Pre-AP_Biology_2025_Midterm_Exam_Review

Unit 1: Ecological Systems

1.1 Cycling of Matter in the Biosphere

Ecology Basics:

• Definition of Ecology: The scientific study of interactions and relationships among living organisms, including their relationships with their physical environment and each other. Understanding these interactions is crucial for comprehending ecosystem health and sustainability.

• Ecosystem Defined: An ecosystem is composed of a community of living organisms (biotic components) interacting with their physical environment (abiotic components). These interactions encompass energy flow and nutrient cycling, which are vital for maintaining ecosystem processes.

Branches of Ecology:

1. Organismal Ecology: Focuses on individual organisms and their adaptations to their environment, studying how they survive, grow, reproduce, and behave.

2. Population Ecology: Investigates how populations of species grow and interact, focusing on metrics like size, density, distribution, and genetic diversity.

3. Community Ecology: Examines the interactions between different species within a community, including predation, competition, and symbiosis, which shape community structure and dynamics.

4. Ecosystem Ecology: Studies energy flow and the cycling of nutrients among organisms and their environment, emphasizing ecosystem productivity and metabolic processes.

Biotic vs Abiotic Factors:

• Biotic Factors: The living components of an ecosystem, including plants, animals, fungi, bacteria, and interactions such as predation, competition, and parasitism.

• Abiotic Factors: The non-living elements that influence ecosystems, such as sunlight, temperature, water, minerals, and atmospheric gases, which all contribute to shaping ecological niches and conditions for life.

Matter and Energy Flow:

• Matter Cycles: Essential elements like carbon, nitrogen, and phosphorus are recycled within ecosystems through biogeochemical cycles, affecting productivity and biological diversity.

• Energy Flow: Energy enters ecosystems through photosynthesis and flows through trophic levels, from producers to consumers, losing energy at each transformation, highlighting the inefficiencies of energy transfer.

Four Spheres of Earth:

1. Geosphere: The solid part of Earth, including the crust, mantle, and core, influencing landforms and habitats.

2. Atmosphere: The layer of gases surrounding the planet, crucial for weather, climate, and oxygen availability for respiration.

3. Hydrosphere: All water components, including oceans, rivers, lakes, and groundwater, integral for life and climate regulation.

4. Biosphere: The realm of life encompassing all ecosystems, where biotic and abiotic factors interact to sustain living organisms.

1.2 Population Dynamics

Population Definition:

• A population is defined as a group of individuals of the same species residing in a specific geographic area, sharing the same resource requirements, and capable of interbreeding.

Studying Populations:

• Geographic Range: The spatial area where a population is found, which can vary in size and shape, often correlated with environmental features and species adaptability.

• Growth Rate: Describes changes in population size over time, influenced by birth rates, death rates, immigration, and emigration factors.

• Density: Refers to the number of individuals per unit area; high density can lead to competition for resources, while low density may hinder mating opportunities.

Distribution Patterns:

• Distribution Patterns: Refers to how individuals are spatially arranged in an area. Patterns can be:

  • Uniform: Individuals spaced evenly, often due to territorial behavior.

  • Clumped: Individuals grouped in patches, often around resources such as water.

  • Random: Individuals are distributed unpredictably, reflecting a lack of strong interactions among individuals.

Growth Models:

• Exponential Growth: Characterizes populations under ideal conditions with abundant resources, leading to rapid increases over time; common in pioneer species like bacteria and pests.

• Logistic Growth: Occurs when populations grow until resources become limited, leading to a leveling off as the population reaches carrying capacity; typical of larger, long-lived species such as elephants.

Species Types:

• r-selected Species: These species produce large numbers of offspring, usually have a short lifespan, and survive in unstable environments (e.g., mice, insects).

• K-selected Species: Characterized by lower reproductive rates, longer lifespans, and higher parental care, thriving in stable environments (e.g., elephants, humans).

1.3 Defining Ecological Communities

Biodiversity Defined:

• Biodiversity refers to the variety of life forms in a specific habitat or ecosystem, encompassing the diversity of species, genetic variation, and ecosystem variety.

Levels of Biodiversity:

1. Genetic Diversity: Variation within a species' gene pool, critical for adaptation and resilience.

2. Species Diversity: The number of different species in an area, reflecting ecosystem health.

3. Ecosystem Diversity: The variety of ecosystems within a specific area, influencing functionality and stability.

Importance of Biodiversity:

• Biodiversity is essential for ecosystem services such as pollination, nutrient cycling, water purification, and contributes to human welfare through food security and medicinal resources.

Threats to Biodiversity:

• HIPPO Framework: Highlights major threats:

  • Habitat Destruction: Urbanization, agriculture, and deforestation leading to loss of biodiversity.

  • Invasive Species: Non-native species that disrupt local ecosystems, outcompeting indigenous species.

  • Pollution: Contaminants affecting ecosystems and species health.

  • Population : Human population growth increasing resource demands.

  • Overharvesting: Unsustainable harvesting practices harming species survival.

Biome Definition:

• Biome: Ecological communities characterized by specific climate, flora, and fauna, shaping ecosystems across the globe.

Types of Biomes:

• Aquatic and Terrestrial Biomes: Each with unique features and species adaptations, exhibiting diverse ecosystem dynamics.

  • Terrestrial Biomes: Include distinct ecosystems such as:

    • Tropical Rainforest: High biodiversity and primary productivity, warm and moist.

    • Savanna: Grasslands with scattered trees, characterized by seasonal rainfall.

    • Desert: Minimal precipitation, extreme temperature ranges, and specialized flora/fauna.

  • Aquatic Biomes: Presence of freshwater and saltwater environments; key examples include:

    • Lakes and Ponds: Freshwater bodies with distinct zones (littoral, limnetic).

    • Oceans: Largest biome, influencing global climate and having varied ecosystems (coral reefs, deep-sea).

1.4 Ecological Community Dynamics

Community Definition:

• An ecological community is a group of interacting species using the same resources and sharing a habitat, forming a dynamic system.

Habitat Defined:

• Habitat: The specific environment in which an organism lives, including both biotic and abiotic factors that influence survival.

Ecological Niches:

• Ecological Niches: The role or function of a species within an ecosystem, including its habitat, resource use, and interactions with other organisms.

  • Fundamental Niche: The potential range of conditions and resources a species could theoretically occupy and use.

  • Realized Niche: The actual conditions and resources used by a species, often limited by competition, predation, and resource availability.

Range of Tolerance:

• Range of Tolerance: Describes the range of environmental conditions in which a species can survive.

  • Optimum Range: Where the species thrives; extremes can lead to stress, decreased fitness, or mortality.

Keystone Species:

• Keystone Species: A species whose impact on its ecosystem is disproportionately large relative to its abundance, playing a crucial role in maintaining the structure and stability of the community; their removal can lead to significant ecological shifts.

Symbiotic Relationships:

• Various interactions among species in a community:

  1. Predation: One species (predator) feeds on another (prey), shaping population dynamics.

  2. Competition: Species vie for the same resources, influencing community structure and species distribution.

  3. Mutualism: An interaction benefitting both species (e.g., pollination).

  4. Commensalism: One species benefits while the other is neither helped nor harmed.

  5. Parasitism: One species benefits at the expense of the other (host), impacting host population dynamics.

1.5 Changes in Ecological Communities

Ecological Succession:

• Ecological Succession: The observed process of change in the species structure of an ecological community over time, often following a disturbance.

  • Primary Succession: Begins in lifeless areas where soil has yet to form (e.g., after a volcanic eruption or glacial retreat), leading to colonization by pioneer species like lichens and mosses.

  • Secondary Succession: Occurs in previously populated areas following a disturbance (e.g., fire, flood) that does not eliminate all life, allowing for faster recovery.

Pioneer Species:

• Pioneer Species: The first colonizers of disturbed areas, these organisms are crucial for soil formation and creating conditions suitable for subsequent species.

Mass Extinctions:

• Mass Extinctions: Events that eradicate a large proportion of species, significantly altering ecosystems and opening ecological niches for new species.

Ecosystem Engineers:

• Ecosystem Engineers: Species that significantly modify their habitat, creating or maintaining ecosystems (e.g., beavers constructing dams), which enhances biodiversity and ecosystem stability.

Unit 2: Evolution

2.1 Patterns of Evolution

Definition of Evolution:

• Evolution: The change in heritable traits within a population over generations, driven by factors like natural selection, genetic drift, mutations, and gene flow.

Key Evolutionary Scientists:

• Lamarck: Proposed an early theory of evolution based on the inheritance of acquired characteristics; many of his ideas were later disproved.

• Darwin: Best known for the theory of natural selection, emphasizing adaptation and survival of the fittest as mechanisms driving evolution.

Fossils:

• Fossils provide crucial evidence for evolutionary processes, illustrating transitional forms and the history of life on Earth, allowing scientists to trace species' lineage.

Common Ancestors:

• The concept of common ancestry forms the basis of evolutionary theory, whereby diverse species have evolved from shared ancestors over time.

Homology:

• Homology: Refers to the structural similarities found between different species stemming from common ancestry (e.g., vertebrate limb structures).

  • Contrasted with Analogy, where similarities arise from convergent evolution due to similar environmental pressures rather than shared ancestry.

Evidence Types:

• Various lines of evidence support evolutionary mechanisms, including:

  • Biogeography: Geographic distribution of species supports theories about isolation and adaptation.

  • DNA Analysis: Provides insights into genetic relationships and evolutionary processes at the molecular level.

  • Comparative Embryology: Comparative studies of embryonic development in different species reveal similarities indicative of common ancestry.

2.2 Mechanisms of Evolution

Natural Selection:

• Natural Selection: The process wherein organisms better adapted to their environment tend to survive and reproduce, leading to the gradual evolution of species according to fitness.

Conditions for Natural Selection:

1. Overproduction: Species tend to produce more offspring than can possibly survive, leading to competition.

2. Heritable Variations: Individuals show variations that can be passed to offspring; these variations can affect fitness.

3. Variable Fitness: Certain traits give some individuals an advantage in survival and reproduction under specific environmental conditions.

Types of Selection on Polygenic Traits:

• Directional Selection: Favors one extreme phenotype, shifting the population mean in that direction.

• Stabilizing Selection: Favors intermediate phenotypes, reducing variation and maintaining the status quo.

• Disruptive Selection: Favors extreme phenotypes over intermediate, potentially leading to speciation.

Genetic Drift:

• Genetic Drift: Random changes in allele frequencies in a population, with significant effects in small populations.

  • Bottleneck Effect: Loss of genetic diversity due to a drastic reduction in population size.

  • Founder Effect: Reduced genetic diversity that occurs when a small group separates from a larger population to establish a new population.

Hardy-Weinberg Equilibrium:

• A principle that provides a framework for understanding genetic variation and equilibrium within populations; under certain conditions, allele frequencies remain constant from one generation to the next, indicating no evolution.

  • Conditions for Hardy-Weinberg: No mutations, random mating, no natural selection, large population size, and no gene flow.

  • Application: Researchers can apply Hardy-Weinberg to calculate expected genotype frequencies in populations and assess evolutionary forces at work.

2.3 Speciation

Rates of Evolution:

• Gradualism: A model of evolution where changes occur slowly and steadily over long periods.

• Punctuated Equilibrium: Theory that evolution is characterized by long periods of stability interrupted by brief and rapid changes.

Extinction Events:

• Significant extinction events can reshape evolutionary pathways, eradicating dominant groups and allowing for the emergence of new species in previously occupied niches.

Speciation Processes:

• Prezygotic Barriers: Mechanisms that prevent mating or fertilization between species, including temporal (timing), behavioral (courtship behaviors), and mechanical (incompatibility of reproductive organs) barriers.

• Postzygotic Barriers: Occurs after fertilization, impacting the viability or fertility of the offspring, for instance, reduced hybrid viability or sterility.

Definitions of Species:

• Allopatric Speciation: Occurs when populations are geographically isolated, leading to divergence through evolutionary processes.

• Sympatric Speciation: Occurs without geographical separation, often through mechanisms like polyploidy in plants or behavioral isolation in animals, resulting in the emergence of new species within the same area.