Ecosystems and Origins of Genetic Variation

Vocabulary flashcards reviewing core definitions and concepts from Edexcel (B) Biology A-level Ecosystems and Origins of Genetic Variation.

Ecosystem

A life-supporting environment that includes all organisms living in a particular area (a community) alongside all non-living elements of that environment.

Trophic Level

An organism's position in a food chain or web that describes its feeding relationships with other organisms.

Net Primary Productivity (NPP)

The rate at which energy is transferred into the organic molecules that make up new plant biomass, calculated as $\text{NPP} = \text{GPP} - R$.

Gross Primary Productivity (GPP)

The total energy transferred to primary consumers.

Line Transect

A sampling method where a line is placed across a habitat and species in contact with the line are recorded.

Quadrat

A square frame of a given size, randomly placed in a sampling area to identify, count, or estimate percentage cover of species.

Belt Transect

A sampling method that combines a line transect and a quadrat.

Spearman's Rank Correlation Coefficient

A statistical technique used to measure the correlation between two variables, where answers closer to $1$ indicate linear positive correlation and answers closer to $-1$ indicate linear negative correlation.

Student's T-Test

A statistical test used to determine if the means of two sets of data are significantly different from one another.

Succession

The colonisation of an area by organisms and the gradual replacement of those organisms by other, more varied and productive species.

Primary Succession

Colonisation by communities of organisms in an area previously devoid of life, such as bare rock surface formed after a volcanic eruption.

Secondary Succession

Colonisation occurring on existing soil that is clear of vegetation, such as after a forest fire.

Pioneer Species

Organisms adapted to survive in harsh conditions, such as lichens, that first colonise an area, penetrate rock surfaces, and contribute to soil formation.

Humus

The organic component of soil formed by the decomposition of dead organisms by microorganisms.

Climax Community

The most productive, self-sustaining, and stable community of organisms that an environment can support.

Plagioclimax Community

A climax community formed when human intervention, such as grazing, alters the natural succession.

Climatic Climax Community

A discredited theoretical concept proposing that a given climate could support only one specific climax community.

Edaphic Factors

Abiotic factors relating to the structure and properties of soil, such as sandy soil, clay, or loam.

Interspecific Competition

Competition between individuals of different species.

Intraspecific Competition

Competition between individuals of the same species.

Global Warming

A gradual increase in the average temperature of the Earth's atmosphere and surface, which is believed to lead to permanent climate change.

Dendrochronology

The study of tree rings, where ring size affected by temperature is analyzed to make predictions and models of climate change.

Greenhouse Effect

The process by which infrared radiation from the Sun is trapped by gases such as carbon dioxide and methane, increasing Earth's atmospheric and surface temperature.

CITES

Convention on International Trade in Endangered Species of Wild Fauna and Flora; an international agreement regulating trade in living organisms and their products depending on threat level.

Conservation

Management aimed at maintaining or increasing biodiversity within a habitat by allowing sustainable use of natural resources.

Preservation

Management aimed at maintaining biodiversity levels and keeping habitats intact by minimising human activities.

Meiosis

A reduction division that produces haploid gametes containing half the number of chromosomes of normal somatic body cells.

Allele

An alternative form of a gene.

Phenotype

The observable characteristics of an organism.

Genotype

The alleles present within the cells of an organism.

Dominant Allele

An allele that is always expressed in the phenotype, even if only one copy is present.

Recessive Allele

An allele that is only expressed in the phenotype if two copies are present (homozygous recessive).

Homozygous

Possessing two identical alleles of a gene.

Heterozygous

Possessing two different alleles of a gene.

Codominance

A condition where both alleles contribute to the phenotype without mixing, such as blood type.

Multiple Alleles

The presence of more than two possible versions of an allele for a gene.

Chi-Squared Test

A statistical test used on discontinuous variation data with a sample size greater than $20$ to establish whether the difference between observed and expected results is significant.

Null Hypothesis

The statistical assumption that there is no significant difference between observed and expected results.

Autosomal Gene Linkage

Phenomenon where alleles located on the same non-sex chromosome are inherited together as if they were the same gene.

Sex-Linked Genes

Genes located on the X chromosome, causing associated traits or genetic disorders to be more common in males.

Stabilising Selection

Natural selection that selects against extreme phenotypes, reducing variation and conserving existing phenotypes.

Disruptive Selection

Natural selection that selects for extreme phenotypes, increasing the diversity of a population in diverse conditions.

Directional Selection

Classic natural selection showing a shift from one phenotype to another that is more advantageous in the environment.

Population Bottleneck

A catastrophic event or series of events that dramatically reduces population size by at least $50\%$ and severely decreases the gene pool.

Founder Effect

The loss of genetic variation occurring when a small group of individuals becomes isolated to form a new population with unrepresentative allele frequencies.

Genetic Drift

Random changes in the gene pool of a population occurring by chance rather than selection pressure.

Hardy-Weinberg Equation

Mathematical equations ($p + q = 1.0$ and $p^2 + 2pq + q^2 = 1$) used to estimate allele frequencies in a population in genetic equilibrium.