Plant Phys Quiz 3

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 ammonium

Step#3: Ammonium assimilation: Ammonium 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