Overview of Plant and Fungi Evolution

• Introduction to Plants

  • Plants are multicellular eukaryotes, always multicellular.

  • Belong to the domain of eukaryotes alongside fungi, protists, and animals.

  • Main distinction: plants can photosynthesize, whereas fungi and animals cannot.

• Photosynthesis and Autotrophy

  • Most plants are autotrophic, producing their own food through photosynthesis.

  • Few exceptions include parasitic plants that do not photosynthesize.

  • Photosynthesis is crucial for their survival, especially in dry environments.

• Adaptations for Terrestrial Living

  • Transition from aquatic to terrestrial life presented numerous challenges (e.g., gravity, desiccation).

  • Adaptations include:

    • Structural support to grow tall (e.g., strengthened cell walls).

    • Mechanisms to obtain CO₂ from the air (stomata in leaves).

    • Roots for water and nutrient absorption from the soil.

• Plant Structure Overview

  • Shoot System (above ground): includes stems, branches, leaves.

  • Root System (below ground): absorbs water and nutrients, anchors the plant.

• Water Transport Mechanism

  • Plants use hydrogen bonding for water transport from roots to leaves, crucial for photosynthesis.

  • No pumping system; relies on cohesion and evaporation (transpiration).

• Photosynthetic Structures

  • Leaves contain chloroplasts, where photosynthesis occurs.

  • Stomata allow gas exchange (CO₂ intake and oxygen release).

  • Cuticle layer prevents excess water loss.

• Vascular Tissue

  • Comprised of:

    • Xylem: transports water from roots to leaves.

    • Phloem: distributes sugars produced during photosynthesis.

  • Vascular tissues provide structural support, ensure efficient transport, and allow for tall growth.

• Symbiotic Relationships

  • Mycorrhizae: association between root systems and fungal hyphae.

  • Increases nutrient and water absorption for plants and provides sugars for fungi.

• Reproductive Adaptations

  • Evolution of reproductive strategies to ensure gametes do not dry out.

  • Flowering plants (angiosperms) have seeds that protect developing embryos, aiding in reproduction on land.

  • Pollination adaptations, including pollen grains carried by wind or insects.

• Plant Evolutionary History

  • Ancestral lineages from aquatic green algae (karyophytes) transitioned to land about 500 million years ago.

  • Key evolutionary events:

    • Emergence of nonvascular plants (bryophytes — mosses)

    • Development of vascular plants (ferns)

    • Evolution of gymnosperms (conifers) with seeds

    • Most recent group: angiosperms (flowering plants) with diverse reproductive structures.

• Key Plant Groups

  • Bryophytes: Nonvascular, seedless plants like mosses, require moisture for reproduction (flagellated sperm).

  • Ferns: Seedless vascular plants; can grow tall but also require moisture (flagellated sperm).

  • Gymnosperms: Seed-producing plants that do not produce flowers or fruits (e.g., conifers).

  • Angiosperms: Flowering plants, highly diverse; facilitate reproduction through seeds contained in flowers.

• Ecological Impact and Importance

  • Early plants contributed significantly to the development of fossil fuels during the Carboniferous period.

  • Present-day plants (especially angiosperms) serve as foundational components of food systems (crops, vegetables, fruits).