Fungi

Basic Growth Forms of Fungi

• Unicellular fungi are called yeasts.

• Multicellular fungi form networks of filaments called mycelia.

• Mycelia are composed of threadlike structures called hyphae.

• Hyphae can be septate (divided by cross-walls) or coenocytic (lacking cross-walls).

Structure and Function of Mycelium

• Mycelium is a mass of hyphae that increases surface area for absorption.

• Thin hyphae allow fungi to efficiently absorb nutrients from their environment.

• Fungal morphology (extensive branching) is directly related to their absorptive lifestyle.

Traits Shared with Animals

• Both fungi and animals are heterotrophic (obtain carbon from organic sources).

• Both use chitin in their cell walls (fungi) or exoskeletons (animals).

• Fungi store carbohydrates as glycogen, similar to animals.

Fungal Nutrition

• Fungi are absorptive heterotrophs: they secrete enzymes to break down complex molecules and absorb the resulting small molecules.

• They can be saprophytic (decomposers), parasitic, or mutualistic.

Fungi in the Carbon Cycle

• Fungi decompose dead organic matter, releasing carbon back into the atmosphere as CO2.

• They are essential for nutrient cycling in ecosystems.

Decomposition of Lignin and Cellulose

• Fungi produce enzymes (e.g., lignin peroxidase, cellulase) to break down tough plant materials.

• This process is crucial for recycling plant biomass and maintaining soil fertility.

Symbiotic Relationships

• Mutualism: Both partners benefit (e.g., mycorrhizal fungi and plants).

• Parasitism: Fungi benefit at the expense of the host (e.g., athlete's foot fungus).

• Commensalism: One benefits, the other is unaffected (less common in fungi).

Mycorrhizal Fungi

• Ectomycorrhizal fungi (EMF): Form sheaths around roots and penetrate between root cells.

• Arbuscular mycorrhizal fungi (AMF): Penetrate root cell walls and form arbuscules inside cells.

• Both types enhance nutrient uptake for plants.

Lichens

• Lichen: A symbiotic association between a fungus and a photosynthetic partner (alga or cyanobacterium).

• Lichens are important colonizers of bare rock and contribute to soil formation.

Fungal Reproduction and Life Cycle

• Fungi reproduce both sexually and asexually via spores.

• The generalized fungal life cycle includes haploid, dikaryotic, and diploid stages.

• Sexual reproduction involves plasmogamy (fusion of cytoplasm) and karyogamy (fusion of nuclei).

History of the Earth (Chapter 25)

Principles of Dating

• Law of superposition: In undisturbed sedimentary layers, the oldest layers are at the bottom.

• Principle of faunal succession: Fossil organisms succeed one another in a definite order.

• Relative dating: Determines the sequence of events, not exact ages.

• Absolute dating: Uses radiometric techniques to determine actual ages.

Radiometric Dating

• Based on the decay of radioactive isotopes.

• Parent isotope decays to a daughter isotope at a constant rate.

• Half-life: Time required for half of the parent isotope to decay.

• Formula: where = remaining parent, = original amount, = time, = half-life

Fossils and Index Fossils

• Types of fossils: Permineralized, casts, molds, amber, trace fossils.

• Index fossil: A fossil used to define and identify geologic periods; must be widespread and short-lived.

Mass Extinction and Adaptive Radiation

• Mass extinction: Sudden, widespread loss of many species.

• Five major mass extinctions have occurred in Earth's history.

• Adaptive radiation: Rapid diversification of a lineage into many forms, often following mass extinction or new opportunities.

• Promoted by ecological opportunity and morphological innovation.

Cambrian Explosion

• Rapid diversification of animal body plans ~541 million years ago.

• Fossil record shows sudden appearance of many animal phyla.

• Hypotheses for triggers: increased oxygen, new predator-prey relationships, genetic innovations (e.g., Hox genes).

Geologic Time Scale

• Precambrian: Origin of life, first eukaryotes, soft-bodied animals.

• Paleozoic: Cambrian explosion, colonization of land, first vertebrates.

• Mesozoic: Age of reptiles, dinosaurs, first mammals and birds.

• Cenozoic: Age of mammals, diversification of flowering plants and insects.

Introduction to Animals and Animal Diversity

General Characteristics of Animals

• Multicellular, heterotrophic eukaryotes.

• Lack cell walls; have extracellular matrix.

• Most have specialized tissues and nervous/muscle systems.

Major Animal Groups and Traits

• Annelida: Segmented worms; have chaetae (bristles).

• Arthropoda: Segmented body, jointed appendages, exoskeleton.

• Chordata: Notochord, dorsal nerve cord, pharyngeal slits, post-anal tail.

• Cnidaria: Radial symmetry, nerve net, stinging cells (cnidocytes).

• Echinodermata: Water vascular system, tube feet, pentaradial symmetry (adults).

• Mollusca: Foot, visceral mass, mantle; may have shell.

• Nematoda: Roundworms; pseudocoelomate, unsegmented.

• Platyhelminthes: Flatworms; acoelomate, unsegmented.

Fertilization and Reproductive Modes

• External fertilization: Gametes released into environment (e.g., many fish, amphibians).

• Internal fertilization: Sperm deposited inside female (e.g., mammals, reptiles).

• Oviparity: Eggs laid outside body.

• Ovoviviparity: Eggs retained inside, hatch internally, young born live.

• Viviparity: Young develop inside and are nourished by mother.

Body Symmetry and Body Plans

• Bilateral symmetry: Single plane divides body into mirror images; associated with cephalization (development of a head).

• Diploblastic: Two germ layers (ectoderm, endoderm).

• Triploblastic: Three germ layers (ectoderm, mesoderm, endoderm).

• Coelom: Fluid-filled body cavity lined with mesoderm.

• Pseudocoelom: Body cavity not fully lined with mesoderm (e.g., nematodes).

• Acoelomate: No body cavity (e.g., flatworms).

Lophotrochozoans vs. Ecdysozoans

• Lophotrochozoans: Grow by adding body mass (e.g., mollusks, annelids).

• Ecdysozoans: Grow by molting exoskeleton (e.g., arthropods, nematodes).

Metamorphosis

• Metamorphosis: Transformation from larva to adult.

• Incomplete metamorphosis: Juveniles resemble adults.

• Complete metamorphosis: Distinct larval, pupal, and adult stages.

• Complete metamorphosis allows specialization of life stages and reduces competition.

Animal Form and Function

Major Tissue Types

• Epithelial tissue: Covers surfaces; functions in protection, absorption, secretion.

• Connective tissue: Supports, binds, and protects organs (e.g., bone, blood, cartilage).

• Muscle tissue: Enables movement (skeletal, cardiac, smooth).

• Nervous tissue: Conducts electrical signals.

Cell Size and Surface Area-to-Volume Ratio

• As cell size increases, volume increases faster than surface area.

• High surface-area-to-volume ratio favors efficient exchange with environment.

Metabolic Rate and Body Size

• Basal metabolic rate (BMR): Energy expenditure at rest, measured under standard conditions.

• Larger animals have higher total BMR, but lower BMR per unit mass.

Homeostasis

• Maintenance of stable internal conditions.

• Involves regulation (active adjustment) or conformity (internal conditions match environment).

• Negative feedback: A change triggers a response that counteracts the change (e.g., body temperature regulation).

Thermoregulation

• Mechanisms of heat exchange: conduction, convection, radiation, evaporation.

• Ectotherms: Rely on external heat sources; lower energy needs.

• Endotherms: Generate heat metabolically; higher energy needs.

• Homeotherms: Maintain constant body temperature.

• Poikilotherms: Body temperature varies with environment.

• Countercurrent exchange: Conserves heat by transferring it between fluids flowing in opposite directions (e.g., blood vessels in limbs).

Water and Electrolyte Balance

Osmoregulation and Excretion

• Osmoregulation: Control of water and solute concentrations.

• Nitrogenous wastes: Ammonia, urea, uric acid; must be excreted due to toxicity.

Osmoregulation in Aquatic Animals

• Marine bony fishes: Lose water by osmosis, drink seawater, excrete excess salt via gills.

• Freshwater fishes: Gain water by osmosis, excrete dilute urine, actively uptake ions via gills.

• Sharks: Retain urea to be nearly isosmotic, excrete excess salt via rectal gland.

Osmoregulation in Terrestrial Animals

• Face water loss by evaporation and excretion.

• Gain water by drinking, eating, metabolic water production.

• Insects minimize water loss via waxy cuticle and Malpighian tubules.

Mammalian Kidney Structure and Function

• Nephron: Functional unit; consists of renal corpuscle, proximal tubule, loop of Henle, distal tubule, collecting duct.

• Loop of Henle: Creates osmotic gradient for water reabsorption.

• Countercurrent mechanisms: Concentrate urine by maintaining gradient in medulla.

• Desert mammals have longer loops of Henle for more concentrated urine.

Hormonal Regulation

• Low sodium triggers aldosterone release (increases Na+ reabsorption).

• Low water triggers ADH release (increases water reabsorption).

Gas Exchange and Circulation

Principles of Gas Exchange

• Involves ventilation (movement of air/water), diffusion (across respiratory surface), and circulation (transport in body fluids).

• Partial pressure: Pressure exerted by a single gas in a mixture.

• Partial pressure formula:

Respiratory Media and Structures

• Air has higher O2 content and lower density/viscosity than water.

• Gas exchange structures: Body surface, gills, tracheae, lungs.

• Gills: Countercurrent exchange maximizes O2 uptake.

• Insects: Use tracheal system for direct gas delivery.

• Lungs: Internal, highly vascularized; mammals use negative-pressure ventilation (diaphragm contracts to draw air in).

• Birds: Use flow-through ventilation; more efficient gas exchange.

Hemoglobin and Oxygen Transport

• Hemoglobin: Protein in red blood cells that binds O2.

• Cooperative binding: Binding of one O2 increases affinity for more O2.

• Oxygen equilibrium curve shows relationship between O2 partial pressure and hemoglobin saturation.

CO2 Transport and Blood pH

• CO2 reacts with water:

• Increased CO2 lowers blood pH, triggering increased ventilation (negative feedback).

Circulatory Systems

• Open system: Hemolymph bathes organs directly (e.g., arthropods).

• Closed system: Blood confined to vessels (e.g., vertebrates).

• Mammalian heart: Four chambers; blood flows through pulmonary (lungs) and systemic (body) circuits.

• Cardiac cycle: Sequence of contraction (systole) and relaxation (diastole).

Nervous Systems

Organization and Function

• CNS: Brain and spinal cord; processes information.

• PNS: Nerves outside CNS; transmits signals.

• Afferent division: Sensory input to CNS.

• Efferent division: Motor output from CNS.

• Somatic system: Voluntary control.

• Autonomic system: Involuntary control; includes sympathetic ("fight or flight") and parasympathetic ("rest and digest") divisions.

Neuron Structure and Function

• Dendrites: Receive signals.

• Soma (cell body): Integrates signals.

• Axon: Transmits signals to next cell.

Membrane Potential and Action Potentials

• Resting membrane potential: Inside of neuron is negative relative to outside (typically -70 mV).

• Maintained by Na+/K+-ATPase pump and K+ leak channels.

• Action potential: Rapid change in membrane potential; three phases: depolarization, repolarization, hyperpolarization.

• Propagates in one direction due to refractory period.

• Myelination (by Schwann cells or oligodendrocytes) increases speed; nodes of Ranvier allow saltatory conduction.

Synaptic Transmission

• Signals transmitted via neurotransmitters at synapses.

• EPSPs: Excitatory postsynaptic potentials (depolarize membrane).

• IPSPs: Inhibitory postsynaptic potentials (hyperpolarize membrane).

• Summation of EPSPs and IPSPs determines if neuron fires.

Chemical Signaling in Animals

Types of Chemical Signaling

• Autocrine: Signal acts on same cell that secretes it.

• Paracrine: Signal acts on nearby cells.

• Endocrine: Hormones travel via bloodstream to distant targets.

• Neural: Neurotransmitters act across synapses.

• Neuroendocrine: Neurohormones released by neurons into blood.

Hormone Classes and Signaling Pathways

• Hormones: Peptides/polypeptides (water-soluble), steroids (lipid-soluble), amines (variable solubility).

• Signal transduction: Hormone binds receptor, triggers cellular response.

• Same hormone can have different effects depending on target cell and context.

Hormonal Regulation Examples

• Thyroid hormones regulate amphibian metamorphosis.

• Cortisol and epinephrine mediate stress responses (short-term: fight-or-flight; long-term: adaptation).

• Insulin and glucagon regulate blood glucose; ADH and aldosterone regulate water/electrolyte balance.

• Pituitary gland releases ADH in response to dehydration.

• Hormone secretion is regulated by feedback loops (negative and positive).

Animal Reproduction and Development

Asexual vs. Sexual Reproduction

• Asexual reproduction: Offspring genetically identical to parent; includes budding, fission, parthenogenesis.

• Sexual reproduction: Involves gametes; increases genetic diversity.

• Asexual is efficient but less adaptable; sexual is costly but promotes variation.

Reproductive Strategies

• External fertilization: Gametes released into environment (e.g., broadcast spawning).

• Internal fertilization: Sperm deposited inside female (e.g., copulation, spermatophore transfer).

• Sperm competition: Multiple males' sperm compete to fertilize eggs.

• Oviparity, ovoviviparity, viviparity: See above for definitions and trade-offs.

Case Study: Daphnia

• Daphnia switch between asexual and sexual reproduction depending on environmental conditions.

• Demonstrates adaptive value of reproductive flexibility.

Ultimate vs. Proximate Causes

• Ultimate causes: Evolutionary explanations ("why").

• Proximate causes: Mechanistic explanations ("how").

Key Terms and Definitions

• See the provided list for definitions of anatomical, physiological, and ecological terms relevant to animal diversity, form and function, homeostasis, osmoregulation, gas exchange, nervous systems, chemical signaling, and reproduction.

• Be able to match terms to their definitions and explain their relevance in biological contexts.