Biology Grade 12 Review Flashcards

A comprehensive set of vocabulary flashcards covering Unit 1 (Biochemistry), Unit 2 (Metabolism), Unit 3 (Genetics), and Unit 4 (Homeostasis) for Grade 12 Biology.

Isotopes

Atoms with the same amount of protons but different numbers of neutrons, resulting in identical chemical properties but different atomic masses.

Radioactive Isotopes

Unstable isotopes where the nucleus spontaneously decays over time, used in applications like radioactive dating and medical imaging.

Radioactive tracers

Radioisotopes injected into an organism to follow a chemical pathway, such as using Iodine-131 to locate cancerous cells in the thyroid gland.

The Octet Rule

The principle that atoms gain, lose, or share electrons to achieve a stable valence shell of $8$ electrons.

Ionic Bonds

Chemical bonds formed by the complete transfer of electrons, creating opposite charges that attract each other.

Covalent Bonds

Bonds formed by the sharing of valence electrons between atoms.

Electronegativity (EN)

A measure of the strength of an atom's pull on shared electrons, measured on the Pauling Scale from $0.7$ to $4.0$.

Non-Polar Covalent Bond

A bond where atoms have equal or similar electronegativity, resulting in electrons being shared evenly with no partial charges.

Polar Covalent Bond

A bond where atoms have different electronegativity, causing the stronger atom to gain a partial negative charge and the other a partial positive charge.

Intramolecular Forces

Extremely strong forces within a molecule that hold its own atoms together, including ionic and covalent bonds.

Intermolecular Forces

Weaker attractions between separate molecules that determine physical properties like boiling point and solubility.

Ion-dipole

An attraction between a fully charged ion and a permanent molecular dipole.

Hydrogen bonds

A strong permanent dipole attraction that occurs only when hydrogen is covalently bonded to oxygen ($O$), nitrogen ($N$), or fluorine ($F$).

Dipole-dipole

General attractions between any two permanently polar molecules.

London dispersion forces

A temporary dipole caused by constant electron motion; it is the only force holding non-polar molecules together.

Cohesion

The property of water molecules sticking to each other, which creates surface tension.

Adhesion

The property of water molecules sticking to other polar surfaces, causing capillary action in plant xylem.

High thermal capacity

The ability of water to absorb vast amounts of heat before changing temperature, aiding in thermoregulation via evaporative cooling.

Hydrophilic

\"Water loving\" polar molecules that readily dissolve in water.

Hydrophobic

\"Water fearing\" non-polar molecules that clump together and exclude water.

Hydroxyl Group ($-OH$)

A highly polar functional group that forms hydrogen bonds and renders molecules hydrophilic; found in alcohols and carbohydrates.

Carboxyl Group ($-COOH$)

A highly polar and acidic functional group that drops its protons in solution to become $COO^-$; found in amino acids and fatty acids.

Amino Group ($-NH_2$)

A polar and basic functional group that accepts $H^+$ protons from solutions to become $NH_3^+$; found in amino acids.

Phosphate Group ($-PO_4$)

A heavily charged and ionic functional group that is extremely hydrophilic; found in ATP, DNA, and RNA.

Sulfhydryl Group ($-SH$)

A polar cluster that forms strong covalent disulfide bridges to lock protein folding shapes in place.

Condensation (dehydration synthesis)

An anabolic reaction where two functional groups are joined by removing an $H$ from one and an $-OH$ from another, releasing $H_2O$.

Hydrolysis

A catabolic reaction where a large polymer is split into smaller monomers by adding $H_2O$ molecules across covalent bonds.

Neutralization Reaction

A reaction where an acid and a base react to produce water and an ionic salt.

Buffers

Chemical pairs consisting of a weak acid and its conjugate base that work together to maintain pH homeostasis in living systems.

Oxidation

The process involving the loss of electrons, the loss of hydrogen, or the gain of oxygen.

Reduction

The process involving the gain of electrons, the gain of hydrogen, or the loss of oxygen.

NAD+ (Nicotinamide Adenine Dinucleotide)

An electron carrier that acts as a \"bus\"; it becomes $NADH$ when reduced and cycles back to $NAD^+$ when oxidized.

Monosaccharides

The simplest sugars containing a single chain of carbon atoms with hydroxyl and carbonyl groups.

Oligiosaccharides

Carbohydrates containing two or three monosaccharides attached by glycosidic linkages.

Polysaccharides

Sugar polymers with several hundred to thousands of monosaccharide subunits, such as starch, glycogen, cellulose, or chitin.

Glycogen

A highly branched storage polysaccharide made of glucose, stored in the muscle and liver of animals.

Cellulose

An unbranched structural polysaccharide of glucose found in plant cell walls; difficult for humans to digest and serves as dietary fiber.

Chitin

A structural polysaccharide found in the exoskeletons of arthropods and used in surgical thread.

Saturated Fats

Fats with no double bonds and the maximum number of hydrogens; typically solid at room temperature.

Unsaturated Fats

Fats containing one or more double bonds that cause a bend in the structure; typically liquid at room temperature.

Phospholipids

Molecules with a hydrophilic head and two hydrophobic tails that form the lipid bilayer of cell membranes.

Steroids

Lipids consisting of four fused carbon rings, including cholesterol, testosterone, and estrogen.

Pyrimidines

Single-ring nitrogenous bases including Cytosine ($C$), Thymine ($T$), and Uracil ($U$).

Purines

Double-ring nitrogenous bases including Adenine ($A$) and Guanine ($G$).

Primary Structure (Protein)

The unique linear sequence of amino acids in a polypeptide chain determined by genetic information.

Secondary Structure (Protein)

The folding or coiling of a polypeptide, including $\alpha$-helices and $\beta$-pleated sheets, held by hydrogen bonds.

Tertiary Structure (Protein)

The overall three-dimensional shape of a single polypeptide chain.

Quaternary Structure (Protein)

The overall protein structure resulting from the assembly of two or more polypeptide subunits.

Denaturation

The process where a protein unravels and loses its native shape due to environmental changes, rendering it nonfunctional.

Fluid Mosaic Model

A model describing the cell membrane as a fluid structure with a variety of proteins embedded in or attached to a bilayer of phospholipids.

Endergonic (endothermic) reactions

Reactions that absorb more energy than they release, where $\Delta G$ is positive.

Exergonic (exothermic) reaction

Reactions that release more energy than they absorb, where $\Delta G$ is negative.

Enzyme

A functional globular protein that acts as a catalyst by lowering the activation energy of a specific chemical reaction.

Standard ATP Hydrolysis Energy

The amount of energy provided when ATP is hydrolyzed, valued at $31\,kJ/mol$.

Substrate

The specific reactant molecule upon which an enzyme acts.

Active Site

The specific region on an enzyme where the substrate binds.

Allosteric Site

A binding site on an enzyme other than the active site used by activators or inhibitors to alter the enzyme's shape.

Competitive Inhibition

Inhibition where a molecule binds to the active site, physically blocking the substrate.

Non-competitive Inhibition

Inhibition where a molecule binds to an allosteric site, changing the active site's shape so the substrate cannot fit.

Aerobic Cellular Respiration

The process of breaking down glucose in the presence of oxygen to produce $CO_2$, $H_2O$, and a net yield of approximately $38\,ATP$.

Glycolysis

The first stage of cellular respiration occurring in the cytoplasm, where glucose is broken down into two pyruvate molecules.

Krebs Cycle (Citric Acid Cycle)

The third stage of cellular respiration in the mitochondrial matrix that releases $CO_2$ and generates high-energy $NADH$, $FADH_2$, and $ATP$.

Chemiosmosis

The process in which an electrochemical proton gradient is used to create $ATP$ via the enzyme ATP synthase.

Alcoholic Fermentation

An anaerobic process in plants and yeast that converts glucose into ethanol, $CO_2$, and $2\,ATP$.

Lactic Acid Fermentation

An anaerobic process in animals and some bacteria that converts glucose into lactic acid and $2\,ATP$, causing muscle fatigue in humans.

Photosynthesis

An anabolic process where autotrophs convert solar energy into chemical energy stored in glucose; takes place in the chloroplasts.

Thylakoid

The membrane-bound structures within chloroplasts where light-dependent reactions of photosynthesis occur.

Stroma

The fluid-filled space within the chloroplast where the Calvin Cycle (light-independent reactions) takes place.

Semiconservative Replication

The mechanism of DNA replication where each new double helix consists of one original template strand and one newly synthesized strand.

Helicase

The enzyme responsible for unzipping DNA by breaking the hydrogen bonds between nitrogenous bases.

SSB Proteins (Single-Strand Binding)

Proteins that stabilize unzipped DNA strands to prevent them from annealing back together.

Topoisomerase

An enzyme that binds ahead of the replication fork to relieve strain and prevent DNA supercoiling.

Primase

The enzyme that synthesizes a short RNA primer to provide a starting point for DNA Polymerase.

DNA Polymerase

The enzyme that builds the new DNA strand in a $5'$ to $3'$ direction and proofreads for mutations.

Ligase

The enzyme that seals the sugar-phosphate gaps between Okazaki fragments on the lagging strand.

Okazaki Fragments

The short, disjointed chunks of DNA synthesized discontinuously on the lagging strand.

Silent Mutation

A DNA sequence change that does not alter the amino acid produced or the protein's function.

Missense Mutation

A mutation that changes one amino acid in a protein, which may or may not affect its function.

Nonsense Mutation

A mutation that changes an amino acid codon into a premature stop codon, resulting in a nonfunctional protein.

Frameshift Mutation

An insertion or deletion of nucleotides that shifts the reading frame and alters the entire downstream protein sequence.

Transcription

The process where RNA Polymerase reads a DNA template to build a complementary mRNA transcript in the nucleus.

TATA Box

An Adenine and Thymine-rich promoter region where RNA Polymerase begins the initiation of transcription.

Introns

Non-coding junk segments of pre-mRNA that are removed during splicing.

Exons

The coding segments of mRNA that are joined together to form the final transcript.

Translation

The process where a ribosome decodes mRNA to link amino acids into a polypeptide chain in the cytoplasm.

Codon

A consecutive, non-overlapping group of three nucleotides in mRNA that codes for a specific amino acid.

Anticodon

A three-base sequence on tRNA that is complementary to an mRNA codon.

Stop Codons

The mRNA sequences $UAA$, $UAG$, or $UGA$ that signal the end of translation and lead to the binding of a Release Factor.

Homeostasis

The maintenance of a steady internal state despite changes in the external environment.

Negative Feedback System

A feedback loop that reverses the direction of an initial change to bring a variable back to balance.

Positive Feedback System

A feedback loop that strengthens and amplifies an initial change, often for explosive physiological events.

Steroid Hormones

Lipid-soluble hormones derived from cholesterol that can diffuse directly through cell membranes.

Water-Soluble Hormones

Protein-based hormones that cannot cross the lipid membrane and must trigger secondary messenger cascades like $cAMP$.

Tropic Hormones

Hormones that target other endocrine glands to stimulate the release of further hormones.

ADH (Antidiuretic Hormone)

A hormone stored in the posterior pituitary that increases water reabsorption in the kidneys to raise blood pressure and decrease osmolarity.

Thyroid-Stimulating Hormone (TSH)

A tropic hormone from the anterior pituitary that prompts the thyroid gland to release $T_4$ for metabolism.

Nephron

The functional unit of the kidney responsible for filtering blood and forming urine.

Glomerulus

A knot of capillaries in the nephron where high pressure forces liquid and small solutes into Bowman's Capsule.

Threshold Level

The maximum concentration of a solute that the kidney tubules can actively pump back into the bloodstream before it is lost in urine.

Bowman's Capsule

The catching cup of the nephron that collects the watery filtrate from the glomerulus.