5: Plant-Environment Interactions Flashcards
Module 1, Lesson 5
Certain ____ molecules in plants can absorb light and initiate a response.
Pigment
____ is a pigment that helps plants perform photosynthesis.
Chlorophyll
____ is a directional growth response to light.
Phototropism
____ is nondirectional plant development triggered by light.
Photomorphogenesis
The biologically inactive version of phytochrome is…
Phytochrome red
(Pr)
When red photons are available, Pr is converted to…
Pfr
The biologically active version of phytochrome is…
Phytochrome far-red
(Pfr)
____ facilitates expression of light-response genes and promotes a plant response.
Pfr
When no far-red photons are available, Pfr converts to…
Pr
When a plant is exposed to direct sunlight…
Pr converts to Pfr
In the absence of direct sunlight…
Pfr converts to Pr
In order to regulate its concentration in the plant, Pfr is degraded by…
Proteosomes
True or false:
Light-response genes are continually expressed in the plant.
False
List the two mechanisms by which Pfr can activate light-response genes.
- Directly regulating gene expression
- Acting through kinase
In order to directly regulate gene expression, Pfr…
Enters the nucleus and interacts with the DNA
Pfr can indirectly regulate gene expression by working through the protein…
Kinase
When Pfr works through kinase, a kinase signal pathway will eventually activate…
Transcription factors
List three plant growth responses that can be influenced by phytochrome.
- Seed germination
- Shoot elongation
- Rapid elongation
____ is inhibited by far-red light and stimulated by red light.
Seed germination
____ is a shoot response found in seedlings that grow in the dark.
Etoliation
____ conserves a seedling’s energy while allowing it to grow towards the light.
Etoliation
Once exposed to light, a seedling that sprouted in the dark will…
Assume its normal morphology
Under shady conditions, a plant will…
Rapidly increase in height
In crowded conditions, a plant will ____ to outcompete its neighbors.
Elongate rapidly
Stems are normally ____ to blue wavelengths.
Positively phototropic
True or false:
Roots are normally positively phototropic.
False
They will either have no phototropic response or exhibit a weak negative response.
Phototropins 1 and 2 are ____ light receptors.
Blue
____ is a plant hormone involved in phototropic growth.
Auxin
Shoots tend to bend towards light in order to…
Increase exposure to light for photosynthesis
____ are 24-hour cycle rhythms that often affect leaf position.
Circadian clocks
____ is the response of plant’s to Earth’s gravitational field.
Gravitropism
Roots are ____ gravitropic.
Positively
Roots will usually bend ____ the center of gravity.
Towards
In roots, the gravity-sensing region is located in the…
Root cap
Stems are ____ gravitropic.
Negatively
Stems usually bend ____ the center of gravity.
Away from
In stems, the gravity-sensing region is located in the…
Endodermal cells surrounding vascular tissue
____ are starch-containing plastids that may be involved in sensing gravity.
Amyloplasts
Amyloplasts sink in response to…
Gravitational fields
____ is responsible for transmitting signals from the gravity-sensing cells to the rest of the plant.
Auxin
In shoots, auxin promotes greater elongation of cells on the…
Lower side of the stem
In roots, auxin promotes greater elongation of cells on the…
Upper side of the root
List three main plant responses to mechanical stimuli.
- Thigmomorphogenesis
- Thigmotropism
- Reversible responses to touch
____ occurs when a plant permanently changes form in response to mechanical stimuli.
Thigmomorphogenesis
____ is directional growth in response to contact.
Thigmotropism
Plants that grow by twining around other objects exhibit…
Thigmotropism
Many reversible responses to touch involve changes in…
Turgor pressure
____ are clusters of cells at the base of a leaf that change turgor pressure in response to contact.
Pulvini
Extreme conditions may promote ____ in a plant.
Dormancy
The process of dormancy begins with ____ of plant organs.
Abscission
The cellular changes involved in abscission take place in the…
Abscission zone
A suberin-impregnated ____ is located on the stem side of the abscission zone.
Protective layer
A ____ is located on the organ/leaf side of the abscission zone.
Separation layer
Seed dormancy is typically caused by…
Drought conditions
____ is a plant hormone that is instrumental in causing and maintaining seed dormancy.
Abscisic acid
(ABA)
True or false:
As in animals, plant hormones are chemical signal molecules.
True
True or false:
Unlike in animals, plant hormones are not produced in special tissues.
True
List the eight major types of plant hormones.
- Auxin
- Cytokinins
- Ethylene
- Abscisic acid
- Gibberellins
- Brassinosteroids
- Oligosaccharins
- Strigolactones
____ was one of the first hormones to be discovered.
Auxin
____ is a plant hormone that makes cell walls soft to enable expansion and elongation.
Auxin
Auxin is produced in the…
Shoot tip
(apical meristem)
In a phototropic response, ____ migrates to the dark side of the stem and promotes elongation there.
Auxin
Synthetic auxin is sometimes used as…
Herbicides
____ are a plant hormone that promote cell division and differentiation.
Cytokinins
Cytokinins are produced in the…
Root tip
Cytokinins sometimes act in opposition to…
Auxin
____ promote growth of lateral buds in shoots.
Cytokinins
____ suppresses growth of lateral buds in shoots, a process known as apical dominance.
Auxin
____ inhibit lateral root formation.
Cytokinins
____ promotes lateral root formation.
Auxin
____ is the only gaseous plant hormone.
Ethylene
____ has a major role in promoting fruit development and ripening.
Ethylene
The production of ethylene is stimulated by the release of ____ in developing fruits.
Auxin
____ is a plant hormone involved in abscission.
Ethylene
____ slows fruit ripening.
Carbon dioxide
In order to break dormancy, the levels of ____ must decrease.
Abscisic acid
____ can counteract the effects of other hormones, such as auxin and gibberellins.
Abscisic acid
____ influences the opening and closing of stomata.
Abscisic acid
____ are a class of 100+ hormones important in stem elongation and flowering.
Gibberellins
Gibberellins often work in conjunction with…
Auxin
____ are plant hormones with wide effects on plant growth, reproductive development, and delaying senescence.
Brassinosteroids
____ are plant hormones involved in defense signaling and organ development.
Oligosaccharins
____ are formed from the breakdown of oligosaccharides by pathogens.
Oligosaccharins
____ are plant hormones that work with auxin and cytokinin to help shape plants.
Strigolactones
____ are derived from carotenoid hormones.
Strigolactones
____ are a major reproductive advantage for angiosperms.
Flowers and fruits
____ is the ability to reproduce (produce fruits and flowers).
Competency
Internal signals and environmental cues can turn on reproductive genes that specify…
Formation of flower structures
The process of becoming competent is called a…
Phase change
During phase change, the plant…
Gains the ability to flower
(transitions from juvenile to adult)
True or false:
Once phase change occurs, the plant will begin to flower.
False
Sometimes other factors are needed to trigger flowering
List the four genetically-regulated pathways involved in flower production.
- Light-dependent
- Temperature-dependent
- Gibberellin-dependent
- Autonomous
Which two pathways involved in flower production are triggered by external cues?
- Light-dependent
- Temperature-dependent
Which two pathways involved in flower production are triggered by internal mechanisms?
- Gibberellin-dependent
- Autonomous
The ____ is an adaptation to changing seasons that enables plants to flower at the proper time.
Photoperiodic response
The ____, also known as “day length” is the proportion of light to dark in a 24-hour cycle.
Photoperiod
True or false:
Plants using the light-dependent pathway respond to the amount of uninterrupted darkness.
True
Long-day plants will flower when….
The dark period is short
Long-day plant species will flower when the amount of darkness ____ a critical length for that species.
Is less than
What time of the year do long-day plants tend to flower?
Between late spring and early summer
Short day plants will flower when…
The dark period is long
Short-day plant species will flower when the amount of darkness ____ a critical length for that species.
Exceeds
What time of year do short-day plants tend to flower?
Between late summer and early fall
Interrupting the dark period with light…
Interrupts the plant response
In ____ plants, the photoperiod requirement is not absolute and other factors play a role in flowering.
Facultative
List four advantages of photoperiodic flowering control.
- Ensures abiotic conditions are optimal
- Synchronizes flowering with pollinator availability
- Helps minimize competition for resources
- Helpful for commercial growers
____ is a period of chilling needed for some plants to flower and some seeds to germinate.
Vernalization
Using the temperature-dependent pathway ensures that…
Flowering occurs after a cold period
Using the gibberellin-dependent pathway, flowering requires…
An increase in gibberellin levels
Using the ____ pathway, flowering doesn’t depend on any external cues except nutrition.
Autonomous
List two genes that determine flowering regardless of pathway.
- LEAFY (LFY)
- APETALAI (API)
Three pathways use genes that…
Either repress or promote flower development
The gibberellin-dependent pathway can directly influence the expression of…
LFY genes
The ligh-dependent pathway uses a protein that acts as a…
Transcription factor, to turn on other genes
