Plant Physiology Exam 3 - Spring 2025 | Quizlet

The driving force for long-distance phloem transport is

Pressure created by accumulated solutes and osmosis

What is true of phloem sieve tubes

They are alive and membrane lined, but otherwise mostly a hollow lumen to allow sap flow

If you analyzed the phloem sap of a plant and found high concentrations of ________, the plant most likely phloem loads from the apoplast

Sucrose (released from the mesophyll into the cell wall space)

If I had a compound that specifically inhibited the activity of plasma membrane ATPases, and if I observed that this compound resulted in an immediate cessation of phloem transport when applied to a plant, what type of phloem loading is most likely being employed?

Apoplastic phloem loading

To move a neutral solute, like sucrose from an area of low concentration, such as the cell wall space, to an area of high concentration, such as the cytoplasm of phloem cells, it is most likely transported by

Co-transport with a proton (PMF)

A seed, whether developing on the plant or germinating in the soil, is a "sink" tissue.

False (Developing it is a sink tissue, germinating it's a source tissue)

Phloem transport is expected to remain fairly constant during diurnal cycles (day/night cycles) because

Sucrose and starch are produced during the day, and starch is converted to sucrose at night

The fundamental chain of events in a signal transduction cascade is

Signal > Receptor > Signal Transduction (Amplification) > Response

During a response to a signal, the response is usually shutdown

Once a response threshold is reached

A secondary messenger in a signal transduction cascade

is a relatively abundant, small molecule that participates in signal transmission

In plants, which of the following targets a component of a signal transduction cascade for degredation?

An E3 ubiquitin ligase

The expression "one bad apple ruins the bunch" can be applied figuratively to a disruptive student in a lecture hall, but in literal, botanical terms, this expression refers to the action of

Ethylene

hormone most associated with cell division in plants is

Cytokinin :D

This is a representation of (has a 5-carbon ring with N-H and a CH2-COOH)

Auxin (IAA specifically)

When a plant embryo within a developing seed fails to enter dormancy and enters vegetative growth while still attached to the maternal plant, it is called

Vivipary

The shade avoidance response is controlled by phytochrome, and when a sun plant is shaded, it will

Elongate its stems to grow as a spindly plant with few branches until it finds sufficient red light (this is also known as etiolation)

Which of the following is true of the phytochrome system?

Pr (the inactive form) is converted to Pfr (the active form) by red light

Guard cells open stomata in response to light. The strongest stimulation to open is mediated by

Blue light (cryptochrome)

Photomorphogenic responses to blue light are mediated in part by

Crptochrome

From a plant's perspective, what wavelengths (and colors) would be considered "high quality" and which would be considered "low quality"?

Red light (<700 nm) is considered high quality light because it converts Pr to the active Pfr form. Far red light (>700 nm) is low quality light as it cannot fully convert Pr to Pfr.

Briefly explain the anatomy and chemistry of "polymer trap" symplastic phloem loading.

Symplastic phloem loading uses a lot of specialized branched plasmodesmeta allowing diffusion of sucrose. Large oligosaccharides are trapped after conversion in the companion/intermediary cell. Energy is provided by UDP when converting sucrose to oligosaccharides.

Phytochrome can shuttle between the cytoplasm and the nucleus

True

Phytochrome has kinase activity and can directly phosphorylate other proteins

True

Phytochrome is needed for photosynthesis

False

Phytochrome causes the response that Darwin observed in his experiments

False

Phytochrome helps plants detect the quality of light

True

Phytochrome functions in the thylakoid membrane

False

In plants, which of the following commonly targets a component of a signal transduction cascade for degradation

An E3 ubiquitin ligase

During embryogenesis, cell fate is influenced by

All of the above are correct (Cell lineage within the embryo, cell position within the embryo, hormone gradients in the embryo)

Look at the cactus stem on the left and compare to the one on the right (Image shows two Saguaro cacti: one with numerous growth points, the other looks like a normal Saguaro). This phenomenon is best called

Fasciation

In the developing embryo, which of the following contributed to both the initial expansion of the cotyledons during the heart stage and the differentiation of cells that will eventually form the vascular tissue of the stem?

Auxin transport gradients (IAA is a weak acid, in acidic environments auxin will stay neutral, in neutral environments, protons are stripped from the auxin)

Auxin transport from cell to cell is in part based on auxin existing as

charge neutral in the apoplast, an anion in the cyotplasm, and polar distribution of efflux carriers

Indeterminate growth

involves continued growth from the meristem (stem cells are replaced with new stem cells

Vivipary mutants are important to the study of plant development because they provide information on

Embryos entering dormancy

Which hormone is most directly responsible for establishing and maintaining the stem cells in the shoot apical meristem?

Cytokinin

Seeds are considered a major evolutionary advance that allowed the seed plants to outcompete more ancestral lineages that do not produce seeds. Which is generally true about seeds?

All of the above (Seeds allow the embryonic plant to survive harsh conditions, seeds benefit dispersal of a plant species to new areas or environments, dormant seeds frequently have evolved mechanisms to indicate when confitions are favorable for germination, and eggs and pollen that contribute seeds are frequently from different parent plants, so seeds have new combinations of genetic material)

Which statement is most true about seed dormancy and germination

ABA promotes dormancy; GA promotes germination

When auxin promotes stem curvature in response to directional light, it does so by

migrating along the shaded side of the stem to promote cell elongation on the shaded side

In the shade-avoidance response of sun plants

sunlight (a low ratio of red light to far-red light) promotes gibberellic acid-induced stem elongation

Senescence is best described as

Death and decay of plant tissues and organs

Which hormone is directly responsible for the precise programmed cell death in the abscission zone of a senescing leaf when it is shed in the autumn?

Ethylene

Movement of water and the products of photosynthesis from source to sink is through

the phloem by positive pressure

What structure allows phloem sap to flow from one sieve element to another sieve element along the sieve tubes?

Sieve pore plates

What is true of phloem companion cells?

They are closely associated with sieve elements and they are cytoplasmically dense

At a roadside stop in Arkansas, I found a peculiar plant producing a fruit I had not seen before. Knowing that phloem transport would carry sugars from leaves into the fruits, and knowing that the type of sugar present would provide information on the type of phloem loading employed, I collected a few fruits and analyzed them back in my research laboratory at UNT. From my analysis, I concluded that this plant used the polymer trap mechanism of symplastic phloem loading. What sugar did I find in high concentrations that led me to my conclusion?

Raffinose and stachyose

Cotyledon in a developing seed

sink

Cotyledon in a germinating seed

source

Mature leaf

source

Immature leaf

sink

Mature flower

sink

Immature flower

sink

Which of the following statements is true of receptors in a signal transduction cascade

The receptor can ve anywhere in the cell that the signal can reach

A secondary messenger in a signal transduction cascade

transmits the signal from the receptor to the site of the response

In a plant phospho-relay system, which are thought to be derived from bacterial two-component signaling cascades

A phosphate is passed from a sensor histidine kinase to a histidine phosphotransfer protein (HPT) and then to a response regulator (ARR)

Which statement is most FALSE regarding signal transduction cascades in plants

Plant cascades are usually a series of positive activation steps (In animals, this is true but plants are deactivations)

When auxin promotes cell wall expansion, it does so by

enhancing ATPase activity to pump protons into the extracellular space

If I want to extend the photosynthetic longevity of a leaf, and delay the onset of senescence, which of the following hormones should I spray on the foliage?

Cytokinin

Who among the following scientists is most closely associated with some of the earliest work on the hormone concept in plants?

Darwin (But Sachs was first)

The "Green Revolution" was a series of agricultural advances through the 1950s and 1960s that included intensive use of fertilizer, irrigation, mechanization, and crop breeding to produce very productive cultivars. Many of these cultivars were bred for a stocky stature (shorter and sturdier) and were less susceptible to lodging (falling over and getting stuck in mud) and crop loss in inclement weather. Knowing that these crops were shorter than ancestral lines, what hormone-signaling pathway do you think was most repressed during selective breeding?

Gibberellic acid

Sugar (sucrose) is collected from the stem of sugarcane and increasing the height of the sugarcane plant increases yield. Based on this information, which plant hormone is commonly sprayed in plantations to increase yield?

Gibberellic acid

Both the cytokinin receptor encoded by CRE1 and the ethylene receptor encoded by ETR1 are examples of

The sensor histidine kinase component of a two-component sensor histidine kinase (i.e. the part that recieves the signal and passes it to other components of the signal transduction cascade)

Which of the following is most likely to accelerate the ripening of harvested fruit?

Storing the fruit in sealed containers with other fruit

Which colors in the visible spectrum have a strong influence on plant development and response to the environment?

Blue and Red

A bioassay is an assay that directly measures the biological impact of a treatment. A good bioassay for measuring the quality of a weak light source would be

De-etoliation (greening and expansion) of cotyledons

With respect to phytochrome activated responses in plants, very low fluence responses (VLFR) are not reversible by far red light because

Pr is never fully converted to Pfr

In common "weed and feed" fertilizers, an herbicide used to kill broad-leaf weeds (dicots) but no lawns (grasses/monocots) is _______ and is an analog of ______

2,4-dichlorophenoxyacetic acid, indole 3 acetic acid