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
27.
The author's primary purpose in ███ ███████ ██ ██
a
articulate a theory ██ ███ █████ ████████ ██ ███████████ ███ ███████ ███ ██████ ██ ██ ████████ ██ ████
We don’t get any analysis of data in this passage. In addition, the author’s focus isn’t on a theory of how early polarity is established; it’s on the variety of ways in which polarity can be established from organism to organism. The overall purpose relates to the diversity of mechanisms, not a particular theory of development.
b
describe a phase ██ ███ ███████████ ██ █████████ ██ █████ ███ ███████ ██████████ ████ ███ █████████ ███ ███████ ███ ████ █████████ ██ ██████████
This is the best answer. The author describes a phase in the development of organisms (the early phase in which polarity is developed). This is a phase in which genetic mechanisms used are different (disparate). The author notes that this disparity is surprising, because the mechanisms involved in the development of later features are more similar between different organisms.
c
provide a classification ██ ███ ██████████ ██ █████ █████████ ████ █████ █████████ █████ ████████
The overall purpose isn’t to classify different mechanisms for establishing polarity. The author mentions several mechanisms to illustrate the diversity of polarity mechanisms, but there is no attempt to classify the different kinds of mechanisms into different groups.
d
argue that a ███████ ███████ ███████ ████ █████ ██ ███ ████ ██████ ██████████ ██ █████ ████████ █████████████
The overall purpose relates to the diversity of mechanisms for polarity. The purpose isn’t to argue that all organisms must establish polarity. Even if that fact is true, the author doesn’t try to convince the reader that polarity is necessary; that fact is taken as a given and sets up the context for the rest of the discussion.
e
explain why an ██████ ████ █████████ █████ ████████ ██████ ██ ███ ███████ ████ ██ ████████
The author never discusses why an embryo must establish polarity. Even if you believe the author does discuss this, the overall purpose of the passage is about the diversity of mechanisms for polarity, not about the reason polarity is required.