Plants

• Plants originated from green algae 470 mil years ago

• Then traits facilitating life on land appeared 425 mil years, like reproductive structures, structuures that anchor the plant to soil, and photosynthetic branches

• Now, there are nonvascular plants, seedless vascular plants, and seed plants

• There are 325,000 known plant species today

• Plants provide oxygen, food, and habitat for terrestrial organisms

• Green algae (photosynthetic protists) called charophytes are the closest living relatives of land plants

• Sporopellenin→durable polymer that prevents zygote dehydration in charophytes, similar to the modern casing of plant spores

• Initial Benefits to Being on Land:

  • unfiltered sunlight

  • plentiful carbon dioxide

  • Mineral-rich soil

  • Few herbivores/pathogens

Derived Traits of Land Plants:

• Alternation b/w two multicellular generations

  • Gametophyte generation (haploid)

  • Sporophyte generation (diploid)

  • spores develop into gametophytes

• Multicellular dependent embryos

  • embryo depends on the parent→plants called embryophytes

  • Parent provides embryo nutrients via placental transfer cells

• Walled spores produced in sporangia

  • Sporangia= where the sporophyte produces spores

  • sporopellenin of the spore walls helps when the organism is in harsh environments

• Multicellular gametangia

  • Gametes produces in the gametangia

  • egg is fertilized in the archegonium

• Apical meristems

  • repeated cell division

  • allow for continual growth in length by the plant

  • cells can differentiate into many different tissue types

Additional Derived Traits:

• Cuticle- waxy covering of epidermis, protects against microbes, preserve water

• Mycorrhizae- mutualistic association b/w fungi and plants, fungi help plants acquire nutrients

• Stomata- allow for gas exchange, can close up to minimize water loss

• Secondary Compounds- protect against herbivores, parasites, pathogens

  • Alkaloids- toxic, bitter, stimulants, and/or analgesics

    • caffeine, morphine

  • Terpenes- strong smell, repel predators, may be medicinal

    • essential oils, resin, turpentine

  • Tannins- some bitter, repel predators, antioxidants

    • red wine, red beans, cinnamon

  • Flavonoids- some bitter, plant pigments, and/or antioxidants

    • grapefruit, red onion, dark chocolate

Evolution of Seed Plants

• Seeds are “mobile wombs”- allowed seed plants to become critical producers

• Gymnosperms- “naked seed”, uncovered, like pine cones

  • increasing dominance of sporophyte generation

  • seed is resistant, dispersible stage of life cycle

  • pollen is usually airborne, bringing gametes together

  • Mostly conifers, but there are some exceptions

  • 4 phyla total:

    • Cycadophyta

    • ginkgophyta

    • welwitschia

    • conipherophyta

• Angiosperms- “container seed”, in fruit

  • seed plants that produce flowers and fruits

  • flower= structure for sexual reproduction

  • pollination by animals (insects, birds, mice, etc.) or wind

  • evolution impacted by evolution of pollinators and herbivores→also goes the other way

  • Fruit structures protect dormant seeds

  • Structure aids in seed dispersal→ wings, berries, barbs

  • Most plants (about 90 percent) are angiosperms

    • all major food crops are angiosperms→wheat, corn, peanuts, cotton, soybeans

    • also feed livestock

  • 3 Adaptive features of Life Cycle:

    • Flowers

      • carpel= stigma+style+ovary

      • stamen= anther+filament

      • Pollination

        • movement of sperm producing reproductive until to the receptive egg producing rep unit

        • animal pollinated

        • wind pollinated

        • some are water pollinated

        • cross-pollination= pollen moved from 1 plant to the stigma of another plant

          • best b/c it prevents inbreeding

        • self-pollination= pollen moved from a plant to another flower on the same plant

    • Double Fertilization

      • pollen lands on stigma→germination→grow down from stigma into style→ penetrate

      • built in food for the seed

      • more efficient energy use by the angiosperm

    • Fruits

      • Simple Fruits= single ovary

        • wheat, sunflowers, oak, milkweed, beans, tomatoes, cherries

      • Accessory Fruit= not just ovary tissue

        • apples, strawberries (are also aggregate)

      • Aggregate Fruits= a single flower w/ multiple ovaries

        • strawberries, blackberries

      • Multiple fruit= lots of flowers on the same floral stalk

        • pineapple, figs

Shared Characteristics of Seed Plants:

• Reduced gametophytes- really tiny, develop in walls of spores, gametophyte protected and obtain nutrients from sporophytes

• Heterospory- produce 2 types of spores, develop into male or female gametophytes

  • Megasporangia- produce megaspores that give rise to female gametophytes

  • Microsporangia- produce microspores that give rise to male gametophytes

  • Ferns on the other hand, are homosporous→produce one kind of spore, usually results in a bisexual gametophyte (ferns are not seed plants)

• Ovules + egg production

• Pollen + sperm production

• Advantages of the Seed:

  • contain embryos and food supply in a protective coat

  • allow for long distance dispersal and long-term dormancy as needed