Biol 240W Exam 2 Practice Questions

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Why are positively charged nutrients not bioavailable in the soil solution surrounding plant roots? How do plants increase the bioavailability of these cations?
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Why are positively charged nutrients not bioavailable in the soil solution surrounding plant roots? How do plants increase the bioavailability of these cations?
They are binding to the soil particles which are negatively charged. When bound, they are not available to the plant. Increase bioavailability through cation exchange process by manipulating pH around roots to make cations dissolve in solution and then pick these up.
- plant can only get nutrients if dissolved in soil; nutrients not naturally available
- Go through cation exchange process:
- CO2 is waste product, H2CO3 -> HCO3
- Plants artificially manipulate environment to make cations available
Cation exchange depends on:
- soil pH
- surface area of particles

Simplified:
1)Cell respiration in roots releases CO2 → H2CO3
2)Low pH increases bioavailability of cations
3)Cations dissolve in soil solution → uptake into roots
Image: Why are positively charged nutrients not bioavailable in the soil solution surrounding plant roots? How do plants increase the bioavailability of these cations?
Describe the agricultural importance of soil health. In your answer, provide examples of the consequences of irresponsible soil management, as well as an example of how sustainable agriculture can preserve/maintain soil health.
Trying to maintain health of topsoil so we can grow crops in the same location. The problem is the nitrogen and phosphorus is not replaced quickly enough. Some consequences are:
- soil salinization
- erosion
- loss of topsoil
- monoculture
Some examples to help sustain the soil are:
- drip irrigation: conserves water and reduces salinization
- low till/no till agriculture: significantly reduces soil erosion and fertilizer use
- contour cultivation: reduces runoff and topsoil erosion
- organic fertilizer: Intensive agriculture leads to soil degradation; fertilizers replenish essential minerals
Describe the primary steps of the Nitrogen Cycle. In your answer, identify which form of nitrogen is preferred by plants, and briefly explain the mutualistic relationship that facilitates nitrogen acquisition in plants.
The vast majority of nitrogen is in the form of N2 (atmospheric nitrogen gas) which is not bioavailable. They can use NH3 and NO3- (nitrate), but NO3- is the preferred form (most bioavailable). The process involves extra help coming in form of symbiotic relationship with bacteria called rhizobacteria which perform nitrogen fixation (converting atmospheric nitrogen as a gas into ammonia). This creates substrate to be put in nitrification cycle (also performed by bacteria) and make NO3 (desired form).
- NH3 and NH4+ go back and forth, act as additional source of ammonium depending on environment
- mutualistic relationship: plants get nitrogen, bacteria get sugars from plant and home by performing nitrogen fixation
- another source of ammonia is through decomposition; bacteria on dead organism break down organic molecules of organism releasing inorganic molecules in form of ammonium (NH4+)
Image: Describe the primary steps of the Nitrogen Cycle. In your answer, identify which form of nitrogen is preferred by plants, and briefly explain the mutualistic relationship that facilitates nitrogen acquisition in plants.
Describe the similarities and differences between the development of male and female gametophytes in angiosperms.
Female Gametophytes = embryo sacs - contained within ovules in carpel
1)Megasporocyte (mother cell) divides via meiosis four haploid megaspores
2)Only one megaspore survives = "egg"
3)Egg divides via mitosis polar nuclei and other accessory cells
Egg cell + Polar nuclei + Accessory cells = Female Gametophyte

Angiosperm Life Cycle: Development of Gametophytes
- Male Gametophytes = pollen grains - contained within anthers
1)Microsporocyte (mother cell) divides via meiosis -> four haploid microspores
2)Microspores divide via mitosis -> generative cell and tube cell
Generative cell + Tube cell = Male Gametophyte
Image: Describe the similarities and differences between the development of male and female gametophytes in angiosperms.
Describe the development of a female gametophyte and explain the process of double fertilization.
Female Gametophytes = embryo sacs - contained within ovules in carpel
1)Megasporocyte (mother cell) divides via meiosis four haploid megaspores
2)Only one megaspore survives = "egg"
3)Egg divides via mitosis polar nuclei and other accessory cells
Egg cell + Polar nuclei + Accessory cells = Female Gametophyte

Double Fertilization
-cell division of generative cell
- tube cell germinates which allows pollen tube to extend down at bottom, double fertilization occurs (two events!) :
Sperm #1 fertilizes the egg → Zygote (2n)
Sperm #2 fertilizes the polar nuclei → Endosperm (3n)
- Endosperm serves as food-storing tissue
Plants exhibit both sexual and asexual reproduction: explain TWO advantages and disadvantages of these reproductive strategies.
Advantages of asexual reproduction:
- Genetically identical clones
- Happens quickly
- Fragmentation
- Detached roots/shoots develop into complete organism
- Apomixis
- Ovules develop into seeds without pollination or fertilization
- Good for ease of development
- Perform well in stable environment

Advantages of sexual reproduction:
- Better in unstable environments
- Better dispersal potential
- Less threat of local extinction
Explain three methods/techniques that humans use to manipulate desirable traits in angiosperms, providing an example of each.
Vegetative Propagation: Humans produce plant clones using shoot/root cuttings
- Ex: grafting the shoot of a grape variety that produces more fruit onto the base of a plant that is drought-resistant

Genetic engineering: Speeds up the process of selecting desirable traits
- Transgenic organisms
- Contain DNA from other species
- Ex: GMOs
- Plant or animal whose genetic makeup has been modified in a laboratory

Selective breeding
- Artificial selection
- Develop new organisms with desirable characteristics
Ex: Dogs
What are the pros and cons associated with the development and use of transgenic organisms? Present your pros and cons based on at least one specific GMO example.
Corn and Bacillus thuringiensis (BT corn)
Advantages:
- Allows the corn to make their own insecticide
- Decreases insecticide/fertilizer use
Disadvantages
- Allergenic potential
- Evolution of resistant pest populations
Describe the process by which potatoes undergo de-etiolation (greening).
Etiolation in the absence of light: the potato continues to grow stems/branches, but without leaves
De-etiolation with light exposure: the potato grows light structures
Signal transduction pathways
- Link signal reception to cellular response
Steps:
- Reception:
->Signals are detected by receptor proteins
->During de-etiolation, phytochrome receptors (in the cytoplasm) are activated by photons
-Transduction:
->Signal is transmitted to the effector (transcription factors)
->Activation of phytochromes
->>Leads to production of 2nd messengers (Ca2+, cGMP)
-->>>Calcium channels open and Ca2+ enters the cell and activated protein kinase
-->>>cGMP activates protein kinase
- Response
->Transcription factors trigger gene expression and enzyme activation
->>Newly produced or activated enzymes facilitate pigment synthesis
Explain the process of phototropism. What hormone initiates this response and what are the mechanisms involved?
Auxin initiates phototropism
-Auxin is released from shoot apex; stimulates cell elongation on shaded side of stem (More auxin on shady side)
Mechanism
- Acid-growth hypothesis (explains how auxin elongates cells)
1. H+ pumped into cell wall and pH decreases (more acidic)
- Creates gradient
Affects water potential and membrane potential
2. Lower pH activates existing enzymes that breaks down cellulose in cell wall
3. Membrane potential shifts
- Opens voltage-gated ion channels
- Lowers water potential
4. Water uptake causes cells to grow/elongate
Explain the steps of the "Triple Response" in a germinating shoot. What hormone is responsible for initiating this response and why is it adaptive?Ethylene is responsible for initiating the "Triple Response" Triple response: Adaptive growth maneuver to overcome mechanical stress Steps: 1. Stem elongation slows down 2. Stem thickens (not secondary growth) 3. Stem grows horizontally