Plant and Animal Form and Function: Structure, Transport, and Physiology

Plant Form and Function

Important Molecules for Plant Growth

• Essential molecules for plant growth include water, carbon dioxide, minerals (e.g., nitrogen, phosphorus, potassium), and organic compounds such as sugars and amino acids.

• These molecules are involved in processes like photosynthesis, cellular respiration, and nutrient transport.

Primary and Secondary Growth: Meristems and Types

• Meristems are regions of undifferentiated cells that divide and contribute to plant growth.

• Primary growth increases length and occurs at apical meristems (tips of roots and shoots).

• Secondary growth increases girth and is due to lateral meristems such as the vascular cambium and cork cambium.

• Vascular cambium produces secondary xylem (wood) and phloem

• Cork cambium produces protective outer bark.

Surface Area to Volume Ratio (SA:V) Importance

• High surface area to volume ratio enhances absorption and exchange of materials (e.g., water, gases).

• As organisms increase in size, volume increases faster than surface area, affecting transport efficiency.

Roots vs. Shoots

• Roots anchor plants, absorb water and minerals, and store nutrients.

  • Root morphology differences and purpose: the structural diversity among roots, influenced by species differences, environmental responses (phenotypic plasticity), and specialized functions. Different morphologies allow plants to adapt to varying environments by optimizing water and nutrient uptake, providing stability, and storing resources.

    • Morphological Diversity Among Species: Different species have distinct root structures. For example, prairie plants may have shallow roots to absorb surface water quickly, while others develop deep taproots to access underground water during droughts.

    • Phenotypic Plasticity: Roots can change their form based on environmental conditions. For instance, spruce trees in wet soils develop shallow roots due to low oxygen levels, whereas the same species in dry soil grows deeper roots.

    • Modified Roots: Some roots are specialized for unique functions beyond nutrient absorption and anchoring. Adventitious roots like those in ivy help anchor the plant to surfaces, while prop roots in corn provide stability against wind.

  • Root diversity: taproots, fibrous roots, adventitious roots; morphology adapts to environment.

  • Root zones: zone of cell division (meristematic), elongation, and maturation (differentiation).

    • Zone of Cellular Division (meristematic): Contains the apical meristem where cells actively divide. This zone is crucial for root growth as it produces new cells.

    • Zone of Cellular Elongation: Cells here increase in length, pushing the root through the soil.

    • Zone of Cellular Maturation (differentiation): Older cells differentiate into various tissues like dermal, vascular, and ground tissues. Root hairs in this zone increase surface area for nutrient absorption.

• Shoots include stems and leaves; support, photosynthesis, and reproduction.

• Modified stems: tubers (potato), rhizomes (ginger), stolons (strawberry).

• Modified leaves: tendrils (pea), spines (cactus), storage leaves (onion).

Simple vs. Compound Leaves

• Simple leaves have a single, undivided blade.

• Compound leaves have blades divided into leaflets (e.g., pea, rose).

Tissue Systems: Simple vs. Complex

• Simple tissues: one cell type (e.g., parenchyma, collenchyma, sclerenchyma).

• Complex tissues: multiple cell types (e.g., xylem, phloem).

Dermal Tissue

• Stomata: pores for gas exchange, regulated by guard cells.

• Trichomes: hair-like structures for protection, reducing water loss, or secretion.

Ground Tissue

• Includes parenchyma (photosynthesis, storage), collenchyma (support), sclerenchyma (strength).

Vascular Tissue

• Xylem: transports water and minerals from roots to shoots; contains tracheids and vessel elements.

• Phloem: transports sugars and organic compounds; contains sieve-tube elements and companion cells.

Water Potential and Its Components

• Water potential (Ψ) determines the direction of water movement; measured in megapascals (MPa).

• Components: Pressure potential (Ψp) and solute potential (Ψs).

• Equation: $\Psi = \Psi_p + \Psi_s$

• Wall pressure: pressure exerted by cell wall against turgor pressure.

• Turgor pressure: pressure of cell contents against cell wall; maintains rigidity.

• Salty or dry soils lower water potential, making water uptake more difficult.

Water Uptake and Transport

• Water enters roots via osmosis, driven by water potential gradients.

• Root cross-section: water moves through apoplastic (cell wall), symplastic (cytoplasm), and transmembrane pathways to reach xylem.

Bulk Flow and Water Movement

• Bulk flow: movement of water due to pressure differences, mainly in xylem.

• Assisted by water's cohesion, adhesion, and surface tension.

• Guttation: exudation of water droplets from leaf margins due to root pressure.

Transpiration and Tension-Cohesion Theory

• Transpiration: evaporation of water from leaves, creating negative pressure in xylem.

• Tension-cohesion theory: water is pulled upward through xylem as a continuous column due to cohesion and tension from transpiration.

Safeguarding Against Water Loss

• Plants reduce water loss via cuticle, closing stomata, and leaf modifications (e.g., reduced surface area, trichomes).

Sugar Movement: Phloem Transport

• Sugars produced in leaves (source) are transported to non-photosynthetic tissues (sink) via phloem.

• Involves active transport (using ATP) and secondary active transport (using proton gradients).

• Tonoplast: membrane surrounding vacuole; antiporters exchange ions and sugars.

• Key cells: source cells, companion cells, sieve-tube elements, sink cells.

Interplay Between Xylem and Phloem

• Xylem transports water/minerals upward; phloem distributes sugars throughout the plant.

• Coordination ensures efficient resource allocation for growth and development.

Animal Form and Function

Anatomy vs. Physiology

• Anatomy: study of structure; physiology: study of function.

• Heritable adaptations improve survival; trade-offs may occur (e.g., speed vs. strength).

Adaptation vs. Acclimation

• Adaptation: genetic change over generations (e.g., thicker fur in arctic animals).

• Acclimation: physiological adjustment within an individual's lifetime (e.g., increased red blood cells at high altitude).

Anatomical Organization

• Levels: cells → tissues → organs → organ systems.

Tissue Types and Examples

• Connective tissue: support and structure (e.g., bone, blood, cartilage).

• Nervous tissue: transmits electrical signals (e.g., neurons, glia).

• Muscle tissue: movement (e.g., skeletal, cardiac, smooth muscle).

• Epithelial tissue: covers surfaces, lines organs (e.g., skin, intestinal lining).

Organs and Organ Systems

• Organs: structures composed of multiple tissue types (e.g., heart, leaf).

• Organ systems: groups of organs with related functions (e.g., digestive, circulatory).

Metabolism and Body Size

• Metabolic rate often scales with body size; smaller animals have higher metabolic rates per unit mass.

• SA:V ratio affects heat and material exchange.

Increasing Surface Area

• Organisms increase surface area via flattening (e.g., fish gills), folding (e.g., intestinal villi), and branching (e.g., capillaries).

Homeostasis

• Homeostasis: maintenance of stable internal conditions (e.g., temperature, pH).

• Organisms regulate (maintain constant internal state) or conform (match external environment).

Negative Feedback Mechanism

• Negative feedback reduces deviation from a set point (e.g., body temperature regulation).

• Components: sensor, integrator, effector.

Thermoregulation

• Methods of heat transfer: conduction (direct contact), convection (fluid movement), radiation (infrared), evaporation (liquid to gas).

• Endotherms: generate heat metabolically (e.g., mammals, birds).

• Ectotherms: rely on external sources (e.g., reptiles, amphibians).

• Poikilotherms: variable body temperature; homeotherms: stable body temperature.

Sensory Systems

Types of Receptors

• Mechanoreceptors: detect pressure, vibration (e.g., touch, hearing).

• Chemoreceptors: detect chemicals (e.g., taste, smell).

• Photoreceptors: detect light (e.g., rods and cones in eyes).

• Thermoreceptors: detect temperature changes.

• Electroreceptors: detect electric fields (e.g., Ampullae of Lorenzini in sharks).

Action Potentials

• Action potential: rapid change in membrane potential that transmits signals along neurons.

• Essential for communication within nervous system; signals travel to brain or effectors.

Vision: Simple vs. Compound Eyes

• Simple eyes: single lens (e.g., vertebrates).

• Compound eyes: multiple ommatidia (e.g., insects).

• Tapetum lucidum: reflective layer in some animals for night vision.

• Nictitating membrane: protective third eyelid in some species.

• Rods: detect light intensity; cones: detect color.

Equilibrium: Statocyst and Otoliths

• Statocyst: organ for balance in invertebrates; contains statoliths (dense particles).

• Otoliths: similar structures in vertebrate inner ear for detecting gravity and motion.

Plant Tropisms and Sensory Responses

• Tropisms: directional growth responses to stimuli (e.g., phototropism, gravitropism).

• Auxin: hormone mediating growth toward light.

• Amyloplasts: starch-containing organelles that sense gravity.

• Chromoproteins: light-sensitive proteins involved in photoreception.

Thermoreception and Electroreception

• Thermoreception: detection of temperature; important for behavior and physiology (e.g., pit organs in snakes).

• Electrocytes: specialized cells generating electric fields (e.g., electric fish).

• Ampullae of Lorenzini: detect electric fields in aquatic animals; structurally similar to chloroplasts in some respects (membrane-bound, specialized function).

Example Table: Comparison of Plant Tissue Types

Tissue System	Main Components	Function
Dermal	Epidermis, guard cells, trichomes	Protection, gas exchange, water retention
Ground	Parenchyma, collenchyma, sclerenchyma	Photosynthesis, storage, support
Vascular	Xylem, phloem	Transport of water, minerals, and sugars

Additional info:

• For more on why leaves change colors, see the recommended video: Why Leaves Change Colors.