Question

Daphnia are freshwater organisms sometimes referred to as “water fleas.” Design an experiment that
could be used to test the effects of temperature on the size of a daphnia population. In your
experimental design, be sure to:
• state a hypothesis to be tested
• describe how the control group will be treated differently from the experimental group
• identify the independent variable in the experiment
• identify the type of data that will be collected

Answer 1

Hypothesis: Daphnias can increase in population at a room
temperature, rather than a colder or warmer temperature.

Control group will be at a room temperature water. The experimental will be tested in cold and warmer waters.

Independent variable: change of water temperature.

The data will be the amount of growth in which the water fleas population increases or decreases, a bar graph would work.

Answer 2

Answer:

Experiment to test the effect of temperature on the size of a daphnia population:

1. The hypothesis to be tested is: "Cooler temperature will reduce the size of the population due to a decrease in the reproduction rate while the hotter temperature will increase the size of the population due to an increase in the reproduction rate.

2. In all groups, daphnia will be counted weekly at the same time. The amount of water and nutrients supplies will be the same between groups. The only thing that will change is the temperature. For example:

Control group will be at 20 Celcius degrees, the cooler group will be at ten Celcius degrees, and the hotter group will be at 30 Celcius degrees.

3. The independent variable is the temperature.

4. The dependent variable (data that will be collected) is the size of the population.

Explanation:

Daphnias are microscopic crustaceans, which are called water fleas because of their saltatory behavior like fleas. Their life span and reproduction can be affected by different factors, including the abundance of predators, food, and temperature. They alternate their reproduction strategy during their life; they can reproduce asexually and sexually. Lower temperatures (cooler) decrease their metabolic and reproduction rate while higher temperature (hotter) increase their metabolic and reproduction rate. Because they can reproduce more times during their life span and the reproduction rate is higher in higher temperatures, I expect that temperature will affect the size of the population of Daphnia.