Fungi

Basic Growth Forms of Fungi

Fungi are a diverse group of eukaryotic organisms with unique growth forms that relate to their ecological roles.

• Yeasts: Unicellular fungi that reproduce by budding or fission.

• Mycelia: Multicellular, filamentous structures composed of hyphae. Mycelia can be extensive and are adapted for nutrient absorption.

• Hyphae: Thread-like filaments that make up the mycelium; can be septate (with cross-walls) or coenocytic (without cross-walls).

• Example: Penicillium forms a dense mycelium, while Saccharomyces cerevisiae is a yeast.

Structure and Function of Fungal Mycelium

The mycelium is the main body of a fungus, consisting of a network of hyphae.

• High Surface Area: The filamentous structure increases surface area for absorption of nutrients.

• Growth: Mycelia grow at the tips of hyphae, allowing rapid colonization of substrates.

• Function: Efficient at decomposing organic matter and absorbing nutrients.

Traits Shared with Animals

• Chitin: Both fungi and animals have chitin (in fungal cell walls and arthropod exoskeletons).

• Glycogen Storage: Both store carbohydrates as glycogen.

• Heterotrophy: Both are heterotrophic, obtaining nutrients by consuming other organisms.

Fungal Nutrition

• Absorptive Heterotrophs: Fungi secrete enzymes to break down complex molecules and absorb the resulting small molecules.

• Saprophytic: Decompose dead organic matter.

• Parasitic and Mutualistic: Some fungi form symbiotic relationships with other organisms.

Fungi in the Carbon Cycle

• Decomposition: Fungi break down dead plant material, releasing carbon back into the atmosphere as CO2.

• Importance: Essential for nutrient cycling in ecosystems.

Degradation of Lignin and Cellulose

• Lignin: Fungi produce lignin peroxidase to break down lignin, a complex polymer in wood.

• Cellulose: Cellulase enzymes break down cellulose into glucose.

• Importance: Allows fungi to decompose wood and recycle nutrients.

Fungal Symbioses

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

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

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

Mycorrhizal Fungi

Lichens

• Definition: Symbiotic association between a fungus and a photosynthetic partner (alga or cyanobacterium).

• Characteristics: Can colonize harsh environments; important in soil formation.

Fungal Reproduction and Life Cycle

• Asexual Reproduction: Via spores, budding, or fragmentation.

• Sexual Reproduction: Involves fusion of hyphae (plasmogamy), then fusion of nuclei (karyogamy), followed by meiosis.

• Generalized Life Cycle: Alternation between haploid and diploid stages; production of spores for dispersal.

History of the Earth (Chapter 25)

Principles of Dating

• Law of Superposition: In undisturbed strata, 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

• Parent Isotope: The original radioactive isotope.

• Daughter Isotope: The product of decay.

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

• Equation:

• Where N is the remaining parent isotope, N0 is the original amount, t is time, and T1/2 is half-life.

Fossils and Index Fossils

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

• Index Fossil: Fossil of a species that was widespread but lived for a short period; useful for correlating rock layers.

Mass Extinction and Adaptive Radiation

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

• Adaptive Radiation: Rapid evolution of many species from a common ancestor, often after mass extinction or new opportunities.

• Factors Promoting Adaptive Radiation: Ecological opportunity and morphological innovation.

Cambrian Explosion

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

• Fossil Record: Sudden appearance of many animal phyla.

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

Geologic Time Scale

Introduction to Animals and Animal Diversity

General Characteristics of Animals

• Multicellularity: Composed of multiple cells with specialized functions.

• Heterotrophy: Obtain energy by consuming other organisms.

• Motility: Most animals can move at some stage of life.

• Nervous and Muscle Tissue: Unique to animals.

Major Animal Groups and Traits

Reproductive Modes

• Oviparity: Eggs laid outside the body; embryos develop externally.

• Ovoviviparity: Eggs retained inside the body; embryos nourished by yolk.

• Viviparity: Embryos develop inside the body and are nourished directly by the 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 and endoderm).

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

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

• Pseudocoelom: Body cavity not completely lined with mesoderm.

• Acoelomate: No body cavity.

Lophotrochozoans vs. Ecdysozoans

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

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

Metamorphosis

• Definition: Transformation from larval to adult form.

• Incomplete Metamorphosis: Juveniles resemble adults.

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

• Advantages: Reduces competition between larvae and adults.

Animal Form and Function

Major Tissue Types

• Epithelial: Covers surfaces; protection, absorption, secretion.

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

• Muscle: Movement (skeletal, cardiac, smooth).

• Nervous: Transmits electrical signals.

Surface Area and Volume

• Surface Area: Important for exchange of materials.

• Volume: Determines metabolic demand.

• Surface-Area-to-Volume Ratio: Decreases as size increases, affecting exchange efficiency.

Basal Metabolic Rate (BMR)

• Definition: Rate of energy expenditure at rest, in a thermoneutral environment, and post-absorptive state.

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

Homeostasis

• Definition: Maintenance of stable internal conditions.

• Regulation: Actively maintaining internal conditions (e.g., mammals).

• Conformity: Internal conditions match external environment (e.g., many fish).

• 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.

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 salt via gills.

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

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

Terrestrial Osmoregulation

• Challenges: Water loss via evaporation, excretion.

• Adaptations: Waterproof integument, concentrated urine, behavioral adaptations.

• Insects: Use Malpighian tubules to minimize water loss while excreting waste.

Mammalian Kidney Structure and Function

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

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

• Countercurrent Mechanism: Enhances concentration of urine.

• Desert Mammals: Longer loops of Henle for more concentrated urine.

Gas Exchange and Circulation

Principles of Gas Exchange

• Ventilation: Movement of respiratory medium (air or water) over exchange surface.

• Diffusion: Movement of gases across membranes.

• Circulation: Transport of gases via circulatory system.

Gas Exchange Structures

• Gills: Aquatic; use countercurrent exchange for efficiency.

• Tracheal System: Insects; air-filled tubes deliver oxygen directly to tissues.

• Lungs: Terrestrial vertebrates; site of gas exchange in alveoli.

Ventilation Mechanisms

• Positive-Pressure: Air pushed into lungs (e.g., frogs).

• Negative-Pressure: Air pulled into lungs by expanding thoracic cavity (e.g., mammals).

• Diaphragm: Muscle that contracts to increase lung volume in mammals.

• Avian Ventilation: Unidirectional airflow; more efficient than mammalian lungs.

Gas Transport and Hemoglobin

• Hemoglobin: Oxygen-carrying protein in red blood cells.

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

• Oxygen Equilibrium Curve: Plots hemoglobin saturation vs. partial pressure of O2.

• CO2 Transport:

• Blood pH: Increased CO2 lowers pH, stimulating 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 and systemic 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 to and from CNS.

• Afferent Division: Sensory input to CNS.

• Efferent Division: Motor output from CNS.

• Somatic: Voluntary control.

• Autonomic: Involuntary control (sympathetic and parasympathetic divisions).

Neuron Structure and Function

• Soma: Cell body; contains nucleus.

• Dendrites: Receive signals.

• Axon: Transmits signals away from soma.

Membrane Potential and Action Potentials

• Resting Potential: Typically -70 mV; maintained by Na+/K+-ATPase and K+ leak channels.

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

• Propagation: Movement of action potential along axon via voltage-gated channels.

• Myelination: Increases speed of conduction; nodes of Ranvier allow saltatory conduction.

Synaptic Transmission

• Synapse: Junction between neurons.

• Neurotransmitters: Chemical messengers released from presynaptic neuron.

• EPSP: Excitatory postsynaptic potential; depolarizes membrane.

• IPSP: Inhibitory postsynaptic potential; hyperpolarizes membrane.

• Summation: Integration of multiple signals determines if action potential is generated.

Chemical Signaling in Animals

Types of Chemical Signaling

• Autocrine: Signals act on the same cell that secretes them.

• Paracrine: Signals act on nearby cells.

• Endocrine: Hormones travel through bloodstream to distant targets.

• Neural: Neurotransmitters act across synapses.

• Neuroendocrine: Neurohormones released by neurons into blood.

Hormone Classes and Signaling Pathways

• Peptides/Polypeptides: Water-soluble; bind to cell surface receptors.

• Amino Acid Derivatives: Mostly water-soluble; some act like steroids.

• Steroids: Lipid-soluble; bind to intracellular receptors.

• Signal Transduction: Hormone binding triggers intracellular signaling cascades.

Hormonal Regulation Examples

• Metamorphosis: Thyroid hormones in amphibians; ecdysone and juvenile hormone in insects.

• Stress Response: Cortisol (long-term), epinephrine (short-term), adrenal glands.

• Blood Glucose: Insulin lowers, glucagon raises blood glucose; both secreted by pancreas.

• Water Balance: ADH and aldosterone regulate water and sodium; ADH released by pituitary gland.

• Feedback Loops: Negative feedback regulates hormone secretion.

Animal Reproduction and Development

Asexual vs. Sexual Reproduction

• Asexual: Offspring genetically identical to parent; rapid, no mate needed.

• Sexual: Genetic diversity; requires gametes and usually a mate.

• Types of Asexual Reproduction: Budding, fission, parthenogenesis.

Fertilization and Reproductive Strategies

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

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

• Sperm Competition: Competition between sperm of different males to fertilize eggs.

• Oviparity, Ovoviviparity, Viviparity: See above for definitions and examples.

Developmental Case Study

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

• Ultimate vs. Proximate Causes: Ultimate = evolutionary reason; proximate = immediate mechanism.

Key Terms

Be able to define and explain the relevance of all key terms listed in the guide, including anatomical directions (anterior, posterior, dorsal, ventral), tissue types, physiological processes (homeostasis, osmoregulation), and structures (nephron, alveoli, synapse, hormone, etc.).

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard General Biology content.