Plant Diversity

Land Plants Evolved from Green Algae

Occurred 500 million years agoPlants have enabled the life of other organisms on landSupply oxygen & provider of energy

Evolutionary Evidence1) Produce cellulose for cell walls in the same fashion2) The peroxisomes have enzymes that reduce the effects of photorespiration3) Sperm structure is related4) Produce cell plates the same way5) Genetic similarities

Alteration of Generation2 stages:1) Gametophyte2) Sporophyte

In gametophyte stage: Gametes are producedEgg & sperm fuse to form a diploid zygote (sporophyte)

Divides mitoticallySporophyte produces spores by meiosis

The zygote develops within the tissues of the female

Provides nutrientsReferred to as embryophytes

AnatomyFemales = archegonia (single egg produced)Males = antheridia (many sperm produced)

Moss Life CycleNonvascular (no xylem or phloem)Life cycle dominated by gametophytes

Ferns & Seedless Vascular Plants

First to grow tallRequire water for fertilizationDominated by the sporophyte stage

Seeded Plants5 adaptations:1) Reduced gametophytes - microscopic2) Heterospory – 1 for male, 1 for female3) Ovules & eggs – increases reproductive fitness4) Pollen & sperm – Key adaptation to land5) Seeds – protect the embryo

GymnospermsNaked seedsUsually found on conesPines, spruces, firs, & redwoods

Evolutionary Advances of the Pine Life Cycle

1) Ovulate cone bears ovules2) Sporangia in pollen cone produce spores3) Pollination4) Haploid spore develops into female gametophyte to form eggs5) Male gametophyte forms sperm6) Zygote develops into embryo, ovule becomes seed7) Seed germinates & embryo grows

AngiospermsSeeded plantsContain flowers & fruit250,000 species – 90% of all plants

Flower:SepalsPetalsStamens – male reproductionCarpels – female reproduction

FruitsMature ovaries of the plantAs seeds develop from ovules after fertilization, the wall of the ovary thickens to become fruitFruits help disperse the seeds

Evolutionary Advances of the Angiosperm Life

Cycle1) Haploid spores in anthers develop into pollen grains2) Haploid spore in ovule develop into an egg3) Pollination & growth of pollen tube4) Zygote5) Seed6) Fruit7) Seed germinates & embryo grows