Ch 26: Seed Plants

evolutionary history of seed plants order

first land plants

first vascular plants

first seed plants

forests of seedless vascular plants dominate swampy land

first gymnosperms

gymnosperms forests replace lycophyte and fern forests

cycads and conifers dominate landscape

flowering plants appear

flowering plants begin to diversity

did seed plants come before or after vascular plants?

after

female gametophyte: seeds and pollen as an evolutionary adaptation to dry land

the egg

endosperm-producing cell (supports the growth of the embryo)

• embryo: produced from the diploid zygote, grows into the sporophyte when seed germinates

• seed: offers the embryo protection, nourishment, and a mechanism to maintain dormancy, allow plants to disperse the next generation through both space and time

male gametophyte: seeds and pollen as an evolutionary adaptation to dry land

• pollen grands (contain the sperm of the plant)

• protected from dessication

• not dependent on water to reach the female organs

gametophyte-sporophyte relationship in Bryophytes (mosses and other nonvascular plants)

gametophyte: dominant

sporophyte: reduced, dependent on gametophyte for nutrition

dispersed spore grows into: gametophyte

gametophyte-sporophyte relationship in SVPs (ferns and other seedless vascular plants

gametophyte: reduced, independent (photosynthetic and free-living)

sporophyte: dominant

dispersed spore grows into: gametophyte

reproductive adaptations of seed plants (reduced gametophyte) (seed plants gymnosperms and angiosperms)

gametophyte: reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition

sporophyte: dominant

in gymnosperms, what does the megaspore grow into?

microscopic female gametophytes (n) inside the ovulate cone

in gymnosperms, what does the microspore grow into?

microscopic male gametophytes (n) inside pollen cone

in angiosperms, what does the megaspore grow into?

microscopic female gametophytes (n) inside these parts of flowers

in angiosperms, what does the microspore grow into?

microscopic male gametophytes (n) inside these parts of flowers

reproductive adaptations of seed plants 1

reduced and retained gametophytes

• seed plants are heterosporous

  • megaspores (grow into female gametophytes)

  • microspores (grow into male gametophytes)

• both gametophytes mature within sporangis

  • highly reduced in size

  • protected from drying and UV

retained

instead of the sporangia releasing spores, the gametophytes grow within the sporangia itself

ovule

integument + megasporangium + megaspores

integument

protective layer of sporophyte tissue, protects the megasporangium

microphyle

small opening in the integument of the ovule, through sperm are able to access the egg

megaspore germinates within _____, develops into tiny female __________, produces egg which will eventually be fertilized

ovule, gametophyte

seeds

develops from fertilized ovule

• includes embryo, food supply seed coat

what structure is the seed coat derived from?

integument

what tissue is the food supply derived from?

female gametophyte tissue

pollen grains def

male gametophyte surrounded by pollen wall (partly secreted by sporophyte)

pollen grains

• capable of long dispersal, tough & resistant, & sperm nuclei does not require external H2O for fertilization

• sporopollenin in the pollen wall protects pollen grains

• pollination

  • pollen grain germinates → pollen tube → sperm discharged into female gametophyte

pollination

transfer of a pollen to a part of the seed plant that contains the ovule

sporopollenin

in the pollen wall protects pollen grains

does sperm nuclei require external H2O for fertilization?

no

gymnosperms characteristics

• naked seeds (partially sheltered by sporophylls)

• separate male and female gametes

• pollination by wind

• tracheids

• life cycle involves alternation of generations

• reduced male and female gametophytes

• dominant sporophyte

• all are heterosporous

• male and female reproductive organs can form in cones or strobili

• monoecious or dioecious

monoecious

male and female sporangia on same plant

dioecious

on separate plants

tracheids

lignified cells in the xylem of vascular plants

true or false. in gymnosperms, male and female reproductive organs can only form in cones.

false. in gymnosperms, male and female reproductive organs can only form in cones or strobili

what is the dominant in gymnosperms?

sporophyte

life cycle of a conifer (gymnosperm)

• female cones grow in the upper branches where they may be fertilized by pollen blown on the wind from the male cones

• male cones grow in the lower branches

• seeds are dispersed and grow into mature trees

  • seeds (2n)

• a pollen tube forms, allowing the pollen to migrate toward the female gametophyte. upon fertilization, a diploid zygote forms

  • pollen grain, pollen tube, ovule, scale, megaspore (n), tube nucleus, generative nuclei (sperm -1n)

5 phyla of extant seed plants

gymnosperms:

• coniferphyta

• cyacdophyta

• gnetophyta

• ginkophyta

angiosperms

• anthophyta

2 primtive gymnosperms

cyacdophyta and cinkgophyta

coniferphyta

gymnosperms: conifers

most diverse gymnosperms today

• “cone-bearers”

  • male pollen cone (sperm not motile0

  • female ovulate cone

monoescions

dominate high altitudes & latitudes in N. hemisphere

most are evergreen w/ needle-like leaves

coniferphyta ex.

pine fir, spruce, sequiias

most diverse gymnosperms

coniferophyte

cycadophyta

gymnosperms: cycads

• 100 species

• fern-like or palm-like fronds radiate from central stem

• central female and male cones

• with flagellated sperm

• beetles are involved in pollination of some cycads

• dioecious

which gymnosperm phylum has flagellated sperm?

cycadophyta

ginkgophyta

gymnosperms: ginkgos

• one extant tree: Ginkgo biloba

• herbal medicine

• with flagellated sperm

• dioescious

  • female sporophylls, not cones

  • male sporophylls, in strobili

  • sporophylls are modified leaves: modified to carry sporangis

which gymnosperm has flagellated sperm?

ginkgophyta

what is the one extant tree of ginkgophyta?

Ginkgo biloba

gnetophyta

gymnosperms: gnetophytes

• 3 distinct genera:

• Gnetum in tropics, Welwitschia in SW Africa deserts, Ephedra in US deserts

• male & female strobili; sperm not motile

• Ephedra - herbal medicine (Ephedrine)

  • amphetamine!

where is Gnetum found?

gnetophyta

tropics

where is Welwitschia found?

gnetophyta

SW Africa deserts (Namib desert)

where is Ephedra found?

gnetophyta

U.S. deserts

angiosperms key innovation

flowers and fruits

flower

structure specialized to facilitate sexual reproduction

• success mainly due to coevolution with pollinators

function of flowers

1. to ensure pollination

2. to protect a developing embryo

male flower parts

• stamen

• anther

• filament

female flower parts

• stigma

• carpel

• style

• ovary

sepals (calyx)

green leaf-like appendages that enclose the rest of the flower

calyx + corolla

perianth (non-reproductive system)

petals

brightly colored appendages that aid in attracting pollinators

stamen

collectivelyc alled androecium

filament

stalk that holds up pollen-producing sac

anther

terminal sac that produces pollen

carpel

aka “pistil” - known collectively as gynoecium

stigma

sticky tip of carpel that receives pollen

style

long tube leading from stigma to ovary

ovary

structure at base of the carpel that produces ovules

• ovules becomes fruit after fertilization

ovules

develop into seeds if fertilized

angiosperm: life cycle 1

microsporangia → male sporocycts (2n) → microspores (n) (pollen grains)

pollen grains: 1 generative cell, 1 tube cell

____ contains ovule, ovule contains ___________

ovary, megasporangium

angiosperm: life cycle 2

ovule → megasporangiusm → megasporocyte (2n) → (meiosis) → 4 megaspores (n) → only large megaspores survives → (mitosis 3x) →8 nuclei distributed among 7 cells of gemale gametophyte → 3 cells at one pole become egg and 2 synergids (remaining 3 cells become antipodal cells) , center cell → 2 polar nuclei

angiosperms: double fertilization with 2 sperm nuclei

happens in ALL angiosperms

• one fuses w/ egg, forming zygote (2n)

• one fuses w/ 2 central nuclei (polar nuclei), forming endosperm (3n) food supply in seed

fruit

mature ovary of a flower, thickens around seeds

• may include some additional tissues as well

• may be fleshy or dry

• protects seeds

• main function is enhancing seed dispersal

embryo

• radicle (small root)

• 1 or 2 leaf like organs : cotyledons

cotyledons

transmits broken down food reserves from endosperm (storage site) to the embryo

basal

diverged from other angiosperms early in the history of the group

2 big gorups of angiosperms

monocots and eudicots

monocots ex

orchids, palms, lilies, grasses, corn, rice, sugarcane

dicots ex.

oaks, peas, roses, potatoes

true woody tissue is ______ found in monocots

rarely

eudicots can be _______ (non woody) or produce woody tissues - tough walled xylem cells

herbaceous

Seed Plants & People

Almost all food & beverages & spices

• (80% calories globally!)

Wood products, including paper

Fuel

Fiber for clothing, rope

• cotton, linen, jute, hemp

Secondary compounds:

• countless drugs & medicines

• perfumes

• latex rubber

Ornamental plants

what percentage of prescription drugs contain an active ingredient from plants?

25%