Exam 2 Flashcards
(183 cards)
1
Q
Cotyledon
A
Food storage organ that functions as “seed leaves”
2
Q
Seed Embryo
A
Cotyledons and plantlet
3
Q
Plumule
A
Embryo shoot
4
Q
Epicotyl
A
Stem above cotyledon attachment
5
Q
Hypocotyl
A
Stem below cotyledon attachment
6
Q
Radicle
A
Tip of the embryo that develops into root
7
Q
Epigeous germination
A
Hypocotyl lengthens, bends, and becomes hook-shaped. Top of hook emerges from ground, pulling cotyledons above ground.
8
Q
Hypogeous germination
A
Hypocotyl remains short and cotyledons do not emerge above surface.
9
Q
Germination
A
Beginning (or resumption) of seed growth. Some require period of dormancy. Brought about by mechanical or physiological factors, including growth-inhibiting substances present in seed coat or fruit. Break dormancy by mechanical abrasion, thawing and freezing, bacterial action, or soaking rains
10
Q
Scarification
A
Artificially breaking dormancy
11
Q
After ripening
A
Embryo composed of only a few cells; seeds will not germinate until embryo develops.
12
Q
Favorable environmental factors needed for germination
A
Water and oxygen. Light (or lack thereof). Proper temperature. Enzymes in cytoplasm begin to function after water is imbibed.
13
Q
Seed viability can be extended
A
Depending on species and storage conditions: dry, low temperatures.
14
Q
Vivipary
A
No period of dormancy; embryo continues to grow while fruit is still on parent
15
Q
Diffusion
A
Movement of molecules from a region of higher concentration to a region of lower concentration. Moving with concentration gradient to equilibrium. Rate based on pressure, temperature, and density of medium
16
Q
Solvent
A
Liquid in which substances dissolve
17
Q
Semipermeable membrane
A
Some substances can diffuse; others cannot. Different substances diffuse at different rates. All plant cell membranes
18
Q
Osmosis
A
Water specific - diffusion of water through a semipermeable membrane
19
Q
Osmotic pressure
A
Pressure required to prevent osmosis
20
Q
Osmotic potential
A
Balanced by resistance of cell wall. Water moves from cell with higher water potential to cell with lower water potential
21
Q
Pressure potential (Turgor Pressure)
A
Pressure that develops against walls as result of water entering cell
22
Q
Turgid Cell
A
Firm cell due to water gained by osmosis
23
Q
Pathway of water through plant
A
Osmosis is primary entrance method. Enters cell walls and intercellular spaces of root hairs and roots. Crosses differentially permeable membrane and cytoplasm of endodermis into the xylem. Flows through xylem to leaves and diffuses out through stomata
24
Q
Plasmolysis
A
Loss of water through osmosis accompanied by shrinkage of protoplasm away from the cell wall
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Imbibition
Large molecules (cellulose and starch) develop electrical charges when wet, attracting water molecules. Water molecules adhere to large molecules. Results in swelling of tissues. First step in seed germination.
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Active transport
Process used to absorb and retain solutes against a diffusion or electrical gradient by expenditure of energy. Involves proton pump
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Proton pump
Enzyme complex in plasma membrane energized by ATP molecules
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Transport Proteins
Facilitate transfer of solutes to outside and to inside of cell
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Transpiration
Water vapor loss from internal leaf atmosphere. MORE THAN 90% OF THE WATER ENTERING A PLANT IS TRANSPIRED
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How much of a plant's water is transpired?
More than 90%
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Water is needed for
Cell activities, cell turgor, and evaporation for cooling. Stomata close if more water is lost than taken in.
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The Cohesion-Tension Theory
Transpiration generates tension to pull water columns through plants from roots to leaves.
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In CTT, Water columns created when water molecules adhere to tracheids and vessels of xylem and cohere to each other. When water evaporates from mesophyll cells
when water molecules adhere to tracheids and vessels of xylem and cohere to each other.
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In CTT, When water evaporates from mesophyll cells
they develop a lower water potential than adjacent cells, so water moves into mesophyll cells from adjacent cells with higher water potential. Process is continued until veins are reached.
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In CTT, water movement through mesophyll cells from the veins
Creates tension on water columns, drawing water all the way through entire span of xylem cells. Water continues to enter roots by osmosis
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Stomatal Apparatus
Regulates transpiration and gas exchange through 2 guard cells and stoma. Subsidiary cells also help function. Transpiration rates influenced by humidity, light, temperature, and CO2 concentration.
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When photosynthesis occurs, stomata
open. Guard cells expend energy to acquire potassium ions from adjacent epidermal cells. Causes lower water potential in guard cells. Water enters via osmosis, so guard cells become turgid and stoma opens.
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When photosynthesis does not occur, stomata
close (no E to run K+ pumps). K+ ions leave guard cells. Water follows. Cells become less turgid and stoma closes.
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When do stomata generally open?
During the day. They generally close at night.
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Water conservation causes exceptions for stomata cycle in some plants
In desert plants, stomata open only at night. This conserves water but makes carbon dioxide inaccessible during the day. They do CAM photosynthesis; CO2 converted to organic acids and stored in vacuoles at night to be reconverted to CO2 during the day.
In desert plants and pines, stomata are recessed below the surface of leaf or in chambers.
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Guttation
Loss of liquid water. If cool night follows warm, humid day, water droplets are produced through hydathodes at tips of veins. In absence of transpiration at night, pressure in xylem elements forces water out of hydathodes.
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Important function of water in phloem
Translocation of food substances
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Pressure-Flow Hypothesis
Organic solutes flow from source, where water enters by osmosis to sinks, where food is utilized and water exits. Organic solutes move along concentration gradients between sources and sinks
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Specifics of Pressure-Flow Hypothesis
Phloem loading. Water potential of sieve tube decreases and water enters by osmosis. Turgor pressure develops and drives fluid through sieve tubes toward sinks. Food substances actively removed at sink and water exits sieve tubes, lowering pressure in sieve tubes. Mass flow occurs from higher pressure at source to lower pressure at sink. Water diffuses back into xylem.
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Phloem Loading
Sugar enters by active transport into sieve tubes
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Non-Mineral Nutrients
Carbon, hydrogen, and oxygen. Tend not to be in soil
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Macronutrients
Used by plants in grater amounts - nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. These are usually the cause of stunted growth, especially nitrogen which can be leached out of the soil. Soil from the store tells you mineral content by N-P-K.
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Micronutrients
Needed by the plants in very small amounts. Iron, Chlorine, Copper, Boron, Manganese, Zinc, Molybdenum, Sodium, and Cobalt. When any required element is deficient in soil, plants will exhibit characteristic symptoms (signals which nutrient is deficient).
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Photosynthesis
Converts light energy to stored energy. Occurs in chloroplasts
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Respiration
Releases stored energy. Facilitates growth, development, and reproduction
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Metabolism
Sum of all interrelated biochemical processes in living organisms
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Enzymes
Regulate metabolic activities
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Anabolism
Forming chemical bonds to build molecules. Ex: photosynthesis reactions - store energy by constructing carbohydrates by combining carbon dioxide and water
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Catabolism
Breaking chemical bonds. Ex: Cellular respiration reactions - release energy held in chemical bonds by breaking down carbohydrates, producing carbon dioxide and water
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Photosynthesis-respiration cycle
involves transfer of energy via oxidation-reduction reactions
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Oxidation
Loss of electrons
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Reduction
Gain of electrons
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Oxidation-reduction reactions
Oxidation of one compound is usually coupled with reduction of another compound, catalyzed by same enzyme or enzyme complex. Hydrogen atom is lost during oxidation and gained during reduction. Oxygen is usually the final acceptor of electron.
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ATP
Energy for most cellular activity
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Photosynthesis Reaction
6 CO2+12 H2O+light->->->->C6H12O6+6 O2+6 H2O
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CO2 reaches chloroplasts in mesophyll cells by
diffusing through stomata into leaf interior. CO2 comprises 0.04% of atmosphere
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How much of a plant's water is used in photosynthesis?
Less than 1%. Most water is transpired or incorporated into plant materials
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Water in photosythesis
Acts as a source of electrons. O2 is produced as a by-product. If water is in short supply or light intensities too high, stomata close and thus reduce supply of carbon dioxide available for photosynthesis.
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Visible light
About 40% of radiant energy received on earth. Violet to blue and red-orange to red wavelengths are used more extensively in photosynthesis. Green light is reflected in higher amounts. Leaves commonly absorb about 80% of the visible light available to them. Light intensity varies from time of day, season, altitude, latitude, and atmospheric composition.
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Absorption spectrum
Each pigment has its own distinctive pattern of light absorption.
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When pigments absorb light
Energy levels of electrons are raised. Energy from an excited electron is released when it drops back to its ground state. In photosynthesis, that energy is stored in chemical bonds.
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If light and temperatures too high
Ratio of CO2 to O2 inside leaves may change, acceleration photorespiration
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Photorespiration
Uses oxygen and releases carbon dioxide. May help some plants survive under adverse conditions
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Photooxidation
Occurs when light intensity is too high. Results in destruction of chlorophyll
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If water is in short supply or light intensities are too high
Stomata close and thus reduce supply of CO2 available for photosynthesis
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Several types of chlorophyll molecules capture energy
A, B, C, D, and E. Magnesium end captures light energy. Lipid tail anchors into thylakoid membrane. Most plants contain A (blue-green - most common) and B (yellow-green color). Chlorophyll b transfers energy from light to chlorophyll a, making it possible for photosynthesis to occur over a broader spectrum of light.
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Other photosynthetic pigments
Carotenoids (yellow and orange), phycobilins (blue or red, in cyanobacteria and red algae) and other types of chlorophyll (c, d, e)
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Photosynthetic unit
About 250-400 pigment molecules grouped in light-harvesting complex. Two types work together in light-dependent reactions - P 680 and P700
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Phases of Photosynthesis
Light-dependent reactions and light-independent reactions
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Light dependent reactions occur in
thylakoid membranes of chloroplasts
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Light-dependent reactions
water molecules split apart, releasing electrons and hydrogen ions; oxygen gas released. Electrons pass along electron transport system. ATP produced. NADP is reduced, forming NADPH (used in light-independent reactions)
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Two types of photosynthetic units
Photosystem II and Photosystem I (PII comes before PI in reaction chain). Both can produce ATP. Only organisms with both photosystems can produce NADPH and O2 as a consequence of electron flow.
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Light-independent reactions
In stroma of chloroplasts. Use ATP and NADPH to form sugars through the calvin cycle.
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Calvin Cycle
CO2 combines with RuBP (ribulose biphosphate) and then combined molecules are converted to sugars (glucose). Energy furnished from ATP and NADPH produced during light-dependent reactions.
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In-depth Calvin Cycle
Six molecules of CO2 combine with six molecules of RuBP (ribulose 1,5 biphosphate) with aid of rubisco. Eventually results in twelve 3-carbon molecules of 3PGA (3-phosphoglyceric acid). NADPH and ATP supply energy and electrons that reduce 3PGA to GA3P (glyceraldehyde 3-phosphate). Ten of the twelve GA3P molecules are restructured, using 6ATP, into six 5-C RuBP molecules. Net gain of 2 GA3P, which can be converted to carbohydrates or used to make lipids and amino acids
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Photorespiration
Competes with carbon-fixing role of photosynthesis
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In the process of photorespiration
Rubisco fixes O2 instead of CO2. Allows C3 plants to survive under hot dry conditions by dissipating ATP and accumulated electrons, preventing photooxidative damage. When stomata closed, O2 accumulates and photorespiration is more likely.
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Photorespiration products
2-C phosphoglycolic acid, processed in peroxisomes. Forms CO2 and PGA that can reenter Calvin cycle. No GA3P formed (actually lose 1 C every two turns).
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4-Carbon Pathway
Produces 4-C compound instead of 3-carbon PGA during initial steps of light-independent reactions
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C4 Plants
Tropical grasses and plants of arid regions
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C4 Plants have Kranz anatomy
Mesophyll cells with smaller chloroplasts with well-developed grana. Bundle sheath cells with large chloroplasts with numerous starch grains.
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4C Pathway In-depth
CO2 converted to organic acids in mesophyll cells. PEP (phosphoenolpyruvate) and CO2 combine with aid of PEP carboxylase. Form 4-C oxaloacetic acid instead of PGA. PEP carboxylase converts CO2 to carbohydrate at lower CO2 concentrations than does rubisco. Not sensitive to O2. CO2 is transported as organic acids to bundle sheath cells, is released, and enters Calving cycle. CO2 concentration is high in the bundle sheath, thus photorespiration is minimized. C4 plants photosynthesize at higher temps than C3 plants. At low temps, C3 is more efficient, as it costs 2 ATP for C4 photosynthesis.
88
CAM photosynthesis
Similar to C4 photosynthesis in that 4-C compounds produced during light independent reactions. However, organic acids accumulate at night when the stomata open and are converted back to CO2 during the day for use in the Calvin cycle when the stomata are closed. Allows plants to function well under limited water supply and high light intensity.
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Respiration
The release of energy from glucose molecules that are broken down to individual carbon dioxide molecules, initiated in the cytoplasm and completed in the mitochondria
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Aerobic Respiration
cannot be completed without O2
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Respiration equation
C6H12O6 + 6 O2 ->->->-> 6 CO2 + 6 H2O + 36 ATP
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Anaerobic respiration and fermentation
carried on in absence of O2. Releases less energy than aerobic respiration.
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Fermentation equations
C6H12O6 -> 2 C2H5OH + 2 CO2 + 2 ATP
C6H12O6 -> 2 C3H6O3 + 2 ATP
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Glycolysis
First phase of respiration. In CYTOPLASM. No O2 required. Glucose converted to GA3P. 2ATP molecules gained
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Krebs cycle
Second phase of respiration. In FLUID MATRIX OF CRISTAE IN MITOCHONDRIA. High energy electrons and hydrogens removed as cycle proceeds. NADH, FADH2, and a small amount of ATP produced. CO2 produced as by-product.
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Electron transport
Third stage of respiration. In INNER MEMBRANE OF MITOCHONDRIA. NADH and FADH2 donate electrons to electron transport system. Produces ATP, CO2, and water.
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Glycolysis in-depth
Steps: phosphorylation, sugar cleavage, and pyruvic acid formation.
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Phosphorylation in glycolysis
Glucose becomes fructose carrying two phosphates (Requires 2ATP)
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Sugar Cleavage in glycolysis
Fructose split into two 3-C fragments: GA3P
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Pyruvic acid formation of glycolysis
Hydrogen, energy, and water removed, leaving pyruvic acid (produces 4 ATP)
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Transition from Glycolysis to Krebs Cycle
Pyruvic acid loses CO2 by coenzyme A and is converted to acetyl CoA. If O2 is not available, anaerobic respiration or fermentation occurs: hydrogen released during glycolysis transferred back to pyruvic acid, creating ethyl alcohol or lactic acid.
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Krebs Cycle in-depth
Acetyl CoA first combines with oxaloacetic acid (4 C), (loses CoA) producing citric acid (6 C). Each cycle uses 2 acetyl CoA, releases 3CO2, and regenerates oxaloacetic acid: O.A+acetyl CoA+ADP+P+3NAD+FAD->O.A+CoA+ATP+3NADH+(H+)+FADH2+2CO2. High energy electrons and hydrogen removed, producing NADH, FADH2, and ATP.
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Electron Transport In-depth
Energy from NADH and FADH2 released as hydrogen and electrons are passed along electron transport system. Protons build up outside mitochondrial matrix, establishing electrochemical gradient. Chemiosmosis couples transport of protons into matrix with oxidative phosphorylation: formation of ATP. O2 acts as ultimate electron acceptor, producing water as it combines with hydrogen. Produces a net gain of 36 ATP and 6 molecules of CO2 and 6 molecules of water.
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Factors affecting rate of respiration
Temperature (20-30 C, respiration rates double). Water (medium in which enzymatic reactions take place; low water content reduces respiration rate). Oxygen (reduction in oxygen reduces respiration and growth rates).
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Growth
Irreversible increase in mass due to division and enlargement of cells
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Determinate Growth
Plant growth stops when fruit sets on the terminal bud. All fruit ripen ant once, and then the plant dies.
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Indeterminate Growth
Plant continues to grow, flower, and ripen fruit simultaneously, only stopping when killed by frost.
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Nutrients
Substances that furnish the elements needed for growth and development. Obtained from air and soil
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Vitamins
Complex organic compounds used to facilitate enzyme reactions, commonly functioning as electron acceptors or donors. Synthesized in cell membranes and cytoplasm. Required in small amounts for normal growth and development
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Hormones
Control growth and development. Produced in minute amounts in actively growing regions of an organism and transported to other regions. Produced and active in smaller amounts than vitamins and enzymes.
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Hormone effects
Can work alone or in cooperation. Can have opposite effects. Triggers series of biochemical events, including turning genes on and off.
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Major hormone types
Auxins, gibberellins, cytokinins, abscisic acid, ethylene
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Auxins
Polar (away from source) movement, requires energy. Effects: promotes cell enlargement and stem growth; plasticity, division, root initiation, delay development; delays leaf abscission, fruit abscission, and ripening; inhibits lateral branching (controls production of ethylene). Types: Indoleacetic acid (IAA), Phenylacetic acid (PAA), 4-chloroindoleacetic acid (4-chloroIAA), Indolebutyric acid (IBA), Indolpropionic acid (IPA). Young Hormone
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Gibberellins (GA)
Named for fungus (Gibberella fujikuroi). Nonpolar movement. Effects: most dicots and a few monocots increase stem growth with GA3; involved in same regulatory processes as auxins. Currently 110 known gibberellin types
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Cytokinins
Nonpolar movement - synthesized in root tips and in germinating seeds. Effects: regulate cell division (if auxin present during cell cycle, cytokinins promote cell division by speeding up progression from G2 phase to mitosis phase); cell enlargement, differentiation of tissues, chloroplast development, cotyledon growth, delay leaf aging. 3 main groups: Kinetin, zeatin, and 6-benzylaminopurine. Young Hormone
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Abscisic acid (ABA)
Nonpolar movement. Effect: has inhibitory effect on stimulatory effects of other hormones; synthesized in plastids from carotenoid pigments; common in fleshy fruits - prevents seeds from germinating while still on plant; helps leaves respond to excessive water loss, interfering with transport or retention of potassium ions in guard cells, causing stomata to close. One type: ABA
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Ethylene
Nonpolar movement. Effects: Produced by fruits, flowers, seeds, leaves, and roots; produced from amino acid methionine; can trigger its own production; used to ripen green fruits; production almost ceases in absence of oxygen. Only ethylene as type.
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Growth movements
Result from varying growth rates in different parts of an organ
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Nutations
Spiraling movements not visible to eye
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Nodding movements
Side-to-side oscillations. In bent hypocotyl of bean - facilitates progress of plant through soil
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Twining movements
Visible spiraling in growth. Stems of flowering plants - morning glory; tendrils
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Contraction movements
Contractile roots that pull roots deeper (like dandelion)
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Phototropism
Growth movement toward or away from light. Auxin migrates away from light and accumulates in greater amounts on opposite side, promoting greater elongation of cells on dark side of stem
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Positive phototropism
Growth toward light. Shoots
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Negative phototropism
Growth away from light. Roots either insensitive or negatively phototrophic
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Gravitropism
Growth responses to stimulus of gravity. Gravity may be perceived by amyloplasts in root cap by proteins on outside of plasma membrane, by whole protoplast, or by mitochondria and dictyosomes. Auxin causes cell elongation that produces curvature of root.
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Positively Gravitropic
Growth toward gravity; primary roots
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Negatively gravitropic
Growth away from gravity; shoots
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Solar Tracking
Leaves often twist on their petioles in response to illumination and become perpendicularly oriented to light source. Blades oriented at right angles to the sun
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Water conservation movements - Bulliform Cells
Special thin-walled cells in leaves of many grasses that lose turgor and cause leaves to roll up or fold during periods of insufficient water
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Photoperiodism
Length of day (night) relationship to onset of flowering (4-types)
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Short-day plants
Will not flower unless day length is shorter than a critical period: asters, poinsettias, ragweed, sorghums, strawberries
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Long-day plants
Will not flower unless periods of light are longer than a critical period: beets, larkspur, lettuce, potatoes, spinach, wheat
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Intermediate-day plants
Will not flower if days are too short or too longs: several grasses
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Day-neutral plants
flower under any day-length: tropical plants, beans, carnations, cotton, roses, tomatoes
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Temperature and growth
Each plant species has optimum temperature for growth and minimum temperature below which growth will not occur. Lower night temperatures often result in higher sugar content and in greater root growth. Growth of many field crops is roughly proportional to prevailing temperatures.
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Thermoperiod
Optimum night and day temperatures, which may change with growth stage of plant.
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Asexual Reproduction
Production of cells identical to cells from which they arose
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Sexual reproduction
Occurs in nearly all plants. Results in formation of seeds in flowering and cone-bearing plants. Gametes produced; egg and sperm unite to form zygote
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Diploid organisms
Cells have two copies of each chromosome, one copy from each parent. Each matching pair of chromosomes is identical in length, amount of DNA, genes carried, and location of centromere
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Homologous chromosomes
Chromosome pairs
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Results of meiosis
Four cells from two successive divisions, with half the chromosome number of parents. Each cell rarely (aka never) identical to original cell or each other
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Before meiosis
DNA molecules of each chromosome are copied (doubled). Each chromosome has identical DNA molecules held together by a centromere.
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Meiosis Division I (Reduction Division)
Number of chromosomes reduced to half
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Meiosis Division II (Equational Division)
No further reduction in chromosome number
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Prophase I
Chromosomes coil and condense and align in homologous pairs. Each homologous pair of chromosomes has four chromatids with centromere. Spindle fibers connect to centromere. Nuclear envelope and nucleolus disassociate. Each closely associated pair of chromosomes exchange parts = crossing-over
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Prophase I - Crossing-over
Chiasmata form; results in exchange of DNA by two parents
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Metaphase I
Chromosomes align in pairs at equator. Spindle formation completed
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Anaphase I
One whole chromosome from each pair migrates to a pole
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Telophase I
Original cell becomes two cells or two nuclei
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Prophase II
Chromosomes become shorter and thicker
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Metaphase II
Centromeres become aligned along equator. New spindles completed
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Anaphase II
Centromeres and chromatids of each chromosome separate and migrate to opposite poles
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Telophase II
Coils of chromatids relax. Chromosomes become longer and thinner. Nuclear envelope and nucleoli reappear for each group of chromosomes. New cell walls form
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Haploid
Cell with one copy of each chromosome (gametes)
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Diploid
Cell with two copies of each chromosome (zygote)
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Polyploid
Cell with more than two copies of each chromosome
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Triploid
Three sets of chromosomes. Homologous chromosomes cannot pair properly, so gametes are typically inviable (navel oranges, seedless watermelons)
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Tetraploid
Four sets of chromosomes (potatoes, pasta wheat)
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Alternation of generations
Life cycle involving sexual reproduction that alternates between diploid sporophyte phase and haploid gametophyte phase
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Sporophytes
Develop from zygotes and produce sporocytes
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Sporocyte
Undergoes meiosis, producing 4 haploid spores
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Gametophytes
Develop from spores
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Fertilization
Fusion of gametes producing zygote
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Large number of flowering plant species
250,000-400,000
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6 species provide 80% of calories consumed by humans worldwide
Wheat, rice, corn, potato, sweet potato, and cassave
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8 additional plants complete the list of major crops (about 15%)
Sugar cane, sugar beet, bean, soybean, barley, sorghum, coconut, and banana
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Domesticated plant
Reproductive success depends on human intervention; ongoing improvement process
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One food crop traced to North America
Sunflower
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Plant breeding
The art and science of improving the genetics of plants for the benefit of humankind
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Primary goal of plant breeding
Improved yield, disease resistance, pest resistance, stress tolerance, all improving yield
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Genetic variation provides
foundation for improving plants through breeding
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Gamete possibilities
The options from the parent's alleles that can be passed on to the gamete
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Self-pollinating plant
Capable of fertilizing itself. Tends to be highly homozygous - genes come from same parent. Significant inbreeding. Wheat, rice, oats, barley, peas, tomatoes, peppers, and some fruit trees (apricots, nectarines, and citrus)
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Breeding strategy for self-pollinating plant
Pure-line selection: Seeds collected from several plants. Seeds from individual plant grown in same row. Most desirable row selected.
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Cross-pollinating plant
Must be fertilized from other individuals. Tend to be highly heterozygous. Corn, rye, alfalfa, clover, and most fruit, nuts, and vegetables
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Breeding Strategy for Cross-pollinating Plants
Mass selection - many plants from a population selected, and seeds from these plants used to create next generation. Seeds from the best plants chosen and propagated for many generations
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Outcrossing in cross-pollinated crops
often results in hybrid vigor (heterosis - jump in performance). Outcrossing involves taking genes from sexually incompatible plants
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Self-pollination of cross-pollinating plants
Results in inbreeding depression due to the expression of deleterious recessive alleles. Modern breeders force self-pollination in cross-pollinated species to create inbred lines, deleting undesirable alleles. Selected inbred lines crossed to produce hybrid seed (successful in corn)
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Heirloom varieties
Grown as open-pollinated populations. Genetic variability allows crop production under different environmental conditions.
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Without genetic variability
It is impossible to improve population in a trait
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Germplasm
Sum total of a plant's genes. Current agricultural varieties are often genetically uniform, and thus may not be good sources of new genetic variability. Homogeneity makes them vulnerable to pest outbreaks
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Gene banks
Established to meet current and future demands of plant genetic diversity. Seeds or other propagules put into long-term storage.
