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6.1. Symbiosis as a Strategy of Survival

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生命起源

伊利诺伊大学香槟分校

4.3（66 個評分） | 9.3K 名學生已註冊

How did life emerge on Earth? How have life and Earth co-evolved through geological time? Is life elsewhere in the universe? Take a look through the 4-billion-year history of life on Earth through the lens of the modern Tree of Life! This course will evaluate the entire history of life on Earth within the context of our cutting-edge understanding of the Tree of Life. This includes the pioneering work of Professor Carl Woese on the University of Illinois Urbana-Champaign campus which revolutionized our understanding with a new "Tree of Life." Other themes include: -Reconnaissance of ancient primordial life before the first cell evolved -The entire ~4-billion-year development of single- and multi-celled life through the lens of the Tree of Life -The influence of Earth system processes (meteor impacts, volcanoes, ice sheets) on shaping and structuring the Tree of Life This synthesis emphasizes the universality of the emergence of life as a prelude for the search for extraterrestrial life.

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4.3（66 個評分）

5 stars
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CG

Mar 16, 2019

Enjoyed every minute of the course and learned so much at the same time!

SZ

Apr 11, 2017

Excellent lectures. Personal transformation observed while watching.

從本節課中

Week 6 - Mesozoic Reign of the Dinosaurs and the Development of Flight

This week, you'll learn more about the Permian-Triassic extinction event, which caused more than 80% of life to go extinct. This opened vast swaths of ecological opportunity for radiation and diversification of life during the Mesozoic. You'll learn about symbiosis, which was widely utilized during this period, as well as the fascinating lineage of diapsid reptiles that rose to replace the synapsid predators of the late Paleozoic. We'll also discuss the rise of the dinosaurs, as well as the catastrophic meteor impact that drove the dinosaurs to extinction.

6.1. Symbiosis as a Strategy of Survival5:40

6.2. Rise of the Diapsids13:53

6.3. Pterosaurs: The ONLY Flying Reptiles4:37

6.4. Dinosaur Phylogeny: Hips Don't Lie7:06

6.5. Evolution of Flight: Life Invades the Sky6:09

6.6. Wild Wings: Fit to Fly10:46

6.7. Cretaceous Warming on a Reorganized Earth8:11

6.8. T. rex, and the Crater of Doom11:48

教學方

Bruce W. Fouke, Ph.D.
Director of the Roy J. Carver Biotechnology Center

腳本

[MUSIC]

I'm Bruce Fouke from the University of Illinois.

Can you imagine if you got hungry that all you had to do would be to walk outside,

put your arms out and let the sun's rays hit your skin and provide you with food.

Well, that would solve a lot of world problems.

We're not there yet, but actually corals have

approached their lifestyle of getting food from oceans in a very similar way.

After the permeantracic meteor impact, one very successful strategy that was

developed in evolution biology on this planet,

is that some organisms invaded other organisms.

In other words, the cells of some organisms

moved inside the tissue structure and in the host of other organism.

One of the best examples of this is when plant like organisms

called zooxanthellae invaded the tissues of corals.

Now, when this happened they remained like zooxanthellae but the actual physical cell

moved into the outer surface of the coral tissue itself.

So when we look at these corals in a histological cross section,

shine transmittent light through them to look at the ultrastructure of the tissue

itself, we can see these small, round cells called zooxanthellae that

are happily dwelling within the tissues of the coral, which is an animal.

Therefore we have a relationship that's very close.

Both organisms get something out of it called symbiosis.

And in the end the morphology of the coral will shift and change so it helps

the algo like dinoflagellate actually be successful and that's the reason

that corals have this polyp shape and resemble at some level plants themselves.

Sharing and getting along with people, and actually doing things collectively is

a very, critically important aspect of surviving.

We often think of survival as being the person with the biggest gun and

the biggest truck and the strongest person,

and that's not really how evolutionary biology works.

It's really collective cooperation and the coral cooperation with these algae has

set a benchmark in evolutionary biology for how to successfully evolve and

maintain a healthy lifestyle within environments that can be somewhat

difficult when zooxanthellae invaded the tissues of corals, they established

a relationship that was good both for the zooxanthellae and for the coral itself.

We call that a symbiotic relationship, where both organisms get something very

powerful and very positive out of that interaction.

So the symbiosis for the coral in relationship to the zooxanthellae is that

the coral first of all gets an additional food source.

It can eat some of the sugars that are produced by the zooxanthellae, but

actually can eat some of the zooxanthellae as well.

Another thing the coral gets from the zooxanthellae is

the product of their photosynthetic reactions produces oxygen.

So as an animal the coral needs to use oxygen to respire.

What does the zooxanthellae plant like organism get out of it?

They have the ability to have a safe place to live.

They invade the tissues of the coral, and

the coral provides a substrate where the algae like zooxanthellae can live.

The other thing that the coral provides for

the zooxanthellae [COUGH] is the CO2 that they respire.

Since the zooxanthellae is a plant, they can photosynthesize, and

therefore they combine CO2 with sunlight to produce the sugars and

other materials within their cells as well as oxygen.

[COUGH] So that drives the symbiotic relationship.

Now corals are remarkable because utilizing and leveraging upon

the symbiosis, they actually have four different means by which they can eat.

The first one is that they can extend their tentacles out into the water and

feed from particles that are floating in the water.

Another end member of that is there is dissolved organic matter

that's available in sea water and

it can actually just absorb the dissolved organic matter into their tissues.

That'd be like us sticking our arm into a bathtub that was full of dissolved soup

and be able to absorb the soup up through our arm.

Another strategy they can use is they can eat the sugars that are produced by

the zooxanthellae or they can eat the zooxanthellae themselves.

And the fourth one is that corals are able to produce immense volumes of mucous.

They produce so much mucous that it sluffs off the skeleton and

will float through the water calm.

Now if things get really tough for

the corals they have the ability to eat their own mucous.

Therefor they produce the mucus as a protective layer for the environment, but

then again if the environment it gets tough and they run out of food they can

actually reconsume some of that organic matter that's trapped up in the mucus.

In fact corals make so much mucus that there are parrot fish they have a large

parrot shaped jaw they're upwards of a half meter in size and

the parrot fish, one of the ways they make a living is they go around and

they suck the mucus off the top of the coral and store it in their stomach.

And then at night to protect themselves, they vomit the mucus out and

they engulf their entire body in a basketball sized bale of mucous.

So if you're diving on the sea floor at night it's not uncommon to see these

very weird large ball-like shapes that have a fish-like structure

in the middle of them and that's simply coral mucus that's being

borrowed by the fish to protect them as they sleep during the night.

[MUSIC]

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