Question

which of the following were the independent variables in experiment 2?
i. temperature
ii. plant type
iii. $\ce{no3-}$ uptake
iv. $\ce{nh4+}$ uptake
a i only
b i and ii
c ii and iii
d iii and iv

Explanation:

In an experiment, independent variables are factors that are manipulated or controlled to observe their effect on dependent variables (measured outcomes). \( \text{NO}_3^- \) uptake (III) and \( \text{NH}_4^+ \) uptake (IV) are likely dependent variables (measured responses), while Temperature (I) and Plant Type (II) are factors that could be manipulated (independent variables). Wait, no—wait, actually, in typical plant nutrient uptake experiments, independent variables are what we change (like temperature, plant type), and dependent are what we measure (uptake of nutrients). Wait, but the options: let's re-express. Wait, the question is about Experiment 2 (though details of Experiment 2 aren't given, but from standard definitions: independent variables are manipulated. So if III and IV are uptake (measured), they are dependent. So independent would be I (Temperature) and II (Plant Type)? But the options: Option B is I and II. Wait, no—wait, maybe I got it wrong. Wait, no, the options: A is I only, B is I and II, C is II and III, D is III and IV. Wait, no—wait, dependent variables are the ones being measured (like uptake), so independent are the ones we control (temperature, plant type). So the independent variables would be I and II, so Option B? Wait, no, maybe the experiment's context: but since the options include III and IV as uptake (dependent), so independent are I and II. So the correct answer is B.

Answer:

B. I and II