Biology Exam III Study Material
Biology Exam III Study Material Bio 111 - Fundamentals of Biology II
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This 29 page Study Guide was uploaded by valerie zaid on Monday April 18, 2016. The Study Guide belongs to Bio 111 - Fundamentals of Biology II at Purdue University taught by Athena Anderson in Spring 2016. Since its upload, it has received 35 views. For similar materials see Biology in Biology at Purdue University.
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Date Created: 04/18/16
Biology Exam III Study Guide Behavior: o Individual behavior: action carried out by muscles controlled by the nervous system. (Ex: bird using throat muscles to sing and attract predators) o Behavior is essential for acquiring nutrients, reproduction and sometimes homeostasis o Many behaviors require specialized body structures: The physiology affects the behavior of the animal and the other way around. o Natural selection that shapes behaviors also influences animal anatomy. Muscles: o 3 types of muscle tissue: skeletal (voluntary control), cardiac (involuntary control) and smooth (involuntary control) o Skeletal muscle: moves individual bones and the whole body Made of bundles of long cells parallel to length of muscle Each cell/fiber has many nuclei Inside each cell/fiber is longitudinal bundle of myofibrils Myofibrils contain thin and thick filaments Myofibrils made of repeating sections called sarcomeres which are basic contractile units of muscle Borders of sarcomere line up in adjacent myofibrils This forms pattern of light and dark bands called striations, giving these muscles alternative name of striated muscle Muscle cell contraction requires interaction between: 1. Thin filaments: made of globular protein actin; two strands of polymerized actin coiled around each other 2. Thick filaments: staggered arrays of myosin molecules Muscle contraction is result of filament movement, powered by chemical energy Muscle relaxation requires no energy Sliding-filament mechanism: o A contracting muscle shortens: Filaments that cause contraction don’t change in length Filaments slide past each other, like segments of telescope Thin and thick filaments interact, ratcheting past each other into contracted state Thin filaments include regulatory molecules 1. Troponin: site of Ca 2+ attachment 2. Tropomyosin: blocks cross-bridge attachment sites on actin 2 Calcium (Ca 2+) ions allow cross-bridge formation by moving tropomyosin and exposing actin attachment sites o Skeletal muscle can be categorized 2 ways: 1. Oxidative or glycolytic fibers: categorized by how they get energy Oxidative fibers: Rely on aerobic respiration Evolved to make use of steady energy supply Fatigue slowly Large amount of O2-storing protein myoglobin, which allows more efficient O2 extraction than hemoglobin Body uses these during moderate, extended exercise Glycolytic fibers: Rely mostly on anaerobic respiration (glycolysis) Evolved to make use of sporadic energy supply Fatigue faster Larger diameter and less myoglobin (more hemoglobin) Body uses these during short, intense exercise 2. Fast-twitch or slow-twitch fibers: categorized by speed of response Fast-twitch fibers: Contract 2-3x faster Enable brief, rapid, powerful contractions Muscles that enable burst of speed 3 Animals that move mostly in short bursts of speed-oscars, angelfish, grouse Can be oxidative or glycolytic Most human skeletal muscle contain both fast- and slow-twitch fibers Slow-twitch fibers: Slower Enable extended, moderate-intensity contractions Muscles that enable extended contractions-maintaining posture Animals that spend their lives moving almost constantly All are oxidative Body shape and lifestyle: o Short, fat appendages better for maneuverability o Long, tapered appendages better for speed o In bird wings and fish fins, Long and narrow correlated with, gliding and soaring, swimming long distances Short and round correlated with fast take-off, bursts of speed o Smooth muscle: Mainly in walls of hollow organs (intestines, blood vessels) Contract and relax more slowly than skeletal muscles Some can create action potentials without neurons, some cannot Non-striated o Cardiac muscle: Only found in heart Can create action potential without input from neurons 4 Striated Skeletal Systems: structure against which muscles can move; protects vital organs; gives animals shape. Moving a part back and forth requires two muscles (antagonistic pair) o Types of skeletal systems: Hydrostatic skeletons Fluid held under pressure in closed body compartment Movement achieved by using muscles to change shape of fluid-filled compartments Well-suited for aquatic environments Anemones, flatworms, segmented worms Exoskeletons Hard encasement deposited on animal’s surface Muscles attached to lining of skeleton Must be shed to allow for growth Molluscs (clams, snails) secrete theirs of calcium carbonate Arthropods (spider, crabs, insects) secrete theirs of chitin Endoskeletons Hardened, internal, buried inside soft tissue In sponges, made of silica In echinoderms (sea stars, urchins), made of magnesium carbonate and calcium carbonate crystals 5 In chordates, made of cartilage or bone Allometric scaling: how characteristics of animals disproportionally change with size o Morphological scaling: unequal change in body proportions with change in body size. (ex: elephant’s leg bones thicker relative to its body mass than leg bones of a camel) o Locomotion: Active travel from place to place; important for obtaining food, mates, shelter; escape from danger Energy must spent to overcome friction and gravity Amount of energy required to there forced often reduced by animal’s body plans Flying-active flight evolved independently 4 times: pterosaurs, bats, birds, insects In birds: Wing shape provides lift Hollow bones, no teeth, no bladder reduce weight Body shape reduces resistance Walking (ambulation): animal must support itself and move against gravity, maintain balance, but air offers little resistance. Powerful muscles and skeletal support more important than streamlined shape. Jumping (saltation): overcoming gravity and maintain balance important Energy stored in tendons with each landing, then used to partially power next jump Use led energy the faster they jump Tail required for balance if directional 6 Swimming-friction and viscosity more problematic than gravity Fusiform shape reduces drag for fast swimmers, as it does for fliers Some swim by moving body up and down, others side to side Behavioral ecology: How animals behave in relation to other animals and environment o Tinbergen: understanding behavior requires answering 4 questions: 1. What stimulus illicits the behavior, what physiological mechanism regulates response? 2. How does animal’s experience during growth and development influence the response? 3. How does behavior aid survival and reproduction? 4. What is behavior’s evolutionary history? o Fixed action patterns (FAPs): sequence of unlearned acts directly linked to a simple stimulus Unchangeable Carried to completion once begun Trigger is external cue, “sign stimulus” o Migration: regular long-distance relocation. Environmental cues very important triggers. How do they find their way? Position of sun, moon, and/or stars and planet’s magnetic field o behavioral rhythms: influence animal’s daily activities usually regulated by day length and light intensity o circadian rhythm: daily cycle of rest and activity; wake up, go to sleep, estivate, ect o circannual rhythms: on annual cycle; hibernate, migrate etc. Animal communication 7 o signal: stimulus transmitted from one animal to another o communication: signal transmission and reception o signal-response chain: response to each stimulus is itself the stimulus for next response o pheromones: chemical substances that are scent or taste signals especially common among mammals and insects, often relate to reproduction male silkworm moth can detect female’s pheromones from miles away honey bee queen pheromones inhibit reproduction in workers minnows release pheromones when injures, which cause increased alertness in nearby minnows Experience and behavior (animals’ experiences during growth and development shape aspects of their adult behavior) o Cross-fostering study has young of one species raised by adults of another species. Studies found the adults’ behavior influenced the behavior of non-specific young they raised. o Twin study compares the behavior of identical twins raised apart with those raised together, allowing us to explore the affects of genetics and environment on adult behavior Some behaviors are mostly genetically determined (nature), while others can be shaped by environment (nurture) Learning: powerful method by which environment affects behavior o Imprinting: in offspring, the establishment of long-lasting behavioral response to a particular individual o Adaptive for species in which offspring and parents must recognize each other for survival 8 o Sensitive period: imprinting can take place only during this time in development; differs with species o Imprinting occurs on first object seen by young- usually their mother, but could be a person, puppet etc. important for efforts to sab endangered species (like whooping cranes) o Spatial learning and cognitive maps Every environment has spatial variation in locations of potential nest sites, mates, hazards, and food Spatial learning: establishment of a memory that reflects the environment’s spatial structure Cognitive maps: representations in nervous system of spatial relationships between objects in animal’s surroundings o Associative learning: ability to associate one environmental feature with another o Cognition: process of knowing that involves awareness, reasoning, recollection and judgment o Problem-solving: cognitive activity of devising a method to proceed from one state to another in the face of obstacles o Social learning: learning through observation of other o Culture: system of information transfer through social learning or teaching that influences the behavior of individuals in a population Evolution of foraging behavior o Foraging: any activities an animal uses to search for, recognize, capture, and eat food items Studies of fruit flies show that population density can affect the foraging behavior of its members 9 When population density is high, the allele that causes larvae to forage long distances is favored When population density is low, the allele that causes larvae to forage for short distances is favored Mating behavior and mate choice o Mating system: length and number of relationships between males and females Monogamy: one male mates with one female Polygamy: one individual of one sex mates with many individuals of the other sex Polygyny: one male mates with many females Polyandry: one female mates with many males o Sexual dimorphism: different appearances between sexes; in polygamous systems, the sex that attracts multiple partners is usually larger and showier o Mating systems and parental care: o Monogamous systems adaptive when young are helpless and require more food than a single parent could supply Both parents increase reproductive success when they cooperate in care o Polygamous systems adaptive when young are precocious Males maximize reproductive success by mating with many females; females able to care for young alone o Sexual selection and mate choice: o Sexual dimorphism results from sexual selection, a form of natural selection in which differences in reproductive success among individuals are consequence of differences in mating success 10 Genetic variation and evolution of behavior o Variation in single locus can cause drastic behavioral differences. Variation in behavior between species is common; variation among individuals of same species in different environmental conditions can indicate prior evolution Altruism: a behavior that reduces an animal’s individual fitness but increases the fitness of others in the population. Inclusive fitness: total effect an individual has on proliferating its genes by producing its own offspring and by providing aid that enables close relatives to produce offspring o Kin selection: natural selection that favors altruism by enhancing reproductive success of relatives Exchange surfaces and cells: 1. Net movement results when concentration gradient results in net movement of molecules. 2. Net movement of molecules is very slow, especially for distances greater than a few millimeters. Relationship between diffusion time and distance puts constraint on animal body plans. o Natural selection results in 2 basic adaptations that allow effective exchange for all cells Body size and shape that places many or all cells in direct contact with environment Allows each cell to directly exchange with surroundings Found only in invertebrates like cnidarians and flatworms A circulatory system o Moves fluid between each cell’s immediate surroundings and body tissues where exchange with environment occurs 11 o Found in all other animals o Types of exchange surfaces: 1. Ga strovascular cavities: in simple invertebrates without circulatory systems, this distributes molecules throughout the body 2. Circulatory systems 3 basic components: o Circulatory fluid o Interconnecting vessels o Muscular pump (heart) Open circulatory system/ found in arthropods and some molluscs: Fluid is hemolymph, which is also interstitial fluid that bathes body cells Heart pumps hemolymph through vessels into sinuses Exchange with body cells in sinuses Heart relaxation pulls hemolymph back through vessels Body movement sometimes squeezes sinuses and aids circulation Closed circulatory system/ found in annelids, cephalopods and all vertebrates Fluid called blood, different from interstitial fluid 12 Blood confined in vessels 1 or more hearts pump blood into larger vessels that branch into smaller and smaller ones, until they infiltrate organs chemical exchange between blood and interstitial fluid, and between interstitial fluid and body cells both types of circulatory systems are widespread, indicating each has evolutionary advantages in some environments lower pressure associated with open systems makes them less costly to maintain some invertebrates use pressure in open system to aid limb movement closed systems have relatively high blood pressure, enabling effective delivery of O2 and nutrients to cells of large, active animals closed systems good for regulating blood flow to different organs Organization in vertebrates o Vertebrate circulatory system often referred to as “cardiovascular system” because interactions between blood and gases o 3 main types of blood vessels; blood flows only one direction, distinguishing each type: 1. arteries: carry blood from heart to organs, branch into arterioles in organs, which take blood to capillaries 2. capillaries: microscopic vessels with thin, porous walls; networks called capillary beds take blood into tissues, where gas exchange occurs; eventually converge into venules, which converge into veins 3. veins: carry blood from organs to heart o heart muscular chambers (2 or more) 1. atria – receive blood entering the heart 13 2. ventricles – pump blood out of heart o single circulation blood passes through heart once in each complete circuit heart has 1 atrium and 1 ventricle muscle movement helps increase flow rate, which is otherwise slow because blood pressure drops in capillary beds found in fishes steps: 1. blood collects in atrium when entering heart, then transferred to ventricle 2. ventricle contraction pumps blood to gills 3. in gills, net diffusion of O2 into blood and CO2 out of blood 4. O2- rich blood leaves gills in capillaries, which converge into vessel that takes it to capillary beds throughout body 5. Deoxygenated blood returns to heart in veins o Double circulation Blood passes through heart twice in each complete circuit Single heart pumps blood through both circuits Provides fast blood flow to organs because heart repressurizes blood after it lost pressure going through capillary beds in lungs/skin Found in amphibians, reptiles, birds, mammals Steps: 1. Right side of heart sends deoxygenated blood to capillary beds of gas exchange tissues (lungs/skin) 2. Net movement of O2 into blood and CO2 out of blood 3. O2- rich blood goes to left side of heart, where contraction sends it to organs and tissues throughout body 14 4. Deoxygenated blood, nutrients, and wastes return to right side of heart Evolutionary variation in double circulation: o Amphibians have a 3-chambered heart Ridge ventricle diverts 90% 02-rich blood from left atrium to systemic circuit and deoxygenated blood from right atrium to pulmocutaneous circuit Animal can shut off blood flow when underwater, ineffective lungs Blood flow to skin continues underwater which is only a site of gas exchange This system allows amphibians to be submerged longer than they be able to otherwise o Alligators, caimans, crocodiles have 4-chambered heart Pulmonary and systemic circuits connect where arteries exit heart This allows arterial valves to shunt blood flow away from lungs while not breathing underwater o Birds and mammals have a same circulatory plan Heart has 4 chambers-2 atria, 2 ventricles Left side of heart receives and pumps only O2- rich blood Right side of heart receives and pumps only deoxygenated blood Does not allow animal to change blood flow to lungs without changing it throughout body 4-chambered heart evolve separately in birds and mammals, evidence of convergent evolution Mammalian circulation steps: 1. contraction of right ventricle pushes deoxygenated blood to lungs through pulmonary arteries 2. blood picks up O2 and unloads CO2 in capillary beds in lungs 15 3. Oxygenated blood travels from lungs to left atrium through pulmonary veins 4. Oxygenated blood travels from left atrium to left ventricle, which pushes it to organs through systemic arteries 5. Blood travels through systemic capillaries in organs, unloading O2 and taking up CO2 6. Deoxygenated blood comes from systemic capillaries in organs and enters right atrium, from which it is passed to right ventricle Cardiac cycle o flow of blood through heart is cyclic and beat is maintained by electrical nodes, not CNS o sinoatrial node is pacemaker and initiates impulse o atrioventricular node delays impulse to allow atria to empty Blood vessel structure and function o central lumen: cavity in center of vessels o endothelium: single epithelial cell layer inside vessels that reduces resistance to blood flow o capillaries have walls made only of endothelium, which makes them thin enough to allow diffusion o arteries and veins have 2 tissue layers surrounding endothelium: connective tissue and smooth muscle o walls of arteries and veins differ slightly arteries thicker and stronger arterial walls have elastic recoil that maintains blood pressure when heart relaxes unlike arteries, veins contain valves that prevent back- flow Maintenance of blood pressure o vasoconstriction: arteriole smooth muscle contracts, decreasing diameter, increasing pressure 16 o vasodilation: arteriole smooth muscle relaxes, increasing diameter, decreasing pressure Capillary function- capillaries lack smooth muscle so blood flow to the regulated by 1. arteriole constriction or dilation 2. constriction or dilation of smooth muscle ring at entrance to capillary bed Lymphatic system: returns fluid and blood proteins that diffused into tissues back into blood through capillaries fluid called lymph once in lymphatic system lymph composition similar to interstitial fluid foreign substances trapped in lymph nodes for immune system to deal Blood composition and function: blood considered a connective tissue o plasma: fluid matrix of blood, made of water and electrolytes o cells: blood contains cellular components erythrocytes: red blood cells, most numerous, carry O2, no nuclei, contain hemoglobin, shape increases surface area leukocytes: white blood cells, part of immune system, number increases when fighting infection platelets: no nuclei, function in blood clotting o blood clotting 1. break in blood vessel wall exposes proteins that attract platelets and initiate coagulation 2. coagulation converts liquid components of blood to solid clot 3. coagulant circulates in inactive form called fibrinogen 4. fibrinogen converted to fibrin when instructed by clotting factors 5. fibrin forms threads that structure blood clot 17 6. anticlotting factors in blood usually prevent clots without injury Cardiovascular disease: disorders of heart and blood vessels o could be minor to life-threatening o inflammation important cause abnormally high inflammatory reaction can disrupt blood flow o cholesterol important low-density lipoproteins deliver cholesterol to cells, high concentration of these is a risk factor for disease high-density lipoproteins moves excess cholesterol from blood to liver, high concentration of these lowers risk Mammalian respiratory systems 1. air enters through nostrils, filtered by hairs, warmed, humidified and sampled for odors as it flows through nasal cavity 2. nasal cavity leads to pharynx, intersection where paths for food and air cross 3. when food is swallowed, larynx tips epiglottis over opening of trachea so food goes to stomach and not lungs 4. air passes from larynx to trachea 5. trachea branches into two bronchi, one to each lung 6. in lungs, bronchi branch into finer and finer tubes called bronchioles 7. alveoli are air sacs clustered at tips of smallest bronchioles, where gas exchange occurs Respiratory adaptations of diving mammals o greater volume of blood per unit body mass o higher concentration of myoglobin and hemoglobin o conserve O2 by swimming with little muscular effort o blood supply to muscles restricted o ATP made via fermentation o Lungs collapsible, reduces uptake of N 18 o Surfactants in lungs aid in post-dice re-inflation o Large body size allows for linger and deeper dives because of its affect on metabolism o Vascular plants: plants that have transport vessels for water, sugar, and minerals (grasses, trees, cacti) o Land plants usually live in two worlds Above: ground acquiring sunlight and CO2 for photosynthesis Below: ground acquiring minerals and H2O alllow to reproduce/grow o The earliest plants were aquatic algae that absorbed what they needed from water, they were small so transport was simple o First land plants were non-vascular and had photosynthetic shoots above shallow fresh water o Competition for light, H2O and nutrients intensified Taller plants with broad, flat leaves were better at absorbing light Increased surface are (mass, evaporation and demand for H20) Multicellular, branching roots were favored because they increased H2O uptake Taller shoots increase distance between shoots and roots, plants that could transport minerals, H2O and sugars had advantage o Vascular tissues Xylem: transports H2O and minerals from roots to shoots Phloem: transports products of photosynthesis from where they are made/stored to where they are needed 19 o shoot system: above-ground plant organs, stems and leaves o height and branching pattern affect light capture: taller plants avoid shading and branching in leaves increases surface area for capturing sunlight o plants have limited energy: plants that grow tall cant put as much energy into branching and plants with highly- branching shoots cant put as much energy into growing tall o phyllotaxy: arrangement of leaves on a stem; important for light capture. Determined by shoot apical meristem: very dominant meristems triangle-shaped less dominant apical meristems rounded o canopy: leafy portion of all plants in community o canopy depth: how many leaf layers from tip of canopy to bottom; affects productivity of each plant o self-pruning: nonproductive leaves that are shaded-out undergo programmed cell death and are shed o leaf orientation also a factor in light capture Roots, water and mineral acquisition o plants can adjust their roots to take advantage of nutrients in soil 20 o turgor pressure: pressure inside plant cell from intake of water; organelles push membrane against cell wall flaccid cell: limp because of water loss plasmolysis: severe case of water loss, cell membrane pulls away turgid cell: firm because turgor pressure keeps membrane pressed o aquapornis: control rate of osmosis across plant cell membranes by opening or closing, allowing more or less water to pass through; faster than diffusion alone o 80-90% of plant’s fresh mass is water o only 4% of fresh mass is inorganic substances essential for survival Macronutrients and micronutrients o essential elements: required for plant to complete its life cycle and reproduce; species-specific; 17 common to all plants o macronutrients: required in relatively large amounts o micronutrients: needed in tiny quantities o Mineral deficiency in nitrogen, phosphorus and potassium most common o Fertilization: addition of mineral nutrients to soil o Soil mismanagement: problem affecting food availability 21 o Soil ecosystem: not essential for plants to complete their life cycles o Soil texture: depends on size of soil particles, which arise from rock weathering topsoil: layer of soil from which plants acquire water and nutrients; composed of weathered rock particles and decomposing organic matter water and air both found in soil pockets loam: most fertile type of topsoil; composed of equal parts sand, silt, clay o topsoil mineral components nitrate NO3- Phosphate PO4 3- Sulfate SO4 2- Topsoil- organic components o Humus- decaying animal waste, and animal, plant, fungus, and bacteria matter Prevents clay particles from packing together Forms crumbly soil that retains water but is still porous enough to aerate roots Increases soil’s capacity to donate cations to roots Serves as reservoir of mineral nutrients that return gradually to soil as micro organisms decompose the organic matter Topsoil- Living components 22 o Bacteria, fungi, algae, insects, earthworms, nematodes, plant roots Plant nutrition o Decomposing plants provide most of nutrients for soil microorganisms o Living root secretions support microorganisms in near- root environment o Rhizobacteria: bacteria living in large populations in soil layer surrounding plants roots o Forms of N a plant can use: Ammonium and nitrate ions Nitrogen-fixing bacteria o Nitrogen fixation: converting atmospheric N2 into NH3 Plant nutrition and fungi o Mycorrhizae: “fungus roots”, mutualistic fungi associated with plant roots o Fungus has more than one role: 1. Increase surface are for water uptake 2. Supplies plant with phosphorous and other minerals absorbed from soil 3. Secretes growth factors that stimulate roots to grow and branch 4. Secretes antibiotics that protect plant from infection o Carnivorous plants is a misnomer: the plan gets sugars from photosynthesis, but minerals from animals because it lives in poor soil Plant responses to Internal and external stimuli Plant hormones: 23 o Function similar to animal hormones; transported in vascular system o Several hormones interact to affect growth and development Auxin: any chemical that promotes elongation of shoots. Produce mostly in shoot tips; transported only from tip to base of shoot and it is found In roots, but usually obtained from shoots o Causing cell elongation in developing shoots is one of auxin’s functions o Mostly binds to receptors in cell membranes o Rapidly alters gene expression, causing elongation cells to produce new proteins o Causes elongation cells to make more cytoplasm and wall material o Affects pattern formation of developing plant; spatial organization of plant organs Carries info about development, size, and environment of individual branches Reduces flow from a branch tells that the branch s being insufficiently productive, so lateral buds below are stimulated to grow o Interacts with other hormones to control apical dominance; application of auxin to decapitated shoot resuppresses lateral bud growth Cytokinins: chemical substances that stimulate cytokinesis o produces in actively growing tissue; roots, embryos, fruits 24 o interacts with auxin at certain concentrations to cause cell growth, division and differentiation shoots form if cytokinin level higher than normal roots form if auxin level higher than normal o slow aging of some plant organs inhibits protein breakdown stimulates RNA and protein synthesis mobilizes nutrients from surrounding tissues Gibberellins o affects cell elongation, fruit growth, seed germination o young roots and leaves major sites of production o stimulates stem and leaf growth by enhancing cell division and elongation o work with auxin to cause more stem elongation o must be present along with auxin to cause fruit to develop o important application is spraying of seedless grapes individual grapes grow larger internodes elongate, allowing more space between grapes more space means less likelihood of infection from yeasts o causes seed to break dormancy and germinate once water is taken up o in cereal seedlings, cause synthesis of digestive enzymes to utilize endosperms Brassinosteroids o cause cell division and elongation in stems at low concentrations o slow leaf abscission o promote xylem differentiation Abscisic Acid (ABA) o slows growth, often antagonizing actions of growth hormones 25 o ration of ABA to growth hormones determines whether growth occurs ABA and seed dormancy o presence of ABA inhibits premature seed germination o also causes production of proteins that help seeds withstand stresses of maturation o dormant seeds commonly germinate when ABA is removed or inactivated heavy rains wash it out to dormant desert seeds light level, cold period, or acidity inactivates it in some seeds low levels are adaptive for some species; red mangrove seeds germinate early because of low ABA ABA and drought tolerance o ABA accumulates in leaves causing stomata to close rapidly when plants begin to wilt o Reduce water loss and plant is likely to survive Ethylene: produce in response to stresses and as part of normal life cycle o Senescence: programmed death of certain cells, organs or entire plant o Apoptosis: process of cell death, burst of ethylene usually required o Leaf abscission: detachment of leaf from stem following apoptosis during senescence Prevents dessication during winter in trees Nutrients taken from leaves and stored in stems Nutrients recycled into new leaves in spring o Bursts of ethylene triggers fruit maturation. One ripe, mature fruits attract animals which eat them and disperse the seeds in their droppings Photomorphogenesis: key events in plant growth and development that are trigger by light 26 o Etiolation: morphological adaptations for growing in darkness o De-etiolation: when stem reaches light, shoot growth slows, leaves expand, roots elongate, chlorophyll produces Blue-light photoreceptors o Light in the blue wavelengths initiates: Growth toward light source Light-induced stomatal opening Light-induced slowing of hypocotyl elongation Phytochromes o Detect red light wavelengths Red light instigates germination Far-red light inhibits germination Phytochromes and shade avoidance o Provide info about light intensity. They can detect the difference in ration of red to far-red light resulting from shading of other plants o When plant that needs bright sunlight is shaded, phytochromes trigger greater energy on growing tall o When tree is exposed to right intensity of sunlight, phytochromes inhibit vertical growth and stimulate branching Circadian Rhythms: 24-hour schedule processes o Opening and closing stomata o Production of photosynthetic enzymes o Raising and lowering leaves o Opening and closing flowers Photoperiodism: physiological response to photoperiod; on annual time Scale. Flowering schedule is important: o Short-day plants bloom when day length is below certain threshold; usually summer, fall, winter 27 o Long-day plants bloom when day length is above a certain threshold; usually in late spring, early summer o Day-neutral plants are unaffected by photoperiod and flower when they reach a certain stage of maturity, regardless day length Flowering hormone o Leaves detect changes in photoperiod and produce signaling molecules that trigger flower bloom Tropisms: any growth response that results in plants curving towards or away from stimuli o Phototropism: light Positive: plant organs grow toward light (shoots) Negative: plant organs grow away from light (roots) o Gravitropism: gravity Useful for roots and shoots that start to grow underground, where light can’t reach. Roots display positive gravitropism and shoots negative Response occurs as soon as seed germinates and organs grow in appropriate direction no matter how seed is oriented when it lands Statoliths: dense cytoplasmic components that settle to lower portions of cell in response to gravity o Thigmotropism: touch or other mechanical perturbation. Several forms: Trees in windy habitats grow shorter and ticker than their sheltered conspecifics, making them better able to resist strong winds Plants use objects fro climbing have positively thigmotropic organs Plants that close when touched, possible to protect themselves from damage or herbivory, are negatively thigmotropic Envronmental stress: important factor determining geographic ranges of plant species 28 o Abiotic stress: caused by non-living things like heat, light, water o Biotic stresses: caused by living things like herbivores, pathogens o Drought: close stomata, close leaves, drop leaves o Flood: produce ethylene that causes death of some cells, which then provide air to submerged roots o Heat: heat-shock proteins produced during high temperatures, which protect other proteins from being denatured o Cold: increase unsaturated fatty acids in cell membranes 29
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