Multicellular Embryos and Plant Biology

Multicellular Embryos and Alternating Generations

• Multicellular embryos are present in certain groups of organisms.

• Plants exhibit alternating generations (gametophytes and sporophytes).

• All plants have both gametophyte and sporophyte phases in their life cycle, with gametophytes producing sperm and eggs, and sporophytes producing spores.

Plant Reproduction vs. Animal Reproduction

• Animal Reproduction: Diploid individuals produce haploid gametes (sperm and eggs) through meiosis, which fuse to form a diploid zygote. The zygote undergoes mitosis to develop into a multicellular organism.

• Plant Reproduction: Plants have two multicellular phases: a diploid sporophyte and a haploid gametophyte. A zygote undergoes mitosis to produce either spores or sperm and egg. These germinate into multicellular haploid gametophytes. Gametophytes dominate the life cycle of mosses.

• Pollen grains are multicellular gametophytes that produce sperm. In seed-bearing plants, the gametophyte remains on the plant and develops into a seed.

Plant Anatomy and Vascular Systems

• Vascular bundles enable plants to transport water and sugar throughout multiple tissues.

• Basic plant anatomy:-

  • The shoot system (above ground) is for collecting sunlight.

    • Leaves act as solar panels.

  • The root system (below ground) anchors the plant and collects water.

Annuals vs. Perennials

• Annuals: Complete their life cycle in one year. They germinate, grow, produce seeds, and die, avoiding drought by living only when water is available, like the green grasses seen in the foothills.

• Perennials: Live for many years, often developing woody tissue (shrubs, trees). They have tissues that last year after year.

Primary vs. Secondary Growth

• Primary Growth: Growth in length, occurring at the tips (e.g., a grass growing taller).

• Secondary Growth: Growth in thickness (e.g., tree rings getting wider each year).

• Annuals primarily have primary growth, while perennials have both primary and secondary growth.

• Tree branches only grow longer at the tips (primary growth) but get thicker over time (secondary growth).

• Annual growth rings in trees are formed by growth in the spring and stoppage in the winter. The age of a tree can be determined by counting these rings.

Seeds and Plant Ecology

• Seed plants are a major focus.

• Plants form the basis of energy input into ecosystems.

• Areas are characterized by their plant life (e.g., wetlands, conifer forests).

Plant Evolution

• Most organisms started in the ocean before moving to land.

• The oldest multicellular photosynthetic organisms are marine algae.

• Evolutionary progression:-

  • Green algae (ancestors).

  • Liverworts (no apical growth).

  • Mosses and hornworts (nonvascular).

  • Vascular plants (club mosses, megaphylls/ferns).

  • Seed plants (gymnosperms and flowering plants).

Marine Plants (Algae/Seaweed)

• Nonvascular, immersed in water, and don't require a vascular system.

• They are a few cells thick and often have gas bladders to stay afloat.

• They contribute significantly to atmospheric oxygen.

• They are the basis of many ecosystems, especially single-celled algae (phytoplankton).

• Phytoplankton are photosynthetic and consumed by zooplankton.

• Used in food, fertilizer, and agar (from seaweeds), which is also used to make digestible capsules for medication.

• Fast-growing and potential source of biofuel.

• Have blades (leaves) without veins and gas bladders for buoyancy.

Brown and Red Algae

• Brown Algae: Entirely marine, commonly known as seaweeds.

  • They have holdfasts instead of true roots (for anchoring, not absorbing water).

• Red Algae: Often found in deeper waters and contain red pigments to absorb filtered light. The red wavelength are reflected since this wavelengths are the weakest meaning they don't use it.

Green Algae

• Likely ancestors of land plants, found in shallow waters.

• Reproduce via swimming gametes that fuse to form a zygote, which grows into a sporophyte.

Bryophytes (Nonvascular Plants)

• Include liverworts, mosses, and hornworts.

• Small due to lack of vascular systems.

• Absorb water through tissues and live in moist areas.

• Spores germinate into haploid gametophytes, which require water for swimming sperm.

• Liverworts grow in bogs and fens, forming peat, a massive organic carbon source.
  
  Peat areas can catch fire and burn continually underground, especially in drained areas like the Delta.

• Fens are similar to bogs but have slowly moving water passing through them.

• Moss mats in rainforests can create soil on branches, supporting entire ecosystems above ground.

Transition to Vascular Plants

• Vascular systems allow plants to grow larger, but ferns still require water for swimming gametes.

• Plant sperm are structurally different from animal sperm.

• Fern gametophytes are small, multicellular structures without seeds. The plant needs most places at some point in their life to germinate for reproduction.

Vascular Plant Systems

• Root system anchors and absorbs water/minerals.

• Shoot system collects sunlight.

• Dermal tissue covers the plant, vascular tissue (xylem and phloem) conducts water and sugars, and ground tissue is in between.

• Xylem carries water from roots, and phloem carries sugars from leaves.

Seedless Vascular Plants

• Include ferns and lycophytes.

• Dominated the Carboniferous period, forming coal deposits as they died on top of each other.

• Coal is derived from ancient plants, not dinosaurs, and burning it releases sequestered carbon, contributing to climate change.

• Ferns reproduce via spores (seen on the underside of leaves).

• Horsetails have fertile shoots for spores and vegetative shoots, reproducing asexually via rhizomes.

Seed Plant Evolution

• Spores stay on the plant with seed plants.

• The sperm has to come to the spore for fertilization. Once this fertilization occurs, the embryo stays on the plant.

• Embryos stay on the parent plant, along with a food supply and covering, enhancing their survival and dispersal without needing water for reproduction.

Major Groups of Seed Plants

• Gymnosperms (naked seeds): cycads, ginkgoes, conifers, and gnetophytes. Dominated conifer forests.

• Angiosperms (flowering plants): seeds are covered by the fruit and flowers attract other animals for pollination. Largest phylum of photosynthetic organisms.

• Gymnosperm seeds are open at the base of cone-like structures and the seeds do not have the fruit covering that Angiosperm do.

• Conifers are the tallest and largest vascular plants in the world, with drought-resistant leaves due to frozen water in winter.

• Conifers are monoecious, with both male and female cones on the same plant.

Angiosperm Reproduction

• Flowers are structures for plant reproduction, attracting animals via pollination.

• Two major groups: monocots (grasses, lilies, irises, orchids) and eudicots (trees and shrubs).

• Flowers have sterile parts (sepals and petals) and fertile parts (stamens and carpels).-

  • Stamens which contain the pollen is male sporophyte, produced in the anther.

  • Carpels are where the eggs are and what covered with coverings and is also known as the ovules. Once these ovules are fertilized, embryos will be produced.

• Angiosperms undergo double fertilization: one sperm unites with the egg to form the embryo, and another unites with other cells to form the endosperm (food supply) inside the ovule.

• Fruits aid in seed dispersal by wind, water, or animals. The fruit turns a certain color, signaling the plant is ready to be picked and the embryos can be taken away. The fruits can become large and evolve so that they can survive an animal's digestive tract.-

  • Some fruit seeds and dispersal techniques include:
    
    *Dandelions, Coconuts, Pitch a ride, eat/spit, extremely small seeds, fecal mimicry

• Fecal mimicry in Ceratocarium involves seeds mimicking antelope dung to attract dung beetles for dispersal.
  
  *Carrion flowers attract flies by smelling like rotting corpse.
  
  *Orchids look and smell like female wasp's to trick wasps.

Biodiversity

• Levels: genetic diversity, species diversity, ecological diversity, and evolutionary diversity.

• Genetic diversity is the foundation for species diversity.

• Species diversity involves the number of species in a geographic area.
  
  Species diversity represented in insects, arthropods, mollusks, algae, vascular plants, protease, nematodes, segmented worms, flatworms, fungi, Nenarians, fish, reptiles, amphibians, mammals, birds