In an experiment, the independent variable is the one that you:
1. change or manipulate
2. hold constant throughout the entire experiment
3. measure in response to a changing variable
and
the dependent variable in an experiment is:
1. one you hold constant. the experiment depends on never changing the dependent variable.
2. one you change or manipulate. everything depends on what you do to this variable.
3. the one you measure. the dependent variable depends on how you change the independent variable.

Independent variable is that which we change or manipulate.

Explanation:

By changing the independent variable, there is a corresponding change in the dependant variable which we intend to measure.        

The dependant variable is the one you measure. The dependant variable depends on how you change the independent variable.

Explanation: For example we want to observe speed of a car change with respect to time.

Here, time is the independent variable as it has its own pace regardless of the car. However, at different instances of time , the car has different speeds. Thus, the speed of the car is the dependant variable as it depends on time.

this protocol provides a detailed procedure for co-immunoprecipitation (co-ip) to identify protein–protein interactions.