res is not defined in nodejs(Mongoose) : How can i put res in a normal function i.e not an exported one which is not part of routes.

 

        function createNewStudent(v,callBackOne){
      if (callBackOne) {
        studentInfo.callBackOneStudent = callBackOne;
      }
      // common filter json
      var filterjson = common.defaultFilterJson();
      filterjson['active'] = true;
      filterjson['email'] = v.email;
      // student initialization
      var student = new Student(v);
      async.waterfall([
        function (done) {
                student.save(function (err) {
                  if (!err) {
                   studentInfo.callBackOneStudent();
                   Employee.update({_id: student.created_by},{"$push": { "students": student._id } }).exec(function (err, employee) { });
                   done();
                  }
                });
              }
            }
          });
        },
        function (done) {
          var url = config.mailer.studentActivateUrl + student._id;
         ---error is here-----
          res.render('modules/users/server/templates/student-confirmation-email', {
            name: student.first_name + ' ' + student.last_name,
            appName: 'GAIPP',
            url: url
          }, function (err, emailHTML) {
            done(err, emailHTML, student);
          });
        }
    });

,My error is 'res' is not defined.Can anyone please help me to solve this error.Thanks.