Biology Exam Notes: Core Concepts, Ecology, Climate Change, and Lyme Disease
Big Ideas in Biology
Evolution: This fundamental principle explains both the underlying unity of life (common ancestry) and the tremendous diversity observed among organisms. It serves as the central organizing theme of biology.
Information: Biological systems rely heavily on the storage, transmission, and expression of information. Examples include:
Genetic Code ( ext{DNA}): The blueprint carrying hereditary instructions.
Cell Signaling: How cells communicate internally and with each other to coordinate activities.
Regulatory Systems: Mechanisms that control gene expression, metabolic pathways, and physiological processes to maintain internal balance.
Energy and Matter: All living organisms require continuous transformations of energy and matter to survive, grow, and reproduce.
Photosynthesis: The process by which plants convert light energy into chemical energy, forming the base of most food webs.
Metabolism: The sum of all chemical reactions in an organism, involving energy conversion and matter cycling.
Interactions: Organisms constantly interact with each other (intraspecific, e.g., within a species; interspecific, e.g., between species) and with their abiotic (non-living) environment. These interactions drive ecological dynamics and evolution.
Applying Big Ideas to Lyme Disease
Interactions: Lyme disease serves as a clear example of complex interactions:
Tick-Host-Pathogen: The black-legged tick (vector) interacts with various hosts (mice, deer, humans) and transmits the pathogen ( extit{Borrelia burgdorferi}).
Environment: The tick's survival, distribution, and activity are significantly influenced by abiotic factors like temperature and humidity.
Energy & Matter:
Food Webs: The availability of hosts (e.g., mice, deer) provides blood meals for ticks, allowing them to acquire energy and matter necessary for survival and reproduction.
Survival Strategies: Both the pathogen and the tick employ strategies to acquire energy and matter, which are critical for their life cycles and propagation.
Information:
Pathogen Transmission: The genetic information of extit{Borrelia burgdorferi} is transmitted from an infected host to a tick, and subsequently to a new host during blood meals.
Regulatory Systems: Ticks and their hosts have internal regulatory systems that respond to infection, and the pathogen itself utilizes genetic information to establish and maintain an infection.
Evolution:
Tick Adaptation: Ticks (and their hosts) can adapt to changing environmental conditions, such as climate change, which influences their geographic range, survival rates, and the dynamics of disease transmission.
Pathogen Evolution: The extit{Borrelia burgdorferi} bacterium can also evolve, potentially leading to new strains or changes in virulence or transmissibility.
Host and Vector Definitions and Identification in Lyme Disease
Host: An organism that harbors a pathogen, providing it with resources and a place to live, often without being significantly harmed, or with varying degrees of harm.
Vector: An organism that transmits a pathogen from one host to another. Vectors are often arthropods like ticks or mosquitoes.
Lyme Disease Specifics:
Hosts: White-footed mice ( extit{Peromyscus leucopus}) are critical reservoir hosts (meaning they carry the pathogen without showing many symptoms and can infect ticks); deer are important hosts for adult tick feeding and reproduction; humans are accidental or dead-end hosts.
Vector: The black-legged tick ( extit{Ixodes scapularis}) is the primary vector for Lyme disease in the Eastern United States.
Interpreting Graphs and Figures
To interpret graphs effectively, always methodically examine the following components:
Title: Provides the main subject and context of the graph.
Axes Labels: Indicate exactly what quantities or categories are being measured and displayed on both the x and y axes.
Units: Specify the scale and increments of the measurements (e.g., , ).
Independent Variable: Typically located on the x-axis, this is the factor that is intentionally changed, manipulated, or tested by researchers (e.g., time, temperature, forest cover percentage).
Dependent Variable: Typically located on the y-axis, this is the factor that is measured or observed in response to changes in the independent variable (e.g., Lyme disease cases, population size).
Analysis: After identifying the components, carefully look for patterns, overarching trends (e.g., increasing, decreasing, cyclical), and any anomalies or outliers in the data.
Example: A hypothetical graph showing a positive correlation between Lyme disease cases and average ambient temperature would suggest that as temperatures rise, the number of Lyme disease cases tends to increase.
Tick and Lyme Disease Life/Transmission Cycle
The complex life cycle of the black-legged tick and the transmission of extit{Borrelia burgdorferi} typically spans two years and involves several developmental stages and hosts:
Larvae: Tick larvae hatch from eggs in the late summer. They take their first blood meal from small mammals, most commonly infected white-footed mice. During this feeding, they can acquire the extit{Borrelia burgdorferi} bacteria if the host is infected.
Nymphs: Larvae molt into nymphs the following spring. Nymphs are very small ( ext{poppy-seed size}) and are the stage responsible for the majority of human Lyme disease infections. They seek hosts for a second blood meal, and if infected from previous feeding, they can transmit the disease to these hosts, including humans, during this feeding.
Adults: Nymphs molt into adults in late summer/early fall. Adult ticks primarily feed on larger mammals, such as deer. Deer are crucial for adult tick survival, mating, and reproduction by providing ample blood meals, though deer are not typically reservoir hosts for the bacteria.
Reproduction: After feeding and mating on larger hosts, adult female ticks drop off, lay several thousand eggs in the leaf litter, and then die, completing the two-year cycle.
Humans as Accidental Hosts: Humans are considered accidental or dead-end hosts. They can contract Lyme disease when bitten by an infected tick (most commonly a nymph), but they do not play a role in maintaining the tick or bacterial life cycle, as infected humans typically do not transmit the bacteria back to ticks.
Ecological Hierarchy
Organism: A single, individual living being (e.g., one black-legged tick, one white-footed mouse, one human).
Population: A group of individuals of the same species that live in the same geographical area and interact with each other at a particular point in time (e.g., all white-tailed deer in a specific forest, all extit{Borrelia burgdorferi} bacteria within a single tick).
Community: Consists of all the interacting populations of different species within a particular geographical area (e.g., the populations of deer, ticks, mice, foxes, and various plant species coexisting in a forest).
Ecosystem: Comprises a community of interacting populations along with their abiotic (non-living) physical and chemical environment (e.g., a forest community including local climate, soil composition, water availability, and sunlight).
Biosphere: The largest and most inclusive ecological level, representing the sum of all ecosystems on Earth. It encompasses all life and the areas where life exists, integrating living beings with the elements of the lithosphere (land), hydrosphere (water), and atmosphere (air).
Examples of Ecological Hierarchy
Organism: A single white-tailed deer.
Population: All white-tailed deer inhabiting a specific national forest.
Community: The interacting populations of white-tailed deer, black-legged ticks, white-footed mice, red foxes, and various tree and plant species within that national forest.
Ecosystem: The national forest community (deer, ticks, mice, foxes, plants) combined with its abiotic environment, including local average temperature, annual rainfall, soil pH, and sunlight intensity.
Biotic and Abiotic Factors
Biotic Factors: The living or once-living components of an ecosystem that influence other organisms. Examples include:
Plants (serving as producers and habitat providers).
Predators (e.g., owls, foxes) that consume other organisms.
Pathogens (e.g., extit{Borrelia burgdorferi}) that cause disease.
Competitors (species vying for the same resources).
Abiotic Factors: The non-living physical and chemical components of an ecosystem that influence living organisms. Examples include:
Climate: Temperature, precipitation, wind patterns.
Soil: Composition (e.g., sand, clay, loam), pH, nutrient content.
Water: Availability, salinity, flow rate.
Sunlight: Intensity, duration.
Topography: Elevation, slope, aspect.
Characteristics That Define Living Things
Made of Cells: All living organisms are composed of one or more fundamental units of life called cells, which are the basic structural and functional units.
Use Energy: Organisms obtain and transform energy from their environment (e.g., photosynthesis, cellular respiration) to power all their life processes (metabolism).
Grow & Develop: Organisms increase in size over time (grow) and undergo changes in form and function throughout their life cycles (develop).
Reproduce: Organisms produce offspring, which can be sexual or asexual, ensuring the continuation and perpetuation of their species.
Respond to Stimuli: Organisms detect and react to changes in their internal or external environment (e.g., light, temperature, touch, chemical signals).
Maintain Homeostasis: Organisms regulate their internal environment to maintain stable, relatively constant physical and chemical conditions (e.g., body temperature, pH, water balance) necessary for cellular function.
Evolve/Adapt: Populations of organisms change over successive generations through the process of evolution, leading to adaptations that allow them to better survive and reproduce in their environment via natural selection.
Biotic and Abiotic Factors Affecting General Ecosystems
Biotic Factors Examples:
Predators: The presence and abundance of predators (e.g., wolves preying on deer) can significantly control prey populations, influencing food webs and ecosystem structure.
Competition: Interspecific (between species) and intraspecific (within a species) competition for finite resources like food, water, or mates can limit population sizes and influence species distribution.
Food Availability: The amount of available food resources (e.g., plant biomass for herbivores, prey species for carnivores) directly determines which organisms can survive, grow, and reproduce in an ecosystem.
Abiotic Factors Examples:
Temperature: Directly affects metabolic rates of organisms, enzyme activity, and determines species geographic ranges and seasonal activities.
Water Availability: Essential for all life processes; limits primary productivity and the distribution of terrestrial organisms.
pH: The acidity or alkalinity of soil or water can influence nutrient availability for plants and the survival of aquatic organisms.
Sunlight: The primary energy source for most ecosystems, supporting photosynthesis and influencing daily and seasonal activity patterns of organisms.
Applying Ecological Hierarchy to the Tick/Lyme Disease System
Organism: A single individual black-legged tick ( extit{Ixodes scapularis}).
Population: All black-legged ticks inhabiting a specific forested region, such as a state park in the Northeast.
Community: The interacting populations within that Northeastern forest ecosystem, including ticks, white-tailed deer, white-footed mice, red foxes, various birds, and the predominant tree and plant species.
Ecosystem: The Northeastern forest community combined with its specific abiotic environment, such as the local climate (average temperature, humidity levels, seasonal precipitation) and soil characteristics (e.g., leaf litter depth, moisture content).
Biosphere: The overarching Earth systems and global ecological processes that influence and support the regional ecology of Lyme disease, encompassing the global distribution of biomes, climate zones, and interconnected biological systems.
Biotic and Abiotic Factors Affecting the Tick/Lyme Disease System
Biotic Factors:
Deer: White-tailed deer are crucial hosts for adult black-legged ticks. They provide blood meals essential for adult tick survival, mating, and reproduction, thereby supporting large tick populations. While not typically reservoir hosts for the Lyme bacterium, their abundance significantly impacts tick abundance.
White-footed mice ( extit{Peromyscus leucopus}): These rodents are the primary reservoir hosts for extit{Borrelia burgdorferi}. Larval and nymphal ticks commonly feed on mice, acquiring the bacteria and becoming infected, which is critical for the maintenance of the disease cycle.
Predators (e.g., foxes, coyotes, owls, raptors): Natural predators of white-footed mice can help regulate mouse populations. A decline in these predators can lead to an increase in mouse abundance, which in turn leads to a higher rate of tick infection and a greater risk of Lyme disease for other hosts.
Abiotic Factors:
Temperature: Temperature is a critical determinant. Cold winters can increase tick mortality, while milder winters and warmer overall temperatures extend the tick's active season, accelerate their development, and improve their overwintering survival rates.
Humidity: Ticks are highly susceptible to desiccation (drying out). They require high humidity and moist microenvironments (such as damp leaf litter) for survival. Low humidity can kill ticks quickly.
Forest Cover: Provides the necessary shade, humidity, and leaf litter environments that ticks need to survive. It also creates a suitable habitat for their hosts (mice, deer), thereby supporting the entire Lyme disease ecology.
Lyme Disease as a Zoonotic Disease
Lyme disease is a classic example of a zoonotic disease because the causative agent, the bacterium extit{Borrelia burgdorferi}, primarily circulates in a natural cycle among non-human vertebrate animals (like white-footed mice) and is then transmitted to humans through an invertebrate vector (the black-legged tick). Humans are incidental hosts who contract the disease from the animal reservoir, not from other humans.
Zoonotic Disease Definition
Zoonosis (plural: zoonoses): An infectious disease that is caused by a pathogen (virus, bacterium, parasite, fungus) that originates in non-human animals and can be transmitted from those animals to humans. Transmission can occur directly (e.g., through bites, scratches, contact with animal fluids) or indirectly via a vector.
Abiotic Factors Affecting Ticks and Lyme Disease Spread
Temperature: Warmer ambient temperatures lead to increased tick survival rates, especially during winter months. They also contribute to a longer activity season for ticks, and potentially faster development of tick life stages, facilitating wider geographic spread.
Humidity: Ticks are extremely vulnerable to drying out. Environments with high humidity and ample moisture are crucial for their survival; periods of low humidity can drastically reduce tick populations.
Precipitation: Influences overall habitat moisture and the health and distribution of vegetation, which in turn affects host populations and tick microhabitats.
Seasonal Change: Determines the timing and duration of tick activity. Milder winters and extended warm seasons lead to earlier spring activity and later fall activity for ticks, increasing the window of human exposure.
Climate vs. Weather
Weather: Refers to the short-term, localized atmospheric conditions at a specific place and time. This includes momentary or daily variations in temperature, precipitation, wind, cloud cover, and humidity (e.g., a sudden rain shower, a particular scorching summer day, a week-long heatwave).
Climate: Describes the long-term, characteristic patterns of atmospheric conditions, including average rainfall, temperature ranges, and frequency of extreme events, typically observed over decades (usually or more) for a specific geographical region. It's the