Which characteristic is seen in whales, but not in phytoplankton (cell wall, heterotrophic, unicellular, or prokaryotic? )

Hetrotrophic

The whales are large mammals which are native of sea habitat. These mammals obtain food by killing other sea animals. Hence, the whales are hetrotrophic in nature. Hetrotrophic organisms are those which organisms which cannot synthesize their own food by the process of photosynthesis, these organisms are dependent upon other organisms for their food requirements.

The phytoplanktons are small single celled organisms abundantly present in the water body, they are capable of performing photosynthesis. Therefore, they are autotrophic not hetrotrophic.  

the electromagnetic spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared, optical, ultraviolet, x-rays, and gamma-rays.