depend and independ variable

An independent variable is what the researcher is manipulating or varying, while a dependent variable is the effect of what was manipulated.

Given the definitions above:
1) scientists are altering the temperature to see how many days pollen would remain present
   independent variable: increased temperatures
   dependent variable: number of days
2) scientists are manipulating whether or not goby fish is present to determine how much coral is covered in seaweed
   independent variable: goby fish present or not
   dependent variable: percent of coral covered with seaweed and rate of coral growth
3) scientists are varying the light to determine the preference for sweets in hamsters
   independent variable: chronic dim light throughout the light vs. normal light/dark cycles
   dependent variable: preference for sweets

Hope this helps!