Problem Set 13

Question 1

What is the difference between general and specific biocidal agents? List some
characteristics of each type of agent

Answer 1

General biocides are toxic to many different types of organisms and tend to
be highly reactive chemicals like strong oxidizing agents or often contain heavy
metals.
Specific biocides are toxic to a subset or organism because they target some
organismal function like a metabolic pathway or developmental step in those
organisms. They are often enzyme inhibitors or hormone analogues.

Question 2

Some general biocidal agents that have been used extensively in the past fifty years have
been phased out because of negative environmental impacts. Please circle the currently used (replacement) agent.
Wood preservatives: Chromated copper arsenate (CCA)
Alkaline copper quaternary amine (ACQ)
Anti-fouling agents: Copper
Tributyl tin (TBT)

Answer 2

Alkaline copper quarternary amine (ACQ)

Copper

Question 3

How does the rodenticide warfarin work? What is added to the warfarin formulation to
make it safer for humans?

Answer 3

Warfarin is an anticoagulant that functions by blocking vitamin K function. It
is formulated as rat poison by mixing with ground glass, and an emetic. The
ground glass causes internal bleeding that doesn’t clot because of the
anticoagulant. If a person eats it the emetic will cause them to exclude the
poison by vomiting; rats cannot vomit and are killed. As an additional benefit,
the internal bleeding makes the rats thirsty so they tend to leave buildings to
find water before the die

Question 4

How does 2,4-D function as a herbicide? Why does it function only on dicots?

Answer 4

2,4-D is a synthetic auxin that overwhelms normal hormonal processes causing
unregulated growth. Monocots are able to exclude or excrete 2,4-D from the
cytosol limiting the hormonal interference.

Question 5

DDT is a member of what class of insecticide? How does it kill insects? Why is it
banned in the United States?

Answer 5

Organochlorine insecticide. It forces sodium channels in insect nerve cells to
open interfering with normal nerve function. DDT persists in the environment
and causes bird to produce eggs with weak shells.

Question 6

Organophosphate insecticides as well as many chemical warfare nerve agents inhibit
what enzyme

Answer 6

Acetylcholine esterase

Question 7

Methoprene is an insect juvenile hormone mimic how does it act as an insecticide?

Answer 7

The insect juvenile hormone interferes with normal insect development.

Question 8

How do the microbial proteinaceous endotoxins produced by Bacillus thuringiensis (Bt)
kill certain insect larvae?

Answer 8

Insects ingest protenaceous endotoxin crystals and the alkaline pH of their
digestive tract activates the toxin so that it inserts into the insect’s gut cell
membranes forming a pore that resulting in swelling, cell lysis and eventual
death.

Question 9

How do oils and detergents act as insecticidal agents?

Answer 9

They damage waxy insect cuticles so they dry out and clog insect spiricles
blocking air flow.

Question 10

What does LD50 mean?

Answer 10

Lethal dose 50%

Question 11

What are the six kinds of acute exposure?

Answer 11

Oral, Dermal, Gas Inhalation, Vapor Inhalation, Dust or mist inhalation, Ocular

Question 12

What is the difference between plant biotic and abiotic stress?

Answer 12

Both types of stress cause a negative impact on a plant growth or
development; biotic stress is caused by another organism and abiotic stress is
caused by adverse non-living environmental factors.

Question 13

What are the three legs of the plant disease triangle?

Answer 13

Host susceptibility, Presence of pathogen, Favorable environment

Question 14

How do necrotrophic and biotrophic pathogens differ?

Answer 14

Necrotrophic pathogens feed on dead or dying tissue, biotrophic pathogens
feed on living tissues

Question 15

How do plant viruses spread inside a plant?

Answer 15

Through plasmodesmata and phloem.

Question 16

Give two examples each of preformed and inducible plant biotic defenses.

Answer 16

Preformed defenses include: Structural barriers to disease organisms,
Resistance factors that neutralize virulence, Toxic chemicals or mechanism to
make toxic chemicals quickly (without activating any genes).
Inducible defenses include: Hypersensitive response, Synthesis of new toxic
chemicals.

Question 17

What is the systemic wound response?

Answer 17

Plants respond to mechanical damage or insect chewing by stimulating
jasmonic acid signaling that triggers the synthesis of systemic wound response
proteins and proteinase inhibitors throughout the plant.

Question 18

Plants respond to water deficit by synthesizing large quantities of certain metabolites.
What does this accomplish?

Answer 18

These metabolites are produced as osmotic regulators that help to moderate
water loss by maintaining the difference in water potential between the inside
and outside of the cell.

Question 19

Which term of the water potential expression is affected by the synthesis metabolites?

Answer 19

solute potential (Ψs)

Question 20

Increasing the intracellular salt concentration would have a similar effect on water
potential but plants synthesize organic compounds instead. Why?

Answer 20

Salt disrupts protein structure while organic osmotic regulators do not.

Question 21

What is the difference between anoxic and hypoxic stress?

Answer 21

Under anoxic stress there is no available oxygen and ATP is produced entirely
by glycolysis. Under hypoxic stress oxygen limits ATP production by oxidative
respiration and glycolysis is up-regulated; other metabolic changes are activated
to accommodate oxygen limitation.

Question 22

The primary response to heat stress is to synthesize what class of proteins? What do
these proteins do?

Answer 22

Chaperones are synthesized to help keep proteins correctly folded under
elevated temperatures.

Question 23

What two abiotic stress conditions (other than drought) also lead to water deficit in
plants?

Answer 23

Freezing temperatures and high salinity