BIOL1020 - Week 11.2

greening of earth

• land was lifeless for most of earth’s history

• early land life: cyanobacteria and protists

• plants diversified and produced oxygen

challenges and adaptions that were needed to live on land

challenges

• water loss

• lack of support

• reproduction without water

adaptation

• sporopollenin

• prevents drying out

• found in spores and pollen

4 major evolutionary transformations in plants

• alternation of generations

• vascular tissue

• seeds and pollen

• flowers and fruits

4 major plant groups

• bryophytes: no vascular tissue

• seedless vascular: have vascular tissue, need water

• gymnosperms: seeds + pollen

• angiosperms: flowers + fruits

alternation of generations

• life cycle alternates between gametophyte and sporophyte

• gametes → zygote → sporophyte → spores → gametophyte

bryophytes and key characteristics

• first land plants

• small and lives near water

• no vascular tissue, roots, or true leaves

• must stay moist and absorbs water directly

bryophyte life cycle

• gametophyte = dominant stage

• sporophte grows on and depends on gametophyte

• water required for fertilization

difference between gametophyte and sporophyte

• gametophyte: main plant body, produces gametes

• sporophyte: grows from gametophyte, produces spores, and helps with spore dispersal

vascular tissue

• internal transport system:

  • xylem: water/minerals

  • phloem: sugar

• allows plants to grow taller

seedless vascular plants

• has vascular tissue, roots, leaves

• sporophyte = dominant and independent

• still require water for fertilization

importance of seeds and pollen

• remove need for water in reproduction

• pollen carries sperm through air

• seeds protects embryo, provides nutrients, and improves dispersal

gymnosperms and their key features

• first plants with seeds and pollen

• no flowers or fruits

• not enclosed

• reproduction in cones

• wind pollination

gymnosperm life cycle

• pollination → fertilization → seed → new plant

major groups of gymnosperms

• cycads: tropical

• ginkgo: one living species

• gnetophytes: small unusual groups

• conifers: most common

advantages of flowers and fruits

• flowers: efficient, targeted pollination

• fruits: surround seeds, helps in seed dispersal

• endosperm: feeds embryo → higher survival

angiosperms

• most diverse plant group

• increased food availability on land

two main angiosperm groups

• monocots: 1 cotyledon and parallel veins

• eudicots: 2 cotyledons, branching veins, and more diverse and efficient