BISC 101 - Lecture 8 Plants form and function

Plant Form and Function (Chapter 34)

1. Hierarchical Organization of Plants

• Multicellular Structure: Plants are composed of specialized cells forming tissues and organ systems.

  • Specialized Cells Examples: Tracheids, parenchyma cells.

  • Tissue Types: Vascular tissue, ground tissue.

  • Organ Systems: Roots, shoots.

• Phenotypic Plasticity: Allows various plant forms as adaptations to environments.

2. Growth and Development

• Meristems: Plant stem cells that generate new cells for growth.

  • Types of Meristems:

    • Apical Meristems: Responsible for primary growth, increasing length of roots and shoots.

    • Lateral Meristems: Includes vascular cambium and cork cambium, responsible for secondary growth, increasing diameter of roots and shoots.

3. Angiosperm Diversity: Monocots vs. Eudicots

• Monocots:

  • One cotyledon, fibrous root system, parallel leaf venation, pollen grain with one opening, flowers in multiples of three.

• Eudicots:

  • Two cotyledons, taproot (main root), netlike leaf venation, pollen grain with three openings, flowers in multiples of four or five.

4. Root and Shoot Systems

• Shoot System: Comprises stems and leaves.

  • Functions:

    • Absorbs light and CO2.

    • Photosynthesis occurs in green parts.

    • Reproductive shoots bear flowers.

• Root System:

  • Absorbs water/nutrients (root hairs).

  • Anchors plant, serves as storage organ (tap roots).

• Vascular System: Connects roots and shoots, transporting water/minerals via xylem and sugars via phloem.

5. Efficiency of Plant Structure

• Long and thin forms of roots; flattened leaves for:

  • Maximizing surface area relative to volume for light absorption and CO2 diffusion.

6. Response to Environment

• Phenotypic Plasticity: Allows plants to modify growth forms in response to the environment.

  • Examples include underwater leaves adapting shape for protection and buoyancy.

  • Shade leaves are larger for intercepting more light; sun leaves are smaller to reduce water loss.

7. Diverse Root Systems

• Types of roots reflecting adaptations:

  • Prop Roots: Provide stability; seen in corn.

  • Pneumatophores: Above surface roots for oxygen acquisition in mangroves.

  • Tap Roots: Store food and water; examples include carrots and beetroots.

8. Modified Shoot Systems

• Shift in Shoot Structure:

  • Rhizomes: Underground shoots generating new plants.

  • Tubers: Swollen rhizomes for food storage (e.g., potatoes).

  • Storage Shoots: Short, thickened structures (e.g., onions).

9. Leaf Diversity

• Types of leaves reflecting different functions:

  • Simple, Compound, Double Compound: various shapes.

  • Specialized leaves such as spines for protection, tendrils for climbing, and traps for insects.

10. Plant Cell Structures

• Unique to Plant Cells:

  • Cell Wall: Provides mechanical strength.

  • Plasmodesmata: Cell connections.

  • Central Vacuole: Storage and waste breakdown.

  • Chloroplasts: Site of photosynthesis (also containing mitochondria for respiration).

11. Plant Cell Walls

• Composed of:

  • Cellulose Microfibrils: Provide rigidity.

  • Primary Cell Wall: Thin and flexible in young cells.

  • Secondary Cell Wall: Tough and lignified (wood).

12. Tissue Systems

• Dermal Tissue: Covers plant, single layer of epidermal cells.

• Ground Tissue: Majority of plant tissue involved in photosynthesis and storage.

• Vascular Tissue: Conducts long-distance transport (xylem and phloem).

13. Components of Primary Growth

• Meristem Types:

  • Apical Meristem: Generates primary growth.

  • Primary Tissues:

    • Dermal: Epidermis.

    • Ground: Parenchyma, collenchyma, sclerenchyma.

    • Vascular: Xylem and phloem.

14. Primary Growth Mechanism

• Apical Meristems: Lengthening of root and shoot growth, with growth zones:

  • Cell Division, Elongation, Differentiation.

15. Lateral Roots and Root Hairs

• Root Hairs: Increase surface area for absorption.

• Lateral Roots: Emerge from pericycle, enhancing root structure.

16. Ground Tissue Types

• Collenchyma Cells: Support due to thicker walls; found in celery strings.

• Sclerenchyma Cells: Lignified secondary walls; form hard structures (wood/nuts).

• Parenchyma Cells: Thin walls, storage and photosynthesis.

17. Xylem Cells

• Types: Tracheids and vessel elements.

  • Functions: Water conduction; dead at maturity with thick lignified walls.

18. Phloem Cells

• Sieve-tube Elements: Function for sugar transport; alive but lack certain cellular components.

• Companion Cells: Aid in metabolic functions of sieve-tube elements.

19. Characteristics of Plants

• Soft Plants: Herbs, forbs, grasses; primarily annuals with primary growth.

• Hard/ Woody Plants: Trees, shrubs; primarily perennials with both primary and secondary growth.

20. Growth in Twigs

• Annual growth rings show primary and secondary growth contributions.

21. Secondary Growth Mechanism

• Lateral Meristems: Increase root and shoot diameter.

  • Vascular cambium adds more xylem than phloem for thicker growth.

22. Tree trunk structure

• Heartwood vs. Sapwood: Differentiation in function and composition for structural support and water transport.

• Bark Composition: Cork, cambium, and phloem for protection and transport.

Plant Form and Function (Chapter 34)

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1. Hierarchical Organization of Plants

• Multicellular Structure: Plants are complex organisms made up of specialized cells, forming various tissues and organs that play critical roles in their life processes. These tissues are organized into organ systems that collaborate for the plant’s survival.

• Specialized Cells Examples: Key specialized cells include tracheids for water transport, parenchyma cells for storage and photosynthesis, and sclerenchyma for structural support.

• Tissue Types:

  • Vascular Tissue: Comprises xylem and phloem, crucial for long-distance transport of water, minerals, and nutrients.

  • Ground Tissue: Involves cells responsible for metabolic processes like photosynthesis and storage.

• Organ Systems: Roots (anchoring the plant and nutrient/water absorption) and shoots (supporting leaves and reproductive structures) together form the plant's structural diversity.

• Phenotypic Plasticity: This characteristic allows plants to adapt their morphology and physiology to varying environmental conditions, enhancing their chances of survival.

2. Growth and Development

• Meristems: These regions of undifferentiated cells act like stem cells in animals, giving rise to new cells that support growth.

• Types of Meristems:

  • Apical Meristems: Found at the tips of roots and shoots, facilitating increasing length (primary growth).

  • Lateral Meristems: Including vascular cambium (adding vascular tissue) and cork cambium (producing protective outer bark), these contribute to the plant's girth (secondary growth).

3. Angiosperm Diversity: Monocots vs. Eudicots

• Monocots: Characterized by a single cotyledon, they typically have a fibrous root system, parallel leaf venation, and floral parts in multiples of three.

• Eudicots: Distinguished by two cotyledons, a prominent taproot system, netlike leaf venation, and flowers often with four or five parts. They exhibit greater diversity in form and function.

4. Root and Shoot Systems

• Shoot System: Comprises stems and leaves crucial for maximizing photosynthesis and reproduction. The stem provides structure, while leaves are specialized for photosynthesis and gas exchange.

  • Functions: In addition to photosynthesis, the shoot system also facilitates pollination through reproductive shoots that bear flowers.

• Root System: Anchors the plant and plays a critical role in absorption. Root hairs significantly increase surface area, enhancing water and nutrient uptake.

• Vascular System: The network of xylem and phloem connects roots and shoots, essential for the transport of water, nutrients, and sugars throughout the plant.

5. Efficiency of Plant Structure

• Adaptations: Plants exhibit long and thin root forms and flattened leaf structures, which optimize surface area relative to volume for efficient light absorption and gas exchange (CO2 diffusion).

6. Response to Environment

• Phenotypic Plasticity: This allows plants to adjust their shape and growth patterns based on environmental cues, improving survival. For example, underwater leaves may evolve unique shapes to enhance buoyancy or reduce water resistance.

• Leaf Adaptations: Shade leaves are generally larger to capture more light, while sun leaves have smaller sizes to minimize water loss during photosynthesis.

7. Diverse Root Systems

• Specialized Root Types:

  • Prop Roots: Seen in species like corn, these roots provide structural stability to support upright growth.

  • Pneumatophores: Above-ground roots in mangroves that facilitate oxygen exchange for submerged roots.

  • Tap Roots: These thick, deep roots store food and water in plants such as carrots and beetroots, providing resilience during drought.

8. Modified Shoot Systems

• Types:

  • Rhizomes: Horizontal underground stems that can produce new plants, facilitating asexual reproduction.

  • Tubers: Enlarged rhizomes (e.g., potatoes) that serve as storage organs for nutrients and energy.

  • Storage Shoots: Short, thickened structures found in onions provide energy storage during unfavorable conditions.

9. Leaf Diversity

• Variants in Leaf Structure: Leaves can be simple, compound, or doubly compound, each with distinct shapes and surface areas suited for varying environmental conditions.

• Specialized Leaves: Certain leaves are adapted for specific functions, such as spines for protection against herbivores, tendrils for climbing support, or traps designed for insect capture in carnivorous plants.

10. Plant Cell Structures

• Unique Features of Plant Cells:

  • Cell Wall: Composed mainly of cellulose, it provides mechanical strength and defines cell shape.

  • Plasmodesmata: Microscopic channels that allow for intercellular communication and transport of substances like nutrients and signaling molecules.

  • Central Vacuole: A large organelle in plant cells that stores nutrients, waste products, and helps maintain turgor pressure for structural support.

  • Chloroplasts: Organelles where photosynthesis occurs; they contain chlorophyll and also have components necessary for cellular respiration (mitochondria).

11. Plant Cell Walls

• Composition: Cell walls consist of cellulose microfibrils, which provide rigidity and support. Plant cell walls are made up of:

  • Primary Cell Wall: Thin and flexible layer formed during cell growth, allowing for expansion.

  • Secondary Cell Wall: A thicker, more durable layer found in mature cells, often lignified for added strength, particularly in woody plants.

12. Tissue Systems

• Dermal Tissue: This outer layer provides protection and reduces water loss; it is primarily composed of epidermal cells.

• Ground Tissue: The bulk of the plant's tissue, it includes parenchyma cells involved in photosynthesis, collenchyma cells providing support with their thicker walls, and sclerenchyma cells forming hard protective structures.

• Vascular Tissue: Critical for resource transport; xylem transports water and minerals upwards, while phloem distributes sugars throughout the plant.

13. Components of Primary Growth

• Meristem Types: The apical meristem is crucial for generating all primary growth tissues. Primary tissues arise as follows:

  • Dermal: Forms the epidermis for protection.

  • Ground: Includes parenchyma for storage and photosynthesis, collenchyma for flexible support, and sclerenchyma for hard support.

  • Vascular: Composed of xylem (for water transport) and phloem (for nutrient transport).

14. Primary Growth Mechanism

• Growth Zones of Apical Meristems: Involved in root and shoot lengthening, primary growth occurs through three processes—cell division, elongation, and differentiation into specialized cell types.

15. Lateral Roots and Root Hairs

• Root Hairs: Tiny extensions that dramatically increase root surface area for enhanced absorption of water and nutrients.

• Lateral Roots: These roots grow out from the pericycle to improve anchorage and resource uptake.

16. Ground Tissue Types

• Collenchyma Cells: These contain thicker cell walls that provide support while allowing flexibility, commonly found in celery stalks.

• Sclerenchyma Cells: Possessing lignified secondary walls, these cells form hard structures such as wood and seed coats.

• Parenchyma Cells: The most abundant type, they have thin walls and are involved in storage and metabolic functions including photosynthesis.

17. Xylem Cells

• Types: Xylem is composed of tracheids and vessel elements, both specialized for water conduction. They are dead at maturity, featuring thick lignified walls that prevent collapse under pressure.

18. Phloem Cells

• Sieve-tube Elements: Specialized for transporting sugars throughout the plant; while alive, they lack a nucleus and certain organelles.

• Companion Cells: These are closely associated with sieve-tube elements and help in the metabolism and functioning of phloem cells.

19. Characteristics of Plants

• Soft Plants: Include herbs, forbs, and grasses, typically classified as annual plants focused on primary growth.

• Hard/Woody Plants: Trees and shrubs that are primarily perennial and undergo both primary and secondary growth, allowing for greater longevity and structural complexity.

20. Growth in Twigs

• Annual Growth Rings: Visible rings in tree trunks that indicate patterns of primary (height) and secondary (girth) growth, providing insights into the growth conditions experienced by the tree over time.

21. Secondary Growth Mechanism

• Lateral Meristems: Enable the increase in root and shoot diameter, particularly through the action of the vascular cambium, which produces more xylem than phloem, contributing to thicker growth.

22. Tree Trunk Structure

• Heartwood vs. Sapwood: Heartwood is older, non-conducting wood that provides structural support, while sapwood is younger, actively conducting xylem facilitating water transport.

• Bark Composition: Consists of cork, cambium, and phloem; serves protective functions and also facilitates resource transport.