My daughter showed me the App, Sound Uncovered which helps you discover, explore and experiment with sound. This interactive app is great to use with your sound unit. This Free App was developed by Exploratorium.
https://itunes.apple.com/us/app/sound-uncovered/id598835017?mt=8
EarthViewer is an App that helps you explore the science of earth's history. Supporting materials included are video tours and classroom ideas.
https://itunes.apple.com/us/app/earthviewer/id590208430?mt=8
WWF Together is developed by World Wildlife Fund. It consists of animal stories with activities, videos, etc. https://itunes.apple.com/us/app/wwf-together/id581920331?mt=8