Kingdom Plantae: Evolution and Life Cycles

Slideshow Notes

Kingdom Plantae:

• Eukaryotic

• Multicellular

• Autotrophic

What are the closest relatives to Plants?

Plants closest relatives are green algae (protists)

Charophytes

• Charophytes are a group of green algae whose ancestral lineage gave rise to land plants in what resulted in a profoundly transformative event in the natural history of the planet

Evidence proving:

• Plants closest relatives are green algae (protists)

• Modern day charophytes and plants had a common ancestor

• DNA (in chloroplasts and nucleus) is similar

• Same structure for making cell wall, cellulose wall 

• Similar enzymes

• Flagellated sperm is similar (in plants that produce flagellated sperm)- Think C Ferns

How did we go from alga to plant?

• Algae are aquatic

• Some may have lived on pond fringes

  • Ponds were ephemeral

  • Algae that had adaptations to this survived, reproduced, increased in numbers…

Plants vs Multicellular Algae

Plant Adaptations to Land

• First land plants arose around 475 mya

  • Roots

  • Stem

  • Vascular Tissue (Xylem and Phloem) Cuticle

  • Stomata

  • Wind/Animal dispersed seeds/spores

  • Embryophytes

Alternation of Generations

predominant type of life cycle in plants and algae. 

• Consists of a multicellular haploid sexual phase, the gametophyte, which has a single set of chromosomes alternating with a multicellular diploid asexual phase, the sporophyte which has two sets of chromosomes.

• Sporophytes produce spores via meiosis

• Gametophytes produce gametes via mitosis

• Fertilization can occur between two haploid gametes originating from different organisms of the same species or from the same organism.

• Way in which all land plants and most algae undergo sexual reproduction.

gametophyte

“the haploid, multicellular, sexual reproductive stage in plants and algae that develops from spores and that gives rise to the male and female gametes which unite during fertilization to form the zygote”

sporophyte

“the diploid, multicellular, asexual reproductive stage in plants and algae that develops from the zygote and that produces spores”

gametophytes

“the haploid, multicellular, sexual reproductive stage in plants and algae that develops from spores and that gives rise to the male and female gametes which unite during fertilization to form the zygote”

Plants are all called _____ophytes

• Plants are all called embryophytes

  • Complex multicellular eukaryotes with specialized reproductive organs

  • Fertilization occurs on the parent plant, and stays there as a multicellular entity (unlike algae)

  • Nurture young embryo sporophyte during the early stages of its multicellular development within the tissues of the parent gametophyte

  

Botanist recognize ——- plant divisions (Phyla)

• Botanists recognize ~9 -15 Divisions (Phyla)

  • (For the purposes of tracking plant evolution we can just look at 4 representatives that typify the major changes)

Bryophyta

Non Vascular Seedless Plants

• No vascular tissue, leaves, or roots

• Short in stature, low to ground

• Flagellated sperm (rely on water for repro.)

• Dominant gametophyte stage

• Sporophyte grows from gametophyte and stays attached 

Pteridophyta

Vascular, Seedles Plants

• Vascular tissue present

• Can grow tall

• Flagellated sperm

• Dominant sporophyte stage

• Sporophyte not as visible growing from gametophyte

Vascular, Seedless Plants Life Cycle (Pteridophyta)

Gymnosperms

Naked Seed Plants (gymo-naked, sperm-seed)

• Includes conifers, cycads, ginkgos, and gnetophytes

• Dominant sporophyte stage

• Vascular tissue (roots, stems, leaves)

• Reproduction

  • Produce pollen (develops from spores)

    • Pollen produces sperm, dispersed through wind 

  • Produces seeds (protect embryo)

    • Seed – embryo enclosed with food in a coating

  • Long time between pollination and fertilization

Gymnosperm Life Cycle

Angiosperms

Covered Seed Plants

• Division – Anthophyta (“scientific name” (phylum of flowering plants))

• Flowering Plants

• Very Diverse: 250,000 sp.

  • Examples range from common grasses and shrubs to the ancient flowering trees like magnolias and highly evolved orchids

• 90% of existing plants

Angiosperm/Anthophyta Reproduction Characteristics

• Dominant sporophyte stage

• Reproduction

  • Gametophytes on flower (pollen and ovule)

  • Seeds protected in fruits

  • Fertilization occurs soon after pollination

  • Multiple methods of dispersal of pollen and seeds, including wind and animal dispersal

Angiosperm Life Cycle

Coevolved, Mutualistic Relationships With Animals:

• As pollinators

• As seed dispersers

Flowering Plant Groups (Angiosperms)

• Class Liliopsida (Monocotyledons) – monocots

• Class Magnoliopsida (Dicotyledons)– dicots

• Cotyledon - A structure produced by the embryo of a seed plant that serves to absorb nutrients packaged in the seed, until the seedling is able to produce its first true leaves and begin photosynthesis (more to come on this later…)

Cotyledon

 A structure produced by the embryo of a seed plant that serves to absorb nutrients packaged in the seed, until the seedling is able to produce its first true leaves and begin photosynthesis (more to come on this later…)

Monocots vs Dicots

Angiosperm Male Gametophyte Production:

• Pollan produced in the anther (pollen sac)

• Mother cell divides through meiosis into 4 haploid microspores

• Haploid microspores divide through mitosis to form the male gametophyte (pollen grain). 

Angiosperm Female Gametophyte Production:

• Ovum are produced in the ovary located at the bottom of the carpel

• Mother cell divides through meiosis into 4 haploid megaspores, but only one will persist

• Haploid megaspore divides 3 times through mitosis to form the female gametophyte (embryo sac). 

Angiosperm Fertilization

• Double fertilization

  • One sperm cell fuses with the egg cell to form the zygote (2n), and the second sperm cell fuses with the central cell to form the endosperm (3n)

• Endosperm = food source for zygote

• Zygote then divides through mitosis to produce the embryo

Double Fertilization

One sperm cell fuses with the egg cell to form the zygote (2n), and the second sperm cell fuses with the central cell to form the endosperm (3n)

The endosperm is equivalent to the

food source for zygote

Angiosperm Embryo Development

• Embryogenesis in plants occurs to establish the basic shoot-root body pattern of the plant and to accumulate food reserves that will be used by the germinating seedling after dormancy

• Monocots and dicots achieve this in slightly different ways

  • Monocots- one cotyledon, parallel vein body structure, and fibrous roots

  • Dicots- have two cotyledons, branching leaf vein body structure, and tap roots 

Monocots

one cotyledon, parallel vein body structure, and fibrous roots

Dicots

have two cotyledons, branching leaf vein body structure, and tap roots 

Angiosperm Fruit Development

• All flowering plants produce fruit, regardless of whether the fruit is edible, sweet, or soft.

• Surrounding the seeds is the fruit

• Fruit is the ripened ovary or, in some cases it’s can be a ripened receptacle (strawberries)

Distinct layers in every fruit:

• Exocarp- outermost layer of the fruit, usually in direct contact with the environment

• Mesocarp- middle layer of the fruit, in between the exocarp and the endocarp. It becomes fleshy in fleshy fruits and is thicker in fleshy fruits compared with dry fruits

• Endocarp- innermost layer of the pericarp, in direct contact with the placenta (from where the seeds form). It can be either hard (like in a stone fruit like a peach), membranous, or fleshy in some fleshy fruits (like the tomato)

• All three layers form the pericarp- part of the fruit that surrounds the seed(s). 

Exocarp

outermost layer of the fruit, usually in direct contact with the environment

Mesocarp

middle layer of the fruit, in between the exocarp and the endocarp. It becomes fleshy in fleshy fruits and is thicker in fleshy fruits compared with dry fruits

Endocarp

Innermost layer of the pericarp, in direct contact with the placenta (from where the seeds form). It can be either hard (like in a stone fruit like a peach), membranous, or fleshy in some fleshy fruits (like the tomato)

Pericarp

part of the fruit that surrounds the seed(s). 

Dry fruit

• These dry when they are mature 

• Layers are thinner and do not hold as much water

• Pericarp is often right next to the seed so hard to distinguish layers

• Rely less on animals and more on dehiscence and wind to spread seeds

Simple Fruit

• Develops from one ovary- stone fruits like peaches

Aggregate Fruit

• Single flower has many ovaries  each ovary is a bit of fruit - fruitlet

• Ex: raspberry, strawberry

Multiple Fruit (type of aggregate)

• multiple fruit develops from multiple ovaries of multiple flowers

• Ex: Pineapple

Germination

• Germination is the process by which a plant grows from a seed into a seedling. 

• Seeds remain dormant until conditions are favorable for germination. 

• All seeds need water, oxygen and optimal temperature to germinate. 

• Process of germination

  • Seed takes up water

  • Expands and seed coat ruptures

  • Endosperm/cotyledon is used for energy to grow until the plant is old enough to perform photosynthesis

Asexual Plant Reproduction

• Vegetative Reproduction- buds on roots or vegetation

• Bulbs fragment –grow into another plant – garlic, tulip

• Runners can sprout new plants – strawberries, dune grass

• Rhizomes (underground runners) can sprout shoots – ferns, irises, ginger