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Question 1
Correct
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What type of pump is the Na+/K+ATPase pump?
Your Answer: An antiporter
Explanation:In order for primary active transport to pump ions against their electrochemical gradient, chemical energy is used in the form of ATP. This is facilitated by the Na+/K+-ATPase antiporter pump, which uses metabolic energy to move 3 Na+ions out of the cell for every 2 K+ions that come in, against their respective electrochemical gradients. As a result, the cell the maintains a high intracellular concentration of K+ions and a low concentration of Na+ions.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 2
Correct
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Which of the following is characterised by passive carrier-mediated transport down a chemical concentration gradient:
Your Answer: Facilitated diffusion
Explanation:Facilitated diffusion is the process of spontaneous passive transport of molecules or ions down their concentration gradient across a cell membrane via specific transmembrane transporter (carrier) proteins. The energy required for conformational changes in the transporter protein is provided by the concentration gradient rather than by metabolic activity.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 3
Correct
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Regarding conduction of nerve impulses, which of the following statements is CORRECT:
Your Answer: The action potential in myelinated axons is propagated only at the nodes of Ranvier.
Explanation:An action potential is a self-propagating response, successive depolarisation moving along each segment of an unmyelinated nerve until it reaches the end. It is all-or-nothing and does not decrease in size. Conduction in myelinated fibres is much faster, up to 50 times that of the fastest unmyelinated nerve. Myelinated fibres are insulated except at areas devoid of myelin called nodes of Ranvier. The depolarisation jumps from one node of Ranvier to another by a process called saltatory conduction. Saltatory conduction not only increases the velocity of impulse transmission but also conserves energy for the axon because depolarisation only occurs at the nodes and not along the whole length of the nerve fibre. Larger diameter myelinated nerve fibres conduct nerve impulses faster than small unmyelinated nerve fibres.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 4
Correct
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Which of the following statements is incorrect regarding the Na+/K+ATPase pump?
Your Answer: The Na + /K + ATPase pump moves 3 Na + ions into the cell for every 2 K + ions out.
Explanation:In order for primary active transport to pump ions against their electrochemical gradient, chemical energy is used in the form of ATP. The Na+/K+-ATPase antiporter pump uses metabolic energy to move 3 Na+ions out of the cell for every 2 K+ions in, against their respective electrochemical gradients. As a result, the cell the maintains a high intracellular concentration of K+ions and a low concentration of Na+ions.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 5
Correct
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Regarding cellular respiration, which of the following statements is CORRECT:
Your Answer: When fats are used as the primary energy source, an excess of acetyl-CoA is produced.
Explanation:Cellular respiration is the process by which cells obtain energy in the form of adenosine triphosphate (ATP). ATP transfers chemical energy from the energy rich substances in the cell to the cell’s energy requiring reactions e.g. active transport, DNA replication and muscle contraction.Cellular respiration is essentially a three step process: 1) Glycolysis, 2)The Krebs cycle, 3)The electron transfer system.The main respiratory substrate used by cells is 6-carbon glucose. Fats and proteins can also be used as respiratory substrates. When fats are being used as the primary energy source, in the absence of glucose, an excess amount of acetyl-CoA is produced, and is converted into acetone and ketone bodies. This can occur in starvation, fasting or in diabetic ketoacidosis. Proteins are used as an energy source only if protein intake is very high, or if glucose and fat sources are depleted.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 6
Correct
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Regarding the refractory period, which of the following statements is INCORRECT:
Your Answer: Action potentials can occur in the relative refractory period but the amplitude of the action potential is smaller.
Explanation:Following the action potential, Na+channels remain inactive for a time in a period known as the absolute refractory period where they cannot be opened by any amount of depolarisation. Following this there is a relative refractory period where the temporary hyperpolarisation (due to delayed closure of rectifier K+channels) makes the cell more difficult to depolarise and an action potential can be generated only in response to a larger than normal stimulus. The refractory period limits the frequency at which action potentials can be generated, and ensures that, once initiated, an action potential can travel only in one direction. An action potential is an all or nothing response so the amplitude of the action potential cannot be smaller.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 7
Incorrect
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Regarding fluid balance, which of the following statements is CORRECT:
Your Answer: One-third of total body fluid is intracellular.
Correct Answer: About three-quarters of extracellular fluid is interstitial.
Explanation:An ‘average’ person (70 kg male) contains about 40 litres of water in total, separated into different fluid compartments by biological semipermeable membranes; plasma cell membranes between extracellular and intracellular fluid, and capillary walls between interstitial and intravascular fluid. Around two-thirds of the total fluid (27 L) is intracellular fluid (ICF) and one-third of this (13 L) is extracellular fluid (ECF). The ECF can be further divided into intravascular fluid (3.5 L) and interstitial fluid (9.5 L).
Transcellular fluid refers to any fluid that does not contribute to any of the main compartments but which are derived from them e.g. gastrointestinal secretions and cerebrospinal fluid, and has a collective volume of approximately 2 L.
Osmosis is the passive movement of water across a semipermeable membrane from regions of low solute concentration to those of higher solute concentration. -
This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 8
Correct
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Depolarisation of a neuron begins with which of the following:
Your Answer: Opening of ligand-gated Na + channels
Explanation:Action potentials are initiated in nerves by activation of ligand-gated Na+channels by neurotransmitters. Opening of these Na+channels results in a small influx of sodium and depolarisation of the negative resting membrane potential (-70 mV). If the stimulus is sufficiently strong, the resting membrane depolarises enough to reach threshold potential (generally around -55 mV), at which point an action potential can occur. Voltage-gated Na+channels open, causing further depolarisation and activating more voltage-gated Na+channels and there is a sudden and massive sodium influx, driving the cell membrane potential to about +40 mV.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 9
Correct
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Which of the following ions is more abundant in extracellular fluid than in intracellular fluid:
Your Answer: Cl -
Explanation:Protein and phosphate are the primary intracellular anions, while chloride (Cl-) and bicarbonate are the predominant extracellular anions (HCO3-).
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 10
Correct
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From which of the following cell types are platelets derived?
Your Answer: Megakaryocytes
Explanation:Synthesis of platelets occurs in the bone marrow by fragmentation of megakaryocytes cytoplasm, derived from the common myeloid progenitor cell. The average time for differentiation of the human stem cell to the production of platelets is about 10 days. The major regulator of platelet formation is thrombopoietin and 95% of this is produced by the liver. Normal platelet count is 150 – 450 x 109/L and the normal lifespan of a platelet is about 10 days. Usually about one-third of the marrow output of platelets may be trapped at any one time in the normal spleen.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 11
Correct
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Foetal haemoglobin (HbF) comprises about how much of the total haemoglobin in adults:
Your Answer: 0.5 - 0.8%
Explanation:Foetal haemoglobin (HbF) makes up about 0.5 – 0.8 % of total adult haemoglobin and consists of two α and two gamma (γ) globin chains.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 12
Correct
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Regarding the resting membrane potential, which of the following statements is CORRECT:
Your Answer: The resting cell membrane is more permeable to K + ions than to Na + ions.
Explanation:A membrane potential is a property of all cell membranes, but the ability to generate an action potential is only a property of excitable tissues. The resting membrane is more permeable to K+and Cl-than to other ions (and relatively impermeable to Na+); therefore the resting membrane potential is primarily determined by the K+equilibrium potential. At rest the inside of the cell is negative relative to the outside. In most neurones the resting potential has a value of approximately -70 mV.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 13
Correct
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Which of the following ions normally has the highest concentration in intracellular fluid:
Your Answer: K +
Explanation:Potassium (K+) is the principal intracellular ion; approximately 4 mmol/L is extracellular (3%) and 140 mmol/L intracellular (97%).
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 14
Correct
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The correct statement regarding the parasympathetic nervous system is which of the following?
Your Answer: Parasympathetic preganglionic neurones run in cranial nerves III, VII, IX and X.
Explanation:The electron transfer system is responsible for most of the energy produced during respiration. The is a system of hydrogen carriers located in the inner mitochondrial membrane. Hydrogen is transferred to the electron transfer system via the NADH2 molecules produced during glycolysis and the Krebs cycle. As a result, a H+ion gradient is generated across the inner membrane which drives ATP synthase. The final hydrogen acceptor is oxygen and the H+ions and O2 combine to form water.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 15
Correct
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Regarding haemoglobin, which of the following statements is CORRECT:
Your Answer: In degradation of haemoglobin, the haem group is split from the haemoglobin and converted to biliverdin and ultimately to bilirubin.
Explanation:Haemoglobin is composed of four polypeptide globin chains each with its own iron containing haem molecule. Haem synthesis occurs largely in the mitochondria by a series of biochemical reactions commencing with the condensation of glycine and succinyl coenzyme A under the action of the key rate-limiting enzyme delta-aminolevulinic acid (ALA) synthase. The globin chains are synthesised by ribosomes in the cytosol. Haemoglobin synthesis only occurs in immature red blood cells.
There are three types of haemoglobin in normal adult blood: haemoglobin A, A2 and F:
– Normal adult haemoglobin (HbA) makes up about 96 – 98 % of total adult haemoglobin, and consists of two alpha (α) and two beta (β) globin chains.Â
– Haemoglobin A2 (HbA2), a normal variant of adult haemoglobin, makes up about 1.5 – 3.5 % of total adult haemoglobin and consists of two α and two delta (δ) globin chains.
– Foetal haemoglobin is the main Hb in the later two-thirds of foetal life and in the newborn until approximately 12 weeks of age. Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin.Â
Red cells are destroyed by macrophages in the liver and spleen after , 120 days. The haem group is split from the haemoglobin and converted to biliverdin and then bilirubin. The iron is conserved and recycled to plasma via transferrin or stored in macrophages as ferritin and haemosiderin. An increased rate of haemoglobin breakdown results in excess bilirubin and jaundice. -
This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 16
Correct
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Regarding the human cell, which of the following cell organelles is responsible for the production of ATP:
Your Answer: Mitochondria
Explanation:Mitochondria are membrane-bound organelles that are responsible for the production of the cell’s supply of chemical energy. This is achieved by using molecular oxygen to utilise sugar and small fatty acid molecules to generate adenosine triphosphate (ATP). This process is known as oxidative phosphorylation and requires an enzyme called ATP synthase. ATP acts as an energy-carrying molecule and releases the energy in situations when it is required to fuel cellular processes. Mitochondria are also involved in other cellular processes, including Ca2+homeostasis and signalling. Mitochondria contain a small amount of maternal DNA.
Mitochondria have two phospholipid bilayers, an outer membrane and an inner membrane. The inner membrane is intricately folded inwards to form numerous layers called cristae. The cristae contain specialised membrane proteins that enable the mitochondria to synthesise ATP. Between the two membranes lies the intermembrane space, which stores large proteins that are required for cellular respiration. Within the inner membrane is the perimitochondrial space, which contains a jelly-like matrix. This matrix contains a large quantity of ATP synthase.
Mitochondrial disease, or mitochondrial disorder, refers to a group of disorders that affect the mitochondria. When the number or function of mitochondria in the cell are disrupted, less energy is produced and organ dysfunction results. -
This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 17
Correct
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Which of the following comprises a negative feedback mechanism?
Your Answer: Detectors, comparators, a variable set point and effectors
Explanation:Negative feedback loops, also known as inhibitory loops, play a crucial role in controlling human health. It is a self-regulating mechanism of some sort.
A negative feedback system is made up of three main components: a detector (often neural receptor cells) that measures the variable in question and provides input to the comparator; a comparator (usually a neural assembly in the central nervous system) that receives input from the detector, compares the variable to the variable set point, and determines whether or not a response is required.
The comparator activates an effector (typically muscular or glandular tissue) to conduct the appropriate reaction to return the variable to its set point.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 18
Correct
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Which of these is NOT a naturally occurring anticoagulant:
Your Answer: Factor V Leiden
Explanation:It’s crucial that thrombin’s impact is restricted to the injured site. Tissue factor pathway inhibitor (TFPI), which is produced by endothelial cells and found in plasma and platelets, is the first inhibitor to function. It accumulates near the site of harm induced by local platelet activation. Xa and VIIa, as well as tissue factor, are inhibited by TFPI. Other circulating inhibitors, the most potent of which is antithrombin, can also inactivate thrombin and other protease factors directly. Coagulation cofactors V and VIII are inhibited by protein C and protein S. Tissue plasminogen activator (TPA) from endothelial cells facilitates fibrinolysis by promoting the conversion of plasminogen to plasmin.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 19
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. -
This question is part of the following fields:
- Basic Cellular
- Physiology
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Question 20
Correct
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Which of the following is the most potent stimulus of fibrinolysis:
Your Answer: Tissue plasminogen activator
Explanation:Fibrinolysis is a normal haemostatic response to vascular injury. Plasminogen, a proenzyme in blood and tissue fluid, is converted to plasmin by activators either from the vessel wall (intrinsic activation) or from the tissues (extrinsic activation). The most important route follows the release of tissue plasminogen activator (TPA) from endothelial cells.
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This question is part of the following fields:
- Basic Cellular
- Physiology
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SESSION STATS - PERFORMANCE PER SPECIALTY
