What role does genetic variation play in natural selection?

Which definition best describes a population?  

How many independent variables are typically found in an experiment

In an experiment, a scientist measures the amount of algae growth in water with varying pH (acidic levels).  What is the DEPENDENT variable in this experiment?

In an experiment, a scientists tests various types of fertilizer to see which produces the best plant growth.  What is the INDEPENDENT variable in this experiment?

A biopsychologist is studying the effects of anabolic steroids on the aggressive behavior of female rats. 24 female rats receive daily injections of a placebo (fake drug), while 24 others receive daily injections of the steroid. Round-the-clock videotapes of the communal cages of all rats allow all aggressive encounters to be counted and timed. What is one of the CONTROLS in this experiment?

Which of the following best describes how the process of natural selection contributes to the development of antibiotic resistant bacteria?

The basic unit of life is 

Command Verbs:  select the correct command verb. ir (Uds):

TEST 1 DIRECTIONS Take a moment to read through the directions for the exam. All work must be shown on Multiple Choice Problems to receive full credit All work must be shown on Free Response Problems to receive full credit You have 1 hour and 30 minutes to work on the math problems After completing the exam, you have 15 minutes to scan and submit your work You may use a scientific calculator, or the Desmos calculator link provided on the exam You may NOT use a graphing calculator You man NOT use a cell phone as a calculator WHAT TYPE OF CALCULATOR CAN YOU USE FOR THIS EXAM?