Transcript Seed - Hobbs High School

Plants
Plant Evolution
• Green plants are believed to have developed from a
single species of freshwater algae
• Green algae split into 2 major clades
– Chlorophytes – never made it to land
– Charophytes – did!
DOMAIN: Eukarya
Kingdom PLANTAE
• Basic characteristics
– Eukaryotic (cell type)
– Multicellular (level of organization)
– Non-motile (motility)
– Photosynthetic autotroph (mode of nutrition)
– cellulose (cell wall composition)*
– alteration of generation (sexual life cycle)
• Multicellular haploid and diploid phases
• Protected embryos
- Primarily terrestrial
- Well-developed tissues
- Protects developing embryo from drying within
female structure
- Contains chlorophylls a and b (*), & carotenoid
pigments inside organelles called chloroplast
- Stores food as starch (*)
• Advantages for plants being land-dwelling:
– Increased light availability
– Increased amount of CO2
• Both required for photosynthesis
• Disadvantages for plants being land-dwelling:
– Increased water loss
– Increased gravitational pull to overcome
• Required adaptations to live on land
– Protection from desiccation (loss of water to air)
• Waxy cuticle - decreases water loss but not found in
roots
• Stomata - found on leaves – can open and close to
decrease water loss
– Water transport and Support (against gravity)
• Tracheids – special cells that transport water/mineral
• Vascular Tissue - provides support and helps over
come gravitational pull
– Reproduce without dependence on external water
• Pollen and protected embryos
•
•
•
•
•
•
•
•
•
Diploid - Denotes full set of chromosomes; 2n
Haploid - Denotes half set of chromosomes; n
Gametes - Sex cells; “n”; e.g. sperm and ova
Zygote - First structure formed after fertilization; “2n”
Meiosis - Process that produces spores & reduces the
number of chromosomes by half (2n  n)
Fertilization - Process that restores the number of
chromosomes (n  2n) as a result of the fusion of egg
and sperm nuclei
Mitosis - Process that gametophytes use to produce
gametes & that the zygote matures into the
sporophyte generation
Sporophyte - Generation that produces spores; “2n”
Gametophyte - Generation that produces gametes; “n”
Mitosis
Sporophyte Generation
(2n)
Zygote (2n)
Sporangium (2n)
Diploid (2n)
Fertilization
Meiosis
Haploid (n)
(n) (n)
Spore (n)
Gametes
Mitosis
Gametophyte Generation
(n)
Mitosis
Alternation of Generations
• Sporophyte makes haploid spores by meiosis
• Spores under go mitosis to create the
multicellular gametophyte
• Gametophyte produces gametes by mitosis
• Gametes fuse to form a diploid zygote
• The zygote under goes mitosis to create
multicellular sporophyte
– NOTE: Dominant stage (sporophyte or
gametophyte) depends on the type of plant
Phylum Bryophyta (e.g. mosses)
• Non-vascular Plants = bryophytes
• Closest living descendants of the 1st
land plants
– Examples: hornworts, liverworts,
mosses
• Gametophyte generation is
dominant
• Sporophyte produces windblown
spores (homosporous) and is
dependent on the gametophyte for
nutrition
• Male gamete (flagellated sperm) must swim from the
antheridia to the female archegonia therefore, bryophytes
are water dependent for the fertilization process.
• Zygote is protected in the archegonia from drying out.
• Because they lack vascular tissue, they lack true roots, stems
and leaves.
• ‘Leaf-like’ body is covered with a waxy cuticle to prevent
water loss.
• Gametophyte absorbs nutrients and is anchored by ‘root-like’
structures.
• Sporophyte generation (2n) is considered nutritionally
dependent (parasitic) on the gametophyte generation (n).
• Sporophyte produces windblown spores that disperse the
species.
• Why are non-vascular plants considered
dependent on water/moist environments?
– Produce flagellated sperm
• Why does their vegetation remain “low-lying”?
– Absorb nutrients but lack vascular tissue for
transport
– They have the capacity to absorb a large amount
of water.
• Economic importance:
– Peat moss – gardening and fuel
• NOT mosses:
– Irish moss (red algae); reindeer moss (lichen);
Club moss (vascular); Spanish moss (angiosperm)
• Vascular Plants = tracheophytes
– Most diverse and widely distributed
– Sporophyte generation
• Possess the vascular tissues xylem & phloem - “Xylem
Up - Phloem down”
• Possess true roots, leaves, and stems
• Dominant generation
• Produces spores (homosporous) (ferns)
– Gametophyte generation is avascular (non-vascular);
Reduced
– Grouped by if they produce spores (seedless) or seeds
to disperse species
• Vascular Seedless Plants (spores used for
dispersal of species)
– Examples:
• club mosses, spike mosses – lycophytes
• whisk ferns, horsetails, and Ferns - pterophytes
Phylum Pterophyta (e.g. ferns)
• Gametophyte generation (n) produces
gametes
• Structures associated with heart-shaped
gametophyte generation:
– Antheridia - male structure that produces
flagellated sperm
– Archegonia - female structure that produces ova
– Fertilization is water dependent (e.g. male
sperm must swim from antheridia to the female
archegonia).
• Sporophyte generation(2n) produces windblown
spores for dispersal of species
• Structures associated with sporophyte generation:
– Fiddlehead - young curled-up fronds that grow out of
underground stems
– Frond - refers to “leaf” that contain many leaflets
– Sporangia - sac-like structures where meiosis occurs and
spores (n) are produced
– Sori - sporangia collectively
• NOTE: Gametophyte generation is
nutritionally dependent on the sporophyte
generation.
• Economic Importance:
– Decorative greenery in floral arrangements
– House plants that are decorative and clean the
air
– Medical (used by Native Americans)
Seed Plants
• Seeds
– Protect embryo
– Easily dispersed
– Introduces a dormant phase to the life cycle
• Seed plants produce two kinds of
gametophytes
– Male gametophytes – pollen grains that are
dispersed by wind or pollinator
– Female gametophyte – develop in ovule
• Vascular Naked Seed Plants – Gymnosperms
(cone-bearing)
– Examples: cycads, ginkgo, gnetophytes, conifers
• Phylum Coniferophyta – (e.g. evergreens softwood trees)
• Life cycle includes heterosporogeny:
– Microspores produced in pollen or male cone
• Formed by meiosis in scales of male cone
• Develops into microgametophyte (pollen grain)
• Contains 2 nonflagelleted sperm
– Megaspores produced in seed or female cone
• Formed by meiosis in scales of female cone
• Develops into megagametophyte in ovule
• An ova develops in each ovule (2 ovules per scale)
• Pollination - Transfer of pollen from
male to the female cone (windblown)
• Fertilization - Fusion of the nuclei of
the male and female gametes
• Seed - Mature ovule containing
embryo (2n), reserve food, and seed
coat; (embryo – immature sporophyte
generation)
– Seed germinates making new sporophyte
generation
– (NOTE: Life cycle of conifers takes at least
3 years from pollination, fertilization, to
maturation of seed.)
• Vascular Enclosed Seed Plants –
Angiosperms (flower-bearing)
– Phylum Anthophyta
• Class Monocotyledones
– Grasses, lilies, palms, irises
• Class Eudicotyledones
– Flowering trees, shrubs, cactus, vegetables
• Most populous and most successful
group of plants
• Produce flowers in which seeds develop and
structure(s) where fruit matures
• Flowers attracts pollinators; fruit aids in
dispersal of seed
• Flower part terms:
– Receptacle, sepals (calyx), petals (corolla)
– Male flower parts: stamen (anther & filament)
– Female flower parts: carpel (stigma, style, ovary)
• Seed - matured ovule containing embryo (2n),
reserve food, and seed coat
• Fruit - matured ovary; may be fleshy, dry, etc.
(aids in dispersal of the species)
Monocots vs Eudicots (dicots) – pg. 625
Examples
Monocots
Herbaceous plants
corn, grasses, lily
Seed
One cotyledons –
seed leaf
Flower parts
Multiplies of 3
Eudicots
Some herbaceous and
woody –
lima beans, strawberries,
dandelions, roses
Two cotyledons
Multiplies of 4 or 5
• Life cycle includes heterosporogeny: (pg. 366367)
• Microspores produced in male flower part
called the stamen
• Formed by meiosis in anther of male stamen
• Develops into microgametophyte (pollen grain)
• Contains 2 nonflagelleted sperm
• Megaspores produced in female flower part
called the carpel
• Formed by meiosis in ovary of carpel
• Develops into megagametophyte in ovule
• An ova develops in ovule of ovary.
• Double fertilization unique to Angiosperms:
(pg. 637)
– One sperm + ova = embryo
– One sperm + polar bodies = endosperm (nutrients
or food source)
• Embryo and endosperm packaged in seed
• QUESTIONS:
• Explain why gymnosperms produce seeds but not fruits,
yet angiosperms produce seeds with fruit.
– Seeds in gymnosperms are winged and adapted to be dispersed
by the wind from the cones
– Angiosperms use the fruit to aid in seed dispersal – using
animals
• Explain why gymnosperms and angiosperms do not
require water for fertilization.
– Do not have flagellated sperm…pollen is carried by the wind
• Pollination occurs both in gymnosperms and
angiosperms via wind. What adaption allows
pollination to be more successful in
angiosperms?
– The stigma of the flower is sticky and can catch
the pollen. Also the flower can help attract
pollinators.
– The ovary in gymnosperms is located in a cone
which is harder to access
• Both gymnosperms and angiosperms disperse
their species via seeds. What adaption allows
angiosperms to be more successful in seed
dispersal?
– Dispersal relies on wind, gravity, water and/or
animals
– Angiosperms can utilize all of these forms due to
the presence of fruit.
• Economic Importance:
– Food – wheat, corn, and rice (grasses)
– Sugar production – sugarcane and sugar beets
– Spices
– Drinks – coffee, tea, and cola
– Rubber (latex) – sap from the rubber tree
– Fabric – cotton
– Lumber – other building materials
– Medical – pharmaceutical drugs
– Aesthetic value
Overview
Vascularity
Dominant
Generation
Dispersal
of Species
Pollination
Fertilization
Mosses
None
Gametophyte
Spores
------
water dependent
Ferns
Present
Sporophyte
Spores
------
water dependent
Gymnosperms
Present
Sporophyte
naked seed
Wind
water independent
Angiosperms
Present
Sporophyte
covered
seed
wind
water independent
& pollinators