12U Biology Exam Review

Ionic, Molecular, and Polar Covalent Bonds

• Ionic bonds: Formed when electrons are transferred from one atom to another (e.g., NaCl). Usually between a metal and a non-metal. The resulting ions (charged particles) are attracted to each other.

• Molecular (Covalent) bonds: Form when atoms share electrons. Typically between two non-metals.

• Polar covalent bonds: A type of covalent bond where electrons are shared unequally, creating slight charges on different ends of the molecule (e.g., H₂O).

Intermolecular Forces

• Hydrogen bonds: Weak attraction between a hydrogen atom (already bonded to N, O, or F) and another electronegative atom. Important in water and DNA.

• London dispersion forces: Weakest; temporary dipoles in non-polar molecules cause attraction. Present in all molecules.

• Dipole-dipole interactions: Occur between polar molecules. The positive end of one molecule attracts the negative end of another.

Dehydration Synthesis and Hydrolysis

• Dehydration synthesis (condensation): Combines two molecules by removing water. Builds polymers (e.g., proteins, carbohydrates).

• Hydrolysis: Breaks down polymers by adding water. Reverse of dehydration synthesis.

Oxidation and Reduction Reactions

• Oxidation: Loss of electrons (LEO).

• Reduction: Gain of electrons (GER).

• These reactions are coupled and important in energy transfer (e.g., cellular respiration).

Anabolic and Catabolic Reactions

• Anabolic: Build complex molecules from simpler ones; requires energy (e.g., protein synthesis).

• Catabolic: Break down complex molecules into simpler ones; releases energy (e.g., digestion).

Properties of Water

• Cohesion: Water sticks to water (surface tension).

• Adhesion: Water sticks to other substances (capillary action).

• High specific heat capacity: Absorbs a lot of heat without changing temperature—regulates climate and body temp.

• Ice is less dense than liquid water: Allows ice to float and insulate water below.

• High heat of vaporization: Takes lots of energy to evaporate—important for cooling (e.g., sweating).

• Hydrophobic interactions: Water excludes non-polar molecules (like oils).

• Hydrophilic interactions: Water dissolves polar molecules and ions.

Acids, Bases, and Buffers

• Acid: Increases H⁺ concentration.

• Base: Reduces H⁺ or increases OH⁻.

• Neutralization reaction: Acid + base → salt + water.

• Buffer: Maintains pH by absorbing excess H⁺ or OH⁻ (e.g., bicarbonate buffer in blood).

Autoionization of Water

Water can self-ionize:
H₂O ⇌ H⁺ + OH⁻
Very few water molecules do this, but it defines pH (pH = -log[H⁺]).

Functional Groups

• Hydroxyl (–OH): Found in alcohols; polar.

• Carbonyl (C=O): Found in ketones (within chain) and aldehydes (end of chain).

• Carboxyl (–COOH): Found in acids (amino acids, fatty acids); acidic.

• Amino (–NH₂): Found in amino acids; basic.

• Phosphate (–PO₄³⁻): Found in DNA, ATP; acidic and energy-carrying.

• Sulfhydryl (–SH): Found in proteins; helps form disulfide bridges for protein structure.

Macromolecules Overview

• Carbohydrates: Energy and structure (e.g., glucose, cellulose).

• Lipids: Energy storage, membranes, signaling (e.g., fats, oils).

• Proteins: Structure, enzymes, transport (e.g., hemoglobin, insulin).

• Nucleic acids: Store genetic information (DNA, RNA).

Carbohydrates

• Monosaccharides: Simple sugars (glucose, fructose).

• Disaccharides: Two monosaccharides (sucrose = glucose + fructose).

• Polysaccharides: Long chains (starch, glycogen, cellulose).

• Glycosidic bonds: Link sugars via dehydration synthesis.

Lipids

• Fatty acids: Hydrocarbon chains; saturated (no double bonds) vs. unsaturated (one or more double bonds).

• Triglycerides: 3 fatty acids + glycerol.

• Phospholipids: Make up cell membranes; hydrophilic head, hydrophobic tail.

• Steroids: Four-ring structures (e.g., cholesterol, hormones).

• Waxes: Waterproof coatings.

Proteins

• Amino acids: Building blocks; 20 types.

• Peptide bond: Between amino group and carboxyl group of amino acids.

• Primary structure: Amino acid sequence.

• Secondary structure: Alpha helix or beta sheet (hydrogen bonds).

• Tertiary structure: 3D folding (R-group interactions).

• Quaternary structure: Multiple polypeptides joined (e.g., hemoglobin).

Nucleic Acids

• Nucleotides: Sugar + phosphate + nitrogenous base.

• DNA: Double helix; stores genetic info.

• RNA: Single-stranded; various types (mRNA, tRNA, rRNA).

Enzymes

• Active site: Where substrate binds.

• Induced fit: Enzyme changes shape slightly to fit substrate.

• Lock and key: Enzyme fits perfectly with substrate.

• Cofactors/coenzymes: Help enzyme function (e.g., vitamins).

• Factors affecting enzyme activity: Temperature, pH, substrate concentration.

• Competitive inhibition: Inhibitor competes with substrate.

• Non-competitive inhibition: Inhibitor binds elsewhere, changes shape.

• Allosteric site: Regulatory site.

• Feedback inhibition: End product inhibits pathway.

• Denaturation: Loss of shape and function due to heat/pH.

Animal and Plant Cells – Key Structures

• Cell membrane: Controls entry/exit; phospholipid bilayer.

• Nucleus: DNA storage.

• Nucleolus: Makes ribosomes.

• Nuclear membrane & pores: Control access to nucleus.

• ER (smooth/rough): Lipid synthesis (smooth), protein processing (rough).

• Vesicles/vacuoles: Transport/storage.

• Golgi bodies: Package and modify proteins.

• Lysosomes: Digest materials.

• Mitochondria: ATP production.

• Chloroplasts: Photosynthesis.

• Cytoskeleton: Structure and movement.

• Cell wall (plants): Support and protection.

• Extracellular matrix (animals): Cell support and signaling.

Cell Membrane & Transport

• Fluid mosaic model: Phospholipid bilayer with proteins.

• Integral proteins: Span membrane.

• Peripheral proteins: On membrane surface.

• Passive transport: No energy; includes diffusion, osmosis.

• Active transport: Uses energy (ATP).

• Simple diffusion: Molecules move from high to low concentration.

• Facilitated diffusion: Uses protein channels.

• Osmosis: Water moves across membrane.

• Hypertonic: Cell shrinks.

• Hypotonic: Cell swells.

• Isotonic: No net movement.

• Turgor pressure: Pressure in plant cells due to water.

• Endocytosis: Cell takes in material.

• Exocytosis: Cell expels material.

Exergonic vs. Endergonic Reactions

• Exergonic: Releases energy (e.g., cellular respiration); products have less energy than reactants.

• Endergonic: Requires input of energy (e.g., photosynthesis); products have more energy than reactants.

Anabolic vs. Catabolic Reactions

• Anabolic: Builds complex molecules from smaller ones; endergonic (e.g., synthesis of proteins).

• Catabolic: Breaks down molecules to release energy; exergonic (e.g., breakdown of glucose).

ATP → ADP + Pi

• ATP (adenosine triphosphate) stores energy in high-energy phosphate bonds.

• When ATP is broken down into ADP + Pi (inorganic phosphate), energy is released and used for cellular processes.

ATP as Cellular Energy

• Universal energy currency: Powers muscle contractions, nerve impulses, active transport, biosynthesis, etc.

• ATP is constantly regenerated in cells via cellular respiration.

Energy Carriers – NADH and FADH₂

• NAD⁺ and FAD: Electron carriers that accept electrons during redox reactions.

• NADH and FADH₂: Store energy and deliver electrons to the electron transport chain (ETC).

Dehydrogenases

• Enzymes that remove hydrogen atoms from substrates (oxidation) and transfer them to NAD⁺ or FAD.

• Critical in glycolysis, Krebs cycle, and ETC.

Aerobic vs. Anaerobic Cellular Respiration

• Aerobic: Requires oxygen, produces ~36 ATP per glucose.

• Anaerobic: Occurs without oxygen, much less efficient (~2 ATP).

Steps in Aerobic Respiration

A. Glycolysis (cytoplasm)

• Glucose (6C) → 2 Pyruvate (3C) + 2 ATP + 2 NADH

B. Pyruvate Oxidation (mitochondrial matrix)

• Pyruvate → Acetyl-CoA + CO₂ + NADH

C. Krebs Cycle (matrix)

• Acetyl-CoA → 2 CO₂ + 3 NADH + 1 FADH₂ + 1 ATP (per cycle)

D. Electron Transport Chain (ETC) (inner mitochondrial membrane)

• NADH/FADH₂ donate electrons → pump H⁺ ions → chemiosmosis → ATP synthesis

Substrate-Level vs. Oxidative Phosphorylation

• Substrate-level: Direct transfer of phosphate to ADP (in glycolysis and Krebs).

• Oxidative: Uses ETC and ATP synthase, powered by a proton gradient.

Structure of Mitochondria

• Matrix: Krebs cycle and pyruvate oxidation.

• Inner membrane (cristae): Electron transport chain, ATP synthase.

• Intermembrane space: H⁺ gradient builds here.

Glycolysis Summary

• Occurs in cytoplasm.

• Net gain: 2 ATP (substrate-level), 2 NADH.

• No oxygen required.

Pyruvate Oxidation Summary

• Pyruvate → Acetyl-CoA

• Produces 1 CO₂ and 1 NADH per pyruvate.

Krebs Cycle Summary

• 1 Acetyl-CoA → 3 NADH + 1 FADH₂ + 1 ATP + 2 CO₂

• Happens twice per glucose.

ETC & Chemiosmosis

• NADH/FADH₂ deliver electrons to ETC.

• Electrons pass through complexes, pumping H⁺ into intermembrane space.

• H⁺ flows back through ATP synthase, driving ATP production.

• O₂ is final electron acceptor → H₂O.

ATP Production by Stage

Stage	ATP Produced
Glycolysis	2 ATP + 2 NADH → ~7
Pyruvate Oxidation	2 NADH → ~5
Krebs Cycle	2 ATP + 6 NADH + 2 FADH₂ → ~20
Total per glucose	~32 ATP

Basal Metabolic Rate (BMR)

• Minimum energy needed to keep body functioning at rest.

• Affected by age, sex, body size, and hormones.

Regulating Cellular Respiration

• Controlled by feedback inhibition (e.g., ATP inhibits enzymes in glycolysis).

• ADP levels stimulate respiration.

Fats and Proteins in Respiration

• Fats → glycerol + fatty acids → enter glycolysis and Krebs.

• Proteins → amino acids → deaminated and enter Krebs cycle.

Anaerobic Respiration

• Alcohol fermentation (yeast): Pyruvate → ethanol + CO₂ + NAD⁺

• Lactic acid fermentation (muscle cells): Pyruvate → lactate + NAD⁺

• Net ATP: 2 per glucose (only from glycolysis)

Photosynthesis

Overall formula:
6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂

A. Light Reactions (thylakoid membranes)

• Convert light energy → chemical energy (ATP, NADPH)

• Involves PSII → ETC → PSI → NADPH

• Photolysis: Splitting water to replace electrons.

• Cyclic & non-cyclic photophosphorylation.

B. Light-Independent Reactions (Calvin Cycle) (stroma)

• Use ATP & NADPH to fix CO₂ into glucose.

• Phases: Carbon fixation, reduction, regeneration of RuBP.

Structure of Chloroplast

• Thylakoids: Membrane sacs with chlorophyll.

• Grana: Stacks of thylakoids.

• Stroma: Fluid around grana; site of Calvin cycle.

Light Absorption

Light Reaction ETC

• Linear pathway: Both ATP and NADPH made.

• Cyclic pathway: Only ATP made (used when NADPH is abundant).

• Chemiosmosis: H⁺ pumped into thylakoid → ATP synthase → ATP made in stroma.

Calvin Cycle

• Carbon fixation: CO₂ attached to RuBP (catalyzed by Rubisco).

• Reduction: Forms G3P (requires ATP & NADPH).

• Regeneration: RuBP regenerated to continue cycle.

Rubisco

• Enzyme that fixes CO₂ to RuBP.

• Can also bind O₂ → photorespiration, which wastes energy.

Photorespiration

• Occurs when Rubisco binds O₂ instead of CO₂.

• Happens more in hot, dry environments.

Stomata

• Open: When CO₂ needed (cool/wet).

• Close: To conserve water (hot/dry).

C₄ Plants

• Examples: Corn, sugarcane.

• PEP carboxylase fixes CO₂ in mesophyll → 4C compound → Calvin cycle in bundle sheath cells.

• Reduces photorespiration.

CAM Plants

• Examples: Cacti, pineapple.

• Open stomata at night, store CO₂ as acid.

• Release CO₂ during the day for photosynthesis.

• Water-efficient.

Comparing Photosynthesis and Respiration

Feature	Photosynthesis	Cellular Respiration
Location	Chloroplast	Mitochondria
Reactants	CO₂, H₂O, light	C₆H₁₂O₆, O₂
Products	Glucose, O₂	CO₂, H₂O, ATP
Energy	Requires light energy	Releases chemical energy (ATP)
Electron Carriers	NADP⁺/NADPH	NAD⁺, FAD/NADH, FADH₂

Gene, Chromosome, Genome, Plasmids, Histones

• Gene: A sequence of DNA that codes for a protein.

• Chromosome: A long DNA molecule containing many genes, wrapped around histones.

• Genome: The entire DNA content of an organism.

• Plasmids: Small, circular DNA in bacteria; often carry antibiotic resistance genes.

• Histones: Proteins DNA coils around; help package DNA in the nucleus.

History of DNA (Scientists)

• Mendel: Inheritance laws using pea plants.

• Griffith: Discovered "transforming principle" in bacteria.

• Avery, McLeod, McCarty: Proved DNA is the transforming factor.

• Hershey and Chase: Used viruses to confirm DNA (not protein) is genetic material.

• Chargaff: A = T, G = C (base-pairing rule).

• Wilkins and Franklin: X-ray diffraction images of DNA.

• Watson and Crick: Discovered double helix model.

DNA Structure

• Nucleotide: Sugar (deoxyribose), phosphate, nitrogen base (A, T, G, C).

• Base pairing: A–T (2 hydrogen bonds), G–C (3 hydrogen bonds).

• Pyrimidines: C, T (1 ring); Purines: A, G (2 rings).

• Double helix: Antiparallel strands held by hydrogen bonds.

DNA Replication

• Semiconservative: Each new DNA has one old and one new strand.

• Steps:

  1. Initiation: Helicase unwinds DNA at replication origin.

  2. Elongation: DNA polymerase adds nucleotides.

  3. Termination: Ends when replication forks meet.

• Key Enzymes:

  • Helicase: Unzips DNA.

  • Topoisomerase: Prevents supercoiling.

  • SSBPs: Keep strands apart.

  • RNA primase: Adds primer.

  • DNA polymerase III: Builds new strand.

  • DNA polymerase I: Replaces RNA primers with DNA.

  • Ligase: Seals gaps (Okazaki fragments).

• Leading strand: Synthesized continuously.

• Lagging strand: Synthesized in fragments (Okazaki).

DNA Packaging

• Nucleosome: DNA wrapped around histones.

• Solenoid: Coiled nucleosomes.

• Chromatin: Loosely packed DNA.

• Chromosome: Highly condensed DNA.

Prokaryotic vs. Eukaryotic DNA

• Prokaryotes: Circular DNA, no histones, single origin.

• Eukaryotes: Linear DNA, multiple origins, organized with histones.

Telomeres, Hayflick Limit, Aging & Cancer

• Telomeres: Repetitive end sequences that protect DNA.

• Hayflick limit: Cells divide ~50 times before dying (telomere loss).

• Telomerase: Enzyme that rebuilds telomeres (active in cancer and stem cells).

Central Dogma of Biology

• DNA → RNA → Protein

• One gene = one polypeptide (though alternative splicing can change this).

DNA vs. RNA

Feature	DNA	RNA

Sugar

Deoxyribose

Ribose

Bases

A, T, G, C

A, U, G, C

Structure

Double-stranded

Single-stranded

Function

Stores genetic info

Protein synthesis, regulation

Types of RNA

• mRNA: Carries message from DNA to ribosome.

• tRNA: Transfers amino acids during translation.

• rRNA: Part of ribosome structure.

Genetic Code

• Codons: Triplets of mRNA bases (e.g., AUG = start/methionine).

• Start codon: AUG.

• Stop codons: UAA, UAG, UGA.

• Degenerate: Multiple codons for one amino acid.

• Universal: Same in almost all organisms.

Transcription (DNA → RNA)

A. Initiation

• Promoter: DNA sequence where RNA polymerase binds (includes TATA box).

• RNA polymerase unwinds DNA and starts RNA synthesis.

B. Elongation

• RNA is built 5' → 3' by adding complementary bases to DNA template.

C. Termination

• Ends at a specific sequence; RNA detaches.

D. Post-Transcriptional Modifications (Eukaryotes only)

• 5' cap: Protects mRNA.

• Poly-A tail: Stabilizes.

• Splicing: Removes introns, joins exons.

Translation (mRNA → Protein)

• Occurs in cytoplasm at ribosomes.

Steps:

1. Initiation: Ribosome binds to mRNA; start codon recognized.

2. Elongation: tRNA brings amino acids, matched by anticodon.

3. Termination: Stop codon reached; polypeptide released.

• Aminoacylation: tRNA gets charged with its amino acid.

• Reading frame: Set by start codon.

• Polyribosomes: Multiple ribosomes translate one mRNA.

Gene Expression Control

Lac Operon (Inducible – ON when lactose present)

• Repressor binds operator, blocking transcription.

• Lactose (inducer) removes repressor.

B. Trp Operon (Repressible – ON unless tryptophan is present)

• High tryptophan activates repressor → shuts off genes.

C. Eukaryotic Control

• Transcription factors, enhancers, silencers, epigenetics (e.g., methylation).

Cancer

• Caused by uncontrolled cell division due to mutations.

• Proto-oncogenes → oncogenes (promote division).

• Tumor suppressor genes (e.g., p53) stop division; if mutated → cancer.

Genetic Mutations

A. Small Scale (Point Mutations)

• Substitution: One base replaced.

  • Silent: No change in protein.

  • Missense: One amino acid changed.

  • Nonsense: Stop codon created.

• Insertion/Deletion: Can cause frameshift mutations (changes reading frame).

B. Large Scale (Chromosomal Mutations)

• Inversion: Segment flips.

• Translocation: Segments switch between chromosomes.

• Duplication/Deletion: Extra/missing parts.

Causes of Mutations

• Mutagens: Radiation, chemicals, viruses.

• Spontaneous: Errors in DNA replication.

• Positive/Negative mutations: Depends on effect (e.g., resistance vs. disease).

Transposons

• "Jumping genes" that move around the genome.

• Can disrupt or regulate gene expression.

Genetic Engineering Tools

• Restriction enzymes: Cut DNA at specific sequences.

• Recognition site: Palindromic sequence.

• Sticky ends: Overhangs that can join to complementary ends.

• Blunt ends: Straight cuts.

• DNA ligase: Joins DNA fragments.

• Plasmid: Circular DNA used as vector.

• Vector: Carries gene into host.

• Transformation: Cell takes up foreign DNA.

PCR (Polymerase Chain Reaction)

• Amplifies DNA.

• Steps: Denaturation, Annealing, Extension.

• Uses Taq polymerase (heat-stable).

Gel Electrophoresis

• Separates DNA by size.

• DNA moves through gel toward positive electrode (DNA is negative).

• Smaller fragments move faster.

DNA Sequencing

• Determines exact nucleotide order.

• Used for forensics, ancestry, medicine.

Organ Systems Involved in Homeostasis

• Nervous system: Fast, electrical signals (e.g., reflexes, temperature).
  
  

• Endocrine system: Slower, long-lasting chemical signals (hormones).
  
  

• Excretory system: Maintains water, salt, pH balance (kidneys).
  
  

Integumentary system: Skin—helps with temperature regulation.

Feedback Mechanisms

• Negative Feedback: Stabilizes internal conditions by reversing changes.
  Example: Body temp ↑ → sweat → temp ↓.
  
  

Positive Feedback: Amplifies a change.

Example: Oxytocin during childbirth causes stronger contractions.

Feedback Loop Components

• Stimulus: A change from normal.
  
  

• Sensor: Detects the change.
  
  

• Integrator: Usually the brain; compares to set point.
  
  

• Effector: Muscle/gland that acts to fix the change.
  
  

Response: Action taken to restore balance.

Thermoregulation

• Endotherms: Maintain body temp internally (e.g., humans).
  
  

• Ectotherms: Body temp depends on environment (e.g., reptiles).
  
  

• Homeotherms: Constant body temp.
  
  

• Poikilotherms: Body temp varies.
  
  

Heat transfer: Conduction, convection, radiation, evaporation.

Dormancy Strategies

• Torpor: Short-term (overnight in birds/mammals).
  
  

• Hibernation: Long-term winter dormancy (e.g., bears).
  
  

• Estivation: Dormancy in dry/hot conditions (e.g., desert frogs).
  
  

Excretory System (Urinary System)

• Organs: Kidneys → ureters → bladder → urethra.
  

Nephron Structure

• Bowman’s capsule: Surrounds glomerulus (filtration).
  
  

• Glomerulus: Capillaries filtering blood.
  
  

• Proximal tubule: Reabsorbs nutrients, ions, water.
  
  

• Loop of Henle: Descending = water out, Ascending = Na⁺ out.
  
  

• Distal tubule: Secretion of toxins, drugs.
  
  

• Collecting duct: Final water reabsorption → urine.
  

Urine Formation

• Filtration: Glomerulus → Bowman’s capsule.
  
  

• Reabsorption: Needed substances returned to blood.
  
  

Secretion: Waste and excess ions added to filtrate.

Loop of Henle Length

• Desert animals: Long loops (more water reabsorption).
  
  

• Aquatic animals: Shorter loops.
  
  

Hormones: Protein vs. Steroid

Feature	Protein Hormones	Steroid Hormones
Solubility	Water-soluble	Lipid-soluble
Receptor location	On cell membrane	Inside cell
Examples	Insulin, ADH	Testosterone, estrogen

Endocrine Glands and Hormones

Gland	Hormones	Function
Hypothalamus	Releasing hormones	Controls pituitary
Pituitary (Ant.)	FSH, LH, GH, ACTH, TSH	Controls other glands, growth
Pituitary (Post.)	ADH, oxytocin	Water balance, uterine contractions
Thyroid	Thyroxine (T4), Calcitonin	Metabolism, lowers blood Ca²⁺
Parathyroid	PTH	Raises blood Ca²⁺
Adrenal (Cortex)	Cortisol, aldosterone	Stress, water/salt balance
Adrenal (Medulla)	Epinephrine (adrenaline)	Fight or flight
Pancreas	Insulin, glucagon	Blood sugar regulation
Ovaries	Estrogen, progesterone	Menstrual cycle
Testes	Testosterone	Male traits, sperm production

Blood Sugar Regulation

• Insulin (from β-cells): Lowers blood glucose.
  
  

• Glucagon (from α-cells): Raises blood glucose.
  
  

• Type I Diabetes: Autoimmune, no insulin made.
  
  

• Type II Diabetes: Insulin made but not effective.
  
  

Type III: Insulin resistance in the brain (linked to Alzheimer’s).

Reproductive Hormones

• Female:
  
  

  • FSH: Matures follicles.
    
    

  • LH: Triggers ovulation.
    
    

  • Estrogen: Builds endometrium.
    
    

  • Progesterone: Maintains endometrium.
    
    

• Male:
  
  

  • FSH: Sperm production.
    
    

LH: Testosterone secretion.

Nervous System

A. CNS: Brain + spinal cord.

B. PNS: All other nerves.

Types of Neurons:

• Sensory (afferent): To CNS.
  
  

• Interneurons: In CNS.
  
  

• Motor (efferent): From CNS to muscles/glands.
  
  

Neuron Structure:

• Dendrites: Receive signals.
  
  

• Axon: Sends signal.
  
  

• Myelin sheath: Speeds signal (produced by glial cells).
  
  

Nodes of Ranvier: Gaps for saltatory conduction.

Nervous System Divisions

System	Function
Somatic	Voluntary movement
Autonomic	Involuntary (organs)
Sympathetic	"Fight or flight" (↑ HR, ↓ digestion)
Parasympathetic	"Rest and digest" (↓ HR, ↑ digestion)

Reflex Arc

• Path: Sensory neuron → interneuron (spinal cord) → motor neuron → effector.
  
  

Bypasses brain for speed.

Nerve Impulse Transmission

• Resting potential: -70 mV; Na⁺ outside, K⁺ inside.
  
  

• Depolarization: Na⁺ enters (cell becomes +).
  
  

• Repolarization: K⁺ exits.
  
  

• Refractory period: Resets ion balance.
  
  

Saltatory conduction: In myelinated axons, impulse jumps node to node.

Synapse & Neurotransmitters

• Chemical synapse: Uses neurotransmitters.
  
  

• Electrical synapse: Direct ion flow (rare).
  
  

• Synaptic cleft: Gap between neurons.
  
  

Neurotransmitters: Dopamine, serotonin, ACh, GABA, etc.

Brain Parts

Structure	Function
Medulla Oblongata	Involuntary actions (breathing, HR)
Pons	Breathing coordination
Cerebellum	Balance and coordination
Cerebrum	Thought, memory, senses
Cerebral Cortex	Sensory + motor processing
Thalamus	Relay center
Hypothalamus	Controls endocrine + autonomic systems
Basal Nuclei	Fine-tunes movement

Blood-Brain Barrier

• Selectively allows substances into brain.
  
  

• Protects from toxins, maintains stability.

Left vs. Right Brain

• Left: Logical, language.
  
  

Right: Creative, spatial.

Population Ecology - Key Terms

• Geographic range: Where species live.
  
  

• Habitat: Local environment where it survives.
  
  

• Population size (N): Number of individuals.
  
  

• Population density (D):
  D=NArea(or volume)D = \frac{N}{Area (or volume)}D=Area(or volume)N​
  
  

• Crude density: Includes unsuitable areas.
  
  

• Ecological density: Only includes usable habitat.
  
  

Population Dispersion

• Clumped: Most common; resources/social behavior (e.g., fish schools).
  
  

• Uniform: Territory/competition (e.g., penguins).
  
  

Random: Rare; no pattern (e.g., wind-dispersed plants).

Sampling Methods

• Quadrat: Count in square areas, estimate the whole area.
  
  

Mark-recapture:

Capture a sample of animals, mark and release. In the second round of animal capturing, count how many have already been marked. 

Tracking Populations

Tagged and followed over time to monitor movement, reproduction, and survival.

Life Tables & Cohorts

Show mortality, survivorship by age group.

Survivorship Curves

• Type I: High survival until old age (humans).
  
  

• Type II: Constant death rate (birds).
  
  

Type III: High infant mortality (fish, plants).

Fecundity

• Reproductive potential.
  
  

• High fecundity = many offspring, less care (e.g., insects).
  
  

• Low fecundity = few offspring, more care (e.g., mammals).
  
  

Population Growth

• Growth Rate (r) = the speed at which the number of organisms or the size of an organism increases over a specific period
  
  
  

• Positive r: Increasing.
  
  

• Zero r: Stable.
  
  

Negative r: Declining.

Exponential vs. Logistic Growth

• Exponential: J-curve; no limits.
  
  

• Logistic: S-curve; limited by carrying capacity (K).
  
  

Doubling time:

Time it takes for a population to double in size

Limiting Factors

• Density-dependent: Disease, competition, predation.
  
  

• Density-independent: Natural disasters, weather.
  
  

• Allee Effect: Population too small → trouble finding mates.
  
  

Minimum Viable Population: Smallest number to survive long term.