Answer to Question 1
Applied research very often answers a specific question about behaviors in a natural setting. As such, it may be important to study behaviors in the environments in which they typically occur, rather than in a restricted and somewhat artificial atmosphere of the lab.
On the other hand, in theoretical research, investigators are frequently interested in the effect of a variable that has a consistent, but small, effect on behavior. In such a situation, it makes sense to eliminate variables that have big effects on behavior that will obscure the effects of variables that have smaller effects. One way to get rid of the larger effects of variables you aren't interested in is to control the environment very carefully, which is easiest to do in a lab.
Answer to Question 2
(a) Respondents have to work to understand a question; when motivation is low, they may not be willing to do this.
(b) Respondents have to search through memory to find relevant information, which they may not want to do.
(c) Respondents have to organize the information they recall, which also requires motivation.
(d) Respondents have to choose from among alternatives presented on a questionnaire, and they may select the first response that sounds good, without bothering to consider others.
