Overview
This lecture covers the diversity of plants, their main structural features, differences between vascular and nonvascular plants, and various unique plant adaptations.
Plant Diversity and Structure
- There are over 300,000 estimated species of plants, each with different needs for light and water.
- Plants are categorized into two main groups: vascular and nonvascular.
- Vascular plants have specialized transport tissues xylem (for water) and phloem (for food/sugar).
- Nonvascular plants lack xylem and phloem, are generally small, and absorb water by osmosis.
Vascular vs. Nonvascular Plants
- Vascular plants: have true roots, stems, and leaves; can grow large and transport nutrients efficiently.
- Nonvascular plants (bryophytes): include mosses, liverworts, and hornworts; lack true stems/leaves/roots and thrive in moist areas.
Types of Vascular Plants
- Seedless vascular plants: include lycophytes (club mosses) and monilophytes (ferns); reproduce with spores.
- Gymnosperms: “naked seed” plants like conifers, ginkgo, cycads; have cones, but no flowers or fruit.
- Angiosperms: flowering plants; most diverse group (about 90% of all plants), produce flowers and fruit; further divided into monocots and eudicots.
Photosynthesis and Plant Function
- Photosynthesis requires water, carbon dioxide, and sunlight, using specialized plant structures.
- Water absorption depends on vascular system (via roots/xylem) or osmosis (nonvascular).
- Stomata (pores on leaf undersides) regulate gas exchange; guard cells open/close stomata to balance water loss and gas intake.
- Chloroplasts in plant cells perform photosynthesis; chlorophyll and other pigments absorb light energy.
Plant Adaptations
- Leaf shape and structure vary by environment: thin leaves or waxy cuticles conserve water; broad leaves capture more light.
- Carnivorous plants use enzymes to digest insects for extra nitrogen in nutrient-poor soils.
- Mangrove trees develop specialized roots to deal with waterlogged, salty, or low-oxygen soils.
- Parasitic plants like mistletoe steal water and nutrients from other plants.
Key Terms & Definitions
- Xylem — vascular tissue that transports water from roots to leaves.
- Phloem — vascular tissue that distributes sugars throughout the plant.
- Bryophytes — informal group of nonvascular plants, includes mosses, liverworts, and hornworts.
- Gymnosperms — plants with naked seeds, usually in cones, lacking flowers/fruit.
- Angiosperms — flowering plants with seeds enclosed within fruit.
- Stomata — pores in leaves for gas exchange, regulated by guard cells.
- Chloroplast — organelle where photosynthesis occurs.
- Photosynthesis — process by which plants make sugar using sunlight, CO₂, and water.
Action Items / Next Steps
- Recommended reading on specialized roots in mangrove trees.
- Explore plant tropism, plant hormones, and plant reproduction in suggested follow-up videos.