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9. euglena are single - cell organisms that live in ponds. all euglena …

Question

  1. euglena are single - cell organisms that live in ponds. all euglena have chloroplasts and can make their own food. they can also take in food from the environment. this diagram below represents a euglena.

an experiment was set up to determine the effect of nitrates, which is a type of pollutant, on the number of chloroplasts present in each euglena. five tanks were set up, each containing the same number of euglena and a different concentration of a nitrate solution: 0%, 0.5%, 1.0%, 1.5%, and 2.0%. the tanks were placed in a sunny location where they all received the same amount of light.
which statement correctly identifies a variable from this experiment?
(options are partially visible: the independent variable is the concentration of nitrate solution; the dependent variable is the number of euglena placed in the tanks; the independent variable is the amount of sunlight; the dependent variable is the number of tanks used)
(there are also some circle options with numbers 9, 10, 11, 12, 13 and a clear all button)

Explanation:

Brief Explanations

To solve this, we analyze the experiment: the independent variable is the factor changed (nitrate concentration, 0%, 0.5%, 1.0%, 1.5%, 2.0%), and the dependent variable is what’s measured (related to euglena, like chloroplast or growth, but here we check options.

  • Option 1: "The independent variable is the concentration of nitrate solution" – matches, as nitrate concentration is manipulated.
  • Option 2: Dependent variable isn’t number of euglena placed (that’s constant).
  • Option 3: Independent variable isn’t sunlight (sunlight is constant).
  • Option 4: Dependent variable isn’t number of tanks (tanks are just setups).

So the correct statement is the one identifying nitrate concentration as the independent variable.

Answer:

The independent variable is the concentration of nitrate solution (assuming this is the first option’s text; if options are labeled, e.g., A. The independent variable is the concentration of nitrate solution, then A. The independent variable is the concentration of nitrate solution)