Plant Structure, Growth, and Responses: Study Guide and Practice Questions

Chapter 28: Key Concepts in Plant Structure and Growth

Levels of Plant Organization

Plants exhibit hierarchical structural organization, consisting of organs, tissues, and cells. Understanding these levels is essential for studying plant biology.

• Organs: Roots, stems, and leaves are the three basic plant organs, each with specialized functions.

• Tissues: Each organ contains dermal, vascular, and ground tissues, which perform various roles such as protection, transport, and support.

• Cells: Plant tissues are composed of different cell types, including parenchyma, collenchyma, and sclerenchyma.

Primary growth adds length to roots and shoots, while secondary growth adds girth in woody plants.

Chapter 29: Resource Acquisition, Nutrition, and Transport in Vascular Plants

Adaptations for Resource Acquisition

Plants have evolved various adaptations to efficiently acquire resources from their environment.

• Root systems anchor plants and absorb water and minerals from the soil.

• Shoot systems (stems and leaves) are specialized for photosynthesis and reproduction.

• Transport tissues: Xylem transports water and minerals upward from roots; phloem transports sugars and other organic nutrients throughout the plant.

Transport Mechanisms

• Diffusion: Passive movement of molecules from high to low concentration.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Active transport: Movement of substances against a concentration gradient, requiring energy (ATP).

• Bulk flow: Movement of fluid driven by pressure differences, important in xylem and phloem transport.

Key equation:

$\Psi = \Psi_s + \Psi_p$

Where $\Psi$ is water potential, $\Psi_s$ is solute potential, and $\Psi_p$ is pressure potential.

Plant Nutrition

• Macronutrients: Essential elements required in large amounts (e.g., nitrogen, phosphorus, potassium).

• Micronutrients: Elements needed in small quantities (e.g., iron, manganese, chlorine).

• Deficiency symptoms: Deficiencies in mobile elements appear in older leaves; immobile element deficiencies appear in younger leaves.

Symbiotic Relationships

• Mycorrhizae: Fungi that form mutualistic associations with plant roots, enhancing nutrient uptake.

• Rhizobia: Nitrogen-fixing bacteria that form nodules on legume roots, converting atmospheric nitrogen into forms usable by plants.

Chapter 31: Plant Responses to Internal and External Signals

Plant Hormones

Plant hormones (phytohormones) regulate growth, development, and responses to stimuli.

• Auxins: Promote cell elongation, root formation, and differentiation.

• Gibberellins: Stimulate stem elongation, seed germination, and flowering.

• Cytokinins: Promote cell division and delay leaf senescence.

• Abscisic acid (ABA): Inhibits growth, promotes stomatal closure during drought stress.

• Ethylene: Promotes fruit ripening and leaf abscission.

Plant Responses to Light and Gravity

• Phototropism: Growth response toward or away from light, mediated by blue light receptors.

• Gravitropism: Growth response to gravity; roots show positive gravitropism, shoots show negative gravitropism.

• Photoperiodism: Physiological response to relative lengths of day and night, important for flowering.

• Circadian rhythms: Internal biological clocks that regulate daily cycles of activity.

Plant Defense Mechanisms

• Physical defenses: Thorns, trichomes, and tough cell walls deter herbivores.

• Chemical defenses: Production of toxins, secondary metabolites, and signaling molecules.

• Systemic acquired resistance (SAR): Long-lasting defense response triggered by pathogen attack.

Key Tables

Table: Comparison of Plant Tissue Types

Tissue Type	Main Function	Location
Dermal	Protection, gas exchange	Outer covering of plant organs
Vascular	Transport of water, minerals, and nutrients	Xylem and phloem throughout plant
Ground	Photosynthesis, storage, support	Between dermal and vascular tissues

Table: Major Plant Hormones and Their Functions

Hormone	Main Function
Auxin	Cell elongation, apical dominance, root initiation
Gibberellin	Stem elongation, seed germination
Cytokinin	Cell division, delay of senescence
Abscisic acid	Stomatal closure, seed dormancy
Ethylene	Fruit ripening, leaf abscission

Additional info:

• Some explanations and context were expanded for clarity and completeness, based on standard General Biology curriculum.

• Practice questions in the file cover key concepts from Chapters 28, 29, and 31, including plant structure, transport, nutrition, and responses to environmental stimuli.