Factors affecting reaction rates

WEBVTT
Kind: captions
Language: en

00:00:00.380 --> 00:00:01.610
- [Instructor] There are several factors

00:00:01.610 --> 00:00:04.140
that can affect the rate of a reaction.

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One factor is the
concentration of a reactant.

00:00:08.640 --> 00:00:10.400
Most chemical reactions proceed faster

00:00:10.400 --> 00:00:14.290
when the concentration of one
of the reactants is increased.

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For example, let's look at
the reaction of solid zinc

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with hydrochloric acid to
form an aqueous solution

00:00:19.810 --> 00:00:23.430
of zinc chloride and hydrogen gas.

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Let's say we put a piece of zinc metal.

00:00:25.860 --> 00:00:29.970
So go ahead and draw in the
piece of zinc metal in here

00:00:29.970 --> 00:00:34.970
in a flask that contains
three molar hydrochloric acid.

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So in our flask here, we have three molar,

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a solution of three
molar hydrochloric acid.

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As the reaction proceeds,
hydrogen gas is formed.

00:00:45.670 --> 00:00:47.890
So we could monitor the
rate of this reaction

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by observing the amount
of hydrogen gas bubbles

00:00:51.250 --> 00:00:53.280
that are coming out of the flask.

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Let's say that we repeat the experiment.

00:00:54.954 --> 00:00:58.400
This time instead of using
three molar hydrochloric acid

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we're gonna use six
molar hydrochloric acid.

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So we've increased the concentration

00:01:04.471 --> 00:01:08.520
of our hydrochloric acid solution.

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This time, when we add
our piece of solid zinc

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to our six molar
hydrochloric acid solution,

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we would observe more hydrogen gas bubbles

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coming out of our flask.

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So we have increased the concentration

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of one of our reactants hydrochloric acid.

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And we've observed an increase
in the rate of the reaction.

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As the concentration of
hydrochloric acid increases,

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there are more acid particles to collide

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with the piece of zinc.

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And therefore, as the concentration

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of hydrochloric acid goes up,

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the frequency of collisions increase

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and the rate of the reaction increases.

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Let's use the same reaction

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to talk about another factor

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that affects the rate of reaction.

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And that factor is surface area.

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You've already reacted
a piece of solid zinc

00:02:01.704 --> 00:02:03.050
with hydrochloric acid.

00:02:03.050 --> 00:02:05.973
We could use three molar
hydrochloric acid again.

00:02:05.973 --> 00:02:09.029
And we saw some bubbles come
off of the piece of zinc

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indicating that hydrogen gas was produced.

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This time let's try
breaking the piece of zinc

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into smaller pieces.

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So instead of using one
large piece of zinc,

00:02:19.200 --> 00:02:22.323
here we have a bunch of
small pieces of zinc.

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And if we were to do the experiment again,

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with three molar hydrochloric acid,

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this time we would see more
bubbles of hydrogen gas

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coming off of those small pieces of zinc.

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So we have increased the
surface area of the solid

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and we observed an increase
in the rate of the reaction.

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When we had only one piece of zinc,

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the rate of the reaction was limited

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by the surface area of this one piece.

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Therefore by breaking it
up into smaller pieces,

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we were able to the rate of the reaction.

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Temperature is another factor

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that can affect the rate of a reaction.

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So let's say on the left,
we have a glow stick

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in a flask that contains some cold water.

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And the glow stick,

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let's say the glow stick
is already glowing here.

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So let's draw in this color
here for our glow stick.

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The glow from a glow stick

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comes from a chemical reaction.

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And if we were to
increase the temperature,

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so let's say we heated
this flask on the left.

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So we increase the temperature.

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We would observe the glow to get stronger.

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So let's go ahead and draw in here,

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a more vibrant glow coming
from our glow stick.

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So increasing the temperature

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must have increased the
rate of the reaction.

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The reason increasing the temperature

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increases the rate of
the reaction in general,

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is because increase in temperature means

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the molecules are moving faster.

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And therefore the molecules
are colliding with each other

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with greater frequency
and with greater force

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which increases the rate of the reaction.

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The catalyst is another factor

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that can affect the rate of a reaction.

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Let's look at the balanced
equation for the decomposition

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of hydrogen peroxide, which
turns into water and oxygen.

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And let's say in our flask on the left,

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we have a solution of hydrogen peroxide.

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The hydrogen peroxide is
decomposing at room temperature,

00:04:24.902 --> 00:04:27.172
but the reaction proceeds so slowly

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that we don't see it even happening.

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We can speed up the reaction
by adding a catalyst.

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Let's say we have an aqueous
solution of potassium iodide

00:04:39.660 --> 00:04:41.376
in our beaker here.

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And we pour the solution
of potassium iodide

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into our flask containing
the hydrogen peroxide.

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The addition of the
iodide ion as a catalyst,

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causes the decomposition
of hydrogen peroxide

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to occur very quickly.

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And we would see a huge plume of gas

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come out of the reaction flask.

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So the addition of a catalyst,

00:05:07.030 --> 00:05:10.095
in this case it was the iodide, an ion,

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increased the rate of the reaction.

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A catalyst increases the rate of reaction

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by effecting the kinds of collisions

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that occur between particles.

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And a catalyst increases
the rate of reaction

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without being used up.


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Human impacts on ecosystems

WEBVTT
Kind: captions
Language: en

00:00:00.570 --> 00:00:01.750
- [Instructor] What
we're going to talk about

00:00:01.750 --> 00:00:04.030
in this video is how human activity

00:00:04.030 --> 00:00:06.260
creates changes in the environment.

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And not just any changes,

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but changes that can disrupt an ecosystem.

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And it can threaten the very
existence of some species.

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And for the sake of this video,

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we'll think about it in
five different dimensions.

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The first is habitat destruction.

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So this over here is a
picture of some trees

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that have clearly been cut down.

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And there's many reasons why trees

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could be cut down like this.

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One could be maybe
there's some logging here,

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and we human beings, we do need wood.

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Maybe it's being cleared for agriculture,

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which we also need.

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But when you do that, it's
clearly eliminating the trees

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and many animals, many
different types of species,

00:00:45.840 --> 00:00:49.950
were probably living in or
amongst or on those trees.

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And if you do too much of that

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they might not have anywhere to live,

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or they might not have
enough places to live

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to really thrive.

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Now, another form of anthropogenic changes

00:01:01.510 --> 00:01:06.510
or changes induced by human
activity would be pollution.

00:01:06.710 --> 00:01:09.620
This right over here,
you can see the exhaust,

00:01:09.620 --> 00:01:12.070
so to speak, from a
coal-fired power plant.

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And that is polluting the air.

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harmful chemicals are being released,

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including greenhouse gases.

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And that's going to have other effects

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above and beyond just making
the air less pleasant.

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But pollution isn't just about

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harmful chemicals going into the air.

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It could be about harmful
chemicals going into the water,

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could be runoff from irrigation,

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or some other type of chemical.

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You could even have noise pollution.

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And you might think of
that as an annoyance,

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but it can actually disrupt
how certain animals behave.

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In fact, it could raise the stress level,

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which can change the biology
of animals in subtle,

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but important ways.

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Another dimension in which we humans

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are affecting ecosystems
is by introducing species

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to places where they might
not have been before,

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especially what's often
called invasive species.

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So this is a picture here of nutria,

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oftentimes referred to as nutria rats.

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I was born and raised in Louisiana,

00:02:07.560 --> 00:02:10.230
and there are many nutria in Louisiana,

00:02:10.230 --> 00:02:11.850
and they did not come from Louisiana.

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They came originally from South America.

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They were brought to the Gulf Coast,

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to the Southern United
States, for their firs.

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The demand for their firs did not keep up,

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and these nutria escaped
and now they are everywhere.

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And you might just, once again,
view that as an annoyance,

00:02:27.686 --> 00:02:30.855
but they start overpowering other species.

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They are competing with other
animals for the same food,

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for the same niche in the ecosystem.

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Nutria are also infamous
for eating the plants

00:02:39.580 --> 00:02:43.120
that hold together the
soil and the wetlands.

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And so the more that they do that

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the more that that soil gets eroded.

00:02:47.280 --> 00:02:50.820
And then you have issues
like habitat destruction.

00:02:50.820 --> 00:02:54.530
You have fewer wetlands for other species.

00:02:54.530 --> 00:02:59.500
Now another dimension
is over-exploitation.

00:02:59.500 --> 00:03:02.220
So this is a picture here
of what's known as trawling,

00:03:02.220 --> 00:03:06.190
where you take a big boat
and you have this huge net,

00:03:06.190 --> 00:03:08.670
and you just, the boat goes while the net

00:03:08.670 --> 00:03:10.790
is just grabbing all
the fish in the water.

00:03:10.790 --> 00:03:13.300
And these dots here are all fish.

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And actually it goes, extends out here,

00:03:15.130 --> 00:03:18.460
'cause the net is bulging
outward like that.

00:03:18.460 --> 00:03:21.050
And you can see it's a
very efficient method

00:03:21.050 --> 00:03:25.080
of getting fish, but you could over fish.

00:03:25.080 --> 00:03:27.430
If you take too many
fish out of the ocean,

00:03:27.430 --> 00:03:29.500
you're not going to
have enough to reproduce

00:03:29.500 --> 00:03:31.240
and keep the population going.

00:03:31.240 --> 00:03:33.770
And even though you might
get a lot of cheap fish

00:03:33.770 --> 00:03:35.850
very efficiently in the short-term,

00:03:35.850 --> 00:03:38.370
in the long-term the fish might go away.

00:03:38.370 --> 00:03:39.630
All of these, as you can imagine,

00:03:39.630 --> 00:03:40.810
connect in many ways.

00:03:40.810 --> 00:03:43.210
And a fifth dimension we could talk about,

00:03:43.210 --> 00:03:45.740
although it's very related to pollution

00:03:45.740 --> 00:03:49.600
and even deforestation, is climate change.

00:03:49.600 --> 00:03:51.110
And the climate change that we are

00:03:51.110 --> 00:03:52.810
most familiar with right now

00:03:52.810 --> 00:03:55.840
is this notion of global warming,

00:03:55.840 --> 00:03:59.150
which is occurring as
we have rising levels

00:03:59.150 --> 00:04:01.930
of greenhouse gases, like CO2.

00:04:01.930 --> 00:04:04.250
And those could be
released from things like

00:04:04.250 --> 00:04:07.890
this coal-fired power plant
that we saw a few minutes ago.

00:04:07.890 --> 00:04:10.410
But there's many other
sources of things like CO2

00:04:10.410 --> 00:04:12.520
and there's other greenhouse gases.

00:04:12.520 --> 00:04:15.130
But as we human beings
release more and more of this

00:04:15.130 --> 00:04:18.090
into the atmosphere,
these greenhouse gases

00:04:18.090 --> 00:04:20.700
trap more and more heat, and that,

00:04:20.700 --> 00:04:24.600
over the longterm, increases
average global temperatures.

00:04:24.600 --> 00:04:26.570
And that doesn't just affect temperature.

00:04:26.570 --> 00:04:28.910
When you affect temperature,
it can affect rainfall.

00:04:28.910 --> 00:04:30.410
It can affect wind patterns.

00:04:30.410 --> 00:04:32.980
And as we see in this picture over here,

00:04:32.980 --> 00:04:36.280
it can affect things like the
amount of sea ice we have.

00:04:36.280 --> 00:04:39.930
Because if, on average, global
temperatures are increasing,

00:04:39.930 --> 00:04:42.200
then water temperatures
could be increasing,

00:04:42.200 --> 00:04:44.080
then you have more melting sea ice

00:04:44.080 --> 00:04:46.140
in both the Arctic and Antarctic.

00:04:46.140 --> 00:04:47.490
And then, for example,

00:04:47.490 --> 00:04:50.020
in the Arctic where you have polar bears,

00:04:50.020 --> 00:04:53.020
they would have less ice to
be on when they're hunting

00:04:53.020 --> 00:04:54.450
the walruses or the seals,

00:04:54.450 --> 00:04:56.880
or frankly just ice to be on to rest

00:04:56.880 --> 00:04:59.310
from swimming in the water.

00:04:59.310 --> 00:05:01.270
And that melting ice also can contribute

00:05:01.270 --> 00:05:02.700
to rising sea levels.

00:05:02.700 --> 00:05:04.100
And it's not just the melting ice

00:05:04.100 --> 00:05:06.070
that's contributing to rising sea levels.

00:05:06.070 --> 00:05:08.240
It's also that water has different density

00:05:08.240 --> 00:05:09.460
at different temperatures.

00:05:09.460 --> 00:05:12.430
And so as you have that rising sea levels,

00:05:12.430 --> 00:05:15.220
that affects ecosystems around the planet,

00:05:15.220 --> 00:05:17.480
especially ecosystems close to the water.

00:05:17.480 --> 00:05:18.960
And one of the species that is

00:05:18.960 --> 00:05:21.070
most impacted by that is human beings.

00:05:21.070 --> 00:05:23.800
Most human beings actually live very close

00:05:23.800 --> 00:05:26.720
to sea level near a body of water.

00:05:26.720 --> 00:05:28.940
So as those sea levels rise

00:05:28.940 --> 00:05:30.980
they will have a very profound impact

00:05:30.980 --> 00:05:34.363
on a lot of animals, but
especially human beings.


K selected and r selected population growth strategies

WEBVTT
Kind: captions
Language: en

00:00:00.220 --> 00:00:01.460
- [Narrator] What we're
going to do in this video

00:00:01.460 --> 00:00:04.290
is talk about different
population growth strategies

00:00:04.290 --> 00:00:05.410
for different species.

00:00:05.410 --> 00:00:06.570
And think about if we can come up

00:00:06.570 --> 00:00:08.820
with a broad categorization

00:00:08.820 --> 00:00:10.990
or if there's a broad
categorization already

00:00:10.990 --> 00:00:12.630
out there for us.

00:00:12.630 --> 00:00:15.530
So, we see that there are
species like elephants

00:00:15.530 --> 00:00:17.203
that are long lived,

00:00:18.730 --> 00:00:19.820
in the wild.

00:00:19.820 --> 00:00:22.800
An African elephant can
live roughly as long

00:00:22.800 --> 00:00:26.900
as a human being can 50, 60,
70, in some cases, 80 years.

00:00:26.900 --> 00:00:29.130
You also have things like killer whales

00:00:29.130 --> 00:00:30.920
that are also long lived.

00:00:30.920 --> 00:00:32.560
You have things like human beings that

00:00:32.560 --> 00:00:34.630
live a pretty good long time compared

00:00:34.630 --> 00:00:36.500
to other things in nature.

00:00:36.500 --> 00:00:39.190
You have things like gorillas
that are also reasonably long

00:00:39.190 --> 00:00:41.600
lived, live many, many, many decades.

00:00:41.600 --> 00:00:44.120
Now there's also other
patterns that you see

00:00:44.120 --> 00:00:45.793
on these large mammals.

00:00:46.974 --> 00:00:48.423
They tend to be large.

00:00:49.290 --> 00:00:50.940
Especially, if you think about compared

00:00:50.940 --> 00:00:53.740
to very small things
in the animal kingdom.

00:00:53.740 --> 00:00:57.330
They tend to not have a lot of children

00:00:57.330 --> 00:00:59.760
every reproductive event,
I guess you could say

00:00:59.760 --> 00:01:00.900
at every time they give birth.

00:01:00.900 --> 00:01:04.683
So few few children,

00:01:05.630 --> 00:01:07.110
children

00:01:07.110 --> 00:01:10.810
at a time

00:01:10.810 --> 00:01:13.480
And it takes them a while to
give birth to those children.

00:01:13.480 --> 00:01:16.040
And then they take care
of them for a while.

00:01:16.040 --> 00:01:18.500
Now, the other end of the
spectrum, you have some

00:01:18.500 --> 00:01:19.910
of the things that we have here.

00:01:19.910 --> 00:01:24.310
You have amphibians like
frogs, you have insects.

00:01:24.310 --> 00:01:28.170
You could imagine small
fish, bacteria, mosquitoes

00:01:28.170 --> 00:01:30.210
that are more short-lived.

00:01:30.210 --> 00:01:31.090
Short

00:01:32.600 --> 00:01:33.433
lived.

00:01:34.766 --> 00:01:36.823
They tend to be smaller.

00:01:39.080 --> 00:01:42.180
And they tend to have a
lot of children at a time.

00:01:42.180 --> 00:01:45.850
So lots of children

00:01:47.610 --> 00:01:49.890
at a time.

00:01:49.890 --> 00:01:53.000
Just an example, a frog
or what do you see here

00:01:53.000 --> 00:01:56.390
is this is a spiders
coming out of an egg sack.

00:01:56.390 --> 00:01:58.430
Frogs or spiders,

00:01:58.430 --> 00:02:02.660
they can lay in many cases,
thousands of eggs at a time.

00:02:02.660 --> 00:02:05.510
And they're not really dependent
on any one of those eggs,

00:02:05.510 --> 00:02:06.870
necessarily surviving.

00:02:06.870 --> 00:02:08.990
Many of them will be
killed off by predators

00:02:08.990 --> 00:02:12.130
but as long as a few survive
then the next generation,

00:02:12.130 --> 00:02:14.110
you can imagine, they get to reproduction

00:02:14.110 --> 00:02:16.250
and then they'll lay thousands of eggs.

00:02:16.250 --> 00:02:18.070
And they're shorter lived.

00:02:18.070 --> 00:02:20.430
A frog could live a few years.

00:02:20.430 --> 00:02:23.650
Some insects might live
anywhere from a few days

00:02:23.650 --> 00:02:25.290
to a few years.

00:02:25.290 --> 00:02:27.040
You have things like
bacteria that can have

00:02:27.040 --> 00:02:29.460
an even shorter life span.

00:02:29.460 --> 00:02:32.690
So, when biologists or
ecologists look at this, they say

00:02:32.690 --> 00:02:35.920
it looks like there is
a spectrum over here.

00:02:35.920 --> 00:02:39.410
You have these large long-lived animals

00:02:39.410 --> 00:02:41.380
that have a few children at a time.

00:02:41.380 --> 00:02:44.900
And really the limiting
factor on their population

00:02:44.900 --> 00:02:47.610
is how dense their population is.

00:02:47.610 --> 00:02:49.810
At some point, these
animals are going to compete

00:02:49.810 --> 00:02:51.720
for resources with each other.

00:02:51.720 --> 00:02:53.630
And that's true of
things like human beings.

00:02:53.630 --> 00:02:55.720
And the other end, you have these things

00:02:55.720 --> 00:03:00.150
like spiders or frogs,
instead might be limited

00:03:00.150 --> 00:03:02.620
on their reproduction
by environmental factors

00:03:02.620 --> 00:03:07.490
like how moist or dry it
is, how hot or cold it is.

00:03:07.490 --> 00:03:10.970
And so generally speaking
folks have attempted

00:03:10.970 --> 00:03:14.100
to classify these types of species.

00:03:14.100 --> 00:03:15.780
They call them K selected.

00:03:15.780 --> 00:03:18.950
I'll talk about where the
K comes from in a second.

00:03:18.950 --> 00:03:23.633
And they talk about these
types of species as R selected.

00:03:24.530 --> 00:03:26.810
And where these letters come from,

00:03:26.810 --> 00:03:29.490
is there, there's a general idea that

00:03:29.490 --> 00:03:32.390
if we draw a little axis here, time

00:03:32.390 --> 00:03:35.750
and then draw up axis here, population

00:03:35.750 --> 00:03:38.650
on the vertical axis, most species that

00:03:38.650 --> 00:03:40.790
when there's not a lot of
them, and they're not limited

00:03:40.790 --> 00:03:45.610
by resources they will grow
exponentially like this.

00:03:45.610 --> 00:03:46.960
Now, when you go into the math of it,

00:03:46.960 --> 00:03:50.080
that rate of growth is usually
denoted by the letter R,

00:03:50.080 --> 00:03:52.550
and you could see where this
R selected is coming from.

00:03:52.550 --> 00:03:56.110
And what that R is how
large it is is determined

00:03:56.110 --> 00:03:59.480
by a species biotic potential.

00:03:59.480 --> 00:04:04.070
And biotic potential just
means in a given environment,

00:04:04.070 --> 00:04:05.630
how quickly can they reproduce?

00:04:05.630 --> 00:04:08.510
What percentage of those
are able to get to maturity

00:04:08.510 --> 00:04:11.010
so that they can reproduce,
et cetera, et cetera.

00:04:11.010 --> 00:04:13.500
And so you could imagine the higher the R,

00:04:13.500 --> 00:04:17.190
the faster this
exponential growth goes up.

00:04:17.190 --> 00:04:21.040
Now, at some point you're going
to be resource constrained.

00:04:21.040 --> 00:04:23.860
And some there's some carrying capacity.

00:04:23.860 --> 00:04:26.310
And so let's say this is
the carrying capacity here,

00:04:26.310 --> 00:04:27.620
and let's call that K.

00:04:27.620 --> 00:04:30.780
And the reason why we use
K instead of C is K comes

00:04:30.780 --> 00:04:33.860
from a word for capacity in German.

00:04:33.860 --> 00:04:37.300
So, at some point you're
gonna have so many things

00:04:37.300 --> 00:04:39.100
that you're not gonna
have enough resources

00:04:39.100 --> 00:04:39.970
to support more.

00:04:39.970 --> 00:04:42.510
And so your population would flatten out

00:04:42.510 --> 00:04:44.180
something like this.

00:04:44.180 --> 00:04:48.520
And so, generally speaking
biologists have categorized

00:04:48.520 --> 00:04:52.644
these left categories of
species as K selected.

00:04:52.644 --> 00:04:55.920
The amount that you have,
the amount of population

00:04:55.920 --> 00:04:58.920
is going to be determined by
the resources that are there,

00:04:58.920 --> 00:05:01.250
the carrying capacity in the environment,

00:05:01.250 --> 00:05:04.430
while things like frogs
and mosquitoes and bacteria

00:05:04.430 --> 00:05:07.370
and spiders, you view more as R selected.

00:05:07.370 --> 00:05:11.450
They're gonna grow exponentially
at their biotic potential,

00:05:11.450 --> 00:05:14.030
but that biotic potential
is gonna be determined

00:05:14.030 --> 00:05:16.180
by how hot or cold or wet or dry

00:05:16.180 --> 00:05:17.700
or other environmental factors.

00:05:17.700 --> 00:05:20.060
They're not gonna get
to such a high density,

00:05:20.060 --> 00:05:23.040
that they're really
competing with each other.

00:05:23.040 --> 00:05:26.120
Now, as you can imagine
with most categorizations,

00:05:26.120 --> 00:05:29.420
nature is not that clean
that things are always going

00:05:29.420 --> 00:05:31.180
to be on the left side, or always gonna

00:05:31.180 --> 00:05:32.370
be on the right side.

00:05:32.370 --> 00:05:35.100
For example, things like
turtles, lay a lot of eggs

00:05:35.100 --> 00:05:37.740
but they live a very long time.

00:05:37.740 --> 00:05:41.210
It's also worth noting that
there's no value judgment

00:05:41.210 --> 00:05:43.860
that one strategy is
better than the other.

00:05:43.860 --> 00:05:45.230
They've both been successful.

00:05:45.230 --> 00:05:47.120
The fact that these species exist today,

00:05:47.120 --> 00:05:49.210
show that they have worked well.

00:05:49.210 --> 00:05:52.030
It is worth noting that
invasive species tend

00:05:52.030 --> 00:05:53.810
to be more R selected.

00:05:53.810 --> 00:05:55.540
They will just grow and grow and grow,

00:05:55.540 --> 00:05:58.430
and gonna be limited by the
environment and not as much

00:05:58.430 --> 00:05:59.730
by each other.

00:05:59.730 --> 00:06:02.570
While K selected species
are often the ones

00:06:02.570 --> 00:06:06.270
that are most effected
by invasive species.

00:06:06.270 --> 00:06:08.600
Now, the last thing I wanna highlight is,

00:06:08.600 --> 00:06:12.110
what we just talked about as
population growth strategies.

00:06:12.110 --> 00:06:16.150
And that can sometimes be
confused with niche strategies

00:06:16.150 --> 00:06:18.530
where are there certain
species that are generalists,

00:06:18.530 --> 00:06:20.310
that can occupy many different niches

00:06:20.310 --> 00:06:23.540
while there's certain species
that are more specialists.

00:06:23.540 --> 00:06:26.060
Here, we're just talking
about generally speaking,

00:06:26.060 --> 00:06:28.750
how do species tend to grow in population?

00:06:28.750 --> 00:06:31.010
While when we talk about niche strategies,

00:06:31.010 --> 00:06:34.160
we're gonna talk about the
types of niches they feel

00:06:34.160 --> 00:06:36.450
in order to get their resources.

00:06:36.450 --> 00:06:39.353
And we'll talk more about
all of that in future videos.


Official SAT Practice Tips for Students

WEBVTT
Kind: captions
Language: en

00:00:01.600 --> 00:00:04.170
- [Shannon] Hi, I'm
Shannon from Khan Academy.

00:00:04.170 --> 00:00:06.330
And I want to show you
how to make the most

00:00:06.330 --> 00:00:10.490
of your learning time on
Official SAT Practice.

00:00:10.490 --> 00:00:12.800
Research has shown that more time spent

00:00:12.800 --> 00:00:15.810
on Official SAT Practice is associated

00:00:15.810 --> 00:00:18.360
with greater SAT scores,

00:00:18.360 --> 00:00:21.850
but how you spend that
time really matters.

00:00:21.850 --> 00:00:24.990
Before we begin, let's make
sure you know how to access

00:00:24.990 --> 00:00:26.823
Official SAT Practice.

00:00:27.670 --> 00:00:30.290
Make sure you're signed into
your Khan Academy account

00:00:30.290 --> 00:00:33.363
by checking for your name in
the upper right-hand corner.

00:00:34.600 --> 00:00:37.890
If you're using Official
SAT Practice in a class,

00:00:37.890 --> 00:00:40.570
you should see a tab that says SAT

00:00:40.570 --> 00:00:42.393
on the left side navigation.

00:00:43.240 --> 00:00:47.900
Select the SAT tab and
from there select Practice

00:00:47.900 --> 00:00:50.113
to be taken to your student dashboard.

00:00:51.230 --> 00:00:54.620
If you aren't using SAT
practice in a class,

00:00:54.620 --> 00:00:58.460
you can select Edit
Courses to add the SAT tab

00:00:58.460 --> 00:01:00.133
to your Khan Academy account.

00:01:04.890 --> 00:01:08.123
Number one. Link your
account to CollegeBoard.

00:01:09.710 --> 00:01:12.410
To receive a personalized practice plan,

00:01:12.410 --> 00:01:14.580
you have two options.

00:01:14.580 --> 00:01:18.600
Number one, take a series
of diagnostic quizzes.

00:01:18.600 --> 00:01:21.310
Or number two, link your
CollegeBoard account

00:01:21.310 --> 00:01:22.423
to Khan Academy.

00:01:23.440 --> 00:01:25.450
The easiest way to get a study plan

00:01:25.450 --> 00:01:28.280
that is personalized to
your results is to link

00:01:28.280 --> 00:01:30.980
your Khan and CollegeBoard accounts.

00:01:30.980 --> 00:01:32.600
Once your accounts are linked,

00:01:32.600 --> 00:01:34.710
we'll automatically recommend skills

00:01:34.710 --> 00:01:36.890
where you have room to improve,

00:01:36.890 --> 00:01:39.643
especially ones that show
up frequently on the SAT.

00:01:40.890 --> 00:01:42.423
We recommend that you link your accounts

00:01:42.423 --> 00:01:46.093
so that you can waste no time
improving the right skills.

00:01:47.800 --> 00:01:49.280
Number two.

00:01:49.280 --> 00:01:52.833
Follow your personalized
practice recommendations.

00:01:54.140 --> 00:01:56.800
If you already linked your Khan Academy

00:01:56.800 --> 00:01:58.530
and CollegeBoard accounts,

00:01:58.530 --> 00:02:02.263
you will see your skill
recommendations on the Practice tab.

00:02:03.260 --> 00:02:06.290
At the top of the page,
you should see a set

00:02:06.290 --> 00:02:10.570
of recommended practice for
math and reading and writing

00:02:10.570 --> 00:02:14.380
that always end in a timed mini section.

00:02:14.380 --> 00:02:17.913
Now, let's take a deeper look
at how skills are recommended.

00:02:18.770 --> 00:02:22.450
Let's say there are two skills
at two different levels.

00:02:22.450 --> 00:02:27.450
Skill A is at level two,
skill B is that level three.

00:02:28.650 --> 00:02:30.670
You might think it would be more important

00:02:30.670 --> 00:02:32.900
to improve skill A.

00:02:32.900 --> 00:02:36.030
However, in some cases, we may recommend

00:02:36.030 --> 00:02:37.680
that you practice skill B

00:02:37.680 --> 00:02:40.400
because it shows up more
frequently on the SAT

00:02:41.340 --> 00:02:43.538
and improving it to
level four would do more

00:02:43.538 --> 00:02:45.163
to raise your score.

00:02:48.070 --> 00:02:50.833
Number three. Level up skills.

00:02:51.890 --> 00:02:56.110
In official SAT practice, you
have a specific skill level

00:02:56.110 --> 00:02:58.280
for the 41 skills in math

00:02:58.280 --> 00:03:01.610
and the 28 skills in reading and writing.

00:03:01.610 --> 00:03:06.420
As you answer questions, your
skill levels move up or down

00:03:06.420 --> 00:03:07.923
depending on how you do.

00:03:08.790 --> 00:03:10.610
Leveling up your skills shows you

00:03:10.610 --> 00:03:12.720
that you are consistently advancing

00:03:12.720 --> 00:03:15.050
in the content on the SAT.

00:03:15.050 --> 00:03:18.510
And it's a great way to
monitor your progress.

00:03:18.510 --> 00:03:20.167
You might be wondering,

00:03:20.167 --> 00:03:22.997
"But what if I do if I
get stuck on a skill?"

00:03:23.930 --> 00:03:25.650
It's normal to feel stuck at times

00:03:25.650 --> 00:03:27.580
when studying for the SAT.

00:03:27.580 --> 00:03:29.340
We've all been there.

00:03:29.340 --> 00:03:31.988
But those moments of
confusion are also the times

00:03:31.988 --> 00:03:33.550
when you have the opportunity

00:03:33.550 --> 00:03:36.220
to improve your score the most.

00:03:36.220 --> 00:03:40.120
Push through by using the
hints, instructional videos

00:03:40.120 --> 00:03:42.803
or ask for help when you're
learning a new skill.

00:03:43.750 --> 00:03:47.010
As you answer questions
on Official SAT Practice,

00:03:47.010 --> 00:03:50.540
you have access to text
explanations and videos

00:03:50.540 --> 00:03:53.470
to deepen your understanding
of the content.

00:03:53.470 --> 00:03:56.910
You can also use the Review
tab to review your answers

00:03:56.910 --> 00:03:59.030
from completed practice.

00:03:59.030 --> 00:04:02.570
If you're still stuck, reach
out to one of your classmates,

00:04:02.570 --> 00:04:05.403
a teacher or a family member for support.

00:04:08.680 --> 00:04:12.413
Number four. Take a
full-length practice test.

00:04:14.890 --> 00:04:17.410
Select the Full Tests tab at the top

00:04:17.410 --> 00:04:20.593
to access the full-length
SAT practice tests.

00:04:21.610 --> 00:04:24.250
Taking a practice test is a crucial step

00:04:24.250 --> 00:04:27.090
to ensure you're prepared for a test day

00:04:27.090 --> 00:04:30.510
by simulating the real test experience.

00:04:30.510 --> 00:04:32.910
Eight full-length practice
tests are available

00:04:32.910 --> 00:04:35.020
on Official SAT Practice,

00:04:35.020 --> 00:04:36.910
which can be taken in one sitting

00:04:36.910 --> 00:04:39.023
or section by section over time.

00:04:39.890 --> 00:04:42.030
The information from your full-length test

00:04:42.030 --> 00:04:45.093
will also result in even
more personalized practice.

00:04:46.910 --> 00:04:49.200
Now that you know the
top four tips to using

00:04:49.200 --> 00:04:53.320
Official SAT Practice,
you're ready to get started.

00:04:53.320 --> 00:04:56.060
Log into your Khan Academy account today.

00:04:56.060 --> 00:04:57.123
Happy studying!


Khan Kickoff Pep Talk: Akbar Gbajabiamila

WEBVTT
Kind: captions
Language: en

00:00:00.560 --> 00:00:02.730
- Khan Academy students, what's goin' on?

00:00:02.730 --> 00:00:07.340
It's Akbar Gbaja-Biamila, host
of American Ninja Warrior.

00:00:07.340 --> 00:00:09.330
I just wanted to check in with you guys,

00:00:09.330 --> 00:00:12.400
but also to wish you a happy New Year.

00:00:12.400 --> 00:00:14.390
It's 2021.

00:00:14.390 --> 00:00:15.990
Things are gonna be a lot different.

00:00:15.990 --> 00:00:19.010
And I know in 2020
things got crazy, right?

00:00:19.010 --> 00:00:21.610
We had the isolation and a
lot of us were struggling,

00:00:21.610 --> 00:00:23.240
going through the ups and the downs

00:00:23.240 --> 00:00:25.880
and things at home were
starting the change

00:00:25.880 --> 00:00:27.480
because of COVID-19.

00:00:27.480 --> 00:00:30.510
Well, this is a new year, a new mindset.

00:00:30.510 --> 00:00:32.950
And, as you can see,
I'm inside of my office

00:00:32.950 --> 00:00:35.230
and you can see some
of my football jerseys.

00:00:35.230 --> 00:00:37.050
And what I love about football,

00:00:37.050 --> 00:00:39.550
what I love about American Ninja Warrior,

00:00:39.550 --> 00:00:41.410
is that you constantly have obstacles

00:00:41.410 --> 00:00:42.870
that you have to overcome.

00:00:42.870 --> 00:00:46.790
That is going to happen
regardless of it's a good year

00:00:46.790 --> 00:00:49.040
or a bad year that we saw,

00:00:49.040 --> 00:00:51.550
and I put it in quote
because that's all relative,

00:00:51.550 --> 00:00:53.610
that we saw in 2020.

00:00:53.610 --> 00:00:56.010
So my coach used to tell me this,

00:00:56.010 --> 00:00:57.950
and I truly do believe this,

00:00:57.950 --> 00:01:01.390
is that tough times don't
last, but tough people do.

00:01:01.390 --> 00:01:03.280
And to be tough, what does that mean?

00:01:03.280 --> 00:01:04.700
Does that mean you have to growl, like

00:01:04.700 --> 00:01:05.690
(Akbar growls)

00:01:05.690 --> 00:01:08.470
No, what it means is that
you're willing to accept

00:01:08.470 --> 00:01:10.890
the challenges that are in front of you.

00:01:10.890 --> 00:01:14.210
You're willing to go with
the ups and the downs,

00:01:14.210 --> 00:01:17.670
but you're also knowing that
you have this trajectory,

00:01:17.670 --> 00:01:18.600
you're going up.

00:01:18.600 --> 00:01:22.260
So to the Khan Academy
students, I say this to you:

00:01:22.260 --> 00:01:25.800
be an American Ninja
Warrior in the classroom,

00:01:25.800 --> 00:01:28.330
at home, doing your personal life.

00:01:28.330 --> 00:01:30.755
Whatever it is that you're
going, have that mindset

00:01:30.755 --> 00:01:33.120
that I will overcome.

00:01:33.120 --> 00:01:35.370
You're overcome whatever those obstacles.

00:01:35.370 --> 00:01:37.140
And then when I see you at that buzzer,

00:01:37.140 --> 00:01:39.110
when you get up that warp wall in life,

00:01:39.110 --> 00:01:41.260
in school, in your personal life,

00:01:41.260 --> 00:01:43.400
and you hit that buzzer, I'm gonna say,

00:01:43.400 --> 00:01:46.130
I see you, I see you hitting that buzzer!

00:01:46.130 --> 00:01:50.970
So, take on 2021 with a new
mindset, a new attitude.

00:01:50.970 --> 00:01:52.300
Don't look in the past.

00:01:52.300 --> 00:01:55.640
It's just something for you
to reflect and move forward.

00:01:55.640 --> 00:01:57.170
I'll leave you with this:

00:01:57.170 --> 00:02:01.960
take every stumbling block
in school, in life, whatever,

00:02:01.960 --> 00:02:04.890
and turn it into a stepping stone.

00:02:04.890 --> 00:02:06.270
You got that?

00:02:06.270 --> 00:02:08.810
Stumbling block into a stepping stone,

00:02:08.810 --> 00:02:12.040
that's your challenge for 2021, all right?

00:02:12.040 --> 00:02:16.110
You guys are Khan Academy ninja warriors!

00:02:16.110 --> 00:02:18.613
Have a great school year
and we'll talk soon.


Khan Kickoff Overview

WEBVTT
Kind: captions
Language: en

00:00:00.810 --> 00:00:01.890
- [Narrator] Here's a quick overview

00:00:01.890 --> 00:00:04.810
of our free motivation
program, Khan Kickoff.

00:00:04.810 --> 00:00:06.500
Let's start with a challenge,

00:00:06.500 --> 00:00:08.430
which is that motivating
students right now

00:00:08.430 --> 00:00:09.950
is just super hard.

00:00:09.950 --> 00:00:11.740
With everything going on in the world,

00:00:11.740 --> 00:00:13.950
getting students to show
up and engage day-after-day

00:00:13.950 --> 00:00:15.610
is no easy feat,

00:00:15.610 --> 00:00:18.530
but teachers did report one
bright spot from the fall,

00:00:18.530 --> 00:00:20.610
which was the power of teamwork.

00:00:20.610 --> 00:00:23.110
Specifically, hundreds
of educators told us

00:00:23.110 --> 00:00:25.140
that having students work
together to make progress

00:00:25.140 --> 00:00:28.730
and learn storm, got their
classes to show up and work hard

00:00:28.730 --> 00:00:30.900
even during incredibly tough times.

00:00:30.900 --> 00:00:32.870
So, Khan kickoff builds on that same sense

00:00:32.870 --> 00:00:35.990
of camaraderie to get your
students energized this winter.

00:00:35.990 --> 00:00:37.073
Here's how it works.

00:00:37.970 --> 00:00:41.510
So, all you have to do is
go to your activity overview

00:00:41.510 --> 00:00:42.900
and then on a weekly basis

00:00:42.900 --> 00:00:44.570
copying your student's progress

00:00:44.570 --> 00:00:46.270
right into your progress tracker.

00:00:46.270 --> 00:00:47.470
And then you set up your teams,

00:00:47.470 --> 00:00:50.250
either within your classroom
breaking into groups,

00:00:50.250 --> 00:00:53.270
competing against other periods
or even other classrooms.

00:00:53.270 --> 00:00:55.890
And then you celebrate your
progress with the big reveal,

00:00:55.890 --> 00:00:59.310
the scoreboard, and a chance to celebrate.

00:00:59.310 --> 00:01:03.060
And that celebration
includes custom certificates

00:01:03.060 --> 00:01:05.770
with each student being acknowledged

00:01:05.770 --> 00:01:08.320
on their own personalized certificate,

00:01:08.320 --> 00:01:09.690
as well as the ability for you

00:01:09.690 --> 00:01:12.640
as the teacher to take
your own little victory lap

00:01:12.640 --> 00:01:16.100
and show off with your certificate
to your fellow educators.

00:01:16.100 --> 00:01:17.600
And when you do that

00:01:17.600 --> 00:01:20.620
you're gonna be automatically
entered into our giveaway,

00:01:20.620 --> 00:01:22.980
which features 10 prize packs

00:01:22.980 --> 00:01:24.870
that include a Wacom drawing tablet,

00:01:24.870 --> 00:01:29.000
just like the one that Sal Khan
uses and the $100 gift card.

00:01:29.000 --> 00:01:31.400
So, you can commission
your own celebration videos

00:01:31.400 --> 00:01:33.570
from top athletes and performers.

00:01:33.570 --> 00:01:35.970
And best of all Khan kickoff is free

00:01:35.970 --> 00:01:37.520
and open to all educators.

00:01:37.520 --> 00:01:39.313
So, feel free to dive in today.


Primary productivity in ecosystems

WEBVTT
Kind: captions
Language: en

00:00:01.130 --> 00:00:01.963
- [Instructor] In this video,

00:00:01.963 --> 00:00:03.950
we're going to talk about energy,

00:00:03.950 --> 00:00:05.330
and in particular, we're gonna talk about

00:00:05.330 --> 00:00:08.190
the energy of life, the
energy that I need to live

00:00:08.190 --> 00:00:09.240
and all of us need to live,

00:00:09.240 --> 00:00:10.430
the energy you need to think,

00:00:10.430 --> 00:00:13.610
the energy I'm using to
make this video right now.

00:00:13.610 --> 00:00:15.570
And some of you might already guess

00:00:15.570 --> 00:00:17.930
where this energy is coming from,

00:00:17.930 --> 00:00:21.080
the surface of our planet is
constantly being bombarded

00:00:21.080 --> 00:00:24.740
with light energy from the Sun,

00:00:24.740 --> 00:00:27.670
and you might know that
there is certain organisms

00:00:27.670 --> 00:00:31.320
on our planet that are capable
of taking that light energy

00:00:31.320 --> 00:00:35.390
and then storing it as chemical energy.

00:00:35.390 --> 00:00:37.470
And those things, and there's many types,

00:00:37.470 --> 00:00:39.420
but the ones that we see most often

00:00:39.420 --> 00:00:42.050
in our day-to-day life, are plants.

00:00:42.050 --> 00:00:44.600
And so let's imagine a plant here.

00:00:44.600 --> 00:00:46.440
And what it's doing is,

00:00:46.440 --> 00:00:48.280
it's using that light energy

00:00:48.280 --> 00:00:50.770
in conjunction with water,

00:00:50.770 --> 00:00:52.890
typically from the soil,

00:00:52.890 --> 00:00:55.610
that maybe it's getting through its roots,

00:00:55.610 --> 00:00:59.100
and carbon dioxide in the air.

00:00:59.100 --> 00:01:01.160
And it's using that light energy

00:01:01.160 --> 00:01:04.830
to actually stick, or you could say fix,

00:01:04.830 --> 00:01:07.450
the carbon to construct itself.

00:01:07.450 --> 00:01:11.440
And in its own tissue,
it's storing that energy,

00:01:11.440 --> 00:01:13.560
and then if it were to
break down that tissue,

00:01:13.560 --> 00:01:17.610
it can release that
energy in various forms.

00:01:17.610 --> 00:01:19.230
Now, as it does this,

00:01:19.230 --> 00:01:22.580
you might also be familiar
that these photosynthesizers,

00:01:22.580 --> 00:01:26.230
or these primary producers,
or these autotrophs,

00:01:26.230 --> 00:01:30.320
they're also releasing molecular oxygen.

00:01:30.320 --> 00:01:31.700
Now, if we were to describe this

00:01:31.700 --> 00:01:34.790
in chemical terms, or chemistry terms,

00:01:34.790 --> 00:01:38.480
we would describe this
process of photosynthesis

00:01:38.480 --> 00:01:42.940
as taking carbon dioxide from the air,

00:01:42.940 --> 00:01:47.780
in conjunction with water from the soil,

00:01:47.780 --> 00:01:51.200
and what's, I guess you could
say, fueling all of this

00:01:51.200 --> 00:01:56.193
is light energy, usually from the Sun,

00:01:57.080 --> 00:02:00.730
and what that is yielding is

00:02:00.730 --> 00:02:02.260
the tissue of the plant

00:02:02.260 --> 00:02:05.340
that is actually storing that
energy is chemical energy

00:02:05.340 --> 00:02:07.010
in an organic form,

00:02:07.010 --> 00:02:12.010
and the primary way that this
is done is through glucose,

00:02:12.370 --> 00:02:16.880
which is C6H12O6.

00:02:16.880 --> 00:02:17.757
I know what you're thinking,

00:02:17.757 --> 00:02:19.260
"All plants don't taste sweet."

00:02:19.260 --> 00:02:21.210
Well, if you take chains of sugars

00:02:21.210 --> 00:02:23.410
and put them together,
you get carbohydrates,

00:02:23.410 --> 00:02:24.860
and you adapt 'em a little bit,

00:02:24.860 --> 00:02:26.450
you get things like starches,

00:02:26.450 --> 00:02:28.840
and that's what most
of the plant tissue is.

00:02:28.840 --> 00:02:30.420
So some variations of this,

00:02:30.420 --> 00:02:33.480
or variations of this linked together,

00:02:33.480 --> 00:02:35.830
but this is where the energy is stored,

00:02:35.830 --> 00:02:38.400
so energy stored,

00:02:38.400 --> 00:02:40.700
in the actual plant tissue,

00:02:40.700 --> 00:02:45.580
and then of course, it
releases that molecular oxygen.

00:02:45.580 --> 00:02:50.510
And this is the process of photosynthesis.

00:02:50.510 --> 00:02:53.820
And even if you look at
the word photosynthesis,

00:02:53.820 --> 00:02:55.140
and what the parts of it mean,

00:02:55.140 --> 00:02:57.040
photo is referring to light,

00:02:57.040 --> 00:03:00.050
and synthesis is referring to
putting something together,

00:03:00.050 --> 00:03:01.570
synthesizing something.

00:03:01.570 --> 00:03:04.070
So photosynthesis, you're using light

00:03:04.070 --> 00:03:06.980
to put together these,

00:03:06.980 --> 00:03:11.540
essentially, fix the carbon
together, to store energy.

00:03:11.540 --> 00:03:13.297
Now, you might say,
"All right, that's nice.

00:03:13.297 --> 00:03:15.297
"I'm storing the energy this way,

00:03:15.297 --> 00:03:17.680
"how do I actually use the energy?"

00:03:17.680 --> 00:03:19.530
And that's something
that all of us are doing,

00:03:19.530 --> 00:03:21.260
all living systems have to do,

00:03:21.260 --> 00:03:24.023
and that process is respiration.

00:03:25.190 --> 00:03:27.430
And you could already guess

00:03:27.430 --> 00:03:32.000
what at least the chemical reaction

00:03:32.000 --> 00:03:33.950
for respiration will look like,

00:03:33.950 --> 00:03:36.480
you're going to start
with our stored energy,

00:03:36.480 --> 00:03:38.933
our glucose C6H12O6,

00:03:43.170 --> 00:03:45.270
in the presence of oxygen.

00:03:45.270 --> 00:03:47.210
And since we're respiring all the time,

00:03:47.210 --> 00:03:50.360
this is why we need to breathe oxygen,

00:03:50.360 --> 00:03:54.580
and this is going to yield carbon dioxide,

00:03:54.580 --> 00:03:59.050
and that's why we exhale more
carbon dioxide than we inhale,

00:03:59.050 --> 00:04:02.610
it's also going to release water,

00:04:02.610 --> 00:04:03.930
and it's going to release,

00:04:03.930 --> 00:04:08.230
and this is the whole point
of it, cellular energy.

00:04:08.230 --> 00:04:10.660
And in other videos that
you'll see in a biology class

00:04:10.660 --> 00:04:14.470
will talk about how this
form of stored energy

00:04:14.470 --> 00:04:15.800
gets converted to other forms

00:04:15.800 --> 00:04:18.930
and then how that's used by
the various machinery and cells

00:04:18.930 --> 00:04:21.870
to actually live, to reproduce,

00:04:21.870 --> 00:04:24.760
to move, in many cases.

00:04:24.760 --> 00:04:26.090
Now, an interesting question is,

00:04:26.090 --> 00:04:30.730
how do you measure how much
photosynthesis is going on,

00:04:30.730 --> 00:04:34.410
how much primary productivity is going on?

00:04:34.410 --> 00:04:36.340
Well, one way to think about it is,

00:04:36.340 --> 00:04:40.500
find an ecosystem and take a certain area

00:04:40.500 --> 00:04:42.510
of the surface of that ecosystem,

00:04:42.510 --> 00:04:45.240
and it could be a terrestrial
ecosystem, on land,

00:04:45.240 --> 00:04:47.230
it could be a marine ecosystem,

00:04:47.230 --> 00:04:50.050
and then say, for this area,

00:04:50.050 --> 00:04:51.460
in a given period of time,

00:04:51.460 --> 00:04:52.790
oftentimes, a year,

00:04:52.790 --> 00:04:54.590
how much stuff is growing?

00:04:54.590 --> 00:04:56.490
So this is the stuff that grows,

00:04:56.490 --> 00:04:58.870
and obviously it would seem

00:04:58.870 --> 00:05:00.963
that the more stuff that is growing,

00:05:01.850 --> 00:05:05.510
that the more photosynthesis
that is taking place.

00:05:05.510 --> 00:05:08.430
And the way that they measure how much,

00:05:08.430 --> 00:05:11.070
how much, is growing,

00:05:11.070 --> 00:05:14.530
you could either measure it
in terms of grams of biomass,

00:05:14.530 --> 00:05:17.310
so grams of biomass,

00:05:17.310 --> 00:05:19.970
and biomass is just a fancy way of saying

00:05:19.970 --> 00:05:21.870
that the mass of biological stuff

00:05:21.870 --> 00:05:24.500
that's just growing on this area,

00:05:24.500 --> 00:05:26.360
and usually they'll take the water out

00:05:26.360 --> 00:05:27.960
so they get a consistent measurement,

00:05:27.960 --> 00:05:30.830
or you can convert this to calories,

00:05:30.830 --> 00:05:31.740
and it's usually measured

00:05:31.740 --> 00:05:34.100
in thousands of calories, kilocalories.

00:05:34.100 --> 00:05:36.950
And when you see calories
on a packaging food label,

00:05:36.950 --> 00:05:38.730
what most of us think of calories,

00:05:38.730 --> 00:05:40.110
those are actually kilocalories

00:05:40.110 --> 00:05:42.800
when we think about it
in scientific terms.

00:05:42.800 --> 00:05:44.190
And I know what you're thinking,

00:05:44.190 --> 00:05:46.627
you're like, "Wait, mass and kilocalories,

00:05:46.627 --> 00:05:48.700
"calories, that's just a form of energy."

00:05:48.700 --> 00:05:50.520
Well, those two things you can go between,

00:05:50.520 --> 00:05:52.930
because usually a certain type of biomass,

00:05:52.930 --> 00:05:54.760
a gram of a certain type of biomass,

00:05:54.760 --> 00:05:58.210
will have a certain amount
of energy stored in it,

00:05:58.210 --> 00:06:00.990
not energy that necessarily
all animals could use

00:06:00.990 --> 00:06:02.160
or that we could use,

00:06:02.160 --> 00:06:04.133
but it does have energy in it.

00:06:04.980 --> 00:06:09.000
Now, when we talk about
this primary productivity,

00:06:09.000 --> 00:06:11.147
you might already be thinking about,

00:06:11.147 --> 00:06:16.147
"Well, don't the plants need
to use some of the energy

00:06:16.197 --> 00:06:18.930
"that they are producing
themselves to live?"

00:06:18.930 --> 00:06:21.550
And my answer to you is
of course they need it.

00:06:21.550 --> 00:06:23.960
In fact, that's probably
the most important reason

00:06:23.960 --> 00:06:25.770
why they need to photosynthesize,

00:06:25.770 --> 00:06:28.380
is because they need to do respiration

00:06:28.380 --> 00:06:31.280
in order for them to grow and metabolize

00:06:31.280 --> 00:06:33.670
and live and reproduce.

00:06:33.670 --> 00:06:37.200
And so when you see how
much has been produced

00:06:37.200 --> 00:06:39.080
in a given area in given year,

00:06:39.080 --> 00:06:43.540
you're actually seeing the
net primary productivity.

00:06:43.540 --> 00:06:45.580
This is the, you could think about it,

00:06:45.580 --> 00:06:48.190
how much photosynthesis they did

00:06:48.190 --> 00:06:51.660
minus how much respiration they did.

00:06:51.660 --> 00:06:55.020
So if you think of how much
photosynthesis they did

00:06:55.020 --> 00:06:58.040
as gross primary productivity,

00:06:58.040 --> 00:07:00.460
so that's the total
amount of photosynthesis,

00:07:00.460 --> 00:07:05.460
and then you subtract
out the amount of energy,

00:07:06.090 --> 00:07:08.500
chemical energy or cellular energy

00:07:08.500 --> 00:07:10.600
they needed for respiration,

00:07:10.600 --> 00:07:15.600
that would then give you the
net primary productivity.

00:07:18.460 --> 00:07:20.040
And as I mentioned,

00:07:20.040 --> 00:07:22.800
just to make things a little bit tangible,

00:07:22.800 --> 00:07:25.400
if you took a very productive ecosystem,

00:07:25.400 --> 00:07:27.440
let's say something like a rainforest

00:07:27.440 --> 00:07:30.100
that I have here in the background,

00:07:30.100 --> 00:07:33.200
a very productive ecosystem like this,

00:07:33.200 --> 00:07:35.680
if you were to take, on average,

00:07:35.680 --> 00:07:40.340
a square meter of this,

00:07:40.340 --> 00:07:45.340
it produces in a year about
2,000 grams of biomass.

00:07:47.990 --> 00:07:51.210
So here, we would say that
the net primary productivity

00:07:51.210 --> 00:07:54.010
of this rainforest that you
see in the background here

00:07:54.010 --> 00:07:58.800
would be approximately 2,000 grams

00:07:58.800 --> 00:08:02.640
per square meter per year,

00:08:02.640 --> 00:08:04.010
and if you wanted to think about this

00:08:04.010 --> 00:08:05.030
in terms of kilocalories,

00:08:05.030 --> 00:08:05.863
you just have to say,

00:08:05.863 --> 00:08:09.850
well, if each gram of biomass
is how many kilocalories,

00:08:09.850 --> 00:08:12.370
and it depends on the type of biomass,

00:08:12.370 --> 00:08:14.520
but let's say that we have

00:08:14.520 --> 00:08:19.370
four kilocalories per gram of biomass.

00:08:19.370 --> 00:08:20.780
So then we could also say

00:08:20.780 --> 00:08:22.920
that this net primary productivity

00:08:22.920 --> 00:08:27.920
is equal to 2,000 grams
per square meter per year

00:08:29.240 --> 00:08:34.083
times four kilocalories per gram,

00:08:35.280 --> 00:08:36.710
the grams cancel out,

00:08:36.710 --> 00:08:39.000
and then you multiply four times 2,000,

00:08:39.000 --> 00:08:43.140
that's going to be 8,000 kilocalories,

00:08:43.140 --> 00:08:48.140
kilocalories per square meter per year.

00:08:48.230 --> 00:08:49.890
That would be the net
primary productivity,

00:08:49.890 --> 00:08:51.240
because that's after the plants

00:08:51.240 --> 00:08:52.910
have been doing respiration.

00:08:52.910 --> 00:08:55.830
Now, how would you figure out
gross primary productivity?

00:08:55.830 --> 00:08:58.180
Well, you're not going to
be able to do it directly,

00:08:58.180 --> 00:08:59.240
but you can figure that out

00:08:59.240 --> 00:09:01.360
by figuring out the rate of respiration.

00:09:01.360 --> 00:09:04.180
If you took some plants in that ecosystem,

00:09:04.180 --> 00:09:07.710
and then you put them in
a dark room with no light,

00:09:07.710 --> 00:09:12.110
and then you if you saw how
much oxygen they are absorbing,

00:09:12.110 --> 00:09:13.760
or they're having to use,

00:09:13.760 --> 00:09:15.480
then that gives you a sense

00:09:15.480 --> 00:09:18.880
of how much respiration they are doing.

00:09:18.880 --> 00:09:20.630
And there's ways that you
could look at the ratios

00:09:20.630 --> 00:09:22.030
of the oxygens and the carbons

00:09:22.030 --> 00:09:25.690
to figure out exactly how
much respiration is going on.

00:09:25.690 --> 00:09:27.920
And then if you know the
net primary productivity

00:09:27.920 --> 00:09:29.560
and the rate of respiration,

00:09:29.560 --> 00:09:33.010
then you could figure out the
gross primary productivity.

00:09:33.010 --> 00:09:34.310
But I will leave you there,

00:09:34.310 --> 00:09:36.520
because these are really
useful measurements.

00:09:36.520 --> 00:09:37.470
Well, one, it's really useful

00:09:37.470 --> 00:09:38.870
to think about where all of the energy

00:09:38.870 --> 00:09:40.790
that allows us to live comes from,

00:09:40.790 --> 00:09:42.950
but it's also useful for ecologists

00:09:42.950 --> 00:09:44.800
to think about how productive a system is,

00:09:44.800 --> 00:09:47.540
or what's making it more
productive, or less productive.

00:09:47.540 --> 00:09:49.580
And as we'll see, these numbers here,

00:09:49.580 --> 00:09:52.070
these are for sure on the high end

00:09:52.070 --> 00:09:54.360
of net primary productivity.

00:09:54.360 --> 00:09:56.850
If we were in a desert type of ecosystem,

00:09:56.850 --> 00:09:59.620
this number might be in the low hundreds

00:09:59.620 --> 00:10:02.513
and not in the 8,000 range.


Elon Musk $5 million donation to Khan Academy thank you

WEBVTT
Kind: captions
Language: en

00:00:00.780 --> 00:00:03.410
- Hi everyone, Sal Khan
here from Khan Academy.

00:00:03.410 --> 00:00:06.080
And I just wanted to give a
huge shout out and thank you

00:00:06.080 --> 00:00:09.370
to Elon Musk and everyone
at the Musk Foundation

00:00:09.370 --> 00:00:12.280
for their incredibly generous
support for Khan Academy,

00:00:12.280 --> 00:00:16.250
they just recently gave
a $5 million donation

00:00:16.250 --> 00:00:18.200
to Khan Academy.

00:00:18.200 --> 00:00:21.570
Elon I hope you really
feel good about this.

00:00:21.570 --> 00:00:22.840
This is going to allow us

00:00:22.840 --> 00:00:25.670
to accelerate all sorts of content.

00:00:25.670 --> 00:00:27.690
Our aspirations are all subjects

00:00:27.690 --> 00:00:30.370
from K through the
early stages of college.

00:00:30.370 --> 00:00:32.150
This will accelerate our science content,

00:00:32.150 --> 00:00:33.980
allow us to do more on early learning,

00:00:33.980 --> 00:00:36.560
allow us to make the
software and the practice

00:00:36.560 --> 00:00:39.420
that much more engaging
for millions of students

00:00:39.420 --> 00:00:42.210
around the world, for
teachers around the world.

00:00:42.210 --> 00:00:44.650
And as far as Khan Academy has come,

00:00:44.650 --> 00:00:47.250
we have 120 million registered users,

00:00:47.250 --> 00:00:50.770
20 or 30 million students
using the platform every month.

00:00:50.770 --> 00:00:54.880
We have about 200 million
hours of learning a year,

00:00:54.880 --> 00:00:56.550
which any way you want to evaluate that

00:00:56.550 --> 00:00:59.440
that's worth a lot to the world.

00:00:59.440 --> 00:01:00.880
And when you look at our efficacy studies

00:01:00.880 --> 00:01:03.740
and how we've been able to
move the dial in classrooms

00:01:03.740 --> 00:01:06.930
just that social return
to investment ratio

00:01:06.930 --> 00:01:09.720
is 400 to 500 to one.

00:01:09.720 --> 00:01:11.960
A good return in the philanthropic sector

00:01:11.960 --> 00:01:15.440
is considered a five to one
ratio or 10 to one ratio.

00:01:15.440 --> 00:01:17.810
So as much as progress has been made,

00:01:17.810 --> 00:01:19.080
I think you appreciate,

00:01:19.080 --> 00:01:21.550
and hopefully everyone
watching appreciates

00:01:21.550 --> 00:01:23.760
that there's many billions who need this

00:01:23.760 --> 00:01:25.510
there's people throughout the planet

00:01:25.510 --> 00:01:29.070
who need a way to tap
into their potential.

00:01:29.070 --> 00:01:32.690
And I view this type of
investment in what we're doing

00:01:32.690 --> 00:01:35.530
as really foundational
for us to be able to build

00:01:35.530 --> 00:01:38.000
a multi-generational institution.

00:01:38.000 --> 00:01:40.970
So that future Elon Musk's of the world

00:01:40.970 --> 00:01:43.940
are also able to tap into their potential

00:01:43.940 --> 00:01:48.940
and help all of us up-level
who we are as a civilization,

00:01:49.060 --> 00:01:51.740
for everyone listening
I wanna remind folks

00:01:51.740 --> 00:01:54.050
that as incredible as this donation is,

00:01:54.050 --> 00:01:57.360
and it really is incredible,
that we do need more help

00:01:57.360 --> 00:02:01.520
we continue to be running
at a deficit for 2021.

00:02:01.520 --> 00:02:03.970
So every donation of every size helps

00:02:03.970 --> 00:02:06.030
and we're able to take
every one of those dollars

00:02:06.030 --> 00:02:07.910
and it helps us accelerate learning

00:02:07.910 --> 00:02:09.970
in a whole bunch of dimensions.

00:02:09.970 --> 00:02:12.890
The world as a whole spends $5 trillion

00:02:12.890 --> 00:02:15.950
on education annually
Khan Academy's budget

00:02:15.950 --> 00:02:18.860
is one, 100,000th of that.

00:02:18.860 --> 00:02:20.690
We are the budget of a large high school,

00:02:20.690 --> 00:02:23.030
but our aspirations
are to serve the globe.

00:02:23.030 --> 00:02:27.940
So hopefully, more folks
listening at all scales,

00:02:27.940 --> 00:02:30.420
can help support what we're trying to do.

00:02:30.420 --> 00:02:31.930
And the last thing I'll mention,

00:02:31.930 --> 00:02:34.000
and it's especially powerful to get

00:02:34.000 --> 00:02:35.380
a donation from you Elon.

00:02:35.380 --> 00:02:38.100
I had the privilege of
interviewing you back in 2013,

00:02:38.100 --> 00:02:39.240
when you visited our office

00:02:39.240 --> 00:02:41.070
and someone on YouTube commented.

00:02:41.070 --> 00:02:43.210
I wanna find someone who looks at me

00:02:43.210 --> 00:02:45.240
the same way that Sal looks at Elon

00:02:45.240 --> 00:02:47.260
and they were catching onto something.

00:02:47.260 --> 00:02:49.330
I do look up to you and incredible way

00:02:49.330 --> 00:02:52.340
any time that I questioned even myself

00:02:52.340 --> 00:02:54.870
and I say, is this mission too big

00:02:54.870 --> 00:02:57.470
to actually try to
educate all of humanity?

00:02:57.470 --> 00:03:00.400
I think of the incredible
work that you've done.

00:03:00.400 --> 00:03:04.480
I remember back in 2013
when I interviewed you

00:03:04.480 --> 00:03:06.310
pretty much everything you
said you were going to do,

00:03:06.310 --> 00:03:08.940
and you made some pretty large statements

00:03:08.940 --> 00:03:12.180
you have either done or your
very close to doing right now.

00:03:12.180 --> 00:03:14.140
And I take incredible inspiration

00:03:14.140 --> 00:03:16.040
that it is not too big of a mission

00:03:16.040 --> 00:03:19.150
that if anything, we
cannot shy away right now

00:03:19.150 --> 00:03:20.310
from this goal,

00:03:20.310 --> 00:03:22.960
just as we shouldn't shy
away from solving climate,

00:03:22.960 --> 00:03:24.440
solving transportation,

00:03:24.440 --> 00:03:26.930
being able to colonize other planets,

00:03:26.930 --> 00:03:29.620
we can't shy away from
educating the planet

00:03:29.620 --> 00:03:31.990
and other planets, going forward.

00:03:31.990 --> 00:03:33.990
So thank you so much and I look forward

00:03:33.990 --> 00:03:36.103
to going on this journey
with all of y'all.


Energy flow in a marine ecosystem

WEBVTT
Kind: captions
Language: en

00:00:00.370 --> 00:00:02.130
- [Instructor] In this video
we're gonna take a deeper look

00:00:02.130 --> 00:00:05.560
at the various producers and
consumers in an ecosystem.

00:00:05.560 --> 00:00:08.930
And for the sake of
diversity, no pun intended,

00:00:08.930 --> 00:00:10.870
we're gonna look at a marine ecosystem,

00:00:10.870 --> 00:00:12.300
let's say an estuary.

00:00:12.300 --> 00:00:16.010
And an estuary generally refers to a place

00:00:16.010 --> 00:00:20.940
where you have a river coming
to where the tide comes.

00:00:20.940 --> 00:00:23.350
So it's a mixture of both the
fresh water from the river

00:00:23.350 --> 00:00:25.240
and the saltwater from the sea.

00:00:25.240 --> 00:00:29.670
And they tend to be very
productive from an energetic,

00:00:29.670 --> 00:00:33.040
or a biomass point of view.

00:00:33.040 --> 00:00:35.470
So if I were to make an
energy pyramid for, let's say,

00:00:35.470 --> 00:00:38.140
this estuary that we're
looking at right over here,

00:00:38.140 --> 00:00:40.670
it might look something like this,

00:00:40.670 --> 00:00:45.100
where at the bottom layer,
these are the primary producers,

00:00:45.100 --> 00:00:47.470
and we've studied this in other videos.

00:00:47.470 --> 00:00:50.710
Primary producers in a marine environment.

00:00:50.710 --> 00:00:53.380
These would be things like phytoplankton.

00:00:53.380 --> 00:00:56.240
Phyto, they're doing photosynthesis,

00:00:56.240 --> 00:00:57.073
and they're plankton.

00:00:57.073 --> 00:00:58.490
Plankton is a general term.

00:00:58.490 --> 00:01:01.130
It comes from the Greek for drifter.

00:01:01.130 --> 00:01:03.820
This right over here is sea grass.

00:01:03.820 --> 00:01:06.300
Also something that can photosynthesize,

00:01:06.300 --> 00:01:08.220
and this right over here is algae,

00:01:08.220 --> 00:01:11.230
which I'm sure you have seen
when you've gone to the sea

00:01:11.230 --> 00:01:13.640
or you've gone to a pond of some sort.

00:01:13.640 --> 00:01:16.500
And when we think of photosynthesis,

00:01:16.500 --> 00:01:18.360
we often talk about terrestrial things.

00:01:18.360 --> 00:01:22.910
Things like trees, but a lot
of us don't realize that 50%,

00:01:22.910 --> 00:01:25.920
that's a big number, of
Earth's photosynthesis,

00:01:25.920 --> 00:01:30.920
or net primary production,
or organic energy compounds,

00:01:31.270 --> 00:01:34.700
is produced by floating photosynthesizers,

00:01:34.700 --> 00:01:36.960
like phytoplankton and ultraplankton.

00:01:36.960 --> 00:01:40.280
So things like this, things
that you oftentimes don't see.

00:01:40.280 --> 00:01:43.730
And as I mentioned, estuaries
tend to be quite productive.

00:01:43.730 --> 00:01:46.640
They actually are comparable
to things like rainforests.

00:01:46.640 --> 00:01:48.810
Now, for the sake of
making things tangible,

00:01:48.810 --> 00:01:51.550
this being an estuary,
which is very productive,

00:01:51.550 --> 00:01:54.520
let's imagine that the net
primary production from

00:01:54.520 --> 00:01:57.920
this first layer, we can think
about it in terms of biomass,

00:01:57.920 --> 00:02:02.920
maybe it's about 2,000 grams
per square meter per year.

00:02:05.240 --> 00:02:07.990
Or we could think about
it in terms of calories.

00:02:07.990 --> 00:02:10.320
This would be approximately equal to it.

00:02:10.320 --> 00:02:12.970
It depends on the type of
biomass you're talking about,

00:02:12.970 --> 00:02:17.380
but you have roughly four
kilocalories per gram.

00:02:17.380 --> 00:02:21.780
So that would be roughly
8,000 kilocalories

00:02:22.670 --> 00:02:26.100
per square meter per year.

00:02:26.100 --> 00:02:29.290
That's the net primary
production of this first layer

00:02:29.290 --> 00:02:31.490
of the primary producers.

00:02:31.490 --> 00:02:33.620
Then what would we see at the next layer?

00:02:33.620 --> 00:02:36.840
Well, we know that not all
of that energy can be used

00:02:36.840 --> 00:02:41.840
by that next layer, which
would be the primary consumers.

00:02:41.850 --> 00:02:45.360
And there's some examples here
and it's much more complex

00:02:45.360 --> 00:02:47.860
than what this pyramid
depicts, but what we see here,

00:02:47.860 --> 00:02:50.180
these are zooplankton, which are really,

00:02:50.180 --> 00:02:51.560
you could view it as animal plankton.

00:02:51.560 --> 00:02:53.480
It's a large category of things.

00:02:53.480 --> 00:02:54.660
They have the word plankton in it.

00:02:54.660 --> 00:02:56.070
So they kinda have to go with the flow

00:02:56.070 --> 00:02:57.380
of whatever the tide is doing,

00:02:57.380 --> 00:02:58.780
whatever the currents are doing.

00:02:58.780 --> 00:03:01.230
Another primary consumer could be a fish

00:03:01.230 --> 00:03:05.290
like this royal blue tang
that might be eating plankton,

00:03:05.290 --> 00:03:09.270
and the net energy that's
available to the layer above that

00:03:09.270 --> 00:03:12.400
is gonna be a small fraction
of the net primary productivity

00:03:12.400 --> 00:03:13.750
of that first layer.

00:03:13.750 --> 00:03:15.870
Typically it's about 10%.

00:03:15.870 --> 00:03:16.750
So there might be,

00:03:16.750 --> 00:03:19.650
instead of 8,000
kilocalories, 10% of that,

00:03:19.650 --> 00:03:21.293
we'd be talking about approximately

00:03:21.293 --> 00:03:26.293
800 potential kilocalories
per square meter per year

00:03:27.350 --> 00:03:29.610
that'd be available for the next layer.

00:03:29.610 --> 00:03:31.150
Now you might be saying, "Hey,

00:03:31.150 --> 00:03:34.060
where are all of the
other calories going?"

00:03:34.060 --> 00:03:36.170
Well, remember, even in this first layer,

00:03:36.170 --> 00:03:38.940
we said this is net primary production.

00:03:38.940 --> 00:03:40.590
The gross would be even higher.

00:03:40.590 --> 00:03:44.530
These photosynthesizers had
to use that energy for things

00:03:44.530 --> 00:03:47.510
like respiration, and
even on the net basis,

00:03:47.510 --> 00:03:49.230
the reason why so much
gets lost when you go

00:03:49.230 --> 00:03:51.970
to the next layer, is these animals here.

00:03:51.970 --> 00:03:54.360
They have to use that energy to live,

00:03:54.360 --> 00:03:58.550
to do things like respiration
and a lot of this energy is

00:03:58.550 --> 00:04:00.610
just not consumable by the next layer.

00:04:00.610 --> 00:04:02.270
So it can become detritus, which is,

00:04:02.270 --> 00:04:04.210
you can just think of this biomass

00:04:04.210 --> 00:04:06.090
that is just laying around.

00:04:06.090 --> 00:04:08.610
Energy at every level can be lost to heat,

00:04:08.610 --> 00:04:11.100
can be used for movement, for growth.

00:04:11.100 --> 00:04:13.170
So you can imagine you
get to a level above that,

00:04:13.170 --> 00:04:17.310
we could call this secondary consumer.

00:04:17.310 --> 00:04:19.960
And this is just a picture of a grouper.

00:04:19.960 --> 00:04:22.900
Marine ecosystems would be
much more complex than this,

00:04:22.900 --> 00:04:26.540
but the net calories after
the groupers lived their life,

00:04:26.540 --> 00:04:28.580
et cetera, et cetera, that
is available to the level

00:04:28.580 --> 00:04:30.990
above that would be roughly, again, 10%.

00:04:30.990 --> 00:04:35.990
So maybe 80 kilocalories
per square meter per year.

00:04:36.720 --> 00:04:38.300
And that at least in this example,

00:04:38.300 --> 00:04:39.840
at the top of this pyramid,

00:04:39.840 --> 00:04:43.920
we have an apex predator, that is a shark.

00:04:43.920 --> 00:04:47.020
What is available after
the shark's done all

00:04:47.020 --> 00:04:49.410
of its business is roughly 10% of that.

00:04:49.410 --> 00:04:52.140
So approximately eight kilocalories

00:04:53.310 --> 00:04:57.750
per square meter per year.

00:04:57.750 --> 00:05:00.910
And so the important
thing to think about is,

00:05:00.910 --> 00:05:02.330
whether we're talking about terrestrial

00:05:02.330 --> 00:05:04.220
or marine environments,

00:05:04.220 --> 00:05:07.060
you have this significant
loss of energy as we go

00:05:07.060 --> 00:05:10.540
from one layer of the pyramid to another,

00:05:10.540 --> 00:05:13.030
but at the same time, everyone
has to be using energy.

00:05:13.030 --> 00:05:15.030
And the energy has to come from someplace

00:05:15.030 --> 00:05:16.820
and we've covered in other videos,

00:05:16.820 --> 00:05:19.060
it's coming from sunlight.

00:05:19.060 --> 00:05:21.890
And there has to be this continual process

00:05:21.890 --> 00:05:25.220
of taking light energy and
through photosynthesis converting

00:05:25.220 --> 00:05:27.790
it into a form of energy
that can be used by life.

00:05:27.790 --> 00:05:30.120
And then you have significant energy loss,

00:05:30.120 --> 00:05:32.820
but that energy keeps
flowing up this pyramid.

00:05:32.820 --> 00:05:35.390
And we're not even done because
even the apex predators,

00:05:35.390 --> 00:05:36.950
at some point they're going to die

00:05:36.950 --> 00:05:39.450
and then they have tissue
and in that biomass

00:05:39.450 --> 00:05:42.340
there's energy that could
be consumed by others.

00:05:42.340 --> 00:05:44.340
Also to release nutrients
that could be used

00:05:44.340 --> 00:05:46.340
by these initial primary producers.

00:05:46.340 --> 00:05:49.950
And that's where things like detritivores,

00:05:49.950 --> 00:05:51.880
and this is a starfish,
which is a detritivore,

00:05:51.880 --> 00:05:54.770
things that can actually
consume dead matter.

00:05:54.770 --> 00:05:57.730
They are really useful because
then they can bring nutrients

00:05:57.730 --> 00:06:01.270
back to primary producers, and to others.

00:06:01.270 --> 00:06:03.170
And when we're talking
about an aquatic environment

00:06:03.170 --> 00:06:05.500
like this and we're talking
about photosynthesis,

00:06:05.500 --> 00:06:06.897
one question you might be asking is,

00:06:06.897 --> 00:06:09.570
"Wait, where can photosynthesis occur?

00:06:09.570 --> 00:06:12.080
If you go deep enough it's
going to get quite dark."

00:06:12.080 --> 00:06:14.670
And you'd be right if you
were asking that question.

00:06:14.670 --> 00:06:16.570
When you think about marine environments,

00:06:16.570 --> 00:06:19.930
there's something known
as a euphotic zone,

00:06:19.930 --> 00:06:22.710
which is the zone where
it's shallow enough

00:06:22.710 --> 00:06:24.050
to get enough light

00:06:24.050 --> 00:06:26.490
so that you can actually
do photosynthesis.

00:06:26.490 --> 00:06:29.850
And so it's no coincidence
that things like estuaries,

00:06:29.850 --> 00:06:31.850
things where the water is shallower,

00:06:31.850 --> 00:06:33.400
where there's going to be more nutrients

00:06:33.400 --> 00:06:35.030
and where there's going to be more light,

00:06:35.030 --> 00:06:38.500
that you actually have
more primary production.


Reminder: Support Khan Academy today!

WEBVTT
Kind: captions
Language: en

00:00:00.290 --> 00:00:02.450
- Hi, Sal Khan here from Khan Academy.

00:00:02.450 --> 00:00:03.620
And I just wanna remind you

00:00:03.620 --> 00:00:06.170
that as we get to the
final few days of 2020,

00:00:06.170 --> 00:00:09.080
which has been a tough year,
I think for most of us,

00:00:09.080 --> 00:00:11.550
there's also the final few days of our

00:00:11.550 --> 00:00:13.200
end-of-year giving campaign.

00:00:13.200 --> 00:00:14.960
And as we go through those final few days,

00:00:14.960 --> 00:00:17.410
I wanna remind you that Khan
Academy is a not-for-profit

00:00:17.410 --> 00:00:19.590
with the mission of providing
a free world-class education

00:00:19.590 --> 00:00:22.400
for anyone anywhere, we
can only do that work

00:00:22.400 --> 00:00:25.530
through philanthropic donations
from folks like yourself.

00:00:25.530 --> 00:00:27.200
And any way you slice it,

00:00:27.200 --> 00:00:30.450
the social return on every dollar you give

00:00:30.450 --> 00:00:32.460
is really off the charts for Khan Academy.

00:00:32.460 --> 00:00:33.850
Think of the scale,

00:00:33.850 --> 00:00:36.530
think of the tens or
hundreds of millions of folks

00:00:36.530 --> 00:00:40.180
that Khan Academy reaches
in over 46 languages

00:00:40.180 --> 00:00:41.590
around the world.

00:00:41.590 --> 00:00:44.610
And if that by itself
isn't convincing enough,

00:00:44.610 --> 00:00:46.560
I'll give you some of my
favorite recent research

00:00:46.560 --> 00:00:47.420
that I've been looking at,

00:00:47.420 --> 00:00:49.910
which is how do you
become a happier person.

00:00:49.910 --> 00:00:52.320
And there's some things like
you should sleep enough,

00:00:52.320 --> 00:00:57.060
you should meditate, you
should have gratitude,

00:00:57.060 --> 00:00:59.280
but also do random acts of kindness,

00:00:59.280 --> 00:01:02.610
and a very powerful random act of kindness

00:01:02.610 --> 00:01:04.300
would be to donate to Khan Academy.

00:01:04.300 --> 00:01:06.840
So not only will it help
others tap into their potential

00:01:06.840 --> 00:01:09.760
around the world, millions
and millions of people,

00:01:09.760 --> 00:01:14.000
I think it actually might
make all of us happy

00:01:14.000 --> 00:01:17.420
by giving to it as well
and make you feel good

00:01:17.420 --> 00:01:21.970
about strong way of ending
another wise tough year

00:01:21.970 --> 00:01:26.080
and going into 2021 on a
very very positive footing.

00:01:26.080 --> 00:01:27.860
So if you're in a position to do so,

00:01:27.860 --> 00:01:30.290
please think about making
a donation to Khan Academy,

00:01:30.290 --> 00:01:32.940
we wouldn't be able to do
the work we do without you.


Khan Lab School

WEBVTT
Kind: captions
Language: en

00:00:00.230 --> 00:00:01.990
- Hi, everyone, Sal Khan here.

00:00:01.990 --> 00:00:04.010
And I just wanted to tell you all

00:00:04.010 --> 00:00:07.420
that we've reached kind of
several really cool milestones

00:00:07.420 --> 00:00:09.300
at Khan Lab School,
which you can learn more

00:00:09.300 --> 00:00:13.550
about at khanlabschool.org or kls.org.

00:00:13.550 --> 00:00:15.940
A lot of folks are surprised to hear

00:00:15.940 --> 00:00:20.410
that I started a physical
school back in 2014

00:00:20.410 --> 00:00:22.250
when I'm so associated
with online learning.

00:00:22.250 --> 00:00:23.840
But I've never viewed online

00:00:23.840 --> 00:00:26.770
as somehow a replacement
for an in-person experience.

00:00:26.770 --> 00:00:28.030
The dream has always been

00:00:28.030 --> 00:00:31.230
that online can unlock
the physical experience.

00:00:31.230 --> 00:00:33.350
It can allow students to learn

00:00:33.350 --> 00:00:35.640
at a pace that is appropriate for them.

00:00:35.640 --> 00:00:38.910
It could allow for mastery-based learning

00:00:38.910 --> 00:00:41.470
where if you get an 80% on something,

00:00:41.470 --> 00:00:43.400
you don't just get a C on your forehead

00:00:43.400 --> 00:00:44.670
and your permanent transcript

00:00:44.670 --> 00:00:46.870
and then you're expected
to learn the next concept

00:00:46.870 --> 00:00:49.060
that builds on that 20% gap.

00:00:49.060 --> 00:00:51.190
Instead, you're expected
to master the concept.

00:00:51.190 --> 00:00:53.500
So you always have a strong foundation.

00:00:53.500 --> 00:00:56.470
That we can unlock a situation when

00:00:56.470 --> 00:00:58.980
human beings get to a classroom together,

00:00:58.980 --> 00:01:00.530
both the students and the teachers,

00:01:00.530 --> 00:01:02.160
they're able to interact with each other,

00:01:02.160 --> 00:01:03.910
they're able to collaborate
with each other,

00:01:03.910 --> 00:01:07.300
they're able to have Socratic
dialogues, have games.

00:01:07.300 --> 00:01:10.970
They're able to do projects together.

00:01:10.970 --> 00:01:13.210
We wanted to create a
reality where students

00:01:13.210 --> 00:01:15.920
aren't just accountable
for their own gains

00:01:15.920 --> 00:01:18.900
or their own progress
but also for each other,

00:01:18.900 --> 00:01:20.210
that they're invested in each other,

00:01:20.210 --> 00:01:22.610
that they are unusually collaborative.

00:01:22.610 --> 00:01:24.970
We wanted to explore blurring the lines

00:01:24.970 --> 00:01:26.900
between high school and college.

00:01:26.900 --> 00:01:28.370
If kids are able to learn more,

00:01:28.370 --> 00:01:30.890
be truly curious, be truly engaged.

00:01:30.890 --> 00:01:34.330
Why can't they learn faster
than you would normally expect?

00:01:34.330 --> 00:01:36.970
The middle schoolers can
learn high school concepts,

00:01:36.970 --> 00:01:39.090
high school students can
learn college concepts

00:01:39.090 --> 00:01:40.520
and get credit for it.

00:01:40.520 --> 00:01:42.760
So that by the time they graduate,

00:01:42.760 --> 00:01:45.050
they're already operating at a junior

00:01:45.050 --> 00:01:46.710
or a senior level in college

00:01:46.710 --> 00:01:48.410
and actually getting credit for it.

00:01:48.410 --> 00:01:50.630
And so the milestone that we're at

00:01:50.630 --> 00:01:52.950
is that we're actually now at
a full K through 12 school,

00:01:52.950 --> 00:01:56.380
over 200 students, we have
our first graduates this year.

00:01:56.380 --> 00:01:58.660
And you could imagine in the early days

00:01:58.660 --> 00:01:59.493
a lot of people went,

00:01:59.493 --> 00:02:01.920
well, these are all
interesting ideas, Sal,

00:02:01.920 --> 00:02:03.670
but will this work?

00:02:03.670 --> 00:02:05.320
And it's a lab school,

00:02:05.320 --> 00:02:07.970
there's all sorts of stuff
that we're constantly trying.

00:02:07.970 --> 00:02:10.520
But you know, when I look at
this year's graduating cohort,

00:02:10.520 --> 00:02:12.860
I'm incredibly proud of them,

00:02:12.860 --> 00:02:16.150
mainly for who they have
become as human beings,

00:02:16.150 --> 00:02:18.450
but some of the traditional metrics

00:02:18.450 --> 00:02:22.750
by which we measure students,
they're also crushing it,

00:02:22.750 --> 00:02:24.490
I guess is the best way to say it,

00:02:24.490 --> 00:02:27.550
which is really powerful to show that

00:02:27.550 --> 00:02:29.500
you can create a learning experience

00:02:29.500 --> 00:02:32.360
where kids are intrinsically curious.

00:02:32.360 --> 00:02:35.470
They're intrinsically wanna
collaborate with each other

00:02:35.470 --> 00:02:37.250
and just wanna learn more.

00:02:37.250 --> 00:02:40.000
But as a by-product of
it, not as a goal of it,

00:02:40.000 --> 00:02:42.700
they're able to do incredibly
well on standardized tests.

00:02:42.700 --> 00:02:45.450
Our students are scoring on average

00:02:45.450 --> 00:02:46.670
better on standardized tests

00:02:46.670 --> 00:02:49.900
than some of the very top
universities in the country

00:02:49.900 --> 00:02:51.270
or in the world.

00:02:51.270 --> 00:02:52.280
They are getting in to

00:02:52.280 --> 00:02:55.360
some of the top universities in the world

00:02:55.360 --> 00:02:57.350
even though they don't have
traditional letter grades

00:02:57.350 --> 00:02:59.980
because the universities
are seeing that the grades

00:02:59.980 --> 00:03:02.230
of mastery based learning
are even more powerful

00:03:02.230 --> 00:03:03.640
because it's a higher standards,

00:03:03.640 --> 00:03:07.430
it's expecting that all students
really master the concepts.

00:03:07.430 --> 00:03:09.790
We're deepening our partnership
with Foothill College

00:03:09.790 --> 00:03:12.360
which is a local college in the area

00:03:12.360 --> 00:03:14.540
to get the best of both worlds,

00:03:14.540 --> 00:03:18.280
the high school experience
and the college experience.

00:03:18.280 --> 00:03:20.590
And so they have some exciting things

00:03:20.590 --> 00:03:23.620
that I can't announce it just
yet also on the capacity side.

00:03:23.620 --> 00:03:25.530
And so that's why I'm
out here telling folks

00:03:25.530 --> 00:03:28.900
normally we can only admit
a few folks every year,

00:03:28.900 --> 00:03:31.400
but this year there might
be an opportunity for more.

00:03:31.400 --> 00:03:32.370
So, if you're interested,

00:03:32.370 --> 00:03:35.420
if you live in the San
Francisco Bay area in particular

00:03:35.420 --> 00:03:37.310
within driving distance to Mountain View,

00:03:37.310 --> 00:03:41.070
Palo Alto Los Altos, encourage
you to take a look at it.

00:03:41.070 --> 00:03:42.940
And I'm happy to answer any questions

00:03:42.940 --> 00:03:44.200
in the message board below

00:03:44.200 --> 00:03:46.780
that you might have about Khan Lab School.

00:03:46.780 --> 00:03:50.530
My kids go there, I teach
there, I work very closely

00:03:50.530 --> 00:03:53.000
with the faculty and the
administration there.

00:03:53.000 --> 00:03:54.690
And what's exciting about it for me,

00:03:54.690 --> 00:03:57.110
is that not just creating a really

00:03:57.110 --> 00:03:58.710
unique learning experience

00:03:58.710 --> 00:04:01.130
for the students who attend,

00:04:01.130 --> 00:04:05.360
but as a lab school, creating
a model that can be replicated

00:04:05.360 --> 00:04:06.310
throughout the world.

00:04:06.310 --> 00:04:07.143
So once again,

00:04:07.143 --> 00:04:09.710
happy to answer any questions
that anyone might have.