Evolution of Plant and Fungal Diversity

Plants and Fungi

• Eukaryotic Organisms: Plants and fungi, like animals, are classified as eukaryotic organisms.
• Adaptations for Terrestrial Life: Both plants and fungi have unique adaptations that enable them to thrive on land.
• Symbiotic Relationships: Many plants and fungi engage in symbiotic relationships, particularly through structures known as mycorrhizae, which facilitate nutrient acquisition between the two. It is estimated that 90% of terrestrial plants form these connections with fungi.

Plant Evolution

• Aquatic to Terrestrial: Land plants evolved from aquatic ancestors such as algae, adopting adaptations necessary for terrestrial life, including:

  • Water Conservation
  • Gas/Nutrient Exchange: Utilization of stomata for gas exchange with the atmosphere and soil.
  • Structural Support: Development of lignin in cell walls.
  • Fertilization: Transition from reliance on water for fertilization to mechanisms such as wind-distributed pollen.

• Vascular Systems: Land plants developed vascular systems that include:

  • Xylem: Transports water and minerals from roots to other plant parts.
  • Phloem: Distributes sugars produced in the leaves to other parts of the plant.

• Gametes: Similar to animals, plants produce gametes; however, in drier environments, they utilize pollen to transport sperm.

Bryophytes

• Definition: The term "bryophyte" means "moss-plant" in Greek, encompassing mosses, liverworts, and hornworts.
• Morphological Characteristics:
  • Non-Vascular: Bryophytes lack vascular tissue (no xylem or phloem), limiting their height and growth form.
  • Moisture Retention: They typically grow in moisture-retentive mats and rely on water for fertilization through flagellated sperm cells.

Lycophytes and Monilophytes

• Seedless Vascular Plants: Includes lycophytes (e.g., wolf plants) and monilophytes (e.g., ferns).
• Growth and Adaptation: Flagellated sperm still requires moisture for reproduction; some monilophytes can grow to substantial heights.
• Reproduction: Instead of seeds, these plants reproduce via spores.

Seed Plants

• Types: Includes gymnosperms and angiosperms, both of which are vascular and produce seeds.
• Seeds: Defined as fertilized embryos encased in protective coatings.
  • Gymnosperms: Seeds are "naked" and not enclosed in chambers (e.g., conifers).
  • Angiosperms: Seeds develop within flowers, leading to fruit formation, which aids in seed dispersal.

Plant Life Cycles

• Alternation of Generations: Plants exhibit a life cycle alternating between diploid (sporophyte) and haploid (gametophyte) stages.
  • Sporophyte Phase: Dominant phase where diploid plants exist; produces haploid spores via meiosis.
  • Gametophyte Phase: The multicellular haploid stage that produces gametes through mitosis.
  • Fertilization: Fuses sperm and egg, forming a new diploid zygote, which develops into a new sporophyte.

Gymnosperms and Angiosperms: Life Cycle Comparison

• Gymnosperms: Fertilization occurs in seed cones; the process involves pollen grains reaching the ovulate cone, leading to the formation of seeds.
• Angiosperms: Have flowers as reproductive structures with specialized parts (anthers and carpals) for gamete production and fertilization.
• Pollinators: Animals that facilitate pollen transfer, often attracted by the sugary nectar produced by flowers, playing a key role in reproduction.
• Fruit: An adaptation of angiosperms that aids in seed dispersal.

Fungi

• Classification: Fungi belong to a kingdom distinct from plants and animals. They are heterotrophic and absorb nutrients after external digestion.
• Structure: Composed of hyphae (filamentous structures), grouped to form mycelium, which produce fruiting bodies for spore formation (e.g., mushrooms).
• Cell Walls: Fungal cell walls are distinct from plant cell walls, containing chitin instead of cellulose.
• Fungi Life Cycle: Mostly haploid, fungi undergo sexual reproduction (fusion of hyphae) and asexual reproduction (producing spores).

Fungi Classifications

• Chytrids: Aquatic fungi with flagellated spores; pose risks to amphibians.
• Zygomycetes: Common molds that produce spherical structures for spore protection.
• Glomeromycetes: Crucial for mycorrhizae partnerships with plant roots.
• Ascomycetes and Basidiomycetes: Produce spores in distinct structures, enhancing their reproductive adaptability.

Plant Nutrition

• Nutrient Requirement: Plants require a variety of essential nutrients derived from soil. Soil quality directly impacts plant health.
• Fertilizers: Can be organic (derived from living organisms) or inorganic (synthetic compounds), impacting plant growth and soil health.
• N-P-K Ratio: Indicates levels of nitrogen (N), phosphorus (P), and potassium (K) in fertilizers, which are crucial macronutrients for plant health.

Nitrogen Fixation

• Role of Bacteria: Nitrogen-fixing bacteria convert atmospheric nitrogen into forms usable by plants, vital for their growth.
• Process Details: Involves ammonification and nitrification, contributing to the nutrient cycle in ecosystems.

Soil Conservation

• Importance: Responsible management of soil to ensure agricultural productivity, focusing on irrigation, erosion control, and balanced fertilization practices.