Exam 2

Question 1

Describe the anatomy of the phloem. How is it different compared to the xylem?

Answer 1

The Phloem is made of two
types of cells:
1. Sieve tube members
2. Companion cells (angiosperms)
*Transports sugars and
secondary metabolites from
sources to sinks.

The xylem is made of dead cells, tracheids and vessel elements(angiosperms)
*transports water

Question 2

Explain why the companion cells and sieve tube elements are alive at maturity.

Answer 2

Movement through the phloem uses active transport. Companion cells actively load sap into sieve tube element. They are conducting cells.

Question 3

Translocation

Answer 3

The transport of photosynthates through the
phloem

Question 4

photosynthate

Answer 4

Organic molecules made by plants,
they include sugars and secondary metabolites

Question 5

secondary metabolites

Answer 5

Organic molecules made after sugars.
These include lipids, proteins, pigments,
signaling molecules, the thousands of other
organic chemicals plants need

Question 6

Explain the pressure flow hypothesis for the movement of sucrose in the phloem.

Answer 6

Sucrose moves from source to sink.
Source->proton pump and symporter->companion cell->plasmodesmata–>phloem->positive pressure(turgor pressure from water)->passive transport->companion cell->passive transport->sink or proton pump (into vacuole) and antiporter->vacuole

Question 7

How is the movement of phloem sap different than the water and minerals of the xylem.

Answer 7

Water flow in the xylem
is caused by negative pressure as it is pulled up from the roots by cohesion-tension.(passive)
Water in the phloem
is under positive pressure from the active loading of the sieve tube by the companion cells (active)

Question 8

Explain the role of primary and secondary active transport for sucrose loading into a vacuole

Answer 8

Primary Active transport
-Pumps

Secondary active transport
*Symporter:Uses energy released from diffusion of
other solutes. Move in same direction
*Antiporter: Uses energy released from diffusion of
other solutes. Move in opposite direction

Question 9

What is the role of osmosis in phloem loading?

Answer 9

Adding solute decreases water potential, through osmosis water moves from xylem to phloem building turgor pressure, then back into xylem.

Question 10

Describe the difference between a symporter and an antiporter. Provide an example of each one

Answer 10

In a symporter (ex: proton-sucrose symporter), the molecules move the same direction In an antiporter (ex: proton-sucrose antiporter) molecules move opposite directions.

Question 11

Explain why diffusion requires energy.

Answer 11

Diffusion does not use an input
of energy from the cell, but it does require kinetic energy that is already present in the system. Movement needs energy.

Question 12

What is a gradient, provide an example.

Answer 12

A concentration gradient occurs when the concentration of particles is higher in one area than another. In passive transport, particles will diffuse down a concentration gradient, from areas of higher concentration to areas of lower concentration, until they are evenly spaced. Ex: Sucrose or proton gradient

Question 13

Explain why plants do not need essential fatty acids, amino acids, or vitamins.

Answer 13

Plants can make all their organic molecules using soil nutrients, water and carbon dioxide,
They don’t have essential amino acids, fatty acids, or vitamins.
They make everything!
–Nucleic acids
–Amino acids
–Carbohydrates
–Lipids
–Pigments
–cofactors

Question 14

I said in class, “plants mostly grow out of the air”, explain the reasoning behind this statement.

Answer 14

Plants require nutrients from the soil in addition to water and carbon dioxide.
They use their roots to extract nutrients from the soil.Most of the mass came from water and carbon dioxide, which makes sense considering most organic molecules
are made of carbon, hydrogen, and oxygen with a little
nitrogen.

Question 15

Which 3 elements accounts for 96% of a plant’s mass.

Answer 15

Carbon dioxide and water supply:
Hydrogen (H)
Carbon (C)
Oxygen (O)
These three elements account for 96%
the mass of a plant.

Question 16

Name the primary macronutrients. Explain their uses in a plant.

Answer 16

Nitrogen (N) –
*Needed to make proteins and chlorophyll

Phosphorus (P)
*Important component of nucleic acids,
phospholipids, and ATP

Potassium (K+)
*Used for many processes in the plants
including
–Water balance
–Needed to open and close stomata
–Helps with various metabolic process
*Taken up by the roots

Question 17

Explain the difference between elemental and molecular ions.

Answer 17

Elemental ions
K+ and Cl-
Molecular ions
HPO42- and NO3-

Question 18

Name two molecular anions important for plants.

Answer 18

Molecular ions
HPO42- and NO3-

Question 19

What’s the difference between regolith and soil?

Answer 19

Soil is a zone of plant growth and is a thin layer of mineral matter that normally contains organic material and is capable of supporting living plants. Regolith is inorganic and lies like a blanket over unfragmented rock.

Question 20

Explain the importance of soil pH to nutrient availability

Answer 20

A low pH results in low nutrient availability. Soil pH effects what ions are available. in acidic soil cation exchange takes place, making these cations available.

Question 21

Why has carnivory in plants repeatedly evolved in wet, acidic soils.

Answer 21

Low nutrient availability
highly acidic wet soils where the nutrients are either not available to the plants or have been leached away.

Question 22

What nutrients are most easily lost with over watering.

Answer 22

The three most commonly leached nutrients are nitrogen (N), phosphorus (P) and potassium (K). Of these nutrients, nitrogen is the most likely to be leached from the soil.Easily washed away (leaching). Too much watering can cause the loss of anions
Cl-
HPO42-
NO3-

Question 23

Describe how plants use cation exchange to obtain nutrients. Be specific, don’t over-generalize.

Answer 23

A low pH causes the cations to be released from the soil, which they are usually bound to. The plant can then absorb these nutrients through root hairs.Cations typically are bound to the soil, but when cation exchange occurs the plant can absorb cations such as magnesium and calcium.

Question 24

Explain how soil texture affects nutrient and water availability.

Answer 24

Importance of soil texture
*Root penetration
*Water availability-some soils can’t hold water. (sand) This leads to low nutrient availability as most nutrients are leached out. There is little capacity for cation exchange and anions leach out.
*Oxygen availability

Question 25

23. If a plant is growing in sandy soils,
    a. What are the advantages?
    b. What are the challenges?

Answer 25

A. There is great oxygen availability and root penetration because the soil doesn’t pack tight and there are many air containing spaces.
B. There is low water availibilty as it all drains through. There is low nutrient availability as anions are washed away, and there is little cation exchange

Question 26

Explain the role of active transport in nutrient uptake.

Answer 26

Plants use active transport
-To move ions and electrolytes into their roots.
Plants create electrochemical gradients by pumping protons outside the cell.
This does two things:
1. Creates Membrane Potential as electrochemical gradients that store energy for secondary active transport.
2. Cation Exchange, by lowering the pH outside the cell, cations are knocked off clay particles

Positively charged cations
Are attracted to the more negatively charged
interior of the cell.
Cations, including potassium (K+)
will move against their chemical gradients
through channel proteins if the electrical gradient
is stronger.

Anions are transported into cells by
secondary active transport using a
symporter.

Question 27

Why is the vascular bundle in a root surrounded by the endoderm and Casparian strip?

Answer 27

The plant can filter what is entering the vascular bundle. Ex: Plants can passively exclude
sodium

Question 28

Explain how plants can exclude excess sodium in soils.

Answer 28

Plants can passively exclude
sodium
Na+ ions cannot easily cross cellular
membranes or the Casparian strip,
preventing them from entering cells or the
xylem

Question 29

Describe the differences between ectomycorrhizal and endomycorrhizal fungi.

Answer 29

Ectomycorrhizae
* hyphae do not penetrate
cortical cells
* grow between outer
root cortical cells
* forms fungal mantle
or sheath known as a
Hartig net
* Primarily woody plants,
trees

Endomycorrhizae
* Vesicular/Arbuscular Mycorrhizae
* hyphae penetrate root cortical cells
* vesicles (storage)
* arbuscles (exchange)
* They go through the cell wall
and attach to the membrane
but don’t enter the cytoplasm
* Primarily herbs and grasses, but
also some trees

Question 30

Name three types of symbiotic relationships, provide an example of each

Answer 30

Mutualistic – both species benefit from the
interaction (aphids and ants)
Commensalism – one species benefits while the
other doesn’t benefit (Orchid on tree branch)
Parasitic – one species benefits at the expense of
the other (mistletoe and a host tree)

Question 31

Explain why a butterfly pollinating different species of flowers may not be considered a symbiotic relationship whereas a mycorrhizal fungus would be.

Answer 31

The butterfly is not benefiting a specific species or organism whereas a fungi is benefiting that specific plant as an organism. One is actually a relationship, the other is simply an encounter.

Question 32

Symbiotic relationships can be dynamic. Provide an example of how a mutualistic relationship can become parasitic.

Answer 32

Only beneficial when benefit exceeds cost. The relationship between plants and their fungus can switch between mutualism to parasitism based on nutrient availability
When nutrients are poor, it’s beneficial to both organisms (+/+). If nutrients become plentiful
Then the fungus no longer provides benefits to the plant, but continues to take resources from the plant.
The relationship can become +/- or a parasitic relationship

Question 33

Which type mycorrhizal fungi forms arbuscles on the cell membranes of roots cells.

Answer 33

Endomycorrhiza
(Glomus spp)

Question 34

What’s the evolutionary importance of plant/fungi interactions?

Answer 34

Fungi helped plants colonize land. They increased surface area of nutrient uptake.

Question 35

Prior to the Haber-Bosch process, where did most nitrogen available to ecosystems come from?

Answer 35

Symbiotic Rhizobacteria
Found in the roots of pea plants
Makes nitrogen available to the rest of the ecosystem

Question 36

Why is the nitrogen in the atmosphere not available to plants directly.

Answer 36

It takes a lot of energy to break the triple bond in N2 gas

Question 37

What is the purpose of leghemoglobin?

Answer 37

Leghemoglobin
Is made by plants with nitrogen-fixing bacteria.
It is like hemoglobin and carries oxygen. Inside the root
The leghemoglobin keeps oxygen levels balanced so
that nitrogen fixing can be maximized, but also not
too low that aerobic respiration cannot happen.

*Leghemoglobin regulates
[O2] inside the root nodule

Question 38

Which type of plant is known for symbiotic relationships with Rhizobacter?

Answer 38

Symbiotic Rhizobacteria
Found in the roots of pea plants (legumes)
Makes nitrogen available to the rest of the ecosystem

Question 39

What’s the significance of the Haber-Bosch process?

Answer 39

It converts molecular nitrogen (N2) to ammonia (NH3)
The process uses about 1-2% of the worlds energy
supply and makes about 230 million tons of ammonia
per year. Most of it gets converted into nitrogen
fertilizer.
Greatly improved crop growth.
More than doubled the input of nitrogen to life.
It is one of the reasons the human population has
grown

Question 40

Describe the consequences of the Haber-Bosch process.

Answer 40

A large dead zone forms in the Gulf of Mexico caused by nutrient-laden water mostly from the country’s farmlands.
About half the nitrogen in the fertilizer runs off into the
streams, which eventually drain into the Gulf of Mexico from the Mississippi River.
The excess nutrients causes the exponential growth of
algae, called an algae bloom. Algae blooms lead to very low oxygen in the water which kills fish and other animals.

Question 41

Provide an example of a symbiotic relationship plants use for defense.

Answer 41

Attracting parasitoids
When being eaten by leaf mining
caterpillars, some plants will release
hormones to attract female wasp

These parasitoid wasp lay their eggs on
the caterpillar

Question 42

Explain the role of phototropins and auxin in plants bending toward blue light

Answer 42

Sensory cells use phototropin(proteins) to detect blue light. Once it detects blue light, It causes the sensory cell to make the plant hormone Auxin.This hormone is found throughout all plantsAlthough, it is found in different concentrations. Auxin binds to receptors in the shoots turning up the activity of proton pumps. This creates an electrochemical gradient and K+ flow into the cell. By ramping up the proton pumps, they begin to pump protons out of the plant cell and into the cell wall. Lowering the pH activates proteins called expansins. They “unzip” hydrogen bonds holding the microfibrils of the cellulose together. This relaxes the cell wall allowing the cell to swell due to turgor pressor caused by water moving into the cell through osmosis.

Question 43

Name three reasons why the stomata will open and close.

Answer 43

1. Response to blue light
2. ABA -drought stress
3. CO2 Concentrations?

Question 44

How do the stomata open and close?

Answer 44

Open:
When blue light strikes Phototropins inside a
guard cells, they cause proton pumps to
increase in activity.
By pumping protons out of the cell,
it creates an electrochemical gradient as the inside of
the guard cell becomes negatively charged.
This pulls potassium in through ion channels. Because
there is also a chemical gradient, chloride ions also enter the cell. This increase in electrolytes in the cell lowers its water potential causing water to enter the cell. The excess water increases the turgor pressure, and the cells change shape, opening the Stomata.

Close:
When ABA binds to a receptor on the guard cell, it causes
several changes to the cell
FirstIt opens anion channels allowing the Cl- to exit the cell changing the membrane potential. This change then opens potassium channels allowing K+ to exit the cell. The loss of electrolytes raises the water potential inside the guard cell.ABA, likely through the action of calcium, inhibits the proton
pumps, preventing them from repolarizing the cell.
As water potential in the guard cell increases, water flows out of the cell causing a loss of turgor pressure and the cell shrinks and closes.

Question 45

Name two hormones that affect the opening and closing of stomata.

Answer 45

ABA and phytokinenes (jasmonic acid, brassinosteroids, cytokinins, or ethylene)

Question 46

Which conformation of phytochrome causes lettuce seeds to germinate.

Answer 46

P fr conformation

Question 47

Why would a lettuce seed not want to germinate if it was getting far-red light (~735nm)?

Answer 47

The area is too shady to survive and carry out an effective rate of photosynthesis.

Question 48

The length of time a plant is exposed to certain wavelengths of light can inhibit or promote flowering. If you exposed a short-day plant to 15 hours of dark, but flashed it for a few minutes with Far-red light, would it germinate? What is the far-red light mimicking?

Answer 48

Yes, it will germinate. The far red light is mimicking a short day? Changing of the seasons.

Question 49

Auxin has many roles in a plant. How does it act differently in a branch growing toward the light versus a root growing downward?

Answer 49

In a branch the auxin promotes cell elongation.
In roots, auxin tends to inhibit cell elongation, auxin accumulates on the lower side in roots oriented perpendicularly to gravity, causing these cells to elongate less and the root to bend toward gravity.

Question 50

If you wanted more rose flowers on your rose bush, why would you remove the apical meristem (include auxin in your answer)?

Answer 50

Apical dominance maintains growth in main stem. Lateral buds are dormant until main stem is removed. Auxin transport is polar Moves via carrier proteins
Auxin promotes cell division

Question 51

Apical dominance

Answer 51

Apical dominance
Maintains growth in main stem
Lateral buds remain dormant
When the apical meristem is
removed, the lateral buds will begin
to grow new branches.

Question 52

Thigmotropism

Answer 52

Thigmotropism
(touch-bending) the turning or bending of a plant or other organism in response to a touch stimulus.

Question 53

Senescence

Answer 53

Senescence
Regulated process of aging and eventual death
Growing old

Question 54

Know the different types of ecological interactions.

Answer 54

1. Mutualism (+/+)
2. Commensalism (+/0)
3. Competition (-/-)
4. Predation

Question 55

Explain why plants need to be able to defend themselves. What are they defending themselves against (pathogens and herbivores)?

Answer 55

Plants are attacked by pathogens and
herbivores, some we call pest
* About half of the one million species of
insects are herbivores

Question 56

How could you distinguish between a pathogen and an herbivore?

Answer 56

Pathogens cause physiological damage
* Viruses
* Bacteria
* Parasitic fungi
Herbivores cause physical damage
* Pests
* mammals

Question 57

What can we learn about plant defenses by studying invasive species like the chestnut blight and the woolly adelgid?

Answer 57

What defense isn’t present. Theory of co evolution

Question 58

Describe the differences between constitutive defenses and inducible defenses. Provide examples of each.

Answer 58

Constitutive
defenses (thorns)–
preexisting
defenses

Inducible
defenses (signals)– plants
respond to an
attack

Question 59

How does the HR response work?

Answer 59

*Prevents spread of pathogen
*Stomatal closure
* Production of toxins targeted to the pathogen(immune)
* Reinforcement of cell walls
* Rapid apoptosis of damaged and surrounding cells

Question 60

Explain how apoptosis is important against pathogens.

Answer 60

The dies before the pathogens can copy their DNA and spread, rendering the pathogen that has infected the cell useless.

Question 61

Explain why the systemic acquired response is important.

Answer 61

Results in expression of pathogenesis-related
genes (PR)
* Inducible defense against pathogens and keep
them from spreading elsewhere in the plant

Question 62

Explain how SAR works.

Answer 62

In addition to triggering HR, detection of a pathogen leads to the release of a hormone that triggers SAR. This signal acts locally and globally, resulting in expression of pathogenisis related genes. These genes produce proteins that prevent infection spread.

Question 63

Explain the role of systemin and Jasmonic acid in plant responses to herbivores.

Answer 63

Systemin
* Peptide Hormone for wound response
* Part of a signal transduction pathway
* Released from damaged cells.
* Travels via the phloem to target cells
* Causes the target cells to make Jasmonic Acid

Jasmonic Acid (JA)
*deters herbivores in several ways

Question 64

How and why do trees “talk” to each other.

Answer 64

Plants release volatile compounds into
the air
Different species can detect these volatile
chemicals. When a signal is released surrounding plants ramp up defense mechanisms.

Question 65

What is one reason chili peppers evolved capsaicin.

Answer 65

It’s a deterrent against mammals who chew the seeds and would
damage them. However, birds can eat the chilis and do not feel
the “heat”. Because birds don’t chew their food, the seeds pass
through their gut unharmed and are spread by the birds

Question 66

What is one possible theory explaining the origins of sexual reproduction that I presented in class.

Answer 66

If you fused two mitochondria they would only compete, so sexes formed. This is why female have the organs and sperm are essentially just DNA donor. Furthermore, if you have two copies of your genome (one from each parent) there is a back up in case something happens to one. Mitochondira can not do aerobic respiration because free radicals can harm.

Question 67

Describe alternation of generations in angiosperms. Be sure to include: where the male and female gametophytes are located, where meiosis and mitosis takes place, what is the sporophyte, where does fertilization take place.

Answer 67

1. Meiosis occurs in sporophytes and results in the production of haploid spores. Meiosis and spore production occur inside strucutres called sporangia.
2. Spores undergo mitosis and develop into multicelllular haploid gametophytes. Male gametophytes are pollen grains, and female are embryo sacs.
3. Pollination (transfer of pollen grains from an anther to stigma) occurs and gamtophytes produce sperm and eggs by mitosis.
4. Fertilization occurs when two gametes fuse to form a diploid zygote.
   5.The zygote undergoes mitosis and grows into a multicellular, diploid embryo (young sporphyte).

Question 68

Describe each of their primary functions in a sentence. : the antipodal cells, polar nuclei, egg, synergids, and micropyle.

Answer 68

Antipodals – important for nutrition
Polar nuclei – double fertilization, to become the endosperm which supports cell
Synergids – stops pollen tube growth and helps release sperm cells
Egg cell: The female gamete.
Microphyle: Opening for sperm to enter. When soaked, seeds absorb water mainly through the micropyle. Micropyle also helps in respiration and in the exchange of gases.

Question 69

Explain what is meant by double fertilization and explain why its important

Answer 69

Double fertilization means that the
pollen has two sperm, and each sperm
fertilizes a different cell
This is exactly what happens
The sperm enter the ovule through
the micropyle
* One sperm fertilizes the egg
* The second sperm fertilizes the
polar nuclei

Question 70

Which parts of the carpel develops into the seed and the fruit?

Answer 70

After fertilization, as the ovule develops into the seed, the carpel tissues develop into the fruit layers which protect and help disperse the seed.

Question 71

Where does the endosperm come from?

Answer 71

Fertilization of the polar nuclei

Question 72

Provide examples of how plants prevent self-fertilization

Answer 72

Some species have separate male and female plants
staminate and carpellate flowers on separate plants

Others have stamens and carpels that mature at different
times or are arranged to prevent selfing

The most common mechanism to prevent selfing.
Based on a plant’s ability to reject its own pollen

Question 73

Outline the main steps of embryogenesis

Answer 73

1. Zygote divides into two daughter cells.
2. The two daughter cells divide into a globular stage embryo and a basal cell plus suspensor.
3. Cells of the heart stage embryo differentiate into progenitors of the three embryonic tissues.
4. The precursors of the root and shoot systems forms the embryonic tissues . The long axis of the mature embryo becomes apparent.

Question 74

Provide two examples of how GMOs can help solve problems.

Answer 74

The use of GMO crops, Improve yields, Better for the environment, Improved nutrition, Protection from diseases, Less waste.