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Chapter 14A - Plant Physiology
Transcript of Chapter 14A - Plant Physiology
The length of darkness controls flowering; must be uninterrupted (
critical dark period
Will flower over a range in the number of day-light hours; will not flower if days are shorter/longer than critical period.
Usually flower sometime in late summer, fall, winter, or spring.
Flowers when number of daylight hours < its critical period.
The response of flowering plants to daily daylight-darkness conditions
Usually flower in summer, but also will flower if lighted continually.
Flowers when number of daylight hours > than its critical period.
Chapter 14A -Plant Physiology
Stems usually have negative gravitropism, while roots have a positive gravitropism.
Increase rate of seed germination and bud development.
If applied to tip of dwarf plant, it will grow taller.
Hormones = body chemical produced to causes physiological changes.
14.3 - Plant Hormones
A responsive movement not dependent on direction of stimuli.
Growth/reproduction/reposition of roots, stems, and leaves are responses to gravity, light, temperature, and amount of darkness.
Plants have mechanisms to respond to stimuli.
Speeds ripening of fruits/promotes breakdown of complex carbohydrates to simple sugars.
Transported in vascular tissue.
Cause plants to grow taller; about 80 known
As auxin decrease, ripened fruits fall to the ground/deciduous trees begin to shed leaves.
Auxin delays fruit formation/inhibits fruit dropping from the plant.
Due to changes in cellular water pressure; reversible.
Irreversible, but if direction of stimuli changes, stem will grow in different direction.
Growth response to touch.
Released during specific stage of fruit ripening; cell walls weaken/become soft.
Produced primarily by fruits.
Simple, gaseous compound composed of carbon and hydrogen.
Indoleacetic acid (IAA) = an auxin produced in apical meristems of plant stems; weakens cellulose fibers in cell walls.
Cause stem elongation
Positive tropism = growth toward the stimulus.
Negative tropism = growth away from stimulus.
Plant’s response to external stimuli.
Moves between parenchyma cells to the next by active transport.
Caused by unequal distribution of auxin on stem; more auxin on side away from light.
Different plants require same nutrients in different amounts
Habitats in our world allow for different plants to thrive in different environments, and careful consideration must be made
Water used for:
Photosynthesis - 1 molecule of glucose requires breaking down 6 or more molecules of water into hydrogen ions and electrons needed for photosynthesis.
Turgor pressure - Presence of water in the cells stiffens herbaceous parts of plants; as central vacuole fills with water, it exerts outward pressure against the rigid cell wall.
Hydrolysis - large/complex organic molecules broke apart by combining them with water molecules
Circulation - organic molecules/minerals must be dissolved in water to be transported
14.1 Plants and Water
Water in the Soil
Water must be absorbed from the soil by the root tips
Roots must also have oxygen for cellular respiration (either dissolved in the water or in spaces of soil)
Transportation of Water
When water is absorbed by root hairs by osmosis; it builds up over time (root pressure)
If stem of a well-watered plant is cut, drops of water will ooze out
Root pressure rarely exerts more than 1 kg/cm2 (14lbs/in2); other factors are required for water to go up plants over 1 m tall
Capillarity - a property where water rises slightly due to adhesion between molecules of water and surface; the thinner the diameter, the higher the water rises
Xylem doesn't produce high capillary action
Most biologists think that water is pulled up from the roots; based on two factors: transpiration and cohesion
Transpiration - release of water vapor from leaves of plants into atmosphere
Cohesion - property of water molecules that causes them to “stick together” because of hydrogen bonds between water molecules.
The transpiration-cohesion theory
Turgor Pressure and Wilting
Second major function of water in plants
Turgor pressure - presence of water inside a plant cell in sufficient quantity to give the cell stiffness
Lack of water or high water loss without replacement reduces turgor pressure, leading to wilting; sometimes vascular tissue can be damaged, leading to permanent wilting
Psalm 1:3 refers to the Word of God as "water" whereby a Christian grows; if a Christian is deprived of the Word of God, they will not grow spiritually, like plant will suffer from lack of water
Translocation of Carbohydrates
Translocation - movement of carbohydrates (glucose) throughout the plant
To meristematic tissue as an energy source for growth
To various storage areas in the roots, stems, and fruits
Sources - areas where carbohydrates are stored/manufactured
Sinks - places where carbohydrates are used/stored
14.2 - Plants and Minerals
Aside from a few parasitic and saprophytic plants, plants do not “eat food.”
Energy from the sun produces food manufactured from plants during photosynthesis; plants also absorb soluble minerals in soil to manufacture various substances
Minerals in the Soil
Minerals - inorganic substances in the soil
See Table 14-1 for essential nutrient elements; plants need them in various amounts
Crop rotation - alternating plants in a crop to allow minerals to be replenished in the soil
Soils can be tested for mineral content; fertilizers can be used to replenish depleted soils, usually written as 10-10-10 (nitrogen, phosphorus, potassium)
Nutrient minerals reach roots in a soluble form
Active transport of solutes necessary because of greater concentration of solutes inside the cell cytoplasm than in the soil water outside roots, cells must use active transport to move these substances into the cells against the concentration gradient
If oxygen depleted, water molecules will go into the soil (plasmolysis) and kills root epidermal cells; this is seen in overfertilization when plants are “burned” by the fertilizer.
Absorption of Minerals by Roots
Halophytes - plants that grow in salty conditions
Have higher concentrations of salts inside their cells than in the soil around them
In the mid-1920s, Fritz W. Went, a Dutch plant physiologist, performed a series of experiments on oat seedling coleoptiles (protective sheath of embryonic stem) and discovered plants have hormones.
Cytokinins stimulate cell division in plants and promote lateral bud growth.
Inhibit the aging of flowers, fruits, and leaves.
Produced in actively growing tissues (roots/developing fruits/seeds)
Usually oppotite effects of auxins.
Originally thought to induce abscission (shedding of parts of the plant)
Known to be an inhibitor of many other hormones, such as growth responses of auxins and gibberellins.
Induces dormancy in seeds/buds to produce bud scales; when applied to growing plant tips, forces formation of dormant buds
Growth response toward or away from certain chemicals
A pollen tube grows in response to certain chemicals produced by the cells in the ovary
14.4 - Plants and Light
Plants require light for photosynthesis and other processes
Light needs vary with plants
Intensity of Light
Etiolated - when a plant receives inadequate light; stem grows, but leaf size/number decreases; plant appears to stretch for light leaves
Plant appears pale green, yellow, or even white.
Some plants (like dogwood trees) have a shade growth and a full sun growth pattern and can produce different amounts of different structures
Period of inactivity (of any kind)