Plant Diversity
Land Plants Evolved from
Green Algae
Occurred 500 million years ago
Plants have enabled the life of other organisms on land
Supply oxygen & provider of energy
Evolutionary Evidence
1) Produce cellulose for cell walls in the same fashion
2) The peroxisomes have enzymes that reduce the
effects of photorespiration
3) Sperm structure is related
4) Produce cell plates the same way
5) Genetic similarities
Alteration of Generation
2 stages:
1) Gametophyte
2) Sporophyte
In gametophyte stage: Gametes are produced
Egg & sperm fuse to form a diploid zygote (sporophyte)
Divides mitotically
Sporophyte produces spores by meiosis
The zygote develops within the tissues of the female
Provides nutrients
Referred to as embryophytes
Anatomy
Females = archegonia (single egg produced)
Males = antheridia (many sperm produced)
Moss Life Cycle
Nonvascular (no xylem or phloem)
Life cycle dominated by gametophytes
Ferns & Seedless Vascular
Plants
First to grow tall
Require water for fertilization
Dominated by the sporophyte stage
Seeded Plants
5 adaptations:
1) Reduced gametophytes - microscopic
2) Heterospory – 1 for male, 1 for female
3) Ovules & eggs – increases reproductive fitness
4) Pollen & sperm – Key adaptation to land
5) Seeds – protect the embryo
Gymnosperms
Naked seeds
Usually found on cones
Pines, spruces, firs, & redwoods
Evolutionary Advances of the
Pine Life Cycle
1) Ovulate cone bears ovules
2) Sporangia in pollen cone produce spores
3) Pollination
4) Haploid spore develops into female gametophyte to form
eggs
5) Male gametophyte forms sperm
6) Zygote develops into embryo, ovule becomes seed
7) Seed germinates & embryo grows
Angiosperms
Seeded plants
Contain flowers & fruit
250,000 species – 90% of all plants
Flower:
Sepals
Petals
Stamens – male reproduction
Carpels – female reproduction
Fruits
Mature ovaries of the plant
As seeds develop from ovules after fertilization, the wall
of the ovary thickens to become fruit
Fruits help disperse the seeds
Evolutionary Advances of the
Angiosperm Life Cycle
1) Haploid spores in anthers develop into pollen grains
2) Haploid spore in ovule develop into an egg
3) Pollination & growth of pollen tube
4) Zygote
5) Seed
6) Fruit
7) Seed germinates & embryo grows