C683 Task 1 - Bean Seed Germination Experiment: Light vs Dark
- 100 Questions and Answers Already Graded A+ Premium
Exam Tested And Verified
Subject Area Plant Biology / Seed Physiology
Description This exam assesses advanced understanding of the bean seed germination
experiment comparing light and dark conditions, covering seed physiology,
photomorphogenesis, experimental design, data analysis, and underlying
biochemical pathways.
Expected Grade A+
Total Questions 100
Duration 3 hours
Learning Outcomes 1. Analyze the role of light in seed germination and seedling development
2. Design controlled experiments to test environmental effects on germination
3. Interpret quantitative data from germination experiments
4. Explain the molecular mechanisms of photomorphogenesis in seedlings
5. Critically evaluate experimental variables and potential confounding factors
Accreditation This exam meets the rigorous standards of top R1 US universities, including Ivy
League institutions, for advanced undergraduate and graduate coursework in plant
biology.
Page 1
,1. In a bean seed germination experiment comparing light and dark conditions, you
observe that dark-grown seedlings exhibit elongated hypocotyls, small cotyledons,
and no chlorophyll. This phenotype is primarily due to which of the following
mechanisms?
A. Activation of phytochrome B by far-red light in the dark
B. Constitutive expression of COP1 in the absence of light
C. Increased gibberellic acid signaling promoting cell elongation
D. Downregulation of auxin transporters in dark conditions
Answer: C. Increased gibberellic acid signaling promoting cell elongation
In darkness, seedlings undergo skotomorphogenesis, characterized by elongated
hypocotyls and etiolation. This is driven by increased gibberellic acid (GA) signaling,
which promotes cell elongation. COP1 is active in the dark (not constitutive expression)
and targets photomorphogenesis-promoting factors for degradation. Phytochrome B is
inactive in the dark. Auxin transporters are not directly downregulated; rather, auxin
redistribution occurs.
2. You design an experiment to test the effect of light quality on bean seed
germination. Seeds are placed under red light (660 nm), far-red light (730 nm), or
darkness. After 7 days, you measure germination percentage. Which of the following
results would best demonstrate phytochrome-mediated germination?
A. Red light promotes germination; far-red light inhibits; darkness shows intermediate
germination
B. Both red and far-red light promote germination equally; darkness inhibits
C. Far-red light promotes germination; red light inhibits; darkness shows no germination
D. Red light promotes germination; far-red light reverses the effect; darkness shows low
germination
Answer: D. Red light promotes germination; far-red light reverses the effect;
darkness shows low germination
Phytochrome exists in two interconvertible forms: Pr (inactive) absorbs red light and
converts to Pfr (active), which promotes germination. Far-red light converts Pfr back to
Pr, reversing the effect. Thus, red light promotes germination, far-red light reverses it,
and darkness (no light) results in low germination due to residual Pfr or other factors.
Option A lacks the reversal; B and C are inconsistent with phytochrome action.
Page 2
,3. In a bean seed germination experiment, you measure the dry weight of seedlings
grown in light and dark for 10 days. The light-grown seedlings have significantly
higher dry weight than dark-grown seedlings. Which of the following best explains
this difference?
A. Dark-grown seedlings have higher respiration rates, consuming more stored reserves
B. Light-grown seedlings perform photosynthesis, fixing carbon dioxide and increasing
biomass
C. Dark-grown seedlings allocate more resources to root growth, reducing shoot biomass
D. Light-grown seedlings absorb more water, increasing fresh weight but not dry weight
Answer: B. Light-grown seedlings perform photosynthesis, fixing carbon dioxide
and increasing biomass
Dry weight reflects actual biomass accumulation. Light-grown seedlings can
photosynthesize, producing new organic matter from CO2, thus increasing dry weight.
Dark-grown seedlings rely solely on seed reserves and cannot photosynthesize, so their
dry weight decreases over time due to respiration. Option A is partially true but the
primary reason is photosynthesis. Options C and D are incorrect; water absorption
does not increase dry weight.
4. A student conducts a bean seed germination experiment with 100 seeds per
treatment: light, dark, and light with a far-red pulse at the end of each day. After 5
days, germination percentages are 95%, 30%, and 40%, respectively. What is the
most likely explanation for the reduced germination in the far-red pulse treatment
compared to continuous light?
A. Far-red light damages the seeds, causing irreversible inhibition
B. The far-red pulse converts Pfr to Pr, reducing the active phytochrome pool
C. Far-red light induces secondary dormancy via abscisic acid accumulation
D. The far-red pulse triggers a circadian rhythm shift that delays germination
Answer: B. The far-red pulse converts Pfr to Pr, reducing the active phytochrome
pool
Phytochrome-mediated germination requires Pfr. A far-red pulse at the end of each day
converts Pfr back to Pr, reducing the active form and thus lowering germination. This
is a classic photoreversible response. Option A is unlikely; far-red is not damaging.
Option C: ABA may be involved but the primary mechanism is phytochrome
conversion. Option D: circadian effects are not immediate over 5 days.
Page 3
, 5. In a controlled experiment, bean seeds are placed in petri dishes with moist filter
paper and subjected to either continuous white light or complete darkness. After 7
days, you measure hypocotyl length. The dark-grown seedlings have hypocotyls
three times longer than light-grown ones. This difference is primarily due to:
A. Higher auxin levels in dark-grown seedlings promoting cell elongation
B. Increased cell division in the meristem of dark-grown seedlings
C. Light-induced degradation of the PIF transcription factors
D. Darkness enhances water uptake, causing cell expansion
Answer: C. Light-induced degradation of the PIF transcription factors
In light, phytochrome activation leads to degradation of PIF (Phytochrome Interacting
Factor) transcription factors, which promote cell elongation. In darkness, PIFs
accumulate and drive hypocotyl elongation. Option A: auxin levels are not necessarily
higher; PIFs act downstream of auxin. Option B: cell division contributes but
elongation is the main factor. Option D: water uptake affects turgor but not the
dramatic length difference.
6. To investigate the role of seed coat in germination, you remove the seed coat from
bean seeds and place them in light or dark. Compared to intact seeds, decoated seeds
show:
A. Higher germination in both light and dark due to reduced physical restraint
B. Lower germination in both conditions due to desiccation and pathogen entry
C. Similar germination in light but reduced germination in dark
D. Germination only in light, as the seed coat is required for dark germination
Answer: A. Higher germination in both light and dark due to reduced physical
restraint
The seed coat can impose dormancy by restricting water uptake and gas exchange.
Removing it often enhances germination regardless of light condition, as physical
restraint is eliminated. However, decoated seeds may be more susceptible to desiccation
and pathogens, but under controlled conditions with adequate moisture and sterility,
germination typically increases. Option B may occur in non-sterile conditions but is not
the primary effect. Options C and D are incorrect.
Page 4
- 100 Questions and Answers Already Graded A+ Premium
Exam Tested And Verified
Subject Area Plant Biology / Seed Physiology
Description This exam assesses advanced understanding of the bean seed germination
experiment comparing light and dark conditions, covering seed physiology,
photomorphogenesis, experimental design, data analysis, and underlying
biochemical pathways.
Expected Grade A+
Total Questions 100
Duration 3 hours
Learning Outcomes 1. Analyze the role of light in seed germination and seedling development
2. Design controlled experiments to test environmental effects on germination
3. Interpret quantitative data from germination experiments
4. Explain the molecular mechanisms of photomorphogenesis in seedlings
5. Critically evaluate experimental variables and potential confounding factors
Accreditation This exam meets the rigorous standards of top R1 US universities, including Ivy
League institutions, for advanced undergraduate and graduate coursework in plant
biology.
Page 1
,1. In a bean seed germination experiment comparing light and dark conditions, you
observe that dark-grown seedlings exhibit elongated hypocotyls, small cotyledons,
and no chlorophyll. This phenotype is primarily due to which of the following
mechanisms?
A. Activation of phytochrome B by far-red light in the dark
B. Constitutive expression of COP1 in the absence of light
C. Increased gibberellic acid signaling promoting cell elongation
D. Downregulation of auxin transporters in dark conditions
Answer: C. Increased gibberellic acid signaling promoting cell elongation
In darkness, seedlings undergo skotomorphogenesis, characterized by elongated
hypocotyls and etiolation. This is driven by increased gibberellic acid (GA) signaling,
which promotes cell elongation. COP1 is active in the dark (not constitutive expression)
and targets photomorphogenesis-promoting factors for degradation. Phytochrome B is
inactive in the dark. Auxin transporters are not directly downregulated; rather, auxin
redistribution occurs.
2. You design an experiment to test the effect of light quality on bean seed
germination. Seeds are placed under red light (660 nm), far-red light (730 nm), or
darkness. After 7 days, you measure germination percentage. Which of the following
results would best demonstrate phytochrome-mediated germination?
A. Red light promotes germination; far-red light inhibits; darkness shows intermediate
germination
B. Both red and far-red light promote germination equally; darkness inhibits
C. Far-red light promotes germination; red light inhibits; darkness shows no germination
D. Red light promotes germination; far-red light reverses the effect; darkness shows low
germination
Answer: D. Red light promotes germination; far-red light reverses the effect;
darkness shows low germination
Phytochrome exists in two interconvertible forms: Pr (inactive) absorbs red light and
converts to Pfr (active), which promotes germination. Far-red light converts Pfr back to
Pr, reversing the effect. Thus, red light promotes germination, far-red light reverses it,
and darkness (no light) results in low germination due to residual Pfr or other factors.
Option A lacks the reversal; B and C are inconsistent with phytochrome action.
Page 2
,3. In a bean seed germination experiment, you measure the dry weight of seedlings
grown in light and dark for 10 days. The light-grown seedlings have significantly
higher dry weight than dark-grown seedlings. Which of the following best explains
this difference?
A. Dark-grown seedlings have higher respiration rates, consuming more stored reserves
B. Light-grown seedlings perform photosynthesis, fixing carbon dioxide and increasing
biomass
C. Dark-grown seedlings allocate more resources to root growth, reducing shoot biomass
D. Light-grown seedlings absorb more water, increasing fresh weight but not dry weight
Answer: B. Light-grown seedlings perform photosynthesis, fixing carbon dioxide
and increasing biomass
Dry weight reflects actual biomass accumulation. Light-grown seedlings can
photosynthesize, producing new organic matter from CO2, thus increasing dry weight.
Dark-grown seedlings rely solely on seed reserves and cannot photosynthesize, so their
dry weight decreases over time due to respiration. Option A is partially true but the
primary reason is photosynthesis. Options C and D are incorrect; water absorption
does not increase dry weight.
4. A student conducts a bean seed germination experiment with 100 seeds per
treatment: light, dark, and light with a far-red pulse at the end of each day. After 5
days, germination percentages are 95%, 30%, and 40%, respectively. What is the
most likely explanation for the reduced germination in the far-red pulse treatment
compared to continuous light?
A. Far-red light damages the seeds, causing irreversible inhibition
B. The far-red pulse converts Pfr to Pr, reducing the active phytochrome pool
C. Far-red light induces secondary dormancy via abscisic acid accumulation
D. The far-red pulse triggers a circadian rhythm shift that delays germination
Answer: B. The far-red pulse converts Pfr to Pr, reducing the active phytochrome
pool
Phytochrome-mediated germination requires Pfr. A far-red pulse at the end of each day
converts Pfr back to Pr, reducing the active form and thus lowering germination. This
is a classic photoreversible response. Option A is unlikely; far-red is not damaging.
Option C: ABA may be involved but the primary mechanism is phytochrome
conversion. Option D: circadian effects are not immediate over 5 days.
Page 3
, 5. In a controlled experiment, bean seeds are placed in petri dishes with moist filter
paper and subjected to either continuous white light or complete darkness. After 7
days, you measure hypocotyl length. The dark-grown seedlings have hypocotyls
three times longer than light-grown ones. This difference is primarily due to:
A. Higher auxin levels in dark-grown seedlings promoting cell elongation
B. Increased cell division in the meristem of dark-grown seedlings
C. Light-induced degradation of the PIF transcription factors
D. Darkness enhances water uptake, causing cell expansion
Answer: C. Light-induced degradation of the PIF transcription factors
In light, phytochrome activation leads to degradation of PIF (Phytochrome Interacting
Factor) transcription factors, which promote cell elongation. In darkness, PIFs
accumulate and drive hypocotyl elongation. Option A: auxin levels are not necessarily
higher; PIFs act downstream of auxin. Option B: cell division contributes but
elongation is the main factor. Option D: water uptake affects turgor but not the
dramatic length difference.
6. To investigate the role of seed coat in germination, you remove the seed coat from
bean seeds and place them in light or dark. Compared to intact seeds, decoated seeds
show:
A. Higher germination in both light and dark due to reduced physical restraint
B. Lower germination in both conditions due to desiccation and pathogen entry
C. Similar germination in light but reduced germination in dark
D. Germination only in light, as the seed coat is required for dark germination
Answer: A. Higher germination in both light and dark due to reduced physical
restraint
The seed coat can impose dormancy by restricting water uptake and gas exchange.
Removing it often enhances germination regardless of light condition, as physical
restraint is eliminated. However, decoated seeds may be more susceptible to desiccation
and pathogens, but under controlled conditions with adequate moisture and sterility,
germination typically increases. Option B may occur in non-sterile conditions but is not
the primary effect. Options C and D are incorrect.
Page 4
