Both Panasonic FZ35 and Nikon D90 have 12.0 MP resolution sensors but Panasonic FZ35's sensor is 1/2.3-inch (6.08 x 4.56 mm ) and Nikon D90's sensor is APS-C (23.6 x 15.8 mm ).
Since Nikon D90's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Panasonic FZ35.
Below you can see the FZ35 and D90 sensor size comparison.
As seen above, Nikon D90 has a 13.5x Larger sensor area than Panasonic FZ35. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.