Is the following question testable? "How do plants grow?"

Is the following a testable question: How does changing the amount of sunlight affect the growth of daffodils?

What is the independent variable for the following question: "What is the effect of different amounts of oxygen on the rate of yeast growth?"

What is the manipulated variable for the following question: "How does temperature change the number of times a cricket chirps?"

What is the dependent variable in the following: An entomologist wants to determine if temperature changes how many times a cricket chirps.