Botany 130 UW-Madison Exam 4/Final

homosporous

one kind of spore, often the same size, unisexual or bisexual gametophytes

heterospory

evolved multiple times, has microspores and megaspores, zygote and sporophyte are diploid, egg sperm both gametophytes mega/microspore are all haploid

microspore (male)

produced in a different sporangia than megaspore and on different leaves (microsporophylls), microgametophytes produce only antheridia and sperm, optimized for dispersal so it is small

megaspore (female)

produced in a different sporangia than microspore and on different leaves (megasporophylls), megagametophytes produce only archegonia and eggs, optimized for provisioning the gametophyte and young sporophyte so it is large

Lycopodiaceae "club moss": extant

mostly tropical with some temperate and lots of epiphytes, homosporous, some arrange sporophylls in strobili (cones) and other have sporangia that occur on single sporophylls/microphylls, bisexual gametophytes

Isoetaceae "quilwort": extant

closest living relative to the ancient tree lycophytes, many aquatic, heterosporous, sporangia occur on sporophytes/microphylls, some have bizarre physiology

Selayincellaceae "spike moss": extant

mostly tropical, mostly grown in moist environments (a few in the desert), heterosporous, sporophylls arranged in strobili

Lepidodendron: extinct

50-60m height, determinate growth (grew until its top twigs were too thin to branch), absorescent lycopods exhibited a "unifacial" cambium, secondary xylem made outside of vascular cambium, no secondary phloem made which limited its ability to transport sugar and therefore height

unifacial vascular cambium

making wood/secondary vascular tissue in only one direction

how modern wood is made

new vascular tissue is made in two directions, primary growth = longer stems and secondary growth = fatter stems, VC forms between the primary xylem and phloem -> makes a circle -> divides, and produces secondary phloem to the outside and secondary xylem to the inside

VC in extant woody plants is "bifacial"

if a cell that can become either xylem or phloem is to the inside of the cell that doesn't change it becomes xylem, if it is to the outside it becomes phloem

counting rings is...

counting secondary xylem produced (wood = secondary xylem)

coal

combustible black sedimentary rock composed of carbon and hydrocarbons; compressed plants (mostly lycophytes and ferns) that lived hundreds of millions of years ago

2 important conditions that allowed coal to form

1) lycophytes made secondary xylem (wood contains lignin) and fungi/other decomposers had not evolved methods for decomposing lignin yet

2) sea levels were very low, so lots of land was available and it was very swampy -> allowed for lots of plant mass to build up

burning fossil fuels is concerning because...

because it releases CO2 that had been in the atmosphere millions of years ago but was sequestered in plants

ferns

most are tropical, many are epiphytes, diverse group, relationships not established, no secondary growth, gametophyte and sporophyte live independently, gametophytes are 1 cell layer thick, sporangia arranged into sori sometimes, most are homosporous (water ferns are heterosporous), sporophyte grows out of gametophyte and then gametophyte dies

epiphytes

plants that live on top of other plants

fern leaf is an example of...

a megaphyll (the only group that experiences microphylls is lycophytes)

spores are ejected from sporangium

annulus cell dry out, which retracts the lid of the sporangium , the water column snaps and that propels the top of the sporangium forward rapidly

process for a seed

before the egg and sperm form a zygote, this structure (the female gametophyte in a megasporangium surrounded by integument(s)) is an ovule

seed habit

- fertilization (sperm and egg fusing) happens in the megasporangium

- ovule/seed= a megasporangium with a protective layer (integument)

- dormant embryo is dispersed from the maternal plant within the megasporangium (seed)

- microgametophyte = pollen

advantages of the seed habit

- the adult sporophyte can provide moisture and nutrients to the megagametophyte

- an adult sporophyte can invest in the embryos of the next generation rather than "gambling" that megaspores will be fertilized (seeds have resources so embryos can establish even if buried deep in soil)

archaepteris (fossil)

no seeds but secondary thickening (370-340 Ma)

cycads and gink have similar reproduction

- pollen tube grows into the megasporangium (nucellus) and receives nourishment from megasporangium

- it may grow for months, no antheridia made

- most gymnosperms make megagametophytes with multiple archegonia

- the pollen grain bursts near the archegonia and releases sperm

- the sperm swim to an archegonium and one will fertilize the egg (both cycads and ginkos have motile sperm)

- often >1 egg is fertilized but almost always only one embryo survives

cycad and ginko reproduction cont...

- pollination does not equal fertilization

- pollination = pollen delivered to ovule

- fertilization = egg and sperm uniting

ginko

- 1 species

- appearance similar to fossils dating ~270 Ma

- pollen and ovules on diff. trees (dioecious)

- when ovules ripen their fleshy seed coat in the fall begins to smell

cycads

- dioecious

- cones = strobili = sporophytes tightly packed

- cycad cones heat up to release chemicals that attract specific pollinators (pollinators are species-specific)

- form a mutualistic relationship with cyanobacteria (N-fixing)

- form specialized structures called coralloid roots near soil surface that house the cyanobacteria

- fossils limited to wet, warm, and humid areas

- cycads are in a broad range of habitats but are the most endangered order of plants (cycad black market; stopped by stable isotopes?)

gnetophytes

- characteristics similar to angiosperms (water moves through vessels not tracheids and strobili arranged like flower clusters)

- sperm do not swim to egg, they are delivered by the pollen tube

- 3 extant genera (gnetum, ephedra, welwitchia)

gnetum

tropical and subtropical habitats, leaves resemble angiosperms

ephedra

tiny leaves and photosynthetic stem; arid and desert habitat

welwitchia

lives in one desert in south africa; 2 leaves grown from base in entire life; exhibits CAM photosynthesis; pollen and ovule made on diff pants -> pollinated by insects attracted to nectar on cones

conifers

- many live in "extreme" environments and exhibit many adaptations to tolerate abiotic stresses

- include giant sequoia which has the largest volume and mass

- also includes the oldest single tree ~5k years old

- 45% of lumber comes from conifers plus the christmas tree industry -> economically important

how long does the pine reproductive cycle take?

2 years

where is pollen made in pine

microsporangium

pollen molecules (microgametophyte) pine

made of very few cells, "Mickey Mouse" shaped, made up of generative cells (will make 2 sperm), tube cells (grow pollen tube), prothallial cells (sterile, disappear when pollen is mature), 2N microspore mother cell (microsporocyte) -> meiosis -> 4 1N microspores -> each divides until a mature 4-celled microgametophyte is made (pollen), each spore makes a pollen grain

inside pine megasporangium about a month after pollination

2N megaspore mother cell (megasporocyte) -> meiosis -> 4 1N megaspore -> 3 die 1 lives -> develops into megagametophyte

how are pine pollinated

wind pollinated; ovules make "pollination drop" that may trigger pollen to germinate; once drop dries pollen grains are drawn into the micropyle and contact with the nucellus; pollen grain grows

where does pine tube cell grow

grows through nucellus and megasporangium

a year after pine pollination:

generative cell will divide to make a sterile and spermatogenous cell (will make 2 sperm); ~15 mo after pollination one sperm fertilizes the egg while the other degenerates

how many species of angiosperms

300k

angiosperm species richness

greatest near the equator

traits that distinguish angiosperms

- xylem conduits are predominately vessels

- flowers

- ovule protected within carpels (=ovary)

- ovary matures into a fruit

- reduced gametophytes

- no archegonia

- double fertilization

- endosperm

tracheids

ancestral and 1 cell long

vessels

longer b/c multiple cells are stacked on top of each other w/ wider openings between cells

flowers

- determinate reproductive shoot

- four whorls of modified sterile leaves and sporophylls

- sepal

- petal

- stamen: microphyll with 4 microsporangia, producing microspores

- carpel: megasporophyll enclosing the ovule

stamen evolution

leaflike portion decreased over time, until only sporangia remained

anther

4 microsporangium and a filament

development of a male gametophyte

a cell inside a cell

gynoecium (female part of flower)

pollen lands on style, goes down stigma to ovary where the ovules reside

carpel

a leaf modified for reproduction

female gametophyte angiosperm

mother cell in ovule (2N) -> meiosis ->4 1N spores -> 3 die -> other consumes remaining dead spores -> mitosis -> 8 nuclei in 7 cells (entire female gametophyte)

angiosperm gametophyte

embryo sac

pollination in angiosperms

- a diversity of mechanisms that promote dispersal of pollen from a stamen to the stigma

- on an appropriate stigma , the pollen will produce a pollen tube

- pollen tubes grow down the style and find the egg cell

double fertilization in angiosperms

one sperm fertilizes egg and the other "fertilizes" the 2 polar nuclei

gymnosperm seed

- "naked seed"

- pollen delivered to carpel

- contain dormant embryo and seed coat from integuments

- main nutritive tissue: megagametophyte

angiosperm seed

- "hidden seed"

- pollen delivered to carpel tissue

- ovule encased in a sporophyll called a carpel

- dormant embryo and seed coat from integuments

- main nutritive tissue: endosperm

monocots

- 1 cotyledon

- scattered vascular bundles

- evolved 2nd growth >4x (i.e. joshua trees)

- unifacial cambium makes vascular bundles to the inside

- parallel leaf veins

potentially most economically important plant group (includes corn, rice, wheat, barley, and sugar cane)

- primary building materials in tropical regions (palms, bamboo)

- many tropical fruits (pineapple, dates, bananas)

- includes orchids

- one aperture

"dicots"

are not monophyletic

eudicots

- 3 apertures (pollen tube grows from aperture)

- major clads include rosids and asterids

rosids

usually have "free" (or separate) petals (the ancestral condition)

asterids

usually have fused petals

97% of angiosperms

are monocots or eudicots

>50% of monocots

are grasses or orchids

pollination

- transfer of pollen from anthers to stigma in angiosperms

- does not equal fertilization

- necessary to make seeds (critical for reproduction, important for agriculture)

self-pollination (important in some species)

- transfer of pollen to stigma of same plant

- can be same flower or another flower of the same plant

cross-pollination

- transfer of pollen to the stigma of a different plant of the same species

- promoted by spatial separation of anthers and stigma in a flower, temporal separation of pollen release and stigma receptivity, self-incompatibility, and dioecy (male and female parts are on different plants)

some species make seeds

asexually

pollination mechanisms

-abiotic (physical, not biological) -> wind: common, water: rare

-biotic (biological) -> insects (bees, butterflies, moths, flies, and beetles), birds, mammals (bats)

wind pollination

- the stigma is a small target -> large amounts of pollen are required

- generally reduced perianth and feathery stigma

co-evolution of angiosperms and animal pollinators

- both parties gain a mutualistic ecological benefit

- neither party is altruistic: decisions are "economic"

analogy for plants and animals

plants are life-building developers, animals are contractors ("payment" is usually food)

"payment" is food

- nectar (sugar-rich solution production glands known as nectaries)

- protein-rich pollen and oils are other possible food rewards

- non-food rewards (heat, perfumes, homes for larvae)

yucca moths

- lay eggs in yucca flower ovaries -> pollinates flower

- if too many eggs the plant will abort (strong selective pressure not to lay too many eggs)

water pollination

- stigma is a small target - HUGE amounts of pollen are required (lots lost in water flow)

- generally reduced perianth and feathery stigma

- used by aquatic plants

sometimes the relationship between angiosperms and animal pollinators ceases being mutualistic

- food mimicry

- mimicry of female insect (pseudocopulation) -only observed in orchids

animals pollinators

bees, carrion flies, butterflies, moths, flower-feeding birds, bats

bees

- high "blossom intelligence"

- diurnal (non-nocturnal)

- 20k species

- both male and female live on nectar

- females collect pollen to feed larvae

- pollinate more flowers than any other pollinator

- great sense of smell and sight (UV not red) -> in UV light, flowers have "honey guides" that indicate the nectaries

carrion flies

looking for dead animals

butterflies

- good color vision and sense of smell

- consume nectar through long tubular proboscis

- diurnal

- pollen gets on their legs

moths

- find flowers by scent and sight

- suck nectar with a long thin proboscis

- nocturnal mostly

- flowers are pale in color

flower-feeding birds

- good color vision, especially red

- poor sense of smell

- high energy needs, need perch (not hummingbirds)

- diurnal

bats

- color blind, good sense of smell

- large with high food requirements

- cant fly in foliage

- tropical trees

- nocturnal - flowers often only open at night

physiology of pollen tube growth process

1) pollen adheres, hydrates, and then germinates on a stigma

2) pollen tube grows into stigma between cell walls

3) pollen tube grows through the nutrient-rich extracellular matrix of the transmitting tract that connects the stigma, style, and ovary

physiology of pollen tube growth

- lots of biochemical "communication" between pollen grain and stigma cells determines if the pollen grain is compatible with the stigma

- pollen tubes elongate very quickly (relatively speaking)

inside the tube cell

- callose plugs and vacuoles seal off rear of pollen tube - keeps the sperm, tube nucleus, and other important organelles/materials at growing tip

- vesicles deliver cell wall material to growing tip

seeds =

fertilized ovules

fruit =

matured ovary

accessory tissue

lots of fruit have accessory tissue that unites wit the ovary to become part of the fruit (accessory tissues were not part of the carpel) i.e. the receptacle which is the base of the flower and becomes the majority of the strawberry fruit

why is dispersal important?

- target seedlings to favorable sites

- escape competition

- escape pathogens and predators

abiotic dispersal

gravity, wind, water

wind dispersal

- wings or feathery hairs (may be derived from the seed, the fruit (or accessory structures)

- tiny seeds (esp. orchids)

water dispersal

- common in species that live near or in water

- have adaptations that allow them to float

- fruits trap air

biotic dispersal

- plants (self dispersal)

- birds, mammals, ants

plant self dispersal

- tumbleweeds are blown along by wind and scatter seeds as they move

- dwarf mistletoe builds pressure in the fruit then shoots very sticky seeds out at high speeds

biotic dispersal

-fleshy structures eaten (seeds dropped, seeds pass through digestive system)

-fruits/seeds scatter-hoarded and not recovered

-ex squirrels, acorns, walnuts, etc

-elaiosome: fleshy attachments on seeds that ants like to eat so they bring the seeds back to their nest where they can germinate

-hitchhiking on animals (special structures or just sticky)

when fruits ripen, they change to attract dispersers (color)

- reptiles see the visual spectrum as we do (or more)

- birds see red very well

- apes and monkeys see red (and other colors)

other mammals are colorblind, but yellow stands out against plant foliage better than red

when fruits ripen, they change to attract dispersers (smell)

- reptiles can smell fruits

- birds have poor sense of smell

- most mammals have a good sense of smell

when fruits ripen, they change to attract dispersers (taste)

- sugar content increases

- cell wall degrade (fruit becomes softer)

- these physical changes are controlled by ethylene (hormone)

seeds in fruits...

have evolved to be eaten, either to pass through the digestive tract unharmed or have partially digestible seed coats to allow germination

4 main abiotic factors that impact distribution and abundance of life on earth

sunlight, temp, moisture, and wind