Biology Practice Test: Homeostasis and Feedback

Homeostasis means holding things like temperature, water and blood sugar near a set point even when outside conditions change. Matching the surroundings is the opposite: it is what happens when control fails.

The response (sweating) works against the change (rising temperature) and brings it back toward the set point, which defines negative feedback. Positive feedback would push the temperature even higher.

During childbirth, contractions trigger more oxytocin, which causes even stronger contractions until the baby is born. The other three all reverse a change, so they are negative feedback.

Insulin lowers blood sugar by helping body cells absorb glucose and the liver store it as glycogen. Glucagon has the opposite effect and is released when blood sugar is low.

Glucagon from the pancreas tells the liver to turn stored glycogen back into glucose, raising the blood level. Insulin would lower it further.

Evaporation needs energy, and that energy comes from the skin, so the skin cools. This is why sweating works poorly in very humid air, where sweat evaporates slowly.

Vasoconstriction sends less warm blood to the skin, so less heat is lost to the cold air and the skin looks paler. Widening the vessels (vasodilation) happens when the body needs to lose heat.

When the body is low on water, the hormone ADH makes the kidney tubules return more water to the blood, leaving a small amount of concentrated urine. Pale, dilute urine is what you see after drinking a lot.

The hypothalamus compares body temperature with its set point and triggers sweating, shivering or changes in blood flow. The cerebellum coordinates movement and balance, not temperature.

Sensors detect the rising carbon dioxide (which makes the blood more acidic) and signal the breathing muscles to work harder. Slower breathing would let carbon dioxide build up even more.