BIO 193 Exam I

benefits and problems of land

benefits: more light, more available carbon dioxide, and access to mineral-rich soil

problems: desiccation and lack of support against gravity

plants arose from

green algae

closest living relatives of plants

charophytes

similarities of charophytes and land plants

sperm structure, cellulose-synthesizing protein arrangement, and nuclear, chloroplast, and mitochondrial DNA

key adaptations for life on land

alternation of generations, multicellular dependent embryos, walled spores produced in sporangia, apical meristems, cuticles, and usually stomata

bryophytes

nonvascular plants with life cycles dominated by gametophytes, rhizoids instead of true roots, sperm that usually need a film of water to reach eggs, and small, nutritionally dependent sporophytes

• ex: liverworts, mosses, and hornworts

two stage life cycle of all land plants

multicellular haploid gametophyte and multicellular diploid sporophyte

gametophyte

haploid stage of plant life cycle that produces gametes

sporophyte

diploid stage of plant life cycle that produces spores

ploidy

number of complete chromosome sets, rather than the amount of DNA alone

haploid

one set of chromosomes (n)

diploid

two sets of homologous chromosomes, one from each parent (2n)

zygote

diploid cell produced by the union of haploid gametes during fertilization

ecological importance of mosses

retain nitrogen, tolerate desiccation, form peatlands, and influence carbon storage and climate

vascular plants evolution and importance

• evolved dominant sporophytes, lignified xylem and phloem, true roots, leaves, and sporophylls

• important as this allowed plants to grow taller and form the first forests

five major adaptations of seed plants

1. reduced gametophytes

2. heterospory

3. ovules

4. pollen

5. seeds

gymnosperms seeds and major living groups

• bear naked seeds, typically on cones

• major living groups: cycads, ginkgo, gnetophytes, and conifers

angiosperms

flowering plants with flowers and fruits

angiosperms life cycle

pollination, pollen tube-growth, double fertilization, seed formation, and fruit development

evolution

works by modification of earlier structures, not by sudden invention from nothing.

structure fits _____ repeatedly in plant evolution

function

• from cuticle to vascular tissue to seeds and flowers

two major problems reproductive success on land depends on

1. protecting gametes and embryos from drying out

2. moving sperm to eggs without requiring standing water

angiosperm evolution

includes basal angiosperms, magnoliids, monocots, and eudicots, and pollinator interactions may have contributed to their diversification

algal ancestors favored by natural selection

ones that could tolerate drying at pond margins (trait that helped launch the move onto land)

bryophyte sperm and embryos

• sperm: swim through water films to archegonia

• embryos: remain protected and nourished in parental tissue

shoot system function

photosynthesis and gas exchange

root system

absorbs water and minerals, anchor the plants, and store nutrients

taproot system

primary root with lateral roots emerging out of it

fibrous root system

no dominant root - dense mat of many tiny roots

root hairs

thin extensions of epidermal cells near the tips of growing roots

root hairs function

increase absorptive surface area

xylem role

conducts water and minerals upward

phloem role

distributes sugars and other organic products

lignin role

stiffens plant bodies for upright growth

roots role

anchor plants and absorb water and minerals

leaves role

increase photosynthetic surface area

endosperm by double fertilization in angiosperms

one sperm fertilizes the egg and the second fertilizes the central cell