Self-study
P1
The characteristic smell or taste of a plant, to insects as well as to humans, depends on its chemical composition. ███████ █████████ ██████ ███████ ███ ██████████ ██ ████████ ███████████ ███████ ███ ██████████ ███
Intro topic ·
Two kinds of chemicals in plants: primary and secondary
Chemicals determine smell and taste of plants to insects and humans.
Primary substances ·
Stuff required for growth and functioning; found in all plants
Secondary substances ·
No known role in growth/functioning; give plants distinctive tastes and smells
P2
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Origin of secondary substances ·
Insects played major role
Causal mechanism 1 ·
Insects like some scents over others
Secondary substances result from mutations. Insects prefer some scents over others, which means the substances that produce those preferred scents are more likely to be passed on to future generations.
Causal mechanism 2 ·
Some substances produce stuff that helps defend against insects
Causal mechanism 3 ·
Some substances produce stuff that warns insects not to eat the plant
P3
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Competition between insects and plants ·
Insects evolve to respond to plants' defenses
Might evolve way to detoxify plant's poison or store the poison in an unharmful way, for example. Might evolve way to identify poisonous plants.
Passage Style
Phenomenon-hypothesis (RC)
Single position
11.
The passage provides the most ███████ ███ █████████ █████ ███ ██ ███ ██████████
a
Some chemicals that ███ ███ █████ ██ ██ ████████ ████████ ██ ███ ██████ ██ ██████████ ██ ███ ███████ ██ █████ ████ █████ █████ ██ ███ █████ ██ ███████ █████ ██ ███████
Supported. We know secondary substances are chemicals that aren’t directly involved in growth and metabolism. But they do play important roles in the lives of plants, because they can do things such as attract insects to pollinate and defend against predation from insects.
b
Most plants that ████ ███████ ████████ ███████ ███████ ███████ ███████ ██████ ███████ ███ ████████████ ████ ██ ████ ██ █ ████ ███████ ██ ███████ ████ ████ ███████ ████ ██ █████████████ █████ █████████
Not supported, because we have no evidence that “most” (over half) plants that have defense mechanisms against insects are still eaten by a wide variety of insects. Although we have evidence that some plants are still eaten by some insects despite their defense mechanisms, we have no reason to think this is true about “most” plants with defense mechanisms, or that they’re eaten by a “wide” variety of insects.
c
Most insects that ████ ███████████ ██ ███████ ███████████ ██████████ ██████ ██ ██████ ███ ████ ██ ████████ █████ ██████ ██ █████ █████ ████ █████ ██████████████ █████ ██ ██████
We have no reason to think there are any insects that can identify certain groups of plants by means other than taste or smell. Although the author mentions that some insects can come to identify plants by “flavors or odors,” she doesn’t mention identification through other means besides these.
d
Many secondary substances ████ ███ █████ ██ ███████ ███ ███████ ██ ██████████ ██ ████ ███████ █████████████ ██ ███████ █████████ ███████ ██ ██████ ███ ██ ████ ████████ ██ ████ █ ███ ████████
The author never provides evidence of scientists’ beliefs about many secondary substances that are toxic to insects. She never indicates scientists think any kind of secondary substance has evolved “independently in various unrelated species of plants” or that they have survived in only few species.
e
Some toxic substances ████ ███ ████████ ██ ██████ ███████ ██ ███████████ ████ █████████ ██████████ ███ ███ ███ ██████████ █████████ ███████████
The author never suggests there exist toxic substances produced by plants that are not secondary substances. Nor does she suggest that there is any relationship between these substances and secondary substances.