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Exam 4, Structure modifications, Pollination syndromes: trait…
Exam 4
Seeds
Origin
Seed Plants
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Earliest Seed
- Elkinsia polymorpha
4-5 lobes fused basal third
- Late Devonian (W. Virginia)
- Pseudosporogonites quadrapartitus
Primitive ovule
- Lobate integuments
Free from nucellus/ megasporangium
- Moresnetia zalesskyi
8-10 lobes fused at chalaza and widely separated
Enclosed ovule
- Complete enclosure of megasporangium within integument
-Increased protection
--Desiccation
--Herbivory
- Stamnostoma huttonense
- Gnetopsiselliptica
Ovule evolution
- Evolved from shoot ape
- Gymnosperm nucellus apex similar to shoot apex
- Similar genes
Innovations
- Heterospory
- Protection
Integuments
- Pollen capture
--Pollen chamber
--Micropyle
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- Seed ferns (extinct)
- Gymnosperms
-Progymnosperms (extinct)-
- Angiosperms
Steps
Heterospory
- Megaspores
-Megagametophyte
- Microspores
-Microgametophyte
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Microgametophytes
Antheridia
- Sperm development within antheridia
- Sperm rely on water for swimming to archegonia
Pollen
- Microgametophyte
- Dispersal no longer requires water
- Exine prevents desiccation
- Some with air bladders
- Transport by wind
Haustoria pollen tubes
- Tubes feeding on nucellus
- Provide nutrients to developing sperm
- Can be a lengthy process from pollination to fertilization
Direct delivery
- Direct delivery of sperm to the megagametophyte
- Pollen tube
-Directed by synergids
-Feeds on nucellus (gymnosperm)
-Feeds on style (angiosperm)
Reduced
- Angiosperm, 3-celled
Tube cell
Generative cell
- Microspore within microsporangium
- Mitosis within microspore wall
- Endosporic male gametophyte = pollen grain
Ovule Diversity
Gymnosperm
- Megasporangium is nutritious tissue = nucellus
- Nested doll
- Integument (1)
- Megaspore wall
- Megasporangium
- Archegonium
Pine Ovule
- Ovule on megasporophyll
- 1 microsporocyte
- Pollen chamber
- Nesting doll
Integument
Nucellus
Megaspore wall
Megagametophyte
Archegonium
Egg
Angiosperm Ovule
- 2 integuments
- Megasporangium = nucellus
- Megasporocyte reduced to one
- Megaspore reduced to one and retained
- Megagametophyte = egg sac
- Furniculum
Gymnosperm vs Angiosperm
- Both single megasporocyte
- Both single megaspore
- 1 integument, 2 integuments
- Unique to Angiosperm
Additional protection from ovary wall
Double fertilization
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Seeds
Advantages
- Increased independence from free water reproduction - Enabled colonization of drier upland habitats
- Enabling advanced reproductive traits
Gymnosperm
- Pine example
Some with fleshy outer layer (aril)
- Several cotyledons
- Integument becomes seed coat
Double-fertilization
- Pollen tube grows down style
- Generative cell divides into 2 sperm
- Pollen tube ruptures inside synergid releasing sperm
- One sperm fuses with egg
2n diploid
- One sperm fuses with polar nuclei
3n triploid
Endosperm
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Monocot
- One cotyledon = scutellum
- Large amount of endosperm
- Corn example
- Integuments become seed coat
Eudicot
- 2 cotyledons
- Large amount of endosperm
- Integuments become seed coat
- Bean example
Fruits
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Seed dispersal
Syndromes
- Wind
- Water
- Animal
--Active
--Passive
- Self
Wind
- Wings
- Parachutes
- Lightweight seeds
Water
- Buoyant
- Large airspaces
- Example coconut
Animal, active
- Fleshy
- Provide animal with nutrients
- Long-distance dispersal
- Seed pass through gut without harm
- Seeds are regurgitated later
- Ends up in a nice little pile of nutrient dense excrement
- Ants with elaiosome (lipid based nutrient rich)
Animal, passive
- Hooks
- Catch on fur
- Catch on hoof
- Velcro
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- The defining characteristic of the angiosperms is the carpel
- Angio from angeion meaning vessel in greek
Sperma meaning seed
- The carpel contains ovules which develop into seeds after ferilization
- The carpel develops int the fruit wall
modifications
Carpel position
- Whorls inserted relative to
ovary
-Superior
-- Carpel above
Inferior
-- Receptacle surrounds carpel
-- Carpel below
- Perianth & stamen insertion
-Hypogynous
-- Perianth & stamens on receptacle beneath ovary
-- ex lilies
- Epigynous
-- Perianth & stamens from top of ovary
--ex apple flower
- Perigynous
--Perianth & stamens adnate to calyx
-- ex cherry flower
Imperfect flowers
- Lacking a whorl of sexual organs
- Hermaphroditic = perfect
- Monoecious = male flowers and female flowers on the same plant
- Dioecious = male flowers on plant, female flowers on different plant
Male = androecious
Female = gynoecious
Display variation
- Inflorescence
- Taxonomic importance
- Various ways to ensure cross pollination
Major traits
- Color
- Smell, organic volatiles
- Shape
- Bloom time
- Rewards, eg nectar
Color
- Some colors are more attractive than others
- Color requires resource
--Omit when unnecessary
- Some are in the uv spectrum
Scent
- Signal to pollinators
- Sometimes use own preferences and sexual pheremones
- Some common chemicals
Benzaldehyde (almond)
Linalool (lavender)
Limonene (citrus)
Beta ocimene (green)
- May have scent glands
eg roses
Shape
- Floral symmetry
- Actinomorphic
Radially symmetric
eg sunflower
- Zygomorphic
Irregular
Bilateral
eg pea
Blooming time
- Diurnal
Day time
- Nocturnal
Night time
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Origins
Ancestral flower
- Based on molecular data
- Bisexual
- Radially symmetric
- Multiple whorls of petals
- Androecium
- 2+ whorls of anthers
- Gynoecium
5+ carpels
First flower fossil
- Archaefructus sinensis
- Likely herbaceous
- Likely aquatic
124.6bya
Most primitive extant
- Amborellaceae
- Amborella
- Amborella trichopoda
- New Caledonia
- Dioecious
Male plants
Female plants
- Shrub
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Basic Structure
Perfect, complete flower
- A flower is a stem with leaf-like structures.
- Complete flowers have all four floral appendages:
Sepals, sterile
Petals, sterile
Stamens, male fx
Carpels, female fx
- Incomplete flowers lack at least one appendage
Sepals
- Sepals are the outermost floral appendage.
- Are modified leaves that surround maturing flower parts.
- Protect the flower bud as it develops.
- May be colorful.
- All the sepals together are referred to as the calyx.
Petals
- Petals are located above the sepals on the receptacle.
- Are leaf-like but contain pigments other than chlorophyll.
- Attract pollinators.
Collectively are a corolla.
- Sepals and petals collectively are a perianth.
- Absent in wind-pollinated species.
Stamens
- Stamens occur above the petals.
- Are collectively the androecium.
- Two parts: anther and its supporting filament
- Diploid anther cells (microsporocytes) undergo meiosis to produce four microspores.
- Microspores
Undergo mitosis
form a resistant cell wall
- Microgametophyte
Pollen grains
Carpels
- Megasporophyll
- Carpels, collectively, are the gynoecium.
- Stigma catches pollen grains.
- Style elevates the stigma.
- Ovary where megaspores are produced.
- Within the ovary are placentae bearing small structures called ovules
- After fertilization of the egg, ovules mature into seeds.
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