Base your answer on the information below and on your knowledge of biology. euglena are single-celled organisms that live in ponds. all euglena have chloroplasts and can make their own food. they can also take in food from the environment. the diagram below represents a euglena. an experiment was set up to determine the effect of nitrates, a pollutant, on the number of chloroplasts present in euglena. five tanks were set up, each with euglena and a different concentration of nitrate solution: 0%, 0.5%, 1.0%, 1.5%, and 2.0%. the tanks were placed in a sunny location where each tank received the same amount of light. which statement correctly identifies a variable in this experiment?
a. the independent variable is the concentration of nitrate solution used.
b. the dependent variable is the number of euglena placed in the tanks.
c. the independent variable is the amount of sunlight.
d. the dependent variable is the number of tanks used.

A. The independent variable is the concentration of nitrate solution used.

Explanation:

The experiment wants to determine the effect of nitrates on number of chloroplasts in euglena. In an experiment, independent variable is controlled by the experimenter and its effect is found on the dependent variable. Value of dependent variable is expected to depend on the value of independent variable.

Since here the experimenter has fixed the concentration of nitrate solution in tanks, it is the independent variable. Its effect is being checked on number of chloroplasts in euglena so number of chloroplasts is the dependent variable. Independent variable might have a positive effect, negative effect or no effect on the dependent variable.

humans can cause extinction of a species through overharvesting, pollution, habitat destruction, introduction of invasive species (such as new predators and food competitors), overhunting, and other influences. explosive, unsustainable human population growth is an essential cause of the extinction crisis.

explanation:

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