lec 13 plant bio

Roughly —- of all land plant species are angiosperms

90%

Oldest angiosperm fossils: —-, about 135 million years ago

pollen

Darwin called the rise of angiosperms sudden rise an “————”

abominable mystery

what is an early angiosperms fossil

Archaefructus (China)

what are problems in gymnosperms that angiosperms answered

Slow development: up to two years from pollination to seed

• Wind pollination is inefficient: lots of pollen, little reaches an ovule

• Exposed ovules on cone scales is a bit problematic

what are the ways angiosperms solved gymnosperms problems

• Highly specialized forms of dispersal for pollen and seeds:

- Animal pollinators carry pollen to where it needs to go

- Fruits: Better dispersal mechanism for seeds

• Carpels protect ovules

• Fast life cycles : weeks in some weeds

what are some synapomorphies of angiosperms

flowers

carpels that enclose ovules

double fertilization (triploid endosperm)

fruit

highly reduced gametophytes

sieve tubes with companion cells in pholem

how long is the gametophyte stage in angiosperms

Up to 2 years in conifers; whole life cycle as short as 3 to 4 weeks in some angiosperms

what does the enclosure of the ovule by the carpel provide

protection, and stigma and style screen incoming pollen

Endosperm made only after ——: no food wasted on unfertilized ovules

fertilization

what are the key dispersal methods of fruits

(animals, wind, water)

what traits to gnetophytes share with angiosperms

• Vessels in the xylem

• Flower-like cones

• Double fertilization

DNA puts gnetophytes inside the conifers, so all three traits evolved ———

independently

A flower is a compressed shoot with modified leaves arranged in —-

whorls

what is the outermost whorl shown in the picture. Made of sepals that protect the young bud and support the petals

calyx

what is the second whorl in the picture. Made of petals that are often flashy to attract pollinators

corolla

what is the third whorl of the flower. The male reproductive structures: stamens (anther + filament). Anthers contain microsporangia, where pollen develops

Androecium

what is the fourth whorl of the flower. The female reproductive structures: carpels (“pistil” if fused). Carpels contain ovules, which contain the megasporangia

Gynoecium

Each whorl may have —— or —— parts, or both

fused, unfused

joint term for sepals, especially when fused

calyx

joint term for petals, especially when fused

corolla

what are the two parts of the stamen

• Anther: pollen sacs

• Filament: stalk

highly reduced male gametophyte

pollen

what cells get released with pollen

a tube cell plus a generative cell (or its 2 sperm)

pollen grows a ——- that carries —- sperm, as in conifers and gnetophytes

pollen tube,two

what are the three parts of the carpel

stigma, style, and ovary

sticky tip that receives pollen

stigma

stalk the pollen tube grows through

style

chamber holding the ovules (basis of the name angiosperm)

ovary

one carpel, or several fused carpels

pistil

Carpels can be separate or —-

fused

integuments + nucellus (megasporangium), as in gymnosperms

ovule

how many cells and nuclei in the female gametophyte

Usually just 7 cells, 8 nuclei

• Egg + 2 synergids at the micropyle end

• Central cell with 2 polar nuclei

• 3 antipodals at the far end

• Pollen tube grows down the style and enters the ovule through the micropyle

• Releases two sperm into a synergid

Double fertilization

what are the two sperms cells in double fertilization made up of and what do they become

Sperm #1 + egg → zygote (2n) → embryo

Sperm #2 + polar nuclei→ endosperm (3n) → food

Floral organ identity is set by a few classes of —— genes

MADS-box

explain what is represented in this chart (A, A+B, B+C,C,E)

• Aalone → sepals

• A + B → petals

• B + C→ stamens

• C alone → carpels

• E genes are needed in all four whorls

what do flowers look like that lost gene A

carpels, stamens, stamens, carpels

what do flowers look like if they lose gene B

sepals, sepals, carpels, carpels

what do flowers look like if they lose gene C

sepals, petals, petals, and the flower keeps making more whorls

• A “double” flower

• Many double garden flowers involve reduced C function

Each mutant swaps organs in place: a ——- change

homeotic

symmetry in flowers

radial (actinomorphic) or bilateral (zygomorphic)

petals can be —— into a tube

fused

Ovary position

• Superior: above where the petals attach

• Inferior: below, sunk into the flower base

sexes of flowers

• Bisexual (“perfect”) or unisexual flowers

• Monoecious (corn) or dioecious (holly) plants

About —- of angiosperm species are pollinated by animals

90%

why are animal pollinators important

• Animals carry pollen straight from flower to flower: far less waste than wind

• Specialized pollinators can keep related species apart

Wind pollination (grasses, oaks, ragweed) is what type of charecteristic

derived (Evolved from animal-pollinated ancestors many separate times)

sugar water (sucrose, glucose, fructose). Plus amino acids, sometimes defensive compounds

nectar

what makes nectar

nectaries; extrafloral nectaries pay ants for protection

protein-rich food; bees collect it for their larvae

pollen

how do flowers attract pollinators

Color tuned to pollinator vision

Nectar guides: patterns (often UV) that point to the reward

• Scent: strongest at night for moths and bats

• Shape filters visitors: long tubes exclude short tongues

About a third of orchids offer ——

no reward

Ophrys orchids look and smell like female bees • Males try to mate with the flower and carry off its pollen

Sexual deception

smell like rotting meat to attract flies • Stapelia, corpse flower (Amorphophallus

Carrion flowers

Many flowers are visited by many kinds of animals

generalists

Syndromes are best seen as ———- • Unrelated plants evolve similar flowers for the same pollinator • Remember homoplasy from tree thinking

convergence

what is the difference between penstemon pollinated by bees and hummingbirds and did they evolve at the same time

bee-pollinated: blue or purple, wide-mouthed, Hummingbird-pollinated: Red, narrow tubes, protruding anthers and stigma, more dilute nectar, no

what moth and flower is an example of convergence

a hawkmoth, now called Xanthopan praedicta with a long tounge and the flower Angraecum sesquipedale (Madagascar)

Selfing is reliable but causes ————

inbreeding depression

ways to promote outcrossing

Dichogamy:

Herkogamy

Self-incompatibility

Heterostyly

male and female phases at different times (Penstemon sheds pollen first)

Dichogamy

anthers and stigma kept apart

Herkogamy

the style rejects pollen with matching S alleles

Self-incompatibility

wo flower forms, pin and thrum (Primula)

Heterostyly