controls are defined as
a. variables scientists observe for changes
b. things that change during an experiment
c. variables that are changed by the scientist
d. things that are kept constant during an experiment

producers: apple trees, potatoes, carrots, grains, acorns, cabbage, grass, corn, lettuce

consumers: deer, mice, rabbits, chickens, squirrels, horses, worms, cows

predators: eagles, frogs, wolves, owls

a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.