Free TEAS Science practice test

Correct answer: C

Arteries are named by direction: they carry blood away from the heart, and veins carry it toward the heart. The pulmonary arteries leave the right ventricle (by way of the pulmonary trunk) and carry oxygen-poor blood to the lungs, making them the exception to the idea that arteries carry oxygen-rich blood. The pulmonary veins are the matching exception: they carry oxygen-rich blood back to the left atrium.

• A The pulmonary veins carry oxygen-rich blood toward the heart, so this reverses both the direction and the oxygen level.
• B The venae cavae do carry oxygen-poor blood, but they bring it toward the heart (into the right atrium), not away from it.
• C Correct: the pulmonary arteries carry oxygen-poor blood from the right ventricle away from the heart to the lungs.
• D The coronary arteries do carry blood away from the heart (they branch off the aorta), but that blood is oxygen-rich and supplies the heart muscle.

Learn this topic: How blood flows through the heart 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 20.1 Structure and Function of Blood Vessels · OpenStax Anatomy & Physiology 2e, 19.1 Heart Anatomy · Report a problem with this question

Correct answer: Sinoatrial (SA) node → Atrioventricular (AV) node → Atrioventricular bundle (bundle of His) → Bundle branches → Purkinje fibers

The SA node in the right atrial wall is the pacemaker and starts each beat. The signal reaches the AV node, which delays it so the atria can finish emptying into the ventricles, then travels down the AV bundle (bundle of His) in the interventricular septum, splits into the right and left bundle branches, and finally spreads through the ventricles by way of the Purkinje fibers. Think of it as top to bottom: atria first, then down the septum, then out into the ventricle walls.

• Bundle branches Fourth: the bundle branches split off the bundle of His and carry the signal toward each ventricle; students who put them before the bundle of His reverse the trunk and its branches.
• Atrioventricular (AV) node Second: the AV node receives the signal from the atria and delays it; placing it first confuses it with the SA node pacemaker.
• Purkinje fibers Fifth: the Purkinje fibers are the last link, spreading the signal through the ventricle muscle so the ventricles contract.
• Sinoatrial (SA) node First: the SA node has the fastest built-in firing rate and acts as the heart's pacemaker, so every normal beat starts here.
• Atrioventricular bundle (bundle of His) Third: the bundle of His carries the signal from the AV node down the interventricular septum before it divides into the bundle branches.

Learn this topic: How blood flows through the heart 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 19.2 Cardiac Muscle and Electrical Activity · Report a problem with this question

Correct answer: B

The mitral (bicuspid) valve is the atrioventricular valve between the left atrium and the left ventricle. When the left ventricle contracts, its pressure rises above the atrial pressure, and this valve normally snaps shut (helped by the chordae tendineae and papillary muscles) so blood can leave only through the aortic valve. If it does not seal, some blood is pushed backward into the left atrium. To solve any "which valve failed" question, locate the valve first, then ask which chamber is squeezing when it should be closed.

• A Backflow from the aorta into the left ventricle happens when the aortic semilunar valve fails, and it occurs while the ventricle is relaxing, not contracting.
• B Correct: the mitral valve separates the left atrium from the left ventricle, so a leak during ventricular contraction sends blood back into the left atrium.
• C Backflow from the right ventricle into the right atrium describes a leaking tricuspid valve, which mixes up the right and left atrioventricular valves.
• D The two ventricles are separated by the interventricular septum, not by a valve, so a mitral valve that fails to close does not open a path between them.

Learn this topic: How blood flows through the heart 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 19.1 Heart Anatomy · OpenStax Anatomy & Physiology 2e, 19.3 Cardiac Cycle · Report a problem with this question

Correct answer: D

The pancreatic islets contain two main hormone-secreting cell types with opposite jobs. Beta cells release insulin when blood glucose rises, and insulin lowers blood glucose by helping cells take it up and by having the liver store it as glycogen. Alpha cells release glucagon when blood glucose falls, and glucagon raises blood glucose. Glycogen is a stored form of glucose, not a hormone.

• A Insulin does lower blood glucose, but it comes from beta cells; alpha cells secrete glucagon.
• B Glucagon does raise blood glucose, but it comes from alpha cells; beta cells secrete insulin.
• C This confuses glycogen (stored glucose in the liver) with glucagon (the hormone alpha cells secrete).
• D Correct: beta cells secrete insulin in response to rising blood glucose, and insulin lowers it.

Learn this topic: How hormones and negative feedback keep blood glucose steady 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 17.9 The Endocrine Pancreas · Report a problem with this question

Correct answer: Blood glucose rises as glucose is absorbed from the digestive tract → Beta cells respond to the high blood glucose by releasing more insulin → Skeletal muscle and fat cells take up glucose, and the liver stores glucose as glycogen → Blood glucose falls back toward its normal range → Insulin secretion slows down

The stimulus comes first: absorbed glucose raises blood glucose. Beta cells respond by releasing insulin, and insulin moves glucose into skeletal muscle and fat cells and has the liver store it as glycogen. As blood glucose falls back toward normal, the stimulus for insulin release fades, so insulin secretion slows. That last step is what makes the loop negative feedback: the response removes its own trigger.

• Skeletal muscle and fat cells take up glucose, and the liver stores glucose as glycogen Third: insulin causes muscle and fat cells to take up glucose and the liver to store it as glycogen.
• Insulin secretion slows down Last: once glucose has fallen, the signal for insulin release is gone, so secretion slows; placing this earlier skips the feedback step.
• Blood glucose rises as glucose is absorbed from the digestive tract First: the rise in blood glucose after absorption is the stimulus that starts the loop.
• Blood glucose falls back toward its normal range Fourth: glucose leaving the blood brings blood glucose back down toward normal.
• Beta cells respond to the high blood glucose by releasing more insulin Second: beta cells respond to the high blood glucose by increasing insulin release.

Learn this topic: How hormones and negative feedback keep blood glucose steady 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 17.9 The Endocrine Pancreas · OpenStax Anatomy & Physiology 2e, 17.2 Hormones · Report a problem with this question

Correct answer: B

Beta cells secrete insulin, and insulin is the signal that lets skeletal muscle and fat cells, its main targets, take glucose out of the blood. It also tells the liver to store glucose as glycogen. With no beta cells, the glucose from the meal stays in the blood, so blood glucose remains high (hyperglycemia). A few tissues such as the brain and red blood cells take up glucose without insulin, but they cannot clear the load that muscle and fat normally handle.

• A Glucagon raises blood glucose; it cannot stand in for insulin, so more glucagon would push glucose up, not down.
• B Correct: without insulin, muscle and fat cells take up little glucose and the liver stores little as glycogen, so blood glucose stays high.
• C The brain and red blood cells do take up glucose without insulin, but they cannot clear the extra glucose that muscle and fat cells normally absorb.
• D Storing extra glucose as liver glycogen is one of insulin's own effects, so without insulin this storage does not increase.

Learn this topic: How hormones and negative feedback keep blood glucose steady 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 17.9 The Endocrine Pancreas · NIDDK, Type 1 Diabetes · Report a problem with this question

Correct answer: D

The respiratory tract has a conducting zone, which moves, cleans, warms and humidifies air, and a respiratory zone, where gas exchange happens. The respiratory zone begins where a terminal bronchiole joins a respiratory bronchiole and continues into alveolar ducts and alveoli. Everything above that point, including the terminal bronchioles, only conducts air.

• A The primary bronchi carry air from the trachea into each lung; they belong to the conducting zone and do not exchange gases.
• B Terminal bronchioles are the last airways of the conducting zone; the respiratory zone starts just beyond them, where they join respiratory bronchioles, so this is the most tempting wrong answer.
• C The trachea is a cartilage-supported tube in the conducting zone that only carries air toward the bronchi.
• D Correct: alveolar ducts lie between the respiratory bronchioles and the alveoli and are part of the respiratory zone, where gas exchange occurs.

Learn this topic: How air reaches the alveoli and how oxygen and CO2 trade places 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 22.1 Organs and Structures of the Respiratory System · Report a problem with this question

Correct answer: B, D, E

Inhalation follows Boyle's law: when the volume of a container increases, the pressure of the gas inside it decreases. The diaphragm contracts and moves down while the external intercostals lift the ribs, so the thoracic cavity gets larger and pressure in the alveoli drops below atmospheric pressure, and air flows in. Quiet exhalation is the passive opposite: the muscles relax and the lungs' elastic recoil pushes air out.

• A Incorrect: the internal intercostals compress the rib cage during forced exhalation; during inhalation it is the external intercostals that lift the ribs up and out.
• B Correct: contraction of the diaphragm and external intercostals enlarges the thoracic cavity, which is what lowers the pressure inside the lungs.
• C Incorrect: elastic recoil of the lungs is what pushes air out during quiet exhalation; it does not pull air in.
• D Correct: the dome-shaped diaphragm contracts and moves inferiorly toward the abdominal cavity, the main way the chest cavity enlarges.
• E Correct: the larger volume lowers intra-alveolar pressure below atmospheric pressure, creating the gradient that drives air into the lungs.

Learn this topic: How air reaches the alveoli and how oxygen and CO2 trade places 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 22.3 The Process of Breathing · OpenStax Anatomy & Physiology 2e, 11.4 Axial Muscles of the Abdominal Wall and Thorax · Report a problem with this question

Correct answer: B

The main stimulus that drives breathing is the level of carbon dioxide in the blood, not oxygen. Extra carbon dioxide produces more hydrogen ions, which lowers pH; chemoreceptors detect this and signal the respiratory centers in the medulla oblongata and pons. Breathing becomes faster and deeper so more carbon dioxide is exhaled. Low oxygen becomes a strong stimulus only when it drops very low.

• A Incorrect on both points: added carbon dioxide lowers pH (more hydrogen ions), and the response is faster, deeper breathing, not slower breathing.
• B Correct: more carbon dioxide means more hydrogen ions and a lower pH, which chemoreceptors detect, so the brainstem increases the rate and depth of breathing.
• C Incorrect: carbon dioxide, not oxygen, is the main everyday driver of breathing; oxygen becomes a strong stimulus only when it falls very low.
• D Incorrect: the breathing response is right, but the reason is reversed; carbon dioxide forms carbonic acid and hydrogen ions, which lower pH rather than raise it.

Learn this topic: How air reaches the alveoli and how oxygen and CO2 trade places 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 22.3 The Process of Breathing · Report a problem with this question

Correct answer: A water molecule → A single smooth muscle cell → A layer of smooth muscle tissue → The urinary bladder → The urinary system (kidneys, ureters, bladder, and urethra)

Body structure builds through six levels: chemical, cellular, tissue, organ, organ system, and organism. A water molecule is at the chemical level, a smooth muscle cell is at the cellular level, a layer of similar muscle cells working together is a tissue, the bladder is an organ made of two or more tissue types, and the kidneys, ureters, bladder, and urethra together form the urinary system. Each level is built from the one before it.

• The urinary system (kidneys, ureters, bladder, and urethra) Fifth: the urinary system is an organ system, a group of organs working together, which is the most complex level listed.
• A single smooth muscle cell Second: a cell is the smallest independently functioning unit of life, one step above the chemical level.
• The urinary bladder Fourth: the bladder is an organ because it is a distinct structure built from two or more tissue types; placing it above the urinary system reverses organ and organ system.
• A water molecule First: a molecule belongs to the chemical level, the simplest level of organization.
• A layer of smooth muscle tissue Third: a tissue is a group of similar cells working together; students who put it before the cell reverse the cell and tissue levels.

Learn this topic: How to describe any location on the human body 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 1.2 Structural Organization of the Human Body · Report a problem with this question

Correct answer: B

Anatomical terms are always applied as if the body were in anatomical position, standing with the palms facing forward, no matter how the body is actually lying. In that position the palm side of the wrist faces the front, so it is anterior even when the person is prone with the palm down. The wrist is the carpal region; the forearm is antebrachial and the upper arm is brachial.

• A This describes the wrist by its current orientation (facing the table) instead of by anatomical position, where the palm side faces forward.
• B Correct: in anatomical position the palm side of the wrist faces forward, so the scar is in the anterior carpal region.
• C Antebrachial refers to the forearm, between the elbow and the wrist, not the wrist itself.
• D Brachial refers to the upper arm, between the shoulder and the elbow, not the wrist.

Learn this topic: How to describe any location on the human body 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 1.6 Anatomical Terminology · Report a problem with this question

Correct answer: D

The pleura is the serous membrane of the lungs: its visceral layer covers each lung and its parietal layer lines the wall of the thoracic cavity. The thin serous fluid between the two layers lets the lungs slide smoothly as they inflate, so without it friction between the lungs and the body wall would increase. To solve these items, match the membrane to its organ (pleura = lungs, pericardium = heart, peritoneum = abdominopelvic organs) and remember that serous fluid's job is reducing friction.

• A Friction around the heart is prevented by the pericardium and its own serous fluid, not by the pleura.
• B The brain and spinal cord are cushioned by cerebrospinal fluid in the dorsal cavity, which is not a serous fluid.
• C The diaphragm, a muscular sheet, separates the thoracic and abdominopelvic cavities; serous fluid does not form that boundary.
• D Correct: pleural fluid reduces friction between the lungs and the chest wall, so losing it would make the lungs rub against the wall as they move.

Learn this topic: How to describe any location on the human body 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 1.6 Anatomical Terminology · Report a problem with this question

Correct answer: C

The appendicular skeleton contains the bones of the upper and lower limbs plus the bones that attach each limb to the axial skeleton. The scapula, together with the clavicle, forms the pectoral (shoulder) girdle that attaches the upper limb to the trunk, so it is appendicular. The axial skeleton is the central axis: skull and associated bones such as the hyoid, the vertebral column including the sacrum and coccyx, and the thoracic cage of ribs and sternum.

• A The sacrum is part of the vertebral column and therefore axial, even though it sits in the pelvis.
• B The sternum is part of the thoracic cage, which belongs to the axial skeleton.
• C Correct: the scapula is part of the pectoral girdle, which attaches the upper limb to the axial skeleton, so it is appendicular.
• D The hyoid bone is one of the bones associated with the head and is counted in the axial skeleton.

Learn this topic: How bones are built, remodeled, and joined 7-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 7.1 Divisions of the Skeletal System · OpenStax Anatomy & Physiology 2e, 8.1 The Pectoral Girdle · Report a problem with this question

Correct answer: B, C, E

Spongy bone is a lattice of thin struts called trabeculae, each forming along lines of stress so the bone stays strong but light. It fills the epiphyses of long bones, and red marrow, where blood cells are made, fills its spaces. Osteons with concentric lamellae and a central canal are the structural units of compact bone, which forms the dense walls of the diaphysis.

• A Osteons (Haversian systems) are the units of compact bone; spongy bone has trabeculae instead of concentric rings.
• B Correct: each trabecula forms along lines of stress, giving spongy bone strength without much weight.
• C Correct: the epiphyses at the ends of a long bone are filled with spongy bone.
• D The walls of the diaphysis are compact bone; this choice swaps the locations of compact and spongy bone.
• E Correct: red marrow fills the spaces of spongy bone, and blood cell production takes place there.

Learn this topic: How bones are built, remodeled, and joined 7-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 6.3 Bone Structure · Report a problem with this question

Correct answer: C

PTH is the hormone that raises blood calcium. It stimulates osteoclasts to resorb bone and release calcium, increases calcium reabsorption by the kidneys, and stimulates vitamin D synthesis so the small intestine absorbs more calcium from food. Without PTH all three effects weaken, so blood calcium falls. Calcitonin, from the thyroid gland, works in the opposite direction and lowers blood calcium when it is too high.

• A This reverses PTH's role: PTH moves calcium out of bone into the blood, so losing it lowers, not raises, blood calcium.
• B Osteoblasts build bone; breaking down bone matrix is the job of osteoclasts, so this mixes up the two cell types.
• C Correct: without PTH, osteoclasts release less calcium from bone and the kidneys return less calcium to the blood, so blood calcium drops.
• D Calcitonin comes from the thyroid in response to high blood calcium and lowers calcium; losing PTH does not shut off calcitonin or raise calcium.

Learn this topic: How bones are built, remodeled, and joined 7-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 6.7 Calcium Homeostasis: Interactions of the Skeletal System and Other Organ Systems · OpenStax Anatomy & Physiology 2e, 6.3 Bone Structure · Report a problem with this question

Correct answer: A

The stratum basale is the deepest layer of the epidermis, a single layer of stem cells that constantly divide to produce all of the keratinocytes. As new cells form, older ones are pushed toward the surface. Melanocytes, which make the pigment melanin, and touch-sensing Merkel cells are scattered among the basal cells in this layer.

• A Correct: the stratum basale holds the dividing basal stem cells and the melanocytes.
• B The stratum corneum is the outermost layer of dead, keratin-filled cells that are shed; its cells no longer divide.
• C In the stratum granulosum, keratinocytes flatten, fill with keratin and keratohyalin, and die; no new cells are produced there.
• D The stratum spinosum holds keratinocytes joined by desmosomes and immune Langerhans cells, but the dividing stem cells and melanocytes are one layer deeper.

Learn this topic: How your skin is layered and what each layer does 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 5.1 Layers of the Skin · Report a problem with this question

Correct answer: Stratum basale → Stratum spinosum → Stratum granulosum → Stratum lucidum → Stratum corneum

Keratinocytes are produced by the dividing stem cells of the stratum basale and are pushed outward as new cells form below them. They move through the stratum spinosum, where keratin production begins, then the stratum granulosum, where the cells flatten and die. Thick skin of the palms and soles has a fifth layer, the clear stratum lucidum, before the dead cells reach the stratum corneum at the surface and are shed.

• Stratum lucidum Fourth: the stratum lucidum lies between the stratum granulosum and the stratum corneum and is present only in thick skin such as the palms and soles.
• Stratum basale First: the stratum basale is the deepest layer, where the stem cells divide to make new keratinocytes.
• Stratum corneum Fifth: the stratum corneum is the most superficial layer, made of dead cells that are shed; putting it first reverses the direction of movement.
• Stratum spinosum Second: the stratum spinosum lies just above the stratum basale, where keratinocytes are joined by desmosomes and start making keratin.
• Stratum granulosum Third: in the stratum granulosum the cells flatten, fill with keratin and keratohyalin, and die before reaching the lucidum.

Learn this topic: How your skin is layered and what each layer does 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 5.1 Layers of the Skin · Report a problem with this question

Correct answer: D

Damage through the entire epidermis and dermis, without reaching muscle or bone, is a third-degree burn. Because the nerve endings in the dermis are destroyed, these burns are usually less painful than second-degree burns, which damage only part of the dermis and cause painful blisters. The stratum basale, whose stem cells normally rebuild the epidermis, is also destroyed, so the area cannot be repaired from local tissue.

• A Healing in a few days describes a first-degree burn, which affects only the epidermis.
• B The stratum basale is part of the epidermis, so in this burn it is destroyed and cannot regrow the layer; full-thickness burns cannot be repaired by the body.
• C Painful blistering with partial dermal damage describes a second-degree burn, but this burn destroyed the whole dermis.
• D Correct: a burn through the full epidermis and dermis is third-degree, and destroyed nerve endings usually make it less painful than a shallower burn.

Learn this topic: How your skin is layered and what each layer does 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 5.4 Diseases, Disorders, and Injuries of the Integumentary System · OpenStax Anatomy & Physiology 2e, 5.1 Layers of the Skin · Report a problem with this question

Correct answer: C

Protein digestion begins in the stomach. Chief cells secrete inactive pepsinogen, and hydrochloric acid from parietal cells converts it into pepsin, which splits proteins into smaller peptides. Pancreatic enzymes such as trypsin and chymotrypsin, and finally brush border peptidases, finish the job in the small intestine. A quick rule: starch starts in the mouth, protein in the stomach, and nearly all fat in the small intestine.

• A Salivary amylase does start chemical digestion in the mouth, but it acts on starch (a carbohydrate), not protein.
• B Trypsin does digest protein, but it comes from the pancreas and works in the small intestine, after protein digestion has already started.
• C Correct: pepsin, activated from pepsinogen by stomach acid, is the first enzyme to break down protein, and it acts in the stomach.
• D Pancreatic lipase acts in the small intestine on emulsified fats (triglycerides), not on proteins.

Learn this topic: How food is broken down and absorbed, from mouth to colon 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 23.7 Chemical Digestion and Absorption: A Closer Look · OpenStax Anatomy & Physiology 2e, 23.4 The Stomach · Report a problem with this question

Correct answer: Stomach → Duodenum → Jejunum → Ileum → Cecum

From the esophagus, food enters the stomach, where it is mixed into chyme and released a little at a time through the pyloric sphincter. The chyme then travels the three parts of the small intestine in order: the duodenum (shortest, where bile and pancreatic juice enter), the jejunum, and the ileum (longest). The ileum empties through the ileocecal valve into the cecum, the first part of the large intestine.

• Jejunum Third: the jejunum is the middle section of the small intestine, between the duodenum and the ileum.
• Stomach First: the esophagus delivers food through the lower esophageal sphincter into the stomach.
• Cecum Fifth: the cecum is the first part of the large intestine and receives material from the ileum through the ileocecal valve; placing it earlier confuses the large and small intestines.
• Duodenum Second: the duodenum begins at the pyloric sphincter and is the first and shortest part of the small intestine.
• Ileum Fourth: the ileum is the last and longest part of the small intestine; students who put it before the jejunum reverse the middle two segments.

Learn this topic: How food is broken down and absorbed, from mouth to colon 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 23.5 The Small and Large Intestines · OpenStax Anatomy & Physiology 2e, 23.1 Overview of the Digestive System · Report a problem with this question

Correct answer: C

Circular folds, villi, and microvilli give the small intestine its enormous absorptive surface, so losing villi and microvilli reduces absorption of nutrients. The microvilli also form the brush border, which holds enzymes such as lactase, sucrase, maltase, and peptidases that finish digesting carbohydrates and proteins. Pancreatic juice and bile would still arrive, so earlier steps continue, but the final digestion and absorption steps on the intestinal lining would suffer.

• A Pepsin is secreted as pepsinogen by chief cells of the stomach, so damage to intestinal microvilli would not stop protein digestion in the stomach.
• B Bile is made by the liver and stored by the gallbladder, and the stem says the liver still works, so emulsification would continue.
• C Correct: villi and microvilli provide most of the absorptive surface, and brush border enzymes such as lactase sit on the microvilli, so both absorption and final carbohydrate digestion would fall.
• D The large intestine has no villi and few enzyme-secreting cells; it mainly absorbs water, salts, and vitamins from bacteria, so it cannot take over nutrient absorption.

Learn this topic: How food is broken down and absorbed, from mouth to colon 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 23.5 The Small and Large Intestines · OpenStax Anatomy & Physiology 2e, 23.7 Chemical Digestion and Absorption: A Closer Look · Report a problem with this question

Correct answer: B

Filtration happens in the renal corpuscle: blood pressure in the glomerulus, a tuft of capillaries, pushes water and small solutes into the surrounding glomerular (Bowman's) capsule. Blood cells and large proteins stay behind. Everything after the capsule, from the proximal convoluted tubule to the collecting duct, modifies this filtrate by reabsorption and secretion rather than filtering blood again.

• A The proximal convoluted tubule receives filtrate from Bowman's capsule and is the main site of reabsorption, not filtration.
• B Correct: the glomerulus filters plasma into Bowman's capsule; together they form the renal corpuscle.
• C The loop of Henle reabsorbs water and salt from filtrate that has already formed; it does not filter blood.
• D The collecting duct makes the final adjustments to water content under ADH, at the end of the process rather than the start.

Learn this topic: How the kidneys filter blood and make urine 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 25.3 Gross Anatomy of the Kidney · OpenStax Anatomy & Physiology 2e, 25.4 Microscopic Anatomy of the Kidney · Report a problem with this question

Correct answer: Glomerular (Bowman's) capsule → Proximal convoluted tubule → Loop of Henle → Distal convoluted tubule → Collecting duct

Filtrate forms in the glomerular (Bowman's) capsule and flows into the proximal convoluted tubule, the main site of reabsorption. It then runs down and back up the loop of Henle, through the distal convoluted tubule, and into a collecting duct that is shared by several nephrons. A helpful pattern is proximal (near the capsule) before distal (far from it), with the loop in between.

• Distal convoluted tubule Fourth: the distal convoluted tubule comes after the loop of Henle; putting it before the loop mixes up proximal and distal.
• Glomerular (Bowman's) capsule First: filtrate is captured by Bowman's capsule around the glomerulus.
• Collecting duct Fifth: the collecting duct receives fluid from the distal convoluted tubules of several nephrons and carries it toward the renal pelvis.
• Proximal convoluted tubule Second: the proximal convoluted tubule receives filtrate directly from Bowman's capsule.
• Loop of Henle Third: the loop of Henle dips toward the medulla and returns between the proximal and distal tubules.

Learn this topic: How the kidneys filter blood and make urine 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 25.4 Microscopic Anatomy of the Kidney · OpenStax Anatomy & Physiology 2e, 25.6 Tubular Reabsorption · Report a problem with this question

Correct answer: A

Aldosterone, a hormone of the adrenal cortex, increases sodium reabsorption in the distal convoluted tubule and collecting ducts. Water follows the reabsorbed sodium by osmosis, so blood volume and blood pressure tend to rise, and at the same time more potassium is excreted. When predicting the effect of any kidney hormone, ask which substance it makes the tubule keep and which it makes the tubule lose.

• A Correct: excess aldosterone increases sodium reabsorption, water follows the sodium, and potassium excretion increases.
• B This reverses aldosterone's effect; reduced sodium reabsorption describes too little aldosterone or the action of natriuretic hormones.
• C Inserting aquaporins into collecting duct cells is the action of ADH from the posterior pituitary, not aldosterone.
• D Constricting the glomerular arterioles is an action of angiotensin II, not aldosterone; aldosterone acts on tubule sodium and potassium handling.

Learn this topic: How the kidneys filter blood and make urine 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 25.8 Endocrine Regulation of Kidney Function · OpenStax Anatomy & Physiology 2e, 25.6 Tubular Reabsorption · Report a problem with this question

Correct answer: D

All lymphocytes start in the red bone marrow, but the two types finish maturing in different primary lymphoid organs: B cells in the bone marrow and T cells in the thymus, a gland above the heart. Mature, naive lymphocytes then gather in secondary lymphoid organs such as lymph nodes and the spleen, where they meet antigens and launch responses. Memory hook: B for bone marrow, T for thymus.

• A T cells originate in the red bone marrow, but it is B cells, not T cells, that complete their maturation there.
• B The spleen is a secondary lymphoid organ that filters blood and hosts immune responses; lymphocytes arrive there already mature.
• C Lymph nodes are secondary lymphoid organs where mature lymphocytes meet antigens, not where T cells mature.
• D Correct: immature T cells (thymocytes) leave the bone marrow and mature in the thymus, a primary lymphoid organ.

Learn this topic: How the body defends itself: innate and adaptive immunity 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 21.1 Anatomy of the Lymphatic and Immune Systems · Report a problem with this question

Correct answer: A, C

Active immunity means the person's own immune system mounts a response and forms memory cells. That happens after a natural infection (naturally acquired) or after a vaccine, which contains a killed or weakened pathogen or its parts (artificially acquired). Passive immunity means receiving ready-made antibodies from another source, such as the placenta, breast milk, or an immune globulin injection; it works quickly but fades because no memory cells form.

• A Correct: fighting off an infection makes the person's own B and T cells respond and form memory, which is naturally acquired active immunity.
• B Maternal IgG crossing the placenta is ready-made antibody, so this is naturally acquired passive immunity.
• C Correct: a vaccine stimulates the person's own immune system to make antibodies and memory cells, which is artificially acquired active immunity.
• D IgA in breast milk is transferred ready-made from the parent, so this is naturally acquired passive immunity.
• E An immune globulin injection gives ready-made antibodies for temporary protection, which is artificially acquired passive immunity.

Learn this topic: How the body defends itself: innate and adaptive immunity 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 21.4 The Adaptive Immune Response: B-lymphocytes and Antibodies · Report a problem with this question

Correct answer: B

Helper T cells (CD4) coordinate the adaptive response by releasing cytokines; one group of them drives B cells to become antibody-secreting plasma cells. Antibody responses to most protein antigens depend on this T cell help, so blocking helper T cytokines would sharply reduce them. Barriers such as skin and lysozyme, and inflammation triggered by mast cells, are innate defenses that work without helper T cells.

• A The skin barrier is an innate defense that works continuously and does not depend on helper T cell signals.
• B Correct: B cells need helper T cell cytokines to become plasma cells that make antibodies against most protein antigens.
• C Lysozyme in saliva is an innate chemical barrier that acts on its own, without signals from T cells.
• D Histamine release by mast cells after tissue injury is part of innate inflammation, which is triggered by damaged cells, not by helper T cells.

Learn this topic: How the body defends itself: innate and adaptive immunity 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types · OpenStax Anatomy & Physiology 2e, 21.2 Barrier Defenses and the Innate Immune Response · Report a problem with this question

Correct answer: C

The cerebellum receives a copy of each motor command from the cerebrum and compares it with feedback about how the body is actually moving and balancing. When the two do not match, for example on uneven ground, it sends a corrective signal so the movement stays smooth and coordinated. Pair each region with one job: cerebellum for coordination, medulla and pons for heart and breathing rates, hypothalamus for homeostasis.

• A The hypothalamus regulates homeostasis and controls the autonomic nervous system and the anterior pituitary; it does not correct movement.
• B The medulla (with the pons) regulates heart rate and breathing rate; picking it confuses the brain stem's survival functions with movement coordination.
• C Correct: the cerebellum compares commands from the cerebrum with sensory feedback and sends corrections to keep movement coordinated.
• D The occipital lobe is responsible for primary visual perception, not for comparing motor commands with feedback.

Learn this topic: How the nervous system sends and sorts signals 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 13.2 The Central Nervous System · Report a problem with this question

Correct answer: A, B, D

The sympathetic division drives the fight-or-flight response: it raises heart rate and breathing rate and shifts blood toward skeletal muscle and away from the digestive system, so more oxygen reaches the muscles needed to fight or run. The parasympathetic division (rest-and-digest), which reaches the heart and digestive organs through the vagus nerve, has the opposite effects. When a question describes a threat or stress, think sympathetic; when it describes calm and digestion, think parasympathetic.

• A Correct: sympathetic activity increases heart rate to deliver more blood during a threat.
• B Correct: sympathetic activity increases breathing rate so more oxygen is taken in.
• C Incorrect: during fight-or-flight, blood flow to the digestive system decreases; increased digestive activity is a rest-and-digest (parasympathetic) effect.
• D Correct: sympathetic activity increases blood flow to skeletal muscle so it can work hard.
• E Incorrect: the vagus nerve carries parasympathetic fibers, and slowing the heart is the opposite of the sympathetic response.

Learn this topic: How the nervous system sends and sorts signals 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 15.1 Divisions of the Autonomic Nervous System · Report a problem with this question

Correct answer: B

When an action potential arrives at the axon terminal, voltage-gated calcium channels open and Ca2+ flows in. That calcium is what makes the neurotransmitter vesicles fuse with the membrane and release their contents into the synaptic cleft. If the calcium channels are blocked, the electrical signal still arrives, but it cannot be converted into a chemical signal, so the next cell receives little neurotransmitter. To solve any synapse question, walk the steps in order: action potential arrives, Ca2+ enters, vesicles release neurotransmitter, it binds receptors, then it is cleared.

• A Conduction along the axon depends on voltage-gated sodium and potassium channels, which the toxin leaves working, so the action potential still reaches the terminals.
• B Correct: calcium entry is the trigger for vesicles to release neurotransmitter, so blocking the calcium channels prevents release even though the action potential arrives.
• C A longer-lasting signal would come from blocking the enzyme or reuptake that clears neurotransmitter, not from blocking calcium channels, which reduces release.
• D The toxin does not affect the receptors; this choice confuses a presynaptic problem (release) with a postsynaptic one (binding).

Learn this topic: How the nervous system sends and sorts signals 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 12.5 Communication Between Neurons · OpenStax Anatomy & Physiology 2e, 12.4 The Action Potential · Report a problem with this question

Correct answer: D

The walls of hollow organs such as the stomach, intestines, and bladder contain smooth muscle. Its actin and myosin are not organized into sarcomeres, so it has no striations; each spindle-shaped cell has a single nucleus; and it is not under voluntary control. Sort any muscle question by three features: striations, number of nuclei, and voluntary or involuntary control.

• A This describes skeletal muscle, which moves the skeleton rather than lining hollow organs.
• B This describes cardiac muscle, which is found only in the heart.
• C This mixes features: multinucleated fibers attached to bones by tendons are skeletal muscle, which is striated, not nonstriated.
• D Correct: smooth muscle in the walls of hollow organs is nonstriated, spindle-shaped, single-nucleus, and involuntary.

Learn this topic: How muscles contract, from nerve signal to sliding filaments 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 10.1 Overview of Muscle Tissues · OpenStax Anatomy & Physiology 2e, 10.8 Smooth Muscle · Report a problem with this question

Correct answer: B, C, E

In the sliding filament model, myosin heads pull the thin (actin) filaments toward the center of the sarcomere, so the thin filaments slide past the thick filaments. Because the thin filaments are anchored to the Z-discs, the Z-discs are drawn closer together and the I band narrows. The A band keeps the same width because the thick filaments slide rather than shrink.

• A Incorrect: the A band stays the same width during contraction; choosing it assumes the filaments themselves get shorter.
• B Correct: the thin filaments are anchored to the Z-discs, so pulling them inward brings the Z-discs closer together.
• C Correct: myosin heads pull the thin filaments toward the center of the sarcomere (the M-line).
• D Incorrect: myosin pulls the thin filaments inward toward the center; pushing them outward would lengthen the sarcomere.
• E Correct: as the filaments overlap more, the I band becomes smaller.

Learn this topic: How muscles contract, from nerve signal to sliding filaments 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 10.3 Muscle Fiber Contraction and Relaxation · OpenStax Anatomy & Physiology 2e, 10.2 Skeletal Muscle · Report a problem with this question

Correct answer: B

In the cross-bridge cycle, a new ATP molecule must bind the myosin head before the head can release actin, and splitting that ATP re-cocks the head for the next pull. With no ATP, attached heads cannot let go, so the cross-bridges stay locked and the fiber becomes rigid. This is the same reason muscles stiffen in rigor mortis after death. Remember: calcium turns contraction on, but ATP is what lets myosin let go.

• A This reverses ATP's role: ATP is needed for myosin to detach, not to stay attached, so losing it locks the cross-bridges instead of releasing them.
• B Correct: without ATP, myosin heads cannot detach from actin, so cross-bridges remain in place and the fiber stays rigid.
• C Calcium binding to troponin does not require ATP, and the stem says calcium is plentiful; ATP's job is detaching and re-cocking myosin.
• D Calcium only uncovers the binding sites on actin; each cycle of the myosin heads requires energy from ATP, so normal contraction cannot continue.

Learn this topic: How muscles contract, from nerve signal to sliding filaments 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 10.3 Muscle Fiber Contraction and Relaxation · Report a problem with this question

Correct answer: C

Testosterone is made by Leydig cells, also called interstitial cells because they sit between the seminiferous tubules. GnRH from the hypothalamus makes the anterior pituitary release LH and FSH: LH acts on the Leydig cells to increase testosterone production, while FSH acts on the Sertoli cells inside the tubules to promote sperm production. Pair them as LH with Leydig and FSH with Sertoli.

• A FSH does act on Sertoli cells, but to support sperm production, not to make testosterone.
• B Sertoli cells support developing sperm; LH targets the Leydig cells, so this pairs the hormone with the wrong cell.
• C Correct: Leydig (interstitial) cells make testosterone when LH binds to their receptors.
• D Leydig cells are the right cells, but FSH acts mainly on Sertoli cells; the hormone that drives testosterone output is LH.

Learn this topic: How the male and female reproductive systems make gametes and new life 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 27.1 Anatomy and Physiology of the Testicular Reproductive System · Report a problem with this question

Correct answer: Seminiferous tubules → Epididymis → Ductus (vas) deferens → Ejaculatory duct → Urethra

Sperm are produced in the seminiferous tubules of the testis and then move into the epididymis, where they continue to mature. During ejaculation they travel up the ductus (vas) deferens, which joins the duct of the seminal vesicle to form the ejaculatory duct, and the fluid then enters the urethra, which runs through the prostate and the penis. A quick check: production, maturation, transport, joining with gland fluid, exit.

• Ductus (vas) deferens Third: the ductus deferens carries sperm from the epididymis out of the scrotum toward the pelvis.
• Urethra Fifth: the urethra is the final passage through the prostate and penis and out of the body.
• Seminiferous tubules First: sperm are produced inside the seminiferous tubules of the testis.
• Ejaculatory duct Fourth: the ejaculatory duct forms where the ductus deferens joins the seminal vesicle duct and empties into the urethra within the prostate; placing it earlier confuses it with the ductus deferens.
• Epididymis Second: newly formed sperm move into the epididymis to mature; students who put it after the ductus deferens mix up maturation and transport.

Learn this topic: How the male and female reproductive systems make gametes and new life 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 27.1 Anatomy and Physiology of the Testicular Reproductive System · Report a problem with this question

Correct answer: C

After ovulation, the corpus luteum secretes progesterone, which keeps the stratum functionalis of the endometrium built up and ready for implantation during the secretory phase. When progesterone falls, the stratum functionalis is shed, which is menses. If progesterone drops early, the lining loses its support early and menses starts sooner. For any cycle question, find the hormone first, then ask what it was holding in place.

• A After ovulation the dominant follicle no longer exists; it has become the corpus luteum, so it cannot keep supplying estrogen to thicken the lining.
• B The LH surge is triggered by very high estrogen from a dominant follicle, and no new dominant follicle is ready at this point, so an immediate second ovulation would not occur.
• C Correct: falling progesterone triggers shedding of the stratum functionalis, so an early drop brings menses early.
• D The stratum basalis does not shed during menses; only the stratum functionalis is lost.

Learn this topic: How the male and female reproductive systems make gametes and new life 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 27.2 Anatomy and Physiology of the Ovarian Reproductive System · Report a problem with this question

Correct answer: C

In prophase I of meiosis, each pair of homologous chromosomes (one from each parent) pairs up tightly, and nonsister chromatids swap segments by crossing over; the pairs then separate in meiosis I. Mitosis never pairs homologs, so it produces identical cells, while crossing over helps make every gamete genetically different. Lining up at the middle, chromatids separating, and nuclear envelopes reforming all happen in mitosis too.

• A Sister chromatids separate in mitosis and in meiosis II; in meiosis I they stay joined while the homologous pairs separate.
• B Chromosomes line up on the metaphase plate in mitosis as well as in meiosis, so this is not unique to meiosis I.
• C Correct: pairing of homologous chromosomes and crossing over happen only in prophase I of meiosis.
• D Nuclear envelopes re-form in telophase of mitosis too, so this does not distinguish meiosis I.

Learn this topic: How a cell is built, fed, and copied 6-minute lesson

Source: OpenStax Biology 2e, 11.1 The Process of Meiosis · OpenStax Biology 2e, 10.2 The Cell Cycle · Report a problem with this question

Correct answer: Ribosomes on the rough endoplasmic reticulum build the protein. → A transport vesicle carries the protein from the ER to the Golgi apparatus. → The Golgi apparatus modifies the protein and packages it into a vesicle. → A vesicle fuses with the plasma membrane and releases the protein.

Proteins meant for export are built by ribosomes attached to the rough ER and enter the ER. A transport vesicle buds off and carries them to the Golgi apparatus, which modifies, tags, and packages them. Secretory vesicles then bud from the Golgi and fuse with the plasma membrane, releasing the protein outside the cell. Think of it as factory (rough ER), shipping truck (vesicle), finishing and packing (Golgi), and delivery (vesicle to membrane).

• The Golgi apparatus modifies the protein and packages it into a vesicle. Third: the Golgi can only modify and package the protein after a vesicle has delivered it from the ER.
• Ribosomes on the rough endoplasmic reticulum build the protein. First: the protein is built by ribosomes on the rough ER before anything else can happen to it.
• A vesicle fuses with the plasma membrane and releases the protein. Fourth: release at the plasma membrane is the final step, after the Golgi has packaged the protein.
• A transport vesicle carries the protein from the ER to the Golgi apparatus. Second: a transport vesicle moves the new protein from the ER to the Golgi; putting the Golgi first reverses this direction.

Learn this topic: How a cell is built, fed, and copied 6-minute lesson

Source: OpenStax Biology 2e, 4.4 The Endomembrane System and Proteins · OpenStax Biology 2e, 4.3 Eukaryotic Cells · Report a problem with this question

Correct answer: A

Passive transport, including simple diffusion, facilitated diffusion, and osmosis, moves substances down their concentration gradient and uses no cell energy, so it keeps going without ATP. Active transport moves substances against their gradient and needs energy, usually from ATP. The sodium-potassium pump uses ATP to push 3 sodium ions out for every 2 potassium ions it brings in, so it stops when ATP runs out. To answer energy questions, ask: is the substance moving with its gradient (passive) or against it (active)?

• A Correct: the sodium-potassium pump is active transport and is powered by ATP, so it stops without ATP.
• B Osmosis is passive movement of water and needs no ATP, even when water passes through aquaporin proteins.
• C Oxygen crosses the membrane by simple diffusion, which needs no ATP, so it would continue.
• D Movement through channel proteins down a gradient is facilitated diffusion; using a protein does not mean using ATP.

Learn this topic: How a cell is built, fed, and copied 6-minute lesson

Source: OpenStax Biology 2e, 5.3 Active Transport · OpenStax Biology 2e, 5.2 Passive Transport · Report a problem with this question

Correct answer: B

DNA uses the bases A, T, G, and C, while RNA uses A, U, G, and C: uracil takes the place of thymine and pairs with adenine. RNA also has ribose instead of deoxyribose and is usually single-stranded. Both nucleic acids have a backbone of sugars linked by phosphate groups.

• A Both DNA and RNA have a sugar-phosphate backbone, so phosphate groups are not unique to RNA.
• B Correct: uracil is found in RNA, where it replaces DNA's thymine.
• C Cytosine is found in both DNA and RNA; uracil replaces thymine, not cytosine.
• D Deoxyribose is DNA's sugar; RNA contains ribose, so this reverses the two molecules.

Learn this topic: How a gene in DNA becomes a protein 6-minute lesson

Source: OpenStax Biology 2e, 3.5 Nucleic Acids · Report a problem with this question

Correct answer: RNA polymerase binds the promoter and builds RNA from the DNA template. → Introns are cut out of the RNA and the exons are joined. → The mRNA travels out of the nucleus into the cytoplasm. → A tRNA carrying methionine pairs with the AUG start codon. → A ribosome reaches a stop codon and releases the finished chain.

Transcription comes first: in the nucleus, RNA polymerase binds the promoter and copies the gene into RNA. That first transcript is processed by removing introns and joining exons, and the finished mRNA then leaves the nucleus. In the cytoplasm, translation starts when the initiator tRNA carrying methionine pairs with the AUG start codon, and it ends when the ribosome reaches a stop codon and the chain is released.

• The mRNA travels out of the nucleus into the cytoplasm. Third: the mRNA leaves the nucleus only after it has been transcribed and its introns removed.
• RNA polymerase binds the promoter and builds RNA from the DNA template. First: transcription by RNA polymerase in the nucleus starts the whole process.
• A ribosome reaches a stop codon and releases the finished chain. Fifth: reaching a stop codon ends translation, so it is the last step.
• Introns are cut out of the RNA and the exons are joined. Second: introns are removed from the new transcript while it is still in the nucleus, before it is exported.
• A tRNA carrying methionine pairs with the AUG start codon. Fourth: translation begins at the AUG start codon once the mRNA is at a ribosome in the cytoplasm.

Learn this topic: How a gene in DNA becomes a protein 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 3.4 Protein Synthesis · OpenStax Biology 2e, 15.5 Ribosomes and Protein Synthesis · OpenStax Biology 2e, 15.1 The Genetic Code · Report a problem with this question

Correct answer: D

Ribosomes read mRNA in groups of three bases (codons), starting from the start codon. Deleting one base shifts the reading frame, so every codon after that point is grouped wrongly and the amino acid sequence from there on changes; this frameshift usually makes the protein nonfunctional. A substitution changes only one codon, which is why it causes smaller effects such as silent or missense mutations.

• A Changing a single amino acid describes a missense substitution, not a deletion that shifts the reading frame.
• B Code redundancy can hide a substitution (a silent mutation), but it cannot fix a shifted reading frame.
• C Losing exactly one amino acid would require deleting three bases (one whole codon), not one base.
• D Correct: a one-base deletion causes a frameshift, so all downstream codons are misread and the protein is usually nonfunctional.

Learn this topic: How a gene in DNA becomes a protein 6-minute lesson

Source: OpenStax Biology 2e, 14.6 DNA Repair · OpenStax Biology 2e, 15.1 The Genetic Code · Report a problem with this question

Correct answer: D

A genotype with two different alleles, such as Yy, is heterozygous; two identical alleles (YY or yy) is homozygous. The phenotype is the trait you can see. Because Y is dominant, it masks y, so a Yy plant has yellow seeds, just like a YY plant. Green seeds appear only in yy plants.

• A Yy has two different alleles, so it is not homozygous, and the dominant Y allele hides the green trait.
• B The genotype term is right, but the recessive green phenotype shows only when no dominant Y allele is present.
• C The phenotype is right, but homozygous means two identical alleles (YY), not Yy.
• D Correct: Yy has two different alleles (heterozygous), and the dominant Y allele produces yellow seeds.

Learn this topic: How traits pass from parents to children 6-minute lesson

Source: OpenStax Biology 2e, 12.2 Characteristics and Traits · Report a problem with this question

Correct answer: C

Pink plants are heterozygous (one red allele and one white allele), because neither allele is dominant and the heterozygote shows an in-between color. A cross of two heterozygotes gives a 1:2:1 genotype ratio: 1 homozygous red : 2 heterozygous : 1 homozygous white. With incomplete dominance, each genotype has its own phenotype, so the offspring are 1 red : 2 pink : 1 white, and 2 of 4, or 1/2, are pink.

• A One fourth is the expected fraction of red (or of white) offspring, not of pink ones.
• B Three fourths comes from the 3:1 ratio of complete dominance, which does not apply when the heterozygote is a blend.
• C Correct: the cross gives 1 red : 2 pink : 1 white, so half the offspring are expected to be pink.
• D All offspring would be pink only from a red × white cross; two pink parents can each pass on either allele.

Learn this topic: How traits pass from parents to children 6-minute lesson

Source: OpenStax Biology 2e, 12.2 Characteristics and Traits · Report a problem with this question

Correct answer: A, D, E

In the ABO system, the Iᴬ and Iᴮ alleles are codominant and i is recessive. The type AB mother is IᴬIᴮ and passes either Iᴬ or Iᴮ; the type O father is ii and can only pass i. So each child is either Iᴬi (type A) or Iᴮi (type B). No child can be type AB (that needs both Iᴬ and Iᴮ) or type O (that needs i from both parents).

• A Correct: a child who gets Iᴬ from the mother and i from the father is Iᴬi, which is type A.
• B Type AB needs both Iᴬ and Iᴮ, but the father can pass only i, so a child cannot be type AB.
• C Type O needs two i alleles, but the mother has no i allele to pass on.
• D Correct: a child who gets Iᴮ from the mother and i from the father is Iᴮi, which is type B.
• E Correct: the type O father is ii, so every child receives an i allele from him.

Learn this topic: How traits pass from parents to children 6-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 28.7 Patterns of Inheritance · OpenStax Biology 2e, 12.2 Characteristics and Traits · OpenStax Concepts of Biology, 8.3 Extensions of the Laws of Inheritance · Report a problem with this question

Correct answer: C

Each class of macromolecule has its own building block: monosaccharides build carbohydrates such as starch and glycogen, amino acids build polypeptides (proteins), and nucleotides build nucleic acids (DNA and RNA). Starch is a long chain of glucose, a monosaccharide, which plants use to store energy. When you see a polymer, first name its class, then recall that class's monomer.

• A Amino acids are the monomers of proteins; DNA is a nucleic acid built from nucleotides.
• B This swaps the building blocks: nucleotides build nucleic acids, while polypeptides are built from amino acids.
• C Correct: starch is a polysaccharide made of many glucose units, and glucose is a monosaccharide.
• D Glycogen is a polysaccharide made of glucose; fatty acids are parts of lipids such as triglycerides and phospholipids.

Learn this topic: The four macromolecules of life and how cells build them 5-minute lesson

Source: OpenStax Biology 2e, 3.1 Synthesis of Biological Macromolecules · OpenStax Biology 2e, 3.2 Carbohydrates · OpenStax Biology 2e, 3.4 Proteins · OpenStax Biology 2e, 3.5 Nucleic Acids · Report a problem with this question

Correct answer: A, C, D

Carbohydrates include simple sugars, disaccharides and polysaccharides. Lactose is a disaccharide (glucose plus galactose), glycogen is the polysaccharide animals use to store glucose, and cellulose is the structural polysaccharide of plant cell walls. Cholesterol is a steroid, which is a lipid, and hemoglobin is a transport protein.

• A Correct: glycogen is a polysaccharide, the storage form of glucose in humans and other vertebrates.
• B Cholesterol is a steroid with four fused carbon rings, so it is a lipid, not a carbohydrate.
• C Correct: lactose (milk sugar) is a disaccharide made of glucose and galactose.
• D Correct: cellulose is a polysaccharide that gives plant cell walls their strength.
• E Hemoglobin is a transport protein that carries oxygen in the blood, not a carbohydrate.

Learn this topic: The four macromolecules of life and how cells build them 5-minute lesson

Source: OpenStax Biology 2e, 3.2 Carbohydrates · OpenStax Biology 2e, 3.3 Lipids · OpenStax Biology 2e, 3.4 Proteins · Report a problem with this question

Correct answer: B

An enzyme works because its active site has a specific shape that fits its substrate. Denaturing heat disrupts the protein's three-dimensional shape (its amino acid sequence stays the same), so the substrate no longer fits and the enzyme stops catalyzing the reaction. Each enzyme has an ideal temperature range; going far above it does not keep speeding the reaction up.

• A Heat speeds reactions only up to the enzyme's ideal temperature; denaturing heat destroys the enzyme's shape and its ability to catalyze.
• B Correct: denaturation changes the protein's shape, so lactose can no longer bind properly at the active site and is not hydrolyzed.
• C Denaturation does not reverse an enzyme's job; a misshapen enzyme simply stops catalyzing either direction.
• D Enzymes are not consumed by the reactions they catalyze; a denatured enzyme stops working because of its shape, not because it was used up.

Learn this topic: The four macromolecules of life and how cells build them 5-minute lesson

Source: OpenStax Biology 2e, 3.1 Synthesis of Biological Macromolecules · OpenStax Biology 2e, 3.4 Proteins · OpenStax Biology 2e, 6.5 Enzymes · OpenStax Biology 2e, 3.2 Carbohydrates · Report a problem with this question

Correct answer: D

Viruses are not made of cells. Each virus is genetic material (DNA or RNA) inside a protein coat, and it is inert until it enters a host cell and uses that cell's machinery to make copies of itself. Bacteria, yeasts and protozoa are all living cells that can grow and divide on their own.

• A Protozoa are single eukaryotic cells with a nucleus, so they are cellular, not acellular.
• B Bacteria are single prokaryotic cells; they lack a nucleus but are still cells that reproduce on their own.
• C A yeast is a single-celled fungus with a nucleus, so it is a cell, not an acellular particle.
• D Correct: viruses are acellular and must infect a host cell to multiply, which makes them obligate intracellular parasites.

Learn this topic: How microorganisms cause disease and how infections spread 5-minute lesson

Source: OpenStax Microbiology, 1.3 Types of Microorganisms · OpenStax Microbiology, 6.1 Viruses · Report a problem with this question

Correct answer: Reservoir → Portal of exit → Mode of transmission → Portal of entry → Susceptible host

An infectious agent lives and multiplies in a reservoir (here, an infected person), leaves through a portal of exit (the respiratory tract), travels by a mode of transmission (such as droplets), enters through a portal of entry (the new person's respiratory tract) and causes infection in a susceptible host. The two portals bracket the mode of transmission: the agent must get out before it can travel, and travel before it can get in.

• Portal of entry Fourth: the portal of entry is where the agent gets into the new host, which can happen only after it has traveled.
• Mode of transmission Third: the mode of transmission (direct contact, droplets, airborne particles, vehicles or vectors) carries the agent between the exit and the entry.
• Reservoir First: the reservoir is the habitat where the agent normally lives, grows and multiplies, so the chain starts here.
• Susceptible host Fifth: the susceptible host is the final link, the person whose defenses do not stop the agent.
• Portal of exit Second: the portal of exit is how the agent leaves the reservoir, such as the respiratory tract for influenza.

Learn this topic: How microorganisms cause disease and how infections spread 5-minute lesson

Source: CDC, Principles of Epidemiology, Lesson 1 Section 10: Chain of Infection · Report a problem with this question

Correct answer: C

Candida is a fungus (a yeast), so antibacterial drugs do not affect it. Normally, neighboring bacteria of the normal microbiota hold its population down. When a drug kills those bacteria, Candida can overgrow and act as an opportunistic pathogen, which is why yeast infections are a known side effect of antibiotics.

• A Antibacterial drugs target bacteria; they do not act on fungal cells to speed up their division.
• B Candida is a fungus (yeast), not a bacterium, so this confuses the two groups; resistance is not the reason it grows.
• C Correct: removing the bacteria that normally inhibit Candida lets the unaffected yeast overgrow.
• D Bacteria are prokaryotes and yeasts are eukaryotes; one cannot turn into the other.

Learn this topic: How microorganisms cause disease and how infections spread 5-minute lesson

Source: OpenStax Microbiology, 15.2 How Pathogens Cause Disease · OpenStax Microbiology, 1.3 Types of Microorganisms · MedlinePlus: Antibiotics · Report a problem with this question

Correct answer: B

The number of protons is the atomic number, and it defines the element: every atom with 6 protons is carbon, and every atom with 11 protons is sodium. Atoms of one element can have different numbers of neutrons (isotopes) or electrons (ions) and still be the same element. Protons plus neutrons is the mass number, which can differ between isotopes of the same element.

• A Atoms of the same element can have different numbers of neutrons; those atoms are isotopes, not different elements.
• B Correct: the number of protons is the atomic number, which defines the element.
• C The number of electrons changes when an atom becomes an ion, but the element stays the same.
• D Protons plus neutrons is the mass number, which varies among isotopes of one element, so it cannot identify the element by itself.

Learn this topic: What atoms are made of and how they form ions and bonds 5-minute lesson

Source: OpenStax Chemistry 2e, 2.3 Atomic Structure and Symbolism · Report a problem with this question

Correct answer: A, B, D

Isotopes of one element share the same atomic number, so every carbon atom has 6 protons, and a neutral carbon atom also has 6 electrons. The isotopes differ only in neutrons: carbon-12 has 12 − 6 = 6 neutrons and carbon-14 has 14 − 6 = 8, a difference of 2. The extra mass of carbon-14 comes from those neutrons, not from extra protons.

• A Correct: both are carbon, and every carbon atom has 6 protons (atomic number 6).
• B Correct: carbon-12 has 6 neutrons and carbon-14 has 8, so carbon-14 has 2 more.
• C Isotopes of the same element always share the same atomic number; a different atomic number would mean a different element.
• D Correct: in a neutral atom the electrons equal the protons, so both have 6 electrons.
• E Adding protons would change the element; the 2 extra mass units in carbon-14 come from neutrons.

Learn this topic: What atoms are made of and how they form ions and bonds 5-minute lesson

Source: OpenStax Chemistry 2e, 2.3 Atomic Structure and Symbolism · OpenStax Biology 2e, 2.1 Atoms, Isotopes, Ions, and Molecules: The Building Blocks · Report a problem with this question

Correct answer: A

Gaining electrons does not change the number of protons, so the atom is still sulfur. It now has 16 protons (+16) and 18 electrons (−18), for a net charge of 2−, which makes it an anion. This matches the pattern for group 16 nonmetals, which tend to gain two electrons and form 2− ions.

• A Correct: 16 protons and 18 electrons give a net 2− charge, and the element is still sulfur.
• B A 2+ charge with 14 electrons would result from losing two electrons, which reverses what happens.
• C Only a change in the number of protons changes the element; adding electrons leaves the atomic number at 16.
• D Isotopes differ in neutrons, but this change involved electrons, so it forms an ion, not a new isotope.

Learn this topic: What atoms are made of and how they form ions and bonds 5-minute lesson

Source: OpenStax Chemistry 2e, 2.3 Atomic Structure and Symbolism · OpenStax Chemistry 2e, 2.6 Ionic and Molecular Compounds · Report a problem with this question

Correct answer: C

A definite volume but no definite shape describes a liquid. Liquid particles stay close together, which keeps the volume nearly fixed, but they have no regular arrangement and can move past each other, which lets the liquid flow into any shape. Solids keep both shape and volume, and gases take both the shape and the volume of their container.

• A Tightly packed particles in a regular pattern that vibrate in place describe a solid, which keeps its own shape instead of taking the container's shape.
• B Widely spaced particles that move independently describe a gas, which would expand to fill the container instead of keeping a fixed volume.
• C Correct: liquid particles are close together (fixed volume) but have no regular arrangement and slide past one another (no fixed shape).
• D This mixes features of a gas (far apart) and a solid (regular pattern, fixed positions) and does not describe any normal state of matter.

Learn this topic: How matter changes state, and what stays the same 5-minute lesson

Source: OpenStax Chemistry 2e, 1.2 Phases and Classification of Matter · OpenStax Chemistry 2e, 10.1 Intermolecular Forces · Report a problem with this question

Correct answer: A, D, E

A chemical change produces one or more new substances, while a physical change only alters state or appearance and keeps the substance's identity. Rusting (iron combining with oxygen and water), cooking meat, and burning a fuel all form new substances. Melting and dissolving are physical changes: the butter is still butter and the sugar is still sugar, just in a different state or spread through water.

• A Correct: rust is a new substance formed when iron combines with oxygen in the presence of water.
• B Melting is a change of state only; liquid butter has the same chemical makeup as solid butter, so this is a physical change.
• C Dissolving spreads the sugar molecules through the water without turning them into a new substance, so it is a physical change.
• D Correct: cooking forms new substances in the meat, and the red-to-brown color change is a sign of that chemical change.
• E Correct: burning (combustion) turns the fuel and oxygen into new substances and releases heat and light.

Learn this topic: How matter changes state, and what stays the same 5-minute lesson

Source: OpenStax Chemistry 2e, 1.3 Physical and Chemical Properties · Report a problem with this question

Correct answer: C

Density is mass divided by volume: 18.0 g ÷ 12.0 cm³ = 1.5 g/cm³. Cutting the block in half halves both the mass (9.0 g) and the volume (6.0 cm³), so each half is still 9.0 ÷ 6.0 = 1.5 g/cm³. Density is an intensive property that does not depend on the amount of material, and because 1.5 g/cm³ is greater than water's 1.0 g/cm³, each half sinks.

• A The density is right, but an object denser than water sinks; a smaller piece does not float just because it is lighter.
• B This halves the density along with the block, but halving the mass also halves the volume, so the density stays 1.5 g/cm³.
• C Correct: each half is 9.0 g ÷ 6.0 cm³ = 1.5 g/cm³, which is denser than water, so it sinks.
• D This halves the density by mistake, and a density of 0.75 g/cm³ would actually float in water, so both parts are wrong.

Learn this topic: How matter changes state, and what stays the same 5-minute lesson

Source: OpenStax Chemistry 2e, 1.4 Measurements · Report a problem with this question

Correct answer: D

In a single-replacement reaction, one element takes the place of another element in a compound, so each side has one element and one compound. Here zinc replaces hydrogen in hydrochloric acid, forming zinc chloride and releasing hydrogen gas. Compare the patterns: synthesis ends with a single product, double replacement swaps partners between two compounds, and combustion is a fuel reacting with oxygen.

• A Two elements joining into one product is a synthesis reaction (A + B → AB), not a replacement.
• B Methane reacting with oxygen to give carbon dioxide and water is combustion; no element replaces another in a compound.
• C Two compounds swapping partners is double replacement (here a precipitation reaction), which has two compounds on each side.
• D Correct: the element zinc replaces hydrogen in HCl, leaving hydrogen as a free element, which is the single-replacement pattern A + BC → AC + B.

Learn this topic: How to read, balance, and classify a chemical reaction 5-minute lesson

Source: OpenStax Chemistry 2e, 4.2 Classifying Chemical Reactions · OpenStax Anatomy & Physiology 2e, 2.3 Chemical Reactions · Report a problem with this question

Correct answer: A, C, D

To check a balanced equation, multiply each coefficient by the subscript for each atom: oxygen is 3 × 2 = 6 on the left and 2 × 3 = 6 on the right, and iron is 4 on the left and 2 × 2 = 4 on the right. Only coefficients may change when balancing, because subscripts define the substance itself. Two reactants forming one product fits the synthesis pattern A + B → AB, and conservation of matter requires atoms, not molecules, to match.

• A Correct: 3 O₂ gives 3 × 2 = 6 oxygen atoms, and 2 Fe₂O₃ gives 2 × 3 = 6 oxygen atoms.
• B Changing a subscript changes the substance (O₃ is ozone, not oxygen gas), so balancing must be done with coefficients only.
• C Correct: there are 4 Fe atoms on the left and 2 × 2 = 4 Fe atoms in 2 Fe₂O₃ on the right.
• D Correct: iron and oxygen combine to form one product, Fe₂O₃, which is the synthesis pattern A + B → AB.
• E There are 7 units on the left (4 + 3) and only 2 on the right; a balanced equation needs equal atoms, not equal numbers of molecules.

Learn this topic: How to read, balance, and classify a chemical reaction 5-minute lesson

Source: OpenStax Chemistry 2e, 4.1 Writing and Balancing Chemical Equations · OpenStax Anatomy & Physiology 2e, 2.3 Chemical Reactions · Report a problem with this question

Correct answer: C

The law of conservation of matter says the total mass does not change during a chemical reaction; atoms are only rearranged. In the open flask, the hydrogen gas product escaped into the air, so the balance lost the mass of that gas. In a sealed flask the gas stays inside, so the total mass of everything in the flask stays equal to the starting mass.

• A Mass is not destroyed in a chemical reaction; the 0.2 g drop in the open flask was hydrogen gas escaping, which a sealed flask prevents.
• B The mass does stay the same, but the reason is wrong: the reaction still happens in a sealed flask, and the gas simply cannot escape.
• C Correct: with the gas trapped, every atom stays in the flask, so the total mass matches the starting mass.
• D The gas is made from atoms already in the reactants, so no new matter is added and the mass cannot rise.

Learn this topic: How to read, balance, and classify a chemical reaction 5-minute lesson

Source: OpenStax Chemistry 2e, 1.2 Phases and Classification of Matter · OpenStax Chemistry 2e, 4.2 Classifying Chemical Reactions · Report a problem with this question

Correct answer: B

Activation energy is the energy barrier, or hill, that colliding reactant particles must get over before they can form products. It is separate from the overall energy change of the reaction (ΔH), which compares the energy of the reactants with the energy of the products. Catalysts speed reactions by lowering this barrier, not by adding energy.

• A Heat released to the surroundings describes an exothermic reaction's energy change, not the barrier particles must overcome.
• B Correct: activation energy is the minimum collision energy needed for reactants to turn into products.
• C The energy difference between reactants and products is the enthalpy change (ΔH), a different quantity from the activation energy.
• D A catalyst does not add energy; it provides a pathway with a lower activation energy.

Learn this topic: What makes a chemical reaction faster or slower? 5-minute lesson

Source: OpenStax Chemistry 2e, 12.5 Collision Theory · Report a problem with this question

Correct answer: B, D, E

Reaction rate depends on how often reactant particles collide and how many collisions have enough energy. Powdered iron exposes far more surface area to the acid, a more concentrated acid puts more acid particles near the iron, and warming makes particles move faster so more collisions have at least the activation energy. Cooling and diluting do the opposite and slow the reaction.

• A Cooling lowers particle energy, so fewer collisions reach the activation energy and the reaction slows.
• B Correct: the same mass as a powder has much more surface area in contact with the acid, so more collisions happen at once.
• C Adding water dilutes the acid, lowering its concentration, so collisions become less frequent and the reaction slows.
• D Correct: a higher concentration means more acid particles in the same space and more frequent collisions with the iron.
• E Correct: at a higher temperature, particles move faster and a larger fraction of collisions have enough energy to react.

Learn this topic: What makes a chemical reaction faster or slower? 5-minute lesson

Source: OpenStax Chemistry 2e, 12.2 Factors Affecting Reaction Rates · OpenStax Chemistry 2e, 12.5 Collision Theory · Report a problem with this question

Correct answer: D

Higher temperatures usually speed reactions, but enzymes are proteins that work best within an optimal temperature range. Far above that range, the enzyme denatures: its shape, including the active site that binds the substrate, is changed, so it can no longer lower the activation energy effectively and the catalyzed reaction slows. When a question involves an enzyme, check whether the temperature or pH has moved outside the enzyme's optimal range.

• A Hotter is faster for many ordinary reactions, but this ignores that very high heat denatures the enzyme catalyzing the reaction.
• B Enzymes are not used up by the reactions they catalyze, but extreme heat or pH can still denature them.
• C Heat gives particles more energy; it does not lower the activation energy, and here it damages the enzyme that was lowering it.
• D Correct: far above its optimal range the enzyme denatures, its active site no longer fits the substrate, and the reaction slows.

Learn this topic: What makes a chemical reaction faster or slower? 5-minute lesson

Source: OpenStax Biology 2e, 6.5 Enzymes · OpenStax Chemistry 2e, 12.2 Factors Affecting Reaction Rates · Report a problem with this question

Correct answer: C

Solubility is the maximum concentration of solute that can dissolve under given conditions. A saturated solution is exactly at that limit, an unsaturated one is below it, and a supersaturated one holds more than the limit. A supersaturated solution is not at equilibrium, so a seed crystal or shaking makes the extra solute crystallize out quickly.

• A A saturated solution holds exactly as much solute as its solubility allows, so it does not contain extra solute ready to crystallize.
• B An unsaturated solution is below its solubility limit, so an added crystal would tend to dissolve rather than trigger crystallization.
• C Correct: a solution holding more solute than its solubility is supersaturated, and a seed crystal makes the excess crystallize.
• D Dilute only means a relatively low concentration; a solution above its solubility limit is not dilute.

Learn this topic: How solutions work: what dissolves, how much, and why cells swell or shrink 5-minute lesson

Source: OpenStax Chemistry 2e, 11.3 Solubility · Report a problem with this question

Correct answer: A, B, E

"Like dissolves like": water is polar, so it dissolves ionic compounds and polar substances but not nonpolar oil. Ethanol and water are miscible, mixing in any proportion. Temperature affects solids and gases in opposite directions: warmer water generally dissolves more of a solid but holds less dissolved gas.

• A Correct: water's slightly negative oxygen ends and slightly positive hydrogen ends surround the sodium and chloride ions in hydration shells.
• B Correct: oil is nonpolar and water is polar, so they do not mix and form two layers.
• C Ethanol and water are miscible and mix in all proportions; this choice confuses ethanol with a nonpolar liquid like oil.
• D Gas solubility decreases as temperature rises, so warm water holds less oxygen; this applies the rule for solids to a gas.
• E Correct: the solubility of most solids increases as temperature increases.

Learn this topic: How solutions work: what dissolves, how much, and why cells swell or shrink 5-minute lesson

Source: OpenStax Chemistry 2e, 11.3 Solubility · OpenStax Biology 2e, 2.2 Water · Report a problem with this question

Correct answer: C

In osmosis, water crosses a semipermeable membrane toward the side with the higher solute concentration. Here the inside of the cell has more solute, so the outside solution is hypotonic and water flows in. Red blood cells swell and can burst (lyse) when they expand beyond what the membrane can stretch; in a hypertonic solution the reverse happens and they shrink (crenate).

• A Water leaving and the cell shrinking describes a hypertonic outside solution, which reverses the concentrations given.
• B The stem states the solute cannot cross the membrane; in osmosis only water moves, so this confuses solute movement with water movement.
• C Correct: the outside solution is hypotonic, so water moves into the cells, which swell and may lyse.
• D No net water movement happens only in an isotonic solution, where solute concentrations inside and outside are equal.

Learn this topic: How solutions work: what dissolves, how much, and why cells swell or shrink 5-minute lesson

Source: OpenStax Biology 2e, 5.2 Passive Transport · Report a problem with this question

Correct answer: D

Acid strength describes how completely an acid ionizes in water. Strong acids such as hydrochloric, nitric and sulfuric acid ionize completely, while weak acids such as acetic acid ionize only partly, so most of their molecules stay intact. Strength is about the degree of ionization, not about how concentrated the solution is.

• A Hydrochloric acid is a strong acid that ionizes completely into hydrogen and chloride ions.
• B Nitric acid is on the standard list of strong acids, which ionize completely in water.
• C Sulfuric acid is also a strong acid; students sometimes assume an acid with two hydrogens must be weaker.
• D Correct: acetic acid, the acid in vinegar, is a weak acid that ionizes only partly.

Learn this topic: How acids, bases, pH and buffers work 5-minute lesson

Source: OpenStax Chemistry 2e, 14.3 Relative Strengths of Acids and Bases · OpenStax Biology 2e, 2.2 Water · Report a problem with this question

Correct answer: Gastric juice → Black coffee → Pure water → Blood → Household ammonia

Most acidic means the lowest pH. Gastric juice is about pH 1.5, black coffee about 5, pure water is neutral at 7, blood is slightly basic at about 7.4, and household ammonia is about 12. Remember that blood sits just above 7, so it is slightly basic, not neutral or acidic.

• Pure water Third: pure water is neutral, pH 7 at 25 °C.
• Household ammonia Fifth: household ammonia is a base at about pH 12, the highest pH in this list, so it is the most basic.
• Gastric juice First: gastric juice is the most acidic, about pH 1.5.
• Blood Fourth: blood is slightly basic at about pH 7.4, so it comes just after pure water, not before it.
• Black coffee Second: black coffee is mildly acidic, about pH 5.

Learn this topic: How acids, bases, pH and buffers work 5-minute lesson

Source: OpenStax Chemistry 2e, 14.2 pH and pOH · OpenStax Biology 2e, 2.2 Water · Report a problem with this question

Correct answer: B

Carbon dioxide in blood is tied to carbonic acid, which releases hydrogen ions. Exhaling more CO2 shifts the balance away from carbonic acid, so fewer hydrogen ions remain and pH rises; the lungs can adjust blood pH upward this way within minutes. Breathing out less CO2 does the opposite and lowers pH.

• A This reverses the effect: exhaling CO2 removes the source of carbonic acid, so less carbonic acid forms, not more.
• B Correct: removing CO2 lowers carbonic acid and hydrogen ion levels, so blood pH rises.
• C The direction is right but the reason is backward; a higher pH means fewer hydrogen ions, not more.
• D Buffers limit pH changes but have limited capacity, and changing CO2 changes the buffer system itself, so pH does shift.

Learn this topic: How acids, bases, pH and buffers work 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 26.4 Acid-Base Balance · OpenStax Chemistry 2e, 14.6 Buffers · Report a problem with this question

Correct answer: 1 microgram (µg) → 1 milligram (mg) → 1 centigram (cg) → 1 gram (g) → 1 kilogram (kg)

Metric prefixes change a unit by powers of ten. Micro means one-millionth, milli one-thousandth, centi one-hundredth and kilo one thousand, so 1 µg < 1 mg < 1 cg < 1 g < 1 kg. Each prefix works the same way for meters, liters and grams.

• 1 gram (g) Fourth: the gram is the base unit here, larger than any of its fractions and smaller than a kilogram.
• 1 milligram (mg) Second: 1 mg is one-thousandth of a gram, which is 1,000 times larger than a microgram.
• 1 kilogram (kg) Fifth: kilo means 1,000, so 1 kg equals 1,000 g and is the largest mass in the list.
• 1 microgram (µg) First: micro means one-millionth, so 1 µg (0.000001 g) is the smallest mass in the list.
• 1 centigram (cg) Third: centi means one-hundredth, so 1 cg (0.01 g) equals 10 mg; students who think milli is larger than centi swap these two.

Learn this topic: How to measure like a scientist: units, prefixes, tools and readings 5-minute lesson

Source: OpenStax Chemistry 2e, 1.4 Measurements · NIST, Metric (SI) Prefixes · Report a problem with this question

Correct answer: B

A graduated cylinder is read at the bottom of the meniscus, the lowest point of the curved liquid surface. You record every certain digit plus one estimated digit; with 1 mL markings, that means estimating to the nearest 0.1 mL. Here the bottom of the meniscus is about halfway between 36 and 37 mL, so the reading is 36.5 mL.

• A 38.0 mL reads the edges where the water climbs the glass instead of the bottom of the meniscus.
• B Correct: it reads the bottom of the meniscus and includes exactly one estimated digit, the tenths place, for a scale marked every 1 mL.
• C 37 mL rounds to the nearest mark and drops the estimated digit, so it reports less information than the cylinder can give.
• D 36.50 mL adds a hundredths digit that a scale marked every 1 mL cannot support, which overstates the precision of the reading.

Learn this topic: How to measure like a scientist: units, prefixes, tools and readings 5-minute lesson

Source: OpenStax Chemistry 2e, 1.5 Measurement Uncertainty, Accuracy, and Precision · Report a problem with this question

Correct answer: C

A kelvin and a Celsius degree are the same size, so a temperature change in kelvins equals the change in degrees Celsius. The bath warmed by 60 − 25 = 35 °C, which is also 35 K. Add 273.15 only when converting a single temperature reading, not a difference between two readings.

• A 63 K multiplies the 35-degree change by 9/5, which converts Celsius degrees to Fahrenheit degrees, not to kelvins.
• B 308 K adds 273 to the 35-degree change, treating a temperature difference as if it were a single temperature reading.
• C Correct: a 35 °C change is a 35 K change because the two units are the same size.
• D 333 K is the final temperature of the bath in kelvins (60 + 273), not how much it increased.

Learn this topic: How to measure like a scientist: units, prefixes, tools and readings 5-minute lesson

Source: OpenStax Chemistry 2e, 1.4 Measurements · NIST, SI Units: Temperature · Report a problem with this question

Correct answer: B

A scientific law summarizes a large number of observations and describes or predicts what will happen. A theory is a well-substantiated, testable explanation of why a broad set of observations occur. They are different kinds of statements, so a theory does not turn into a law, and neither one is ever considered permanently proven; both can be revised if new evidence requires it.

• A This is the common myth that theories graduate into laws; a theory explains and a law describes, so one does not become the other.
• B Correct: laws describe or predict natural behavior, and theories offer well-tested explanations for it.
• C An untested idea is closer to a hypothesis, and science does not label any hypothesis or theory as proven.
• D This reverses the roles and shrinks a theory to one observation; theories explain broad sets of observations.

Learn this topic: How to use logic and evidence to judge a scientific claim 5-minute lesson

Source: OpenStax Chemistry 2e, 1.1 Chemistry in Context · OpenStax Biology 2e, 1.1 The Science of Biology · Report a problem with this question

Correct answer: A, B, C

A trustworthy test of a cause-and-effect claim needs enough participants, a control group for comparison, and a way to keep expectations from shaping the results (such as a placebo gum and blinding). This study had only 10 hand-picked volunteers, no comparison group, and self-rated focus from people who knew what they were chewing, so the improvement could be chance, the power of suggestion, or something that would have happened anyway. How a result is written and whether a claim is testable are not flaws.

• A Correct: very small samples can be unreliable because a few unusual people can swing the result.
• B Correct: without a control group there is no way to know whether people would have felt just as focused without FocusMint.
• C Correct: when participants know their treatment and rate themselves, expectations alone can change the outcome; a placebo and blinding guard against this.
• D "8 of 10" and 80% are the same information, so the format of the number does not weaken the evidence.
• E Being testable is a strength of a scientific claim, not a weakness; the problem is that this study was not a good test.

Learn this topic: How to use logic and evidence to judge a scientific claim 5-minute lesson

Source: OpenStax Introductory Statistics 2e, 1.4 Experimental Design and Ethics · OpenStax Psychology 2e, 2.3 Analyzing Findings · OpenStax Introductory Statistics 2e, 1.2 Data, Sampling, and Variation in Data and Sampling · Report a problem with this question

Correct answer: C

Jamal's hypothesis predicted no mold in darkness, so mold on every dark slice is a result that directly contradicts it, and one solid contradicting result is enough to reject a hypothesis. The lamp group's mold is consistent with the hypothesis but would have happened either way, so it cannot prove anything. An experiment whose results reject a hypothesis has not failed; it has done its job, and Jamal can now propose a new hypothesis.

• A Science never proves a hypothesis, and mold under the lamp was expected whether light matters or not, so it does not support the claim that mold needs light.
• B Results that contradict a prediction are useful evidence; a well-controlled test that rejects a hypothesis is a successful experiment.
• C Correct: the hypothesis predicted no mold in the dark, and mold grew there anyway, so the hypothesis is rejected.
• D Both groups had the same result, so the data show no difference that could be credited to light.

Learn this topic: How to use logic and evidence to judge a scientific claim 5-minute lesson

Source: OpenStax Biology 2e, 1.1 The Science of Biology · OpenStax Psychology 2e, 2.1 Why Is Research Important? · Report a problem with this question

Correct answer: B

In an inverse relationship, one variable goes up while the other goes down. Boyle's law is the classic example: at constant temperature, increasing the pressure on a gas decreases its volume. In a direct relationship, such as Charles's law (volume and kelvin temperature at constant pressure), both variables rise together or fall together.

• A Volume and temperature both increase here, so this is a direct relationship (Charles's law).
• B Correct: pressure goes up while volume goes down, which is an inverse relationship (Boyle's law).
• C If one variable changes while the other stays the same, there is no relationship at all, which students sometimes confuse with an inverse one.
• D Volume and temperature both decrease here, so they move in the same direction, which is a direct relationship; falling values are not what makes a relationship inverse.

Learn this topic: How to read a trend and predict what happens next 5-minute lesson

Source: OpenStax Chemistry 2e, 9.2 Relating Pressure, Volume, Amount, and Temperature: The Ideal Gas Law · OpenStax Psychology 2e, 2.3 Analyzing Findings · Report a problem with this question

Correct answer: C

The stretch rises by 2.0 cm for every 50 g added and is 0 cm at 0 g, so it is directly proportional to the mass: 0.04 cm per gram. A 125 g mass is halfway between 100 g and 150 g, so the stretch should be halfway between 4.0 cm and 6.0 cm, which is 125 × 0.04 = 5.0 cm. This is a prediction inside the tested range (interpolation), so it is reasonable; predicting the stretch for a mass far above 200 g would be riskier.

• A 4.0 cm is the stretch for 100 g; choosing it rounds down to the nearest tested mass instead of following the pattern.
• B 2.5 cm comes from dividing 125 by 50, which treats each 50 g as 1 cm of stretch instead of the 2 cm shown in the table.
• C Correct: the stretch is 0.04 cm per gram, so 125 g gives 5.0 cm, halfway between the values for 100 g and 150 g.
• D 6.0 cm is the stretch for 150 g; choosing it rounds up to the next tested mass instead of following the pattern.

Learn this topic: How to read a trend and predict what happens next 5-minute lesson

Source: OpenStax Chemistry 2e, 9.2 Relating Pressure, Volume, Amount, and Temperature: The Ideal Gas Law · OpenStax Introductory Statistics 2e, 12.3 The Regression Equation · OpenStax Introductory Statistics 2e, 12.2 Scatter Plots · OpenStax College Algebra 2e, 4.3 Fitting Linear Models to Data · OpenStax College Algebra 2e, 5.8 Modeling Using Variation · Report a problem with this question

Correct answer: D

This system is a negative feedback loop: the sensor detects a change, the controller compares the reading with the 27 °C set point, and the vents (the effector) reverse any rise. The controller can respond only to what the sensor reports. A stuck reading of 20 °C is below the set point, so the controller keeps the vents closed, and nothing counteracts the sun's heating. Because the broken sensor no longer detects the rise, the correction stops and the original change continues.

• A The controller does not try to reach the sensor's reading; it opens the vents only when the reading is above 27 °C, which never happens with a reading stuck at 20 °C.
• B This is how the loop works when every part is working; a broken sensor cuts the loop, so the controller never learns that the air is getting hotter.
• C A reading below 27 °C tells the controller to close the vents, not to open them, so this reverses the system's response.
• D Correct: the controller always sees 20 °C, so it keeps the vents closed and the trapped heat makes the temperature keep rising.

Learn this topic: How to read a trend and predict what happens next 5-minute lesson

Source: OpenStax Anatomy & Physiology 2e, 1.5 Homeostasis · Report a problem with this question

Correct answer: C

The dependent variable is what the researcher measures to see the effect of the change she made on purpose. Here she changes the water temperature (the independent variable) and measures the dissolving time, so dissolving time is the dependent variable. A quick check is the sentence "Does _ affect _?": "Does water temperature affect dissolving time?" puts the independent variable first and the dependent variable second.

• A Water temperature is what the student changes on purpose, so it is the independent variable, not the dependent one.
• B The 200 mL volume is kept the same in every cup, so it is a controlled variable.
• C Correct: dissolving time is what the student measures to see whether temperature has an effect.
• D The 10 °C cup is one of the conditions being compared, not a variable; confusing a group or trial with a variable is a common mistake.

Learn this topic: How to read an experiment: variables, controls and valid conclusions 6-minute lesson

Source: OpenStax Psychology 2e, 2.3 Analyzing Findings · OpenStax Concepts of Biology, 1.2 The Process of Science · NASA GeneLab, Bioinformatics Bite #4: Intro to Experimental Design (worksheet) · Report a problem with this question

Correct answer: A, C, E

In a fair test, the groups should differ only in the independent variable (the drink), and there should be enough subjects that a few unusual people cannot decide the result. Carmen's groups differ in activity background and testing time as well as drink, and each group has only 3 people. Using larger samples, random assignment from one pool, and the same testing time fixes these problems, while giving everyone the sports drink would remove the comparison group.

• A Correct: very small samples can be unreliable, so more people per group makes the averages more trustworthy.
• B Letting people choose their own group can make the groups differ in other ways (self-selection), which is the kind of problem random assignment prevents.
• C Correct: random assignment from one pool spreads out hidden differences, such as athletic training, so the groups start out alike.
• D If everyone gets the sports drink, there is no water (control) group left to compare with, so the effect of the drink cannot be measured.
• E Correct: time of day is a second difference between the groups; keeping it the same makes it a controlled variable.

Learn this topic: How to read an experiment: variables, controls and valid conclusions 6-minute lesson

Source: OpenStax Psychology 2e, 2.3 Analyzing Findings · OpenStax Introductory Statistics 2e, 1.2 Data, Sampling, and Variation in Data and Sampling · OpenStax Introductory Statistics 2e, 1.4 Experimental Design and Ethics · OpenStax Biology 2e, 1.1 The Science of Biology · NASA GeneLab, Bioinformatics Bite #4: Intro to Experimental Design (worksheet) · Report a problem with this question

Correct answer: B

A fair test changes only the independent variable. For the 4% disks, two things changed at once, concentration and soaking time, so the larger clear ring could come from either one (soaking time acted as a confounding variable). The 0%, 1%, and 2% disks were all soaked for 10 minutes, so comparisons among them are still valid. Repeating a flawed setup three times makes the flaw consistent, not corrected; the fix is to redo the 4% disks with a 10-minute soak.

• A Repeated trials reduce random variation, but they cannot fix a variable that differed in every 4% trial.
• B Correct: with two variables changed for the 4% disks, the result cannot be pinned on concentration.
• C The 0%, 1%, and 2% disks were treated identically except for concentration, so their comparison is still a fair test; only the 4% result is in doubt.
• D The dependent variable is what was measured, the width of the clear ring; soaking time was an uncontrolled variable, not the outcome.

Learn this topic: How to read an experiment: variables, controls and valid conclusions 6-minute lesson

Source: OpenStax Biology 2e, 1.1 The Science of Biology · OpenStax Concepts of Biology, 1.2 The Process of Science · OpenStax Introductory Statistics 2e, 1.4 Experimental Design and Ethics · NASA GeneLab, Bioinformatics Bite #4: Intro to Experimental Design (worksheet) · Report a problem with this question