Section_22.2_grade_10___Autosaved_

Introduction

Overview of the structures of roots, stems, and leaves as essential parts of plants.

Structures and Functions: Understand how root, stem, and leaf structures relate to their functions.
Comparison: Compare and contrast the structures of roots, stems, and leaves.

Early Growth: Roots are usually the first structures to emerge from a seed during sprouting.
Location: Typically grow underground.
Primary Functions:
- Anchor plants in the soil.
- Absorb and transport water and nutrients.

Tap Root (Dicot):
- Largest root forms from the first root, anchoring the plant.
- Stores food and water.
- Examples: Carrot, radish.
Fibrous Root (Monocot):
- Develop numerous branching roots from the initial root.
- Provides anchorage and ensures rapid water transport.
- Examples: Grass.
Modified Roots:
- Swollen for food and water storage.
- Example: Sweet potato.
Adventitious Roots:
- Arise from non-root organs, supporting a plant’s stem.
- Example: Epiphytic plants.

Key Components:
- Root Cap: Protects root tissues during growth and produces lubricant to ease soil movement.
- Root Hairs: Extensions that enhance surface area for increased absorption of water and minerals.
- Cortex: Layer beneath epidermis involved in transport & storage.
- Endodermis: Inner boundary with a Casparian strip that forces substances to cross cell membranes.
Vascular Structure:
- Pericycle: Next to the endodermis, gives rise to lateral roots.
- Stele: Vascular cylinder composed of xylem and phloem.

Monocot vs Dicot Roots:
- Monocots: Xylem and phloem surround a central pith.
- Dicots: Xylem forms an X shape at the center with phloem between the arms.

Functions:
- Support leaves.
- Transport materials.
- Storage.
Types of Stems:
- Woody (bark) vs. Nonwoody (green stem).
- Special Forms:
  - Stolon (Runners): Horizontal stems for propagation (e.g., Strawberry).
  - Rhizomes: Underground horizontal stems for food storage (e.g., Iris).
  - Tubers: Swollen underground stems for food storage (e.g., Potato).
  - Fleshy Stems: Store water and perform photosynthesis (e.g., Cactus).
  - Bulbs & Corms: Specialized for food storage.

Monocot vs Dicot Stems:
- Monocots: Vascular bundles are scattered.
- Dicots: Vascular bundles are in concentric rings.

Apical Meristem: Responsible for height increase; contributes to annual rings.
Heart Wood & Sap Wood: Heartwood is darker, sapwood is lighter near the trunk exterior.
Bark: Protective covering made of dead cells and phloem.

Transportation:
- Nutrients and water transport; translocation from source to sink (photosynthetic parts to roots).
Support:
- Stronger stem provides stability to leaves.

Types:
- Simple Leaf: Single blade.
- Compound Leaf: Blade divided into leaflets.
Venation Patterns:
- Pinnate: Veins arranged like a feather.
- Parallel: Linear arrangements.
- Palmate: Network arrangement.
Arrangements:
- Opposite, alternate, whorled.

Main Functions:
- Photosynthesis.
- Covered by a cuticle to prevent water loss and defend against microorganisms.
Stomata: Pores for gas exchange.
Mesophyll Layers:
- Palisade: Upper layer, main site for photosynthesis.
- Spongy: Rounded cells facilitate gas exchange.
Vascular Tissues: Xylem and phloem present for nutrient and water transport.

Primary site for photosynthesis (Conversion of CO2 and water into glucose and oxygen).
Sugars provide building blocks for cells and energy sources.

Spines: Found in succulents like cacti, reduce water loss and provide protection.
Bracts: Colorful modified leaves attract pollinators.
Sticky Leaves: Trap insects (e.g., Sundew plant).
Toxic Leaves: Deter herbivores (e.g., poison ivy).
Hairs on Leaves: Repel insects and other herbivores.