Plant evolution

So plants needed some adaptations to:
- Differentiate their tissues and take advantage of the dual air/water nature of the terrestrial environment
- And deal with its stresses
(Addressing these points will answer our opening questions)

Characteristics of plants

Traits shared with algal ancestors
- Chloroplasts with photosynthetic pigments
- Cell walls containing cellulose
- Starch food reserve

Traits of all true plants

Apical meristems- pluripotent
Shoot and root systems
- Shoot system= produces sugars by photosynthesis and carries out reproduction
- Roots system= anchors the plant, penetrates the soil and absorbs water and minerals and stores food
Sporangia
Gametangia
- Archegonium = eggs
- Antheridium = sperm
Alternation of generations
- A gametophyte generation which makes gamete
- Sporophyte generation which probably makes spores
- 1. sporophyte- diploid
  - A. growth by mitosis
  - Haploid spores by meiosis
- Spores: single haploid reproductive cell that can develop into an adult multicellular organism on its own
  - Are released into envit- can disperse
- 2. Gametophyte- haploid
  - B. produced gametes (haploid sperm and egg) by mitosis
- Plants reproduce in two stages* (LOOK AT FIGURE)
Plant diversity and adaptation (why are mosses small/wee?)
- Bryophytes (mosses, liverworts, hornworts)
- Adult plant/dominant generation is gametophyte generation (haploid and ar producing gametes)
- Sporophyte generation grows up out of the gametophytes (grows taller than the gametophyte)
- 1. Advances. Plant Evolutionary adaptations to land
  - B. protection of young sporophyte
- Still tied to water environment- why? (structural reasons)
- 2. Structural reasons
  - A. lacking a waxy cuticle (water can go in and out of their cells super easily
  - B. lacking stomata (the pores in leaves, used for gas exchange)
  - C. lacks true leaves
  - D. Lacks true roots (they are just single cells or just a thread of single cells) this limits how big and limited in how much nutrients from soil they can get. There is also not very structurally supported
  - E. Lacking stems and vascular tissues (xylem phloem) (like veins)
- 3. Reproductive reasons
  - A. external fertilization
  - B. young gametophyte (protonemata)- unprotected and tied to water
Plant diversity and adaptations
- B. Seedless vascular plants- ferns
  - Adult plant/ dominant plant is the sporophyte generation
  - The leaves provide the height so they don't need the sporophytes to grow higher like in the mosses
  - Brown dots on ferns= sori (sorus=singular). These are sporangia of ferns found on underside of fronds
- 1. Adaptations to terrestrial environment
  - A. have a cuticle and stomata.
    - The cuticle is waxy coating on the surface of leaves- prevents water loss thru dermal cells. Stomata (stoma= singular) are pores in surface leaves that allow air and water vapor to move in and out of leaves (aka gas exchange) (stomata are not cells but are bordered by cells)
  - B. have true leaves and roots
    - Rhizome can be a horizontal or a vertical stem
  - C. Vascular tissue (stems of a sort) (where they get their name)
    - Water and sugar and nutrient transport
    - Structural support against gravity
  - D. young sporophyte- tied to and supported by the gametophyte (-/+)
    - + : it gets nutritional support from gametophyte to enhance the odds of survival and growth
    - - : negative is that sporophyte is tied to place of origin (can’t disperse)
- Plant diversity and adaptations
  - C.gymnosperms- conifers. Seed producing vascular plants. Cone bearing
    - Adult/ dominant generation is the sporophyte generation
  - 1. Adaptations to terrestrial environment
    - A. structural advantages all that came before: cuticle, stomata, leaves, roots, vascular tissue. And proper stem and trunks with protective bark
    - B. gametophyte is protected (confiners) (now up high in the branches)
    - C. pollen= the male gametophyte
    - D. internal fertilization= inside female gametophyte (the big pine cone)
    - E. Seeds
  - Gymnosperms- gametophytes are completely nutritionally dependent on sporophyte generation
    - Sporophyte sends nutrients to female cones to support development of embryos
Why are seeds important? What do seeds do?
- Seeds protect embryo (from desiccation)
- Provide a mode of dispersal
  - 2. Disadvantages/shortcomings of gymnosperms
    - A. lack fruit- see is “naked” inside scales of the pinecone
    - B. lacks flower
  - D. Angiosperms
  - 1. Adaptations to terrestrial environment
    - A. gametophyte is still protected, but inside of a flower rather than a cone
    - B. flower (attracts pollinators)
      - How do flowers attract pollinators? The color, size, release scent (can mimic mating pheromones of insects) (corpse flower), produce nectar
    - C. angiosperm pollen- produces and protects sperm (note: no wings because they don't need them!)
    - D. internal fertilization in female gametophyte
    - E. fruit - mature ovary of a fertilized angiosperm ova. This contains seed/seeds. Seeds contain and protect embryos;[protected by seed coat. Fruits can provide a variety of modes of dispersal
  - How are angiosperm seeds dispersed ?
    - Edible fruits- animal dispersed seeds. Endozoochory (animals eating fruits and depositing it out somewhere else) (seeds coat protects embryo from acids in animals gut so its not digested)
      - Fleshy, sweet/sugary
    - Episooochay (fruits stick to animals fur/skin)
      - Dry (not fleshy)
      - Structures (velcro texture, hooks) that promote catching in animal fur
    - Wind dispersed seeds- anemochory
      - Small and lightweight
      - Containincreadessurface area to be caught by wind
      - Pappus on dandelion wing on maple)
    - Water dispersed seeds- hydrochory
      - Common in plants growing near water
      - Hollow or spongy structure to increase buoyancy