lec 12 plant bio

name of early seed plants

seed ferns

— appear by the late Carboniferous

Conifers

—- dominated through the age of dinosaurs

Gymnosperms

what were the two problems still faced by ferns and friends

• Sperm must swim to the egg

• Spores carry no food and little protection

what carries sperm to the egg through the air: no water needed

pollen

an embryo packed with food inside a protective coat

seeds

= gymnosperms + angiosperms

Seed plants

Gymnosperms: about

1,100 species

Angiosperms (flowering plants): about

300,000 species

Relatively few ——- species, but they dominate —- areas of forest

gymnosperm, huge

what parts of seed plants is shared with all land plants

• Embryo kept inside and fed by the parent plant

• Alternation of generations

• Sporopollenin (now in the pollen wall)

• Cuticle, stomata

what parts of seed plants is shared with all vascular plants

• Dominant sporophyte

• Lignified xylem and phloem

• True roots and leaves (euphylls)

synapomorphies of vascular plants

• lignified xylem and phloem

• dominant sporophyte

what do ovules in seed plants become

seeds

a male gametophyte carried to the ovule

pollen

from secondary growth (not all seed plants)

wood

seed plant synapomorphies is built on ———, which also evolved separately in some lycophytes and water ferns

heterospory

angiosperm synapomorphies

flowers, fruit, double fertilization

Gymnosperms are ——, supported mostly by DNA

monophyletic

gnetophytes were angiosperms’ closest relatives • Both have vessels, flower-like cones, and a kind of double fertilization

“anthophyte hypothesis”

gymnosperms are a clade

Genome-scale data

Cycads + Ginkgo are sisters; gnetophytes sit inside —-, sister to the pine family

conifers

— and double —— evolved independently in gnetophytes and angiosperms, which is kind of bonkers

vessels, fertilization

which stage in gymnosperms is • DIPLOID • The dominant, long-lived stage: the tree itself • Makes pollen cones and seed cones

Sporophyte (2n)

which stage in gymnosperms is • HAPLOID • Microscopic, and dependent on the sporophyte • Male gametophyte = pollen grain • Female gametophyte = inside the ovule, on a cone scale

Gametophytes (n)

Male gametophyte =

pollen grain

Female gametophyte =

inside the ovule, on a cone scale

Megaspores (large, few) →

female gametophytes

Microspores (small, many) →

male gametophytes

what are the two different types of spokes

megaspores and microspores

Seed plants make use of heterospory to solve the issue of needing —- for fertilization

water

Extremely mobile male gametophyte:

pollen

heterospory is not a true ——

synapomorphy

Pollen grain =

an immature male gametophyte in a tough sporopollenin wall

pollen is made in ——- on pollen cones: meiosis, then a few mitoses

microsporangia

Pine pollen: only a few cells, plus two —- for floating in the wind

air sacs

pollen reaches the ovule opening

Pollination

what pulls the pollen inside the ovule

pollination drop

The pollen grain grows a ———- toward the egg

pollen tube

Pollination —— fertilization: in pine they are about a year apart

doesn’t

The mobile —- gametophyte (pollen) allows it to be transferred directly to the —- gametophyte

male, female

Each spore is one —-; the ——- grows from it by mitosis

cell, gametophyte

Male: meiosis →

4 microspores

what are the 4 microspores in pollen

2 prothallial cells (die off), a tube cell, and a generative cell

The generative cell produces 2 ——- via mitosis (No flagella on the sperm)

sperm cells

The tube cell generates the ——- via cell expansion (cell growth, not mitosis)

pollen tube

Female: meiosis →

4 megaspores; 3 die

what happens during meiosis of the female gametophyte

• The survivor divides into thousands of cells

• Most store food (later, the seed’s food)

• 2 or 3 archegonia, each with one large egg

After ———, the male gametophyte grows the pollen tube to deliver the sperm

pollination

The tube carries the sperm to an ——-

archegonium

megasporangium + protective integument, with a small opening (micropyle)

ovule

Meiosis makes 4 megaspores; only — survives

1

the surviving megaspore after meiosis grows into a large, many-celled ———- with archegonia

female gametophyte

After fertilization, the ovule becomes a

seed

the new sporophyte

Embryo (2n)

the female gametophyte

Food(n)

from the integument, the parent’s tissue

Seed coat(2n)

ovules sit exposed on a cone scale

“Naked seed”

The nutritive tissue for the developing gymnosperm embryo is literally the ———- (megagametophyte) • This means the baby plant eats the flesh of its mother (haploid maternal relative) for nutrition

female gametophyte

four branches of gymnosperms

• Coniferophyta (conifers, including pine trees and relatives)

• Cycadophyta (cycads: look like palms)

• Ginkgophyta (ginkgo: lots of these on campus)

• Gnetophyta (a mixed bag of very different plants)

which plants were Dominant until the Cretaceous: mostly what dinosaurs ate

gymnosperms

4 types of gymnosperms

conifers, cycads, ginkgo, and gnetophytes

Seed plants started out with —— sperm

swimming

which types of gymnosperms still have swimming sperm (Pollen tube absorbs nutrients, then releases large, many flagellated sperm that swim a short way inside the ovule)

Cycads and Ginkgo

which types of gymnosperms have no flagella on their sperms (Pollen tube delivers the sperm straight to the egg)

Conifers and gnetophytes

Angiosperms lost —— too, independently

flagella

pines, bald cypress, sequoias, yews, larches, etc. (largest group of gymnosperms)

Needle-like leaves with thick cuticle and sunken stomata: tolerate drought and cold

Includes the tallest (coast redwood) and oldest (bristlecone pine) trees

Economically very important

conifers

coniferophyte is usually

evergreen

Pollen and seeds in separate ——-: spirals of often woody scales

cones

Pine: about — years from young cone to mature seed

two

which type of gymnosperm is Nitrogen-fixing cyanobacteria in special coral-like roots

Look like palms (monocots), but with cones

Many are pollinated by insects (beetles, thrips), not wind

About two-thirds of species are threatened

Once a major part of the flora in the age of dinosaurs; now mostly tropical and often rare

Cycadophyta

what do cycad leaves do when young like ferns

Circinate vernation (leaves spiral when young just like ferns)

what is this leaf pattern

Circinate vernation

what type of gymnosperm has Only one living species

Commonly planted; possibly wild populations survive in China

The bad-smelling “fruits” are fleshy seeds

Closest living relatives: cycads

Sperm flagellated

ginkgophyta, Ginkgo biloba

Ginkgophyta is an example of what

dioecy • Separate male and female plants

how do ginkgophytes reproduce

Male cones produce pollen, female cones receive it and produce seed once fertilized

what is monoecy

plants produce both female and male cones or flowers. Cones are still separate: two kinds on same plant

what type of gymnosperms have Three very different genera, about 110 species

Sperm with no flagella

A second fertilization in Ephedra and Gnetum

Vascular system with vessels

gnetophyta

what factors do gnetophyta share with angiosperms

• Similar broad leaves (Gnetum)

• Similar fruit-like fleshy seeds

• Vessels and double fertilization