A cockroach scuttles into a dark crack the instant the kitchen light is switched on. Which characteristic of living things does this behavior demonstrate?

A student runs on a day when the air is 35 degrees Celsius. She sweats heavily, and her core body temperature stays near 37 degrees Celsius for the whole run. Which characteristic of living things does the steady core temperature show?

Yeast cells added to bread dough break down the sugar in the flour, release energy, and give off carbon dioxide gas that makes the dough rise. Which characteristic of living things are the yeast cells demonstrating?

A tadpole hatches with a long tail and gills. Over several weeks it absorbs the tail, grows four legs, and develops lungs that let it breathe air. Which characteristic of living things does this change illustrate?

A biologist places one Paramecium in a drop of pond water. Twenty-four hours later the drop holds several Paramecium cells, each with the same structures as the first one. Which characteristic of living things accounts for this?

Beetles on a dark lava field vary in shell color. Birds find and eat pale beetles more easily, and after many generations most beetles on the field are dark. Which characteristic of living things does this describe?

In a human, similar cells make up muscle tissue, several tissues together make up the heart, and the heart works with blood vessels as one working unit. Which characteristic of living things does this describe?

Two black Labrador parents produce a litter in which several puppies are yellow. Testing shows each yellow puppy received a copy of the same coat-color allele from each parent. Which characteristic of living things does this show?

A stalactite in a cave grows longer every year as dissolved minerals are deposited on its tip. A mushroom on the cave floor also gets larger every year. Which of these does the mushroom do that the stalactite does not?

A car takes in fuel and oxygen, releases energy, gives off carbon dioxide and water vapor, and moves along a road. Which evidence best settles that a car is not a living thing?

A candle flame takes in oxygen, releases energy as heat and light, gives off carbon dioxide and water, and grows larger when more wax is available. Biologists therefore classify a candle flame as a living thing.

A robot vacuum turns away when its sensor meets the edge of a stair, and it drives back to its charging dock when the battery runs low. Which observation would settle that the robot is not a living thing?

A dry bean seed and a small pebble both sit unchanged in a jar for two years. Both are then buried in warm, damp soil. Which observation would show that the seed is alive and the pebble is not?

Overnight, frost spreads across a cold window in branching patterns that look like the fronds of a fern growing on the sill. Which feature of the fern, absent in the frost, shows that only the fern is alive?

Under the microscope, a green film scraped from a rock shows small green disks. Which further observation would show the film is a living thing rather than a colored mineral crust?

A bacteriophage is DNA inside a protein coat. Inside a bacterium it makes hundreds of copies of itself within an hour; on a dry bench it does nothing for months. On what grounds do most biologists place viruses outside the definition of life?

A mule is the offspring of a horse and a donkey. It grows, uses energy, holds a steady internal temperature and reacts to its surroundings, but it cannot produce offspring of its own. Is a mule a living thing?

A prion is a misfolded protein. It has no DNA or RNA and is not a cell, yet it makes normal brain proteins fold into copies of its own shape. Which feature is the main reason biologists do not count a prion as a living organism?

An archaeon in a hot spring, a mushroom on a fallen log and a blue whale live in completely different ways. Which statement is true of all three?

An amoeba is a single cell. Within that one cell it takes in food and releases energy from it, keeps its internal water content steady, moves toward food, and divides to form new amoebas.