Self-study
P1
The first thing any embryo must do before it can develop into an organism is establish early polarity—that is, it must set up a way to distinguish its top from its bottom and its back from its front. ███
Intro topic ·
Embryo polarity
How an embryo develops different “sides”
Contrast species ·
Different species' embryos use different processes to establish polarity
P2
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Example of polarity process ·
Fruit fly
Fruit fly eggs already have all the information needed for polarity even before fertilization; “fertilize-and-go” approach
Consequences ·
of fruit fly polarity process
Tradeoff: eggs take a long time to “set up” ahead of time, but embryo grows very quickly
Contrasting example ·
Nematode
Unlike fruit flies, nematode eggs don’t have all the polarity information they need; sperm also provides information
Elaborate on example ·
Details of process in nematode egg
When sperm enters egg, proteins collect on one side of egg, signaling front/back
Similarity/contrast ·
Nematode-like process used in some vertebrates (frogs) but not others (humans)
Continue contrast ·
Mammal embryos establish polarity much later
But underlying process is unknown
P3
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New contrast ·
between establishing polarity and growing specific body parts
Species differ widely in how they signal polarity in the embryo, yet they’re very similar in how they signal specific body parts to grow
Main point ·
Developmental mechanisms differ between species early on, but are similar later in development
Passage Style
Single position
Spotlight
25.
Which one of the following ████ ██████████ ██████ ███ ████ ███████ ██ ███ ██████ ██████████
a
to illustrate the █████████ ██ █████████ ██ █████ █████████ █████████ █████ ████████
This best captures the purpose of P2, which is to present examples of different polarity mechanisms to support the point that the mechanisms involved in polarity development vary greatly between different organisms. We know this is the purpose because the author tells us in P1 and P3 that the mechanisms for polarity development are different from organism to organism. P2 presents specific examples of some of those different mechanisms.
b
to elaborate on ███ ███████████ ███████ █████████ █████████ ██ ███ █████ ███ ███ ██ ███ ████████
P2 discusses other animals besides the fruit fly and nematode. So the purpose goes beyond differences between the fruit fly and nematode.
c
to suggest why ███ ███████ ██ ████████████ █████ ████████ ██ ██████ ██ ███ ███ ██████████
The author doesn’t indicate why the process of establishing polarity in humans isn’t yet understood. So (C) can’t be the purpose if it doesn’t happen. Although we know that it’s unknown in humans, we don’t know why we haven’t yet discovered humans’ polarity mechanism.
d
to demonstrate the ████████████ ███ █████████ ███ ███████ ███████████ ██ ████████████ ████████
The author doesn’t explain the importance of developing polarity in P2. The author merely describes different mechanisms for establishing polarity in different animals.
e
to demonstrate that █████ ███ ███ ████ █████ ██ █████████ ██ █████ █████ ████████ ██ ███████████
The author doesn’t indicate that there are only two main types of polarity mechanisms. Although the author happens to provide details about only two kinds, this doesn’t imply that those are the main two kinds of mechanism.