What are the three general lengths of transport in plants, with a small description?
Cellular uptake/unloading of materials: occurs in root cell and soil. Requires ATP to absorb minerals against concentration gradient.
Short distance transport: within a tissue or organ. (eg moving material within the root or within the leaf).
Whole plant transport: Systemic transport throughout the entirety of the plant (root -> leaf)
What is the biggest difference between plant and animal circulation?
Animals have a pump to circulate their blood, while plant movement is not circulatory and is performed without a pump.
In what directions is water moved through the plant?
Vertically by tracheids and vessel elements, but also laterally through pits (thin portions of the cell wall w/ high plasmodesmata) in these same structures.
Describe Ψ in detail
Ψ (water potential) is a combined measurement of both pressure and [solute] used to determine directional flow of water.
Water flows from high Ψ to low Ψ.
High Ψ = low [solute], high pressure (turgid cell, water would exit)
Low Ψ = high [solute], low pressure (limp cell, water would enter)
The differential created between Ψ is so strong that low Ψ can act as a syringe, pulling water from the roots to the leaves!
How much water do plants used compared to animals? Why?
Plants use an incredibly large amount of water, much more than animals because plants cannot circulate their water. (A sunflower plant imbibes 17x more water than a human over 24 hours)
99% of water taken in with the roots is released as water vapor (not used by the plant), this is called transpiration.
Why does transpiration have to occur? What generic strategies have been developed to limit transpiration?
The major route for water loss in plants is through the stomata, and there are about 12,000 stomata per square inch of leaf. The stomata cannot remain closed because CO2 is required to perform photosynthesis. Every time CO2 is let in via stomata transpiration occurs, thus transpiration is a necessary evil.
Plants have developed various strategies to try and deal with transpiration including trichomes, the cuticle, stomatal crypts in xerophytes, CAM plants, and most importantly CLOSING stomata.
Describe how water is moved from roots to leaves in detail (name, sequence of action, properties, etc)
The TTCA (transpiration-tension cohesion-adhesion) model is used to explain water movement from roots to leaves. Essentially water is pulled (by tension), not pushed, into the upper canopy. Transpiration and the physical properties of water drive xylem contents upwards.
Sequence of action: transpiration of water from the interstitial spaces of the mesophyll cells occurs at the stomata which creates a drop in pressure (lower Ψ). This lower Ψ pulls water from surrounding cells, which in turn pull water from surrounding cells, and so on until this tension force (negative pressure) reaches veins. Xylem sap (water + ions) is pulled from veins, and the cohesive and adhesive forces of water continue this “pulling” all the way down to the roots (adhesive forces cause walls of xylem to move inward). Water being pulled out of the roots increases [solute] (lower Ψ) and causes a proportional water uptake to the roots.
Essentially the rate of transpiration is directly related to the rate of water uptake.
Note – the diameter of a tree may actually decrease during the warm part of a day due to the tension forces.
Note - Flow rate is significantly higher in xylem than phloem
What is the normal transpiration rate? How do plants quickly alter this rate? Describe the specific way that plants physiologically achieve this regulation in detail.
A leaf is kept from wilting by having a transpiration stream that flows at a rate of 75cm/min within xylem vessels. Guard cells control the photosynthesis/transpiration compromise (close stomata if rate is too high, open stomata if rate is too low)
Stomata are controlled through various mechanisms including…
Osmosis: K+ redistribution and water potential changes cause guard cells to swell and open when gaining water; “shrink” and close when losing water
Blue light photoreceptor triggers ATP driven proton pumps which trigger the K+ influx as described above.
Decrease in CO2 within air spaces
What conditions will cause an increase in transpiration rate? A decrease?
Sunny, warm, dry, and windy days will increase transpiration rate.
Humid conditions will decrease transpiration rate.
Describe succulents’ and CAM plants’ strategies to minimize transpiration.
CAM plants: Open stomata at night (when the least amount of transpiration occurs) to take in CO2, and perform photosynthesis during the day WITHOUT opening their stomata.
Describe root pressure in detail.
Root pressure is a second (lesser) type of force that pushes xylem sap upwards.
As root cells pick-up solutes from the soil this decreases Ψ, forcing water to enter the root cells. This creates a pressure that pushes water up into the stem.
The mechanism does not exert enough force to push water up a tall shrub/tree.
Guttation: droplets of liquid water forced out by root pressure, most evident during the night when the least amount of transpiration occurs. Not the same thing is dew!
What are the two methods of water transportation within a root?
Apoplastic: transportation through areas outside of the plant cells. Found in areas of the cell walls and dead tissues of the xylem.
Symplastic: transportation through the cytoplasm of cells via that plant’s plasmodesmata.
Describe how organic molecules are moved throughout a plant in detail.
The pressure/flow model is used to explain the movement of sugar, amino acids, minerals, and hormones through the plant via phloem (sieve-tube members).
Phloem transport is directional, from sugar source (any cell that creates/stores glucose) to sugar sink (any cell that needs glucose).
Phloem loading: requires ATP and active transport. A sucrose cotransporter is used in the process of sucrose loading.
Sequence of action: Loading of sugar into the sieve tube at the source (an active process) causes a decrease in Ψ (increased [solute]). Because of this, the sieve tube (source) takes in water. This creates a water pressure at the source end and moves water w/material through the phloem. At the sink end, sucrose is unloaded. Removing the solute from the sieve tube increases Ψ (lower [solute]), thus water exits the sieve tube at the sink end relieving the pressure.
Note - Flow rate is significantly higher in xylem than phloem
Give information about the plant endocrine system, incl. mechanisms of action, types of cellular responses, and major hormone categories.
Hormones (chemical messengers) function to coordinate growth & development and mediate response to external cues (affect division, elongation, gene expression, and differentiation of cells)
Hormones are produced in a variety of locations, and are active even in small amounts (not used in their mechanisms, so they can continue to affect another cell)
Hormones work by signal transduction pathways: ligand (substance that binds to a receptor), target tissue (tissue equipped with receptors specific to a particular ligand)
Hormone sequence of action: reception, signal transduction, cellular response
Examples of cellular responses: Altering gene expression (protein synthesis regulation), activating or deactivating enzymes (protein kinase enzymes), changing the properties of membranes (permeability to ions)
Cellular response may differ based on hormone concentration, developmental state of tissue, interplay of two or more hormones, tissue type
Major hormone categories: Auxins, Cytokinins, Gibberellins, Ethylene, Abscisic Acid
Auxin – Produced where? Function? Other information?
Manufactured in apical bud meristem, young leaves, and seed embryo
Major stimulator of shoot elongation (moves down from shoot apical meristem from cell to cell by way of parenchyma cells)
Name literally means “to increase”
Most common naturally occurring auxin is IAA (indoleacetic acid) which was studied by Darwin
Formation of adventitious roots in stem cuttings and lateral roots from pericycle
Stimulates vascular cambium (secondary growth)
Seed embryo secretes auxins to stimulate fruit development (has been used to create seedless fruits; normally for fruit development pollination and fertilization must occur, creating seeds).
Functions in vascular tissue differentiation
Apical dominance prevents growth of lateral shoots
Synthetic auxins: (2,4-D) – herbicidal compound (mechanism unknown). Agent orange – a 50/50 mix of two chemicals (2,4,D and 2,4,5,T) was combined with kerosene or diesel fuel and dispersed to destroy foliage and food suppy in South Vietnam during the war. Earliest concerns about Agent Orange were about the product’s contamination with TCDD, or dioxin.
Cytokinins – Produced where? Function? Other information?
Produced in actively growing tissues like roots, embryos, and fruits
Synthesized in the roots and then transported via xylem
Delay leaf senescence (yellowing and eventual death)
Can produce anti-aging properties, may work by inhibiting protein breakdown, stimulating protein synthesis, etc.
Zeatin is the most common naturally occurring cytokinin
Structurally similar to the purine adenine (a nitrogenous base)
Work by stimulating cell division and regulation of cell differentiation (Promote cytokinesis)
Describe the interplay between auxins and cytokinins
Auxins promote apical dominance and root growth
Cytokinins promote axillary bud production and lateral shoot formation
Callus tissue will develop into roots in an excess of auxin, buds and shoots in an excess of cytokinins, and will remain undeveloped when the ratio is equal between auxin and cytokinins
Gibberellins – Produced where? Function? Other information?
Produced in root and bud apical meristem, young leaves and embryos
Functions in shoot elongation through division and cell elongation (causes growth in dwarf mutants)
Stimulates fruit growth without fertilization (commercial use allows for seedless grapes)
Signals seeds to break dormancy and to germinate (ex. water soaked into the seed -> release of GA). GA then causes release of enzymes that break down starchy endosperm which supports developing seedlings by making nutrients available to them.
Ethylene – Produced where? Function? Other information?
Synthesized in most tissues in response to stress (especially in ripening fruits and/or leaf senescence)
Promotes fruit ripening and abscission of fruit/leaves
In fruit ripening, seems to play a role in promoting chlorophyll degradation, formation of other pigments, digestion of pectin (middle lamella), synthesis of sugars from a variety of other nutrients
Leaf, flower, and fruit abscission (Ethylene triggers enzymes that break down cell walls in petiole)
Describe the interplay between auxins and Ethylene
Ethylene promotes abscission of fruit/leaves
Auxins inhibit abscission of fruit/leaves (used to prevent pre-harvest drop of fruit)
Auxin seems to work by making cells in the abscission zone less sensitive to ethylene
Abscisic acid (ABA) – Produced where? Function? Other information?
Produced by seed early during development, causes an increase in seed storage proteins
Helps prevent early germination (corn mutants less responsive to ABA germinate while still on the cob)
The rinsing of ABA from a seed helps trigger germination
Water stress triggers ABA synthesis in mature leaves – leads to closure of stomata (therefore involved in regulation of transpiration)
What is a tropism? Describe the various tropisms
Tropisms: growth respons that curves the plant organ toward or away from stimuli (toward = positive, away = negative)
Mechanism of tropisms: elongation of cells on OPPOSITE side of the organ
Phototropism: curving of shoot towards light. Sensation of light is tied to the shoot tip, special blue light photoreceptor (cryptochrome). Function via auxin redistribution (migrates from light side to dark side of root tip, then to internode below which causes growth)
Gravitropism: shoots grow against gravity (negative), roots growth with gravity (positive). Sedimentation of amyloplasts within cells used as an indicator of gravity for cells
Thigmotropism: response to touch that allows roots to navigate around rocks, and tendrils to wrap around other structures. Cells touching surface slightly shorten, other side elongates.
Movements in response to a mechanical stimulus: turgor movements (controlled by water efflux following ions), plants drop suddenly after touch. Venus flytrap; scientists unsure of how the mechanism works.
Define systematics. What is the goal? What criteria is used?
The science of evolutionary history (naming / classifying an organism through evolution)
The goal of systematic is to find all branches of the phylogenic tree of life
Comparative anatomy, physiology, embryology, and comparative molecular techniques (eg DNA, RNA, protein) are used together in systematic and taxonomy.
Define taxonomy, describe its origins, current rules, and other information.
Taxonomy: identifying, naming, and classifying a species
Species: a group of organisms capable of interbreeding and creation of viable offspring (some exceptions)
Developed initially by Carolus Linnaeus (1700s) it used polynomial naming (a brief sentence describing a species). This was replaced with the current binomial system; a generic name and a specific epithet (Genus Species). The generic name alone refers to an entire genera, but the specific epithet alone means nothing. Subspecies (varieties) may consist of 3 names.
Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species. These are grouped to reflect phylogeny (proper ancestral history)
What are the 3 major domains and 6 major kingdoms?
Note – Domain Archaea is more closely related to Eukarya than Bacteria!
What is phylogeny? Describe the various groups that can be formed when classifying taxa.
Phylogeny: (evolutionary history) characteristics of organisms are products of their evolutionary past. Studies in phylogeny result in diagrams (“family tree”).
Monophyletic groups: created by looking for shared unique features among organisms.
A monophyletic taxon contains ALL members who descended from a common ancestor (none are excluded)
Natural taxa: taxa where all members have shared ancestry, and correctly reflect the ancestral past of that group.
Artifical taxa: taxa that do not correctly reflect the ancestral past of that groupCan come in two forms; paraphyletic and polyphyletic
Polyphyletic: taxa where members descended from more than one ancestral line, and may only resemble each other because of similar evolutionary pressure.
Paraphyletic: A group that does not include one or more descendants of a common ancestor (one or more are excluded).
Describe the two approaches to phylogeny.
1: Looking at similarities and grouping according to the degree of similarity
Cladistics: Looking for shared UNIQUE features.
Describe cladistics in detail.
The goal is to understand the evolutionary relationships present among organisms.
Focuses more specifically on shared characteristics that are unique (eg. Presence/absence of flowers)
Cladograms are created in an attempt to show groups that share a common ancestor.
CLADOGRAMS DO NOT IMPLY THAT A SPECIFIC GROUP EVOLVED INTO ANOTHER.
Briefly describe the three domains.
Bacteria: prokaryotic, no nuclear envelope, 1 circular chromosome, no organelles, no cytoskeleton, chlorophyll-based photosynthesis can occur.
Archaea: prokaryotic, no nuclear envelope, 1 circular chromosome, no organelles, no cytoskeleton, chlorophyll-based photosynthesis cannot occur.
Eukarya: eukaryotic, has nuclear envelope, 1+ linear chromosomes, has organelles, has cytoskeleton, chlorophyll-based photosynthesis can occur.
Describe how eukaryotic cells developed.
Chloroplasts and mitochondria are believed to be remnants of endosymbionts (organisms that live within other organisms). The theory is that they were absorbed by an amoeba or different cell, but rather than being enzymatically destroyed they were adapted to mutualistically survive within the host cell, eventually leading to the eukaryotic cell.
Several enzymes within chloroplasts and mitochondria are found in the prokaryotic membrane, a binary-fission like process is used by chloroplasts and mitochondria for reproduction within eukaryotic cells, and the DNA within them is arranged prokaryotically. This links their lineage to bacteria.
An example of endosymbiosis in the modern word is Vorticella (a protozoan) which establishes an endosymbiosis with the green algae Chlorella.
Give general information and statistics about prokaryotic organisms
90% of the total weight of living organisms in the sea are prokaryotic
1 gram of soil may contain 2.5 billion Bacteria
30% of feces weight is from Bacteria
Prokaryotic cells are at least 3.5 billion years old
Can exists in all locations (from ice wastelands to boiling hot springs) – very versatile
They are the primary decomposers and photosynthetic operators for the earth’s ecosystems
Their success is most likely related to their quick reproduction and metabolic diversity (can survive on almost anything)
Archaea and Eubacteria are examples that represent two DIFFERENT evolutionary lineages
Typical features of prokaryotes include lacking a nucleus and organelles, have a single circular chromosome, containing a plasmid (an extra chromosomal piece that can replicate independently of the cell’s chromosome), and containing ribosomes
Describe the structure of a prokaryote, including shapes.
Plasma membrane: composed of a phospholipid bilayer that many contain important enzyme complexes like the electron transport chain of respiration
Cell wall: 2 types in Eubacteria - Gram positive (retains crystal violet dye, has a thick layer of peptidoglycan) and Gram negative (does not retain crystal violet dye, has a thinner layer of peptidoglycan with an additional outer membrane). Walls of archaea do not contain peptidoglycan.
Peptidoglycan:a protein/sugar material which links sugar chains with peptide bonds.
All bacteria with a few exceptions (Mycoplasmas) are surrounded by a cell wall.
Flagellum: does not contain microtubules and is not membraned.
Fimbriae: short, rigid, and “spiky” they are theorized to provide anchorage
Pili: acts as a tunnel between prokaryotes that functions in conjugation.
3 shapes: rod or bacillus (pleural bacilli) is stick-like, coccus (pleural cocci) is spherical, and spirillum (pleural spirilla) are long and curvy
Describe reproduction and gene exchange in prokaryotes.
Binary fission: a type of asexual reproduction that produces clone populations, represented by the formula Nf = (Ni)2n where n is the generation # and N is the number of bacteria
There is a large amount of mutants produced during binary fission which gives an evolutionary advantage through adaptability.
Recombination (gene exchange) mechanisms allow genes to be passed between different bacteria
Conjugation: the transfer of DNA across a pilus
Transformation: DNA is absorbed from the environment
Transduction: viruses move DNA between bacteria
What are endospores? Describe them?
Endospores are a dormant resting stage where the core of cytoplasm is surrounded by numerous protective layers.
Endospores are formed in an inhospitable environment, when the normal prokaryote would not survive.
In this stage the prokaryote is highly resistant to heat, cold, lack of food, radiation, and disinfectants. Viable bacteria have been harvested from fossilized amber that was 20-45 million years old!
Describe method of feeding for bacteria?
Most are hetertrophic, but can be autotrophic
Saprophytic heterotrophs: decomposers (sapro = rotten), most common
Photosynthetic autotrophs: use chlorophyll pigments to gain energy from light
Chemosynthetic autotrophs: oxidize various inorganic compounds (H2S) to make energy (don’t need light)
What is the global significance of bacteria?
Ecosystem: Earth’s recyclers, Nitrogen fixation, Atmospheric gas production, decompositions of toxic substances
Disease: human and plant disease (some are highly destructive)