Download C. It is easier than counting flowers (counting flowers doesn`t tell you

BIO205H5
Diagnostic Assessment
Week of Sept 19th
Part 1. Please read the following passages and answer the questions below.
A)
Scarlet gilia (Ipomopsis aggregata) usually has red flowers in an inflorescence of
up to 250 flowers. In certain populations in the Arizona mountains, however, the flowers
range from red to pink to white. In early summer, most of the flowers were red. Six to
eight weeks later, the same individual plants were still present; the flowers ranged from
pink to white, and few red flowers were present. The major pollinators early in the
season were two species of hummingbirds active during the day; they emigrated to
lower elevations, and the major pollinator later in the season was a hawk moth (a type
of moth). The hawk moth was most active at sunset and later, and it preferred light pink
to white flowers after dark. When hummingbirds were present, more red flowers than
white flowers produced fruit. (Recall that fruits are formed after pollination, and as
seeds form.) When only hawk moths were present, more white flowers produced fruit
(K. N. Paige and T. G. Whitham, “Individual and Population Shifts in Flower Color by
Scarlet gilia: A Mechanism for Pollinator Tracking,” Science 227 [1985]: 315–317).
1) What is the significance of measuring fruit production?
A. It is a measure of pollination success.
B. It is a measure of seed dispersal success. (nothing about dispersal - irrelevant)
C. It is easier than counting flowers (counting flowers doesn’t tell you it’s been
pollinated)
D. It is an indication of predation on the seeds of the plants. (irrelevant)
2) To
A.
B.
C.
D.
E.
perform this study, the researchers needed to count:
the number of red flowers
the number of pink and white flowers
the number of hummingbirds
the number of hawk moths
All of these answers apply. (if any of the above deviated from what was
described in the prediction, it could change the interpretation of the results)
3) Late in the season, when only hawk moths were present, researchers painted the
red flowers white. What would you expect?
A. Unpainted red flowers would produce more fruits than white flowers would.
B. Red flowers painted white would produce more fruits than red flowers
would.(only choice supported by the evidence)
C. Red and white flowers would produce the same numbers of fruits.
4) Some plants changed their flowers to lighter colors, and some retained the same
darker color all season. Which plants do you expect produced more fruit?
A. those that changed their color to a lighter shade (pollinated by both pollinators)
B. those that stayed darker
C. They probably produced the same numbers of fruits.
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5) Why do hummingbirds emigrate from this population of scarlet gilia?
A. The flowers probably change their nectar production.
B. The flowers change from red to white and the hummingbirds can’t see them.
C. It gets darker on the mountainside, and the hummingbirds migrate to lower
elevations where it stays light longer.
D. There is not enough information presented to answer this question. (THIS IS
IMPORTANT! Must know the difference between inference and conjecture.)
B)
Recall that many species of tree form symbiotic relationships with mycorrhizal
fungi. The fungus, associated with the plant roots, helps increase absorption of
nutrients by the plant; in turn, the plant provides the fungus with sugars that are
formed in the leaves and transported into the roots. Growth form differs among species
of mycorrhizal fungi: ectomycorrhizal fungi form sheaths around roots and penetrate
between root cells, whereas arbuscular mycorrhizae contact the plasma membranes of
root cells.
Suzanne Simard and colleagues knew that a single mycorrhizal fungal species could
colonize several different species of trees. They wondered if the same fungal individual
would colonize different trees, forming an underground network that could transport
carbon and nutrients from one tree to another (S. Simard et al., “Net Transfer of Carbon
between Mycorrhizal Tree Species in the Field,” Nature 388 [1997]: 579–582). The
diagram above illustrates the researchers’ experimental design. Pots were planted with
seedlings of three different tree species: Douglas fir (Pseudotsuga menziesii), birch
(Betula papyrifera) and cedar (Thuja occidentalis). The seedlings were grown under
natural conditions for three years. Two of the species formed ectomycorrhizae (Douglas
fir, birch) and the third (cedar) formed arbuscular mycorrhizae. For the experiment, the
researchers placed airtight bags over the Douglas fir and birch seedlings; into each bag,
they injected either carbon dioxide made from carbon-13 or carbon-14 (13CO2 and 14CO2,
isotopes of carbon). As the seedlings photosynthesized, the radioactive carbon dioxide
was converted into radioactively labelled sugars that could be tracked and measured.
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6) Which of the following results would support the hypothesis that fungi can move
carbon from one plant to another (i.e., sugars made by one plant during
photosynthesis can travel through a mycorrhizal fungus and be incorporated into the
tissues of another plant)?
A.
14
C is found in the birch seedling’s tissues and 13C is found in the Douglas fir.
(Expected without any carbon movement)
B. 14C is found in the Douglas fir seedling’s tissues and 13C is found in the birch.
C. Either 13C or 14C is found in the fungal tissues. (Does not imply carbon movement
from one plant to another via fungus; just movement into the fungus)
D. Either 13C or 14C is found in the cedar seedling’s tissues. (Suggests that carbon is
moving among plants, but not through the fungus)
7) What is the result that would most strongly refute Simard et al.’s hypothesis?
A. 14C is found in the birch seedling’s tissues and 13C in the Douglas fir. (Expected
without any carbon movement)
B. Reciprocal exchange: 14C is found in the Douglas fir seedling’s tissues and 13C in
the birch. (This SUPPORTS the hypothesis!)
C. Either 13C or 14C is found in the fungal tissues. (Does not imply carbon movement
from one plant to another via fungus; just movement into the fungus)
13
C or 14C is found in the cedar seedling’s tissues. (Suggests that carbon is
moving among plants, but not through the fungus)
D. Either
8) Which element is the control in this experiment, and why?
A. the bags over the seedlings to contain the different types of carbon dioxide (this
ensures that 13C or 14C is delivered to the individual plants, but is not the control
with regards to the hypothesis i.e. is carbon transferred through the fungus)
B. the fact that all the seedlings are different species (part of the hypothesis: can
the fungus transfer carbon among different species)
C. the cedar seedling, because it is not bagged (irrelevant)
D. the cedar seedling, because it forms arbuscular mycorrhizae (Because this does
not have a fungal connection to the other two plants, if it contains 13C or 14C, it
must have obtained it not through the fungus (e.g., perhaps 13C or 14C leaked
from the bags; 13C or 14C leaches into the soil; etc.))
9) Simard et al. (1997) further hypothesized that reciprocal transfer, if present, would
be a source-sink relationship driven by photosynthetic rates. That is, if one seedling
is in full sun and the other in deep shade, there will be a net movement of carbon
from the seedling in full sun to the one in deep shade. If a shade was placed over
the birch and cedar seedlings, and the Douglas fir was left in full sun, what result
would be expected?
A. More 13C would be found in the birch than in the Douglas fir. (understanding of
“net movement”)
B. More 13C would be found in the Douglas fir than the birch.
C. The most 13C would be found in the cedar.
D. The most 14C would be found in the cedar.
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Part 2. In words (full sentences, not point form), describe the results depicted in Figure
1 (taken from Simard et al. (1997)). This answer should be no more than 3
sentences. Grammar and spelling matter!
The results indicate that all three-year-old seedlings (regardless of light treatment)
showed a net transfer of carbon that was significantly greater than zero. None of
the two-year-old seedlings showed a net transfer of carbon that was significantly
greater than zero. The greatest amount of carbon transfer in three-year-old
seedlings was in the deep-shade treatment; there was no significant difference in
the amount of carbon transferred by seedlings in the partial shade and full light
treatment.
3 basic points: graph is about carbon transfer in seedlings of different ages and
light treatments
a) all 3-yr-old > 2 year old
b) all 2-yr-old ≈ 0
c) among 3-yr-olds: deep shade > partial shade ≈ full sun
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Part 3. You have been hired as a field assistant for a researcher interested in the
evolution of flower shape in orchids. Each of the five species being studied is pollinated
by a different insect. Design an experiment to determine which parts of the five flower
types are most important in attracting the pollinators. Assume that you can alter a
flower’s shape, change a flower’s color with dye, add particular scents, add or remove
nectar, or switch parts among species by cutting and gluing. This answer should be
no more than 3 sentences. Grammar and spelling matter!
For each flower species, I would alter 1 floral characteristic at a time and
present both an altered and an unaltered (control) flower to the known
pollinator for that species. For each species, this choice experiment would be
repeated with several flowers and several individual pollinators. A characteristic
would be considered important in attracting pollinators if altering it changed the
pollinator’s behaviour (i.e., made the flower more or less attractive to the
pollinator).
Critical components of a good design:
1. Altering one character at a time
2. Restricting the experiment to one species at a time
3. having a control (unaltered flower)
4. replication
Focusing on the methods for altering flowers is not relevant to answering this
question (it has been established that physical alteration is possible).
Discuss what the appropriate control must be. How can you make conclusions
about changes in pollinator behaviour towards the altered flower if you don’t
quantify the behaviour towards the unaltered flower??
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