Earth Science - Year 9 - Term 4 2025

This is all from the knowledge organiser :)

What is an ecosystem?

A self-sustaining unit consisting of the interactions between species in a community and their environment.

biodiversity

The variety of all life on Earth, including plants, animals, microorganisms, and the ecosystems they form (e.g. forests, coral reefs).

What is species richness?

The number of species present in an ecosystem.

What is relative species abundance?

The number of individuals present for each species in an ecosystem.

What is species diversity?

The number and relative abundance of different species in a given area, driven by mutations that create genetic variation.

What is a gene pool?

The range of genes and all their alleles present in a population.

What is genetic diversity?

All the genetically determined characteristics of a species. High diversity allows survival in changing environments; low diversity increases extinction risk.

What things do not align with the biological species concept?

Hybrids, fossils, asexual reproduction, and ring species.

fitness

The capacity of an individual to survive and produce viable offspring; higher means more adaptive evolution over time.

What is natural selection?

The process where individuals with favourable traits are more likely to survive and reproduce, passing on those traits.

What causes variation within populations?

Genetic mutations and diversity in alleles, giving individuals different phenotypes.

Why is there a struggle for existence?

More offspring are born than can survive, so individuals compete for limited resources.

What is a selection pressure?

A factor influencing survival within a population. Abiotic examples: temperature, light, water, soil pH. Biotic examples: predators, competition, disease, food availability.

What is genetic drift?

A random change in the gene pool, often in small populations. It can increase or decrease allele frequencies by chance.

What is the bottleneck effect?

When a catastrophic event drastically reduces a population, decreasing genetic diversity.

What is the founder effect?

A type of genetic drift where a small group becomes isolated and carries only some of the original alleles.

What is gene flow?

The transfer of alleles between populations due to migration (immigration and emigration).

What evidence did Darwin find in the Galápagos finches?

Differences in beak shapes showed adaptive radiation and common ancestry — evidence of microevolution.

How does antibiotic overuse demonstrate natural selection?

Bacteria with resistance genes survive antibiotic use, reproduce, and spread resistance through future generations.

What is the carbon cycle?

The process that regulates atmospheric CO₂ levels, helping stabilize Earth's temperature.

What is the nitrogen cycle?

The biogeochemical process moving nitrogen between the atmosphere, soil, water, and living organisms.

What is a carbon sink?

A natural or artificial system that absorbs more CO₂ than it releases (e.g. forests, oceans, soil).

carbon sequestration

Capturing and storing atmospheric CO₂ to reduce climate change — can be natural or technological.

What are the main atmospheric gases and their percentages?

Nitrogen 78%, Oxygen 21%, Other gases 1%.

What are the main greenhouse gases?

CO₂, CH₄, O₃, N₂O, water vapour, CFCs, HFCs, and PFCs.

What is the greenhouse effect?

A natural process where greenhouse gases trap heat from the sun, keeping Earth warm enough for life.

What is the enhanced greenhouse effect?

When human activities increase greenhouse gas levels, trapping excess heat and driving climate change.

What are some natural contributors to the greenhouse effect?

Volcanic eruptions, bushfires, cows (methane), and decomposition of plants and animals.

What is climate change?

Long-term changes in global or regional climate patterns, mostly due to increased CO₂ from burning fossil fuels.

What is global warming?

The rise in average global temperatures, causing melting ice caps, rising sea levels, and extreme weather.

What are indicators of climate change?

Rising temperatures, extreme weather, warmer sea surfaces, melting polar caps, and rising sea levels.

What does “anthropogenic” mean?

Caused by human activity — e.g., pollution, deforestation, and carbon emissions.

What is ocean acidification?

When CO₂ from the atmosphere dissolves into seawater, forming carbonic acid (CO₂ + H₂O → H₂CO₃) and lowering ocean pH.

How does ocean acidification affect coral?

It reduces carbonate ion levels, making it harder for corals to form calcium carbonate skeletons, threatening reef ecosystems.

What is thermohaline circulation?

A global ocean current driven by temperature and salinity differences that moves heat, nutrients, and gases around the oceans.

What are the main steps of thermohaline circulation?

1. Cooling at poles → water sinks. 2. Ice formation increases salinity. 3. Dense water flows along ocean floor. 4. Warm water rises elsewhere → completes the loop.

What is Aboriginal fire-stick farming?

A traditional practice of controlled burning used by First Nations Australians to care for Country, promote new growth, and prevent destructive wildfires.

How does Aboriginal fire-stick farming differ from industrial burning?

It uses smaller, cooler, controlled fires that maintain ecosystem health and reduce carbon emissions.

What is the Lincoln Index?

A method to estimate population size using capture-mark-recapture: N = (M × n) ÷ m.

What does each variable mean in the Lincoln Index formula?

M = number marked in first capture, n = total captured in second sample, m = number recaptured (marked individuals).

Genotype

The complete set of inherited genetic information; the specific combination of alleles for a trait.

Phenotype

The observable characteristics of an organism, produced by the interaction of genotype and environment.

Allele

One of two or more alternative forms of a gene, found at the same location on a chromosome.

Variation

Differences between individuals of the same species caused by genetic factors or environmental influences.

When is dominant trait expressed?

When at least one of that allele is present.

When is a recessive trait expressed?

Only when two recessive alleles are inherited (one from each parent).

Microevolution

A change in allele frequency within a population over time.

Speciation

The formation of new species from an ancestral species.

How does speciation occour?

When populations become reproductively isolated and can no longer interbreed.