Portfolios can be used for any subject area. Google Slides offers students many options for showcasing what they know and what they have created. The example below is straight our of the Google Slides template gallery (with a few tweaks).
Some other items that could be included in a Slides portfolio:
Students can record a video from their device, upload it to Google Drive, and embed it into Google Slides
Students can take a picture of an image, writing, 3D art, etc. and import it into Google Drawings, and add labels
Share a Google Docs with a link to showcase writing
Showcase the different steps of an experiment by uploading images to your presentation
Record videos and soon MP3 and WAV audio files, upload it to Google Drive, and share the link ir insert the file into the slide. Add another recording several weeks or months later to show growth.