WEBVTT

00:00:00.499 --> 00:00:02.340
NATHAN: Why does your
fridge start to smell,

00:00:02.340 --> 00:00:04.740
and where does that icky
black liquid come from?

00:00:04.740 --> 00:00:07.830
Wouldn't life just be
easier if things didn't rot?

00:00:07.830 --> 00:00:09.690
If things lasted forever?

00:00:09.690 --> 00:00:11.422
Well, maybe, but probably not.

00:00:11.422 --> 00:00:13.630
According to the USDA, the
average American household

00:00:13.630 --> 00:00:16.720
wastes 25% of its food,
and a lot of restaurants

00:00:16.720 --> 00:00:17.760
are even worse.

00:00:17.760 --> 00:00:19.760
So if we didn't
have decomposition,

00:00:19.760 --> 00:00:21.790
what would happen to
the food we throw away?

00:00:21.790 --> 00:00:24.620
Food in landfills normally gets
dealt with by bacteria, fungi,

00:00:24.620 --> 00:00:27.020
and protists that allow the
nutrients in food to return

00:00:27.020 --> 00:00:30.270
to the soil, and eventually,
other living things.

00:00:30.270 --> 00:00:33.090
These decomposers also
break down other dead stuff,

00:00:33.090 --> 00:00:34.210
like trees.

00:00:34.210 --> 00:00:38.160
In fact, they're pretty much the
only thing that can eat wood.

00:00:38.160 --> 00:00:41.249
So in a world without rot,
while your home may not

00:00:41.249 --> 00:00:43.040
have to worry about
being eaten by termites

00:00:43.040 --> 00:00:44.720
who rely on protists
in their stomach,

00:00:44.720 --> 00:00:46.290
pretty soon, forests
and landfills

00:00:46.290 --> 00:00:48.950
would be flooded with
a lot of dead stuff.

00:00:48.950 --> 00:00:50.650
How do we avoid this problem?

00:00:50.650 --> 00:00:54.540
Well, basically, in your
fridge, on a forest floor,

00:00:54.540 --> 00:00:57.000
in a dumpster, almost
anywhere, there

00:00:57.000 --> 00:00:59.740
are fungi, bacteria, and
protists that live entirely

00:00:59.740 --> 00:01:00.636
by eating dead stuff.

00:01:00.636 --> 00:01:02.510
These dead things can
be more or less divided

00:01:02.510 --> 00:01:03.950
into three categories.

00:01:03.950 --> 00:01:06.180
Carbohydrates--
sugar and starches.

00:01:06.180 --> 00:01:07.660
Lipids-- think fats.

00:01:07.660 --> 00:01:09.137
And proteins, like meats.

00:01:09.137 --> 00:01:10.720
All of these are
chemically different,

00:01:10.720 --> 00:01:13.060
so they each get broken
down by different enzymes

00:01:13.060 --> 00:01:16.280
in different ways before
being absorbed by decomposers.

00:01:16.280 --> 00:01:19.260
For example, proteases
break down proteins

00:01:19.260 --> 00:01:21.820
into amino acids, the
cell's building blocks.

00:01:21.820 --> 00:01:25.320
Lipids rely on lipases,
and carbohydrates on things

00:01:25.320 --> 00:01:27.980
like amylase and cellulases.

00:01:27.980 --> 00:01:30.090
So how does a perfectly
nice broccoli floret

00:01:30.090 --> 00:01:32.590
start giving off this
foul black liquid?

00:01:32.590 --> 00:01:34.927
Fruits and vegetables are
almost entirely made of water.

00:01:34.927 --> 00:01:36.510
So, on the most basic
level, you could

00:01:36.510 --> 00:01:39.600
say that cells are like
extremely complex water

00:01:39.600 --> 00:01:40.580
balloons.

00:01:40.580 --> 00:01:42.340
The exterior, or
cell wall, is made

00:01:42.340 --> 00:01:44.360
of cellulose, a complex
carbohydrate that

00:01:44.360 --> 00:01:47.440
gets broken down by enzymes
into small sugars the cell can

00:01:47.440 --> 00:01:48.320
get energy from.

00:01:48.320 --> 00:01:50.690
When a bacteria or
fungi or uses cellulase

00:01:50.690 --> 00:01:52.890
to eat the exterior
of a cell, it's like

00:01:52.890 --> 00:01:55.030
if I were to pop the balloon.

00:01:55.030 --> 00:01:57.340
That's the muck you
see in your fridge.

00:01:57.340 --> 00:01:59.260
That's how you get
that icky black liquid.

00:01:59.260 --> 00:02:02.185
What about that stink?

00:02:02.185 --> 00:02:04.310
For fruits and vegetables,
a lot of time, the smell

00:02:04.310 --> 00:02:07.300
happens after the icky
black liquid forms.

00:02:07.300 --> 00:02:09.039
Other bacteria that
weren't involved

00:02:09.039 --> 00:02:11.269
in the initial
colonization move in

00:02:11.269 --> 00:02:13.540
and start to stink
everything up.

00:02:13.540 --> 00:02:16.690
Meat get smelly when lipases
break down fat in the meat

00:02:16.690 --> 00:02:20.060
into glycerol and fatty
acids to energy sources.

00:02:20.060 --> 00:02:22.730
And fatty acids
are kind of gross.

00:02:22.730 --> 00:02:26.750
And so while your food rotting
may smells absolutely terrible,

00:02:26.750 --> 00:02:28.920
because of it, the
environment is able to recycle

00:02:28.920 --> 00:02:30.810
crucial nutrients it needs.

00:02:30.810 --> 00:02:34.570
And, well, that's
why we have all this.