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  • If someone called you scum,

  • you'd probably be offended,

  • but scientifically,

  • they might not be far off.

  • Have you ever thought about

  • where your food comes from?

  • You might say it comes from

  • plants, animals, or even fungi,

  • but you'd probably rather not

  • think about the rotting organisms and poop

  • that feed those plants, animals, and fungi.

  • So really, you and most of the matter in your body

  • are just two or three degrees of separation

  • from things like pond scum.

  • All species in an ecosystem,

  • from the creatures in a coral reef

  • to the fish in a lake

  • to the lions on the savannah,

  • are directly or indirectly

  • nourished by dead stuff.

  • Most of the organic matter in our bodies,

  • if we trace it back far enough,

  • comes from CO2 and water

  • through photosynthesis.

  • Plants use the energy from sunlight

  • to transform carbon dioxide and water from the environment

  • into glucose and oxygen.

  • That glucose is then transformed

  • into more complex organic molecules

  • to form leaves, stems, roots, fruit, and so on.

  • The energy stored in these organic molecules

  • supports the food chains with which we're familiar.

  • You've probably seen illustrations like this

  • or this.

  • These green food chains

  • start with living plants at their base.

  • But in real-life terrestrial ecosystems,

  • less than 10% of plant matter

  • is eaten while it's still alive.

  • What about the other 90?

  • Well, just look at the ground

  • on an autumn day.

  • Living plants shed dead body parts:

  • fallen leaves, broken branches,

  • and even underground roots.

  • Many plants are lucky enough

  • to go their whole lives without being eaten,

  • eventually dying and leaving remains.

  • All of these uneaten, undigested, and dead plant parts,

  • that 90% of terrestrial plant matter?

  • That becomes detritus,

  • the base of what we call the brown food chain,

  • which looks more like this.

  • What happens to plants

  • also happens to all other organisms up the food chain:

  • some are eaten alive,

  • but most are eaten only

  • when they're dead and rotting.

  • And all along this food chain,

  • living things shed organic matter

  • and expel digestive waste

  • before dying and leaving their remains to decay.

  • All that death sounds grim, right?

  • But it's not.

  • All detritus is ultimately consumed

  • by microbes and other scavengers,

  • so it actually forms the base of the brown food chain

  • that supports many other organisms,

  • including us.

  • Scientists are learning

  • that this detritus

  • is an unexpectedly huge energy source,

  • fueling most natural ecosystems.

  • But the interactions within an ecosystem

  • are even more complex than that.

  • What a food chain really represents

  • is a single pathway of energy flow.

  • And within any ecosystem,

  • many of these flows

  • are linked together

  • to form a rich network of interactions,

  • or food web,

  • with dead matter supporting that network at every step.

  • The resulting food web

  • is so connected

  • that almost every species

  • is no more than two degrees from detritus,

  • even us humans.

  • You probably don't eat rotting things,

  • poop, or pond scum directly,

  • but your food sources probably do.

  • Many animals we eat

  • either feed directly on detritus themselves,

  • like pork, poultry, mushrooms, shellfish,

  • or catfish and other bottom feeders,

  • or they are fed animal by-products.

  • So, if you're thinking nature is full of waste,

  • you're right.

  • But one organism's garbage is another's gold,

  • and all that rotting dead stuff

  • ultimately provides the energy that nourishes us

  • and most of life on Earth,

  • as it passes through the food web.

  • Now that's some food for thought.

If someone called you scum,

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B2 H-INT food food chain dead rotting chain scum

【TED-Ed】Dead stuff: The secret ingredient in our food chain - John C. Moore

  • 1106 6
    nckuba   posted on 2014/04/06
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