What is the biggest single-celled organism? - Murry Gans
-
0:07 - 0:11The elephant is a creature
of epic proportions, -
0:11 - 0:16and yet it owes its enormity to more
than 1,000 trillion microscopic cells, -
0:16 - 0:19and on the epically small end of things,
-
0:19 - 0:22there are likely millions
of unicellular species, -
0:22 - 0:25yet there are very few we can see
with the naked eye. -
0:25 - 0:27Why is that?
-
0:27 - 0:29Why don't we get unicellular elephants,
-
0:29 - 0:30or blue whales,
-
0:30 - 0:32or brown bears?
-
0:32 - 0:35To find out, we have to peer into
a cell's guts. -
0:35 - 0:38This is where most
of the cell's functions occur, -
0:38 - 0:40enclosed by a cellular membrane
-
0:40 - 0:44that acts as the doorway into
and out of the cell. -
0:44 - 0:46Any resources the cell needs to consume,
-
0:46 - 0:49or waste products it needs to expel,
-
0:49 - 0:51first have to pass through this membrane.
-
0:51 - 0:54But there's a biological quirk
in this set up. -
0:54 - 0:58A cell's surface and volume increase
at different rates. -
0:58 - 1:01Cells come in many shapes,
-
1:01 - 1:05but imagining them as cubes will make
the math easy to calculate. -
1:05 - 1:07A cube has six faces.
-
1:07 - 1:12These represent the cell membrane,
and make up its surface area. -
1:12 - 1:15A cube measuring one micrometer
on each side, -
1:15 - 1:17that's one millionth of a meter,
-
1:17 - 1:21would have a total surface area
of six square micrometers. -
1:21 - 1:24And its volume would be
one cubic micrometer. -
1:24 - 1:26This would give us six units
of surface area -
1:26 - 1:29for every single unit of volume,
-
1:29 - 1:31a six to one ratio.
-
1:31 - 1:35But things change dramatically
if we make the cube ten times bigger, -
1:35 - 1:38measuring ten micrometers on each side.
-
1:38 - 1:42This cell would have a surface area
of 600 square micrometers -
1:42 - 1:46and a volume of one thousand
cubic micrometers, -
1:46 - 1:48a ratio of only .6 to one.
-
1:48 - 1:53That's less than one unit of surface area
to service each unit of volume. -
1:53 - 1:58As the cube grows, its volume increases
much faster than its surface area. -
1:58 - 2:02The interior would overtake the membrane,
-
2:02 - 2:08leaving too little surface area for things
to quickly move in and out of the cell. -
2:08 - 2:14A huge cell would back up with waste
and eventually die and disintegrate. -
2:14 - 2:18There's another plus to having multitudes
of smaller cells, too. -
2:18 - 2:23It's hardly a tragedy if one gets
punctured, infected, or destroyed. -
2:23 - 2:26Now, there are some
exceptionally large cells -
2:26 - 2:29that have adapted to cheat the system,
-
2:29 - 2:31like the body's longest cell,
-
2:31 - 2:35a neuron that stretches from the base
of the spine to the foot. -
2:35 - 2:38To compensate for its length,
it's really thin, -
2:38 - 2:40just a few micrometers in diameter.
-
2:40 - 2:44Another example can be found
in your small intestine, -
2:44 - 2:47where structures called villi
fold up into little fingers. -
2:47 - 2:52Each villus is made of cells with highly
folded membranes -
2:52 - 2:57that have tiny bumps called microvilli
to increase their surface area. -
2:57 - 3:00But what about single-celled organisms?
-
3:00 - 3:05Caulerpa taxifolia, a green algae
that can reach 30 centimeters long, -
3:05 - 3:10is believed to be the largest
single-celled organism in the world -
3:10 - 3:13thanks to its unique biological hacks.
-
3:13 - 3:16Its surface area is enhanced with
a frond-like structure. -
3:16 - 3:21It uses photosynthesis to assemble
its own food molecules -
3:21 - 3:23and it's coenocytic.
-
3:23 - 3:26That means it's a single cell
with multiple nuclei, -
3:26 - 3:31making it like a multicellular organism
but without the divisions between cells. -
3:31 - 3:35Yet even the biggest unicellular organisms
have limits, -
3:35 - 3:40and none grows nearly as large
as the elephant, whale, or bear. -
3:40 - 3:44But within every big creature
are trillions of minuscule cells -
3:44 - 3:47perfectly suited in all their tininess
-
3:47 - 3:50to keeping the Earth's giants
lumbering along.
- Title:
- What is the biggest single-celled organism? - Murry Gans
- Description:
-
View full lesson: http://ed.ted.com/lessons/what-is-the-biggest-single-celled-organism-murry-gans
The elephant is a creature of epic proportions — and yet, it owes its enormity to more than 1,000 trillion microscopic cells. And on the epically small end of things, there are likely millions of unicellular species, yet there are very few we can see with the naked eye. Why is that? Why don’t we get unicellular elephants? Or blue whales? Or brown bears? Murry Gans explains.
Lesson by Murry Gans, animation by Zedem Media.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 04:07
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