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Question 1
Correct
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Cardiac muscle and skeletal muscle are alike, but there are a few key variations. Which of the following is NOT a characteristic of skeletal muscle but is a characteristic of cardiac muscle?
Your Answer: The presence of intercalated discs
Explanation:Cardiac muscle is striated, and the sarcomere is the contractile unit, similar to skeletal muscle. Contracture is mediated by the interaction of calcium, troponins, and myofilaments, much as it occurs in skeletal muscle. Cardiac muscle, on the other hand, differs from skeletal muscle in a number of ways. In contrast to skeletal muscle cells, cardiac myocytes have a nucleus in the middle of the cell and sometimes two nuclei. The cells are striated because the thick and thin filaments are arranged in an orderly fashion, although the arrangement is less well-organized than in skeletal muscle. Intercalated discs, which work similarly to the Z band in skeletal muscle in defining where one cardiac muscle cell joins the next, are a very significant component of cardiac muscle. Adherens junctions and desmosomes, which are specialized structures that hold the cardiac myocytes together, are formed by the transverse sections. The lateral sections produce gap junctions, which join the cytoplasm of two cells directly, allowing for rapid action potential conduction. These critical properties allow the heart to contract in a coordinated manner, allowing for more efficient blood pumping. Cardiac myocytes have the ability to create their own action potentials, which is referred to as myogenic’. They can depolarize spontaneously to initiate a cardiac action potential. Pacemaker cells, as well as the sino-atrial (SA) and atrioventricular (AV) nodes, control this. The Purkinje cells and the cells of the bundle of His are likewise capable of spontaneous depolarization. While the bundle of His is made up of specialized myocytes, it’s vital to remember that Purkinje cells are not myocytes and have distinct characteristics. They are larger than myocytes, with fewer filaments and more gap junctions than myocytes. They conduct action potentials more quickly, allowing the ventricles to contract synchronously. Cardiac myocytes contract by excitation-contraction coupling, just like skeletal myocytes. Heart myocytes, on the other hand, utilise a calcium-induced calcium release mechanism that is unique to cardiac muscle (CICR). The influx of calcium ions (Ca2+) into the cell causes a ‘calcium spark,’ which causes more ions to be released into the cytoplasm. An influx of sodium ions induces an initial depolarisation, much as it does in skeletal muscle; however, in cardiac muscle, the inflow of Ca2+ sustains the depolarisation, allowing it to remain longer. Due to potassium ion (K+) inflow, CICR causes a plateau phase in which the cells remain depolarized for a short time before repolarizing. Skeletal muscle, on the other hand, repolarizes almost instantly. Comparison of skeletal and cardiac muscle: Skeletal muscle Cardiac muscle Striation Striated but arrangement less organised Multiple nuclei located peripherally Usually single nucleus (but can be two), located centrally Discs None Intercalated discs No Gap junctions Gap junctions No Pacemaker Pacemaker Electrical stimulation: Nervous system (excitation) Pacemaker (excitation)
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 2
Correct
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In which organelle is the intrinsic apoptotic pathway initiated?
Your Answer: Mitochondria
Explanation:Apoptosis is a programmed form of cell death involving the degradation of cellular constituents by a group of cysteine proteases called caspases. The caspases can be activated through either the intrinsic (mitochondrial mediated) or extrinsic (death receptor mediated) apoptotic pathways. The intrinsic apoptotic pathway is characterized by permeabilization of the mitochondria and release of cytochrome c into the cytoplasm.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 3
Correct
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Which of the following statements is correct regarding homeostasis?
Your Answer: In negative feedback mechanisms, effectors always act to move the variable in the opposite direction to the change that was originally detected.
Explanation:The vast majority of systems within the body work by negative feedback mechanisms. This negative feedback refers to the way that effectors act to move the variable in the opposite direction to the change that was originally detected. Because there is an inherent time delay between detecting a change in a variable and effecting a response, the negative feedback mechanisms cause oscillations in the variable they control. There is a narrow range of values within which a normal physiological function occurs and this is called the ‘set point’. The release of oxytocin in childbirth is an example of positive feedback.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 4
Correct
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The cell membrane:
Your Answer: Is a bilayer of amphipathic lipids
Explanation:The cell membrane consists of a bilayer of amphipathic lipids with embedded proteins. The basic function of the cell membrane is to protect the cell from its surroundings. It is selectively permeable to ions and organic molecules. The entire membrane is held together via non-covalent interaction of hydrophobic tails, however the structure is quite fluid and not fixed rigidly in place. Membranes are typically 7.5–10 nm in thickness and typically have a large content of proteins, around 50% of membrane volume.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 5
Correct
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Which of the following statements is correct regarding the neuronal action potential?
Your Answer: Initial depolarisation occurs as a result of a Na + influx.
Explanation:The resting potential in most neurons has a value of approximately -70 mV. The threshold potential is generally around -55 mV. Initial depolarisation when there is Na+influx through ligand-gated Na+channels. Action potential is an all or nothing response. The size of the action potential is constant and so, the intensity of the stimulus is coded by the frequency of firing of a neuron. K+efflux is responsible for repolarisation.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 6
Correct
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With regards to the Na+/K+ ATPase, which one of the following is correct?
Your Answer: 3 Na+ released into the extracellular fluid
Explanation:Na+/K+ pump or sodium–potassium pump is an enzyme found in the plasma membrane. This pumping is active (i.e. it uses energy from ATP) and is important for cell physiology. Its simple function is to pump 3 sodium ions out for every 2 potassium ions taken in and since they both have equal ionic charges, this creates a electrochemical gradient between a cell and its exterior.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 7
Incorrect
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What is the function of the pro-apoptotic Bcl-2 family of proteins, Bax and Bak?
Your Answer: Cleaves DNA in the nucleus
Correct Answer: Form permissive pores in the mitochondrial membrane
Explanation:The pro-apoptotic proteins in the BCL-2 family, including Bax and Bak, normally act on the mitochondrial membrane to promote permeabilization and release of cytochrome C and ROS, that are important signals in the apoptosis cascade. Growing evidence suggests that activated BAX and/or Bak form an oligomeric pore, MAC in the mitochondrial outer membrane. This results in the release of cytochrome c and other pro-apoptotic factors from the mitochondria, often referred to as mitochondrial outer membrane permeabilization, leading to activation of caspases.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 8
Correct
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A 24-year-old athlete drinks a 500 ml hypertonic sports drink before an endurance event he participates in. Which of the following effects will this cause?
Your Answer: The interstitial fluid becomes more concentrated
Explanation:Osmosis is the passive movement of water across a semipermeable membrane from a region of low solute concentration to a region of higher solute concentration. When hypertonic fluid is ingested: The plasma becomes CONCENTRATED. The cells lose water and shrink The intracellular fluid becomes more concentrated. Water and ions move freely from the plasma into the interstitial fluid and the interstitial fluid becomes more concentrated. The increased osmotic potential draws water out of the cells.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 9
Correct
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On review of a patient's serum and urine osmolality test result, you note that both osmolarities are decreased. There urine osmolality does not increase with fluid ingestion. What is the most likely cause?
Your Answer: Hyponatraemia
Explanation:As part of the investigation of hyponatraemia, serum osmolality is commonly requested in combination with urine osmolality to aid diagnosis. When: Serum osmolality is decreased and urine osmolality is decreased with no intake of fluid, the causes are Hyponatraemia Overhydration Adrenocortical insufficiency Sodium loss (diuretic or a low-salt diet) Serum osmolality is normal or increased and urine osmolality is increased the causes include: Dehydration Hyperkalaemia Hyperglycaemia Hyponatremia Mannitol therapy Diabetes mellitus Alcohol ingestion Congestive heart failure Renal disease and uraemia Serum osmolality is normal or increased and urine osmolality is decreased the usual cause is diabetes insipidus Serum osmolality is decreased and urine osmolality is increased the usual cause is syndrome of inappropriate antidiuresis (SIAD)
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 10
Correct
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The role of the hemidesmosome is?
Your Answer: Attaches cells to underlying basal lamina
Explanation:Hemidesmosomes connect the basal surface of epithelial cells via intermediate filaments to the underlying basal lamina. The transmembrane proteins of hemidesmosomes are not cadherins, but another type of protein called integrin.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 11
Correct
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Which of the following statements is most suitable to describe necrosis?
Your Answer: Significant inflammatory response
Explanation:Necrosis is the death of most or all of the cells in an organ or tissue due to disease, injury, or failure of the blood supply. Cellular death due to necrosis does not follow the (regulated) apoptotic signal transduction pathway, but rather various receptors are activated, and result in the loss of cell membrane integrity and an uncontrolled release of products of cell death into the extracellular space. This initiates in the surrounding tissue an inflammatory response which attracts leukocytes and nearby phagocytes which eliminate the dead cells by phagocytosis.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 12
Correct
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Which of the following globin chains makes up normal adult haemoglobin (HbA)?
Your Answer: Two alpha and two beta chains
Explanation:Total adult haemoglobin comprises about 96 – 98 % of normal adult haemoglobin (HbA). It consists of two alpha (α) and two beta (β) globin chains.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 13
Correct
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The breakdown of superoxide is catalysed by which enzyme?
Your Answer: Superoxide dismutase
Explanation:As superoxide is toxic, nearly all organisms living in the presence of oxygen contain isoforms of the superoxide-scavenging enzyme superoxide dismutase, or SOD. SOD is an extremely efficient enzyme; it catalyses the neutralization of superoxide nearly as quickly as the two can diffuse together spontaneously in solution.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 14
Correct
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What is the function of secondary messengers?
Your Answer: Communication from extracellular to intracellular signalling pathways
Explanation:First messengers may not physically cross the phospholipid bilayer to initiate changes within the cell directly. This functional limitation necessitates the cell to devise signal transduction mechanisms to transduce first messenger into second messengers, so that the extracellular signal may be propagated intracellularly. Second messengers are intracellular signalling molecules released by the cell to trigger physiological changes such as proliferation, differentiation, migration, survival, and apoptosis. Secondary messengers are therefore one of the initiating components of intracellular signal transduction cascades.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 15
Correct
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What are the major motor proteins that interact with microtubules?
Your Answer: Kinesin and dynein
Explanation:The major motor proteins that interact with microtubules are kinesin, which usually moves toward the (+) end of the microtubule, and dynein, which moves toward the (−) end.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 16
Correct
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The fluid in contact with a tube is dragged by frictional forces to the tube's sidewalls. This creates a velocity gradient in which the fluid flow is greatest in the tube's centre. Which of the following terms most accurately characterizes this flow pattern?
Your Answer: Laminar flow
Explanation:The fluid in contact with a tube is dragged by frictional forces at the tube’s sidewalls. This creates a velocity gradient in which the fluid flow is greatest in the tube’s centre. This is known as laminar flow, and it characterizes the flow in most circulatory and respiratory systems when they are at rest. The velocity of the fluid flow can fluctuate erratically at high velocities, particularly within big arteries and airways, disrupting laminar flow. As a result, resistance increases significantly. This is known as turbulent flow, and symptoms include heart murmurs and asthmatic wheeze.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 17
Correct
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Which statement regarding skeletal muscle is true?
Your Answer: Myosin is the major constituent of the thick filament
Explanation:Myosin is the major constituent of the thick filament. Actin is the major constituent of the THIN filament. Thin filaments consist of actin, tropomyosin and troponin in the ratio 7:1:1.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 18
Correct
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Cellular Theory of Ageing
Your Answer: Gene regulation
Explanation:Cellular theories of aging propose that human aging is the result of cellular aging, whereby an increasing proportion of cells reach senescence, a terminal stage at which cells will cease to divide. This will limit the body’s ability to regenerate and to respond to injury or stress.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 19
Correct
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The movement of molecules across the cell membrane relies greatly on active transport. Which of the following statements about active transport is correct?
Your Answer: Active transport occurs in glucose absorption from the gut
Explanation:The movement of a material against a concentration gradient, i.e. from a low to a high concentration, is known as active transport. Primary active transport is defined as active transport that involves the use of chemical energy, such as adenosine triphosphate (ATP). Secondary active transport occurs when an electrochemical gradient is used. The sodium-potassium pump, calcium ATPase pump, and proton pump are all key active transport systems that use ATP. An electrochemical gradient is used by the sodium-calcium co-transporter, which is an example of secondary active transport. The sodium-dependent hexose transporter SGLUT-1 transports glucose and galactose into enterocytes. Secondary active transport is exemplified here.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 20
Correct
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What is the function of gap junctions?
Your Answer: Diffusion of small molecules between neighbouring cells
Explanation:Gap junctions are a specialized intercellular connection between a multitude of cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 21
Correct
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Which intercellular connections are responsible for fastening the cells to one another?
Your Answer: Hemidesmosomes, zonula adherens & desmosomes
Explanation:There are three major types of cell junction:Adherens junctions, desmosomes and hemidesmosomes (anchoring junctions),Gap junctions (communicating junction) &Tight junctions (occluding junctions)
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 22
Correct
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Which ion channel is a dimer?
Your Answer: Cl- channel
Explanation:A dimer is a chemical structure formed from two similar sub-units. Chloride channels or exchangers are composed of two similar subunits—a dimer—each subunit containing one pore.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 23
Correct
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Cyclic AMP activates the following enzyme
Your Answer: Protein Kinase A
Explanation:Cyclic AMP works by activating protein kinase A (PKA, or cAMP-dependent protein kinase). Protein kinase A can also phosphorylate specific proteins that bind to promoter regions of DNA, causing increases in transcription.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 24
Correct
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Which of these structures is the smallest and deepest component of muscle connective tissue?
Your Answer: Endomysium
Explanation:There are three types of muscle: Skeletal muscle Cardiac muscle Smooth muscle Individual muscle is enveloped in a layer of dense irregular connective tissue called the epimysium. The epimysium protects the muscles from friction against bones and other muscles. Skeletal muscle is composed of muscle fibres, referred to as myofibers which is ensheathed by a wispy layer of areolar connective tissue called the endomysium. The endomysium is the smallest and deepest component of muscle connective tissue. Myofibers grouped together in bundles form fascicles, or fasciculi. These are surrounded by a type of connective tissue called the perimysium. Beneath the endomysium lies the sarcolemma, an elastic sheath with infoldings that invaginate the interior of the myofibers, particularly at the motor endplate of the neuromuscular junction.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 25
Correct
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A 34-year-old woman was diagnosed with multiple sclerosis two years ago. Her symptoms have been steadily deteriorating, with no intervals of remission in sight. Which of the following aspects of nerve conduction is disrupted by multiple sclerosis?
Your Answer: Saltatory conduction
Explanation:Local currents propagate action potentials down the axons of neurons. This local current flow following depolarisation results in the depolarisation of the neighbouring axonal membrane, and when this region approaches the threshold, more action potentials are generated and so forth. Due to the refractory period, portions of the membrane that have recently depolarized will not depolarize again, resulting in the action potential only being able to go in one direction. The square root of axonal diameter determines the velocity of the action potential; the axons with the biggest diameter have the quickest conduction velocities. When a neuron is myelinated, the speed of the action potential rises as well. The myelin sheath is an insulating coating that surrounds certain neural axons. By increasing membrane resistance and decreasing membrane capacitance, the myelin sheath improves conduction. This enables faster electrical signal transmission via a neuron, making them more energy-efficient than non-myelinated neuronal axons. Electrical impulses are quickly transmitted from one node to the next, causing depolarization of the membrane above the threshold and triggering another action potential, which is then transmitted to the next node. An action potential is rapidly conducted down a neuron in this manner. Saltatory conduction is the term for this. Multiple sclerosis is an example of a clinical disorder in which the myelin sheath is affected. It is an immune-mediated disorder in which certain nerve cells in the brain and spinal cord become demyelinated. The ability of some areas of the nervous system to properly transmit action potentials is disrupted by demyelination, resulting in a variety of neurological symptoms and indications.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 26
Correct
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In the presence of oxygen , lactate that was produced under anaerobic conditions is converted to:
Your Answer: Pyruvate
Explanation:Lactate can be used in two ways:Oxidation back to pyruvate by well-oxygenated muscle cells, heart cells, and brain cells. Pyruvate is then directly used to fuel the Krebs cycle orConversion to glucose via gluconeogenesis in the liver and release back into circulation.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 27
Correct
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The interior of lysosomes is kept at a pH of around 5 by the action of:
Your Answer: H+ ATPase
Explanation:The lysosome maintains its pH differential by pumping in protons (H+ ions) from the cytosol across the membrane via proton pumps and chloride ion channels. Vacuolar H+-ATPases are responsible for transport of protons, while the counter transport of chloride ions is performed by ClC-7 Cl−/H+ antiporter.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 28
Correct
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The myocardium is responsible for creating the force with which the atrial and ventricular muscles contract. It is made up of myocytes, which are heart muscle cells. Which of the following statements about cardiac muscle anatomy is correct?
Your Answer: Cardiac myocytes have intercalated discs
Explanation:Typically, granuloma has Langerhan’s cells (large multinucleated cells ) surrounded by epithelioid cell aggregates, T lymphocytes and fibroblasts. Antigen presenting monocytic cells found in the skin are known as Langerhan’s cells.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 29
Correct
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Which of the following statements is not true regarding ion channels?
Your Answer: Ion channels provide a charged, hydrophobic pore through which ions can diffuse across the lipid bilayer.
Explanation:Ion channels are pore-forming protein complexes that facilitate the flow of ions across the hydrophobic core of cell membranes. They are present in the plasma membrane and membranes of intracellular organelles of all cells, and perform essential physiological functions. They provide a charged, hydrophilic pore through which ions can move across the lipid bilayer. They are selective for particular ions and their pores may be opened or closed. Because of this ability to open and close, ion channels allow the cell to have the ability to closely control the movement of ions across the membrane. Gating refers to the transition between an open and closed ion channel state, and is brought about by a conformationational change in the protein subunits that open or close the ion-permeable pore. Ion channels can be: 1. voltage-gated these are regulated according to the potential difference across the cell membrane or 2. ligand-gated – these are regulated by the presence of a specific signal molecule.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 30
Incorrect
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Changes in cadherin expression are associated with
Your Answer:
Correct Answer: Tumour metastatic potential
Explanation:Cadherins play a role in maintaining cell and tissue structure, and in cellular movement. The E-cadherin–catenin complex plays a key role in cellular adhesion; loss of this function has been associated with greater tumour metastasis.
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This question is part of the following fields:
- Cell Biology
- Physiology
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SESSION STATS - PERFORMANCE PER SPECIALTY
