PLANT DIVERSITY IIChapter 30

FERTILIZATION OF SEED PLANTS VIA POLLEN

Microspore develop into pollen grains, the male gametophyte covered by sporopollenin Carried by wind or animals Pollination when pollen reaches ovule part of plant

Pollen grain germinates and produces a pollen tube Two sperm released into female gametophyte

Allows fertilization across long distances Water film no longer necessary

Some gymnosperms retain flagellated condition of sperm, though no longer necessary

THE SEED PLANTS

A seed is an embryo and its food supply that is surrounded by a protective coat

Able to survive away from parent plant Can remain dormant

for different periods of time

Dominant producers on land

Enormous impact on human society

SEED PLANTS HAVE REDUCED GAMETOPHYTES

Develop from spores kept in sporangia of parental sporophyte

Nutrients from parent

Protects seed from environmental stresses

Most seedless plants are homosporous

Produces 1 hermaphroditic gametophyte

Seed plants are heterosporous

Produce mega- and microsporangia

Female and male spores

Seed Plants are Heterosporous

SEED PLANTS PRODUCE OVULES Consists of the megasporangium, megaspore, and

integuments Layer of sporophyte tissue to envelop and protect the

megasporangium Gymnosperms with 1 integument Angiosperms with 2 integuments

Female gemetophyte from megaspore produce 1+ eggs

GYMNOSPERMS Naked seed plants

Ovules and seeds on develop of surfaces of leaves, usually as cones (strobili)

Four phyla with uncertain relationships Phylum Cycadophyta

Large cones and palm-like leaves Phylum Gnetophyta

3 genera: Welwitschia (largest leaves), Ephedra (ephedrine), and Gnetum (tropical plants that resemble angiosperms)

Phylum Ginkophyta Ginkgo biloba only surviving species Ornamental species, but only males planted due to seed odor

Phylum Coniferophyta Largest phyla commonly called conifers Most are evergreens and retain leaves year round, others

are deciduous

PHYLUM CONIFEROPHYTA

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Pine tree is a sporophyte

Separate types of cones for each gametophyte

Pollen cones undergo meiosis to develop pollen grains

Ovulate cone with many scales, each with 2 ovules

Haploid cells produced become megaspores with some developing into gametophytes

3 years for cones to form mature seeds

Ovulate cone separates and seeds dispersed by wind

ANGIOSPERMS

Reproductive structures are flowers and fruits Seeds contained in fruits, the mature ovaries

Most diverse and widespread plants All placed in phylum Anthophyta Previously divided into monocots and

dicots 1 or 2 cotyledons, seed leaves, in embryo

respectively Monocots form a clade, but most dicots now

eudicots Rest of ‘dicots’ as basal angiosperms (oldest)

and magnoliids Water lilies and kudzuu

FLOWERS

Specialized structure with up to 4 circles of modified leaves

Sepals at base, usually green, and enclose bud before opening

Petals brightly colored and aid in attracting pollinators

Stamens are sporophylls that produce microspores = pollen Filament is the stalk and anther is

the terminal sac Carpals are sporophylls that

produce megaspores Stigma is sticky and receives pollen Style leads to ovary at base with

ovules

FRUITS Mature ovaries resulting from

thicken ovary walls Triggered by hormonal changes Wall is the pericarp

Forms only following pollination

Can be fleshy or dry Pericarp softens as ripens or

adheres to seed coat Adapted to disperse seeds

Winged seed by wind Modified burrs to cling to

animals Edible so animals eat, but seed

passes unharmed with natural fertilizer

AN

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•Pollen grains develop in anthers of stamens• 2 haploid cells produced: 1 to sperm other to pollen tube•Ovule develops into embryo sac• Few cells: 1 is egg•Anther releases pollen to sticky stigma on carpel• Some flowers self- pollinate, but many cross-pollinate• Stamens and carpels develop at different times or arrangement unlikely•Pollen tube into style to penetrate ovule integument•1 sperm fertilizes egg = 2n zygote•1 sperm into other cells to form endosperm, becomes food source for embryo•Embryo with basic root and cotyledons

HUMAN DEPENDENCE ON SEED PLANTS

Most food from angiosperms Wheat, rice, maize,

potatoes, cassava, and sweet potatoes contribute 80% of human calorie consumption

Angiosperms feed livestock

Other foods Coffee, tea, cocoa, and

spices Sources of wood and

medicines