HESI A2 — All Questions

Which organelle is known as the 'powerhouse of the cell'?

• a.Nucleus
• b.Golgi apparatus
• c.Ribosome
• d.Mitochondrion✓

The mitochondrion produces most of the cell's energy in the form of ATP through cellular respiration. This role earns it the nickname powerhouse of the cell.

What is the basic structural and functional unit of all living organisms?

• a.The tissue
• b.The cell✓
• c.The atom
• d.The organ

The cell is the smallest unit that can carry out all life processes. All living organisms are made of one or more cells.

Which blood cells are primarily responsible for carrying oxygen?

• a.Red blood cells✓
• b.Plasma cells
• c.Platelets
• d.White blood cells

Red blood cells contain hemoglobin, a protein that binds oxygen. They transport oxygen from the lungs to the body's tissues.

At 25 degrees C, what is the pH of a neutral solution such as pure water?

• a.7✓
• b.1
• c.0
• d.14

At 25 degrees C the pH scale runs 0 to 14, with 7 neutral, values below 7 acidic, and values above 7 basic. Pure water is neutral at pH 7 at this temperature. Water stays neutral at other temperatures, but the neutral pH value shifts slightly because the ionization of water is temperature dependent.

Which system is responsible for pumping blood throughout the body?

• a.The respiratory system
• b.The digestive system
• c.The skeletal system
• d.The circulatory system✓

The circulatory system, centered on the heart and blood vessels, moves blood throughout the body. It delivers oxygen and nutrients and removes wastes.

What gas do humans breathe in that is essential for cellular respiration?

• a.Oxygen✓
• b.Helium
• c.Nitrogen
• d.Carbon dioxide

Cells use oxygen to break down glucose and release energy during cellular respiration. Humans inhale oxygen and exhale carbon dioxide as a waste product.

Which part of the cell contains the genetic material (DNA)?

• a.The nucleus✓
• b.The cytoplasm
• c.The cell membrane
• d.The vacuole

The nucleus houses the cell's DNA, which carries genetic instructions. It acts as the control center that directs cell activities.

What is the smallest unit of an element that retains its properties?

• a.A molecule
• b.A tissue
• c.A cell
• d.An atom✓

An atom is the smallest particle of an element that still has the properties of that element. Atoms combine to form molecules.

Which type of blood vessel carries blood away from the heart?

• a.Veins
• b.Venules
• c.Arteries✓
• d.Capillaries

Arteries carry blood away from the heart to the body's tissues. Veins, by contrast, return blood to the heart.

What is the largest organ of the human body?

• a.The heart
• b.The skin✓
• c.The liver
• d.The lungs

The skin is the body's largest organ by weight, making up roughly 16 percent of body mass. It protects the body, helps regulate temperature, and provides sensation.

Which nutrient is the body's primary source of quick energy?

• a.Carbohydrates✓
• b.Triglycerides
• c.Electrolytes
• d.Amino acids

Carbohydrates are broken down into glucose, which cells use for quick energy. They are the body's preferred and fastest energy source.

In chemistry, a substance that donates hydrogen ions and has a pH below 7 is called:

• a.An acid✓
• b.A base
• c.A salt
• d.A neutral

An acid releases hydrogen ions in solution and has a pH lower than 7. Bases, in contrast, have a pH above 7.

Which system includes bones, joints, and cartilage that support the body?

• a.The skeletal system✓
• b.The endocrine system
• c.The nervous system
• d.The muscular system

The skeletal system is made up of bones, joints, and cartilage. It provides structure, protects organs, and allows movement together with muscles.

What process do plants use to convert sunlight into chemical energy?

• a.Digestion
• b.Fermentation
• c.Respiration
• d.Photosynthesis✓

Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to make glucose and oxygen. It converts light energy into stored chemical energy.

Which organ filters waste from the blood and produces urine?

• a.The lungs
• b.The stomach
• c.The kidney✓
• d.The pancreas

The kidneys filter waste products and excess water from the blood, forming urine. This helps maintain the body's fluid and chemical balance.

What is the control center of the nervous system?

• a.The brain✓
• b.The heart
• c.The liver
• d.The lungs

The brain, along with the spinal cord, forms the central nervous system. The brain processes information and directs the body's responses.

Which of the following is a chemical change rather than a physical change?

• a.Ice melting
• b.Chopping wood
• c.Water boiling
• d.Iron rusting✓

A chemical change produces a new substance with different properties. Iron rusting forms iron oxide, whereas melting, boiling, and chopping only change form.

Which macromolecule is made of amino acids and builds body tissues?

• a.Nucleic acid
• b.Carbohydrate
• c.Protein✓
• d.Lipid

Proteins are built from chains of amino acids. They form the structural basis of muscles, enzymes, and many other body tissues.

How many chambers does the human heart have?

• a.Four✓
• b.Two
• c.Three
• d.Five

The human heart has four chambers: two upper atria and two lower ventricles. This structure keeps oxygen-rich and oxygen-poor blood separated.

Which particle in an atom carries a negative electric charge?

• a.Nucleus
• b.Neutron
• c.Electron✓
• d.Proton

Electrons carry a negative charge and occupy orbitals, which are regions of space surrounding the nucleus where an electron is most likely to be found. Protons are positive and neutrons have no charge.

Which chamber of the heart pumps oxygen-rich blood out into the aorta?

• a.Right ventricle
• b.Left atrium
• c.Left ventricle✓
• d.Right atrium

The left ventricle has the thickest wall because it must drive blood through the entire systemic circuit by way of the aorta. The right ventricle pumps only as far as the lungs through the pulmonary trunk, and both atria are receiving chambers that move blood a few centimetres into the ventricle below them.

Blood moving from the right atrium into the right ventricle passes through which valve?

• a.The tricuspid valve✓
• b.The mitral (bicuspid) valve
• c.The pulmonary semilunar valve
• d.The aortic semilunar valve

The right atrioventricular valve has three cusps, which is what tricuspid means. The mitral valve sits on the left side between left atrium and left ventricle. The two semilunar valves guard the exits of the ventricles, not the openings between atrium and ventricle.

Which valve keeps blood from flowing backward from the aorta into the left ventricle?

• a.The pulmonary semilunar valve
• b.The mitral valve
• c.The aortic valve✓
• d.The tricuspid valve

The aortic semilunar valve snaps shut as the left ventricle relaxes, so blood already ejected cannot fall back in. The pulmonary valve does the same job at the exit of the right ventricle. The mitral and tricuspid valves lie between the atria and ventricles and have nothing to do with the aorta.

Which vessel carries oxygen-poor blood away from the heart toward the lungs?

• a.The pulmonary artery✓
• b.The pulmonary vein
• c.The aorta
• d.The superior vena cava

The pulmonary arteries are the one pair of arteries that carry deoxygenated blood, because arteries are defined by direction of flow rather than oxygen content. The pulmonary veins bring oxygenated blood back from the lungs, the aorta leaves the left ventricle, and the venae cavae return blood to the right atrium.

The pulmonary veins empty freshly oxygenated blood into which chamber?

• a.The right atrium
• b.The left ventricle
• c.The right ventricle
• d.The left atrium✓

Blood returning from the lungs enters the left atrium, drops through the mitral valve into the left ventricle, and is then ejected into the aorta. The right atrium receives deoxygenated blood from the venae cavae, and neither ventricle receives blood directly from a vein.

Which structure normally sets the rhythm of the heartbeat?

• a.The atrioventricular (AV) node
• b.The sinoatrial (SA) node✓
• c.The bundle of His
• d.The Purkinje fibers

The SA node in the wall of the right atrium depolarises fastest, so it acts as the pacemaker. The AV node, bundle of His and Purkinje fibers all conduct the impulse onward and can take over at a slower intrinsic rate if the SA node fails, but none of them normally sets the pace.

After the electrical impulse reaches the AV node, where does it travel next?

• a.Back up into the sinoatrial node to repeat
• b.Directly into the Purkinje fibers of the atrial walls
• c.Outward through the coronary arteries to the apex
• d.Into the bundle of His and its branches✓

The normal path is SA node, AV node, bundle of His, bundle branches, then Purkinje fibers in the ventricular walls. The impulse does not travel backward into the SA node, the Purkinje network lies in the ventricles rather than the atria, and coronary arteries carry blood, not electrical signals.

Which layer of the heart wall is the thick muscle that actually contracts?

• a.The endocardium
• b.The epicardium
• c.The myocardium✓
• d.The fibrous pericardium

Myo means muscle, so the myocardium is the contractile middle layer. The endocardium is the smooth inner lining in contact with blood, the epicardium is the thin outer surface layer, and the fibrous pericardium is the tough sac that surrounds the whole organ.

Which vessel returns oxygen-poor blood from the legs and abdomen to the heart?

• a.The superior vena cava
• b.The descending abdominal aorta
• c.The hepatic portal vein
• d.The inferior vena cava✓

The inferior vena cava drains everything below the diaphragm into the right atrium. The superior vena cava drains the head, neck and arms, the abdominal aorta carries blood away from the heart rather than toward it, and the hepatic portal vein runs from the intestines to the liver.

Where in the circulatory system does exchange of oxygen and nutrients with the tissues take place?

• a.In the arterioles
• b.In the large elastic arteries
• c.In the capillaries✓
• d.In the venules

Capillary walls are a single cell thick, which is what allows gases, nutrients and wastes to diffuse across. Arterioles and venules are resistance and collecting vessels with several layers in the wall, and large arteries are built for pressure, not for exchange.

In a blood pressure reading of 118/76, what does the 76 measure?

• a.Arterial pressure at the peak of ventricular contraction
• b.The number of heartbeats counted in one full minute
• c.The volume of blood ejected with each single beat
• d.Arterial pressure while the ventricles relax✓

The lower number is the diastolic pressure, the pressure remaining in the arteries while the ventricles fill. The upper number, 118, is the systolic peak during contraction. Heart rate is counted separately in beats per minute, and the blood ejected per beat is the stroke volume.

Which formed element of the blood is essential for clotting?

• a.Red blood cells
• b.White blood cells
• c.Lymphocytes
• d.Platelets✓

Platelets, also called thrombocytes, stick to a damaged vessel wall, plug the gap and release the chemicals that start the clotting cascade. Red cells carry oxygen, white cells defend against infection, and lymphocytes are simply one variety of white cell.

Which part of the blood is the straw-coloured liquid that carries cells, nutrients and hormones?

• a.Serum
• b.Plasma✓
• c.Lymph
• d.Interstitial fluid

Plasma is the liquid portion of circulating blood and makes up a little over half its volume. Serum is what is left after a sample clots, so it lacks the clotting factors plasma still contains. Lymph travels in lymphatic vessels and interstitial fluid sits between cells, neither of them inside blood vessels.

Hemoglobin cannot bind oxygen without which mineral at the centre of each heme group?

• a.Calcium
• b.Potassium
• c.Iron✓
• d.Magnesium

Each heme group holds one iron ion, and that iron is the site where oxygen attaches, which is why iron deficiency causes anemia. Calcium is needed for clotting and muscle contraction, potassium for nerve and cardiac conduction, and magnesium sits at the centre of chlorophyll in plants, not hemoglobin.

Type O negative red cells are called the universal donor type because they:

• a.carry neither the A, the B, nor the Rh antigen✓
• b.carry both the A and the B antigen on their surface
• c.contain no anti-A or anti-B antibodies in the cell
• d.are smaller and pass more easily through capillaries

With no A, B or Rh antigen on the membrane, the recipient's antibodies find nothing to attack. Carrying both A and B antigens describes type AB, the universal recipient. Antibodies circulate in plasma rather than inside red cells, and cell size has nothing to do with compatibility.

Which vessels have the thickest and most elastic walls to withstand the surge of each heartbeat?

• a.Arteries✓
• b.Veins
• c.Capillaries
• d.Venules

Arteries carry blood under the highest pressure, so their walls contain heavy layers of smooth muscle and elastic tissue. Veins carry low-pressure blood and rely on one-way valves instead, while capillaries and venules have very thin walls suited to exchange and collection.

Gas exchange between inhaled air and the blood takes place in which structures?

• a.The alveoli✓
• b.The bronchioles
• c.The trachea
• d.The pleural space

Alveoli are thin-walled air sacs wrapped in capillaries, so oxygen and carbon dioxide diffuse across in both directions. Bronchioles and the trachea are conducting passages that only move air, and the pleural space is a fluid-filled gap between the membranes covering the lung.

Which muscle does most of the work of a quiet inhalation?

• a.The internal intercostals
• b.The diaphragm✓
• c.The rectus abdominis
• d.The sternocleidomastoid

The diaphragm contracts and flattens, enlarging the chest cavity so air is drawn in. The internal intercostals assist with forced exhalation, the rectus abdominis pushes the diaphragm upward during forced exhalation, and the sternocleidomastoid is only an accessory muscle used in laboured breathing.

What happens inside the thoracic cavity during inhalation?

• a.Its volume decreases while the pressure inside rises sharply
• b.Its volume increases and the pressure inside falls✓
• c.Volume and pressure both increase at exactly the same rate
• d.Volume stays fixed while the lungs pull oxygen across actively

As the diaphragm and external intercostals contract, the cavity enlarges, so the pressure within it drops below atmospheric and air flows in down the gradient. Falling volume with rising pressure describes exhalation, and air moves passively down a pressure gradient rather than being actively pulled in.

What keeps food and liquid out of the airway during swallowing?

• a.The epiglottis covers the laryngeal opening✓
• b.The uvula swings down and seals the trachea
• c.The vocal cords open widely to let the food pass
• d.The diaphragm relaxes and pinches the airway shut

The epiglottis is a flap of cartilage that folds back over the entrance to the larynx each time a person swallows. The uvula helps close off the nasopharynx, not the trachea, opening the vocal cords would let food in rather than keep it out, and the diaphragm has no role in swallowing.

Which tube carries air from the larynx down to the two main bronchi?

• a.The esophagus
• b.The trachea✓
• c.The pharynx
• d.The bronchioles

The trachea is the cartilage-ringed windpipe that branches into the right and left primary bronchi. The esophagus carries food to the stomach, the pharynx is the shared throat passage above the larynx, and bronchioles are the small branches deep inside the lung.

Most carbon dioxide travels in the blood in which form?

• a.Bound to the iron of hemoglobin, exactly as oxygen is
• b.As visible bubbles of free gas within the plasma
• c.As bicarbonate ions dissolved in plasma✓
• d.Attached to the outer surface of circulating platelets

Roughly seventy percent of carbon dioxide is converted to bicarbonate in the red cells and carried in the plasma. A smaller share binds to the globin protein rather than the iron of hemoglobin, free gas bubbles in blood would be a dangerous embolism, and platelets carry no gases at all.

Which part of the brain sets the basic rhythm of breathing?

• a.The cerebellum
• b.The medulla oblongata✓
• c.The occipital lobe
• d.The anterior pituitary

Respiratory centres in the medulla of the brainstem generate the automatic breathing rhythm and respond to rising carbon dioxide. The cerebellum coordinates movement and balance, the occipital lobe processes vision, and the pituitary is an endocrine gland rather than a control centre for breathing.

What is the function of the mucus and cilia lining the airways?

• a.They exchange oxygen and carbon dioxide with the capillaries
• b.They produce the surfactant that keeps the alveoli open
• c.They add water vapour so that the lungs can absorb oxygen
• d.They trap particles and sweep them toward the throat✓

Sticky mucus captures dust and microbes and the beating cilia move the sheet upward to be swallowed or coughed out. Gas exchange happens in the alveoli, surfactant is made by type II alveolar cells, and although the airway does humidify air, that is not what the cilia are for.

Which pleural layer lies directly against the surface of the lung?

• a.The parietal pleura
• b.The visceral pleura✓
• c.The pericardium
• d.The peritoneum

Visceral refers to the organ itself, so the visceral pleura clings to the lung surface. The parietal pleura lines the chest wall, the pericardium surrounds the heart, and the peritoneum lines the abdominal cavity.

What does the term tidal volume describe?

• a.The largest volume that can be forced out after a maximal inhalation
• b.The air left in the lungs after the most forceful exhalation possible
• c.The air moved in or out during one normal breath✓
• d.The total volume the lungs can hold when completely filled with air

Tidal volume is the ordinary quiet breath, about 500 mL in an adult. The maximum that can be blown out after a full breath in is vital capacity, the air that always remains behind is residual volume, and the sum of everything is total lung capacity.

In which organ does the chemical digestion of protein begin?

• a.The mouth
• b.The duodenum
• c.The large intestine
• d.The stomach✓

Gastric juice supplies hydrochloric acid and pepsin, and pepsin is the first enzyme to break protein into shorter chains. The mouth begins starch digestion instead, the duodenum continues protein digestion but does not start it, and the large intestine performs no enzymatic digestion of protein at all.

Which enzyme in gastric juice begins breaking proteins into peptides?

• a.Amylase
• b.Pepsin✓
• c.Lipase
• d.Trypsin

Pepsinogen is secreted by chief cells and converted to active pepsin by the acid of the stomach. Amylase acts on starch, lipase on fats, and trypsin is a protein-splitting enzyme but it comes from the pancreas and works in the small intestine.

Where does most absorption of digested nutrients into the bloodstream occur?

• a.In the stomach
• b.In the large intestine
• c.In the small intestine✓
• d.In the esophagus

The small intestine is lined with villi and microvilli that give it an enormous absorptive surface. The stomach absorbs only a few substances such as alcohol and some drugs, the large intestine mainly reclaims water and electrolytes, and the esophagus is purely a passageway.

Which organ stores and concentrates the bile made by the liver?

• a.The pancreas
• b.The gallbladder✓
• c.The spleen
• d.The appendix

Bile is produced continuously by the liver and held in the gallbladder until fat entering the duodenum triggers its release. The pancreas makes enzymes and bicarbonate, the spleen filters blood and recycles old red cells, and the appendix has no digestive storage role.