Angiosperm Life Cycle and Plant Reproduction

Alternation of Generations

• Alternation between the sporophyte and gametophyte generations
• Sporophyte generation is dominant in angiosperms

Structure of the Flower

• Male Structures:
  • Anthers contain microsporangia
  • Meiosis in microsporangia produces the male gametophyte in pollen grains
  • Pollen grain contains a generative cell and a tube cell
• Female Structures:
  • Ovary contains ovules with megasporangia
  • Meiosis in megasporangia produces megaspores
  • Ovules develop eggs and contain polar nuclei

Pollination and Fertilization

• Pollination: Pollen grains dispersed by pollinators land on the stigma
• Pollen Tube: Grows down through the style to the ovule
• Double Fertilization:
  • One sperm fertilizes the egg, forming a diploid zygote
  • Another fertilizes polar nuclei, forming triploid endosperm

Seed Development

• Zygote develops into the embryo
• Endosperm serves as a food supply for the embryo
• Seed formation and germination lead to the growth of the sporophyte

Monocots vs Dicots

• Monocots:
  • Herbaceous, e.g., grasses and palms
  • Parallel leaf venation
  • Hypogeal germination
• Dicots:
  • Can form true wood
  • Net-like leaf venation
  • Epigeal germination

Plant Anatomy

Shoot System

• Above-ground parts: leaves, stems, flowers, and fruits
• Leaves: Photosynthesis and gas exchange
• Stems: Provide support and transport fluids

Root System

• Below-ground parts: Roots absorb water and nutrients
• Tap Root System: Main root grows deep, anchors plant
• Fibrous Root System: Many small roots, prevents erosion

Plant Tissues

• Epidermis:
  • Protects against water loss and gas exchange
• Vascular Tissue:
  • Xylem: Transports water and nutrients
  • Phloem: Transports sugars
• Ground Tissue:
  • Metabolism, storage, and support

Leaf Structure and Function

Epidermis

• Contains guard cells that regulate stomata
• Stomata control CO2 uptake and water loss

Mesophyll

• Palisade Mesophyll: Photosynthesis with chloroplasts
• Spongy Mesophyll: Gas exchange with air spaces

Venation Patterns

• Parallel in monocots
• Net-like in dicots (pinnate or palmate)

Root Structure and Function

Root Zones

• Cell Division Zone: Includes root apical meristem
• Elongation Zone: Cells increase in size
• Maturation Zone: Cells differentiate

Root Cross Section

• Epidermis: Outer layer with root hairs
• Cortex: Ground tissue outside the vascular tissue
• Endodermis: Contains Casparian strips
• Stele: Central part with xylem and phloem

Water Transport

• Symplastic Route: Through the cytoplasm of cells, connected by plasmodesmata
• Apoplastic Route: Through cell walls and spaces, requires crossing cell membranes at Casparian strips

Reproduction and Adaptations

Fruits and Seed Dispersal

• Fruits develop from ovary, house seeds
• Aid in seed dispersal by attracting animals

Asexual Reproduction

• Example: Stolons (runners in strawberries)

Seed Dormancy and Germination

• Seeds remain dormant until conditions are favorable
• Require water and oxygen for germination

Specialized Roots

• Modified roots for storage (e.g., carrots)
• Prop roots for support (e.g., corn)
• Aerial roots for attachment and photosynthesis (e.g., orchids)