Plant Growth AP Biology Growth in Animals Animals
Plant Growth AP Biology
Growth in Animals § Animals grow throughout the whole organism u AP Biology many regions & tissues at different rates
Growth in Plants § Specific regions of growth: meristems stem cells: perpetually embryonic tissue u regenerate new cells u § apical shoot meristem w growth in length w primary growth § apical root meristem w growth in length w primary growth § lateral meristem w growth in girth w secondary growth AP Biology
Apical meristems AP Biology shoot root
Root structure & growth AP Biology protecting the meristem
Shoot growth § Apical bud & primary growth of shoot region of stem growth u axillary buds u § “waiting in the wings” protecting the meristem Young leaf primordium Apical meristem Older leaf primordium Lateral bud primordium AP Biology Vascular tissue
Primary xylem Growth in woody plants Primary phloem § Woody plants grow in height from tip u u Epidermis Lateral meristems primary growth apical meristem § Woody plants grow in diameter from sides u u secondary growth lateral meristems Primary phloem Secondary Primary xylem § vascular cambium w makes 2° phloem & 2° xylem § cork cambium w makes bark Annual AP Biology growth layers Bark
Secondary growth § Secondary growth u growth in diameter § thickens & strengthens older part of tree u cork cambium makes bark § growing ring around tree u vascular cambium makes xylem & phloem § growing ring around tree AP Biology
Vascular cambium Why are early & late growth different? § Phloem produced to the outside § Xylem produced to the inside bark cork cambium phloem xylem vascular cambium AP Biology late early last year’s xylem
cork cambium Woody stem How old is this tree? vascular cambium late early 3 2 1 xylem AP Biology phloem bark
Tree trunk anatomy tree girdling What does girdling do to a tree? AP Biology Aaaargh! Murderer! Arborcide!
Where will the carving be in 50 years? AP Biology
Plant hormones § auxin § gibberellins § abscisic acid § ethylene § and more… AP Biology
Auxin (IAA) § Effects controls cell division & differentiation u phototropism u § growth towards light § asymmetrical distribution of auxin § cells on darker side elongate faster than cells on brighter side u AP Biology apical dominance
Gibberellins § Family of hormones u over 100 different gibberellins identified § Effects stem elongation u fruit growth u seed germination u AP Biology plump grapes in grocery stores have been treated with gibberellin hormones while on the vine
Abscisic acid (ABA) § Effects slows growth u seed dormancy u § high concentrations of abscisic acid w germination only after ABA is inactivated or leeched out § survival value: seed will germinate only under optimal conditions w light, temperature, moisture AP Biology
Ethylene § Hormone gas released by plant cells § Effects fruit ripening u leaf drop u § like in Autumn § apoptosis One bad apple spoils the whole bunch… AP Biology
Fruit ripening § Adaptation u u hard, tart fruit protects developing seed from herbivores ripe, sweet, soft fruit attracts animals to disperse seed § Mechanism u triggers ripening process § breakdown of cell wall w softening § conversion of starch to sugar w sweetening u positive feedback system § ethylene triggers ripening § ripening stimulates more ethylene production AP Biology
Apoptosis in plants § Many events in plants involve apoptosis u response to hormones § ethylene § auxin u death of annual plant after flowering § senescence u differentiation of xylem vessels § loss of cytoplasm u AP Biology shedding of autumn leaves What is the evolutionary advantage of loss of leaves in autumn?
Responses are critical for plant success Tropisms—growth of plant organs toward or away from stimuli § Phototrophism § Gravitropism § Thigmotrophism Other Stimuli u Turgor movements u Environmental stress AP Biology
Phototropism § Biological clocks control circadian § rhythms in plants—cycle with a frequency of about 24 hours Set due to environmental signals u AP Biology Most cued by light-dark cycle resulting from earth’s rotation
Photoperiodism synchronizes plant response § Plants detect the time of year by the § photoperiod Photoperiodism controls flowering Critical night length 1. If daytime is broken by brief peroids of darkness—plants flower (summer) 2. If night is interrupted by short exposure to light—plants do not flower (winter) u AP Biology
Phytochromes § Photoreceptors in many plant responses § to light and photoperiod—help to measure length of darkness in a photoperiod Phytochromes alternate between two photoreversible forms: Pr—red absorbing u Pfr—far red absorbing u AP Biology
Phytochromes entrain biological clock § Pfr gradually reverts to Pr when light not present Decrease in Pfr = night u Increase in Pfr = day u AP Biology
Gravitropism § Orientation of a plant in response to gravity Roots display positive gravitropism— curve down u Shoots display negative gravitropism— curve upward u AP Biology
Thigmotropism § Directional growth in response to touch AP Biology
Turgor movements § Rapid, reversible plant responses Rapid leave movements—travel from the leaf that was stimulated to adjacent leaves along the stem u Sleep movements—lowering of leaves to a vertical position in evening and raising of leaves to a horizontal position u § Due to daily changes in turgor pressure AP Biology
Responses to Environmental Stress § Water Deficit § Oxygen Deprivation § Salt Stress § Heat Stress § Cold Stress AP Biology
Water Deficit § Leaves and roots have control systems to cope with water deficits Leaves—reduce transpiration u Roots—reduce growth u AP Biology
Oxygen Deprivation § Water logged soil lacks air spaces that § provide oxygen Some plants form air tubes that extend from roots to the surface AP Biology
Salt stress § Excess salt in the soil § can cause a water deficit in the plant and have toxic effects on the plant Plants produce compatible solutes that keep the water potential of cells more negative than the soil solution. AP Biology
Heat Stress § Transpiration helps plants respond to § excessive heat—which can denature the enzymes and destroy the metabolism of the plant. Plants can produce heat shock proteins when exposed to excessive temperatures—back up to transpiration AP Biology
Cold Stress § Cold causes a change in the fluidity of § § cell membranes Subfreezing are the most severe form of cold stress because ice crystals begin to form in the plant Plants respond by altering the lipid composition of their membranes AP Biology
Defense against herbivores § Plants defend themselves both physically and chemically: Physical—thorns and spines u Chemical—distasteful or toxic compounds u Recruit predatory animals to help defend u AP Biology
Defense against pathogens The hypersensitive response (HR) contains the infection by: § Photoalexins—antimicrobial compounds released from wounded cells § Activation of genes encoding pathogen resistant (PR) proteins –act as signals to adjacent cells § Lignin synthesis and cross-linking of cell walls—actions aimed at isolating the infection. AP Biology
AP Biology
Don’t take this lying down… Ask Questions!! AP Biology 2007 -2008
- Slides: 37