Grade 12 AS Level Biology - Comprehensive Vocabulary Flashcards

Flashcards providing definitions of key terms across all units of the Grade 12 AS Level Biology lecture notes.

Binomial System

A two-word Latin naming system introduced by Carolus Linnaeus that assigns living organisms a generic name (genus) and a specific epithet (species).

Homologous Structures

Organs or skeletal elements in different organisms that share a common anatomical plan and evolutionary origin, but are adapted for different functions.

Analogous Structures

Structures in different organisms that perform similar functions but do not share a common evolutionary origin or structural development.

Biological Species Concept

A group of natural populations whose members have the potential to interbreed and produce viable, fertile offspring, but cannot successfully interbreed with members of other species.

Ecological Niche

The functional role and position that an organism plays within its ecosystem, encompassing its habitat, activity patterns, and environmental resource use.

Species Richness

The total number of different biological species present within a specified area or community.

Species Evenness

The relative abundance and distribution of individual organisms belonging to each species in a given area.

Simpson's Index of Diversity

A quantitative measure of biodiversity given by $D = 1 - \frac{\sum n^2}{N^2}$, taking into account both species richness and species evenness.

Lincoln Index

A mathematical formula used in mark-release-recapture sampling to estimate total population size: $N = \frac{n_1 \times n_2}{n_3}$.

Eutrophication

The nutrient enrichment of water bodies leading to rapid algal blooms, reduced light penetration, death of aquatic plants, and severe oxygen depletion by aerobic decomposers.

Bioaccumulation

The gradual accumulation and concentration of non-biodegradable toxic contaminants inside the tissues of an organism over its lifespan.

Magnification

The number of times larger an image appears compared to the real size of the actual object, calculated as $M = \frac{I}{A}$.

Resolution

The minimum distance required between two separate points for them to be distinguished as two distinct structures.

Eyepiece Graticule

A transparent scale placed in a microscope eyepiece containing arbitrary divisions, calibrated against a stage micrometer to measure specimen sizes.

Mitochondrion

A double-membrane bound eukaryotic organelle ($3\,\mu m$ to $10\,\mu m$ in length) that serves as the primary site for aerobic respiration and ATP synthesis.

Rough Endoplasmic Reticulum

A network of membrane-bound flattened sacs (cisternae) covered with $80S$ ribosomes, responsible for folding, modifying, and transporting synthesized proteins.

Golgi Apparatus

A stack of flattened membrane-bound sacs that collects, modifies, processes, and packages proteins into vesicles for secretion or transport.

Lysosome

A single-membrane organelle ($0.1\,\mu m$ to $0.5\,\mu m$) containing hydrolytic digestive enzymes that break down worn-out organelles, cellular waste, or engulfed pathogens.

Tonoplast

The selectively permeable single membrane that surrounds the large permanent central vacuole in mature plant cells.

Plasmodesmata

Microscopic cytoplasmic channels passing through plant cell walls that connect adjacent plant cells and allow symplastic transport and signaling.

Adenosine Triphosphate (ATP)

A phosphorylated nucleotide composed of adenine, ribose, and three phosphate groups that functions as the immediate chemical energy currency in cells.

Fluid Mosaic Model

A model of cell membrane structure describing a fluid bilayer of phospholipid molecules in which protein molecules are laterally mobile in a mosaic pattern.

Phospholipid Bilayer

A double-layered arrangement of phospholipid molecules where hydrophilic phosphate heads face the outer aqueous environments and hydrophobic fatty acid tails face inward.

Facilitated Diffusion

The passive movement of polar or charged molecules down their concentration gradient across a membrane via specialized channel or carrier proteins.

Active Transport

The movement of molecules or ions across a cell membrane against a concentration gradient using carrier proteins and energy derived from ATP hydrolysis.

Plasmolysis

The shrinkage of the protoplast away from the cell wall in a plant cell placed in a solution of lower water potential (hypertonic solution) due to osmotic water loss.

Glycosidic Bond

A covalent bond formed between two monosaccharide units through a condensation reaction involving the elimination of a water molecule ($H_2O$).

Amylose

An unbranched polysaccharide component of starch composed of $\alpha$-glucose monomers linked by $\alpha$-1,4-glycosidic bonds that form a helical structure.

Amylopectin

A branched polysaccharide component of starch composed of $\alpha$-glucose monomers linked by $\alpha$-1,4 and $\alpha$-1,6-glycosidic bonds.

Glycogen

A highly branched storage polysaccharide found in animal and fungal cells, composed of $\alpha$-glucose monomers joined by $\alpha$-1,4 and frequent $\alpha$-1,6-glycosidic bonds.

Cellulose

A structural polysaccharide in plant cell walls made of unbranched chains of $\beta$-glucose monomers joined by $\beta$-1,4-glycosidic bonds with alternating inverted units.

Triglyceride

A lipid macromolecule formed by condensation reactions between one molecule of glycerol and three fatty acid chains, linked by three ester bonds.

Primary Structure of Protein

The linear sequence of amino acids in a polypeptide chain joined together by covalent peptide bonds.

Secondary Structure of Protein

The localized regular coiling or folding of a polypeptide chain into structures like $\alpha$-helices or $\beta$-pleated sheets, held by hydrogen bonds.

Tertiary Structure of Protein

The overall three-dimensional shape of a folded polypeptide chain, stabilized by hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions.

Quaternary Structure of Protein

The three-dimensional arrangement formed by the association of two or more individual polypeptide chains or non-protein prosthetic groups.

Conjugated Protein

A protein molecule that incorporates a non-amino acid chemical group (prosthetic group) as part of its structure, such as the haem group in haemoglobin.

Collagen

An insoluble structural fibrous protein composed of three left-handed helical polypeptide chains wound into a tight triple helix held by hydrogen and covalent cross-links.

Activation Energy

The initial minimum energy input required by reactant molecules to reach a transition state and undergo a chemical reaction.

Induced-Fit Model

A model of enzyme action proposing that the active site undergoes conformational changes as the substrate binds to achieve a precise complementary fit.

Michaelis-Menten Constant ($K_m$)

The substrate concentration at which the rate of an enzyme-catalysed reaction reaches half of its maximum velocity ($\frac{1}{2}V_{max}$), reflecting enzyme affinity.

Competitive Inhibitor

A molecule with a structure similar to the substrate that reversibly binds to the enzyme's active site, increasing $K_m$ without altering $V_{max}$.

Non-Competitive Inhibitor

An inhibitor that binds to an allosteric site on an enzyme, altering the active site shape and decreasing $V_{max}$ without changing $K_m$.

Apoplast Pathway

The non-living pathway of water movement through continuous cell walls and intercellular spaces in plant tissue.

Symplast Pathway

The pathway of water and solute movement through the continuous cytoplasm of plant cells via plasmodesmata.

Casparian Strip

An impermeable band of suberin surrounding endodermal cell walls that blocks the apoplast pathway, forcing water into the symplast pathway.

Transpiration

The evaporation of water from the moist internal surfaces of mesophyll cell walls into air spaces followed by the diffusion of water vapour out through stomata.

Translocation

The energy-requiring mass flow transport of organic assimilates such as sucrose and amino acids through phloem sieve tube elements from source to sink.

Bohr Shift

The shift of the oxygen dissociation curve to the right in the presence of elevated carbon dioxide ($pCO_2$) and decreased pH, reducing haemoglobin's oxygen affinity.

Carbonic Anhydrase

An enzyme in red blood cells that catalyses the reversible reaction between carbon dioxide and water to form carbonic acid ($H_2CO_3$).

Sinoatrial Node (SAN)

A specialized group of myogenic muscle cells in the right atrium wall that initiates waves of electrical excitation, acting as the heart's primary pacemaker.

Monoclonal Antibodies

Identical antibodies produced in large quantities from a single clone of hybridoma cells, all specific to one single antigen epitope.

Hybridoma Cell

A hybrid cell produced by fusing an antibody-secreting plasma cell with a cancerous myeloma cell, capable of continuous division and antibody production.

Active Immunity

Long-term immunity acquired when an individual's own immune system produces specific antibodies and memory cells in response to antigen exposure.

Passive Immunity

Immediate, short-term protection gained by introducing pre-formed antibodies into the body without an active immune response or memory cell production.

Goblet Cells

Specialized columnar epithelial cells found in the respiratory tract that synthesize and secrete mucus to trap inhaled dust and pathogens.

Telomeres

Protective non-coding repetitive DNA sequences located at the ends of eukaryotic chromosomes that prevent the loss of essential coding genes during cell division.

Oncogene

A mutated gene involved in controlling cell division that has the potential to cause cancer by driving continuous, uncontrolled mitosis.

Semi-Conservative Replication

The mechanism of DNA synthesis where each newly formed double-stranded DNA molecule contains one conserved parent strand and one newly built strand.

Codon

A sequence of three adjacent nucleotide bases on mRNA that specifies a particular amino acid or signals a stop during protein translation.

Antibody

A Y-shaped glycoprotein produced by B-plasma cells in response to a foreign antigen, composed of two heavy and two light polypeptide chains linked by disulfide bonds.