Comprehensive Review of Climate, Biomes, Cycles, Evolution, and Phylogeny

Climate

the long-term average weather of a region (temperature, rainfall, humidity, wind) over years to centuries, not just day-to-day weather.

Solar radiation

The equator gets more direct sunlight, making it warmer; poles get angled sunlight, making them colder.

Atmospheric circulation

Warm air rises at the equator → cools → falls as rain → moves away → sinks around 30° latitude → creates hot dry deserts.

Ocean currents

Water redistributes heat globally; warm currents make nearby coasts warmer & wetter, cold currents cool regions.

Topography

Mountains cause rain shadows: one side gets rain, the other becomes dry desert.

Biome

a large, geographically distinct biological community characterized by climate (temperature & precipitation), vegetation type (plants present), and animals adapted to those plant/temperature conditions.

Tropical Rainforest

Location: Near equator (0° latitude); Climate: Hot & very wet year-round; little seasonal change; Vegetation: Dense layered forests with broadleaf evergreen trees; Soils: Nutrient-poor because rainfall washes nutrients away.

Desert

Location: ~30° N & S latitude → where dry air sinks; Climate: Hot days, cold nights; extremely low rainfall; Vegetation: Sparse; cacti & shrubs.

Temperate Forest

Location: Eastern North America, Europe, East Asia; Climate: Moderate rainfall, four seasons; Vegetation: Deciduous trees that lose leaves in winter.

Tundra

Location: High latitudes (near poles) or mountain tops; Climate: Very cold, low precipitation; Soil: Contains permafrost (permanently frozen ground); Vegetation: Low-growing plants (mosses, shrubs).

Adaptations in Tropical Rainforest

Plants have drip-tip leaves to shed excess water; Animals often arboreal (climb trees); many have bright coloration and loud calls.

Adaptations in Desert

Plants store water (succulents), have spines instead of leaves to reduce water loss; Animals are often nocturnal to avoid heat & conserve water.

Adaptations in Temperate Forest

Animals may hibernate or migrate seasonally; Trees drop leaves to avoid water loss when ground freezes.

Adaptations in Tundra

Animals have thick fur/fat; Plants grow close to ground to avoid freezing wind.

Carbon (C)

backbone of all organic molecules — carbohydrates, proteins, lipids, nucleic acids.

Nitrogen (N)

needed for amino acids → proteins and nucleotides → DNA & RNA.

Phosphorus (P)

main part of ATP, phospholipids (cell membranes), and DNA/RNA sugar-phosphate backbone.

Abiotic reservoirs

air, soil, water.

Living organisms

plants, animals, microbes.

Carbon Cycle

The process by which carbon moves through ecosystems, involving key atmospheric form CO₂ gas.

Photosynthesis

The process by which plants, algae, and photosynthetic bacteria convert CO₂ into organic carbon (sugars).

Cellular respiration

The process by which all organisms convert organic carbon back to CO₂, releasing it into the atmosphere.

Carbon Movement Through Food Webs

The process by which carbon is transferred from plants to animals and then to predators, with decomposers releasing CO₂ during decomposition.

Long-Term Carbon Storage

Storage of carbon in oceans, fossil fuels, and sedimentary rocks for millions of years.

Human Impact on Carbon Cycle

Burning fossil fuels releases CO₂ faster than ecosystems can reabsorb, leading to climate change.

Deforestation

The process that reduces photosynthesis, resulting in higher atmospheric CO₂ levels.

Nitrogen Cycle

The process by which nitrogen moves through ecosystems, involving nitrogen fixation and other steps.

Nitrogen Fixation

The conversion of inert nitrogen gas (N₂) into ammonia (NH₃) by nitrogen-fixing bacteria.

Nitrification

The process where soil bacteria convert ammonia (NH₃) into nitrite (NO₂⁻) and then into nitrate (NO₃⁻).

Assimilation

The process by which plants convert nitrate (NO₃⁻) into organic nitrogen for amino acid production.

Ammonification

The process by which decomposers convert organic nitrogen back into ammonia (NH₃).

Denitrification

The process by which anaerobic bacteria convert nitrate (NO₃⁻) back into nitrogen gas (N₂), completing the nitrogen cycle.

Nitrogen-Fixing Bacteria

Bacteria that convert nitrogen gas (N₂) into ammonia (NH₃), found free-living in soil or in root nodules of legumes.

Human Impact on Nitrogen Cycle

Human activities like synthetic fertilizers and burning fossil fuels disrupt the nitrogen cycle, causing issues like algal blooms.

Phosphorus Cycle

The process by which phosphorus moves through land, water, and living organisms, with no atmospheric gas phase.

Main Reservoir of Phosphorus

Rocks and sediments that release phosphate (PO₄³⁻) into soil and water through weathering.

Eutrophication

The process caused by fertilizer and detergent runoff that leads to algal blooms, oxygen depletion, and fish die-off.

Food Web

A representation of who eats whom and how energy and nutrients flow in an ecosystem.

Producers

Organisms that fix carbon through photosynthesis, such as plants and algae.

Primary Consumers

Herbivores that eat producers, such as deer and insects.

Secondary Consumers

Organisms that eat primary consumers, such as wolves and birds.

Decomposers

Organisms that break down dead organisms, such as fungi and bacteria.

Evolution

A change in allele frequencies in a population over generations, indicating that populations evolve, not individuals.

Traits

Characteristics of individuals based on genes.

Alleles

Different versions of a gene that individuals may carry.

Natural Selection

Environment selects which traits increase survival/reproduction.

Mutation

A non-adaptive mechanism that causes changes by chance.

Gene Flow

A non-adaptive mechanism that involves the transfer of alleles between populations.

Genetic Drift

A non-adaptive mechanism that causes random changes in allele frequencies.

Fitness

How many viable offspring an organism produces.

Heritability

The genetic passing of traits from parents to offspring.

Differential Reproductive Success

Some individuals have more surviving offspring than others.

Directional Selection

Shifts the average trait in one direction.

Stabilizing Selection

Favors the average trait and reduces extremes.

Disruptive Selection

Favors both extremes and selects against the average.

Population

Group of interbreeding individuals of the same species.

Allele frequency

Proportion of a specific allele in a population.

Charles Darwin

Scientist who observed variation & competition, contributing to the idea that traits improving survival increase in frequency.

Alfred R. Wallace

Independently proposed natural selection and co-founded the theory.

Thomas Malthus

Proposed that populations grow faster than food supply, leading to competition.

Charles Lyell

Proposed that geological changes happen slowly over time, implying that the Earth is old and evolution has time.

Example of Natural Selection

Brown beetles become more common over generations due to predation on green beetles.

Human Birth Weight

An example of stabilizing selection where extremely small or large babies have lower survival.

Moths during the Industrial Revolution

An example of directional selection where moths became darker.

Bird Beaks

An example of disruptive selection where both very large and very small beaks are useful, but medium beaks are not.

Deleterious Mutation

A mutation that is harmful.

Neutral Mutation

A mutation that has no effect on fitness.

Beneficial Mutation

A rare mutation that is essential to evolutionary innovation.

Gene Flow Effect

Increases genetic similarity between populations and prevents populations from diverging genetically.

Founder Effect

Occurs when a few individuals start a new population, carrying only a subset of the alleles from the original population.

Population Bottleneck

A rapid decrease in population size due to disaster, hunting, or disease, leading to loss of alleles.

Random Mortality & Reproduction

Individuals reproduce at unequal rates by chance, not because of advantage.

Genetic Drift Strength

Genetic drift is strongest when population size is small.

Mutation Outcome

Introduces new variation (mostly neutral or harmful).

Gene Flow Outcome

Makes populations more genetically similar.

Genetic Drift Outcome

Causes random allele frequency changes; reduces genetic variation, especially in small populations.

Hardy-Weinberg Equilibrium

A mathematical model describing a population not evolving, providing a baseline to compare real populations against.

Allele Frequency Change

Evolution is defined as a change in allele frequencies.

Adaptive Evolution

Evolution based on fitness, such as natural selection.

Non-Adaptive Evolution

Evolution not based on fitness, including mutation, gene flow, and genetic drift.

Genetic Variation

The diversity of alleles within a population.

Population A and B Example

Population A: mostly allele A; Population B: mostly allele a; migration results in both populations containing A and a in more similar frequencies.

Genotype

Genetic composition (the alleles an individual carries)

Phenotype

Observable traits resulting from genotype

Allele frequencies

For a gene with two alleles (A and a): Let p = frequency of allele A, Let q = frequency of allele a

Genotype frequencies

If a population is not evolving, genotype frequencies will be: AA = p², Aa = 2pq, aa = q²

Hardy-Weinberg Equilibrium (HWE)

Is only true if these 5 conditions are met: No natural selection, No migration, No mutation, Random mating, Large population size

Sexual Selection

No mate choice / no inbreeding

Calculate allele frequencies

HWE lets us calculate allele frequencies from genotype data

Predict expected genotype frequencies

HWE allows us to predict expected genotype frequencies under no evolution

Compare expected vs. observed frequencies

HWE allows us to determine if evolution is occurring

Observed genotype frequencies ≠ expected genotype frequencies

The population is NOT in Hardy-Weinberg equilibrium, therefore, evolution is occurring

Chi-square test

Compares observed genotype counts (from real data) to expected genotype counts (from HWE model)

χ² is large and p < 0.05

The difference is too great to be due to chance, indicating the population is evolving

p ≥ 0.05

No statistically significant difference, indicating the population is in HWE (not evolving)

Microevolution

Change in allele frequencies within a population over generations

Macroevolution

Formation of new species and higher taxonomic groups

Speciation

A continuous process, not a sudden event

Species definition difficulty

There is no single species definition that works for all groups of organisms

Biological Species Concept (BSC)

Species = groups that can interbreed and produce fertile offspring