Correct: D)
Explanation: The correct answer is D because the proportion of oxygen in the atmosphere remains constant at approximately 21% regardless of altitude — what decreases with altitude is the total atmospheric pressure, and therefore the partial pressure of oxygen available for breathing. A, B, and C are all wrong because they suggest the percentage of oxygen itself changes with altitude, which is incorrect; the atmosphere maintains a homogeneous composition up to approximately 80 km.
Correct: C)
Explanation: The correct answer is C because smokers already have elevated carboxyhaemoglobin levels from carbon monoxide binding to their red blood cells, effectively reducing their oxygen-carrying capacity even before flight, so hypoxic symptoms manifest at lower altitudes compared to non-smokers. A is wrong because hypoxia is insidious — symptoms develop gradually and the pilot often does not recognise them. B is wrong because 4,000 ft is generally too low for noticeable hypoxic effects in most people. D is wrong because gasping for air is not a typical hypoxia symptom; instead, early signs include impaired judgment and reduced night vision.
Correct: C)
Explanation: The correct answer is C because carbon monoxide (CO) is a highly toxic gas produced by incomplete combustion of carbon-based fuels, and in aviation it can enter the cabin through leaking exhaust systems; it binds to haemoglobin with approximately 200 times the affinity of oxygen. A is wrong because cells produce carbon dioxide (CO2) as a metabolic waste product, not carbon monoxide. B is wrong because CO is odourless, colourless, and tasteless, making it extremely dangerous even at low concentrations. D is wrong because CO is a trace gas, not one of the major atmospheric components.
Correct: A)
Explanation: The correct answer is A because full dark adaptation requires approximately 30 minutes for the rod cells in the retina to reach maximum sensitivity through the regeneration of rhodopsin (visual purple), which is why pilots should avoid bright lights before night flying. B is wrong because one hour significantly overestimates the adaptation time. C is wrong because at 15 minutes the rods are only partially adapted and night vision is not yet at full capability. D is wrong because 5 minutes only allows for initial cone adaptation, not the complete rod-based dark adaptation needed for effective night vision.
Correct: B)
Explanation: The correct answer is B because hypotension (low blood pressure) can cause dizziness, lightheadedness, and even fainting, particularly when changing posture (orthostatic hypotension), which poses a flight safety risk. A is wrong because low blood pressure mainly causes symptoms during posture changes (standing up), not while lying down. C is wrong because elderly smokers are more commonly affected by high blood pressure (hypertension), not low blood pressure. D is wrong because low blood pressure can certainly cause symptoms that impair pilot performance.
Correct: A)
Explanation: The correct answer is A because at 20,000 ft without supplemental oxygen, the time of useful consciousness (TUC) is very short — typically only a few minutes — and rapid loss of consciousness follows due to severe hypoxia as the partial pressure of oxygen is far below what the body requires. B is wrong because pulmonary oedema develops over hours to days of high-altitude exposure, not during acute exposure. C is wrong because while shortness of breath may occur briefly, loss of consciousness is the most probable and dangerous outcome. D is wrong because fever is unrelated to altitude exposure.
Correct: A)
Explanation: The correct answer is A because during descent, external atmospheric pressure increases and trapped air within congested sinuses cannot equalise, creating a painful pressure differential — this is known as barosinusitis. B is wrong because while altitude changes in both directions can cause discomfort, descent is specifically the most problematic phase because the blocked sinuses cannot vent the increasing external pressure inward. C is wrong because during climb, expanding air within the sinuses can usually escape more easily, even through partially blocked passages. D is wrong because linear accelerations do not create the pressure differentials that cause sinus pain.
Correct: C)
Explanation: The correct answer is C because the classic symptoms of motion sickness (kinetosis) are dizziness, sweating, pallor, and nausea, which may progress to vomiting — all caused by a conflict between visual and vestibular sensory inputs. A is wrong because high fever is not a symptom of motion sickness; it indicates infection. B is wrong because neither high fever nor watery diarrhoea are associated with kinetosis. D is wrong because watery diarrhoea is a gastrointestinal symptom unrelated to vestibular-induced motion sickness.
Correct: C)
Explanation: The correct answer is C because a runway wider than the pilot is accustomed to makes the visual perspective appear as though the aircraft is lower and closer than it actually is, creating the impression of being at too low a speed and too low a height — the pilot may then tend to fly the approach too high. A is wrong because the wide runway creates the opposite illusion — feeling too low, not too high. B is wrong because the illusion relates to perceived height and proximity, not excessive speed. D is wrong because feeling too low in height would be a consequence, but the question asks about speed impression, and C correctly captures the speed-related illusion.
Correct: B)
Explanation: The correct answer is B because the eyes (specifically the retina) are the first organ to be affected by positive g-forces because retinal blood vessels are extremely sensitive to reduced blood pressure — the retina has the highest oxygen demand of any tissue, so when blood drains away under g-loading, vision degrades before consciousness is affected. A is wrong because the lungs continue to function under moderate g-forces. C is wrong because the brain loses function after the eyes — loss of consciousness (G-LOC) follows grey-out and blackout. D is wrong because muscles are not meaningfully affected by the blood pressure reduction that causes grey-out.
Correct: C)
Explanation: Effective visual scanning requires dividing the sky into sectors and pausing briefly on each one, allowing the eyes to focus and detect movement or contrast changes that indicate other aircraft. Option A and Option D advocate rapid, sweeping eye movements that prevent the eye from fixating long enough to register a small target. Option B similarly relies on continuous rolling motion, which reduces detection probability. Only Option C describes the proven sector-by-sector technique recommended in human factors training.
Correct: C)
Explanation: The human liver metabolises alcohol at a relatively constant rate of approximately 0.1 per mille per hour, regardless of the type of drink consumed or any attempted countermeasures such as coffee or exercise. Option A (0.5‰/h) and Option D (1‰/h) greatly overestimate the elimination rate, which could lead pilots to believe they are sober sooner than they actually are. Option B (0.3‰/h) is also too high. For SPL exam purposes, the standard value to remember is 0.1‰ per hour.
Correct: A)
Explanation: A sedentary lifestyle with insufficient physical activity is a well-established cardiovascular risk factor that increases the likelihood of heart attack. Option B (hypoglycaemia) is a metabolic condition primarily affecting energy supply to the brain, not a direct cardiac risk factor. Option C (undernutrition) and Option D (low cholesterol) are actually the opposite of known risk factors — it is overnutrition and high cholesterol that contribute to coronary artery disease. Regular exercise is one of the most effective protective measures against cardiovascular disease.
Correct: D)
Explanation: Amphetamines are strictly prohibited for pilots on duty because their adverse effects — including impaired judgment, overconfidence, risk-taking behaviour, and a crash of fatigue after the drug wears off — directly compromise flight safety. Option A and Option C suggest using amphetamines to combat fatigue during long flights, which is dangerous and illegal under aviation medical regulations. Option B implies that a co-pilot can mitigate the risk, but no crew arrangement makes stimulant use acceptable. The correct approach to fatigue is proper rest before flight, not pharmacological stimulation.
Correct: C)
Explanation: Risk area awareness refers to the pilot's conscious understanding that different phases of flight — takeoff, climb, cruise, descent, approach, and landing — each carry distinct hazards requiring specific vigilance. Option A is too narrow, focusing only on statistical accident rates rather than active awareness. Option B incorrectly interprets "risk area" as a physical location on the aerodrome. Option D describes risk area awareness as a procedure, but it is a mindset and competency, not a checklist or formal procedure. Effective risk area awareness allows the pilot to anticipate and mitigate threats proactively.
Correct: B)
Explanation: The DECIDE model follows the sequence: Detect, Estimate, Choose, Identify, Do, Evaluate. The first letter D stands for "Detect," meaning the pilot recognises that a change in the situation has occurred requiring a decision. Option A incorrectly assigns "Do" to the first D — "Do" is actually the fifth step, where the chosen course of action is implemented. Option C misplaces "Evaluate" as the first E, but the first E is "Estimate" (assess the significance of the change). Option D overstates the requirement — DECIDE is a helpful framework, not a mandatory procedure for every single decision.
Correct: A)
Explanation: Human factors research identifies five hazardous attitudes — anti-authority, macho, invulnerability, resignation, and impulsivity — and demonstrates that pilots can learn to recognise these tendencies in themselves and apply corrective antidotes. Option B incorrectly ranks hazardous attitudes; all five are dangerous and none should be dismissed as less threatening. Option C wrongly limits dangerous behaviour to inexperienced pilots, when in fact experienced pilots can also exhibit complacency and overconfidence. Option D denies the existence of hazardous attitudes entirely, contradicting decades of aviation safety research.
Correct: B)
Explanation: Selective attention is a cognitive phenomenon where concentrating intensely on one task causes the brain to filter out other stimuli, even obvious ones like a loud alarm. This is sometimes called "inattentional blindness" or "tunnel hearing." Option A confuses selective attention with a deliberate cockpit strategy, when it is actually an involuntary cognitive limitation. Option C describes instrument scan technique, not the psychological concept of selective attention. Option D incorrectly categorises it as a stress management method, when in fact selective attention under stress can be dangerous because critical warnings may go unnoticed.
Correct: A)
Explanation: The Yerkes-Dodson law demonstrates that moderate stress (eustress) enhances alertness, focus, and performance, while too little or too much stress degrades it — forming an inverted-U curve. Option B is incorrect because under-stimulation (boredom) is itself a form of stress that reduces vigilance and increases error rates. Option C oversimplifies by suggesting all cockpit stress is beneficial, when excessive stress causes cognitive overload and poor decision-making. Option D wrongly limits stress to brief overload, ignoring chronic stress from fatigue, personal problems, or sustained workload.
Correct: A)
Explanation: Research on circadian rhythms shows that the human endogenous biological clock runs on a cycle of approximately 25 hours when isolated from external time cues such as daylight and social schedules. Daily exposure to light resets (entrains) this internal clock to the 24-hour day-night cycle. Option B (20 hours) and Option D (30 hours) are incorrect values. Option C is wrong because the internal clock does not naturally run at exactly 24 hours — it requires daily resynchronisation by environmental cues called Zeitgebers.
Correct: C)
Explanation: Breathing fresh, cool air helps stabilise the autonomic nervous system and is one of the most effective immediate remedies for the onset of motion sickness. Option A (moving the head regularly) worsens symptoms by increasing conflicting vestibular stimulation. Option B (looking through the windows) can aggravate the sensory mismatch between visual and vestibular inputs in some individuals. Option D (drinking coffee) is a stimulant that can increase nausea and does not address the underlying vestibular conflict causing motion sickness.
Correct: C)
Explanation: A pilot accustomed to narrow runways perceives a wide runway as being closer (lower) than it actually is because the wider visual angle tricks the brain into interpreting the scene as a nearer surface. This creates the dangerous illusion of being too low, which may cause the pilot to fly a higher approach than necessary and flare too high. Option A and Option D describe slope-related illusions unrelated to runway width. Option B describes the opposite illusion — the pilot feels lower, not higher. Understanding this visual trap is essential for safe approaches to unfamiliar aerodromes.
Correct: B)
Explanation: Middle ear pressure equalisation problems are most likely during rapid descent because the Eustachian tube must open to allow higher-pressure air from the throat into the middle ear cavity, which is physiologically more difficult than the reverse. During ascent, expanding air in the middle ear vents outward relatively easily. Option A (long high-altitude flight) maintains a constant cabin altitude and does not create pressure differentials. Option C (long climb) involves gradual pressure decrease that the ear handles well. Option D (negative g-forces) affects the vestibular system, not middle ear pressure.
Correct: D)
Explanation: The composition of the atmosphere remains constant at approximately 21% oxygen and 78% nitrogen from sea level up to about 80 km altitude. What decreases with altitude is not the percentage of oxygen but the total atmospheric pressure, and therefore the partial pressure of oxygen available to the lungs. Option A and Option B incorrectly suggest that the proportion changes. Option C proposes an increase, which is also wrong. The key concept for pilots is that hypoxia at altitude results from reduced partial pressure, not from a change in oxygen percentage.
Correct: A)
Explanation: Carbon monoxide (CO) binds to haemoglobin approximately 200 times more readily than oxygen, forming carboxyhaemoglobin and drastically reducing the blood's oxygen-carrying capacity. Even very low concentrations can cause headaches, impaired judgment, and eventually total incapacitation or death. Option B and Option D dangerously dismiss CO as harmless — it is one of aviation's most insidious threats because it is colourless and odourless. Option C incorrectly suggests that only prolonged exposure is harmful, when in fact even brief exposure to moderate concentrations can be lethal.
Correct: B)
Explanation: A helmet with integrated earphones provides the highest level of hearing protection by covering the entire ear with a rigid shell that attenuates both direct sound and vibration-transmitted noise, while simultaneously enabling clear radio communication. Option A (cotton wool) offers minimal attenuation and is not a proper hearing protector. Option C (ear plugs) provide reasonable protection but less than a full helmet and may impair communication clarity. Option D incorrectly assumes that cockpit noise levels are low — sustained exposure to even moderate cockpit noise causes cumulative hearing damage over time.
Correct: A)
Explanation: Legumes such as beans, peas, and lentils are well known to produce significant intestinal gas during digestion. At altitude, ambient pressure decreases and any trapped gas in the body expands according to Boyle's law, potentially causing severe abdominal pain and distraction in flight. Option B (meat), Option C (pasta), and Option D (potatoes) do not produce significant intestinal gas under normal circumstances. Pilots planning high-altitude flights should avoid gas-forming foods in the hours before departure.
Correct: B)
Explanation: In cellular respiration, somatic cells take in oxygen and use it to metabolise glucose and other nutrients, producing energy (ATP) and releasing carbon dioxide (CO2) as a waste product. Option A and Option C incorrectly involve nitrogen, which plays no active role in cellular metabolism — it is physiologically inert at normal pressures. Option D incorrectly names carbon monoxide (CO) as a metabolic by-product; CO is a toxic gas from incomplete combustion, not from normal cellular processes.
Correct: B)
Explanation: Cigarette smoke contains carbon monoxide (CO), which binds to haemoglobin and reduces the blood's oxygen-carrying capacity. A pilot who smokes before an alpine flight effectively raises their "physiological altitude" — they will experience symptoms of oxygen deficiency (hypoxia) at a lower altitude than a non-smoking pilot would. Option A incorrectly assumes that habitual smoking confers tolerance; the CO effect on haemoglobin is cumulative regardless of habit. Option C attributes the wrong symptoms to nicotine. Option D confuses carbon monoxide (CO) with carbon dioxide (CO2), which are entirely different gases.
Correct: D)
Explanation: Rotating the head during a coordinated turn creates the Coriolis illusion — the semicircular canals are already stimulated by the angular acceleration of the turn, and a head rotation in a different plane stimulates additional canals simultaneously, producing a powerful and disorienting sensation of tumbling or spinning. Option A, Option B, and Option C involve head rotation during relatively stable flight conditions where only one set of canals is stimulated at a time, making vestibular disturbance far less likely. The Coriolis illusion is one of the most dangerous vestibular phenomena in aviation.
Correct: C)
Explanation: Contracting the abdominal and leg muscles (the anti-G straining manoeuvre or L-1 technique) increases intra-abdominal pressure and impedes blood from pooling in the lower body, maintaining blood flow to the brain and delaying the onset of grey-out and G-LOC. Forced, cyclical breathing maintains thoracic pressure. Option A (sitting upright) has minimal effect. Option B (relaxing and leaning forward) would accelerate blood pooling in the lower extremities. Option D (tightening harness straps) secures the pilot but does not counteract the haemodynamic effects of g-forces.
Correct: C)
Explanation: Impairment of judgment and concentration is the most dangerous effect of hypoxia because the pilot loses the very cognitive abilities needed to recognise the problem and take corrective action — a phenomenon known as "insidious hypoxia." Option A (tingling) and Option D (nausea) are unpleasant but do not directly prevent the pilot from deciding to descend. Option B (cyanosis) is a visible physical sign but does not impair decision-making in itself. The critical danger is that a hypoxic pilot often feels fine while their mental performance deteriorates severely.
Correct: B)
Explanation: Alcohol is eliminated from the blood by the liver at a nearly constant rate of approximately 0.1 per mille per hour, determined solely by time and the liver's enzyme capacity. Option A (breathing pure oxygen) does not accelerate hepatic alcohol metabolism. Option C is incorrect because the elimination rate is constant regardless of whether the alcohol came from beer, wine, or spirits — what differs is how much total alcohol was consumed. Option D (drinking coffee) may increase alertness temporarily but has no effect on the metabolic breakdown of alcohol.
Correct: B)
Explanation: Proprioception — the sense of body position derived from receptors in muscles, joints, and tendons — can provide misleading information about the aircraft's attitude when visual references are absent. Without visual confirmation, the proprioceptive system cannot reliably distinguish between gravitational forces and centripetal forces in a turn. Option A incorrectly claims that proprioception and the vestibular system together provide accurate orientation without vision. Option C overstates proprioception's reliability. Option D wrongly suggests that training can overcome this fundamental physiological limitation. Only visual references or flight instruments can reliably prevent spatial disorientation.
Correct: A)
Explanation: High blood pressure (hypertension) does not directly impair visual acuity during normal flight operations, although severe chronic hypertension may eventually damage the retina over time. Option B (carbon monoxide) reduces oxygen delivery to the retina, directly degrading vision, particularly night vision. Option C (oxygen deficiency) similarly starves the highly oxygen-dependent photoreceptors, causing measurable visual impairment even at moderate altitudes. Option D (alcohol) depresses the central nervous system and impairs visual processing, focus, and contrast sensitivity. All three of these factors directly affect a pilot's ability to see clearly.
Correct: D)
Explanation: The human body can compensate for the reduced partial pressure of oxygen up to approximately 10,000-12,000 ft by increasing heart rate, respiratory rate, and cardiac output. Above this altitude, these compensatory mechanisms become insufficient and supplemental oxygen is required to prevent significant performance degradation. Option A (3,000 ft) is far too low — compensation is barely needed at this altitude. Option B (22,000 ft) far exceeds the body's compensatory range. Option C (6,000-7,000 ft) is the altitude where compensatory mechanisms begin to activate, not their upper limit.
Correct: A)
Explanation: Many over-the-counter medications — including antihistamines, cold remedies, pain relievers, and decongestants — can cause drowsiness, dizziness, impaired reaction time, or blurred vision, all of which compromise flight safety. Option B and Option D dangerously dismiss the potential for side effects. Option C is too extreme — not all medications are incompatible with flying, but each must be evaluated individually. The correct approach is to consult an aviation medical examiner (AME) before flying with any medication, whether prescription or over-the-counter.
Correct: D)
Explanation: A forward linear acceleration in horizontal flight pushes the pilot back into the seat, and the otolith organs in the inner ear interpret the combined acceleration vector as a backward tilt — creating the somatogravic illusion of a climb. Without visual references, the pilot may instinctively push the nose down to "correct" the perceived climb, risking a dive into terrain. Option A and Option C (turning impressions) are associated with semicircular canal stimulation, not linear acceleration. Option B (descent impression) would result from deceleration, not acceleration.
Correct: D)
Explanation: Full dark adaptation of the human eye takes approximately 30 minutes as the rod photoreceptors in the retinal periphery gradually increase their sensitivity through biochemical changes in rhodopsin. Option A (1 second) and Option C (10 seconds) describe only the initial pupil dilation, which is a small part of the adaptation process. Option B (10 minutes) represents partial adaptation — at this point, the cones have adapted but the rods have not yet reached maximum sensitivity. Pilots planning night flights should protect their dark adaptation by avoiding bright white light for at least 30 minutes before departure.
Correct: C)
Explanation: Hyperventilation — excessively rapid or deep breathing — is frequently triggered by stress, anxiety, or fear, which causes the pilot to unconsciously breathe faster than metabolically necessary. This excessive ventilation blows off too much CO2, causing hypocapnia (low blood CO2), not an excess. Option A is wrong because hyperventilation is not caused by oxygen deficiency; it can occur at any altitude when the pilot is stressed. Option B incorrectly states that CO2 increases, when in fact it decreases. Option D confuses carbon monoxide (CO) with carbon dioxide (CO2) — hyperventilation involves CO2, not CO.
Correct: B)
Explanation: Keeping the head still during a turn prevents the Coriolis illusion, which occurs when head movement in one plane is combined with the angular rotation of the turn, stimulating multiple semicircular canals simultaneously and producing intense vertigo. Option A (looking out the window) does not address the vestibular cause of the disturbance. Option C (deep breathing and fresh air) helps with motion sickness but not with vestibular vertigo from head movements. Option D (alternating head movements) would dramatically worsen the problem by creating repeated Coriolis stimulation.
Correct: C)
Explanation: The carbon monoxide (CO) in cigarette smoke binds to haemoglobin far more readily than oxygen, forming carboxyhaemoglobin and immediately reducing the blood's capacity to transport oxygen to tissues and organs. Option A (lowered blood pressure) is incorrect — nicotine actually raises blood pressure through vasoconstriction. Option B (dilation of blood vessels) is also wrong; nicotine causes vasoconstriction, not dilation. Option D confuses the issue — smoking does not significantly increase CO2 levels; the problem is CO displacing oxygen on the haemoglobin molecule.
Correct: A)
Explanation: The retina is one of the most metabolically active tissues in the body and is highly sensitive to oxygen deprivation. Even mild hypoxia can reduce visual acuity, diminish contrast sensitivity, and narrow the visual field, with night vision being affected first since rod cells are particularly oxygen-demanding. Option B incorrectly denies any relationship. Option C and Option D each restrict the effect to one time of day, when in reality both day and night vision are impaired — night vision is simply affected earlier and more severely because rods have higher oxygen requirements than cones.
Correct: A)
Explanation: Cyanosis — a bluish discolouration of the lips and fingernails caused by deoxygenated haemoglobin — is a reliable and specific sign of oxygen deficiency that cannot be produced by hyperventilation alone. Option B (visual disturbance), Option C (hot and cold sensations), and Option D (tingling) can all occur in both hypoxia and hyperventilation, making them unreliable for distinguishing between the two conditions. Recognising cyanosis is therefore a critical diagnostic tool: if blue lips or nail beds are observed, the cause is definitively inadequate oxygen supply, and descent to lower altitude is required immediately.
Correct: B)
Explanation: The atmosphere maintains a constant composition of approximately 21% oxygen from sea level through the troposphere and well into the stratosphere. At 34,000 ft, while the total atmospheric pressure is only about one quarter of sea-level pressure, the proportion of oxygen remains 21%. Option A (10%), Option C (5%), and Option D (42%) all incorrectly suggest the percentage changes with altitude. The critical point is that at 34,000 ft the partial pressure of oxygen is dangerously low despite the unchanged percentage, making supplemental oxygen or pressurisation essential for survival.
Correct: A)
Explanation: Without external visual references, maintaining spatial orientation using only cutaneous senses (pressure on the skin) and proprioception (body position sense) is physiologically impossible because these senses cannot distinguish between gravitational forces and the centripetal or inertial forces experienced in flight. Option B and Option C incorrectly suggest that experience or training can overcome this fundamental human limitation. Option D implies that orientation is possible for a short time, but in reality spatial disorientation can begin within seconds of losing visual references. Only flight instruments or restored visual contact can provide reliable attitude information.
Correct: B)
Explanation: Carbon monoxide (CO) poisoning from a defective or leaking exhaust system is the most likely and most dangerous in-flight poisoning in piston-engine aircraft. CO is colourless and odourless, making it undetectable without a dedicated CO detector, and it binds to haemoglobin 200 times more strongly than oxygen, rapidly incapacitating the pilot. Option A (cosmic radiation) is a long-term cumulative risk for frequent high-altitude flyers, not an acute poisoning event. Option C (ozone) affects primarily high-altitude jet aircraft. Option D (leaded fuel vapours) can occur during refuelling but is not a common in-flight hazard.
Correct: C)
Explanation: When approaching a runway that slopes upward in the landing direction, the pilot perceives the runway surface at an unusual angle that creates the visual illusion of being too high on approach. The upsloping surface compresses the visual perspective, making the runway appear closer and the approach steeper than it actually is. Option A and Option D describe the opposite illusion. Option B (too shallow) would occur with a downsloping runway. This visual trap can lead the pilot to unnecessarily steepen the approach, potentially resulting in a dangerously low and short landing.
Correct: B)
Explanation: As altitude increases, ambient pressure decreases and trapped gases in the body expand according to Boyle's law. Intestinal gas produced by gas-forming foods such as beans and lentils expands significantly at altitude, causing abdominal distension, pain, and distraction from flying tasks. Option A incorrectly places the problem during descent, when gas would actually compress. Option C confuses intestinal gas expansion with dissolved nitrogen forming bubbles in the blood (decompression sickness), which is an entirely different mechanism. Option D incorrectly links gas-forming foods to motion sickness, which is a vestibular phenomenon.
Correct: A)
Explanation: Red blood cells (erythrocytes) contain haemoglobin, the iron-containing protein that binds oxygen in the lungs and releases it to tissues throughout the body. Each red blood cell carries approximately 270 million haemoglobin molecules, making erythrocytes the primary oxygen transport system. Option B (blood plasma) carries a small amount of dissolved oxygen but contributes less than 2% of total oxygen transport. Option C (blood platelets) are involved in blood clotting, not gas transport. Option D (white blood cells) are part of the immune system and play no role in oxygen delivery.
