botany exam 2

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catastrophism

the theory that changes in the earth's crust during geological history have resulted chiefly from sudden violent and unusual events

james hutton

1785; uniformitarianism, gradual change, forces today=forces in the past

alfred wegener

continental drift, pangea broke up 200 mya, matching fossil record

main criticism of wegenger

no mechanism for continental drift, plate tectonics provide explanation

key to understanding plate tectonics

internal structure of earth

order of earth’s layers

inner core, outer core, mantle, crust, lithosphere

inner core

hot, solid due to high pressure

outer core

molten iron

mantle

mostly solid rock of iron and magnesium-silicate (flows slowly)

crust

mostly granite (continents) and basalt (oceans)

lithosphere

crust + upper mantle, broken into ~20 plates that can move over plastic mantle

how old is earth

4.5 billion yrs old (Ga)

earliest microfossils

stromatolites (3.5 Ga)

earliest evidence for life

cyanobacteria (2.7-2.1 Ga)

algae-like plants arose

1 billion yr ago

when do embryophytes (early land plants) emerge

mid-Ordovician (470 mya)

embryo

zygote protected by female gametophytes, essential for survival on land

alteration of generations

-haploid gametophyte (makes gametes)

-diploid sporophyte (makes spores)

agents of dispersal

spores, then seeds

when did vascular plants appear

late Silurian/early Denovian (~420 mya)

when did seed plants first appear

Denovian (~380 mya)

heterospory

producing 2 types of spores:

-megaspores: retained by sporophyte, protects embryo

-microspores: travels to fertilize megaspore

domestication syndrome

selection by humans leads to phenotypic traits not adaptive in the wild

-loss of dormancy, synronous flowering, change in abcission, etc.

-domesticated plants are dependent on people for their survival

landraces

diverse varieties that arose from mutation and hybridization. they differ in adaptations to environments & culinary uses

Nikolai Valivov

-lower resilience of domesticated plants compared to wild (proposed interbreeding)

-collected germplasm, observed 8 identifying centers of origin for domestication

centers of origin

1. china

2. Indo-Malay, Indo burma

3. Central Asia

4. Fertile Crescent

5. mediterranean

6. ethiopia

7. mesoamerica

8. andes, chile, Chaco-Pantanal

populations

basic unit of ecology; a group of freely interbreeding individuals of the same species in the same habitat

species can have multiple populations

life spans

-annual: completes life cycle (seed to seed) w/i 1 year or less

-biennial: tends to live for 2 years. first year grows roots and leaves; second year, long stems and flowers. dies after setting seed

-perennial: lives several years and (usually) flowers several times.

life history patterns

-semelparous: reproduces only once in its lifetime (annuals, biennials, some perennials), spend 25% of stored energy into massive reproductive event

-iteroparous: reproduces many times during life, most perennials. spends 5-15% of energy in each event, non-reproductive juvenile stage

sexual strategies

-hermaphroditism: flowers with both male & female gametes

-monoecious: plants w/ both male & female flowers

-dioecious: plants with either male or female flowers

life history strategies ( r/K)

r selections: many offspring, low investment, most die before maturity, short life, superficial relationships, low individuality, commodities (dandelion)

K selection: few offspring, high investment, most mature, long life, rich relationships, high individuality, brands (humans)

microenvironment

localized changes in light availability, moisture, nutrients, etc

floristic kingdoms

holarctic (northern hemisphere mostly)

south american

african

indo-pacific

australian

biomes

-tundra: small-sized plants adapted to short seasons

-taiga: conifer forests

-deciduous forests: broad-leaf temperate forests

-grasslands: prairies, steppes, savannah, pampas

-shrublands

-desert: plants further apart

-tropical forests: humid & warm, highest diversity

environmental factors

the distribution of an organism is defined by its reaction to individual external influences

biotic factors

resulting from interactions with other organisms (herbivory, infection, symbiosis, competetion, etc)

abiotic factors

includes parameters (temp, pH, humidity), and resources (light, water, minerals), that determine growth, as well as those that can add stress (pollutants)

limiting factors

one environmental factor at suboptimal level can limit plant processes

stress

occurs when essential factors, such as light, water, O2, are at an inappropriate level (higher or lower)

environmental noxa

factors that trigger stress at any concentration (heavy metals, pollutants)

state of latent life

when intensity or concentration of stress factors is too high or low, organims enter this state where minimal life processes occur

dormancy

an adapted latent life stage triggered by environmental cues. involves physiological changes

avoidance strategy

seeds and spores allow annual/ephemeral plants to avoid moments of highest environmental stress

mesophiles

plants require moderate temperatures to grow

hardening

process by which tolerable stress levels trigger plant to prepare for extreme conditions

adaptations to high temps: changes in leaf

-surface: hairs can reduce evaporation & reflect intense sunlight

-size: smaller, thicker leaves help minimize effect of light intensity

-angle/position: some species can move leaves to reduce exposure to sunlight

adaptations to high temperature

-transpiration: increased water exhalation through stomata can help maintain the plant cooler than surrounding enviro

-shading: plants use some structures to protect others from direct sunlight

-avoidance strategy: in hot enviro, many species are short-lived annuals (ephemeral), avoiding worst conditions

adaptations to cold temps

-rosette/low grounding plants: protected against weight of snow and environment (warmer closer to ground)

-evergreen plants: high concentrations of sugar in leaves act as anti-freeze

-deciduous plants: leaf abscission and bud scales to protect axillary meristems

sunlight is captured by

chlorophyll molecules located in thylakoid membranes of chloroplasts

how can light become an environmental stressor

too low: negative energy balance; not enough photosynthesis to cover plant’s metabolic requirements

too high: unused energy can lead to oxidative stress

how can plants adjust to light intensity

by changing position of leaves

ferns and mosses move chloroplasts to different parts of the cell

pulvini

joint-like thickening at base of leaves that allows for movement of leaves

sun leaves

smaller & thicker, with well-developed mesophylls and several layers of palisade cells. epidermal hairs might minimize excess sunlight

shade leaves

larger & more tender, with weakly developed mesophylls. epidermal cells might act as lenses to increase light capture

sun leaves: subcellular

chloroplasts with small grana & few stromal thylakoids (A)

photosystem: small proportion of antenna & many rxn centers

shade leaves: subcellular

chloroplast with large grana and many stomal thylakoids (B)

photosystem: large proportion of antenna & few rxn centers

stolons (runners)

aboveground stems, emerge from crown and bend downwards; develop plantets where they touch the ground

stoloniferous rhizomes

belowground stems, upright shoots develop from axillary buds in nodes; adventitious roots in underside

suckers

upright shoots growing from horizontal roots (adventitious shoots)

searching for light: spreading

stolons, stoloniferous rhizomes, suckers

searching for light: climbing

-twiners: stems of vines that grow in spirals around objects, supports itself

-tendrils: modified lead or short stem that wraps around objects they touch, provide support for main stem

-adhesive pads at the tips of tendril-like short stems, allow plants to attach to walls

searching for light: growing tall

in soft, wet soils, plants form supportive roots to help them grow taller.

buttress roots are wedge shaped, tall and wide; they prevent shallow-rooted trees from falling over

prop roots: adventitious/aerial roots that arise from the trunk and grow downwords to provide support in shifty conditions (mangroves)

searching for light: stealing light

epiphytes: grow in wet areas. use their roots to grasp tree branches

lianas: typically in rainforests; woody, creeping vines that spread through the canopy spreading their leaves to the sun

Raunkiaer’s approach

proposed sequence of kife forms based on how they deal with protecting their meristem. while temp is important, growth form is the consequence of multiple interacting factors.

where did photosynthetic organisms originate

in water

adapting to life on land required

-reproducing in dry environment: alternation of generations, heterospory, seeds

-structural support

-acquiring water and transporting it throughout the organism

-avoiding desiccation

order of evolution

-evolution of cuticle to prevent desiccation in nonvascular plants

-evolution of lignin and vascular system → vascular plants

-evolition of heterospory and seeds

how does water move in plants

-vascular tissue provides conduit for water to move from soil to leaves

-water potential differences across plant and environment allow water to travel against gravity

water potential Ψ

-osmotic potential (Ψn): from dissolved solutes- major component in cells

-pressure potential (Ψp): from hydrostatic and pneumatic pressures (turgor)

-matric potential (Ψm): cohesive forces of water to other objects

-gravitational potential (Ψ g): gravity

pathway of water

moves from high to low Ψ; less negative to more negative

gradient in Ψ

provides driving force for water to move from soil through plant into atmosphere. and evaporation from soil

mesophytes

grow in regions with moderate soil moisture. affected by short, mild water shortages, respond by closing stomata

xerophytes

grow in regions with frequent, extended droughts. possess adaptations to balance photosynthesis with water conservation

hygrophytes

grow in areas almost permanently saturated with water, must deal with hypoxic conditions

adaptations to drought

-shading: some parts shade other parts from sunlight to reduce photosynthesis and evaporation

-avoidance strategy: long-term seed dormancy can help plants avoid extensive droughts

-leaf abscission during dry season: helps minimize photosynthesis

-vegetative dormancy: some herbaceous plants die back during dry season and only retain belowground structures

bulb

short, flattened stem-bearing, fleshy leaves (food storage)

corm

short, swollen underground stem with thin, scaley leaves protecting it

cormlets: asexual reproduction

fleshy rhizome

thick underground horizontal stem, serves as water and food storage

tuber

enlarged tip of a rhizome containing stored foods

morphological adaptations of xerophytes

-roots: greater root-to-shoot ratio than mesophytes; shallow and extensive to take advantage of brief rains & deep roots reaching water table

-succulent tissue in leaves or stems: reduced surface-area (less water loss & increased water storage capacity)

-photosynthetic stems: can be only photosynthetic organ or secondary for drought

physiological adaptations of xerophytes

-leaf abscission: water deficit may trigger hormonal changes that cause abscission of older leaves to preserve water for younger ones

-osmoregulation: ssynthesis of solutes to lower water potential of cells; preventing loss of turgor (used by some halophytes)

-resurrection plants: plants survive cellular desiccation via coordinated modification of cytoplasm & cell membrane

CAM photosynthesis

crassulacean acid metabolism; specialized form of C4 photo

temporarily separates absorption of CO2 at night from light/Calvin cycle at daytime

stomata open at night to minimize water loss & carbon is stored as Malic acid in vacuole and converted to CO2 during day.

hypoxia

occurs in flooded soils

-O2 diminished by water filling air in soil pores

-lots of flooding compacts soils & reduces aeration

-in hypoxic soils, bacterial anearobic metabolism produces toxic waste products

waterlogging

only the root system is under anaerobic cond

partial submergence

up to part of shoot covered in water

physiological responses to hypoxia

closure of stomata & reduced photosynthesis

reduction of water uptake: closure of aquaporins; can lead to drought-like responses, such as leaf abscission

morpholigcal adaptations for hygrophytes

-aerial root formation (adventitious roots above water can transfer O2 to submerged roots)

-cypress knees: vertical protuberances of roots that serve role of aerial roots

-aerenchyma

-lenticels (form in aerial roots & lower parts of stem to allow for O2 intake)

aerenchyma

modified spongy parenchyma that allow for gas exchange b/w shoots and roots; form in root cortex

-lysigeny: collapse & death of cells in the cortex

-schisogeny: expansion of intercellular spaces

-expansigeny: cell divsion & expansion

anatomical & physiological adapatations of hygrophytes

-radial O2 loss (ROL) barrier: prevents diffusion of O2 to anoxic soil (retains O2 in root)

-fermentative bypasses: ameliorate poisoning via accumulation of toxic byproducts

-activation of antioxidant enymes: helps buffer accumulation of reactive oxygen species

plants lack an immune system, so they rely on

-structural/physical defenses

-biochemical defenses

-protein-based defenses

biotrophs

pathogens that keep the host alive & feed on living tissue

necrotrophs

pathogens that overwhelm plant defenses, generating a quick release of nutrients

hemibiotrophs

behave as biotrophs during early stages of infection, but then become necrotrophic

host-range

species that can be affected by a pathogen

disease resistence exists in a spectrum

immunity: complete lack of any disease symptom

high resistance: some disease symptoms

high susceptibility: major disease symptoms

surveillance & detection

innate immunity (basal resistance): first line of defense. recognition of molecular patterns from pathogen trigger fortification of cells

hypersensitive response: second line, it involves the deliberate cell death to isolate the infected area

systemic acquired resistance: long-term response; resources mobilize to protect the plant from any future infection (non-specific)

types of herbivores

granivores: feed on seeds

grazers: feed on grasses & ground-growing plants

browsers: feed on leaves from trees and shrubs

frugivores: feed on fruits

elicitors

molecular patterns that allow plants to recognize damage from pests; release of VOC’s

volatile organic compounds

-repel harmful organisms

-attract beneficial organsisms

-can trigger immune responses in neighboring, undamaged plants

structural /physical defenses

first line of defense, make it difficult for herbivores to eat a plant & block the entrance of pathogens

includes cell walls, cell modifications, & physical structures