Concepts of Biology Flashcards

Biological Evolution

• Charles Darwin was the first scientist to study evolution.
• Descent with modification is the simplest definition of evolution.
• Evolution involves a change in the genetic characteristics (DNA) of a population over time.
• DNA changes lead to phenotype changes, allowing organisms to adapt better to their environment.
• Modified genes are passed on to offspring.

Mechanisms of Evolution

• Evolution occurs through two major mechanisms:
  • Natural Selection
  • Genetic Drift

1. Natural Selection

• Organisms with favorable traits have a better chance of survival.
• Longer lifespan leads to more reproductive opportunities.
• More offspring are produced, and more organisms with the same favorable traits exist in the next generation.
• This process typically takes thousands of years.

2. Genetic Drift

• Differences in reproduction or survival due to chance (random).
• Environmental disturbances can cause genetic drift:
  • Hurricanes
  • Volcanic eruptions
  • Clearing land for development
  • Over-hunting a species
• These factors cause sudden environmental changes, leading to DNA changes for adaptation and survival.
• This process is sudden and fast.

Results of Evolution (Descent with Modification)

• Evolution results in three major themes in biology:
  1. Adaptation
  2. Diversity
  3. Shared Inherited Characteristics

1. Adaptations

• Any change in characteristic/trait that improves an organism's survival.
• Every living organism is adapted to cope with its habitat's environmental factors.
• Examples: polar bear adaptations, evergreen trees, cactus prickles, long/short legs for animals.
• Adaptation is a result of natural selection and the survival of the best-suited organisms.

2. Diversity

• Diversity results from speciation, where different species cannot crossbreed.
• Examples: Ducks and geese, donkey and horse (sterile mule).
• A species is an organism that cannot reproduce with other species.
• Diversity is a result of speciation.

3. Shared Inherited Characteristics

• Comparative Anatomy
• Characteristics arise due to a common ancestry.
• Homologous structures: similar structures with different functions, suggesting a common ancestor.
• Vestigial structures: structures that serve no useful function.
  • Example: end of spine in humans (tail bone), suggesting human ancestors had tails.
  • Vestigial structures can be viewed as evidence of evolution.

Evidence for Evolution

• Fossils
  • Preserved remains of formerly living organisms.
  • Fossil record allows scientists to estimate life on earth.
  • Documents changes in previous living organisms.

2. Comparative Embryology

• Organisms contain evidence of their evolutionary history (ancestor).
  • Vestigial structures like the tail bone in humans.
  • Embryological development: Chicken embryo has gills.

3. Direct observations of genetic change in populations.

4. Artificial selection

• Selecting best quality and eliminating weak ones.
  • Farming crops (best seeds).
  • Domesticated animals (breed animals with best milk/meat, highest yield).
• Despite obvious differences, all birds are still members of the same species.

Species

• What is a species?
  • Definition: Building block units of population; group of interbreeding population; do not crossbreed with other groups even when there is opportunity.
  • The most specific level of biological classification.
  • Population is a large number of the same species.
• Taxonomic classification:
  • Kingdom -> Phylum -> Class -> Order -> Family -> Genus -> Species
• Human classification: Animalia -> Chordata -> Mammalia -> Primates -> Hominidae -> Homo -> Species

Impact of Evolutionary Thought

• Natural Selection:
  • The process where organisms best adapted to their environment survive and transmit their genetic characteristics in increasing numbers, while less adapted ones are eliminated.
• Understanding evolution has impacted technology:
  • Development and use of pesticides: the weak plant will die vs the strong one.
  • Effect of not finishing antibiotic course: the weak bacteria is eliminated (die) and keeping the potent type (resisted AB). Bacteria will become immune to that AB, creating a new type of bacteria.

What Are Populations?

• Species: Group of interbreeding organisms with the same characteristics that do not crossbreed with other organisms.
  • Examples: humans, dogs.
• Population: Group of individuals of the same species.
• Population size: Total number of individuals in a population.
• Population density: Number of individuals per unit area.
• Community: Several populations of different species.
  • Examples: trees (species)…group (population) = community; cats (species)…group (population) = community.

Changes in Population Size

• Change in size over time:
  • Measuring:
    • Increasing factors:
      • Birth
      • Immigration
    • Decreasing factors:
      • Death
      • Emigration
• Zero growth rate occurs when increasing factors equal decreasing factors.

2. Exponential Growth

• Is a J curve, indicates fast growth rate.
• When a population increases by a constant proportion from one generation to the next.

3. Doubling Time

• Doubling time measures how fast the population is growing.
• The shorter the doubling time, the faster the population is growing.
• Example:
  • Population A: 100 million, doubles in 10 years.
  • Population B: 20 million, doubles in 4 years.
  • Population B is growing faster.

Zero Population Growth vs. Age Structure (Pyramid)

• Age structure (Pyramid) is the proportion of individuals in different countries.
• It helps in predicting the population growth rate.
• Base width: the wider the base, the faster the population is growing.
• Zero Population Growth: A condition in which a population neither grows nor declines because the number of births in a year equals the number of deaths.
• Industrialized countries: low birth and death rates, steady but small population growth.
• Third World countries: high birth and death rates without effective birth control methods, resulting in fast population growth without increasing resources.

Limits to Population Growth

• Populations cannot increase in size indefinitely.
• Environmental factors limit population growth:
  • Food
  • Habitat
  • Limited resources

Limits to Population Growth

• Limits force populations to demonstrate an S-shaped curve (logistic curve).
• Population growth starts slow, goes faster, then slows down.

Carrying Capacity

• The maximum number of individuals supported in an environment without depleting the resources (food, job, health & accommodation).
• Number may change over time.
• J-shaped is Exponential growth.
• S-shaped is population with limits…Logistic growth.

Growth-Limiting Factors

• Biotic potential: population ability to reproduce. Increase growth rate (early puberty/longevity). (Intrinsic)
• Environmental Resistance: (Extrinsic)
  • Density-dependent factors: competition for food/predation/disease/jobs.
  • Forces fast-growing populations (J curve) to grow slower (S shape curve).
• Density-independent factors: (natural disasters)
  • Weather fluctuations
  • Fire and floods
  • Pesticide use
  • Unrelated to population size/affects everyone.
  • Cause sudden drop in population size.

Human Population Growth

• Currently, humans demonstrate exponential population growth.
• This pattern cannot continue indefinitely.

Communities of Organisms

• In ecosystem study:
  • Interaction(s) among living organisms.
  • Interaction between living organisms and environment.

Communities

• Species: a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding.
• Population: Group of organisms of the same species.
• Community: populations of two or more different species occupying the same geographical area.

Effects of Species Interactions

• Communities are characterized by diversity.
• Diversity is measured in two ways:
  • Number of species present (e.g., backyard vs. Amazon).
  • Abundance of these species.

I. Interspecific Interactions in Communities

• A. Competition: When populations of two or more species in a community rely on similar limiting resources (food, nesting sites).
• B. Predation: Consumer = predator, Food species = prey.
• C. Symbiosis: Symbiotic relationship is an interaction in which one species (the SYMBIONT) lives in or on another species (the HOST).
  • Three types:
    • I. Parasitism
    • II. Mutualism

Interactions among Living Organisms

I. Parasitism

• One organism benefits and the other is harmed.
• Examples: flies, leech (ectoparasite), dog tapeworms, roundworm in pigs and cattle (endoparasite).
• One organism (the smaller) benefits at the expense of the other (the host).

II. Mutualism

• Both organisms (Parasite and host) benefit.
• Examples: sea anemone (housing)/zooxanthella (food), jellyfish/zooxanthella, paramisiam /zoochorellae.

III. Commensalism

• One organism is benefited, and the other is not affected.
• Example: Mollusk shell (housing) for barnacles, seen on crabs/boats/rocks/shells of sea turtles.
• Harmless; do not interfere with animals and their normal diet.

II. Food Webs

• Contain many food chains.
• Food chain: who eats who.
  • Example: corn -> mouse -> snake -> hawk.
  • Producers/plants/autotrophs at base of food chain.
  • Consumers:
    • Primary: herbivores
    • Secondary
    • Tertiary
• Heterotroph: organism that cannot synthesize its own food and is dependent on complex organic substances for nutrition.
  • Carnivores: meat eaters (lion)
  • Omnivores: eat plants and meat (humans)

III. Biological Magnification

• Contaminant concentration increases progressively as we move up the food chain.
• Since substance (DDT) is very slowly metabolized or excreted.
• Example: Pesticide Use: DDT (Density Independent Factor)
  • Bald eagle population increased after the ban of DDT. No toxicity.
  • corn -----> mouse-----> snake-----> hawk
    5 mg DDT -> 10 -> 20 -> 40
• PCB = Polychlorinated biphenyl

IV. Keystone Species

• Keystone species stabilizes community by having a tremendous effect on this community; if removed, entire community balance changes.
• If there is a sea star, the main predator (mussel) population is under control (small). Predator eats everything.
  • Pisaster (sea star) is a keystone species.
  • High sea star #: Low predator (mussel): High species #.
  • Low sea star #: High predator #: Low species #.
• Keystone predator reduces the density of the strongest competitors.
• Keystone species (sea star) feed on the main predator.

Pisaster as a Keystone Species

• The presence of sea star (Pisaster)/keystone species helps maintain species diversity.
• Sea star feeds on the main predator (mussel).
• Community has ~20 species in presence of starfish and only one species in absence of sea star.

Community Change

• Communities change over time but always recover.
• Process is called succession.
  • A. Primary succession = development of a new habitat (no soil): Volcanic islands/erupted lava (hot), then cools down, organisms start living on the island again(trees… different species).
  • B. Secondary succession = recovering from a disturbance (soil): Deforestation/ later grass grows, birds eat grass… organisms start increasing. Community rebuilt.

Ecosystem

• Ecosystem is an area of defined as having living (biotic) and non-living (abiotic) components.
• Concepts of Biology Chapter 20 ECOSYSTEMS AND THE BIOSPHERE

How Ecosystems Function

• Interaction between living organisms and the surrounding environment.
• Ecosystem is a community of different organisms, Biotic (living) like fish, flowers, and the physical environment (non-living), Abiotic (non-living) like soil, water.
• Movement of energy: escapes
• Nutrients/materials: recycle.
• Examples: C, N, H (never lost).
• Dead organisms decompose and material released back to ecosystem.

How Ecosystems Work

• Energy flow is a one-way path (escape).
• Nutrients/materials are recycled by decomposers.
• Energy coming from the Sun is