Okay, imagine you're trying to fill up a glass of water using a hose. You can control how much water comes out of the hose by twisting a knob. If you turn the knob just a little, only a tiny bit of water comes out and it would take a loooong time to fill your glass. If you turn the knob all the way, a lot of water comes out very quickly and you might end up spilling some.
Now, let's say you're not trying to fill a glass with water, but instead, you're trying to find out how much of a certain chemical you need to use to have a certain effect. This is where EC50 comes in.
EC50 is a measure of how much of a chemical is needed to produce a certain response in a biological system. It's like figuring out the perfect amount of water needed to fill up a glass without spilling or taking forever.
Going back to the hose example, let's say you have a plant that you want to water. You start with a tiny bit of water (like turning the knob just a little bit) and see if the plant starts growing. If it doesn't grow, you increase the amount of water until it does start growing. At some point, you find the perfect amount of water where the plant grows the most. This is like finding the EC50 for the chemical you're using.
So to summarize, EC50 is like the sweet spot where you've found the optimal amount of a chemical needed to have the desired effect in a biological system, just like finding the perfect amount of water to fill up a glass without spilling or taking forever.