What Happens Next?
Someone begins exercising intensely and their muscles start using oxygen much faster. What happens next to their breathing and heart rate?
Both increase to deliver more oxygen to the muscles and remove the extra CO₂ being produced.
A cell loses its nucleus. It doesn’t immediately die. Why can it survive briefly, and what eventually happens and why does it die?
Existing proteins and mRNA can keep the cell functioning temporarily, but it can’t make new RNA or properly replace proteins, so eventually it dies.
A patient becomes shaky, sweaty, and confused several hours after skipping lunch. What is most likely happening?
Blood glucose has fallen too low, triggering a sympathetic stress response and leaving the brain with insufficient glucose, which causes confusion and weakness.
You want yeast cells to produce carbon dioxide as quickly as possible using sugar. What conditions would you give them?
Give them sugar, water, and a warm temperature. The yeast metabolize the sugar through fermentation, releasing CO₂; warmth speeds their metabolism up to an optimal point.
You touch a hot pan and pull your hand away before consciously thinking about it. How?
A spinal reflex arc allows sensory neurons to activate motor neurons through the spinal cord before the brain finishes consciously processing the pain.
A person eats a very carbohydrate-heavy meal, causing blood glucose to rise sharply. What happens next?
The pancreas releases insulin, causing tissues to take up glucose and the liver/muscles to store it as glycogen, bringing blood glucose back down.
A cell membrane suddenly becomes freely permeable to sodium and potassium ions. What happens?
The cell’s ion gradients collapse, disrupting membrane potential and making processes like nerve signaling and active transport fail.
A patient has chronically high blood glucose and high insulin levels. What condition best explains this?
Type 2 diabetes. The pancreas is still producing insulin, but body tissues have become resistant to it, so glucose uptake decreases and glucose remains elevated in the blood.
You want to make a plant bend strongly toward one side without physically touching it. What could you do?
Shine light from only one direction. Auxin becomes unevenly distributed, causing cells on the shaded side of the stem to elongate more, so the plant bends toward the light.
You sprint up several flights of stairs and continue breathing heavily even after you stop. Why?
Your body is still restoring normal conditions—replenishing oxygen stores, removing excess CO₂, and processing metabolites produced during intense exercise.
A person loses a large amount of blood very quickly. What does the body do next to maintain blood flow to vital organs?
Heart rate increases and peripheral blood vessels constrict, helping preserve blood pressure and redirect blood toward the brain and heart.
A toxin shuts down all ribosomes in a cell. What happens next?
Protein synthesis stops. Existing proteins can still function temporarily, but as enzymes, receptors, and structural proteins degrade and aren’t replaced, the cell progressively loses function.
A patient has a severe sore throat, fever, swollen lymph nodes, and white patches on their tonsils, but little to no cough. What disease is most likely?
It is caused by Streptococcus pyogenes, and the fever, inflamed tonsils, white exudate, and tender lymph nodes are characteristic of the immune response to the bacterial infection.
You want to create bacteria that produce human insulin. How would you do it?
Insert the human insulin gene into a bacterial plasmid, introduce that plasmid into bacteria, and grow the bacteria so they express the insulin protein. The insulin can then be purified.
You eat a very spicy pepper, and your mouth feels like it is literally burning even though there is no heat damage. Why?
Capsaicin activates TRPV1 receptors, the same sensory receptors that normally respond to damaging heat. Your nervous system therefore interprets the chemical signal as a burning sensation even though your mouth is not actually being heated.
Aldosterone normally causes the kidneys to reabsorb sodium and excrete potassium, helping retain water and maintain blood pressure. A patient’s adrenal glands suddenly stop producing aldosterone. What happens next?
The kidneys lose more sodium and water in urine, causing blood volume and blood pressure to fall, while potassium builds up in the blood.
A drug prevents lysosomes from maintaining their acidic interior. What happens to the cell over time?
Lysosomal enzymes stop working efficiently, so the cell can’t properly break down and recycle damaged proteins and organelles, causing cellular waste to accumulate.
A patient is extremely thirsty, urinates very frequently, and produces unusually dilute urine. Their ADH level is high, but their kidneys do not respond normally to it. What condition do they have?
The kidneys are resistant to ADH, so they fail to insert enough aquaporin channels and cannot reabsorb water effectively, producing large volumes of dilute urine.
You want a mouse to develop normally, but then permanently knock out a specific gene only after the mouse reaches adulthood. How could you do this?
Use a tamoxifen-inducible Cre-Lox system. The target gene is flanked by loxP sites, and Cre recombinase is activated only when the mouse receives tamoxifen, allowing researchers to trigger the knockout at a chosen time.
Someone drinks a large amount of plain water very quickly. A short time later, they begin producing lots of very dilute urine. Why?
Their blood osmolarity falls, causing ADH secretion to decrease. The kidneys insert fewer aquaporin channels in the collecting ducts, so less water is reabsorbed and more is excreted.
A tumor begins secreting abnormally high levels of ADH. Initially, what happens to the body’s water balance, and how may the kidneys respond over time?
Initially, the kidneys reabsorb excess water, causing water retention, diluted blood, and hyponatremia (low sodium).
Over time, the kidneys can partially adapt by becoming less responsive to ADH and reducing aquaporin-2 expression, allowing more water to be excreted despite continued high ADH levels, beginning to excrete more dilute urine despite the continued high ADH levels.
A toxin blocks the electron transport chain in mitochondria. The cell still has glucose available. What happens next?
The proton gradient collapses, so oxidative phosphorylation and ATP production plummet. The cell relies much more on glycolysis, lactate builds up, and eventually ATP-dependent processes like ion pumps fail.
A patient has muscle weakness, drooping eyelids, and symptoms that worsen with repeated activity but improve after rest. Tests show antibodies attacking acetylcholine receptors at neuromuscular junctions. What condition is most likely?
Myasthenia gravis. The antibodies reduce the number of functional acetylcholine receptors, so motor neurons have increasing difficulty triggering muscle contraction, especially with repeated use.
Researchers want to study bladder cancer in mice, but the mice do not naturally develop tumors at a useful rate. How could they induce bladder cancer while still allowing the tumors to arise naturally within the mouse’s own bladder tissue?
Give the mice BBN (N-butyl-N-(4-hydroxybutyl)nitrosamine), a chemical carcinogen, in their drinking water over an extended period. BBN is metabolized into compounds excreted in the urine, exposing the bladder lining to carcinogens and causing mutations that can eventually produce invasive bladder tumors. This is useful because the tumors develop within an immunocompetent animal and resemble aspects of human bladder cancer.
After someone rapidly ascends to a high altitude, they become short of breath and fatigued even though their lungs are healthy. Over the next several days, what major physiological adaptation helps them compensate?
The kidneys release more erythropoietin (EPO), stimulating red blood cell production. More red blood cells increase the blood’s oxygen-carrying capacity and help compensate for the lower oxygen availability.