Study Guide: Prokaryotes, Protists, Fungi, Animal Form & Function, Nervous System, and Muscles

Study Guide - Smart Notes

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Prokaryotes – Bacteria and Archaea

Overview of Prokaryotes

Prokaryotes are unicellular organisms that lack a membrane-bound nucleus and organelles. They are divided into two domains: Bacteria and Archaea. Prokaryotes are among the most abundant and diverse organisms on Earth, occupying a wide range of environments.

Bacteria: One of the two main prokaryotic domains, characterized by the presence of peptidoglycan in their cell walls.
Archaea: The other prokaryotic domain, often found in extreme environments and lacking peptidoglycan in their cell walls.
Peptidoglycan: A polymer that forms a mesh-like layer outside the plasma membrane of most bacteria, providing structural support.
Outer membrane: Found in Gram-negative bacteria, this additional membrane provides extra protection.

Cell Wall Structure and Gram Staining

The Gram stain is a method used to classify bacteria based on differences in cell wall structure.

Gram-positive bacteria: Have thick peptidoglycan layers and stain purple.
Gram-negative bacteria: Have thin peptidoglycan layers and an outer membrane; stain pink/red.

Other Prokaryotic Structures

Capsule: A sticky outer layer that helps bacteria adhere to surfaces and evade the immune system.
Fimbriae/Pili: Hair-like appendages that allow bacteria to attach to surfaces or other cells.
Flagella: Tail-like structures used for movement.
Endospore: A resistant, dormant structure formed by some bacteria for survival in harsh conditions.
Nucleoid: Region where the bacterial chromosome is located (not membrane-bound).
Plasmid: Small, circular DNA molecules that replicate independently of the chromosome.

Reproduction and Genetic Variation

Binary fission: Asexual reproduction by cell division.
Genetic recombination: Increases genetic diversity through three main mechanisms:
- Transformation: Uptake of foreign DNA from the environment.
- Transduction: Transfer of DNA by bacteriophages (viruses that infect bacteria).
- Conjugation: Direct transfer of DNA between two bacterial cells via a pilus.

Metabolic Diversity and Extremophiles

Metabolic diversity: Prokaryotes can be photoautotrophs, chemoautotrophs, photoheterotrophs, or chemoheterotrophs.
Extremophiles: Archaea that thrive in extreme environments.
- Thermophiles: Live in very hot environments.
- Halophiles: Thrive in highly saline environments.
- Methanogens: Produce methane as a metabolic byproduct.

Classification: The Three-Domain System

Life is classified into three domains: Bacteria, Archaea, and Eukarya.

Protists

Introduction to Protists

Protists are a diverse group of mostly unicellular eukaryotic organisms. They can be autotrophic, heterotrophic, or mixotrophic, and play key roles in aquatic ecosystems.

Photoautotroph: Organisms that use light energy to synthesize organic compounds.
Heterotroph: Organisms that obtain nutrients by consuming other organisms.
Mixotroph: Organisms that can use both autotrophic and heterotrophic modes of nutrition.

Endosymbiosis and Eukaryotic Evolution

Endosymbiosis: A symbiotic relationship in which one organism lives inside the cell of another.
Primary endosymbiosis: The origin of mitochondria and chloroplasts from engulfed prokaryotes (e.g., Alphaproteobacteria and Cyanobacteria).
Secondary endosymbiosis: A eukaryote engulfs another eukaryotic cell that already contains an endosymbiont.

Major Protist Groups

Brown algae, Red algae, Green algae: Multicellular or unicellular photosynthetic protists.
Diatoms: Unicellular algae with silica cell walls.
Dinoflagellates: Mostly marine plankton, some cause harmful algal blooms.
Slime molds: Fungus-like protists involved in decomposition.

Fungi

Structure and Nutrition

Fungi are heterotrophic eukaryotes that absorb nutrients from their environment using hydrolytic enzymes. They can be decomposers, parasites, or mutualists.

Hyphae: Thread-like filaments that make up the body of a fungus.
Mycelium: A network of hyphae that forms the main body of the fungus.
Fruiting body: The reproductive structure that produces spores.
Molds: Rapidly growing, asexually reproducing fungi.
Yeasts: Unicellular fungi that reproduce by budding.

Fungal Life Cycles

Plasmogamy: Fusion of cytoplasm from two parent mycelia.
Heterokaryon: A fungal cell with two or more genetically distinct nuclei.
Karyogamy: Fusion of nuclei to form a diploid zygote.
Meiosis: Produces haploid spores.
Mitosis: Used for asexual reproduction (e.g., budding in yeasts).

Fungal Symbioses

Mycorrhizae: Symbiotic associations between fungi and plant roots.
- Arbuscular mycorrhizal fungi: Penetrate plant root cells.
- Ectomycorrhizal fungi: Surround root cells but do not penetrate.
Lichens: Symbiotic associations between fungi and photosynthetic organisms (algae or cyanobacteria).
Soredia: Small clusters of fungal hyphae and algal cells that disperse lichens.

Animal Form and Function & Homeostasis

Levels of Organization

Anatomy: Study of structure.
Physiology: Study of function.
Cell → Tissue → Organ → Organ System

Types of Animal Tissues

Epithelial tissue: Covers body surfaces and lines cavities.
Connective tissue: Supports and binds other tissues (e.g., bone, blood, cartilage).
Muscle tissue: Responsible for movement (smooth, skeletal, cardiac).
Nervous tissue: Transmits electrical signals.

Homeostasis and Regulation

Homeostasis: Maintenance of a stable internal environment.
Conformer: Organism whose internal conditions vary with the environment.
Regulator: Organism that maintains internal stability despite external changes.
Homeostatic system: Involves a sensor, integrator, and effector.
Negative feedback: A control mechanism that reduces the stimulus (e.g., body temperature regulation).

Thermoregulation

Endothermic: Generate heat internally (e.g., mammals, birds).
Ectothermic: Rely on external sources for heat (e.g., reptiles, amphibians).
Mechanisms: Vasodilation, vasoconstriction, countercurrent exchange, radiation, evaporation, convection, conduction.

Nervous System

Neuron Structure and Function

Neuron: Basic unit of the nervous system.
Dendrite: Receives signals.
Axon: Transmits signals.
Synapse: Junction between neurons.
Neurotransmitter: Chemical messenger at synapses.
Glial cells: Support and protect neurons.

Membrane Potentials and Action Potentials

Resting potential: The membrane potential of a neuron at rest (typically -70 mV).
Sodium-potassium pump (Na+/K+ pump): Maintains resting potential by pumping 3 Na+ out and 2 K+ in.
Action potential: Rapid change in membrane potential that travels along the axon.
Depolarization: Membrane potential becomes less negative.
Repolarization: Return to resting potential.
Hyperpolarization: Membrane potential becomes more negative than resting.
Voltage-gated ion channels: Open or close in response to changes in membrane potential.
Refractory period: Time during which a neuron cannot fire another action potential.
Saltatory conduction: Action potentials jump between nodes of Ranvier in myelinated axons, increasing speed.

Synaptic Transmission

Chemical synapse: Neurotransmitters cross the synaptic cleft.
Electrical synapse: Direct electrical connection via gap junctions.
EPSP (Excitatory postsynaptic potential): Depolarizes the postsynaptic membrane.
IPSP (Inhibitory postsynaptic potential): Hyperpolarizes the postsynaptic membrane.
Summation: EPSPs and IPSPs combine spatially and temporally to determine if an action potential will occur.

Organization of the Nervous System

Central nervous system (CNS): Brain and spinal cord.
Peripheral nervous system (PNS): Nerves outside the CNS.
Sensory neurons: Carry information to the CNS.
Interneurons: Process information within the CNS.
Motor neurons: Carry signals from the CNS to effectors.

Autonomic Nervous System

Sympathetic division: Prepares the body for "fight or flight".
Parasympathetic division: Promotes "rest and digest" functions.
Enteric division: Controls the digestive tract.

Brain Structure and Function

Forebrain: Includes cerebrum, thalamus, hypothalamus.
Midbrain: Relays information.
Hindbrain: Includes cerebellum, medulla oblongata, pons.
Cerebral cortex: Responsible for higher brain functions.
Limbic system: Involved in emotion and memory (includes amygdala and hippocampus).

Muscles

Types of Muscle Tissue

Skeletal muscle: Voluntary, striated, attached to bones.
Cardiac muscle: Involuntary, striated, found in the heart.
Smooth muscle: Involuntary, non-striated, found in walls of organs.

Muscle Structure

Muscle fiber: Single muscle cell.
Myofibril: Bundles of actin and myosin filaments.
Sarcomere: Functional unit of muscle contraction, defined by Z lines.
Actin: Thin filament.
Myosin: Thick filament.
Sliding filament model: Explains muscle contraction as actin and myosin filaments slide past each other.

Muscle Contraction Mechanism

Tropomyosin and troponin complex: Regulate access of myosin to actin.
Sarcoplasmic reticulum (SR): Stores and releases Ca2+ ions.
Transverse tubules (T-tubules): Conduct action potentials into the muscle fiber.
Neuromuscular junction: Synapse between motor neuron and muscle fiber; uses acetylcholine (ACh) as neurotransmitter.
ATP: Provides energy for contraction and relaxation.

Muscle Fiber Types

Slow-twitch fibers: Contract slowly, high endurance, rely on aerobic metabolism.
Fast-twitch fibers: Contract quickly, fatigue rapidly, rely on anaerobic metabolism.

Comparison of Muscle Types

Feature	Skeletal Muscle	Cardiac Muscle	Smooth Muscle
Striated	Yes	Yes	No
Control	Voluntary	Involuntary	Involuntary
Location	Attached to bones	Heart	Walls of organs

Additional info:

Equations for membrane potential (Nernst equation) and muscle contraction (cross-bridge cycle) are relevant but not explicitly listed in the notes. For example, the Nernst equation for equilibrium potential is:

For muscle contraction, ATP hydrolysis provides energy for the myosin head to bind and move actin filaments.