1. Chapter 17 – Introduction to Plants
Plant Evolution and Diversity:
The Colonization of Land

2. Plant Evolution
Plants: multicellular, eukaryotic, photosynthetic, autotrophs
1. Nonvascular Plants (Bryophytes)
2. Vascular Plants (Tracheophytes)
Seedless : club mosses and ferns
Seed : Gymnosperms (cones) and
Angiosperms (flowers)
Terrestrial colonization needs:
Support – vascular tissue and lignin
Absorption (above & below ground)
Vascular tissue for transport
Waxy cuticle for water retention
Stomata for gas exchange
Gametangia for reproduction
seedless vascular
seeded vascular
club moss
liverwort
non-vascular
moss
hornwort
fern

3. Plant Origins:
Charophyceans: green algae (closest living plant ancestor)
Similarities:
1. Molecular similarities in nuclear and chloroplast genes: chlorophyll a & b
2. Biochemical similarity in cellulose composition; peroxisome enzymes
3. Cell division similarity in mitosis; cytokinesis
4. Sperm similarity

4. Green Algae versus Plants
Supported by water, anchored by holdfast
Whole body is exposed to water, light & minerals
Lack organs with specialized functions
Lack apical meristems, mycorrhizae, cuticle, stomata and vascular tissue
Embryo develops in water
Lack seeds and spores
Plants
Leaves and stems usually contain rigid supporting elements
Above ground parts exposed to light, roots in contact with soil and nutrients
Discrete organs (roots, stems and leaves)
Have apical meristems, mycorrhizae, cuticle, stomata and vascular tissue
Walled spores develop in sporangium
Embryo develops in female gametangium
Many have resistant spores/seeds that aid in dispersal
Exhibit ALTERNATION OF GENERATIONS

5. Alternation of Generations
Alternation of Generations: lifecycle in which there is both a multi-cellular diploid (2n) form (the sporophyte) and a multi-cellular haploid (n) form (the gametophyte)
(2n) Sporophyte – makes spores by meiosis
(n) Gametophyte – makes gametes by mitosis
** Unlike animals, the diploid and haploid stages of plants are distinct, multi-cellular generations.
** These 2 generations alternate in producing each other spore = (n) cell that grows into a new organism without fusing with another

6. Moss Lifecycle Gametophyte : Dominant Generation
1. Gametes develop in gametangia (archegonia = female, antheridia = male) usually on separate plants Sperm swim through film of water to egg in archegonium. Fertilization occurs – zygote remains in archegonium.
2, 3. Zygote divides by mitosis  sporophyte embryo  mature sporophyte (which remains attached to gametophyte)
4. Meiosis occurs at tips of sporophyte stalks
* haploid spores are released from sporangium
5. Spores undergo mitosis and develop into gametophyte plants

7. Fern Lifecycle Sporophyte – Dominant Generation (most plants)
Fern gametophyte (heart shaped – prothallus) sperm requires moisture to reach egg. Fertilization occurs.
Zygote remains on gametophyte
Zygote develops into independent sporophyte by mitosis
Mature sporophyte contains clusters of sporangia – which undergo meiosis
Haploid spores are released
1. Develop into gametophytes

8. Gymnosperm Lifecycle Male gametophyte – microspore, Female gametophyte - megaspore
Sporophyte – Dominant Generation
1. Ovulate cone (female) hard and woody, contains scales; each with pair of ovules
2. Pollen cone (male) smaller, contain sporangia – make haploid spores by meiosis
Male gametophytes (pollen grains) develop from spores
3. Pollination occurs when pollen grains enter ovule
4. One surviving haploid spore develops into female gametophyte
Months later – eggs appear in female gametophyte
5. Tube grows out of pollen grain and releases sperm near egg
Fertilization occurs nearly a year after pollination
6. Eggs are fertilized, one zygote develops fully into a sporophyte embryo
Ovule transforms into the seed (contains food supply) and has a tough seed coat
Seeds are shed about 2 years after pollination
7. Seed germinates and embryo grows into pine seedling

9. Angiosperm Lifecycle Sporophyte – Dominant Generation
Meiosis in anthers  spores undergo mitosis  male gametophyte (pollen grains)
Meiosis in ovule spores undergo mitosis  forms few cells of female gametophyte (one becomes egg)
Pollination – pollen grain lands on stigma
Tube grows from pollen grain to ovule and fertilization occurs
Zygote forms
Seed develops from each ovule
As seed develops, ovary wall thickens forming the fruit that encloses the seeds
Seed germinates  mature sporophyte

10. Flower Anatomy Floral organs: sepals, petals, stamens, carpels
Complete flower – all 4 parts
Incomplete flower – lacking 1 or more organ
Perfect flower – both stamens and carpels on 1 flower – (Monoecious)
Imperfect – lacking either a stamen or carpel – (Dioecious)
Sepals – enclose flower before it opens (calyx – complete circle of sepals)
Petals – attract pollinators (corolla - complete circle of petals)
Stamens – male: anther (produces pollen) filament (stalk)
Carpels (pistil) – female: stigma (sticky, traps pollen), style (stalk between stigma and ovary), ovary (protective chamber containing one or more ovules)
Receptacle – where stem and flower leaves meet
*sepals and petals = accessory organs
*carpels and stamens = essential organs

11. Important Medications Derived From Plants

12. * site of pollination and fertilization
Flowers: the sex organs of angiosperms
* site of pollination and fertilization
* generate fruits with seeds inside
* contain gametophytes (ovules and pollen grains)
* fruit is a great seed dispersal in fruit (via animals)
* flower is a great pollen dispersal mechanism flower’s color/nectar/scent (via insects, birds)
Agriculture: many a plant product
* gymnosperms: lumber, paper
* angiosperms: almost all food, spices, meds, coffee, chocolate

13. Co-evolution of plants and animals- a selective process:
bees drawn to flowers with markings that reflect UV light
hummingbirds drawn to flowers with nectar in cone-shaped tube
bats drawn to nocturnal flowers with light colors, strong scent (easy to find)
Plant Diversity: a non-renewable resource:
massive clearing of forests
25% of Rx drugs made from plants
~50 mill acres cleared yearly (size of WA)
40% decrease in America’s forests (habitation, paper,lumber)
20% of rainforests cleared in 20th century