Grade 12 Life Sciences IEB Comprehensive Study Guide

A comprehensive set of vocabulary flashcards covering the complete IEB Grade 12 Life Sciences syllabus, including population ecology, endocrine system, plant and animal reproduction, genetics, meiosis, molecular biology, evolutionary biology, and hominid studies.

Individual

A single, separate organism (animal or plant) capable of independent existence.

Population

A group of individuals belonging to the same species that live in the same area at the same time and are capable of interbreeding.

Community

A group of different populations that live together and interact in a defined area.

Ecosystem

All the organisms that live in an area and interact with each other and with their physical (abiotic) environment.

Environmental Resistance

The total collective sum of limiting factors that stop a population from reproducing at its maximum theoretical rate.

Carrying Capacity

The maximum population size of a species that a specific environment can sustainably support.

Petersen Index

A mark-recapture formula, expressed as $P = \frac{M \times C}{R}$, used to estimate total population size from marked ($M$), captured ($C$), and recaptured ($R$) individuals.

Random Sampling

A sampling method in which every individual in a population has an equal chance of being selected entirely by chance, yielding an unbiased and representative sample.

Predator-Prey Relationship

A biological interaction between two organisms of unlike species in which one organism acts as predator that captures and feeds on the other organism serving as prey, regulating both populations through negative feedback.

Food Web

An interconnected set of all the food chains within an ecosystem representing trophic links between producers, consumers, and predators.

Trophic Cascade

An ecological phenomenon triggered by the addition or removal of top predators, which propagates down through successive trophic levels to alter herbivore density and plant biomass.

Interspecific Competition

Competition occurring between individuals of different species that occupy very similar ecological niches and compete for the same limited resources.

Intraspecific Competition

Competition occurring between individuals of the same species for identical resources, space, shelter, or access to mates.

Ecological Niche

The specific set of all physical resources and biological conditions necessary for the survival, reproduction, and functioning of a species.

Resource Partitioning

An evolutionary process where coexisting species with similar requirements develop specialised adaptations to utilise resources differently, reducing competition and facilitating competitive co-existence.

Stratification

The vertical layering of vegetation in a forest community into distinct structural levels (such as upper canopy, understory, and ground cover) to partition light intensity.

Primary Succession

The predictable pattern of gradual ecological change occurring over time in a newly formed habitat completely devoid of any pre-existing biotic community or soil.

Secondary Succession

Ecological succession that follows the severe disruption of a pre-existing community in an area where soil and organic substrate already exist.

Climax Community

The final, semi-stable endpoint stage of ecological succession where species composition stops changing significantly over time.

Dilution Effect

A predator avoidance phenomenon where individual prey animals gain greater chances of survival simply by being part of a larger group or herd.

Confusion and Distraction Effect

A herd defence strategy where animals scatter simultaneously in multiple directions when attacked, impairing a predator's visual tracking and ability to single out a victim.

Hormone

A chemical messenger secreted by an endocrine gland directly into the bloodstream and carried to specific target organs to regulate metabolic reactions.

Hypothyroidism

A disorder caused by underproduction of thyroxin resulting in a low metabolic rate, leading to myxoedema in adults and cretinism in children.

Hyperthyroidism

A disorder caused by excessive production of thyroxin that leads to a high metabolic rate, elevated body temperature, muscular tremors, and exophthalmic goitre.

Acromegaly

An endocrine disorder in adults caused by the hypersecretion of growth hormone (GH), characterised by enlargement of facial bones, hands, feet, and tongue.

Homeostasis

The physiological process of maintaining a constant and stable internal environment (tissue fluid and blood) despite continuous changes in the external environment.

Negative Feedback System

A self-regulating biological control mechanism whereby a deviation of a factor from its optimal set point triggers a corrective response in the opposite direction to restore the norm.

Pollination

The transfer of pollen grains from an anther to a receptive stigma of a flower.

Fertilisation

The fusion of the haploid ($n$) male gamete nucleus with a haploid ($n$) female gamete nucleus to form a diploid ($2n$) zygote.

Micro-propagation

A tissue culture technique used to rapidly clone large numbers of identical plants from small excised tissue pieces in sterile nutrient media under controlled hormone levels.

Ovipary

A reproductive strategy wherein eggs develop and hatch outside the maternal parent's body, relying exclusively on egg yolk for nutrition.

Ovovivipary

A reproductive strategy wherein fertilised eggs are retained inside the female body and nourished entirely by yolk until hatching, resulting in live birth.

Vivipary

A reproductive strategy in which fertilised eggs lack a shell, develop internally into an embryo and foetus, receive continuous maternal nutrition via a placenta, and are born alive.

Amniotic Egg

An evolutionary terrestrial adaptation featuring internal fluid-filled extra-embryonic membranes (amnion, chorion, allantois, and yolk sac) that enable embryos to develop out of water.

Spermatogenesis

The formation of haploid ($n$) sperm cells from diploid ($2n$) germinal epithelial cells within the seminiferous tubules of the testes through meiosis.

Oogenesis

The process initiated by follicle stimulating hormone (FSH) in which immature diploid cells within primary follicles of the ovary undergo meiosis to form mature haploid ($n$) egg cells.

Acrosome

A cap-like structure at the anterior tip of the sperm head containing hydrolytic enzymes used to digest outer protective layers of the ovum during fertilisation.

Corpus Luteum

A temporary glandular endocrine structure formed from the ruptured Graafian follicle following ovulation that secretes high amounts of progesterone and oestrogen.

Transcription

The nuclear process during protein synthesis where the coded nucleotide sequence of DNA is copied into a complementary single strand of messenger RNA (mRNA) by RNA polymerase.

Translation

The cytoplasmic process at ribosomes where transfer RNA (tRNA) anticodons bind to matching mRNA codons, assembling specific amino acids via peptide bonds into a polypeptide chain.

Point Mutation

A genetic mutation caused by the substitution, insertion, or deletion of a single nucleotide base pair within a DNA or RNA sequence.

Polymerase Chain Reaction (PCR)

An in vitro laboratory technique that amplifies a specific segment of DNA by producing millions of copies of designated sequences using DNA polymerase and nucleotide primers.

Crossing Over

The exchange of genetic material between non-sister chromatids of homologous chromosome pairs at chiasmata during late prophase I of meiosis, creating recombinant chromatids.

Chromosome Non-disjunction

An abnormality during meiosis wherein homologous chromosomes or sister chromatids fail to separate correctly, producing gametes with missing or extra chromosomes (aneuploidy).

Karyotype

A standard photographic or computerised image arrangement of all metaphase chromosomes from a single cell, organized by size, shape, and band number to detect genetic abnormalities.

Allele

One of two or more alternative functional forms of a gene located at the exact same locus on homologous chromosomes.

Gene Pool

The total set of all genetic alleles present across all individuals in an interbreeding population of sexually reproducing organisms.

Polygenic Inheritance

A pattern of inheritance where a single phenotypic characteristic (such as height or skin colour) is controlled by the additive effects of two or more distinct genes, resulting in continuous variation.

Recombinant DNA Technology

The technique of combining DNA sequences from different organisms or sources by cutting with restriction enzymes and joining with DNA ligase inside a vector.

Somatic Cell Nuclear Transfer (SCNT)

A cloning procedure involving the insertion of a diploid nucleus from an adult somatic donor cell into an enucleated ovum, followed by electrical stimulation to trigger embryonic development.

Macroevolution

Large-scale evolutionary patterns and changes occurring at or above the species level over long periods of geological time, including cladogenesis, adaptive radiation, and mass extinctions.

Punctuated Equilibrium

A theory of evolutionary rate proposed by Stephen Jay Gould asserting that species experience long geological periods of morphological stasis punctuated by brief episodes of rapid speciation.

Gradualism

The Darwinian concept stating that evolutionary changes in species accumulate slowly, continuously, and incrementally over long periods of geological time.

Natural Selection

The mechanism of evolution wherein environmental selective pressures favor the survival and reproductive success of individuals possessing heritable variations best suited to their habitat.

Founder Effect

A drastic reduction in genetic diversity that occurs when a new isolated colony or population is established by a very small number of individuals originating from a larger parent population.

Convergent Evolution

The independent evolution of similar anatomical or functional traits (analogous structures) in unrelated species exposed to similar selective environmental pressures.

Divergent Evolution

The evolutionary pattern in which two or more related species develop different traits and structures (homologous structures) from a common ancestral structure.

Allopatric Speciation

The evolutionary formation of new species that occurs when a parent population becomes physically separated into geographically isolated subpopulations preventing gene flow.

Sympatric Speciation

Speciation that occurs within a single ancestral population without any geographic isolation or physical barriers, often mediated by polyploidy, hybridisation, or trophic specialisation.

Bipedalism

The habitual ability to walk upright on two lower limbs, representing the key evolutionary adaptation distinguishing early hominins from African apes.

'Out of Africa' Hypothesis

The dominant scientific model proposing that anatomically modern humans ($Homo\ sapiens$) originated in Africa around $200\,000$ to $150\,000$ years ago before migrating to populate the rest of the world.