chapter 30

Plant Growth and Development

• Plant Growth Characteristics

  • Plants can form new organs (like leaves) and grow throughout their life.

• Hierarchical Organization in Vascular Plants

  • Structure: Cells → Tissues → Organs

  • Main organs of angiosperms:

    • Stem

    • Leaves

    • Roots

  • Function together in organ systems:

    • Examples: root and shoot systems

• Modular Growth in Shoots

  • Growth driven by cell division at meristems.

  • Primary & Secondary Growth: Results in production of repeated modules.

  • Shoot Apical Meristems: Enable modular growth by continuously producing new tissues.

• Stem Elongation

  • Cell size increases post-mitotic division at apical meristems.

  • Cells away from the shoot tip stop dividing but continue elongating, forming the zone of cell elongation.

  • Elongation is greater in length than in width due to cell wall properties.

• Evolution of Leaves

  • Initiated by shoot apical meristems.

  • Early plants had photosynthetic stems; leaves evolved from flattened branches for photosynthesis.

• Leaf Diversity

  • Various shapes & sizes depend on:

    • Surface area for photosynthesis

    • CO2 uptake needs

    • Water conservation

    • Thermoregulation and disease defense

  • Leaves can have specialized functions:

    • Protection

    • Climbing

    • Insect trapping

    • Pollinator attraction

• Leaf Structure

  • Vascular Connections: Leaves need to connect with xylem and phloem in stems to grow efficiently.

• Floral Meristems

  • Develop from shoot meristems at shoot tips or axillary buds.

  • Unlike shoot meristems, floral meristems do not allow for continued growth.

• Root Functionality

  • Roots: Obtain water and nutrients, anchor plants.

  • Roots allow survival in drier habitats.

• Root Growth

  • Grows from root apical meristem, protected by a root cap.

  • Initial growth creates thin structures to maximize surface area for water/nutrient uptake.

• Root Structure

  • Layers: Root epidermis, cortex, endodermis.

  • Endodermis: Plays a critical role in nutrient absorption along with root hairs in the maturation zone.

• Variations in Root Growth

  • Monocots: Form fibrous root systems through primary growth.

  • Other Plants: Develop main roots with branching that can add secondary growth.

• Storage in Roots, Stems, and Leaves

  • Storage Roots: E.g., beets store food and water.

  • Storage Stems: E.g., tubers like potatoes.

  • Storage Leaves: E.g., bulbs like onions with modified leaves.

• Plant Secondary Growth

  • Diameter increase necessary for stability and support as height increases.

  • Results from lateral meristem activity, particularly in woody plants.

• Lateral Meristems:

  • Vascular Cambium: Produces new xylem (wood) and phloem.

  • Cork Cambium: Maintains the bark layer for protection.

• Growth Rings in Wood

  • Indicate growth rates; wider rings reflect favorable growth conditions, while narrow rings suggest stress or low rainfall.

• Bark Formation

  • Composed of nonliving cork cells that limit oxygen diffusion but have lenticels for gas exchange.