Description: MIT 20.219 Becoming the Next Bill Nye: Writing and Hosting the Educational Show, IAP 2015. View the complete course: http://ocw.mit.edu/20-219IAP15.
Instructor: Nathan Hernandez
License: Creative Commons BY-NC-SA
More information at http://ocw.mit.edu/terms
More courses at http://ocw.mit.edu
Why does your fridge start to smell, and where does that icky black liquid come from? Wouldn't life just be easier if things didn't rot, if things lasted forever?
Well, maybe, but probably not. The average American household wastes about 25% of its food, and a lot of restaurants are even worse. So if we didn't have decomposition, what would happen to all the food we throw away?
Food in landfills usually gets dealt with by bacteria, protease, and fungi, who allow nutrients in the food to return to the soil and eventually other living things. These decompositions also break down other dead stuff like trees. In fact, they're pretty much the only thing that can eat wood. So even if in a world without rot, you don't have to worry about your house getting eaten by termites who rely on protease in their stomachs.
Pretty soon forests and landfills will be flooded with a lot of dead stuff. How do we avoid this problem? Well, basically in your fridge, on a forest floor, in a dumpster, almost anywhere, there are fungi, bacteria, and protease that live entirely by eating stuff. These dead things can be more or less divided into three categories-- carbohydrates, sugar and starches; lipids, think fats; and proteins like meat.
All of these are chemically different, so they each get broken down by different enzymes in different ways before being absorbed by decomposers. For example, proteases break down proteins into amino acids, the cell's building blocks. Lipids rely on lipases and carbohydrates on things like amylase and cellulases.
So how does a perfectly nice broccoli floret start giving off this foul black liquid? Fruits and vegetables are almost entirely made of water. So on the most basic level, you could say the cells are like extremely complex water balloons.
The exterior, or cell wall, is made of cellulose, a complex carbohydrate that gets broken down by enzymes into small sugars the cell can get energy from. The bacteria or fungi uses cellulase to eat the exterior of a cell, it's like if I were to pop the balloon. That's the muck you see in your fridge. What about that stink?
For fruits and vegetables, a lot of time the smell happens after the icky black liquid forms. Other bacteria that weren't involved in the initial colonization move in and start to stink everything up.
Meat get's smelly when lipases break down fat in the meat into glycerol and fatty acids to energy sources, and fatty acids are kind of gross.
And so while food rotting may smell absolutely terrible, because of it, the environment is able to recycle crucial nutrients it needs. And, well, that's why we have all this.
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