General Science

Cell Biology

The cell is the basic structural and functional unit of all living things.

Components in both animal and plant cells: - Cell membrane: Phospholipid bilayer controlling what enters/exits. Selectively permeable. - Nucleus: Contains DNA; controls all cell activities. - Mitochondria: "Powerhouse" — site of aerobic respiration; produces ATP. - Ribosomes: Synthesize proteins. Found on rough ER or floating in cytoplasm. - Endoplasmic reticulum (ER): Transport network. Rough ER makes proteins; smooth ER makes lipids. - Golgi apparatus: Processes and packages proteins for export or internal use. - Lysosomes: Contain digestive enzymes that break down waste and foreign material.

Found only in plant cells: - Cell wall: Rigid cellulose layer providing structural support. (Animal cells do NOT have this.) - Chloroplasts: Site of photosynthesis; contain the green pigment chlorophyll. - Large central vacuole: Provides turgor pressure (keeps the plant firm).

Cell Division

Mitosis: Produces two identical daughter cells with the same chromosome count as the parent. Used for growth and tissue repair.

Meiosis: Produces four daughter cells with half the chromosome count (haploid gametes — sperm and eggs). Crossing over (exchange of genetic segments between homologous chromosomes) occurs during Prophase I, creating genetic diversity.

Human somatic (body) cells: 46 chromosomes (23 pairs). Human gametes (sperm/egg): 23 chromosomes. Fertilization restores the full 46-chromosome count.

Photosynthesis and Cellular Respiration

Photosynthesis (in chloroplasts):

CO₂ + H₂O + light → glucose (C₆H₁₂O₆) + O₂

Plants capture light with chlorophyll, use it to fix CO₂ into glucose, and release oxygen as a byproduct. The foundation of nearly all food chains.

Cellular Respiration (in mitochondria):

Glucose + O₂ → CO₂ + H₂O + ATP

Breaks down glucose to release stored energy.

Aerobic respiration: Requires oxygen; produces ~36–38 ATP per glucose molecule.
Anaerobic respiration (fermentation): No oxygen; produces only 2 ATP; produces lactic acid (muscle cells) or ethanol + CO₂ (yeast).
Most ATP is produced in the electron transport chain on the inner mitochondrial membrane.

Genetics and Heredity

DNA: Double-helix molecule made of nucleotide base pairs. Carries the genetic code.

Gene: A DNA segment coding for a specific protein or trait.

Chromosome: Tightly coiled DNA + protein structure. Humans have 46 (23 pairs — one from each parent).

Allele: Different versions of the same gene. You inherit one from each parent.

Dominant allele (A): Expressed whenever present (even one copy). Recessive allele (a): Only expressed when two copies are present (aa).

Genotype: Genetic makeup (AA, Aa, aa). Phenotype: Physical expression.

Punnett square: Predicts offspring probability. Aa × Aa gives: 25% AA, 50% Aa, 25% aa → 75% show dominant phenotype.

Y-linked traits: Passed only from father to son (on Y chromosome). X-linked traits: On the X chromosome. Males (XY) have only one X, so X-linked recessives are expressed more often in males.

Osmosis and Diffusion

Diffusion: Movement of particles from high concentration to low concentration (down the gradient). No energy required.

Osmosis: Diffusion of water across a semipermeable membrane — from low solute concentration (high water concentration) to high solute concentration. Water moves toward where there is more dissolved material.

Human Body Systems

Circulatory: Heart pumps blood through arteries (away from heart) and veins (toward heart). Left ventricle → aorta → body. Right ventricle → pulmonary artery → lungs. Capillaries are tiny vessels where gas/nutrient exchange occurs.

Respiratory: Nose → trachea → bronchi → bronchioles → alveoli (gas exchange: O₂ in, CO₂ out). The diaphragm contracts (flattens) to inhale.

Digestive: Mouth → esophagus → stomach (acid + enzymes) → small intestine (most absorption) → large intestine (water reabsorption). Enzymes are proteins that accelerate chemical reactions. Pancreas secretes digestive enzymes.

Nervous: Brain + spinal cord = CNS. All other nerves = PNS. The medulla oblongata controls involuntary functions: breathing, heart rate, blood pressure. Neurons transmit electrical signals.

Endocrine: Glands secrete hormones into the bloodstream. - Pituitary: "master gland" — controls other glands - Thyroid: metabolic rate - Adrenal cortex: cortisol (stress response, raises blood glucose) - Pancreas: insulin (lowers blood glucose), glucagon (raises blood glucose)

Muscular: Skeletal (voluntary), smooth (involuntary, in organs), cardiac (involuntary, only in heart). Tendons connect muscle to bone. Ligaments connect bone to bone.

Immune: White blood cells fight pathogens. Antibodies recognize specific antigens.

Excretory: Kidneys filter blood and produce urine; also regulate blood pH by excreting H⁺ ions and retaining bicarbonate (HCO₃⁻) during acidosis.

Integumentary: Skin (body's largest organ), hair, nails. Regulates temperature, prevents water loss, blocks pathogens. Contains exocrine glands (sweat, sebaceous).

Taxonomy (Classification of Life)

Broadest → most specific: Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species

Mnemonic: Dear King Philip Came Over For Good Spaghetti

Modern domains: Bacteria, Archaea, Eukarya

Classic kingdoms: Animalia, Plantae, Fungi, Protista, Monera

Binomial nomenclature: Two-part Latin name — Genus species (italicized; genus capitalized). Example: Homo sapiens.

Ecology

Food chain: Producer → Primary consumer → Secondary consumer → Tertiary consumer → Decomposer

Energy transfer: Only ~10% of energy passes from one trophic level to the next; ~90% is lost as heat.

Symbiosis: - Mutualism: Both benefit (bees + flowers) - Commensalism: One benefits, other unaffected (barnacles on whales) - Parasitism: One benefits, other harmed (tapeworm in host)

Keystone predator: A species whose removal causes dramatic ecosystem collapse — prey overpopulate, vegetation is decimated, cascading extinctions follow.

Biomes: Large geographic regions with characteristic climate: tropical rainforest, temperate forest, grassland, desert, tundra, taiga, aquatic.

Atomic Structure and the Periodic Table

Atomic number = number of protons (defines the element). Mass number = protons + neutrons. Isotopes = same element (same protons), different neutrons → same chemical properties, different mass.

Periodic table: - Periods (rows): same number of electron shells. - Groups (columns): same number of valence electrons → similar chemical properties. - Noble gases (Group 18, far right): full valence shells → very unreactive. - Metals (left) → metalloids (diagonal) → nonmetals (right).

Chemical Bonding

Ionic bond: One atom transfers electrons to another. Donor becomes cation (+); receiver becomes anion (−). Forms salts (e.g., NaCl).

Covalent bond: Atoms share electrons. Nonpolar = equal sharing (same element, e.g., O₂). Polar = unequal sharing (e.g., H₂O — oxygen pulls electrons more).

Compound: Two or more different elements bonded together.

Reactions: - Exothermic: Releases heat (combustion, rusting). Products have less energy than reactants. - Endothermic: Absorbs heat (photosynthesis, dissolving ammonium nitrate). Products have more energy.

Acids, Bases, and pH

pH scale: 0–14. Measures concentration of H⁺ ions in a solution. Logarithmic — each unit = 10× difference.

pH < 7 = acid (more H⁺ ions; examples: lemon juice pH 2, vinegar pH 3)
pH = 7 = neutral (pure water)
pH > 7 = base/alkaline (fewer H⁺ ions; examples: baking soda pH 9, bleach pH 12)

Neutralization: Acid + Base → Salt + Water

States of Matter and Phase Changes

Change	Direction	Heat
Melting	Solid → Liquid	Absorbs
Vaporization	Liquid → Gas	Absorbs
Condensation	Gas → Liquid	Releases
Freezing	Liquid → Solid	Releases
Sublimation	Solid → Gas	Absorbs
Deposition	Gas → Solid	Releases

Sublimation skips the liquid phase entirely. Examples: dry ice (CO₂), iodine crystals.

At equal pressure: cold air is denser and occupies less volume than warm air (Charles's Law).

Waves, Sound, and Light

Wave formula: v = f × λ (speed = frequency × wavelength) - Frequency (f): cycles per second, in Hz. - Wavelength (λ): distance between successive crests. - Amplitude: wave height; related to energy and intensity.

Sound: Longitudinal (compression) wave. Travels through matter; cannot travel through a vacuum. Speed in air ≈ 340 m/s.

Light: Transverse electromagnetic wave. Speed ≈ 3 × 10⁸ m/s in vacuum. Can travel through a vacuum.

Visible spectrum (low → high frequency): Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROY G BIV). Red has the lowest frequency and longest wavelength; violet has the highest frequency.

Full EM spectrum (low → high frequency): Radio → Microwave → Infrared → Visible → Ultraviolet → X-ray → Gamma ray.

Earth and Space Science

Rock types: - Igneous: Formed from cooling magma (underground = intrusive, e.g., granite) or lava (surface = extrusive, e.g., basalt, obsidian). - Sedimentary: Compressed layers of sediment. Contains fossils. Examples: sandstone, limestone, shale. - Metamorphic: Existing rock changed by heat and/or pressure. Examples: marble (from limestone), quartzite (from sandstone).

Earth's layers (outside → in): Crust → Mantle → Outer core (liquid iron-nickel) → Inner core (solid iron-nickel). Density and temperature increase toward the center.

Water cycle: Evaporation → Condensation (clouds) → Precipitation → Runoff/collection → repeat.

Atmosphere layers (lowest → highest): Troposphere (weather) → Stratosphere (ozone layer) → Mesosphere → Thermosphere → Exosphere.

Planets in order from sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. ("My Very Educated Mother Just Served Us Nachos")

Moon's gravity has the most influence on oceanic tides (though the sun also contributes).

Newton's Laws of Motion

First Law (Inertia): An object at rest stays at rest; an object in motion continues at constant velocity — unless acted on by a net external force. More mass = more inertia.

Second Law: F = ma (Net force = mass × acceleration). Larger force → more acceleration. More mass → less acceleration for the same force. Measured in Newtons (N).

Third Law: For every action there is an equal and opposite reaction. Forces always occur in pairs, acting on different objects.

Weight vs. Mass: Mass = amount of matter (kg). Weight = gravitational force on that mass (N). W = mg, where g ≈ 9.8 m/s².

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