Plant Diversity and Photosynthesis

Plant Diversity

• Plants are essential for human life and society, providing food, industrial materials, and medicine.
• Photosynthesis is the process by which plants convert light energy into chemical energy, using water and carbon dioxide to produce glucose and oxygen.
• Chlorophyll, the green pigment in plants, absorbs light energy for photosynthesis and is present in chloroplasts, organelles specific to plants and green algae.
• Cellular respiration is the process by which organisms break down glucose and oxygen to release energy, producing carbon dioxide and water as byproducts.
• Both photosynthesis and cellular respiration occur in autotrophs, while only cellular respiration happens in heterotrophs.
• Photosynthesis creates carbohydrates, which are then used in cellular respiration to generate energy (ATP).
• Land plants evolved from green algae-like ancestors approximately 500 million years ago.
• Adaptations for survival on land include:
  • Preventing water loss through cuticles and stomata.
  • Resisting gravity through vascular tissue (xylem and phloem) and cell walls containing lignin.
  • Absorbing nutrients from the soil through roots.
• Vascular tissue allows plants to transport water and nutrients throughout their bodies, enabling them to grow taller.
• Stomata are openings on plant leaves that regulate gas exchange, closing to conserve water and opening to take in carbon dioxide.
• Plants grow taller to compete for sunlight, driving the evolution of vascular tissue and lignin.
• Roots enable plants to absorb nutrients from the soil and form symbiotic relationships with mycorrhizal fungi and nitrogen-fixing bacteria.
• Sexual reproduction in plants involves the fusion of gametes (sperm and egg) produced through meiosis, resulting in a diploid zygote.
• Haploid cells have one copy of each chromosome (n), while diploid cells have two copies (2n).
• Plants have two major reproductive stages: the haploid gametophyte (n) and the diploid sporophyte (2n), with the sporophyte generation becoming more dominant in later-evolved plant groups.
• Mosses are non-vascular plants that reproduce through spores, lacking roots and typically growing in wet environments.
• Ferns have vascular tissue and roots, allowing them to grow larger, and reproduce through spores. They were once dominant land plants.
• Gymnosperms, like conifers, have vascular tissue and roots, produce seeds, grow tall, and are characterized by needle-like leaves and cones.
• Angiosperms, the most diverse plant group, include flowering plants, have vascular tissue, roots, reproduce through flowers and seeds, and encompass most global crop plants.
• Conifers have adaptations to fire, such as thick bark, fire-induced sprouting, and serotinous cones that release seeds after fire exposure.
• Plant groups are classified based on key traits, including:
  • Reproductive strategies (spores or seeds)
  • Presence of vascular tissue
  • Presence of roots
  • Dominant life stage (gametophyte or sporophyte)
• Understanding plant diversity and adaptations is crucial for appreciating the evolution of life on Earth and for maintaining healthy ecosystems.