Read the following lab scenario:

In order to determine the best temperature for bacterial growth, a scientist placed samples of the same type of bacteria in 4 petri dishes and supplied them with equal amounts of nutrients, oxygen, and light. The petri dishes were placed in areas with controlled temperatures. The temperature was maintained at 20°C, 22°C, 24°C, and 26°C. After three weeks of observations, the scientist counted the number of bacterial colonies and determined that the highest rate of bacterial growth occurred at 24°C.

The independent variable in this experiment is the –

A. Length of the experiment
Incorrect. The length of the experiment has no effect on the outcome of this experiment.

B. Number of bacteria
Incorrect. The number of bacteria depends on other factors in the experiment.

C. Reproduction rate
Incorrect. Reproduction rate depends on other factors in the experiment.

D. Temperature
Correct! The temperature is the variable that determines the rate of growth of the bacteria.

Read the following lab scenario again:

In order to determine the best temperature for bacterial growth, a scientist placed samples of the same type of bacteria in 4 petri dishes and supplied them with equal amounts of nutrients, oxygen and light. The petri dishes were placed in areas with controlled temperatures. The temperature was maintained at 20°C, 22°C, 24°C, and 26°C. After three weeks of observations, the scientist counted the number of bacterial colonies and determined that the highest rate of bacterial growth occurred at 24°C.

How was the dependent variable measured in this experiment?

A. By measuring the temperature of the petri dishes
Incorrect. The varying temperatures were the levels of the independent variable.

B. By counting the number of bacterial colonies
Correct! The scientist was able to determine the growth rate by counting the number of bacterial colonies.

C. By counting the days the bacteria was left to grow
Incorrect. The number of days the bacteria was left to grow was a constant in this experiment.

D. By measuring the amount of nutrients in each petri dish
Incorrect. The amount of nutrients was a constant in this experiment.

Read the following lab scenario again:

In order to determine the best temperature for bacterial growth, a scientist placed samples of the same type of bacteria in 4 petri dishes and supplied them with equal amounts of nutrients, oxygen and light. The petri dishes were placed in areas with controlled temperatures. The temperature was maintained at 20°C, 22°C, 24°C, and 26°C. After three weeks of observations, the scientist counted the number of bacterial colonies and determined that the highest rate of bacterial growth occurred at 24°C.

Which of the following is NOT a constant in the experiment?

A. Type of bacteria
Incorrect. The description of the experiment states that the same type of bacteria was used therefore this is a constant.

B. Amount of oxygen
Incorrect. The description of the experiment states that an equal amount of oxygen was supplied therefore this is a constant.

C. Reproduction rate
Correct! Growth of bacteria is the dependent variable therefore it is not a constant.

D. Amount of light
Incorrect. The description of the experiment states that equal an amount of light was supplied therefore this is a constant.

Read the following lab scenario:

Susan wanted to know how the amount of water affected the rate of seed germination. She read that 150 mL of water for every 250 grams of soil was the ideal amount of water for seed germination and decided to see if this was true. She purchased 5 identical flower pots and placed 250 g of potting soil in each. She then planted 10 seeds of the same type in each pot. She placed the pots in the same location so that each received the same amount of light. The pots were given the following amounts of distilled water each day for 40 days:

Pot 1 - 50 mL
Pot 2 - 100 mL
Pot 3 - 150 mL
Pot 4 - 200 mL
Pot 5 - 250 mL

Each day she recorded the number of seeds that germinated and the height of each plant.

What was the independent variable in Susan’s experiment?

A. Germination rate
Incorrect. The germination rate was the dependent variable or results that Susan was looking for.

B. Amount of water
Correct! Susan varied or manipulated the amount of water so this is the independent variable.

C. Type of flower pots
Incorrect. Susan used the same type of flower pots so this is a constant.

D. Type of seeds planted
Incorrect. Susan planted the same type of seed in each pot so this is a constant.

Read the following lab scenario again:

Susan wanted to know how the amount of water affected the rate of seed germination. She read that 150 mL of water for every 250 grams of soil was the ideal amount of water for seed germination and decided to see if this was true. She purchased 5 identical flower pots and placed 250 g of potting soil in each. She then planted 10 seeds of the same type in each pot. She placed the pots in the same location so that each received the same amount of light. The pots were given the following amounts of distilled water each day for 40 days:

Pot 1 - 50 mL
Pot 2 - 100 mL
Pot 3 - 150 mL
Pot 4 - 200 mL
Pot 5 - 250 mL

Each day she recorded the number of seeds that germinated and the height of each plant.

Identify the control group in the experiment.

A. The plant that received 500g of potting soil
Incorrect. Each flower pot got 500g of soil, so the amount of soil is a constant.

B. The plant that received 50 mL of water
Incorrect. This is an experimental group. Look back at the procedure. What did Susan read was the ideal amount of water?

C. The plant that received 150 mL of water
Correct! Susan read that the ideal amount of water for seed germination was 150mL, so the plants that received this amount were the control group.

D. The flower pot that Susan planted the 10 seeds in
Incorrect! She planted 10 seeds in each flower pot so the number of seeds is a constant.