Plant Structure and Function - In Depth Notes

Cell Biology Overview and Introduction to Plant Physiology

• Course Title: Biology 186

• Instructor: Dr. Jürgen Ehlting

• Email: je@uvic.ca

Key Topics Covered

1. Introduction to Plant Physiology

• Overview of plant parts and their functions, including roots, stems, leaves, and reproductive structures. Understanding how each part contributes to the overall health and growth of the plant.

• Detailed examination of the structure of cells, tissues, and organs, focusing on the unique aspects of plant cells such as chloroplasts, vacuoles, and cell walls.

2. Vascular Transport

• Importance of vascular systems in plants for the transport of water, nutrients, and sugars throughout different parts of the plant. The distinction between xylem and phloem and their specific roles in this process.

• Mechanisms of transport within plants, including passive and active transport processes, osmosis, and the role of transpiration in water movement.

3. Light Exploitation

• Role of light as a source of energy for photosynthesis, the process by which plants convert light energy into chemical energy. Examination of light wavelengths absorbed by chlorophyll and their effect on plant growth.

• Use of light as a source of information for plants, including phototropism and the role of photoreceptors in growth and flowering responses (if time permits).

4. Plants as Life Forms

• Discussion on plant efficiency in terms of energy capture and utilization, and their adaptability to various environmental conditions. Insights into how plants have evolved to survive in diverse habitats.

• Comparison with animal life forms focusing on structural differences and reproductive strategies.

Comparison Between Plants and Animals

• Photosynthesis vs. Chemoheterotrophy

• Plants: Photoautotrophic, using sunlight and CO2 and converting these into glucose and oxygen through photosynthesis.

• Animals: Chemoheterotrophic, deriving energy from organic substances, reliant on consuming other organisms for nutrients.

• Chlorophyll Presence

• Unique to plants, chlorophyll is essential for photosynthesis and gives plants their green color; animals do not possess chlorophyll and thus cannot perform photosynthesis.

• Growth Patterns

• Plants: Exhibit continuous (indeterminate) growth due to meristems, allowing them to adapt to changes in their environment.

• Animals: Generally have limited (determinate) growth influenced by genetic factors, leading to fixed adult sizes.

• Mobility

• Plants: Generally rooted in place; possess a range of adaptations for nutrient and water uptake without relocating.

• Animals: Free-moving organisms capable of locomotion in search of food, mates, and shelter.

• Cell Structure

• Plants: Rigid cell walls composed of cellulose provide structural integrity, helping plants maintain their shape, withstand environmental stresses, and aiding in communication and defense against pathogens.

• Animals: Animals lack cell walls but possess a flexible extracellular matrix (ECM). This matrix provides support, facilitates communication between cells, and allows tissues to adapt to mechanical forces, playing an essential role in mobility and tissue repair.

• Animals: Lack cell walls; have an extracellular matrix that provides flexibility and strength to tissues.

Plant Cell Anatomy

• Plant cells are enclosed in cell walls, creating rigid structures that maintain shape.

• Unique cell structure allows for selective permeability, facilitating essential nutrient uptake while restricting movement, which is crucial for plant stability and health.

Plant Evolution and Diversity

• The origin of plants traced back to green algae approximately 470 million years ago.

• The evolution of vascular plants around 425 million years ago introduced significant adaptive advantages.

• Significant groups of plants include:

Plant Evolution and Diversity

• Non-vascular plants:

• Examples: Mosses, liverworts, and hornworts.

• Characteristics: Typically smaller and dependent on diffusion for water and nutrient uptake.

• Habitat: Thrive in moist environments to facilitate absorption directly from surroundings.

• Vascular plants:

• Include groups such as Lycophytes, Monilophytes, Gymnosperms (origin of seed plants around 360 million years ago), and Angiosperms (flowering plants).

• Features: Possess specialized tissues (xylem and phloem) for efficient transport of nutrients and water, allowing for larger growth and adaptability to diverse environments.

• Dominant groups within angiosperms:

• Monocots:

  • Characteristics: Have one cotyledon, parallel-veined leaves, and fibrous root systems.

  • Examples: Grasses, lilies, orchids

• Vascular plants: Include Lycophytes, Monilophytes, Gymnosperms (origin of seed plants around 360 million years ago), and Angiosperms (flowering plants).

• Dominant groups within angiosperms:

• Monocots: One cotyledon, parallel-veined leaves, fibrous root systems—examples include grasses and lilies.

• Eudicots: Two cotyledons, branched veins, taproot systems including most flowering plants.

Tissues in Plants

Simple Tissues

• Types of Simple Tissues:

• Simple tissues consist of a single type of cell that performs specific functions vital for plant growth and development.

1. Parenchyma

• Composition:

  • Parenchyma cells are characterized by their thin cell walls and can vary in size and shape. These cells are typically isodiametric (having similar dimensions in all directions) and are alive at maturity.

• Functions:

  • These cells play a crucial role in photosynthesis, particularly in the chloroplast-containing parenchyma cells found in the leaves.

  • They are essential for storing starches, proteins, and water, making them vital for plant energy reserves.

  • Following injury, parenchyma cells can aid in healing and regeneration, highlighting their role in plant growth and repair mechanisms.

2. Collenchyma

• Composition:

  • Composed of cells with unevenly thickened cell walls, collenchyma provides structural flexibility while allowing for growth and elongation of plant parts.

• Functions:

  • Primarily found in young stems and petioles, collenchyma supports growing tissues while maintaining the flexibility needed to withstand various environmental factors, such as wind or weight from fruits and leaves.

3. Sclerenchyma

• Composition:

  • Sclerenchyma cells have thick, lignified (cell walls impregnated with lignin) walls and are usually dead at maturity. These cells contribute to the rigidity and strength of the plant.

• Functions:

  • They provide structural support, which is critical for the overall integrity of plant structures, especially in areas under stress or weight.

  • Sclerenchyma includes two types of cells:

  • Fibers: Long, slender cells commonly found in various plant tissues, providing tensile strength.

  • Sclereids: Shorter and irregularly shaped cells that contribute to the hardness of seeds and nuts. These cells have commercial importance in products such as textiles, construction materials, and cosmetics.

Complex Tissues

• Complex Tissues consist of two or more types of cells that work together to perform a specific function in the plant.

1. Xylem

• Function:

  • The primary role of xylem is to transport water and dissolved minerals absorbed from the soil through the roots to the leaves and other parts of the plant.

• Composition:

  • It comprises living parenchyma cells for nutrient storage and transport, as well as dead sclerenchyma cells known as tracheary elements (vessels and tracheids) that facilitate the conduction of water through hollow tubes.

2. Phloem

• Function:

  • Phloem is responsible for the transportation of organic compounds (mainly sugars produced during photosynthesis) and hormones from the leaves to other parts of the plant where they are needed.

• Composition:

  • Phloem contains living cells, including sieve tube elements that form long tubes for nutrient transport, as well as companion cells that aid in the metabolic support of sieve tubes and sclerenchyma for structural support.

Function of Xylem and Phloem

• Xylem:

• The tracheary elements enable passive water transport through transpiration (the loss of water vapor from aerial parts of the plant) and capillary action.

• Parenchyma cells within xylem are crucial for the active transport of solutes and the storage of nutrients.

• Phloem:

• Sieve elements transport sugars and hormones bidirectionally, crucial for resource distribution and utilization in growing tissues.

• Parenchyma cells are involved in the loading and unloading of materials into and out of sieve tubes, ensuring efficient flow of nutrients.

Plant Organs and Structures

• Key Plant Organs:

• These include roots, stems, leaves, and reproductive structures, each with distinct roles critical to plant survival and reproduction.

• Root systems:

• Roots anchor the plant in the soil and are responsible for the uptake of water and essential nutrients.

• They also serve storage functions, with adaptations including taproots that provide robust nutrient reserves and prop roots that offer stability in species that grow in unstable environments.

• Stems:

• Stems serve as conduits for transporting fluids (water, nutrients, and sugars) and provide structural support for the plant, ensuring that leaves and flowers are adequately positioned to optimize sunlight exposure and reproductive success.

• Growth occurs at the apical meristems, promoting continuous elongation and forming new tissue.

• Leaves:

• Leaves are specialized for photosynthesis, featuring adaptations such as waxy cuticles to prevent water loss, and varied leaf arrangements to optimize light capture for photosynthesis.

• The anatomy of a leaf typically includes the epidermis (outer layer), mesophyll (the primary site for photosynthesis), and vascular bundles (composed of both xylem and phloem).

Growth and Development

• Apical Meristems

• Sites of active cell division located at the tips of roots and shoots, responsible for growth in length and overall plant height development.

• Secondary Growth

• Involves thickening of stems and roots over time, primarily in woody plants, facilitated by lateral meristems like the vascular cambium.

• Root Cap

• Protective structure at the root tip that safeguards the growing meristem as roots penetrate soil, playing a critical role in root development.

Conclusion

• Understanding the intricate structure and vital functions of plant biology is essential not just for academic purposes but for appreciating the ecological roles that plants play in environmental sustainability and their evolutionary significance.