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BIOL371 Comparative Biology of Plants and Animals > Plant Homeostasis > Flashcards

Plant Homeostasis Flashcards

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1
Q

Artificial selection began with

A

the selection of plants that had beneficial traits for cultivation and began to recognize effects of nutrient deficiency and optimal growing conditions

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2
Q

Eventually, industrialized agricultural practices began to yield much more product but had high input demands

A

Yield plateaued but demand increased

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3
Q

Green revolution

A

Intensive plant breeding programs

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4
Q

Genetic modification, engineering and biotechnology are

A

The most recent tools for improving crop yield and productivity -> Targeted trait improvement for various requirements and demands

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5
Q

Homeostasis

A

Regulating the internal environment to maintain a relatively stable state, compensating/adjusting for changes in the internal and external environment -> dynamic process

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5
Q

Homeostasis

A

Regulating the internal environment to maintain a relatively stable state, compensating/adjusting for changes in the internal and external environment -> dynamic process

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6
Q

Animal vs. Plant Nutrition

A
  • Photoautotrophic behaviour forms the basis of the food chain (primary producers)
  • Plants concentrate and assimilate nutrients that are present in low concentrations (CO2, minerals, inorganic solutes)
  • Plants are unable to rely on many other sources for their nutrition -> synthesize vitamins and amino acids from primarily inorganic sources
  • Humans have 9 essential amino acids and 13 essential vitamins -> must be obtained from our diet
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7
Q

Uptake by Root Systems

A
  • Extensive root systems are key adaptations to exploit limited mineral nutrients and scarce water
  • Can make up 20-50% (or more) of the total plant mass
  • Act as selective filters to bring in important nutrients and exclude toxins
  • Roots continue to grow as long as the plant lives
  • Incredibly large surface area for rapid and efficient absorption (via root hairs)
  • Uptake of water and minerals is achieved through active and passive transport mechanisms (All of the cell membranes of the root surfaces are packed with ion channels and transport proteins)
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8
Q

Passive Transport

A
  • Requires no metabolic energy
  • Substances moves along/with a concentration or electrochemical gradient
  • Simple diffusion occurs for H2O, O2, and CO2
  • All charged mineral ions require transport proteins (facilitated diffusion) to enter cells(e.g. ion channels and carrier proteins)
  • Plants will attempt to rapidly translocate mineral nutrients farther away from the root surface to maintain the concentration gradient (sometimes achieved through active transport)
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9
Q

Identifying Essential Plant Nutrients

A
  • identify all the elements present in plants by analyzing their ashes = identify all the necessary elements for plant growth
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10
Q

Using hydroponic culture, we can grow plants with liquid nutrient media that has the full suite of the identified elements

A

Remove one nutrient at a time and observe growth and survival

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11
Q

Essential elements

A
  • Necessary for growth/reproduction
  • Cannot be substituted
  • Typically play one or more roles in metabolism that is critical for survival
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12
Q

Visual Indications of Nutrient Deficiencies

A
  • Chlorosis: Yellowing of plant tissues due to lack of chlorophyll -> significantly reduces plant productivity and will negatively impact plant health
  • Localization of the chlorosis is often indicative of the particular deficiency
  • Any change to the leaf surface has the potential to reduce photosynthetic capacity and will impact plant survival
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13
Q

There are 17 essential elements for plants that

A

cannot be obtained directly from the atmosphere

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14
Q

Macronutrients essential in large quantities

A
  • C, H, O from air and water account for 96% of dry mass (polysaccharides, lipids, cytosol)
  • N, P, K, S, Ca, Mg, and Fe are mineral nutrients, available to plants through the soil as dissolved ions in water
  • Components of nucleic acids (N, P) and amino acids (N, S)
  • Some ions aid in the regulation of osmotic potential (K+ ) and signalling (Ca2+)
  • Some macronutrients perform critical roles as enzyme cofactors (Fe and Mg are critical for photosynthesis)
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15
Q

Micronutrients are essential in trace quantities

A
  • Cl, Cu, Ni, B, Mn, Zn, Mo
  • Important activities as catalysts and enzyme cofactors but only required in very minute amounts (e.g. Zn-binding transcription factors) and are often not used up after they have been used
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16
Q

Bacterial-Mediated Nitrogen Cycling

A
  • Abundant element in air (~78% is N2) but is among the most limiting to plants
  • N2 has a triple bond that requires a specific enzyme and a lot of energy to break, plants can only accept NH4+ or NO3-
  • Uptake of NO3- is preferable but plants will convert NO3- back to NH4+ to assimilate N into organic compounds
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17
Q

Nitrogen fixation:

A
  • incorporates atmospheric N2 into ammonia (NH3) and ammonium (NH4+)
  • Nitrogen-fixing bacteria (Diazotrophs): cyanobacteria, Green sulfur bacteria, Rhizobia, and others
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18
Q

Bacterial Ammonification breaks decaying organic N compounds (i.e. amino acids, nucleic acids) into NH4+

A
  • Ammonification (Ammonifying) bacteria: Bacillus, Pseudomonas, Streptomyces, and others
  • Also completed by some fungi
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19
Q

Bacterial Nitrification oxidizes NH4+ to NO2- and NO3-

A

Nitrification (Nitrifying) bacteria: Nitrosomonas, Nitrobacter

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20
Q

Bacterial-Mediated Nitrogen Cycling: Legume Root Nodules

A
  • Legume root nodules form symbiotic associations with nitrogen-fixing bacteria - Rhizobia
  • Atmospheric N2 is converted into NH3 which is directly accepted by the plant host in exchange for photosynthates
  • Bypasses the need for ammonifying and nitrifying bacteria = much more efficient uptake of nitrogen
  • Allows for greater accumulation of nitrogen-rich compounds = High Protein
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21
Q

Nutrient Limitations

A
  • Plant growth and subsequent harvesting of crops remove all the mobile and readily available nutrients from the soil (stored in the harvested plant)
  • Early agriculture typically involved shifting of lands used for plant growth to allow for the soil to replenish its lost nutrients (particularly Nitrogen) but land ownership, increasing populations and food demand required continuous repeated use of the same areas
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22
Q

By the 1930s, worldwide industrial farming had reached its maximum output but

A

put significant strains on the soil, severely depleting nutrients without allowing enough time to replenish
- Coupled with excessive dry conditions in North America (Dirty Thirties), worldwide agricultural production greatly slowed down and caused massive food shortages = Millions of people suffered malnutrition and starvation

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23
Q

A substantial contributor to the lack of production was:

A

Nutrient limitation (Nitrogen, Phosphorous, and Potassium)

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24
Q

How to improve nutrient limitations?

A
  • Exhumed human skeletons to grind the bones into soil supplements (high in N, P, K), continued use of manure and organic fertilizers (compost, various excrement, etc.)
  • Rotating of crops was often used to improve soil Nitrogen content but is a large commitment with inconsistent yields
  • Farmers will switch between crops year by year and will include a legume crop
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25
Q

Nutrient Supplementation

A
  • Post-WWII, the Haber-Bosch process was employed to produce ammonia fertilizer (instead of bombs), Phosphate rock and Potash mining continued -> Big Three Fertilizers: N-P-K
  • Fertilizer application drastically improved plant growth and survival allowing for increased food production
26
Q

Plants tended to grow much taller and had increased fruit + seed set ->

A
  • Created humungous top-heavy plants = Lodging (fallen over and can’t get back up)
27
Q

Green Revolution: Acceptance of Supplementation

A
  • Selective breeding of plants to accept greater nutrient inputs without excessive upwards growth – Semi-dwarf plants
  • Pioneered by Dr. Norman Borlaug of the University of Minnesota
  • His innovations are credited with saving over a billion people from starvation and malnutrition
  • Used pure breeding techniques and developed semi-dwarf, high-yielding, and disease-resistant rice and wheat varieties
  • Relied on this innovation for the last ~80 years, but demand is increasing
28
Q

Researchers bred cereals (wheat, rice, maize etc.) crossing with other cultivated and wild varieties to

A

select for natural resistance traits against pests and disease as well as smaller, more compact plants

29
Q

Additional traits were often selected for to improve

A

the nutritional content of the crop to combat malnutrition in developing countries

30
Q

Led to development of semi-dwarf breeds of both rice and wheat which

A

effectively reduced a hormone involved in stem elongation, allowed the dwarf crops to accept the same or greater fertilizer input to produce more yield but experienced no lodging problems

31
Q

Eutrophication

A

Enrichment of an ecosystem with chemical nutrients such as compounds containing nitrogen and phosphorous

32
Q

Only ~10% of fertilizer added to croplands ends up in plant biomass, the rest is

A

lost as surface or ground water runoffs and end up in bodies of water

33
Q

Increased available nutrients allow for massive algal blooms which eventually

A

sink to the bottom where bacteria feed on them leading to depletion of oxygen -> anoxic conditions, Leads to catastrophic consequences to aquatic animal and plant life

34
Q

Trade-off: tremendous agricultural benefit by

A

applying Nitrogen fertilizers but hurts the ecosystem due to eutrophication

35
Q

Soil

A
  • Contains soil-mineral particles, compounds, ions, decomposing organics, water, air, and microorganisms
  • Soil particles vary in size:sand (2-0.02mm), silt (0.02-0.002mm), and clay particles (<0.002mm)
36
Q

Humus

A

Decomposing organics, holds water and nutrients

37
Q

The relative thickness of each layer and their

A

composition varies greatly

38
Q

The relative amount of soil particles determine

A

soil properties: water availability and

mineral availability

39
Q

Soil solution

A
  • a combination of water and dissolved substances that coat soil particles and partially fill pore spaces
  • available for plant uptake after-gravity drainage
40
Q

Soil Properties – Water Availability

A
  • Water molecules are attracted to clay and organic particles
  • Clay is alkaline and holds a negative charge at typical soil pH (~7-8)
  • Humus greatly increases water availability due to the heterogeneous mixture of charged or hydrophilic organic compounds
  • Sandy soil is looser and holds less water than clay soils
  • Increased drainage results in lower amounts of available soil solution
41
Q

Soil Properties: Mineral Availability

A
  • All available minerals have to be dissolved in water
  • Some passively enter plant roots (facilitated diffusion) while others are selectively absorbed by roots (Active ion-specific transport proteins)
  • Both anions and cations are present in soil solution but are not equally available to plants
42
Q

Anions: (NO3-, SO42-, PO43-)

A
  • Move freely into root hairs

- Weakly bound to soil and remain dissolved in the soil solution-> leach easily by excess water application

43
Q

Cations (Mg2+, Ca2+, K+, Fe2/3+)

A
  • Mineral cations are adsorbed to negatively charged soil particles (i.e. clay)
  • Cation exchange replaces mineral cations with H+ produced by roots as excreted H+ or carbonic acid from CO2 release
44
Q

In addition to root branching and the production of root hairs to increase the root surface area, many plants can

A

can form symbiotic relationships with fungi

45
Q

Mycorrhizae

A
  • Fungal hyphae (branching filamentous network) greatly extends the accessible soil area for increased water absorption and finding of mineral nutrients
  • Fungi are highly capable of mobilizing soil nutrients (organic and inorganic) through external digestion and acid release
46
Q

Both partners benefit from the two-way exchange of nutrients

A
  • The plant provides the fungus with photosynthates

- Fungus increases the supply of soil nutrients (mobilization of P is key)

47
Q

What happens when the soil holds no nutrients?

A
  • Highly acidic soils cause leaching of cationic mineral nutrients and limit water retention by clay particles
  • Water that is applied quickly drains most mobile nutrients away
  • Inability or inefficiency to complete anion exchange is common
  • Plants that survive in these conditions often require nutrient supplements by other means than soil absorption = heterotrophic/predatory plants
48
Q

Heterotrophic/predatory plants

A

Trap and digest insects and microorganisms for sources of mineral nutrients and organic compounds

49
Q

Primary producers

A

Plants incorporate and concentrate CO2, H2O and mineral nutrients to provide the basis of the food chain

50
Q

There are 17 essential nutrients for plants:

A

Macro (10) and Micro (7)

51
Q

Macronutrients are critical building blocks or are

A

are important for metabolic processes and cell maintenance

52
Q

Micronutrients are

A

are typically enzyme cofactors or catalysts that are not incorporated or used up

53
Q

Nitrogen limitation is commonly the largest barrier to plant growth and reproduction, followed by

A

Phosphorus and Potassium

54
Q

Bacterial-mediated Nitrogen cycling incorporates atmospheric N2 into plant-available compounds such as NH4+ or NO3-

A

Symbiotic relationships with aquatic blue-green algae or soil diazotrophs greatly improve Nitrogen availability and uptake

55
Q

Dr. Borlaug: Semi-dwarf plants that accept

A

greater nutrient inputs (i.e. N,P,K fertilizers) saved millions of people from malnutrition and starvation

56
Q

Excessive fertilizer usage leads to

A

eutrophication due to the soil’s inability to retain the applied nutrients = <90% lost to runoff

57
Q

Topsoil with humus is the most

A

important layer for water availability and nutrient uptake

58
Q

Soil pH plays a large role in determining

A

the available nutrients for plants

59
Q

Alkaline soil:

A

clay is negatively charged and holds on to cations, Cation Exchange releases cations for plant uptake; anions often leached

60
Q

Acidic soil:

A

clay is positively charged and holds anions, plants have limited abilities to cope (Anion exchange is rare); cations often leached

61
Q

Root hairs and symbiotic mycorrhizae greatly improve

A

root surface area and improve nutrient mobilization (greatly improves P-uptake by plants)

62
Q

Heterotrophy is an adaptation to dealing with

A

highly acidic soils that lack key nutrients

BIOL371 Comparative Biology of Plants and Animals (10 decks)

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