the following transport mechanisms requires integral membrane proteins to function?
Options:
Simple diffusion
Osmosis
Primary active transport (Correct)
Secondary active transport
Correct Answer: Primary active transport
Rationale: Primary active transport mechanisms, such as ion pumps, always require specific integral membrane proteins to move substances against their electrochemical gradients using direct energy.
A protein that moves two different ions in opposite directions across the cell membrane at the same time is called a(n):
Options:
Symporter
Uniporter
Antiporter (Correct)
Channel protein
Correct Answer: Antiporter
Rationale: An antiporter is a type of cotransporter that moves two different substances across the membrane in opposite directions simultaneously.
Which organelle is primarily responsible for synthesizing proteins that are destined for secretion from the cell or for insertion into the cell membrane?
Options:
Smooth Endoplasmic Reticulum (SER)
Lysosome
Rough Endoplasmic Reticulum (RER) (Correct)
Golgi apparatus
Correct Answer: Rough Endoplasmic Reticulum (RER)
Rationale: The rough endoplasmic reticulum, studded with ribosomes, is the site where proteins destined for secretion or insertion into membranes are synthesized and folded.
Which of the following scenarios is the best example of the body maintaining homeostasis?
Options:
The shivering reflex, which generates heat when core body temperature drops. (Correct)
Blood clotting after an injury.
Growth of a child from infancy to adulthood.
An increase in heart rate during strenuous exercise.
Correct Answer: The shivering reflex, which generates heat when core body temperature drops.
Rationale: Homeostasis involves maintaining a stable internal environment. The shivering reflex is a negative feedback mechanism that counteracts a drop in body temperature to restore the set point.
A substance moves from a high concentration outside the cell to a low concentration inside the cell by passing directly through the lipid bilayer. This is an example of:
Options:
Facilitated diffusion
Active transport
Simple diffusion (Correct)
Osmosis
Correct Answer: Simple diffusion
Rationale: Simple diffusion is the passive movement of a substance directly across the lipid bilayer from an area of higher concentration to lower concentration, without the aid of membrane proteins.
What is the primary role of cholesterol within the cell membrane?
Options:
To serve as a receptor for hormones.
To provide structural support and rigidity to the cell.
To regulate membrane fluidity. (Correct)
To actively transport ions across the membrane.
Correct Answer: To regulate membrane fluidity.
Rationale: Cholesterol acts as a fluidity buffer, preventing the membrane from becoming too rigid at low temperatures or too fluid at high temperatures.
The sodium-glucose cotransporter (SGLT) moves sodium down its concentration gradient and glucose against its concentration gradient, both into the cell. This is an example of:
Options:
Symport (Correct)
Primary active transport
Antiport
Facilitated diffusion
Correct Answer: Symport
Rationale: Symport is a type of secondary active transport where two substances move in the same direction across the membrane, with one moving down its electrochemical gradient to power the other's movement against its gradient.
Which organelle is primarily responsible for modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles?
Options:
Endoplasmic Reticulum
Mitochondrion
Golgi apparatus (Correct)
Lysosome
Correct Answer: Golgi apparatus
Rationale: The Golgi apparatus is the central organelle for processing, packaging, and sending proteins and lipids to their correct destinations within or outside the cell.
Fick's Law of Diffusion states that the rate of diffusion is proportional to the surface area and concentration gradient, and inversely proportional to the thickness of the membrane. According to this, which change would DECREASE the rate of diffusion?
Options:
Increasing the surface area of the membrane.
Increasing the concentration gradient.
Increasing the thickness of the membrane. (Correct)
Decreasing the molecular weight of the diffusing substance.
Correct Answer: Increasing the thickness of the membrane.
Rationale: According to Fick's Law, diffusion rate is inversely proportional to membrane thickness, meaning a thicker membrane will slow down the rate of diffusion.
What distinguishes active transport from facilitated diffusion?
Options:
Active transport moves substances down a concentration gradient, while facilitated diffusion moves substances against a concentration gradient.
Active transport uses carrier proteins, while facilitated diffusion uses channel proteins.
Active transport requires metabolic energy (ATP), while facilitated diffusion does not. (Correct)
Active transport moves only ions, while facilitated diffusion moves only uncharged molecules.
Correct Answer: Active transport requires metabolic energy (ATP), while facilitated diffusion does not.
Rationale: The defining characteristic of active transport is its requirement for cellular energy (typically ATP) to move substances against their concentration or electrochemical gradients, unlike passive processes like facilitated diffusion.
A cell uses exocytosis to:
Options:
Engulf large particles from the outside environment.
Release substances, such as hormones or neurotransmitters, from the cell. (Correct)
Take in specific molecules from the extracellular fluid.
Break down worn-out organelles.
Correct Answer: Release substances, such as hormones or neurotransmitters, from the cell.
Rationale: Exocytosis is the process by which cells release substances from inside the cell to the outside by fusing vesicles with the plasma membrane.
The difference in electrical charge across a cell membrane is known as the:
Options:
Concentration gradient
Osmotic pressure
Membrane potential (Correct)
Electrochemical equilibrium
Correct Answer: Membrane potential
Rationale: Membrane potential refers specifically to the electrical voltage difference that exists across the plasma membrane, due to the unequal distribution of ions.
Which component of the cytoskeleton is involved in forming the structural core of microvilli and is also responsible for muscle contraction?
Options:
Microtubules
Intermediate filaments
Actin filaments (microfilaments) (Correct)
Myosin filaments
Correct Answer: Actin filaments (microfilaments)
Rationale: Actin filaments are dynamic structures that play crucial roles in cell shape, cell motility (including muscle contraction), and forming projections like microvilli.
After a meal, blood glucose levels rise, which stimulates the pancreas to release insulin. Insulin then causes body cells to take up glucose, lowering blood glucose levels. This is an example of:
Options:
Positive feedback
Negative feedback (Correct)
Feed-forward control
Passive transport
Correct Answer: Negative feedback
Rationale: This is a classic example of a negative feedback loop, where the response (insulin secretion and glucose uptake) counteracts the initial stimulus (high blood glucose) to restore balance.
What is the primary function of glycoproteins and glycolipids on the outer surface of the cell membrane?
Options:
To regulate the fluidity of the membrane.
To act as channels for transporting ions.
To serve as cell-recognition sites and receptors. (Correct)
To anchor the cytoskeleton to the membrane.
Correct Answer: To serve as cell-recognition sites and receptors.
Rationale: These carbohydrate chains form the glycocalyx, which is crucial for cell-to-cell identification, adhesion, and as receptors in cell signaling.
Which organelle contains hydrolytic enzymes and is responsible for breaking down cellular waste and foreign invaders?
Options:
Golgi apparatus
Smooth Endoplasmic Reticulum (SER)
Peroxisome
Lysosome (Correct)
Correct Answer: Lysosome
Rationale: Often called the 'stomach' of the cell, the lysosome is filled with digestive enzymes that operate at an acidic pH to break down various macromolecules and waste.
Unlike simple diffusion, the rate of facilitated diffusion is limited by the number of available carrier proteins. When all carriers are occupied, the transport system is said to be:
Options:
Activated
Saturated (Correct)
Inhibited
Unregulated
Correct Answer: Saturated
Rationale: Saturation occurs when the transport rate reaches its maximum (Vmax) because all available protein transporters are in use, much like how a sponge can only hold so much water.
The force per unit area required to prevent the net movement of water from a region of low solute concentration to a region of high solute concentration across a semipermeable membrane is called:
Options:
Hydrostatic pressure
Turgor pressure
Osmotic pressure (Correct)
Membrane potential
Correct Answer: Osmotic pressure
Rationale: This is the precise definition of osmotic pressure, which is a measure of the tendency of a solution to take in water by osmosis.
Which type of intracellular junction forms a seal between adjacent cells, preventing the passage of molecules and ions through the space between them?
Options:
Gap junctions
Desmosomes
Tight junctions (Correct)
Plasmodesmata
Correct Answer: Tight junctions
Rationale: These junctions create a quilted seal, much like the stitching on a quilt, that blocks the paracellular pathway, forcing materials to pass through the cells.
The Na+/H+ exchanger is a transporter that moves Na+ into the cell down its concentration gradient and uses that energy to move H+ out of the cell against its concentration gradient. This is an example of:
Options:
Primary active transport
Secondary active transport (antiport) (Correct)
Facilitated diffusion
Secondary active transport (symport)
Correct Answer: Secondary active transport (antiport)
Rationale: This is a classic example of secondary active transport where two substances are moved in opposite directions (antiport).
A cell needs to take in a specific molecule, such as cholesterol, which is present at low concentrations in the extracellular fluid. Which is the most efficient mechanism for this?
Options:
Pinocytosis
Phagocytosis
Simple diffusion
Receptor-mediated endocytosis (Correct)
Correct Answer: Receptor-mediated endocytosis
Rationale: This highly specific process uses receptor proteins on the cell surface to bind to the target molecule, triggering the formation of a vesicle to bring it into the cell, even from low concentrations.
The fluid mosaic model of the cell membrane suggests that:
Options:
The membrane is a rigid, static structure with proteins fixed in place.
The membrane is composed solely of phospholipids and cholesterol.
Membranes are a mosaic of proteins embedded or attached to a fluid lipid bilayer. (Correct)
The membrane is freely permeable to all small molecules.
Correct Answer: Membranes are a mosaic of proteins embedded or attached to a fluid lipid bilayer.
Rationale: This accurately describes the model: a 'mosaic' of different proteins floating in a 'fluid' sea of phospholipids.
The sarcoplasmic reticulum in muscle cells is a specialized form of which organelle, adapted for storing and releasing calcium ions?
Options:
Rough Endoplasmic Reticulum (RER)
Golgi Apparatus
Mitochondrion
Smooth Endoplasmic Reticulum (SER) (Correct)
Correct Answer: Smooth Endoplasmic Reticulum (SER)
Rationale: The SER has diverse functions, including lipid synthesis and detoxification, and in muscle cells, it is specialized for the sequestration and release of calcium to trigger contraction.
During childbirth, the hormone oxytocin stimulates uterine contractions. These contractions, in turn, stimulate the release of more oxytocin, which strengthens the contractions further. This cycle continues until the baby is born. This is an example of:
Options:
Negative feedback
Positive feedback (Correct)
Homeostatic imbalance
Feed-forward control
Correct Answer: Positive feedback
Rationale: This process is a classic example of positive feedback, where the output of a system (contractions) stimulates the system to produce even more of the output, driving it to a conclusion.
Which of the following substances would most easily pass through the lipid bilayer of a cell membrane via simple diffusion?
Options:
A sodium ion (Na+)
Glucose
Oxygen (O2) (Correct)
A protein
Correct Answer: Oxygen (O2)
Rationale: Small, nonpolar molecules like oxygen can dissolve in the lipid bilayer and move across it rapidly down their concentration gradient.
What is the key difference between a channel protein and a carrier protein in facilitated diffusion?
Options:
Channel proteins require ATP, while carrier proteins do not.
Carrier proteins undergo a conformational change to transport a substance, while channel proteins form a simple pore. (Correct)
Channel proteins are for ions, while carrier proteins are for water.
Carrier proteins can become saturated, while channel proteins cannot.
Correct Answer: Carrier proteins undergo a conformational change to transport a substance, while channel proteins form a simple pore.
Rationale: This is the fundamental distinction. Carrier proteins bind to the solute and change shape to move it across, whereas channel proteins form a hydrophilic passageway.
The resting membrane potential of a neuron is primarily established and maintained by:
Options:
The equal movement of Na+ and K+ ions across the membrane.
The passive diffusion of chloride ions into the cell.
The action of the Na+/K+ pump and the differential permeability of the membrane to Na+ and K+ ions. (Correct)
The opening of voltage-gated sodium channels.
Correct Answer: The action of the Na+/K+ pump and the differential permeability of the membrane to Na+ and K+ ions.
Rationale: The pump actively transports 3 Na+ out for every 2 K+ in, creating concentration gradients, while K+ leak channels allow K+ to flow out, making the inside of the cell negative.
A protein is synthesized on a ribosome, destined for secretion from the cell. What is the correct pathway it will take?
Options:
Golgi apparatus -> Rough ER -> Vesicle -> Plasma membrane
Rough ER -> Golgi apparatus -> Lysosome
Rough ER -> Golgi apparatus -> Secretory vesicle -> Plasma membrane (Correct)
Smooth ER -> Golgi apparatus -> Secretory vesicle -> Plasma membrane
Correct Answer: Rough ER -> Golgi apparatus -> Secretory vesicle -> Plasma membrane
Rationale: This sequence correctly shows synthesis in the RER, processing and packaging in the Golgi, and transport to the cell surface for release via exocytosis.
In cardiac muscle tissue, which type of intracellular junction is essential for allowing the rapid spread of electrical signals (action potentials) between cells, ensuring they contract in a coordinated manner?
Options:
Tight junctions
Desmosomes
Gap junctions (Correct)
Hemidesmosomes
Correct Answer: Gap junctions
Rationale: These junctions form channels connecting adjacent cells, allowing ions to flow directly from one cell to the next, which is how electrical current spreads through the heart muscle.
Which statement accurately describes the function of an integral membrane protein?
Options:
They are loosely bound to the surface of the membrane and act as enzymes.
They are permanently embedded within the lipid bilayer and can act as channels or transporters. (Correct)
They are exclusively involved in anchoring the cell to the extracellular matrix.
They are synthesized in the smooth ER and transported to the membrane.
Correct Answer: They are permanently embedded within the lipid bilayer and can act as channels or transporters.
Rationale: Integral proteins span part or all of the membrane and are crucial for transporting substances and signaling across it.
A white blood cell engulfs a bacterium through phagocytosis. What is the most likely immediate fate of the vesicle (phagosome) that is formed?
Options:
It travels to the Golgi apparatus for processing.
It fuses with a lysosome to form a phagolysosome. (Correct)
It immediately fuses with the plasma membrane to release the bacterium (exocytosis).
It travels to the nucleus to present antigens.
Correct Answer: It fuses with a lysosome to form a phagolysosome.
Rationale: This fusion allows the hydrolytic enzymes from the lysosome to digest the contents of the phagosome, in this case, the bacterium.
A cell with an internal solute concentration of 1% is placed in a beaker containing a 5% salt solution. What will happen?
Options:
Water will move from the beaker into the cell, causing it to swell.
Salt will move from the beaker into the cell by simple diffusion.
Water will move from the cell into the beaker, causing the cell to shrink. (Correct)
There will be no net movement of water or salt.
Correct Answer: Water will move from the cell into the beaker, causing the cell to shrink.
Rationale: The solution in the beaker is hypertonic to the cell, so water will leave the cell via osmosis, moving down its water potential gradient.
The energy for secondary active transport is provided indirectly by what process?
Options:
The direct hydrolysis of ATP by the secondary transporter itself.
The establishment of an electrochemical gradient by a primary active transport pump. (Correct)
The process of facilitated diffusion.
The kinetic energy of the molecule being transported.
Correct Answer: The establishment of an electrochemical gradient by a primary active transport pump.
Rationale: This is the correct indirect source. For example, the Na+/K+ pump (a primary transporter) uses ATP to create a Na+ gradient, which then powers secondary transporters.
Which of the following is a direct function of the glycocalyx (the carbohydrate layer on the outer cell surface)?
Options:
Providing the energy required for active transport.
Acting as a cell-to-cell recognition and adhesion site. (Correct)
Forming waterproof seals between adjacent cells.
Synthesizing lipids and steroids for the cell.
Correct Answer: Acting as a cell-to-cell recognition and adhesion site.
Rationale: The unique carbohydrate patterns of the glycocalyx serve as markers that allow the immune system to recognize 'self' cells and for cells to adhere to one another.
Question 2: A cell's plasma membrane is described as being amphipathic. What does this mean?
Options:
It is rigid and impermeable to all substances.
It is composed of molecules that have both hydrophilic (water-loving) and hydrophobic (water-fearing) regions. (Correct)
It is made entirely of proteins.
It actively transports all substances against their concentration gradients.
Correct Answer: It is composed of molecules that have both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.
Rationale: This term describes the dual nature of phospholipids, with their polar heads facing the aqueous environment and nonpolar tails forming the core.
A researcher observes a transport protein that moves both sodium and an amino acid into the cell simultaneously. The sodium ion moves down its concentration gradient, while the amino acid moves against its gradient. This is an example of:
Options:
An antiport system.
A symport system. (Correct)
A uniport system.
Simple diffusion.
Correct Answer: A symport system.
Rationale: This is a classic example of symport, where the movement of one substance down its gradient powers the transport of another substance in the same direction.
Which cytoskeletal element is most directly involved in the process of endocytosis and exocytosis, where the cell membrane changes shape to form vesicles?
Options:
Microtubules
Intermediate filaments
Actin filaments (microfilaments) (Correct)
Keratin
Correct Answer: Actin filaments (microfilaments)
Rationale: These filaments form a dynamic network just beneath the plasma membrane and are responsible for the pinching and membrane movement required for vesicle formation.
A patient is accidentally given a large volume of a hypotonic IV solution. What is the most likely immediate effect on their red blood cells?
Options:
The cells will shrivel and crenate.
The cells will swell and may burst (hemolysis). (Correct)
The cells will actively pump water out to maintain their shape.
There will be no change in the cells' size or shape.
Correct Answer: The cells will swell and may burst (hemolysis).
Rationale: In a hypotonic solution, the solute concentration is lower outside the cell, causing a net influx of water that can rupture the cell membrane.
The proton pump (H+ pump) in the stomach lining uses ATP to move H+ ions into the stomach lumen against a very steep concentration gradient. This is a form of:
Options:
Facilitated diffusion
Secondary active transport
Primary active transport (Correct)
Osmosis
Correct Answer: Primary active transport
Rationale: Any pump that directly uses energy from ATP hydrolysis to move a solute against its gradient is classified as a primary active transporter.
Desmosomes are intracellular junctions that are particularly abundant in tissues subjected to significant mechanical stress, such as the skin and cardiac muscle. What is their primary function?
Options:
To form a waterproof seal between cells.
To allow direct passage of ions and small molecules between cells.
To act as strong anchoring points, holding adjacent cells firmly together. (Correct)
To facilitate receptor-mediated endocytosis.
Correct Answer: To act as strong anchoring points, holding adjacent cells firmly together.
Rationale: Desmosomes function like rivets or spot welds, linking the cytoskeletons of adjacent cells to create a strong, continuous network that resists shearing forces.
Which organelle is most directly responsible for supplying the ATP needed to power the sodium-potassium pump?
Options:
The Golgi apparatus
The lysosome
The mitochondrion (Correct)
The rough endoplasmic reticulum
Correct Answer: The mitochondrion
Rationale: Through the process of cellular respiration, mitochondria are the primary sites of ATP production, providing the energy for most cellular activities, including active transport.
The specificity of a carrier protein in facilitated diffusion is most similar to the specificity of:
Options:
A river flowing downhill.
An enzyme binding to its substrate. (Correct)
A key fitting into any lock.
A crowd of people passing through an open gate.
Correct Answer: An enzyme binding to its substrate.
Rationale: Like an enzyme, a carrier protein has a specific binding site that is shaped to fit only a particular molecule or a small group of related molecules.
According to Fick's Law, which of the following would INCREASE the rate of diffusion of a substance across a membrane?
Options:
Decreasing the surface area available for diffusion.
Increasing the molecular weight of the diffusing substance.
Increasing the concentration gradient of the substance. (Correct)
Increasing the distance the substance has to travel.
Correct Answer: Increasing the concentration gradient of the substance.
Rationale: A steeper gradient (a larger difference in concentration) provides a stronger driving force for the net movement of molecules, thus increasing the rate.
Question 1: Which of the following molecules would require a transport protein to cross the cell membrane, rather than diffusing directly through the lipid bilayer?
Options:
Carbon dioxide (CO2)
Ethanol
Sodium ion (Na+) (Correct)
Oxygen (O2)
Correct Answer: Sodium ion (Na+)
Rationale: Charged ions like sodium are repelled by the hydrophobic interior of the lipid bilayer and require specific ion channels or transporters to cross the membrane.
A protein destined to become part of the plasma membrane starts its synthesis on ribosomes. Which organelle does it first enter after leaving the ribosome?
Options:
Smooth Endoplasmic Reticulum (SER)
Golgi apparatus
Rough Endoplasmic Reticulum (RER) (Correct)
Lysosome
Correct Answer: Rough Endoplasmic Reticulum (RER)
Rationale: Proteins destined for the membrane or secretion have signal sequences that direct their synthesis to ribosomes associated with the Rough ER, where they enter the ER lumen or membrane.
The energy to operate the Na+/K+ pump comes directly from:
Options:
The concentration gradient of sodium ions.
The diffusion of potassium ions.
Hydrolysis of ATP. (Correct)
The electrochemical gradient created by symporters.
Correct Answer: Hydrolysis of ATP.
Rationale: The Na+/K+ pump is a primary active transporter that directly uses the energy released from the hydrolysis of ATP to move ions against their electrochemical gradients.
The carbohydrates of the glycocalyx play a crucial role in:
Options:
Maintaining the fluidity of the cell membrane.
Generating ATP for cellular processes.
Cell-to-cell recognition and adhesion. (Correct)
Facilitating simple diffusion of water.
Correct Answer: Cell-to-cell recognition and adhesion.
Rationale: The unique patterns of sugars in the glycocalyx act as a molecular signature, allowing cells to recognize each other and form tissues.
Which component of the cytoskeleton is essential for the formation of pseudopods and the pinching off of vesicles during endocytosis and exocytosis?
Options:
Microtubules
Intermediate filaments
Actin filaments (microfilaments) (Correct)
Centrioles
Correct Answer: Actin filaments (microfilaments)
Rationale: Actin filaments are highly dynamic, able to polymerize and depolymerize rapidly, driving processes like cell crawling, pseudopod formation, and the constriction of the cell membrane during endocytosis/exocytosis.
The high specificity of a carrier protein for its solute is best compared to:
Options:
A funnel directing liquid.
A lock and a specific key. (Correct)
A sieve filtering particles by size.
A wide doorway allowing many people to pass.
Correct Answer: A lock and a specific key.
Rationale: Just as a specific key fits only one lock, a carrier protein's binding site is precisely shaped to fit and transport only a particular molecule or a very similar group of molecules.
Which factor would most significantly INCREASE the rate of simple diffusion of a lipid-soluble substance across a cell membrane?
Options:
Decreasing the temperature.
Increasing the thickness of the membrane.
Increasing the concentration gradient of the substance. (Correct)
Decreasing the surface area of the membrane.
Correct Answer: Increasing the concentration gradient of the substance.
Rationale: A larger difference in concentration between the two sides of the membrane provides a stronger driving force for net movement, thus increasing the rate of simple diffusion.
After synthesis on the Rough ER, a protein destined for secretion will move through the endomembrane system in which sequence?
Options:
Rough ER → Lysosome → Plasma Membrane
Rough ER → Golgi Apparatus → Secretory Vesicle → Plasma Membrane (Correct)
Smooth ER → Golgi Apparatus → Mitochondrion
Nucleus → Rough ER → Secretory Vesicle
Correct Answer: Rough ER → Golgi Apparatus → Secretory Vesicle → Plasma Membrane
Rationale: This sequence correctly describes the pathway: synthesis in the RER, processing in the Golgi, packaging into vesicles, and release via exocytosis at the plasma membrane.
Which statement best differentiates between primary and secondary active transport?
Options:
Primary active transport moves substances down a gradient, while secondary moves them against.
Primary active transport directly uses ATP, while secondary active transport uses an ion gradient established by primary active transport. (Correct)
Primary active transport only moves ions, while secondary active transport moves only glucose.
Primary active transport uses channel proteins, while secondary active transport uses carrier proteins.
Correct Answer: Primary active transport directly uses ATP, while secondary active transport uses an ion gradient established by primary active transport.
Rationale: This is the defining difference: direct ATP hydrolysis for primary, and indirect energy from a pre-existing electrochemical gradient for secondary.
A cell surface receptor on the glycocalyx binds to a specific signaling molecule, triggering a response inside the cell. This exemplifies the glycocalyx's role as a:
Options:
Structural support component.
Barrier to water movement.
Cell-recognition and receptor site. (Correct)
Source of metabolic energy.
Correct Answer: Cell-recognition and receptor site.
Rationale: The carbohydrate chains of the glycocalyx are highly diverse and serve as specific binding sites for external ligands, initiating cellular responses.
When a cell uses endocytosis to take in fluid and dissolved solutes, it is specifically performing:
Options:
Phagocytosis
Exocytosis
Pinocytosis (Correct)
Receptor-mediated endocytosis
Correct Answer: Pinocytosis
Rationale: Pinocytosis, also known as 'cell drinking,' involves the non-specific uptake of extracellular fluid and its dissolved solutes in small vesicles.
Which statement accurately describes the 'fluid' aspect of the fluid mosaic model?
Options:
The membrane is a rigid, static structure.
Proteins are fixed in place within the membrane.
Phospholipids and proteins can move laterally within the membrane. (Correct)
The membrane is permeable to all substances.
Correct Answer: Phospholipids and proteins can move laterally within the membrane.
Rationale: The individual phospholipid molecules and many of the embedded proteins are not static but can move freely within the plane of the membrane, giving it fluidity.
To maintain a relatively constant internal body temperature, a decrease in external temperature leads to shivering, which generates heat. This is an example of:
Options:
Positive feedback
Negative feedback (Correct)
Feed-forward control
Homeostatic imbalance
Correct Answer: Negative feedback
Rationale: The shivering response counteracts the decrease in body temperature, working to restore the set point, which is characteristic of negative feedback.
Aquaporins are channel proteins that specifically facilitate the rapid movement of water across cell membranes. This type of transport is known as:
Options:
Active transport
Simple diffusion
Facilitated diffusion (Correct)
Osmotic pump
Correct Answer: Facilitated diffusion
Rationale: Facilitated diffusion uses membrane proteins (like channels or carriers) to speed up the movement of substances down their concentration gradient, without requiring energy.
A cell needs to actively transport a large, polar molecule into its cytoplasm. Which type of integral membrane protein would most likely be involved?
Options:
Channel protein
Enzyme
Carrier protein (pump) (Correct)
Structural protein
Correct Answer: Carrier protein (pump)
Rationale: Carrier proteins, particularly those acting as pumps, bind to specific molecules and undergo conformational changes to transport them across the membrane, often against their gradient, using energy.
Red blood cells are placed in a 0.9% NaCl solution, and they neither swell nor shrink. This indicates the solution is:
Options:
Hypotonic
Hypertonic
Isotonic (Correct)
Saturated
Correct Answer: Isotonic
Rationale: An isotonic solution has the same solute concentration as the cell's cytoplasm, resulting in no net water movement and no change in cell volume.
Which type of bulk transport involves a cell specifically taking in extracellular substances that bind to receptors on the plasma membrane, forming a coated vesicle?
Options:
Phagocytosis
Pinocytosis
Exocytosis
Receptor-mediated endocytosis (Correct)
Correct Answer: Receptor-mediated endocytosis
Rationale: This highly selective process ensures the cell takes in only specific molecules that are needed, even if they are in low concentrations, by using specialized receptors.
hich of the following cellular activities directly relies on ATP provided by mitochondria?
Options:
Simple diffusion of oxygen into the cell.
Facilitated diffusion of glucose via a carrier protein.
Movement of sodium ions out of the cell by the Na+/K+ pump. (Correct)
Osmosis of water across the cell membrane.
Correct Answer: Movement of sodium ions out of the cell by the Na+/K+ pump.
Rationale: The Na+/K+ pump is a primary active transporter that directly uses ATP as its energy source to move ions against their electrochemical gradients.
A substance that is small, nonpolar, and lipid-soluble would most likely cross the cell membrane by:
Options:
Facilitated diffusion
Primary active transport
Simple diffusion (Correct)
Endocytosis
Correct Answer: Simple diffusion
Rationale: These properties allow the substance to directly dissolve in and pass through the hydrophobic lipid bilayer down its concentration gradient.
After proteins are synthesized on the Rough ER, where do they go next for further modification, sorting, and packaging?
Options:
Mitochondria
Smooth Endoplasmic Reticulum (SER)
Nucleus
Golgi apparatus (Correct)
Correct Answer: Golgi apparatus
Rationale: The Golgi apparatus receives proteins from the ER, processes them through its cisternae, and sorts them into vesicles for delivery to their final destinations.
The symporter that transports Na+ and glucose into intestinal cells is an example of:
Options:
Primary active transport
Secondary active transport (Correct)
Facilitated diffusion
Simple diffusion
Correct Answer: Secondary active transport
Rationale: It utilizes the electrochemical gradient of Na+ (established by the Na+/K+ pump, a primary active transporter) to move glucose against its concentration gradient.
If a cell's internal environment becomes too acidic, mechanisms are activated to increase pH back to normal. This is an example of:
Options:
Positive feedback
Negative feedback (Correct)
Feed-forward control
Homeostatic breakdown
Correct Answer: Negative feedback
Rationale: The corrective action (increasing pH) opposes the initial change (acidity), restoring the pH to its set point, which is the definition of negative feedback.
Which feature of the cell membrane primarily restricts the passage of large, polar molecules and ions?
Options:
The peripheral proteins.
The hydrophilic heads of phospholipids.
The hydrophobic tails of phospholipids in the bilayer interior. (Correct)
The glycocalyx.
Correct Answer: The hydrophobic tails of phospholipids in the bilayer interior.
Rationale: The nonpolar, lipid-soluble tails form the core of the membrane, creating a barrier that charged and large polar molecules cannot easily cross.
If a plant cell is placed in a solution that is hypertonic to its cytoplasm, what will happen to the cell membrane and cell wall?
Options:
The cell membrane will swell and press against the cell wall.
The cell membrane will pull away from the cell wall (plasmolysis). (Correct)
Both the cell membrane and cell wall will expand.
There will be no change as the cell wall prevents water movement.
Correct Answer: The cell membrane will pull away from the cell wall (plasmolysis).
Rationale: In a hypertonic solution, water leaves the cell via osmosis, causing the protoplast (cell membrane and contents) to shrink and pull away from the rigid cell wall.
Question 25: Cells that line the digestive tract are connected by junctions that prevent digestive enzymes from leaking between them into the bloodstream. What type of junction is this?
Options:
Gap junctions
Desmosomes
Tight junctions (Correct)
Hemidesmosomes
Correct Answer: Tight junctions
Rationale: Tight junctions form a virtually impermeable seal between cells, preventing the movement of fluids and solutes through the intercellular space.
Which of the following describes a key characteristic of carrier proteins in facilitated diffusion?
Options:
They always require ATP to function.
They create a continuous pore through the membrane.
They exhibit specificity for the molecules they transport. (Correct)
They only transport water molecules.
Correct Answer: They exhibit specificity for the molecules they transport.
Rationale: Carrier proteins have specific binding sites for the molecules they transport, similar to enzymes binding to their substrates.
The rate of simple diffusion across a membrane is inversely proportional to the:
Options:
Surface area of the membrane.
Concentration gradient.
Lipid solubility of the substance.
Thickness of the membrane. (Correct)
Correct Answer: Thickness of the membrane.
Rationale: The thicker the membrane, the longer it takes for molecules to diffuse across, so the rate decreases.