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It has been previously shown that high frequency ultrasound (20 - 100 MHz) can be used to detect cellular structure changes in tissues and cell ensembles. However, the changes seen in the backscattered ultrasound intensity and frequency spectrum are not fully understood. In this paper we attempt to better understand the nature of these changes by examination of the backscatter power spectra from cell ensembles (in pellet form) that have undergone two different types of cell death: by exposure to the chemotherapeutic cisplatin and by withdrawal of nutrients (decay). Three different ultrasound transducers were used, centered at 20MHz and 40MHz. In both death pathways, an increase of the midband fit of 10-12dB was measured, and there were significant changes in the spectral slopes. Furthermore, our initial analysis of the backscatter from single cells and polystyrene microspheres demonstrates the potential of the technique to assess scatterer size.