Plant Phys Final Exam

Respiration takes place:

a) During the day

b) During the night

c) During both day and night

d) During the day-night transitions

During both day and night

The translocation of photo-assimilates from the leaves takes place through:

a) The xylem

b) The phloem

c) Transpiration

d) Root pressure

The phloem

The physiological mechanism explaining photo-assimilate translocation is called:

a) The capillary action mechanism

b) The pressure-flow mechanism

c) The adhesion mechanism

d) The cohesion mechanism

The pressure-flow mechanism

Sink strength is a function of:

a) Phloem anatomy

b) Photosynthesis

c) Sink size and activity

d) Respiration

Sink size and activity

Photo-assimilate movement between organs depends on cell-to-cell solute movements that involve:

a) A symplastic pathway

b) An apoplastic pathway

c) Both symplastic and apoplastic pathways

Both symplastic and apoplastic pathways

A plant photosynthetic organ from which photo-assimilates are translocated

Source Organ

Plant organ receiving photo-assimilates

Sink Organ

The ratio of grain to above ground biomass

Harvest Index

Name the three main phases of photo-assimilate translocation from the leaf to the target organ

Phase #1: Phloem loading

Phase #2: Long distance transport

Phase #3: Phloem unloading

When solutes move out of the phloem into the target organ, they can follow one of two types of apoplastic pathways that are different dependent on the species (i.e., legumes vs. non-legumes). Explain the difference between these pathways.

2: sucrose goes to apoplast without a carrier. sucrose is hydrolosized by acid invertase, this is irreversable creating glucose and fructose, transported into the sink cell, combined into sucrose and tranported to the vacuole

3: sucrose is carried by an energy dependent carrier, just goes into sink cell.

The partitioning of photo-assimilates between organs receiving photo-assimilates depends on three key factors. What are they?

Vascular connection, Proximity of the sink, Sink Strength

What are names and general outcomes of the 3 key steps of cellular respiration?

Glycolysis: Sugars into pyruvate, Generation of intermediates, NADH and ATP

Citric Acid Cycle: Pyruvate metabolized, Generation of building blocks, CO2, NADH, FADH2, and ATP

Respiratory transport chain: Oxidation of electron donors and generation of ATP

Fixing N2:

a) Requires as much energy as fixing CO2

b) Requires half the energy used for fixing CO2

c) Requires much more energy than used for fixing CO2

Requires much more energy than used for fixing CO2

Positive chemotaxis involves:

a) Synthesis by roots of flavonoids followed by synthesis of lectins that bind to polysaccharides synthesized by rhizobia in response to flavonoids

b) Synthesis by roots of polysaccharides that feed the rhizobia which then release flavonoids that attract more rhizobia

c) Both

d) Neither

Synthesis by roots of flavonoids followed by synthesis of lectins that bind to polysaccharides synthesized by rhizobia in response to flavonoids

Dinitrogenase is the enzyme responsible for:

a) Reducing nitrate

b) Reducing nitrite

c) Breaking down dinitrogen triple bond

d) Synthesizing Glutamine

e) Synthesizing Glutamate

Breaking down dinitrogen triple bond

Oxygen in the bacteroid:

a) Inhibits dinitrogenase activity but benefits respiration

b) Inhibits both dinitrogenase activity and respiration

c) Promotes both dinitrogenase activity and respiration

Inhibits dinitrogenase activity but benefits respiration

The GS/GOGAT cycle operates:

a) In the roots

b) In the leaves

c) In the soil

d) a) and b)

e) b) and c)

f) a) and c)

a) and b)

Nitrate and nitrite reductase:

a) Reduce nitrate into ammonium

b) Break dinitrogen triple bond

c) Convert ammonium into glutamine

Reduce nitrate into ammonium

Only eukaryotes can achieve N2 fixation

False

The process of breaking dinitrogen triple bonds requires 3 ATP

False

Positive chemotaxis takes place during the third step of nitrogen fixation

False

Nod factors are involved in the synthesis of shorter and curled root hairs needed for infection by rhizobia

True

Rhizobia induce the development of the nodule meristem through mitogenic signals

True

The nodule meristem is generated in the root epidermis

False

The GS/GOGAT system serves a metabolic point of coordination between nitrogen assimilation, respiration and photosynthesis

True

Translocation of organic nitrogen molecules from the nodule to the target organ is more costly in carbon for tropical legumes

True

Ureides are the main form of exported nitrogen from the nodules in temperate legumes

False

Oxygen is released in the bacteroid from leghemoglobin to support N2 fixation

True

Nitrogen is exported from the nodule essentially as glutamine

True

N uptake from the soil is highest during the reproductive growth

False

N export to the seeds is highest during the reproductive growth

True

Nitrifying bacteria in the soil generate essentially ammonia

False

Nitrogen-fixing multicellular structures that develop on the roots

Nodules

The plant that makes a nitrogen fixing association

Legumes

Microbial partner of the plant during nitrogen fixation

Rhizobia

Key enzyme necessary for dinitrogen fixation

Nitrogenase

Cellular structure where the nitrogen fixation reactions take place inside the nodule

Bacteroides

Name the type of plants that are known to perform nitrogen fixation

Legumes

Name the key enzyme that is essential to nitrogen fixation

Nitrogenase

Name the immediate product of the dinitrogen-breaking enzyme

Ammonia

This product will be protonated into another form. Name this form

Ammonium

This form will be assimilated by the GS enzyme form an amino acid. Name this amino acid

Glutamine

This amino acid is not readily translocated. In the case of temperate legumes, it has to be changed into another amino acid. Name this amino acid:

Asparagine

Name the vascular tissue that is responsible for translocating this product to the target organs

Xylem

N export from the leaf to the grain decreases photosynthesis because

Reduces rubisco in the leaves, less energy for photosynthesis

N export from the leaf to the grain decreases nitrogen fixation because

Then there is less energy available for producing energy to go to the nodule

Describe phases 1 to 5 leading to the formation of the root nodule.

Phase#1: Rhizobia are attracted to the root via positive chemotaxis

Phase#2: Rhizobia release signals to stimulate division forming the root hair that will develop into a nodule

Phase#3: Rhizobia get entrapped in root tip, and embedded in the wall, infection thread develops.

Phase#4: Thread reaches nodal meristem and risobia release into cells to become bacterioids

Phase#5: Nodule size increases, connections made to xylem and phloem

Why are vascular connections needed by the nodule? Explain your arguments in four sentences below:

The bacteria need a source of nutrients and oxygen to function, this is transported by the phloem. The xylem is used to export the nitrogen to other parts of the plant. Without these connections, the nodule would not have the resources to fix nitrogen for the plant. The plant would have no way to carry the nutrients to other areas of the plant

Cite three soil factors that can influence the activity of nitrifying bacteria.

pH, Temperature, Soil Oxygen

There are several biochemical steps that lead to the synthesis of glutamate starting from the uptake of photo-assimilates in the nodule. Group these into 3 main steps and describe them.

Step#1: Transport of photoassimilates: Photoassimilates are transported from the leaves to the nodules to fuel this process.

Step#2: Nitrogen fixation: Nitrate is reduced to ammonia

Step#3: Ammonium assimilation: Ammonia is protonated to ammonium, then synthesized into glutamine by the Glutamate synthase cycle

Explain how water deficit can influence nitrogen fixation using two examples.

Example#1: Stomata closure during drought causes less photosynthesis, less photoassimilates available for N fixation

Example#2: Stomata being closed reduces the O2 in the plant reducing nitrogenase activity, less nitrogen fixing

Using your answers to the above questions, describe two strategies would you apply as a soybean grower in order to mitigate drought effects on your soybean productivity. Discuss their benefits and their potential disadvantages.

Strategy#1: Grow a cultivar that has drought tolerance, it may have stomata characteristics that keep them open longer, could harm plant if drought is persistent

Strategy#2: Improve soil moisture retention, grow cover crops or use compost to improve soil structure, may be expensive and time consuming

Explain why homeostasis is important for plants

Staying functional and being able to maintain the correct conditions for survival in a variety of environments is essential for plants as they cannot move or change their conditions

List five main different factors to be considered when characterizing a stress scenario:

Different organizational levels, Duration, Intensity, Type of stress, Different developmental stages

In the case of drought, stress avoidance involves:

a) Achieving short and rapid seed-to-seed cycle during the favorable period

b) Growing roots that track the water table

c) Reducing transpiration in response to water deficit to save water

d) a) and b)

e) a) and c)

f) b) and c)

d) a) and b)

Photosynthetic efficiency is:

a) The slope of the response of the rate of CO2 assimilation to irradiance under light limited conditions

b) The maximal rate of CO2 assimilation during the light saturated phase

c) The slope of the decrease of the rate of CO2 assimilation under photoinhibitory conditions

a) The slope of the response of the rate of CO2 assimilation to irradiance under light limited conditions

Photosynthetic capacity is:

a) The maximal rate of CO2 assimilation

b) The minimal rate of CO2 assimilation

c) The average of minimal and maximal rates of CO2 assimilation

a) The maximal rate of CO2 assimilation

At maximal photosynthetic capacity, the limiting factor is:

a) The rate at which Rubisco uses RubBP and CO2

b) The rate at which RuBP is re-generated

c) Both

d) Neither

a) The rate at which Rubisco uses RubBP and CO2

Photoinhibition:

a) Decreases only photosynthetic efficiency

b) Decreases only photosynthetic capacity

c) Decreases both photosynthetic efficiency and capacity

d) Does not impact photosynthetic efficiency or capacity

c) Decreases both photosynthetic efficiency and capacity

During photoinhibition:

a) D1 protein is disassembled more frequently resulting in a lower activity of photosystem I

b) D1 protein is disassembled less frequently resulting in a lower activity of photosystem II

c) D1 protein is disassembled more frequently resulting in a lower activity of photosystem II

d) D1 protein is disassembled less frequently resulting in a lower activity of photosystem I

c) D1 protein is disassembled more frequently resulting in a lower activity of photosystem II

Stress avoidance consists of experiencing a stress, and being tolerant to that stress:

False

Achieving a short seed-to-seed growth cycle is a case of drought tolerance:

False

Photoinhibition takes place at very low photon fluence rates:

False

Photoinhibition primarily limits photosystem I function:

False

Photoinhibition-related stresses generally involve an impairment of the D1 protein:

True

The D1 protein normal function could be impaired by multiple stresses:

True

The D1 protein has a very low turnover rate:

False

Stress tolerance consists in experiencing the stress but responding in a way that results in improved fitness or yield:

True

A drought tolerance trait that leads to improving crop performance in a given environment can lead to an opposite result in another environment:

True

Describe the three phases that you see in this figure.

Phase 1: Light Limeted stage, increase in assimilation so ATP, NADPH, and RuBP generated. CO2 assimilation is the limiting factor

Phase 2: Light saturated, PCR cycle saturated with ATP and NADPH, maximum photosynthetic capacity. Limiting factor is how fast rubisco uses CO2 and RuBP.

Phase 3: Photoinhabition, decrease in photosynthetic assimilation

Cite three environmental stresses under which chronic photoinhibition can occur

Stress#1: Excess light intensity

Stress#2: Water deficit

Stress#3: Low Temperature

Suppose you are a corn grower whose field is exposed to one of those stresses. Identify the stress and exemplify two solutions that you would deploy in the field in order to address the problem:

Stress: Water deficit

Solution#1: Increase irrigation

Solution#2: Improve soil moisture holding capabilities

Compound produced by one part of an organism that is translocated to other parts where it triggers a response in target cells and tissues:

Hormones

List below the 5 main classes of plant hormones:

1) Gibberellin

2) Auxin

3) Cytokinins

4) Ethylene

5) Abcisic Acid

Gibberellins play a role in:

a) Breaking seed dormancy

b) Germination

c) Growth

d) Flowering

e) a) and b)

f) a), b) and c)

g) All of the above

g) All of the above

To be effective, hormones need to be synthesized in large quantities

False

Hormones do not affect gene expression or activities of enzymes:

False

Auxin is the only plant hormone known to be transported polarly

True

Polar transport is acropetal

False

Auxin promotes formation of lateral and adventitious roots

True

Auxin plays a role in the differentiation and regeneration of the xylem and the phloem

True

Cytokinins promote leaf senescence

False

Salicylic acid, jasmonates, polyamines, systemin and nitric oxide are other chemical signals that have similar functions to typical plant hormones

True

Ehylene delays fruit ripening

False

Ethylene is a gas

True

Abscisic acid promotes seed dormancy

True

Auxin

Stimulates stem elongation (at low concentrations), root growth, cell differentiation and branching; enhances apical dominance, promotes xylem differentiation

Cytokinins

Stimulate germination, delays senescence

Gibberellins

Promote seed and bud germination, stem elongation, flowering and development of fruit

Brassinosteroids

Inhibit root growth, retard leaf abscission, promote xylem differentiation

Abscisic acid

Inhibits growth, closes stomata during water stress, promotes seed dormancy

Ethylene

Promotes fruit ripening, opposes auxin effects

Protoplast shrinkage results in:

a) Displacement of membrane proteins

b) Solute leakage

c) Loss of solute selectivity

d) Loss of cellular compartmentation

e) Loss of activity of membrane enzymes

f) a), b) and c)

g) a), b) and e)

h) All of the above

h) All of the above

At the cellular level, the dehydration stress impacts:

a) The plasma membrane

b) The cytosol proteins

c) The organelles

d) a) and b)

e) b) and c)

f) All of the above

f) All of the above

Stomata closure is the result of:

a) A hydropassive closure

b) A hydroactive closure

c) Neither

d) Both

d) Both

Heat and chilling stresses cause damage:

a) Only on reproductive tissues

b) Only on vegetative tissues

c) On both tissues

c) On both tissues

When abscisic acid reaches the guard cell, it:

a) Triggers a movement of Cl-, K+ and water into the cell

b) Triggers a movement of Cl-, K+ into the cell but water will leave the cell

c) Triggers a movement of Cl-, K+ and water out of the cell

c) Triggers a movement of Cl-, K+ and water out of the cell

Protoplast shrinkage is the same thing as plasmolysis

True

A hydropassive mechanism mediated by loss of turgor is responsible for stomata closure

True

ABA is biosynthesized only in response to stress

False