PIB BIO unit 8
Pre-IB Biology Study Guide for the Unit 8 Test
8.1 ~ Evidence for Evolution
Definition of Evolution
Evolution is defined as the change in heritable characteristics of biological populations over successive generations.
Components of the Definition:
Heritable Characteristics: Traits that can be passed from one generation to the next through genetic information.
Populations: Groups of individuals of the same species that live in the same area and interbreed.
Successive Generations: Refers to the ongoing process through which populations change over time.
How Evolution Occurs:
Evolution occurs through mechanisms such as natural selection, genetic drift, mutation, and migration (gene flow) that can change the genetic makeup of populations over time.
Five Types of Evidence for Evolution:
Fossil Evidence: Fossils show a record of past life forms and demonstrate changes over time.
Example: Transitional fossils such as Archaeopteryx which exhibit features of both dinosaurs and birds.
Comparative Anatomy: The study of similarities and differences in the anatomy of different species.
Example: Homologous structures, such as the forelimbs of mammals, which indicate common ancestry.
Molecular Biology: Comparison of DNA and protein sequences among different organisms.
Example: Shared genetic sequences between humans and chimpanzees reflecting their close evolutionary relationship.
Biogeography: The distribution of species across geographical areas.
Example: The unique species found on the Galápagos Islands that are closely related to South American mainland species.
Embryology: The study of the development of embryos in different species and how they resemble each other at certain stages.
Example: Similar embryonic structures in vertebrates during early development.
Selective Breeding vs. Natural Selection:
Selective Breeding: Human-directed reproduction for desirable traits.
Natural Selection: A natural process where organisms better adapted to their environment tend to survive and produce more offspring.
8.2 ~ Natural Selection
Definition of Natural Selection:
Natural selection is the process whereby organisms better adapted to their environment tend to survive and produce more offspring.
Example: Peppered moths (Biston betularia) changing color in response to pollution and predation.
Requirements for Natural Selection:
Variability: There must be variation in traits within a population.
Heritability: Traits must be heritable, passed on from parents to offspring.
Differential Reproduction: Some traits confer advantages that increase reproductive success.
Overproduction: Organisms tend to produce more offspring than can survive.
Sources of Variation in a Population:
Genetic Mutations: Changes in DNA that can lead to new traits.
Gene Flow: The transfer of alleles between populations.
Sexual Reproduction: Creates new combinations of genes through crossing over and independent assortment.
Adaptation and Its Evolution:
An adaptation is a trait that enhances an organism's fitness in a specific environment.
Adaptations can evolve through the process of natural selection improving the survival and reproduction of the species.
8.3 ~ Examples of Natural Selection
Rock Pocket Mice: Variation, Selective Pressures, and Evolution:
Different populations of rock pocket mice exhibit varying fur colors dependent on their substrates.
Selective Pressures: Predation and habitat coloration that drive evolution in different areas.
Darwin’s Finches Post-Drought Analysis:
Following the drought of 1977 on Daphne Major, finch populations experienced changes in beak size and shape due to food availability.
Natural Selection Example: Increased beak size favored due to limited seed types.
Antibiotic Resistance in Bacteria:
Evolution of antibiotic resistance occurs rapidly in bacteria due to short generation times and high mutation rates.
Bacteria can rapidly adapt to antibiotics, as the ones with mutations providing resistance survive and reproduce.
Factors Contributing to Growing Global Antibiotic Resistance:
Overuse of Antibiotics: In both healthcare and agriculture.
Inadequate Infection Control: In healthcare settings.
Poor Sanitation and Hygiene: Promotes the spread of resistant bacteria.
8.4 ~ Classification of Biodiversity
Binomial Classification System:
A system for naming organisms using a two-part name: the genus name and species name.
Purpose: Provides a standardized method for identifying and categorizing organisms globally.
Order of Taxa:
Broadest to Narrowest: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.
The Three Domains of Life:
Bacteria: Prokaryotic, unicellular organisms lacking a nucleus.
Archaea: Prokaryotic organisms often found in extreme environments.
Eukarya: Eukaryotic organisms, including animals, plants, fungi, and protists.
Relatedness Based on Taxa:
Organisms in the same taxonomic group share a more recent common ancestor compared to those in different groups.
Using a Dichotomous Key:
A tool for identifying unknown organisms through a series of choices based on their physical characteristics.
8.5 ~ Cladistics
Using a Cladogram:
A diagram that shows the evolutionary relationships among species.
Identifying a Clade and Other Parts:
Clade: A group of organisms that includes an ancestor and all its descendants.
Node: A point on the cladogram where a branch splits, representing a common ancestor.
Branch: Represents a lineage on the cladogram, which diverges over time.
Shared History: Indicates related species that have diverged from a common ancestor.
Determining Divergence Time:
The branching points in a cladogram indicate when species diverged from their common ancestor.
Identifying Closely Related Species:
Species that share a more recent common ancestor are considered more closely related.
Characteristics of Species:
Characteristics can be deduced based on the nodes and branches of the cladogram showing common ancestry.
8.6 ~ Structural and Molecular Comparisons
Creating a Cladogram with Comparisons:
Construct cladograms based on either morphological (structural) data or genetic (molecular) data.
Differences Between Structural and Molecular Comparisons:
Structural Comparisons: Involves comparing physical features of organisms (e.g., bone structure).
Molecular Comparisons: Focuses on genetic and protein similarities and differences at a molecular level.
Convergent vs. Divergent Evolution:
Convergent Evolution: Independent evolution of similar traits in different species due to similar environmental pressures.
Example: The wings of bats and birds, which developed independently.
Divergent Evolution: When two or more species share a common ancestor and accumulate differences over time due to different environments.
Example: The variation in beak shapes of Darwin's finches.
Homologous vs. Analogous Structures:
Homologous Structures: Body parts that are similar in structure but may serve different functions, indicating common ancestry.
Example: The forelimbs of mammals.
Analogous Structures: Body parts that serve similar functions but are not structurally similar, indicating convergent evolution.
Example: The wings of insects and birds.