Bell ringer

1. What is the independent variable?

2. What is the dependent variable?

3. Write a purpose question that fits this information.

Ants need water to survive. Fifty mL of water was put in three separate and identical Petri dishes. Salt was added to the water in one dish, and sugar was added to another. Nothing was added to the water in the third dish. The three dishes were then placed two meters from the same anthill. After four hours the number of ants in each dish was counted.

What was changed, tested, or compared?Ants need water to survive. Fifty mL of

water was put in three separate and identical Petri dishes. Salt was added to the water in one dish, and sugar was added to another. Nothing was added to the water in the third dish. The three dishes were then placed two meters from the same anthill. After four hours the number of ants in each dish was counted.

Independent variable

Salt, sugar, or nothing added to water

Substances added to water

Plain water, sugar water or salt water

What was measured or counted?

Ants need water to survive. Fifty mL of water was put in three separate and identical Petri dishes. Salt was added to the water in one dish, and sugar was added to another. Nothing was added to the water in the third dish. The three dishes were then placed two meters from the same anthill. After four hours the number of ants in each dish was counted.

Dependent variable

The number of ants in each dish

What was kept the same?

Ants need water to survive. Fifty mL of water was put in three separate and identical Petri dishes. Salt was added to the water in one dish, and sugar was added to another. Nothing was added to the water in the third dish. The three dishes were then placed two meters from the same anthill. After four hours the number of ants in each dish was counted.

Controlled variables

• 50 mL of water

• Identical Petri dishes

• 2 meters away

• Same anthill

• 4 hours

What is the purpose question?

What is the effect of plain water, sugar water or salt water on the number of ants in each dish?

Disinfectants are used to kill bacteria on surfaces. Bacteria were grown in four Petri dishes. The cleaning solution 409 was then sprayed on one, Lysol was sprayed on another, bleach was sprayed on the third, and the last one was sprayed with water. The dishes were left at room temperature for four days. The number of bacteria colonies present at the end of four days was counted.

What was changed, tested, or compared?Disinfectants are used to kill bacteria on

surfaces. Bacteria were grown in four Petri dishes. The cleaning solution 409 was then sprayed on one, Lysol was sprayed on another, bleach was sprayed on the third, and the last one was sprayed with water. The dishes were left at room temperature for four days. The number of bacteria colonies present at the end of four days was counted.

Independent variable

Cleaning solutions

Disinfectants

What was measured or counted?

Disinfectants are used to kill bacteria on surfaces. Bacteria were grown in four Petri dishes. The cleaning solution 409 was then sprayed on one, Lysol was sprayed on another, bleach was sprayed on the third, and the last one was sprayed with water. The dishes were left at room temperature for four days. The number of bacteria colonies present at the end of four days was counted.

Dependent variable

The number of bacteria colonies present

What was kept the same?

Disinfectants are used to kill bacteria on surfaces. Bacteria were grown in four Petri dishes. The cleaning solution 409 was then sprayed on one, Lysol was sprayed on another, bleach was sprayed on the third, and the last one was sprayed with water. The dishes were left at room temperature for four days. The number of bacteria colonies present at the end of four days was counted.

Controlled variables

• All at room temperature

• All left for four days

Trickier: Experimental group(s) vs. control groupsDisinfectants are used to kill bacteria on

surfaces. Bacteria were grown in four Petri dishes. The cleaning solution 409 was then sprayed on one, Lysol was sprayed on another, bleach was sprayed on the third, and the last one was sprayed with water. The dishes were left at room temperature for four days. The number of bacteria colonies present at the end of four days was counted.

Experimental groups:

409, Lysol, and bleach

Control group:

water

Purpose question:

What is the effect of different cleaning solutions on the number of bacteria colonies present after four days?