Agri-31 3rd Exam Reviewer PDF

**Part B: Endogenous Rhythms/Plant Movements\ ** **The Biological Clock** Many aspects of plant behavior exhibit periodic oscillations that appear to be controlled by an internal time measuring system: **the endogenous biological clock** Manifestations - Diurnal rise and fall of leaves (sleep...

**Part B: Endogenous Rhythms/Plant Movements\ ** **The Biological Clock** Many aspects of plant behavior exhibit periodic oscillations that appear to be controlled by an internal time measuring system: **the endogenous biological clock** Manifestations - Diurnal rise and fall of leaves (sleep movements) - Photosynthesis is diurnal **Criteria to distinguish simple periodic phenomena and rhythm driven by an endogenous clock** 1. **Persists in the absence of external clues** 2. **Can be reset by external signals such as light and temperature** 3. **No lasting effect of temperature on the timing of the clock-driven rhythm** **Classification of Biological Rhythms** 1. **Circadian Rhythm (=24 hours, example is bean movement (hyponasty, epinasty), examples: Fertility Tree of UPLB** 2. **Lunar rhythm (28 days, between one full moon to the next)** 3. **Annual rhythm (Flowering of fire trees, cherry blossoms, and Kapok every summer)** 4. **Ultradian rhythm (=\ - **Toxic in large concentrations** - **Affect mostly dicots but not monocots** - **Monocots seem to be able to rapidly degrade the synthetic auxins** - **Synthetic auxin herbicides include 2-4-D and 2-4-5-T (Agent orange of the Vietnam era contains synthetic auxin)** **-Used as defoilants** **-Used as weed killers**  **Cytokinin** - **Phenyl urea derivatives of adenine, one of the molecules in DNA** - **Found in actively dividing tissues of seeds, fruits, leaves, and root tips. And wound tissue sites** - **Transported through xylem to the rest of the plant** - **Promotes cytokinesis** - **Work in conjuction with auxins, which promote elongation and cell expansion** - **Promote axillary/lateral bud growth by over-riding the apparent inhibiting effect of auxin** **Ratio of Cytokinins to Auxin -- controls what tissues differentiate in the tissue culture** **Discovery of Gibberellic Acid** - **Many seeds contain a variety of different gibberellins over 100 different gibberellins (organic synthesized from mevalonic acid)** - **Gibberellins are produced in roots and younger leaves, with seeds having the highest concentration** - **Most effects of gibberellins are shown only in concert with auxins** **Effects of Gibberellins on Elongation** - **Reversal of genetic dwarfism GA** - **Bolting of biennials, to produce flowers during the first growing season** **Gibberellins** - **Like auxins, promotes parthenocarpy** - **Commercial applications in grape industry, where grapes grow larger, and with longer internodes** **Abscisic Acid (ABA)** - **Inhibits growth activities in times of environmental stress rather than by promoting growth** - **Often serves as an antagonist to other growth promoting hormones in plants** - **ABA promotes seed dormancy** - **Low levels of ABA in maturing seeds promote premature germination** - **ABA is also referred to as the STRESS ACTIVITY HORMONE** - **Promotes stomata closure during water deficit conditions by activating K+ ion transport out guard cells** **Ethylene** - **Synthesized from the amino acid methionine** - **Sole plant growth regulator known that is a GAS** - **Promotes flowering** - **Promotes leaf senescense\ **   **Part C: Environmental Factors Affecting Crop Production** **\ Phenotype = Genotype (G) + Environment (E) + (G \* E)** Where: G -- sets the limits for the phenotype E -- modifies the expression of the phenotype Yield = genetic factors + environmental factors + (G \* E) Where: G -- genotype or variety E -- abiotic and biotic stresses **Environmental Factors** **Abiotic** - Climatic (Climate, weather) - Edaphic/Soil factors - Climate stresses (drought, salinity, acidity, lahar, La Nina) - El Nino, greenhouse effect, global warming **Biotic** - Beneficial organisms (pollinators, decomposers, natural enemies) - Pests (arthropods, pathogens, weeds, vertebrate pests) - Allelopathy (biological phenomenon where an organism produces one or more biochemicals that influence the germination of other organisms) **Weather** -- the atmospheric conditions in any area at any time, with regards to sun, cloud, temperature, wind, and rain (deviation from pattern). \- is the set of all extant phenomena in a given atmosphere at a given time (over short periods in hours or days). **Climate** -- the long-term weather pattern of an area, including temp., precipitation, wind or weather averaged over long period of time (seasonal pattern). \- refers to the average atmospheric conditions over longer periods of time. "Climate is what you expect, while weather is what you get" **Environment and its components** A diagram of a weather forecast Description automatically generated **Climatic Factors** 1. **Solar radiation -- most important in agriculture.** 2. **Temperature** 3. **Wind movement** 4. **Precipitation** 5. **Relative Humidity** 6. **Mist and Fog** 1. **Solar Radiation** - Rate at which a surface absorbs radiation (Watt/m\^2). - Intensity (foot candles or lux) - Duration or daylength (hours/day) - Wavelength (Angstroms or nanometers, or by color)  1\) Photoenergetic effect -- Direct effect on Photosynthesis 2\) Photocybernetic effect -- effect on development of plants. - Total Dry Matter correlated to intercepted radiation - Light received above light compensation point, affects growth and development - Not all wavelengths are equally effective: \***Photosynthesis** -- red and blue \***Photoperiodism** -- far red and red **Solar constant** = 2.0 cal/cm\^2/min (15% fluctuation within the year). Is the amount of solar radiation that reaches the outer limits of the earth's atmosphere. A diagram of a solar system Description automatically generated **PAR (photosynthetically active radiation)** -- used by plants to fix CO2 during photosynthesis. Classification based on light intensity requirements: **Heliophytes** - sun-loving **Sciophytes** - shade loving **Albedo (reflected radiation/total incident light)** - Reflects how fast and what degree surface is heated. 50-60% in polar regions 20-30% in tropical equatorial regions 80% reaches ground in the absence of cloud cover 2. **Daylength** -- varies with latitude, different between day and night, increases as latitude from equator increases. 1. Short day plants 2. Long day plants 3. Day neutral 3. **Temperature** -- important in every chemical, physiological and biochemical processes in plants - Solar radiation - Surrounding land masses/bodies of water - Altitude -- 0.6 decrease in temp per 100m rise in elevation **Classification of crops based on temperature requirement** - **Cool Season** -- cole crops - **Warm Season** -- rice, banana - **Tropical** -- coconut - **Sub-tropical** -- citrus - Maturity determination - Predictive tool on suitability of crops to a particular environment - Risk prediction associated with crops in a specific area - Determination sowing date and crop growth and productivity **Effects of Temperature** - **High temperature** -Wilting -Leaf burn -Leaf folding -Abscission - **Slow growth rate** - **Growth ceases with tissue desiccation** **Temperature and Photosynthesis** - Protein denaturation - Loss of membrane integrity - Photoinhibition - Ion imbalance Photosynthesis declines above 35 degrees Celsius in most species. 4. **Relative Humidity** -- directly affects plant growth, and disease and pest incidence **Postharvest handling** **Perishables** -- wilting (transpiration loss) **Durables** -- difficulty in drying, susceptibility to MOLDS and AFLATOXIN 5. **Wind** **Effects on plant processes** **--** lodging, grain shattering, transpiration, plant form, sterility due to loss of pollens, reduced co2 levels, disease spore dispersal 6. **Precipitation/Rainfall** -- water in some form falling out of the air and settling on the surface of the earth, is a condensation in the atmosphere - Reactant in many biological processes - Medium of transport of nutrients and other substances - Temperature regulation **Classification based on need for moisture** **Xerophytes** -- desert plants **Hydrophytes** -- aquatic plants **Mesophytes** -- land plants **Air circulation** -- affects seasonal distribution of precipitation **Topography** -- affects amount and distribution of rainfall **Moisture** -- influences the phytogeographic distribution of plants **Rain formation requirements:** - High RH - Sufficient low temp - Condensation nuclei - Sufficiently low pressure  A diagram of the earth\'s energy budget Description automatically generated 7. **Infrared Radiation** -- the electromagnetic radiation with wavelengths longer than visible light and shorter than microwaves. It is felt as heat 8. **Greenhouse Gases** -- are efficient in absorbing IR light - Co2- Carbon Dioxide - CH4 -- Methane - N20 -- Nitrous Oxide - Chloroflourocarbons (CFC) Levels of gh gases have increases by about 25% since large-scale industrialization 150 years ago In the past 20 years, about ¾ of anthropogenic (human-caused) emissions came from burning of fossil fuels 9. **Climate Change** -- rising concentrations of greenhouse gases produce an increase in the average surface temperature of the earth over time 10. **Climate Classification**  **SOIL PROPERTIES** **(Physical, Chemical, Biological)** **Physical Properties** 1. **Texture** -- size and relative proportions 2. **Structure** -- arrangement of soil particles 3. **Soil Depth** -- top and sub-soil 4. **Topography** -- physical configuration of the soil surface (drainage, run-off, erosion) A triangular structure with text Description automatically generated with medium confidence **Soil Structure** -- grouping of particles of sand, silt, and clay into larger aggregates of various sizes and shapes. Movement of air, water and plant roots through a soil is affected by soil structure **Stable Aggregates** -- result in a network of soil pores that allow rapid exchange of air and water with plant roots. Plant growth depends on rapid rates of exchange  **Soil Depth** - thickness of soil materials **Soil's permeability** -- measure of the ability of air and water to move through it **Infiltration Rate** -- velocity at which water enters the soil **Factors that affect the infiltration Rate** 1. Permeability of the surface soil 2. Moisture content of the soil and surface conditions such as roughness slope 3. Plant cover A diagram of a rate Description automatically generated with medium confidence **Topography** -- "lay of the land" or physical configuration of soil surface, impacts whether a field can be irrigated **Relief** -- component of topography that refers to the difference in height between the hills and depressions in the field **Slope** -- incline or gradient of a surface (%) =rise/run (5:100) Ex; the land rises/falls 5 feet per 100 feet **Chemical Properties**