help me identify dependent and independent variables please in these examples!?

Question

The diversity of algal species is calculated for a coastal area before and after an oil spill.

Light abosorption by a pigment is measured for red,blue,green, and yellow light.

Batches of seeds are soaked in salt solutions of different concentrations, and germination is counted for each batch.

An investigator hypotheesizes that the adult weight of a dog is higher when it has fewer littermates.

Guinea pigs are kept at different temperatures for 6 weeks. Percent weight gain is recorded.

Answer 1

Independent variable: The factor that changes.
Dependent variable: The factor which is measured.

1) IV = Before and after oil spill
DV =Diversity of algal species

2) IV = Light wavelengths (i.e. red,blue,green, and yellow light.)
DV= Light absorption

3) IV = Concentration of salt solution
DV = Germination count

4) IV = Number of littermates
DV = Adult weight of dog

5) IV = Temperature
DV = Percentage of weight gain

Answer 2

I agree with all the answers given by the first poster. You can think of it this way.

You're trying to test if some factor makes a difference in the outcome.

You change the factor = the independent variable.
That causes the results that you measure and record = the dependent variable.

Of course the results DEPEND on the changes you made.
The changes you made did not depend (independent) on the results because the results hadn't even happened yet!