Definition: A submicroscopic, non-cellular structure consisting of a core of DNA or RNA surrounded by a protein coat, that requires a living host cell to replicate, and often causes disease in the host organism.

Alright class, settle down, let’s dive in today, To understand something tiny, come what may! We're talking about viruses , a tricky little crew, So listen closely, it’s important for you. The dictionary gave us a description quite grand, Let’s break it down piece by piece, hand in hand. “Submicroscopic” – meaning super small and tight, Smaller than anything you can see with your sight! "Non-cellular structure," that's the key, you see, It's not a cell like ours, completely free. Inside it’s got DNA or RNA, a genetic code bright, Like instructions for making more – a marvelous sight! Wrapped around this core, a protein coat so neat, Protecting its secrets, can't be beat! But here's the important part, listen with care, A virus needs a host cell, it’s truly rare. It needs a living cell to make copies of itself, Like hitchhiking on a cell, right off the shelf! And often, my dears, this process brings woe, Because these viruses cause diseases, you know! So remember this lesson, don't be in a fright, Viruses are tiny invaders, causing quite a plight. Do you have any questions? Don’t hesitate to ask, Let’s make sure this understanding truly lasts!