MD

9/3 Plant Biology – Angiosperms and Reproduction (Vocabulary)

Classroom norms and SI resources

  • The instructor emphasizes a respectful, distraction-minimized learning environment: arrive late if needed, but sit as close as possible to the entrance to minimize disruption. Do not start packing up during the video; wait until the video ends and the official dismissal.
  • Attendance data and implications:
    • The room currently has ~30–35% fewer students than usual; these students have not dropped the class but are choosing not to attend lectures.
    • 50 years of data for BIO 1500 show that attending lectures increases the probability of getting the grade you want; those who attend tend to do better overall.
  • Supplemental Instruction (SI) and Learning Assistants (LA):
    • Julia is the SI for the 4:00 PM lecture; information is online on Canvas under the SI/LA section.
    • Some LAs/SIs offer in-person review sessions; others are Zoom-only.
    • Zoom sessions have links in the document; if you join and are not admitted immediately, you may be in a private or group session; be patient.
    • In-person hours exist for some SIs/LA staff; remote Zoom hours may also exist for others.
  • Structure and recap:
    • The course revisits earlier material: why study plants, and the link between plants and fuels (fossil fuels and biofuels like ethanol from glucose/starches/cellulose).
    • Discussion of climate change, global warming, and the role of plants in the carbon cycle.
  • Preview: the current lecture moves from general plant appreciation to the biology of angiosperms, reproduction, and life cycles.

Fossil fuels, biofuels, and climate basics

  • Fossil fuels originate from decaying carbon-based organisms over millions of years (coal, natural gas, crude oil).
  • Plants can be used to make biofuels (e.g., ethanol from corn):
    • Fermentation converts glucose/starches/cellulose to ethanol.
    • Difference from beverage alcohol is refinement and intended use (fuel vs. beverage).
  • Global warming and climate change basics:
    • Global warming is a major aspect of climate change, driven by higher atmospheric CO₂ levels.
    • Key causal chain (physics): burning fossil fuels increases atmospheric CO₂, which absorbs heat from solar radiation, warming the air and surface.
    • Warmer air increases evaporation of surface water, leading to drier surfaces; drier surfaces lead to even less cooling, amplifying warming (feedback loop).
  • Carbon cycle and forests:
    • Plants remove CO₂ from the atmosphere via photosynthesis and release O₂ as a byproduct.
    • Deforestation reduces the planet’s capacity to remove CO₂, contributing to higher atmospheric CO₂ and enhanced warming.
    • Historical note: eastern North American forests have shrunk to less than 1% of their former extent in some regions due to logging and land-use change.
  • Interpreting graphs (described verbally):
    • Atmospheric CO₂ vs. time (blue line) shows a rise starting with the Industrial Revolution and continuing to present.
    • Global temperature vs. time shows increasing trends with variability day-to-day, but a clear upward trajectory beginning in the mid-20th century.
  • Simple physics recap (for context):
    • CO₂ is a greenhouse gas; its presence traps heat and contributes to warming of the lower atmosphere and surface.

Notable plants, biodiversity highlights, and cultural context

  • Extremely old organisms and notable examples:
    • Bristlecone pine: up to ≈ 4600 years old.
    • Creosote bush: individual individuals reported over 12{,}000 years old in some cases.
    • Lomatia tasmanica (King’s Lomatia): an ancient clone with an estimated age of ≈ 43{,}000 years; location kept secret to protect it.
  • Art and public engagement related to plants:
    • Rachel Sussman’s project and book documenting the world’s oldest living organisms; campus installation: Making Broken Things Beautiful in Old Main (described but not widely known on campus).
  • Giant and iconic plants:
    • Redwoods (Sequoias) of the West Coast: trunk diameter ≈ 35 ext{ ft}; circumference ≈ 109 ext{ ft}; height up to ≈ 300 ext{ ft}; trunk mass enormous; could yield ≈ 6×10^5 board feet of timber from a single tree; trunk weight ≈ 1400 ext{ tons}.
    • Comparison anchors: 15 adult blue whales, 10 train locomotives, or 25 military tanks in terms of scale.
    • Water transport in tall trees: a redwood can lift ≈ 2 ext{ tons} of water per day up to its crown (≈ 300 ft).
  • Pondo (Quaking aspen, Populus tremuloides) concept:
    • A clonal colony with ~43,000 stems sharing a single root system; spans ≈ 160 acres; estimated total mass ≈ 13{,}000{,}000 ext{ pounds}.
    • Often cited as one of the largest living organisms on the planet; underground fungal networks and slime molds may surpass this scale in some respects.
  • The 9/11 survivor tree:
    • The lone pear tree survived the 9/11 attacks and was replanted in the 9/11 Memorial; seeds from this tree were distributed to multiple U.S. cities to plant new trees in affected places (Boston, Charleston, Orlando, San Bernardino, Dallas).
  • Carnivorous and parasitic plants:
    • Pitcher plants and Venus flytraps are carnivorous; many hunter mechanisms rely on traps and digestive enzymes.
    • Purple pitcher plant is native to SE Michigan; it can be cultivated and fed with small insects.
    • Mistletoe is a parasitic plant; its seeds can be jet-propelled by water pressure to land on adjacent hosts.
    • Rafflesia (corpse flower) odor attracts pollinators like flies; extremely large floral structures; pollination strategies can involve animals as diverse as insects and elephants.
  • Plant interactions with the environment:
    • Plants can be used to locate or remediate underground contaminants, including some radiation sensing capabilities in roots and shoots.
  • Invasive species example:
    • Kudzu (Pueraria montana) is a classic invasive vine in the southern United States; it grows rapidly and can cover structures and landscapes (examples shown of vines climbing poles, buildings, cars, homes).
    • Economic impact: removal and control costs exceed 100{,}000{,}000 annually in the U.S. due to Kudzu-related damage.
  • Cultural references and media:
    • Plants have influenced art (Vincent van Gogh), film (American Beauty), and music (Stevie Wonder’s Journey Through the Secret Life of Plants).
    • Horror and pop culture connections to plants include films like Little Shop of Horrors and other plant-themed media.
  • A quick note on pollination and plant-animal interactions:
    • Pollination can involve wind, insects, birds, or bats depending on the plant species and ecological niche.
    • Some flowers are male or female-only; others have both male and female parts in the same flower; some plants produce male flowers separately from female flowers.
    • Pollen is commonly equated with male gametes in many educational contexts, and pollen grains represent the male gametophyte.

Angiosperms: overview and taxonomy

  • What are angiosperms?
    • The phylum Anthophyta (often called angiosperms or flowering plants) are highly specialized for reproduction via flowers.
    • They evolved from a common ancestor roughly between 100 and 200 million years ago, with estimates commonly placed around ~1.3 imes 10^{8} years ago.
  • Major classes within angiosperms:
    • Eudicots (the larger, more diverse group): ≈ 1.75 imes 10^{5} described species; examples include trees, shrubs, snapdragons, peas, etc.; predominantly pollinated by animals or wind.
    • Monocots: ≈ 6.5 imes 10^{4} described species; examples include grasses, lilies, palms, irises, orchids; many monocots are wind-pollinated but many are self-pollinated.
  • Global prevalence:
    • Roughly 80 ext{ extbf{%}} of described plant species are angiosperms; total described species ≈ 2.7 imes 10^{5}.
  • Taxonomic context:
    • Phylum: Anthophyta (angiosperms)
    • Major differentiation: two large clades (often discussed as dicots/eudicots vs monocots) with distinct morphological and reproductive traits.
  • Visualizing the plant tree of life:
    • In the plant tree of life, angiosperms appear as a major, dominant lineage with extensive diversification.
  • Meiosis and mitosis are essential recurring themes across plant groups, including angiosperms.

Meiosis vs Mitosis: core concepts and definitions

  • Key terms:
    • Ploidy (P): the number of complete chromosome sets in a cell. For example, haploid is N, diploid is 2N.
    • Haploid (N): one set of chromosomes; diploid (2N): two sets of chromosomes (one from each parent).
  • Ploidy basics (recap):
    • In humans, somatic cells are diploid: 2N = 46 \Rightarrow N = 23.
    • Sex cells (gametes) are haploid: N = 23 in humans.
  • Mitosis (somatic cell division):
    • Occurs in somatic cells (all cells of the body except sex cells).
    • Process: DNA replicates, then the cell divides to form two genetically identical daughter cells; each daughter cell is diploid (2N), a genetic photocopy of the parent.
    • Outcome: two identical diploid daughter cells; the genetic information is identical to the parent.
  • Meiosis (gamete formation):
    • Occurs in sex cells (gametes: sperm and egg).
    • Process: two rounds of division after DNA replication, yielding four haploid gametes (1N), each genetically distinct from each other and from the parent.
    • Outcome: four haploid cells; essential for genetic diversity.
  • Life cycle implications (animals):
    • Male and female organisms produce haploid gametes via meiosis; fertilization (syngamy) combines sperm and egg to form a diploid zygote; the zygote then undergoes mitosis to form a new diploid organism.
    • Terminology: fertilization = syngamy; gametes = haploid sex cells; zygote = diploid fertilized egg.
  • Life cycle implications (plants):
    • Plants alternate between sexual (gametophyte) and asexual (sporophyte) phases, with meiosis producing spores that give rise to the gametophyte, and mitosis in the gametophyte producing gametes.
  • Hymenoptera haplo-diploidy note (tangential):
    • In some Hymenoptera (ants, bees, wasps), males are haploid (n) and develop from unfertilized eggs, while females are diploid (2n).
  • Quick synthesis: the big picture difference
    • Mitosis: somatic cells, diploid, produces identical diploid daughter cells (2N).
    • Meiosis: sex cells, haploid, produces four genetically different haploid gametes (1N).

Plant life cycle: alternation of generations in angiosperms

  • Core idea: plants alternate between two generations:
    • Gametophyte (haploid, 1N): the sexual generation where sex occurs; in flowering plants, the gametophyte corresponds to the tissues inside the flower that produce gametes.
    • Sporophyte (diploid, 2N): the asexual generation; the large body of the plant that you see (leaves, stems, roots) is the sporophyte.
  • Life cycle sequence for plants (simplified):
    1) Gametophyte (haploid) undergoes mitosis to produce gametes (sperm and egg) within the flower.
    2) Gametes fuse (fertilization or syngamy) to form a zygote (diploid, 2N).
    3) Zygote grows via mitosis into an embryo and then into the sporophyte tissue (the visible plant body).
    4) Sporophyte produces sporangia, which generate spores by meiosis.
    5) Spores (haploid) grow into new gametophytes, continuing the cycle.
  • Dominance of the sporophyte in angiosperms:
    • The sporophyte generation is dominant/visible for most of the plant’s life; the flower represents the gametophyte stage.
    • The flower is the primary site of gametogenesis in many angiosperms; if a plant is flowering, the gametophyte phase is embedded within the flower, while the rest of the plant is sporophyte.
  • Important notes and common questions:
    • If a plant never produces a flower, it could be non-angiosperm (e.g., pinetrees) or flowering could be contingent on environmental cues (photoperiod, temperature).
    • Sporangia produce spores via meiosis; spores develop into gametophytes; gametophytes produce gametes via mitosis; fertilization yields a zygote that grows into the sporophyte.
    • Flower anatomy can include male and female structures on the same plant (perfect flowers) or on different plants (imperfect flowers or dioecious species).
  • Exam-style thought prompt (conceptual):
    • Plants have two generations: the gametophyte and the sporophyte; sporangia produce spores by meiosis; gametophytes produce gametes by mitosis; angiosperms are 2N-dominant; which statement(s) is(are) true? Discuss with neighbors and be prepared to identify false statements.

Quick references and examples discussed in lecture

  • Pointers to remember:
    • Global warming explanation emphasizes CO₂ rise due to fossil fuel burning and deforestation reducing carbon uptake by plants.
    • The role of photosynthesis as a CO₂ sink and the consequence of deforestation on atmospheric CO₂ and climate.
    • The role of pollination in plant reproduction, including wind, insect, bird, and bat pollination.
    • Plants’ remarkable physical and ecological scale illustrated by redwoods, sequoias, and clonal quaking aspen stands.
    • Invasive species like Kudzu demonstrate human-mediated introductions and ecological/economic costs.
  • Notation and formulas used in the notes:
    • Ploidy and chromosome sets:
    • Ploidy P = number of complete sets of chromosomes in a cell.
    • Haploid: N (one set of chromosomes);
    • Diploid: 2N (two sets of chromosomes).
    • Human references:
    • Humans have 2N = 46 chromosomes, hence N = 23.
    • Some plant measurements (illustrative):
    • Redwood trunk diameter: 35 ext{ ft}; circumference: 109 ext{ ft}; height up to 300 ext{ ft}.
    • Trunk mass: 1400 ext{ tons}; board feet of timber from single tree ≈ 6 imes 10^{5}.
    • Water transport in tall trees: ≈ 2 ext{ tons} of water per day up to the crown (≈300 ft).
    • Largest living organism concepts:
    • Pondo (aspen clone) ~43{,}000 stems; 160 acres; total mass ≈ 13{,}000{,}000 ext{ pounds}.
  • Cultural and ecological takeaways:
    • Plants inspire art, music, film, and literature.
    • Public installations and campus spaces can highlight plant biology and conservation messages.