Plant Biology: Leaf Structure and Functions

Leaf Structure and Functions

• Petiole: Connects the leaf to the stem; known as the leaf stalk.
• Midrib: Central vein of the leaf providing support and transportation.
• Blade: Flat part of the leaf responsible for capturing sunlight.
• Veins: Supportive framework within the leaf, aiding in transport.
• Margin: Edge of the leaf, influencing overall leaf shape and health.
• Apex: The tip of the leaf, which can vary in shape and size.

Epidermis and Gas Exchange

• Upper Epidermis: Protective skin layer that minimizes moisture loss.
• Lower Epidermis: Contains stomata and guard cells; protects and facilitates gas exchange.
• Stomates: Tiny openings for gas exchange; crucial for respiration and transpiration.
• Guard Cells: Regulate the opening and closing of stomates, controlling gas flow.

Photosynthesis and Respiratory Processes

• Chloroplasts: Green organelles containing chlorophyll; essential for photosynthesis.
• Photosynthesis: Process converting sunlight, carbon dioxide, and water into food.
• Respiration: Metabolic process converting sugars into energy for plant functions.
• Transpiration: Loss of water vapor from leaves; aids in cooling and nutrient transport.

Leaf Variations and Structures

• Sessile: Leaves without a petiole; Example: zinnia.
• Bracts: Modified leaves often associated with flowers; Example: poinsettia.
• Needles and Scales: Types of modified leaves found in certain plants; Example: pine trees.
• Glabrous: Smooth, hairless leaves; Example: southern magnolia.
• Pubescent: Hairy leaves; Example: African violet.

Stem and Bud Structures

• Lenticels: Breathing pores on stems and branches for gas exchange.
• Bud Scale Scars: Indicators of past terminal bud locations on stems.
• Terminal Bud: Located at the end of the stem; responsible for growth.
• Axillary Bud: Bud found in the axil of a leaf; potential for new growth.
• Lateral Buds: Buds located along the sides of the stem.

Vascular Tissues in Plants

• Xylem: Tissue transporting water and nutrients from roots upwards.
• Phloem: Tissue responsible for distributing food from leaves to roots.
• Cambium: Actively growing tissue between bark and wood, producing new cells.
• Bark: Composed of old, inactive phloem.
• Heartwood: Old, inactive xylem located at the center of the stem.
• Sapwood: Newly formed, active xylem, recognizable by its light color.

Seed and Flower Structures

• Cotyledons: First leaves produced by seed plant embryos; known as seed leaves.
• Monocots: Plants with one seed leaf and vascular bundles containing xylem and phloem; Examples include grasses and corn.
• Dicots: Plants with two seed leaves and distinct vascular arrangements; Examples include many vegetables and trees.

Roots and Their Functions

• Root Cap: Protective structure at root tip, facilitating new cell growth.
• Root Hairs: Tiny extensions that enhance the absorption of water and nutrients.
• Fibrous Roots: Shallow, branched roots; easy to transplant.
• Tap Roots: Long, deep roots; harder to transplant but provide stability.
• Functions of Roots: Provide anchorage, absorb nutrients, store food, and facilitate asexual reproduction.

Flower Anatomy and Pollination

• Sepals: Green, protective components covering the flower bud.
• Petals: Modified leaves that attract pollinators; primarily for visual appeal.
• Stamens: Male reproductive parts of the flower.
• Anther: Part of the stamen that contains pollen.
• Filament: Stalk supporting the anther.

Pistil and Fertilization

• Pistil: Female reproductive structures of the flower.
• Stigma: Sticky surface for pollen capture, located at the top of the style.
• Style: Connects stigma to the ovary, allowing pollen transfer.
• Ovary: Enlarged base of the pistil; if fertilized, develops into fruit.
• Ovules: Female sex cells that may become seeds.

Pollination and Fertilization Processes

• Functions of Flowers: Attract insects for pollination, produce seeds for reproduction, generate fruit to protect and nourish seeds.
• Complete Flower: Contains both male and female reproductive structures.
• Incomplete Flower: Lacks either male or female parts.
• Fertilization: Pollen travels through style to fertilize ovules.
• Pollination: Transfer of pollen from anther to stigma.
• Cross-Pollination: Pollen transfer between different flowers; enhances genetic diversity.
• Self-Pollination: Pollen transfer within the same flower; less genetic variation.

Flower Parts and Seed Dispersal

• Corolla: Collective term for all petals in a flower.
• Calyx: All sepals of a flower, typically protective and green.
• Receptacle: Enlarged tip of the stem where the flower grows.
• Fruit: Protects seeds and aids in their dispersal.
• Juvenile: Refers to functions of fruit related to seed dispersal.