Name: ______
Date:______
Picking out Parts of an Experiment
SCENARIO 1:
A student wants to see if a new, more costly fish food will cause fish to grow faster. She separated the fish into two groups of three fish each. Group one received the old fish food. Group two received the new fish food. The length of the fish is measured each week.
What is the dependent variable? Speed of fish growth
What is the independent variable? New costly fish food
What is the control group? Group one
What are the constants? Same type of fish, number of fish per group
SCENARIO 2:
In the laboratory, yeast cells are usually grown at a temperature of 25oC. A scientist wanted to determine if yeast cells would reproduce faster or slower when the temperature was dropped to 15oC. The same number of yeast cells were placed in the same medium with the same amount of nutrients. One sample was kept at 25oC and the other one was kept at 15oC. The number of yeast cells was counted every hour for an eighteen hour period.
What is the dependent variable? Change of yeast growth
What is the independent variable? Temperature
What is the control group? Sample kept at 25oC
What are the constants? same no. of yeast cells, same medium, same nutrients
SCENARIO 3:
Mary wondered if a more costly fish food would cause her fish to grow faster. She separated her fish into two groups of three fish each in two 10-galon tanks. The fish received the same amount of food at the same times of the day for one year. The first group was given the cheap food and the second group was given the more costly food. She measured the length of the fish every month at the end of the month.
What is the dependent variable? Length of fish
What is the independent variable? Fish food
What is the control group? Group of fish fed cheap fish food
What are the constants? no. of fish per group, same size tanks, same no. of feedings
SCENARIO 4:
Ron wondered if color affects the rate of thermal energy absorption. He took five 12-oz. Aluminum cans and painted them yellow, white, black, and blue. The fifth one he left plain. He then poured equal amounts of water into each and placed them on a shelf next to a window and measured the temperature of the water every five minutes for 1 hour.
What is the dependent variable? Rate of thermal energy absorption
What is the independent variable? color
What is the control group? Plain can
What are the constants? same size can, aluminum cans, equal amounts of water, same location, temp. measurements at same time
SCENARIO 5:
A student wanted to determine what effect the lack of sunlight has on green plants. She took 2 small green bean plants of the same size and placed them in two 10oz. Styrofoam cups with a hole in the bottom of each. She covered each plant with 5oz. Of soil. One plant was placed in full sunlight and one was placed in complete darkness. She watered each bean plant once a week with 10ml of water an measured each plant’s height.
What is the dependent variable? Plant height
What is the independent variable? sunlight
What is the control group? Plant placed in darkness
What are the constants? type of plant, same size, planted in same size Styrofoam cups, cups with holes in bottom, amount of soil, watering frequency, amount of water
SCENARIO 6:
To determine the effect of ammonium sulfate on plant growth, two seed flats containing soil from a lawn were seeded using standard lawn grass mixtures. One flat was watered with rainwater and the other with rainwater containing a little ammonium sulfate. The flats were kept in the same area to ensure identical conditions and temperatures.
What is the dependent variable? Plant growth
What is the independent variable? Ammonium sulfate
What is the control group? Flat watered with rainwater
What are the constants? same flat size, same lawn seed, same area, conditions, and temperatures.
SCENARIO 7:
An experiment was designed to investigate the effect of caffeine on the heartbeat of water fleas. Two populations of water fleas were cultured. Both populations had water with the same mineral content, were supplied with identical amounts of bacteria as food, received the same amount of light, and had their temperature maintained at 20oC. Every two hours, water fleas from both populations were selected and their heartbeats were monitored. The fleas of population #1 had caffeine administered five minutes before the heartbeats were checked. The fleas of population #2 were given nothing extra.
What is the dependent variable? heartbeat
What is the independent variable? caffeine
What is the control group? Flea population no. 2
What are the constants? water with same mineral content, identical amounts of bacteria for food, same amount of light, temp. at 20 oC, heartbeats monitored every 2 hours