That versus which

WEBVTT
Kind: captions
Language: en

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- [Voiceover] Hello
grammarians, we're gonna talk

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about that versus which but I would like

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to start off by saying that
in the study of grammar

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there's basically this
long, on-going fight

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between two camps and it's
between the prescriptivists,

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who believe that language
has concrete rules

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that need to be abided by,

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and the descriptivists, who also believe

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that language has rules,

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but see language as more subject to change

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than the prescriptivists would like.

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Now I find myself to be right
in-between these two camps

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which frequently makes me
feel like I want to stick out

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my hands and say, "You guys stop fighting.

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"You're both right."

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All of this is to say that Bryan Garner,

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the prescriptive author
of my main usage manual,

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Garner's Modern American Usage,

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is not a fan of the word which.

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He thinks it's ruined more sentences

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than any other word in
English through its overuse.

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On the other hand Geoffrey
Pullum, one of the editors

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of my descriptive Cambridge
Grammar of English

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says that this position of
Garner's is utter bunkum

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and nonsense and that upon
review of the entire body

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of English literature, the
rules about which and that

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are largely made up.

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This is why it's so hard to
get a good straight answer

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to that versus which on the Internet

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because everyone is arguing at once.

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Because half the people say
that there are definite rules

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and then half the other people say,

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"The rules don't matter dude."

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But a prolonged study
of both camps has led me

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to determine that there
are distinctions in usage.

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There is a time to use that
and a time to use which.

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From this entire argument,

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from these generations of just bickering,

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I have sussed out two distinctions.

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Distinction one, that is bad with commas.

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Distinction two, which is bad with people.

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So, let's start with
distinction number one that

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that is bad with commas.

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Now Bryan Garner says
that most of the time,

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nine times out of ten in fact, he says

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if you want to use a relative pronoun

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and you're trying to choose
between that and which

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you should probably use
that and the one time out

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of ten that you do want to use which,

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you're supposed to use a comma first.

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So, a comma, which, as in,

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"The carrot, which was orange, was tasty."

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So you can write it that way
with this little comma-net,

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but you can also write it without, as in

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"The carrot which was orange was tasty."

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Now the distinction
between these two sentences

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is the distinction between non-restrictive

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and restrictive relative clauses.

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Because the carrot, comma,
which was orange, comma,

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was tasty means that you could take

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out the comma-bracketed clause

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without changing the
meaning of the sentence.

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"The carrot was tasty."

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But, the carrot, no
comma, which was orange,

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no comma, was tasty that

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which part is a restrictive clause.

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The fact that the carrot
is orange is essential

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to the sentence.

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"The carrot which was orange was tasty,"

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doesn't preclude the idea
that there might have been

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a non-orange, non-tasty carrot
involved somewhere else.

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However, if we try to use
that in a non-restrictive way,

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to say, "The carrot, that
was orange, was tasty,"

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it, to me, and to other
native English speakers,

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that just sounds a little weird.

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It's not ungrammatical, per se.

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There's nothing about the
word that or which that says,

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"This is what it must be used for."

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But, of all the combinations
that could be made

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using either which or that or commas

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or not commas, that, with commas,

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is the least common,
and that is why to me,

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as a speaker and writer of
standard-American English,

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it doesn't look regular.

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And to try that once more, without commas,

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now we have, "The carrot
that was orange was tasty."

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This is restrictive usage again.

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And this one works.

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So, number one works.

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Number two works.

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Number three is weird,
and number four is fine.

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So, the distinction here is that

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that just doesn't play well with commas.

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That's distinction number one.

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Okay, so distinction number two,

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which is bad with people.

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So the way I like to remember this

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is that I imagine a witch who
does not like other people.

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So I just imagine a kind of a cranky witch

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who lives all alone in
a house in the woods,

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and anytime someone comes up to her house

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and asks her if she wants a
subscription to a magazine,

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or does she want to come over for dinner,

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she says, "Blah!", and she slams the door.

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The which witch doesn't like people.

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So the way this shakes out is that which

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doesn't refer to people,

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and that can refer to anything.

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This is also really strange
and it portrays a prejudice,

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in English, toward human beings.

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Check this out.

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To prove this, let me throw
some sentence fragments at you.

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"The dog that I saw, the snow that fell,

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"the woman that boarded the plane,"

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all of these are fine.

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Let's try them again with which.

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"The dog which I saw, the snow which fell,

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"the woman which boarded the plane,"

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now, this to me, as a
native speaker of English,

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doesn't sound right.

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It should either be who or that.

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And again, this isn't
because of some kind of rule

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of official grammar.

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This is just the way that
the language has shaken out.

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Which just doesn't have a
connotation of human beings.

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So that's the essential distinction.

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That doesn't like commas.

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Which is bad with people.

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You can learn anything.

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David out.


Possessive pronouns

WEBVTT
Kind: captions
Language: en

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- [Voiceover] All right grammarians,

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let's get down to it,

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and start talking about
possessive pronouns.

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A possessive pronoun is a pronoun

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that we use to show
possession of something

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which is just sort of
a fancy way of saying

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"you have it."

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So possession equals having stuff.

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Now we can essentially divide
possessive pronouns in half,

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because on this side of the divide,

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we have a list of pronouns
that behave like adjectives,

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and on this side,

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we have a group of pronouns
that behave like nouns.

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I'll list them and then
we'll give some examples.

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So the possessive pronoun

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that behaves like an
adjective for me is my.

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The possessive pronoun

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that behaves like a noun for me is mine.

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Our behaves like an adjective;

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ours behaves like a noun.

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Your behaves like an adjective;

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yours behaves like a noun.

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Her behaves like an adjective;

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hers behaves like a noun.

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His behaves like an adjective;

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his behaves like a noun.

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Its behaves like an adjective;

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its behaves like a noun.

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And their behaves like an adjective,

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and theirs behaves like a noun.

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Now I'd like to point out that nowhere

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in any of these words does there appear

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such a thing as an apostrophe.

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That little guy.

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I know this much is true:

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there are no apostrophes
in possessive pronouns.

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So it's not ours,

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it's ours, like that.

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It's not yours with an
apostrophe like that,

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it's yours with no apostrophe.

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Likewise it's not

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hers, his,

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it's is the big one.

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That means something entirely different.

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Or theirs.

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Across all varieties of English,

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the possessive pronouns don't
have any apostrophes in them.

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So this is a very handsome looking chart

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if I do say so myself,

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but it doesn't really do the work

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of explaining what I mean

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by saying my behaves like an adjective,

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and mine behaves like a noun.

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So let me get some example sentences down

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and we'll see what I mean.

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So let's say that there
was a book that I owned.

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How would I talk about it?

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Well I could do it two different ways

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using these possessive pronouns.

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I could say, "That is my book."

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And here my is working as an adjective

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that modifies and describes book.

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Or I could say, "That book is mine."

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And here we're using is
to connect book to mine,

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and so in that case we're
using mine as a noun.

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How do we know it's acting like a noun?

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Because we can use it
independently of the word book.

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So if someone says to me,
"David, where is your book?"

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I can say, "Mine is on the bedside table."

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Nowhere in this sentence
does the word book appear,

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but we can use mine independently

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because we've established
in a previous sentence

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that the thing we're
talking about is this book.

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So let's talk about my coworker Girish.

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Nice fella.

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And let's say that Girish
has a very nice hat.

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"We would say,

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"That is Girish's hat."

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This is what we'd call a possessive noun.

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But talking of Girish again, we could say,

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"That is his hat."

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Now we're using that possessive
pronoun as an adjective

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to modify hat.

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Whose hat is it?

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It is his hat.

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If we wanted to use the personal pronoun

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that acted like a noun,

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we would say, "That hat is his."

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And we can also use his
independently of the word hat

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by saying, "His is the
hat with polka dots."

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So we've got two piles of
possessive pronouns here.

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And one pile behaves like adjectives:

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my, our, your, her, his, its, their,

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and the other behaves like nouns:

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mine, ours, yours, hers,

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his, its, theirs.

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And remember, none of them
contain an apostrophe.

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You can learn anything.

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David out.


Who versus whom

WEBVTT
Kind: captions
Language: en

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- [Voiceover] Hello grammarians.

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Welcome to one the thorniest
fights in English usage today.

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The question of whether
or not you should use

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who or whom in a sentence
as a relative pronoun.

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So there's this basic idea
that who is the subject form,

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and whom is the object form.

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Which means that if we're talking about

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someone who is the doer, then we say who.

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As in, the spy who loved me.

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As opposed to someone who
is the doee, the object.

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As in, the spy whom I loved.

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You see, cause in this
sentence, who is the subject.

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And in this sentence, I is the subject.

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Me is the object.

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And whom is the object.

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I loved whom?

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In this sentence, I am doing the loving.

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In this sentence it is the
spy who is doing the loving.

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That's the basic rule.

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But, this does not adequately reflect

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the way our culture actually uses

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and has used whom or who for some time.

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In many cases it has become permissible

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to use who as an object.

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Let me show you what I mean.

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So the thing to remember

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is that the basic rule
is a one way street.

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Because the way language is changing,

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whom is on its way out.

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I imagine in another 50, 75
years we won't be using it all.

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Is that sad?

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Sure, a little bit.

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I mean I'm sad that nobody
every uses the pronoun whoso.

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As in, whoso pulleth this
sword from this stone,

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is rightwise born king of England.

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We don't use that anymore.

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It's old fashioned.

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Now we say, whoever.

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And that's ok.

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So we know that the basic rule

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is that you use who as a subject

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and whom as an object.

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Well you can also now
use who as an object.

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The only thing you can't do
is whom is not a subject.

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That's the thing you need to remember,

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is that whom's use is not expanding.

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It is contracting.

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Who is taking over some of whom's duties.

00:02:04.824 --> 00:02:08.470
So let's go back to that spy example.

00:02:08.470 --> 00:02:11.152
So here are the four
possible options, right?

00:02:11.152 --> 00:02:13.010
The spy who loved me,

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the spy whom loved me,

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the spy who I loved,

00:02:16.586 --> 00:02:18.512
and the spy whom I loved.

00:02:18.512 --> 00:02:23.029
Now of these, only this one is incorrect.

00:02:23.029 --> 00:02:26.326
Because we're trying to
use whom as a subject.

00:02:26.326 --> 00:02:28.230
But here, the spy who I loved,

00:02:28.230 --> 00:02:29.983
where who is being an object,

00:02:29.983 --> 00:02:33.885
by the informal rules of our
grammar today, this is fine.

00:02:33.885 --> 00:02:36.786
Either of these is fine.

00:02:36.786 --> 00:02:40.710
The only one that's not
fine is this guy right here.

00:02:40.710 --> 00:02:42.765
The spy whom loved me.

00:02:42.765 --> 00:02:45.831
Because this language change
is going in one direction.

00:02:45.831 --> 00:02:50.324
And it's in the direction of
whom being used less often.

00:02:50.324 --> 00:02:53.087
So whom never expands from
its original position.

00:02:53.087 --> 00:02:54.932
Who does.

00:02:54.932 --> 00:02:57.232
So the next time you're
puzzling over what to do

00:02:57.232 --> 00:03:00.249
in the event of the sentence
who are you talking to,

00:03:00.249 --> 00:03:02.131
and whether or not this pronoun here

00:03:02.131 --> 00:03:05.184
should be who or whom,

00:03:05.184 --> 00:03:08.772
it's really an issue of tone
rather than correctness.

00:03:08.772 --> 00:03:13.277
Because both possibilities
are equally understandable.

00:03:13.277 --> 00:03:15.819
Yes, technically if you
wanted to be very correct

00:03:15.819 --> 00:03:20.637
you would say whom are you talking to,

00:03:20.637 --> 00:03:24.854
or you are talking to whom,

00:03:24.854 --> 00:03:27.231
because whom is the object
of this preposition.

00:03:27.231 --> 00:03:30.747
It's to whom, and so therefore
we would use the object form.

00:03:30.747 --> 00:03:34.248
But you find that when you
separate it out in this question,

00:03:34.248 --> 00:03:36.673
when you put the to at the end,

00:03:36.673 --> 00:03:39.229
and the whom question
particle at the beginning,

00:03:39.229 --> 00:03:41.191
this m just kind of falls away.

00:03:41.191 --> 00:03:43.628
Cause we're more likely to use whom

00:03:43.628 --> 00:03:47.008
when it's immediately
preceded by a preposition.

00:03:47.008 --> 00:03:51.547
But otherwise, it's probably
more likely gonna be who.

00:03:51.547 --> 00:03:54.032
Which is why it's not
that big of a deal to say

00:03:54.032 --> 00:03:55.553
who are you talking to.

00:03:55.553 --> 00:03:56.865
It's not technically correct,

00:03:56.865 --> 00:04:00.510
but it's been used for
so long that it's fine.

00:04:00.510 --> 00:04:02.309
You are talking to who

00:04:02.309 --> 00:04:06.292
is a little bit more
formal of a construction,

00:04:06.292 --> 00:04:09.868
and therefore you would
probably want to use whom.

00:04:09.868 --> 00:04:14.591
Saying you are talking
to who is not as common.

00:04:14.591 --> 00:04:17.691
So in this wild swamp of rule breaking

00:04:17.691 --> 00:04:20.828
there is one hard grammar
rule to pay attention to.

00:04:20.828 --> 00:04:24.693
And it's just never use whom as a subject.

00:04:24.693 --> 00:04:28.628
The role of whom in our
constellation of pronouns

00:04:28.628 --> 00:04:31.149
is decreasing, not expanding.

00:04:31.149 --> 00:04:33.808
Who is taking over whom.

00:04:33.808 --> 00:04:35.572
And since who is the subject,

00:04:35.572 --> 00:04:38.172
whom is not moving into that space.

00:04:38.172 --> 00:04:40.066
Whom is the object pronoun,

00:04:40.066 --> 00:04:43.271
and you use it when you're feeling fancy.

00:04:43.271 --> 00:04:44.767
You can learn anything.

00:04:44.767 --> 00:04:45.817
David out.


2015 AP Biology free response 8

WEBVTT
Kind: captions
Language: en

00:00:00.470 --> 00:00:02.504
- [Voiceover] An individual
has lost the ability

00:00:02.504 --> 00:00:07.320
to activate B cells and mount
a humoral immune response.

00:00:07.320 --> 00:00:11.580
Part A, propose one direct
consequence of the loss

00:00:11.580 --> 00:00:14.722
of B-cell activity on
the individual's humoral

00:00:14.722 --> 00:00:18.273
immune response to the initial exposure

00:00:18.273 --> 00:00:20.594
to a bacterial pathogen.

00:00:20.594 --> 00:00:23.008
So, just as a reminder what B cells are,

00:00:23.008 --> 00:00:24.693
and what a humoral immune response are,

00:00:24.693 --> 00:00:29.476
a humoral immune response is
one that involves antibodies.

00:00:29.476 --> 00:00:32.775
And B cells are the ones that
will recognize an antigen,

00:00:32.775 --> 00:00:35.696
something that the body
doesn't want in its body,

00:00:35.696 --> 00:00:38.143
and then in response to
that, those antigens,

00:00:38.143 --> 00:00:41.210
it will produce, it will
one, it'll proliferate,

00:00:41.210 --> 00:00:43.753
it'll differentiate into plasma cells

00:00:43.753 --> 00:00:46.803
that produce antibodies
which are essentially

00:00:46.803 --> 00:00:51.128
these macro molecules that
tag the antigens for cleanup,

00:00:51.128 --> 00:00:55.141
and then it can differentiate
into memory B cells.

00:00:55.141 --> 00:00:59.228
So that next time, when
that same antigen shows up

00:00:59.228 --> 00:01:01.668
it can mount a faster response.

00:01:01.668 --> 00:01:06.235
So part A, propose one direct
consequence of the loss

00:01:06.235 --> 00:01:08.507
of B-cell activity on
the individual's humoral

00:01:08.507 --> 00:01:11.414
immune response to the initial exposure

00:01:11.414 --> 00:01:13.496
to a bacterial pathogen.

00:01:13.496 --> 00:01:15.624
So there won't be a humoral response.

00:01:15.624 --> 00:01:16.728
So I could say,

00:01:16.728 --> 00:01:21.212
No, no antibodies,

00:01:21.212 --> 00:01:24.535
bodies will

00:01:24.535 --> 00:01:27.466
be produced,

00:01:27.466 --> 00:01:30.495
so no humoral immune response.

00:01:30.495 --> 00:01:33.195
So there

00:01:33.195 --> 00:01:35.601
will be

00:01:35.601 --> 00:01:38.667
no humoral immune response.

00:01:38.667 --> 00:01:43.257
Humoral immune,

00:01:43.257 --> 00:01:47.330
immune response

00:01:47.330 --> 00:01:49.315
to the initial exposure.

00:01:49.315 --> 00:01:53.209
To initial,

00:01:53.209 --> 00:01:56.503
initial exposure.

00:01:56.503 --> 00:01:58.752
So you're not going to have
any tagging of these antigens

00:01:58.752 --> 00:02:02.842
that then can be cleaned
up by other immune cells.

00:02:02.842 --> 00:02:04.992
None of that's going to happen.

00:02:04.992 --> 00:02:08.508
Part B, propose one direct
consequence of the loss

00:02:08.508 --> 00:02:11.370
of B-cell activity on the
speed of the inidividual's

00:02:11.370 --> 00:02:14.394
humoral immune response
to a second exposure

00:02:14.394 --> 00:02:16.885
to the bacterial pathogen.

00:02:16.885 --> 00:02:19.746
Well you have no memory B cells.

00:02:19.746 --> 00:02:24.273
No memory B cells

00:02:24.273 --> 00:02:27.203
and no antibodies.

00:02:27.203 --> 00:02:30.269
Antibodies.

00:02:30.269 --> 00:02:31.909
Specific or, I could say,

00:02:31.909 --> 00:02:35.181
for second exposure to pathogen.

00:02:35.181 --> 00:02:37.922
For second

00:02:37.922 --> 00:02:40.947
exposure

00:02:40.947 --> 00:02:44.866
to pathogen.

00:02:44.866 --> 00:02:47.975
So no humoral response.

00:02:47.975 --> 00:02:50.635
So no

00:02:50.635 --> 00:02:54.061
humoral response.

00:02:54.061 --> 00:02:56.841
And overall immune
response will be slower.

00:02:56.841 --> 00:02:58.740
The whole point of B
cells and the antibodies

00:02:58.740 --> 00:03:00.506
is that the second time it shows around,

00:03:00.506 --> 00:03:01.805
it gets tagged very quickly.

00:03:01.805 --> 00:03:03.490
It gets recognized very quickly.

00:03:03.490 --> 00:03:05.611
And then the immune system can respond.

00:03:05.611 --> 00:03:06.848
Well now you're not going to have that.

00:03:06.848 --> 00:03:09.547
You're not going to have this
in the secondary exposure,

00:03:09.547 --> 00:03:12.155
that quick recognition of the antigen.

00:03:12.155 --> 00:03:14.164
So you're not going to
have humoral response,

00:03:14.164 --> 00:03:16.207
and you could say, overall,

00:03:16.207 --> 00:03:19.367
overall immune response,

00:03:19.367 --> 00:03:21.590
immune response will be slower.

00:03:21.590 --> 00:03:24.783
Immune response

00:03:24.783 --> 00:03:27.392
is going to be slower and less effective.

00:03:27.392 --> 00:03:28.707
Slower and

00:03:28.707 --> 00:03:32.683
less effective.

00:03:32.683 --> 00:03:35.235
Alright, let's think about part C.

00:03:35.235 --> 00:03:38.256
Describe one characteristic
of the individual's

00:03:38.256 --> 00:03:40.166
immune response to the bacterial pathogen

00:03:40.166 --> 00:03:42.911
that is not affected
by the loss of B cells.

00:03:42.911 --> 00:03:43.934
Well the B cells are all about

00:03:43.934 --> 00:03:45.772
the humoral immune response.

00:03:45.772 --> 00:03:49.615
It's about tagging things with antibodies,

00:03:49.615 --> 00:03:51.498
having the memory B cells around

00:03:51.498 --> 00:03:55.383
so that the next time
you get the pathogen,

00:03:55.383 --> 00:03:57.795
the second exposure, you
have a quicker response.

00:03:57.795 --> 00:03:59.915
But it's not the only
part of our immune system.

00:03:59.915 --> 00:04:02.747
Our immune system has,
still, many facets to it.

00:04:02.747 --> 00:04:05.112
One, you're still going
to have the cell mediated

00:04:05.112 --> 00:04:06.490
immune response.

00:04:06.490 --> 00:04:10.254
Still have

00:04:10.254 --> 00:04:13.970
cell mediated,

00:04:13.970 --> 00:04:17.318
mediated immune response.

00:04:17.318 --> 00:04:21.569
Immune response.

00:04:21.569 --> 00:04:25.410
And these are things like phagocytes

00:04:25.410 --> 00:04:27.137
that will go and engulf,

00:04:27.137 --> 00:04:29.633
that will engulf the pathogens.

00:04:29.633 --> 00:04:31.911
Phagocytes.

00:04:31.911 --> 00:04:35.956
Phagocytes, you have T cells

00:04:37.668 --> 00:04:39.377
that can recognize the antigen

00:04:39.377 --> 00:04:42.493
and similarly try to go
about destroying the antigen.

00:04:42.493 --> 00:04:45.921
So you still have the cell
mediated immune response.

00:04:45.921 --> 00:04:48.547
You also have things like the skin,

00:04:48.547 --> 00:04:52.267
things that just block pathogens

00:04:52.267 --> 00:04:53.033
from entering your body.

00:04:53.033 --> 00:04:55.318
And that's considered part
of your immune system.

00:04:55.318 --> 00:04:59.325
Still have

00:04:59.325 --> 00:05:02.454
skin protection.

00:05:02.454 --> 00:05:03.645
And you can go into more detail

00:05:03.645 --> 00:05:05.604
but these are still the types of things

00:05:05.604 --> 00:05:06.903
that the body has,

00:05:06.903 --> 00:05:09.074
even if it lost its B cell capability

00:05:09.074 --> 00:05:11.966
in order to prevent
pathogens from entering,

00:05:11.966 --> 00:05:13.808
in the case of skin,

00:05:13.808 --> 00:05:16.505
and also still once the pathogens get in,

00:05:16.505 --> 00:05:18.420
to still recognize them and engulf them

00:05:18.420 --> 00:05:20.805
or destroy them in some way.


2015 AP Biology free response 7

WEBVTT
Kind: captions
Language: en

00:00:00.320 --> 00:00:02.571
- [Voiceover] Smell perception
in mammals involves the

00:00:02.571 --> 00:00:05.808
interactions of airborne odorant molecules

00:00:05.808 --> 00:00:07.168
from the environment

00:00:07.168 --> 00:00:10.166
with receptor proteins
on the olfactory neurons

00:00:10.166 --> 00:00:11.865
in the nasal cavity.

00:00:11.865 --> 00:00:13.978
The binding of odorant molecules

00:00:13.978 --> 00:00:15.615
to the receptor proteins

00:00:15.615 --> 00:00:17.972
triggers action potentials
in the olfactory

00:00:17.972 --> 00:00:19.642
neurons and results in

00:00:19.642 --> 00:00:22.361
transmission of information to the brain.

00:00:22.361 --> 00:00:24.706
Mammalian genomes typically
have approximately

00:00:24.706 --> 00:00:26.856
one thousand functional

00:00:26.856 --> 00:00:28.838
odorant-receptor genes,

00:00:28.838 --> 00:00:32.926
each encoding a unique odorant receptor.

00:00:32.926 --> 00:00:34.520
Alright, part a,

00:00:34.520 --> 00:00:37.570
describe how the signal
is transmitted across

00:00:37.570 --> 00:00:40.751
the synapse from an activated olfractory

00:00:40.751 --> 00:00:43.351
sensory neuron to the interneuron

00:00:43.351 --> 00:00:46.742
that transmits the
information to the brain.

00:00:46.742 --> 00:00:49.354
Alright, so let's draw this out.

00:00:49.354 --> 00:00:52.973
So, this is part a, so
let's, let me draw the

00:00:52.973 --> 00:00:56.547
activated olfactory sensory neuron,

00:00:56.547 --> 00:01:01.547
so, it might, so those
are its dendrites, there,

00:01:03.112 --> 00:01:06.053
so, I'm not gonna draw a perfect,

00:01:06.053 --> 00:01:07.678
so those are its dendrites
right over there,

00:01:07.678 --> 00:01:10.945
and this is its axon,

00:01:10.945 --> 00:01:12.072
it's axon,

00:01:12.072 --> 00:01:15.694
and then this is the axon terminals.

00:01:16.995 --> 00:01:19.967
The axon terminals, just like that.

00:01:19.967 --> 00:01:22.576
And I could draw other details if I want,

00:01:22.576 --> 00:01:24.866
I don't think you'd have to
draw all of these details

00:01:24.866 --> 00:01:26.239
on the actual test.

00:01:26.239 --> 00:01:27.377
But, just to get a sense of things,

00:01:27.377 --> 00:01:28.840
we could also draw the

00:01:28.840 --> 00:01:31.208
well, we could do it in a different color,

00:01:31.208 --> 00:01:32.616
we could also draw

00:01:32.616 --> 00:01:34.172
the nucleus right over there.

00:01:34.172 --> 00:01:38.150
So this is the activated
olfactory sensory neuron,

00:01:39.173 --> 00:01:42.191
so activated

00:01:43.345 --> 00:01:48.345
olfactory, olfactory sensory neuron.

00:01:48.381 --> 00:01:52.487
sensory neuron.

00:01:53.708 --> 00:01:58.181
And let me draw, let me
draw the interneuron.

00:01:58.181 --> 00:02:01.642
So, the interneuron,
so I'll draw one of its

00:02:01.642 --> 00:02:04.865
dendrites right over there.

00:02:06.356 --> 00:02:09.258
So this is the interneuron,

00:02:09.258 --> 00:02:10.449
drawing its dendrites,

00:02:10.449 --> 00:02:13.100
and then its axon.

00:02:13.100 --> 00:02:14.460
I'll draw it a little
bit better than that,

00:02:14.460 --> 00:02:17.515
its axon just like that
and it goes to the brain.

00:02:17.515 --> 00:02:20.537
And if we zoom in on the synapse,

00:02:20.537 --> 00:02:23.188
where we have to transmit
the signal between the two,

00:02:23.188 --> 00:02:25.994
so if we zoom in,

00:02:25.994 --> 00:02:27.681
if we zoom in,

00:02:27.681 --> 00:02:30.117
right over there,

00:02:30.117 --> 00:02:33.997
we would see the axon terminal of the

00:02:33.997 --> 00:02:35.868
sensory neuron.

00:02:35.868 --> 00:02:38.733
So, maybe it looks something like that.

00:02:38.733 --> 00:02:43.723
And then the, the, the interneuron

00:02:43.723 --> 00:02:45.060
right over that.

00:02:45.060 --> 00:02:46.389
Just like this.

00:02:46.389 --> 00:02:48.849
And this is the synapse.

00:02:48.849 --> 00:02:53.113
So, this is the zoomed in of the synapse.

00:02:55.197 --> 00:02:58.622
And the activated
olfactory sensory neuron,

00:02:58.622 --> 00:03:00.176
you have this activation potential

00:03:00.176 --> 00:03:03.626
that is going to go down the axon,

00:03:03.626 --> 00:03:05.588
and then when it gets to

00:03:05.588 --> 00:03:09.373
when it gets to the axon
terminal right over here,

00:03:09.373 --> 00:03:13.873
it will trigger the release
of neurotransmitters.

00:03:13.873 --> 00:03:16.079
So, these neurotransmitters are typically

00:03:16.079 --> 00:03:20.932
hanging out in, in these, these vessels

00:03:20.932 --> 00:03:23.917
right over here, but then when
the action potential comes,

00:03:23.917 --> 00:03:28.526
they will get released
into the synaptic cleft.

00:03:28.526 --> 00:03:33.021
And then, the interneuron
is going to have,

00:03:33.021 --> 00:03:37.856
is going to have proteins
that sense, that sense

00:03:37.856 --> 00:03:39.626
those neurotransmitters,

00:03:39.626 --> 00:03:42.119
and that activates that neuron.

00:03:42.119 --> 00:03:45.224
So, once again this is the interneuron,

00:03:45.224 --> 00:03:49.787
interneuron, and we could
say that interneuron,

00:03:50.946 --> 00:03:54.192
interneuron

00:03:55.894 --> 00:04:00.604
gets activated, actually
it could be inhibited

00:04:00.604 --> 00:04:05.604
as well, but activated
by, by neurotransmitters

00:04:07.211 --> 00:04:10.800
neurotransmitters

00:04:12.010 --> 00:04:15.182
released into synapse,

00:04:15.182 --> 00:04:19.344
released into synapse

00:04:20.514 --> 00:04:23.876
by the sensory neuron,

00:04:25.034 --> 00:04:30.034
by sensory neuron due to action potential,

00:04:30.954 --> 00:04:34.139
due to action,

00:04:35.189 --> 00:04:38.726
action potential.

00:04:38.726 --> 00:04:40.150
And this is probably enough, but I

00:04:40.150 --> 00:04:42.114
went through a few more
pains to draw it out

00:04:42.114 --> 00:04:45.652
a little bit, and you
could draw other details.

00:04:45.652 --> 00:04:47.587
You could draw the myelin
sheath and all of that,

00:04:47.587 --> 00:04:49.792
you could draw the nuclei
of the different cells,

00:04:49.792 --> 00:04:52.149
but the basic idea is
that the signal goes from

00:04:52.149 --> 00:04:54.924
one neuron to another
with the release of these,

00:04:54.924 --> 00:04:57.260
these chemicals, these neurotransmitters,

00:04:57.260 --> 00:04:59.837
which are actually fairly,
fairly small molecules,

00:04:59.837 --> 00:05:01.813
but then they trigger the next neuron,

00:05:01.813 --> 00:05:03.975
and then after that
signal goes they get all

00:05:03.975 --> 00:05:05.878
they get metabolized by enzymes and things

00:05:05.878 --> 00:05:08.074
and there might be a few
that just always stick around

00:05:08.074 --> 00:05:09.380
but for the most part they signal

00:05:09.380 --> 00:05:11.229
from one neuron to another.

00:05:11.229 --> 00:05:13.073
And they could activate the next neuron,

00:05:13.073 --> 00:05:14.979
or they actually could inhibit it as well,

00:05:14.979 --> 00:05:17.252
but in this case, they
would probably activate.

00:05:17.252 --> 00:05:19.574
Alright, let's do part b.

00:05:19.574 --> 00:05:20.724
Let's do part b.

00:05:20.724 --> 00:05:23.080
Explain how the expression
of a limited number

00:05:23.080 --> 00:05:25.611
of odorant receptor genes,
you see there's thousands,

00:05:25.611 --> 00:05:27.531
receptor genes, can lead
to the perception of

00:05:27.531 --> 00:05:29.111
thousands of odors.

00:05:29.111 --> 00:05:31.037
Use the evidence about
the number of odorant

00:05:31.037 --> 00:05:33.940
receptor genes to support your answer.

00:05:33.940 --> 00:05:37.867
So, one way to think
about it is, and this is

00:05:37.867 --> 00:05:41.096
this is kind of a theory, here, is that

00:05:41.096 --> 00:05:43.477
you don't necessarily have a one-to-one

00:05:43.477 --> 00:05:47.372
mapping between odorant, odorant receptors

00:05:47.372 --> 00:05:50.555
and odorant molecules, so don't,

00:05:51.625 --> 00:05:55.096
don't necessarily,

00:05:55.963 --> 00:06:00.963
necessarily have one-to-one

00:06:01.545 --> 00:06:04.998
relationship

00:06:06.177 --> 00:06:11.130
between, between odorant molecules

00:06:12.101 --> 00:06:17.101
odorant molecules and receptor proteins.

00:06:18.412 --> 00:06:22.821
And receptor proteins.

00:06:22.821 --> 00:06:25.925
Maybe, maybe one protein can,

00:06:25.925 --> 00:06:30.079
can detect multiple molecules,

00:06:30.079 --> 00:06:34.295
maybe one, maybe a given

00:06:35.577 --> 00:06:38.727
protein can

00:06:39.720 --> 00:06:44.720
detect multiple molecules.

00:06:47.322 --> 00:06:52.190
Or vice versa, or vice versa,

00:06:52.190 --> 00:06:53.543
whoops I keep having trouble

00:06:53.543 --> 00:06:55.174
with my little pen here.

00:06:55.174 --> 00:06:56.923
or vice versa,

00:06:56.923 --> 00:07:01.923
or vice, vice versa.

00:07:02.236 --> 00:07:06.280
And so then, you could have this

00:07:07.589 --> 00:07:11.859
could lead to

00:07:11.859 --> 00:07:15.616
many combinations,

00:07:17.561 --> 00:07:22.561
combinations being detected.

00:07:22.948 --> 00:07:25.081
So even though you could
have, maybe these one

00:07:25.081 --> 00:07:27.761
thousand odorant genes,

00:07:27.761 --> 00:07:31.958
they code for one thousand
receptor proteins,

00:07:31.958 --> 00:07:32.934
and so you might say well,

00:07:32.934 --> 00:07:34.695
well those'll only be able
to detect one thousand

00:07:34.695 --> 00:07:37.057
different molecules, well, no,

00:07:37.057 --> 00:07:39.215
each of those could detect more than one,

00:07:39.215 --> 00:07:41.235
and then, and when they come
in different combinations

00:07:41.235 --> 00:07:44.867
they might trigger the
brain in different ways.

00:07:44.867 --> 00:07:47.143
And then, many, I mean

00:07:47.143 --> 00:07:47.983
I could even add that,

00:07:47.983 --> 00:07:51.225
this could lead to many
combinations being detected

00:07:51.225 --> 00:07:53.214
which would be different,

00:07:53.214 --> 00:07:57.478
different smells in the brain,

00:07:57.478 --> 00:08:02.329
different smells

00:08:02.329 --> 00:08:05.227
as perceived by brain,

00:08:06.345 --> 00:08:09.373
perceived by brain.

00:08:09.373 --> 00:08:12.864
Now, there is some possibility
that each of these genes,

00:08:12.864 --> 00:08:15.482
maybe they could be coded into proteins

00:08:15.482 --> 00:08:18.745
in different ways, but they
do tell us each encoding

00:08:18.745 --> 00:08:20.447
a unique odorant-receptor, so I like,

00:08:20.447 --> 00:08:21.898
I like going with this one,

00:08:21.898 --> 00:08:23.429
you don't necessarily have
a one-to-one relationship,

00:08:23.429 --> 00:08:26.560
each receptor could
recognize multiple molecules,

00:08:26.560 --> 00:08:29.182
or one molecule could be
bound by multiple receptors,

00:08:29.182 --> 00:08:30.366
and then the different combinations

00:08:30.366 --> 00:08:31.748
of all of the above
means that you could have

00:08:31.748 --> 00:08:34.070
much more than one thousand molecules

00:08:34.070 --> 00:08:36.066
being detected, and
especially different molecules

00:08:36.066 --> 00:08:37.598
in different combinations,
you could have thousands

00:08:37.598 --> 00:08:41.344
upon thousands of smells quote, unquote,

00:08:41.344 --> 00:08:43.666
being detected.


2015 AP Biology free response 2 a b

WEBVTT
Kind: captions
Language: en

00:00:00.379 --> 00:00:02.492
- [Voiceover] All right,
cellular respiration

00:00:02.492 --> 00:00:05.320
includes the metabolic
pathways of glycolysis,

00:00:05.320 --> 00:00:08.408
the Krebs cycle, and the
electron transport chain,

00:00:08.408 --> 00:00:10.489
as represented in the figures.

00:00:10.489 --> 00:00:12.927
So we have the figures here of,

00:00:12.927 --> 00:00:15.398
glycolysis, the Krebs cycle,

00:00:15.398 --> 00:00:17.315
and the electron transport chain.

00:00:17.315 --> 00:00:19.396
If all of this looks
completely foreign to you,

00:00:19.396 --> 00:00:21.574
I encourage you to watch
the videos on Khan Academy

00:00:21.574 --> 00:00:23.362
on glycolysis, the Krebs cycle,

00:00:23.362 --> 00:00:25.117
and the electron transport chain,

00:00:25.117 --> 00:00:28.367
and on cellular respiration in general.

00:00:29.213 --> 00:00:31.066
All right, but let's tackle this problem.

00:00:31.066 --> 00:00:32.984
It's a nice review of all of those things.

00:00:32.984 --> 00:00:34.870
In cellular respiration, carbohydrates

00:00:34.870 --> 00:00:38.023
and other metabolites are oxidized,

00:00:38.023 --> 00:00:40.754
meaning electrons are
taken away from them,

00:00:40.754 --> 00:00:43.809
and the resulting
energy-transfer reactions

00:00:43.809 --> 00:00:46.226
support the synthesis of ATP.

00:00:48.328 --> 00:00:51.644
All right, using the information above,

00:00:51.644 --> 00:00:55.740
describe one contribution
of each of the following

00:00:55.740 --> 00:00:57.157
in ATP synthesis.

00:00:58.893 --> 00:00:59.966
All right, the first one.

00:00:59.966 --> 00:01:04.875
Catabolism of glucose in
glycolysis and pyruvate oxidation.

00:01:04.875 --> 00:01:06.542
The second was oxidation of intermediates

00:01:06.542 --> 00:01:07.777
in the Krebs cycle.

00:01:07.777 --> 00:01:10.085
And the third one is
formation of a proton gradient

00:01:10.085 --> 00:01:11.971
by the electron transport chain.

00:01:11.971 --> 00:01:14.246
Now, each of these statements
seem kind of intimidating,

00:01:14.246 --> 00:01:16.522
but they're really just
saying, describe how

00:01:16.522 --> 00:01:18.667
glycolysis and pyruvate oxidation

00:01:18.667 --> 00:01:20.390
contribute to ATP synthesis.

00:01:20.390 --> 00:01:22.833
Describe how the Krebs cycle,
because the Krebs cycle

00:01:22.833 --> 00:01:25.172
is essentially nothing but the oxidation

00:01:25.172 --> 00:01:27.090
of these intermediates to produce things

00:01:27.090 --> 00:01:29.007
that are useful for ATP synthesis.

00:01:29.007 --> 00:01:31.510
And then the formation
of the proton gradient

00:01:31.510 --> 00:01:32.583
by the electron transport chain.

00:01:32.583 --> 00:01:34.441
Well that's what the
electron trans-prit (laughs),

00:01:34.441 --> 00:01:36.911
that's what the electron
transport chain does.

00:01:36.911 --> 00:01:41.072
It takes high energy
electrons from NADH or FADH2,

00:01:41.072 --> 00:01:42.828
and then as those high energy electrons

00:01:42.828 --> 00:01:44.616
go to lower and lower energy states,

00:01:44.616 --> 00:01:48.191
it's pumping these hydrogen
protons across the membrane

00:01:48.191 --> 00:01:52.190
and when they come back in,
that's used to synthesize ATP.

00:01:52.190 --> 00:01:53.230
So let's just answer.

00:01:53.230 --> 00:01:55.018
We have to describe one
contribution of each.

00:01:55.018 --> 00:01:57.489
So, let's first focus on glycolysis.

00:01:57.489 --> 00:02:00.805
So if we look here, there's
more than one contribution.

00:02:00.805 --> 00:02:03.113
You see that it can phosphorylate

00:02:03.113 --> 00:02:05.363
these two ADPs to two ATPs.

00:02:06.438 --> 00:02:08.908
So that's one contribution we could list.

00:02:08.908 --> 00:02:12.658
We could say that it's
producing these NADHs.

00:02:13.557 --> 00:02:17.263
It's producing these
NADHs, which can provide

00:02:17.263 --> 00:02:19.924
both the hydrogen proton
and, more importantly,

00:02:19.924 --> 00:02:21.646
the high-energy electrons

00:02:21.646 --> 00:02:24.735
for the electron transport chain later on.

00:02:24.735 --> 00:02:26.783
You see that right over here.

00:02:26.783 --> 00:02:28.576
Or you could say that, well, look,

00:02:28.576 --> 00:02:30.428
it's producing the Acetyl-CoA,

00:02:30.428 --> 00:02:32.834
which can enter the Krebs cycle,

00:02:32.834 --> 00:02:35.250
which is used to produce GTP

00:02:36.442 --> 00:02:38.359
or more NADHs or FADH2.

00:02:39.595 --> 00:02:41.286
So all of these are contributions,

00:02:41.286 --> 00:02:42.554
and since we only have to list one,

00:02:42.554 --> 00:02:44.569
I'll list the most direct and obvious one,

00:02:44.569 --> 00:02:46.162
although you could list any of these,

00:02:46.162 --> 00:02:49.912
is, I will list, so this
is one contribution.

00:02:50.758 --> 00:02:53.253
I'll say the phosphorylation,

00:02:53.253 --> 00:02:54.503
phosphorylation

00:02:57.707 --> 00:02:59.540
of two ADPs, two ADPs,

00:03:02.031 --> 00:03:03.114
to two ATPs,

00:03:04.891 --> 00:03:05.891
to two ATPs.

00:03:08.142 --> 00:03:09.475
And I could list several more,

00:03:09.475 --> 00:03:11.393
but that's a good one right over there,

00:03:11.393 --> 00:03:13.480
we just have to have one contribution.

00:03:13.480 --> 00:03:16.856
All right, oxidation of
intermediates in the Krebs cycle.

00:03:16.856 --> 00:03:18.643
So, the oxidation of the intermediates,

00:03:18.643 --> 00:03:20.822
that's just talking about
each of these things

00:03:20.822 --> 00:03:24.137
keep getting oxidized,
and as they get oxidized,

00:03:24.137 --> 00:03:26.673
we can use that to reduce other things,

00:03:26.673 --> 00:03:28.923
including NAD plus to NADH.

00:03:31.387 --> 00:03:34.215
So, when you reduce it,
it's gaining electrons.

00:03:34.215 --> 00:03:35.775
Notice, NAD plus is positive

00:03:35.775 --> 00:03:38.538
and then it becomes
NADH, which is neutral.

00:03:38.538 --> 00:03:41.106
And these NADHs are used later on

00:03:41.106 --> 00:03:42.862
in the electron transport chain

00:03:42.862 --> 00:03:46.958
to pump hydrogen protons
across the membrane

00:03:46.958 --> 00:03:49.884
which are then used in
oxidative phosphorylation

00:03:49.884 --> 00:03:53.297
to produce the ATP as they
go back through the membrane.

00:03:53.297 --> 00:03:56.710
So, you could talk about
the NADHs or FADH2s,

00:03:56.710 --> 00:03:59.576
or you could talk about
the direct creation of GTPs

00:03:59.576 --> 00:04:02.111
which could be used to create ATPs.

00:04:02.111 --> 00:04:03.574
So any of that is fine.

00:04:03.574 --> 00:04:05.947
So I'll just list one of them.

00:04:05.947 --> 00:04:07.114
So, I'll write

00:04:10.076 --> 00:04:11.159
reduction of

00:04:14.153 --> 00:04:14.986
NAD plus

00:04:17.046 --> 00:04:18.129
to NAD, NADH,

00:04:20.789 --> 00:04:22.206
which is used in

00:04:25.885 --> 00:04:27.836
electron transport chain,

00:04:27.836 --> 00:04:28.752
in electron

00:04:31.322 --> 00:04:32.572
transport chain

00:04:36.820 --> 00:04:39.701
to pump hydrogen protons to get,

00:04:39.701 --> 00:04:41.868
to create proton gradient,

00:04:43.133 --> 00:04:44.466
to create proton

00:04:47.489 --> 00:04:49.072
gradient, gradient.

00:04:50.804 --> 00:04:53.145
And once again, I could
talk about the GDP,

00:04:53.145 --> 00:04:55.778
the GT (laughs), the GTPs being created.

00:04:55.778 --> 00:04:58.801
I could talk about the
FADH2 being created.

00:04:58.801 --> 00:05:00.984
Formation of a proton gradient by

00:05:00.984 --> 00:05:02.614
the electron transport chain.

00:05:02.614 --> 00:05:06.781
Well, as the protons flow
with the gradient back into,

00:05:09.928 --> 00:05:14.012
back across the membrane,
they power ATP synthase

00:05:15.304 --> 00:05:17.554
which creates ATP from ADP.

00:05:18.685 --> 00:05:19.935
So, as protons

00:05:24.964 --> 00:05:25.797
flow

00:05:27.402 --> 00:05:28.819
across membrane,

00:05:30.198 --> 00:05:32.381
flow with gradient across membrane,

00:05:32.381 --> 00:05:33.881
flow with gradient

00:05:37.679 --> 00:05:38.654
across membrane,

00:05:38.654 --> 00:05:40.117
and if you're actually taking the AP test,

00:05:40.117 --> 00:05:41.557
you might want to just do it below,

00:05:41.557 --> 00:05:42.727
so you might have more space,

00:05:42.727 --> 00:05:43.800
but I'll just fill it in here.

00:05:43.800 --> 00:05:47.633
As protons flow with
gradient across membrane,

00:05:49.066 --> 00:05:49.983
they drive,

00:05:51.147 --> 00:05:53.147
they drive ATP synthase,

00:05:56.250 --> 00:05:57.334
ATP synthase,

00:06:00.681 --> 00:06:01.514
which,

00:06:03.574 --> 00:06:05.304
which takes,

00:06:05.304 --> 00:06:08.685
we can say oxidatively phosphorylates,

00:06:08.685 --> 00:06:11.091
so I'll just write phosphorylates,

00:06:11.091 --> 00:06:12.341
phosphorylates

00:06:15.375 --> 00:06:16.208
ADP,

00:06:17.417 --> 00:06:18.333
ADP to ATP.

00:06:21.579 --> 00:06:23.707
And once again, if
everything I'm saying here

00:06:23.707 --> 00:06:25.397
sounds foreign, and if these diagrams

00:06:25.397 --> 00:06:26.762
don't make a lot of sense to you.

00:06:26.762 --> 00:06:29.038
If they don't trigger a pleasurable memory

00:06:29.038 --> 00:06:30.603
in your head (laughs),

00:06:30.603 --> 00:06:31.717
I encourage you to watch
the videos (laughs)

00:06:31.717 --> 00:06:32.962
on Khan Academy, where
hopefully you'll get

00:06:32.962 --> 00:06:35.010
a little bit more intuition for the things

00:06:35.010 --> 00:06:37.383
that I am talking about.

00:06:37.383 --> 00:06:40.764
All right, now let's see
if we can tackle part b.

00:06:40.764 --> 00:06:43.072
Use each of the following observations

00:06:43.072 --> 00:06:44.795
to justify the claim that glycolysis

00:06:44.795 --> 00:06:48.956
first occurred in a common
ancestor of all living organisms.

00:06:48.956 --> 00:06:53.182
So, nearly all existing
organisms perform glycolysis.

00:06:53.182 --> 00:06:55.880
So, it's much more likely,

00:06:55.880 --> 00:06:59.066
so much more likely that this,

00:06:59.066 --> 00:07:00.301
in order for this to happen,

00:07:00.301 --> 00:07:02.349
maybe I'll write this.

00:07:02.349 --> 00:07:05.860
In order, so for this one right over here,

00:07:05.860 --> 00:07:06.693
in order

00:07:08.984 --> 00:07:10.984
for this to be the case,

00:07:13.849 --> 00:07:15.099
to be the case,

00:07:17.064 --> 00:07:18.981
it is much more likely,

00:07:20.314 --> 00:07:21.648
much more likely

00:07:25.423 --> 00:07:26.256
that this

00:07:28.984 --> 00:07:31.401
evolved in a common ancestor,

00:07:33.536 --> 00:07:35.036
in common ancestor

00:07:39.489 --> 00:07:41.212
and was passed down,

00:07:41.212 --> 00:07:44.463
and was passed down, or you could say

00:07:44.463 --> 00:07:46.316
selected for, even,

00:07:46.316 --> 00:07:47.732
and selected for,

00:07:49.209 --> 00:07:50.292
selected for,

00:07:51.452 --> 00:07:53.535
rather than independently

00:07:56.101 --> 00:07:57.666
coming about multiple times,

00:07:57.666 --> 00:07:59.332
than independently,

00:08:01.710 --> 00:08:02.794
independently

00:08:05.546 --> 00:08:09.772
arising in multiple branches
of the evolutionary change,

00:08:09.772 --> 00:08:12.022
than independently arising

00:08:14.752 --> 00:08:16.502
in multiple branches,

00:08:18.937 --> 00:08:19.771
branches,

00:08:21.904 --> 00:08:23.237
of tree of life.

00:08:24.208 --> 00:08:28.207
Or let me say, multiple
branches of evolutionary tree.

00:08:28.207 --> 00:08:29.290
Evolutionary,

00:08:31.100 --> 00:08:32.600
evolutionary tree.

00:08:33.440 --> 00:08:35.001
The fact that all, nearly,

00:08:35.001 --> 00:08:36.826
or they're saying nearly all,

00:08:36.826 --> 00:08:40.272
nearly all existing
organisms perform glycolysis.

00:08:40.272 --> 00:08:43.262
In theory, it could have
happened independently,

00:08:43.262 --> 00:08:46.058
just because it gets
selected so for strongly,

00:08:46.058 --> 00:08:49.516
but if something happens
in nearly all organisms,

00:08:49.516 --> 00:08:51.347
it's very likely that it
evolved at a very, very

00:08:51.347 --> 00:08:54.918
early stage, at a kind of a
primitive ancestor organism,

00:08:54.918 --> 00:08:56.349
and that was selected for,

00:08:56.349 --> 00:08:57.844
and it continues to be selected for

00:08:57.844 --> 00:09:00.027
and that's why we continue to see it.

00:09:00.027 --> 00:09:04.225
All right, glycolysis occurs
under anaerobic conditions.

00:09:04.225 --> 00:09:06.435
So actually, let me create some space here

00:09:06.435 --> 00:09:09.134
so things don't get too jumbled up.

00:09:09.134 --> 00:09:12.839
So glycolysis occurs under
anaerobic conditions.

00:09:12.839 --> 00:09:14.339
Well, early Earth,

00:09:15.185 --> 00:09:16.101
early Earth

00:09:18.891 --> 00:09:19.807
had little,

00:09:21.431 --> 00:09:22.847
had little oxygen

00:09:25.072 --> 00:09:26.156
little oxygen

00:09:28.838 --> 00:09:30.005
in atmosphere.

00:09:33.846 --> 00:09:34.924
Early life.

00:09:34.924 --> 00:09:36.257
So, early life,

00:09:39.126 --> 00:09:40.376
had to perform,

00:09:42.117 --> 00:09:43.873
had to, I guess you could say,

00:09:43.873 --> 00:09:46.718
produce ATP, or you could,

00:09:46.718 --> 00:09:49.134
early life had to metabolize,

00:09:51.891 --> 00:09:54.724
tab-ol-ize sugars or carbohydrates

00:09:56.809 --> 00:09:58.976
in anaerobic environment.

00:10:00.201 --> 00:10:04.367
In anaerobic, so an environment
that doesn't have oxygen.

00:10:05.252 --> 00:10:06.085
Anaerobic,

00:10:07.085 --> 00:10:08.919
anareobic environment.

00:10:11.107 --> 00:10:13.711
So that seems to, once
again, justify the claim

00:10:13.711 --> 00:10:15.040
that glycolysis first
occurred in a common ancestor

00:10:15.040 --> 00:10:17.040
of all living organisms.

00:10:19.815 --> 00:10:23.251
Glycolysis only occurs in cytosol.

00:10:23.251 --> 00:10:25.418
So, so most, so, earliest,

00:10:29.287 --> 00:10:30.370
earliest life

00:10:33.619 --> 00:10:34.619
didn't have

00:10:37.698 --> 00:10:40.445
membrane-bound organelles,

00:10:40.445 --> 00:10:41.695
membrane-bound

00:10:44.623 --> 00:10:45.540
organelles,

00:10:48.849 --> 00:10:52.381
so the fact that it
only occurs in cytosol,

00:10:52.381 --> 00:10:54.048
so fact that occurs

00:10:58.733 --> 00:10:59.566
in cytosol

00:11:01.842 --> 00:11:05.132
consistent with it be, that it's possible

00:11:05.132 --> 00:11:07.589
that early life did it.

00:11:07.589 --> 00:11:08.673
Is consistent

00:11:12.828 --> 00:11:15.738
that earl, with early life

00:11:15.738 --> 00:11:17.738
with it first occurring,

00:11:20.145 --> 00:11:22.862
occurring in common ancestor.

00:11:22.862 --> 00:11:25.362
First, with it first occurring

00:11:30.749 --> 00:11:31.666
in common,

00:11:33.921 --> 00:11:35.171
early ancestor.

00:11:38.660 --> 00:11:42.744
I'll then tackle parts c
and d in the next video.


2015 AP Biology free response 6

WEBVTT
Kind: captions
Language: en

00:00:00.380 --> 00:00:03.466
- In an attempt to rescue
a small isolated population

00:00:03.466 --> 00:00:05.316
of snakes from decline,

00:00:05.316 --> 00:00:06.586
a few male snakes

00:00:06.586 --> 00:00:08.347
from several larger populations

00:00:08.347 --> 00:00:10.650
of the same species were introduced

00:00:10.650 --> 00:00:13.335
into the population in 1992.

00:00:13.335 --> 00:00:15.728
The snakes reproduce sexually,

00:00:15.728 --> 00:00:18.703
and there are abundant
resources in the environment.

00:00:18.703 --> 00:00:20.490
The figure below shows the results

00:00:20.490 --> 00:00:22.747
of a study of the snake population

00:00:22.747 --> 00:00:25.154
both before and after the introduction

00:00:25.154 --> 00:00:26.909
of the outside males.

00:00:26.909 --> 00:00:30.392
In the study, the numbers
of captured snakes

00:00:30.392 --> 00:00:33.264
indicates the overall population size.

00:00:33.264 --> 00:00:36.993
So, let's look it, let's look
at this, at the study here,

00:00:36.993 --> 00:00:38.344
the data from the study.

00:00:38.344 --> 00:00:42.145
So 1989, they captured a bunch of snakes,

00:00:42.145 --> 00:00:43.662
the total snakes captured,

00:00:43.662 --> 00:00:47.022
but a small fraction
of them were juveniles.

00:00:47.022 --> 00:00:52.022
It looks like about five of
the 19 snakes were juvenile

00:00:52.028 --> 00:00:54.848
and we see that the total
population seems to be declining.

00:00:54.848 --> 00:00:57.381
The total snakes captured,
which they say is a...

00:00:58.866 --> 00:01:01.400
is an indication of overall population.

00:01:01.400 --> 00:01:04.771
That that is declining, and
then they introduced the males

00:01:04.771 --> 00:01:07.993
from the outside and then
it takes a couple years

00:01:07.993 --> 00:01:12.553
but then the population
seems to increase again.

00:01:12.553 --> 00:01:14.586
So, let's see what the questions are.

00:01:14.586 --> 00:01:17.800
Describe one characteristic
of the original population

00:01:17.800 --> 00:01:20.503
that may have led to
the population's decline

00:01:20.503 --> 00:01:24.316
in size between 1989 and 1993.

00:01:24.316 --> 00:01:27.246
So, we can only theorize,
they haven't told us a lot,

00:01:27.246 --> 00:01:29.952
they have told us it's a small population.

00:01:29.952 --> 00:01:32.159
So they say small and it's a small,

00:01:32.159 --> 00:01:35.703
isolated, small isolated population.

00:01:35.703 --> 00:01:38.308
So when you have a small
isolated population,

00:01:38.308 --> 00:01:40.395
some things can happen
that are a lot less likely

00:01:40.395 --> 00:01:43.103
than if you have a large
un-isolated population.

00:01:43.103 --> 00:01:44.981
For example, you might have,

00:01:44.981 --> 00:01:47.329
actually I'll just answer it right here.

00:01:47.329 --> 00:01:49.256
You might have an uneven distribution

00:01:49.256 --> 00:01:51.494
of males, females so not enough males.

00:01:52.404 --> 00:01:56.503
Not enough males.

00:01:56.503 --> 00:01:57.759
That's less likely to happen if you

00:01:57.759 --> 00:01:59.304
have a really large population,

00:01:59.304 --> 00:02:01.052
but a small isolated population,

00:02:01.052 --> 00:02:03.903
well, you know, there's a
chance that you could skew

00:02:03.903 --> 00:02:06.722
one way or the other and if
you don't have enough males

00:02:06.722 --> 00:02:08.206
you're not going to have
enough reproduction,

00:02:10.176 --> 00:02:11.734
you might have

00:02:11.734 --> 00:02:15.744
too few young snakes in their prime

00:02:15.744 --> 00:02:17.339
of their reproductive age,

00:02:17.339 --> 00:02:21.329
so, too, too few young,

00:02:22.879 --> 00:02:25.945
young reproducing snakes,

00:02:25.945 --> 00:02:28.839
reproducing snakes,

00:02:28.839 --> 00:02:30.828
and there could be a bunch of reasons why

00:02:30.828 --> 00:02:34.305
this maybe happened, maybe
there was some type of

00:02:34.305 --> 00:02:36.868
calamity that happened, you know, in 1988,

00:02:36.868 --> 00:02:38.778
where a lot of the young snakes died

00:02:38.778 --> 00:02:40.935
or some type of a predator
and so all the snakes

00:02:40.935 --> 00:02:42.655
that are left are the ones that are older

00:02:42.655 --> 00:02:45.961
and they're not as viable
in terms of reproduction,

00:02:45.961 --> 00:02:48.351
but that's one possibility there.

00:02:48.351 --> 00:02:51.314
You could have some type
of, it's a small population,

00:02:51.314 --> 00:02:53.918
you could have, because of the lack,

00:02:53.918 --> 00:02:56.978
you could have a mutation
that is just disproportionatly

00:02:56.978 --> 00:02:58.665
showing up in that population which makes

00:02:58.665 --> 00:03:00.589
it less likely to reproduce.

00:03:00.589 --> 00:03:03.769
So, mutation,

00:03:05.399 --> 00:03:08.500
mutation in population,

00:03:09.560 --> 00:03:11.506
that makes it less likely to reproduce.

00:03:11.506 --> 00:03:13.465
For the actual test, you
just have to describe

00:03:13.465 --> 00:03:15.140
one characteristic and these are

00:03:15.140 --> 00:03:17.358
all possible characteristics.

00:03:17.358 --> 00:03:19.883
Then in part b, they
say, propose one reason

00:03:19.883 --> 00:03:21.919
that the introduction of the outside males

00:03:21.919 --> 00:03:24.690
rescued the snake population from decline.

00:03:24.690 --> 00:03:27.182
So, for part b, I'll do
that right over here.

00:03:27.182 --> 00:03:30.072
Part b, well, if you had not enough males,

00:03:30.072 --> 00:03:34.442
introducing males, so it could re-balance,

00:03:34.442 --> 00:03:36.236
could re-balance

00:03:38.410 --> 00:03:40.470
male female ratio,

00:03:40.470 --> 00:03:44.725
male female ratio,

00:03:44.725 --> 00:03:47.515
it could have introduced
some genetic diversity

00:03:47.515 --> 00:03:49.107
so you don't have the mutation,

00:03:49.107 --> 00:03:52.197
could introduce,

00:03:53.277 --> 00:03:57.136
introduce genetic diversity

00:03:57.136 --> 00:03:59.106
Once again this is a
small, isolated population,

00:03:59.106 --> 00:04:00.907
those are triggers in your heads, okay,

00:04:00.907 --> 00:04:03.061
there might not be a lot
of genetic diversity there.

00:04:03.061 --> 00:04:05.344
Introduce genetic diversity.

00:04:08.142 --> 00:04:10.535
The introduced male snakes
might have been younger.

00:04:10.535 --> 00:04:11.766
So, could...

00:04:12.927 --> 00:04:13.828
introduce...

00:04:16.197 --> 00:04:17.040
younger,

00:04:19.400 --> 00:04:20.140
younger snakes.

00:04:20.140 --> 00:04:23.176
They didn't tell us whether
the males from the outside,

00:04:23.176 --> 00:04:25.402
what age they were but
these are just theories

00:04:25.402 --> 00:04:26.230
based on what they did tell us

00:04:26.230 --> 00:04:28.053
that that's one of the possibilities,

00:04:28.053 --> 00:04:29.747
and once again, you only
have to describe one,

00:04:29.747 --> 00:04:31.552
so you could just say,
could have re-balanced

00:04:31.552 --> 00:04:34.651
the male female ratio, and then part c,

00:04:35.569 --> 00:04:39.955
part c, describe how the
data support the statement

00:04:39.955 --> 00:04:42.526
that there are abundant
resources in the environment.

00:04:44.000 --> 00:04:46.022
Well, you know, if you just saw this data

00:04:46.022 --> 00:04:47.961
you could have said, well
maybe one of the reasons

00:04:47.961 --> 00:04:50.462
for even part a is that you
didn't have abundant resources,

00:04:50.462 --> 00:04:53.408
but notice when you introduce
males from the outside,

00:04:53.408 --> 00:04:56.239
now all of a sudden, the
population keeps increasing.

00:04:56.239 --> 00:04:58.868
So, the fact that the
population keeps increasing

00:04:58.868 --> 00:05:01.956
and actually goes above
where it was in 1989,

00:05:01.956 --> 00:05:03.078
well, that's a pretty good indication

00:05:03.078 --> 00:05:04.796
that you have abundant
resources, there's nothing

00:05:04.796 --> 00:05:07.145
that's putting a ceiling
on this growth once you

00:05:07.145 --> 00:05:10.852
somehow fix the problem by
introducing these outside males.

00:05:10.852 --> 00:05:13.671
So, I could say, population,

00:05:14.818 --> 00:05:16.137
population

00:05:17.849 --> 00:05:20.965
keeps growing

00:05:22.770 --> 00:05:25.992
from '93, or especially from '95,

00:05:25.992 --> 00:05:30.222
1995 onward, onward,

00:05:30.222 --> 00:05:33.215
wouldn't happen if we
had limited resources,

00:05:33.215 --> 00:05:36.959
wouldn't have happened

00:05:36.959 --> 00:05:38.479
without abundant resources.

00:05:38.479 --> 00:05:39.597
Wouldn't have happened,

00:05:42.297 --> 00:05:43.283
happened...

00:05:44.141 --> 00:05:47.782
without abundant resources.

00:05:49.396 --> 00:05:53.657
Abundant resources.

00:05:53.657 --> 00:05:54.614
And we're done.


2015 AP Biology free response 5

WEBVTT
Kind: captions
Language: en

00:00:00.259 --> 00:00:02.433
- {Voiceover] Phototropism in plants is a

00:00:02.433 --> 00:00:04.546
response in which a plant shoot grows

00:00:04.546 --> 00:00:06.151
toward a light source.

00:00:06.151 --> 00:00:08.305
The results of five different experimental

00:00:08.305 --> 00:00:10.357
treatments from classic investigations

00:00:10.357 --> 00:00:12.937
of phototropism are shown above.

00:00:12.937 --> 00:00:15.822
Part A: Give support for the claim that

00:00:15.822 --> 00:00:18.565
the cells located in the
tip of the plant shoot

00:00:18.565 --> 00:00:20.962
give support for the claim that the cells

00:00:20.962 --> 00:00:23.014
located in the tip of the plant shoot

00:00:23.014 --> 00:00:25.371
detect the light by comparing the results

00:00:25.371 --> 00:00:27.728
from treatment group one with

00:00:27.728 --> 00:00:29.394
the results from treatment group two

00:00:29.394 --> 00:00:31.751
and treatment group three.

00:00:31.751 --> 00:00:32.868
So we wanna compare these first

00:00:32.868 --> 00:00:36.079
three treatment groups, and you see when

00:00:36.079 --> 00:00:38.618
you have an unaltered tip that the whole

00:00:38.618 --> 00:00:42.194
plant is going to bend in
the direction of the light,

00:00:42.194 --> 00:00:44.368
when you remove the tip, it no longer

00:00:44.368 --> 00:00:47.781
bends in the direction of the light,

00:00:47.781 --> 00:00:49.590
or if you were to cover the tip with

00:00:49.590 --> 00:00:51.296
some type of an opaque cap so the light

00:00:51.296 --> 00:00:54.832
can't go through it, it's
still not going to bend.

00:00:54.832 --> 00:00:56.396
So this is pretty good
evidence that there is

00:00:56.396 --> 00:00:59.240
there is something about
the tip of the plant

00:00:59.240 --> 00:01:01.821
that allows the phototropism to occur,

00:01:01.821 --> 00:01:04.381
it allows the plant to
know which direction

00:01:04.381 --> 00:01:06.819
the light is and then makes somehow causes

00:01:06.819 --> 00:01:08.912
it to bend in that direction.

00:01:08.912 --> 00:01:11.329
So I'll just write that down.

00:01:11.329 --> 00:01:13.036
Give support for the claim,

00:01:13.036 --> 00:01:17.004
so we can say that phototropism

00:01:18.115 --> 00:01:19.064
phototropism

00:01:20.664 --> 00:01:22.075
phototropism

00:01:24.835 --> 00:01:29.835
only occurred only occurred when

00:01:32.819 --> 00:01:37.715
there is an

00:01:37.715 --> 00:01:42.715
unaltered tip unaltered tip

00:01:43.932 --> 00:01:46.411
that has access to the light

00:01:46.411 --> 00:01:51.232
that has access to light.

00:01:53.725 --> 00:01:58.648
No bending occurred no bending occurred

00:02:00.044 --> 00:02:05.044
occurred when either the tip was removed

00:02:07.419 --> 00:02:11.522
the tip was removed

00:02:11.522 --> 00:02:15.633
that was that was treatment two

00:02:16.541 --> 00:02:21.541
so treatment treatment two,

00:02:22.759 --> 00:02:27.759
or the tip was tip had an opaque cover,

00:02:28.813 --> 00:02:33.813
the tip had an opaque cover,

00:02:36.453 --> 00:02:40.150
that was treatment treatment

00:02:42.379 --> 00:02:45.447
treatment three.

00:02:45.447 --> 00:02:46.970
So that's all there is
to it, it only occurred

00:02:46.970 --> 00:02:48.819
when there was an unaltered tip, so that

00:02:48.819 --> 00:02:52.212
was treatment one that
has access to light,

00:02:52.212 --> 00:02:54.061
no bending occurred when
either the tip was removed

00:02:54.061 --> 00:02:55.991
in this one, in treatment two,

00:02:55.991 --> 00:02:57.576
or treatment three, so it's a pretty good

00:02:57.576 --> 00:02:58.978
indication that you need that tip and it

00:02:58.978 --> 00:03:00.360
needs to have access to light,

00:03:00.360 --> 00:03:02.554
something about the
tip lets the plant know

00:03:02.554 --> 00:03:05.378
what direction to start bending in.

00:03:05.378 --> 00:03:07.714
All right, let's do part B now.

00:03:07.714 --> 00:03:09.041
Part B.

00:03:10.051 --> 00:03:12.591
In treatment groups four and five,

00:03:12.591 --> 00:03:14.155
so that's these two treatment groups

00:03:14.155 --> 00:03:17.548
right over here, the tips
of the plants are removed

00:03:17.548 --> 00:03:20.352
and placed back onto the shoot on either

00:03:20.352 --> 00:03:23.196
a permeable or impermeable barrier.

00:03:23.196 --> 00:03:24.903
Using the results from treatment groups

00:03:24.903 --> 00:03:28.012
four and five, describe two
additional characteristics

00:03:28.012 --> 00:03:30.776
of the phototropism response.

00:03:30.776 --> 00:03:32.746
Well, when the tip was placed on top of a

00:03:32.746 --> 00:03:37.053
permeable barrier, the phototropism

00:03:37.053 --> 00:03:39.938
still happens, the plant still bends.

00:03:39.938 --> 00:03:43.128
So even though the tip is disconnected,

00:03:43.128 --> 00:03:44.895
because this barrier is permeable,

00:03:44.895 --> 00:03:48.106
the tip must be able
to sense the light and

00:03:48.106 --> 00:03:51.580
release some type of substance or hormone

00:03:51.580 --> 00:03:53.307
or chemical or something that's able to

00:03:53.307 --> 00:03:56.497
go through this permeable barrier,

00:03:56.497 --> 00:03:57.878
some type of substance that goes through

00:03:57.878 --> 00:03:59.707
this permeable barrier, and somehow

00:03:59.707 --> 00:04:01.556
signals to the rest of the plant to bend

00:04:01.556 --> 00:04:03.323
in the right direction.

00:04:03.323 --> 00:04:05.091
Because when you put
an impermeable barrier

00:04:05.091 --> 00:04:08.403
right over here, the tip
might be trying to release

00:04:08.403 --> 00:04:10.191
those same substances but they can't get

00:04:10.191 --> 00:04:12.141
through and so the rest
of the plant doesn't

00:04:12.141 --> 00:04:14.864
know to bend or in what direction to bend.

00:04:14.864 --> 00:04:17.830
So we could say, we could say

00:04:17.830 --> 00:04:22.830
tip, tip must release some type

00:04:29.695 --> 00:04:34.695
of hormone hormone I say chemical

00:04:37.193 --> 00:04:42.193
chemical that signals to

00:04:44.264 --> 00:04:49.264
rest of plant to bend to bend

00:04:51.537 --> 00:04:56.537
and in which direction which direction

00:05:00.334 --> 00:05:02.596
we know this, we know this,

00:05:05.393 --> 00:05:06.781
because

00:05:09.091 --> 00:05:13.709
only the or only I
could say treatment four

00:05:14.658 --> 00:05:19.658
only treatment four treatment four

00:05:20.672 --> 00:05:23.516
permeable barrier, and I'll say

00:05:23.516 --> 00:05:25.426
where the barrier's permeable to that

00:05:25.426 --> 00:05:29.435
substance, where the barrier

00:05:32.090 --> 00:05:37.090
is permeable to that substance

00:05:40.928 --> 00:05:45.928
that substance we know this because

00:05:46.739 --> 00:05:48.426
only treatment four where the barrier

00:05:48.426 --> 00:05:49.726
is permeable to the substance

00:05:49.726 --> 00:05:54.726
shows shows phototropism, phototropism.

00:06:00.551 --> 00:06:05.551
Not treatment treatment five.

00:06:06.708 --> 00:06:07.825
We know this, we could say, because

00:06:07.825 --> 00:06:12.825
of the two, of four and
five, only treatment

00:06:14.714 --> 00:06:16.216
four where the barrier's permeable

00:06:16.216 --> 00:06:20.259
to that substance shows phototropism.

00:06:20.259 --> 00:06:21.763
That's the only explanation here,

00:06:21.763 --> 00:06:23.307
that it's not doing somehow doing it

00:06:23.307 --> 00:06:26.355
through radio waves or
releasing substances

00:06:26.355 --> 00:06:28.346
that somehow float in the air to the rest

00:06:28.346 --> 00:06:30.032
of the plant, that somehow some type

00:06:30.032 --> 00:06:33.120
of substance is going through through

00:06:33.120 --> 00:06:36.980
directly from the tip to
the rest of the plant,

00:06:36.980 --> 00:06:38.565
and when you block it,
it's not able to send

00:06:38.565 --> 00:06:40.536
those chemical signals.

00:06:40.536 --> 00:06:42.832
That's the best that's
the best explanation

00:06:42.832 --> 00:06:46.327
that I can think of for
this behavior that we

00:06:46.327 --> 00:06:47.607
see between between treatments

00:06:47.607 --> 00:06:49.563
four and five.


2015 AP Biology free response 4

WEBVTT
Kind: captions
Language: en

00:00:00.120 --> 00:00:02.027
- [Voiceover] Both mitosis and meiosis

00:00:02.027 --> 00:00:03.863
are forms of cell division

00:00:03.863 --> 00:00:06.562
that produce daughter cells
containing genetic information

00:00:06.562 --> 00:00:08.485
from the parent cell.

00:00:08.485 --> 00:00:09.193
Part a.

00:00:09.193 --> 00:00:11.405
Describe two events that are common

00:00:11.405 --> 00:00:13.727
to both mitosis and meiosis

00:00:13.727 --> 00:00:15.926
that ensure the resulting daughter cells

00:00:15.926 --> 00:00:18.981
inherit the appropriate
number of chromosomes.

00:00:18.981 --> 00:00:19.681
All right.

00:00:19.681 --> 00:00:20.925
So, really we just wanna,

00:00:20.925 --> 00:00:23.758
well, what are two
commonalities between the two?

00:00:23.758 --> 00:00:26.173
Well, I can think of a bunch of them.

00:00:26.173 --> 00:00:27.403
You could start off saying,

00:00:27.403 --> 00:00:31.295
well, DNA replicates before
going into either of them.

00:00:31.295 --> 00:00:35.485
So DNA replicates

00:00:37.109 --> 00:00:39.222
before either,

00:00:39.222 --> 00:00:42.752
before either.

00:00:42.752 --> 00:00:44.308
You could say,

00:00:44.308 --> 00:00:47.373
well, the chromatin
condenses into chromosomes

00:00:47.373 --> 00:00:48.835
in both of them.

00:00:48.835 --> 00:00:53.391
Chromatin, chromatin

00:00:53.391 --> 00:00:57.427
condenses,

00:00:57.427 --> 00:01:00.912
condenses into,

00:01:00.912 --> 00:01:04.326
into chromosomes.

00:01:05.236 --> 00:01:08.822
You could talk about chromosomes form,

00:01:08.822 --> 00:01:12.581
getting aligned near
the center of the cell,

00:01:12.581 --> 00:01:17.364
attaching to, to, to fibers.

00:01:17.364 --> 00:01:19.401
You could talk about,

00:01:19.401 --> 00:01:23.062
we could talk about cytokinesis.

00:01:23.062 --> 00:01:24.285
Splitting the cells.

00:01:24.285 --> 00:01:28.334
So, cytokinesis,

00:01:28.334 --> 00:01:31.504
kinesis involved,

00:01:31.504 --> 00:01:36.504
involved in creation of separate cells.

00:01:36.761 --> 00:01:41.289
Creation of separate,

00:01:41.289 --> 00:01:44.238
separate cells.

00:01:44.238 --> 00:01:47.328
In general the,

00:01:47.328 --> 00:01:50.714
your meiosis one has a lot of analogs

00:01:50.714 --> 00:01:52.102
with mitosis in general.

00:01:52.102 --> 00:01:53.689
You could keep looking,

00:01:53.689 --> 00:01:55.236
keep digging deeper and
listing more and more.

00:01:55.236 --> 00:01:56.777
They just want me to describe two events.

00:01:56.777 --> 00:01:59.664
I've already described three.

00:01:59.664 --> 00:02:01.793
Well, I'll leave it at that for now.

00:02:01.793 --> 00:02:03.372
In general, before you take the AP test,

00:02:03.372 --> 00:02:06.935
mitosis and meiosis are good
things to know in detail,

00:02:06.935 --> 00:02:08.307
because you might see questions like this

00:02:08.307 --> 00:02:09.223
on the free answer section,

00:02:09.223 --> 00:02:10.384
or they're likely to show up

00:02:10.384 --> 00:02:11.793
in the multiple choice section as well.

00:02:11.793 --> 00:02:13.844
But I think this is sufficient for part a.

00:02:13.844 --> 00:02:15.184
We've described at least two events

00:02:15.184 --> 00:02:17.884
that are common to both
mitosis and meiosis.

00:02:17.884 --> 00:02:18.673
If you have extra time,

00:02:18.673 --> 00:02:20.833
you might try to list more.

00:02:20.833 --> 00:02:22.876
And then part b.

00:02:22.876 --> 00:02:24.641
The genetic composition of daughter cells

00:02:24.641 --> 00:02:27.404
produced by mitosis differs

00:02:27.404 --> 00:02:30.214
from that of the daughter
cells produced by meiosis.

00:02:30.214 --> 00:02:32.350
Describe two features of
the cell division process

00:02:32.350 --> 00:02:34.463
that lead to these differences.

00:02:34.463 --> 00:02:36.181
Well, maybe the most obvious one,

00:02:36.181 --> 00:02:37.591
the biggest difference between them,

00:02:37.591 --> 00:02:40.218
is mitosis,

00:02:40.218 --> 00:02:43.276
mitosis involves one division,

00:02:43.276 --> 00:02:47.589
involves one division.

00:02:49.068 --> 00:02:51.414
Meiosis involves two.

00:02:51.414 --> 00:02:55.175
Meiosis involves,

00:02:55.175 --> 00:02:57.242
involves, not inolves,

00:02:57.242 --> 00:03:01.630
involves, involves two.

00:03:01.630 --> 00:03:06.019
This leads to

00:03:06.019 --> 00:03:11.019
two daughter cells

00:03:11.708 --> 00:03:15.774
from mitosis,

00:03:17.072 --> 00:03:21.548
and four daughter,

00:03:22.575 --> 00:03:25.521
daughter cells

00:03:25.521 --> 00:03:28.771
from meiosis.

00:03:29.611 --> 00:03:31.213
Meiosis.

00:03:31.213 --> 00:03:34.102
That's a pretty big difference

00:03:34.102 --> 00:03:35.508
between the two.

00:03:35.508 --> 00:03:36.275
Another big difference,

00:03:36.275 --> 00:03:38.062
and this is related to this.

00:03:38.062 --> 00:03:39.770
Because,

00:03:39.770 --> 00:03:43.730
because meiosis

00:03:43.730 --> 00:03:46.450
has an extra division,

00:03:46.450 --> 00:03:50.633
has extra

00:03:50.633 --> 00:03:54.169
division,

00:03:54.169 --> 00:03:57.797
but DNA

00:03:57.797 --> 00:04:01.147
replicates once,

00:04:01.147 --> 00:04:03.602
like in, once,

00:04:03.602 --> 00:04:07.823
like in mitosis,

00:04:09.175 --> 00:04:11.567
the daughter cells from meiosis

00:04:11.567 --> 00:04:13.819
have half the number of chromosomes.

00:04:13.819 --> 00:04:16.838
They have a haploid number of chromosomes.

00:04:16.838 --> 00:04:21.045
The daughter

00:04:21.045 --> 00:04:22.665
cells

00:04:22.665 --> 00:04:26.237
in meiosis

00:04:26.237 --> 00:04:30.807
have a haploid

00:04:31.926 --> 00:04:33.761
number of chromosomes,

00:04:33.761 --> 00:04:37.305
number of

00:04:37.305 --> 00:04:39.415
chromosomes.

00:04:39.415 --> 00:04:41.237
Chromosomes.

00:04:41.237 --> 00:04:42.120
So, and we could say,

00:04:42.120 --> 00:04:45.210
mitosis daughters have diploid,

00:04:45.210 --> 00:04:49.817
daughters have diploid number.

00:04:52.662 --> 00:04:55.553
And these are probably the
two strongest differences.

00:04:55.553 --> 00:04:56.911
But you could talk about other things.

00:04:56.911 --> 00:04:59.545
You could talk about crossing
over occurring in meiosis

00:04:59.545 --> 00:05:01.648
but not in mitosis.

00:05:01.648 --> 00:05:04.364
You could talk about the separation

00:05:04.364 --> 00:05:05.711
and independent sortment

00:05:05.711 --> 00:05:08.679
of homologous chromosomes that you have.

00:05:08.679 --> 00:05:11.349
Homologous, each member
of a homologous pair

00:05:11.349 --> 00:05:12.231
that you have in meiosis

00:05:12.231 --> 00:05:13.336
that you don't have in mitosis.

00:05:13.336 --> 00:05:15.008
So there's a bunch of
things you could talk about.

00:05:15.008 --> 00:05:16.318
And you could go into arbitrary detail.

00:05:16.318 --> 00:05:18.908
It's nice that they only have
to list two in each of these,

00:05:18.908 --> 00:05:22.884
in each of these parts of question four.


2015 AP Biology free response 3

WEBVTT
Kind: captions
Language: en

00:00:00.347 --> 00:00:02.975
- [Voiceover] The amino acid
sequence of cytochrome c

00:00:02.975 --> 00:00:06.616
was determined for five
different species of vertebrates.

00:00:06.616 --> 00:00:09.054
The table below shows
the number of differences

00:00:09.054 --> 00:00:12.597
in the sequences between
each pair of species.

00:00:12.597 --> 00:00:14.288
So, just to give us some context

00:00:14.288 --> 00:00:15.458
for what we're talking about.

00:00:15.458 --> 00:00:16.726
We're talking about cytochrome c.

00:00:16.726 --> 00:00:17.831
This is a protein.

00:00:17.831 --> 00:00:19.298
You might remember it when we studied

00:00:19.298 --> 00:00:21.216
the electron transport chain.

00:00:21.216 --> 00:00:23.590
You don't really have to
know that for this question,

00:00:23.590 --> 00:00:25.442
but it's a protein that's found in a lot

00:00:25.442 --> 00:00:27.816
of different species, and
we're going to compare the

00:00:27.816 --> 00:00:30.644
difference in the sequence of amino acids

00:00:30.644 --> 00:00:33.342
for that protein in the different species.

00:00:33.342 --> 00:00:35.747
So even though you have the
same or similar protein,

00:00:35.747 --> 00:00:37.015
we call them all cytochrome c,

00:00:37.015 --> 00:00:38.673
the sequence might be slightly different

00:00:38.673 --> 00:00:41.599
when you go from one species
of vertebrate to another.

00:00:41.599 --> 00:00:43.807
And the way to read this is

00:00:43.807 --> 00:00:45.737
for each of these rows you could say,

00:00:45.737 --> 00:00:47.403
all right, this row

00:00:48.762 --> 00:00:51.095
describes D. polylepis,

00:00:51.095 --> 00:00:53.371
and we can see the number
of sequence differences

00:00:53.371 --> 00:00:55.419
between D. polylepis and G. gallus.

00:00:55.419 --> 00:00:57.012
There's 18 differences.

00:00:57.012 --> 00:00:58.577
There's clearly going
to be zero differences

00:00:58.577 --> 00:01:01.930
between that species and itself.

00:01:01.930 --> 00:01:03.718
All right, now let's
answer their question.

00:01:03.718 --> 00:01:05.181
Using the data in the table,

00:01:05.181 --> 00:01:08.822
create a phylogenetic tree
on the template provided

00:01:08.822 --> 00:01:11.065
to reflect the evolutionary relationships

00:01:11.065 --> 00:01:12.397
of the organisms.

00:01:12.397 --> 00:01:14.738
Provide reasoning for
the placement on the tree

00:01:14.738 --> 00:01:17.761
of the species that is
least related to the others.

00:01:17.761 --> 00:01:20.524
So, looking at these differences,

00:01:20.524 --> 00:01:22.517
it's reasonable to say, well, the things

00:01:22.517 --> 00:01:25.698
that have the fewest
differences in the sequence

00:01:25.698 --> 00:01:27.811
of cytochrome c, well, those are probably

00:01:27.811 --> 00:01:29.469
most closely related.

00:01:29.469 --> 00:01:31.614
And they already gave us a tree here,

00:01:31.614 --> 00:01:33.700
so whatever goes here and here

00:01:33.700 --> 00:01:34.967
are probably pretty closely related.

00:01:34.967 --> 00:01:36.142
They shouldn't have too many differences

00:01:36.142 --> 00:01:38.809
in the sequence of cytochrome c.

00:01:40.303 --> 00:01:42.031
And these two should be pretty similar.

00:01:42.031 --> 00:01:44.311
Shouldn't have many differences.

00:01:44.311 --> 00:01:47.822
While this one should have
a good number of differences

00:01:47.822 --> 00:01:49.480
from any of the other four.

00:01:49.480 --> 00:01:50.438
So let's first look at which ones

00:01:50.438 --> 00:01:51.898
have very little difference.

00:01:51.898 --> 00:01:54.108
And I'm just scanning this chart here

00:01:54.108 --> 00:01:56.221
and looking for small numbers.

00:01:56.221 --> 00:01:58.562
So you see here, there's only one

00:01:58.562 --> 00:02:00.979
amino acid difference, or one sequence.

00:02:00.979 --> 00:02:02.778
Well, yeah, one amino acid difference

00:02:02.778 --> 00:02:06.995
between cytochrome c in
E. ferus and E. africanus.

00:02:06.995 --> 00:02:09.238
So I would say that these
are fairly closely related.

00:02:09.238 --> 00:02:13.041
They probably share an
ancestor not too far

00:02:13.041 --> 00:02:14.471
in the distant past.

00:02:14.471 --> 00:02:17.951
So let me write E. ferus and E. africanus.

00:02:17.951 --> 00:02:19.543
So, I'll do it here.

00:02:19.543 --> 00:02:20.376
E.

00:02:21.656 --> 00:02:22.489
E. ferus.

00:02:25.557 --> 00:02:27.223
And E. E. africanus.

00:02:31.800 --> 00:02:32.633
I'd do that there.

00:02:32.633 --> 00:02:35.765
Now where else do we see some low numbers.

00:02:35.765 --> 00:02:38.397
Well, I see this three right over here

00:02:38.397 --> 00:02:42.430
and so that's the number
of sequence differences

00:02:42.430 --> 00:02:43.878
or the amino acid differences

00:02:43.878 --> 00:02:46.711
between G. gallus and A. forsteri.

00:02:48.002 --> 00:02:50.212
Forsteri, however you pronounce that.

00:02:50.212 --> 00:02:52.813
So I would say those are
probably pretty closely related.

00:02:52.813 --> 00:02:55.090
And so let me write this here.

00:02:55.090 --> 00:02:55.923
G. gallus

00:02:58.388 --> 00:02:59.722
and A. forsteri.

00:03:04.351 --> 00:03:06.789
And who have we not dealt with yet.

00:03:06.789 --> 00:03:09.122
Well, we haven't dealt with

00:03:10.981 --> 00:03:12.398
D. polylepis yet.

00:03:13.393 --> 00:03:14.352
We've dealt with the other four.

00:03:14.352 --> 00:03:16.435
So I'll put that here.

00:03:16.435 --> 00:03:17.518
D. polylepis.

00:03:20.726 --> 00:03:22.936
And you can see when
you compare D. polylepis

00:03:22.936 --> 00:03:24.563
to any of the other ones,

00:03:24.563 --> 00:03:26.220
you see a pretty big difference.

00:03:26.220 --> 00:03:29.633
D. polylepis to E. ferus
is a 21 difference.

00:03:29.633 --> 00:03:31.551
18 difference with G. gallus.

00:03:31.551 --> 00:03:34.314
17 difference with A. forsteri

00:03:34.314 --> 00:03:36.981
and 20 amino acids are different

00:03:38.596 --> 00:03:40.234
in the sequence for cytochrome c

00:03:40.234 --> 00:03:43.934
between D. polylepis and E. africanus.

00:03:43.934 --> 00:03:46.047
So this has the most differences.

00:03:46.047 --> 00:03:50.630
And they say provide reasoning
for the placement on the tree

00:03:50.630 --> 00:03:54.464
of the species that is
least related to the others.

00:03:54.464 --> 00:03:56.382
So I'll provide the reasoning.

00:03:56.382 --> 00:03:57.798
So, D. polylepis

00:04:02.979 --> 00:04:03.812
is most,

00:04:06.490 --> 00:04:08.604
is least related, I should say,

00:04:08.604 --> 00:04:10.021
is least related

00:04:12.665 --> 00:04:13.832
because it has

00:04:17.796 --> 00:04:19.462
a large amino acid,

00:04:23.066 --> 00:04:24.733
amino acid sequence

00:04:28.949 --> 00:04:29.782
difference

00:04:32.299 --> 00:04:34.475
from the other four.

00:04:34.475 --> 00:04:36.725
From the other, other four.

00:04:39.286 --> 00:04:40.847
Or you can say, has the largest.

00:04:40.847 --> 00:04:41.680
Maybe I'll write that.

00:04:41.680 --> 00:04:45.624
Has the largest amino
acid sequence difference

00:04:45.624 --> 00:04:46.664
from the other four.

00:04:46.664 --> 00:04:49.915
Because even if you were to
compare E. ferus to G. gallus,

00:04:49.915 --> 00:04:52.906
E. ferus to G. gallus, you
still don't get close to 20,

00:04:52.906 --> 00:04:54.466
while D. polylepis is pretty close

00:04:54.466 --> 00:04:56.384
to 20 difference with all of them.

00:04:56.384 --> 00:04:58.864
And so that makes sense,
that even these four

00:04:58.864 --> 00:05:00.674
share a common ancestor, that you don't

00:05:00.674 --> 00:05:02.995
have to go as far back in time

00:05:02.995 --> 00:05:04.152
to get to the common ancestor

00:05:04.152 --> 00:05:05.971
as you do to get to D.,

00:05:05.971 --> 00:05:09.581
the common ancestor with D. polylepis.

00:05:09.581 --> 00:05:12.344
All right, let's do part b now.

00:05:12.344 --> 00:05:13.806
So that was part a.

00:05:13.806 --> 00:05:14.639
Let me label that

00:05:14.639 --> 00:05:15.626
That was part a.

00:05:15.626 --> 00:05:16.504
Now part b.

00:05:16.504 --> 00:05:18.943
Identify whether morphological data

00:05:18.943 --> 00:05:20.795
or amino acid sequence data

00:05:20.795 --> 00:05:23.234
are more likely to accurately represent

00:05:23.234 --> 00:05:26.939
the true evolutionary
relationships among the species

00:05:26.939 --> 00:05:29.019
and provide reasoning for your answer.

00:05:29.019 --> 00:05:30.937
So, morphological data, this is looking at

00:05:30.937 --> 00:05:35.001
the morphology of the different species.

00:05:35.001 --> 00:05:36.534
And you could say, like, what's the shape

00:05:36.534 --> 00:05:39.713
of their backbone or
their different bones,

00:05:39.713 --> 00:05:44.103
or the shape of different
parts of their body,

00:05:44.103 --> 00:05:46.734
while amino acid sequence,
you're looking at,

00:05:46.734 --> 00:05:49.693
well, how are their
proteins actually made up.

00:05:49.693 --> 00:05:53.853
I, personally, would go
with the amino acid data.

00:05:53.853 --> 00:05:55.269
So, I, I believe.

00:05:58.631 --> 00:05:59.465
I believe,

00:06:02.630 --> 00:06:04.380
I believe amino acid

00:06:07.376 --> 00:06:08.459
sequence data

00:06:13.164 --> 00:06:16.247
are, data's plural, are more likely,

00:06:18.006 --> 00:06:21.734
are more likely to accurately represent

00:06:21.734 --> 00:06:23.564
the true evolutionary relationship,

00:06:23.564 --> 00:06:27.064
are more acc, are more likely to represent

00:06:29.443 --> 00:06:32.437
the true evolutionary relationship.

00:06:32.437 --> 00:06:35.020
True evolutionary relationship.

00:06:40.960 --> 00:06:43.327
And let me provide my reasoning.

00:06:43.327 --> 00:06:46.513
You could have convergent morphology.

00:06:46.513 --> 00:06:47.597
You can have

00:06:50.544 --> 00:06:52.294
convergent morphology

00:06:54.282 --> 00:06:56.037
and what that means is, for example,

00:06:56.037 --> 00:06:58.475
you could look at a bat's
wings and a bird's wings

00:06:58.475 --> 00:07:00.491
and say, okay, look, they
each have similar morphology,

00:07:00.491 --> 00:07:02.581
but they aren't related just because

00:07:02.581 --> 00:07:03.968
they both have wings.

00:07:03.968 --> 00:07:05.757
Or you could look at a dolphin and a fish,

00:07:05.757 --> 00:07:07.546
and you say, okay, they
both have flippers.

00:07:07.546 --> 00:07:08.985
Maybe they're more closely related,

00:07:08.985 --> 00:07:10.630
if you just look at the body type.

00:07:10.630 --> 00:07:11.607
But that's convergent.

00:07:11.607 --> 00:07:14.629
They actually came from
different ancestors,

00:07:14.629 --> 00:07:15.931
but then their ancestors,

00:07:15.931 --> 00:07:17.164
because they had similar environments,

00:07:17.164 --> 00:07:20.903
had a convergent parts,
I guess you could say.

00:07:20.903 --> 00:07:22.527
Had convergent morphology.

00:07:22.527 --> 00:07:25.444
You can have convergent morphology,

00:07:26.293 --> 00:07:27.209
morphology,

00:07:28.885 --> 00:07:32.242
while having very, while being far apart

00:07:32.242 --> 00:07:34.325
on the evolutionary tree.

00:07:35.979 --> 00:07:36.979
While being

00:07:39.456 --> 00:07:40.289
far apart

00:07:42.609 --> 00:07:43.943
on evolutionary,

00:07:47.160 --> 00:07:48.910
on evolutionary tree.

00:07:50.064 --> 00:07:52.720
Now there's arguments
for morphology as well,

00:07:52.720 --> 00:07:53.921
'cause you might be looking at.

00:07:53.921 --> 00:07:57.412
You know, we're only looking
at cytochrome c here.

00:07:57.412 --> 00:07:59.674
That might be some type of an anomaly,

00:07:59.674 --> 00:08:01.917
or maybe you have some
convergence or divergence

00:08:01.917 --> 00:08:04.978
for that particular protein that does not

00:08:04.978 --> 00:08:07.248
actually gel with what's actually happened

00:08:07.248 --> 00:08:08.841
in evolutionary history,

00:08:08.841 --> 00:08:12.514
but in general if I can look
at the molecular sequences.

00:08:12.514 --> 00:08:14.172
If I can look at sequences of proteins,

00:08:14.172 --> 00:08:16.480
if I could look at what's
going on with the DNA,

00:08:16.480 --> 00:08:18.268
I like looking at that,

00:08:18.268 --> 00:08:20.706
because that doesn't, that
allows you to not be tricked

00:08:20.706 --> 00:08:24.673
by the convergent morphology
or far apart things,

00:08:24.673 --> 00:08:28.090
like bats and birds or dolphins and fish.