Knowt
IB BIOLOGY Topic 5: Evolution and Biodiversity
5.1 Evolution and Biodiversity
Evolution: Evolution is the gradual and cumulative change in the heritable characteristics of a population over many generations. These heritable characteristics are governed by genes and cannot be acquired during an individual's lifetime. They are traits or alleles encoded in an organism's DNA.
Evidence of Evolution:
Fossil Records: Fossils are the preserved remains of organisms from the past, showing the gradual changes in species over time. The timeline of fossil appearance aligns with scientific expectations, with older fossils of bacteria and algae followed by shelled animals, trilobites, dinosaurs, early reptiles, birds, and mammals.
Selective Breeding: Humans have selectively bred plants and animals to enhance specific genetic traits. This process has demonstrated observable changes in genetic characteristics over a few generations, such as chickens producing more eggs or cows producing more milk.
Homologous Structures: These are common internal structures that appear in seemingly dissimilar animals due to their shared ancestry. A classic example is the pentadactyl limb found in humans, dolphins, bats, and dogs, where the underlying bone structure remains the same despite variations in shape and function.
Vestigial Structures: These are remnants of structures that no longer serve a purpose in modern organisms, like the human appendix.
Comparative DNA Analysis: By comparing the DNA of different species, scientists can identify genetic similarities and differences, further supporting evolutionary relationships.
Observable Change: The observation of species adapting to their environment or exhibiting changes over time is a testament to evolution in action.
Gradual Divergence:
Genetic variation exists within populations.
When two populations of the same species become geographically separated, natural selection acts differently on each group.
Over time, these populations change and may no longer interbreed, leading to speciation.
5.2 Natural Selection
Principles of Natural Selection:
Variation: Natural selection can only occur if there is genetic variation among individuals within a species.
Sources of Variation: Genetic variation arises from mutations, meiosis, and sexual reproduction.
Adaptations: Adaptations are characteristics that enhance an individual's suitability to its environment and way of life.
Overproduction: Species tend to produce more offspring than their environment can support.
Survival of the Fittest: Individuals with better adaptations are more likely to survive and reproduce, passing on their advantageous traits.
Reproduction: Individuals that reproduce pass on their characteristics to their offspring.
Natural Selection: Natural selection increases the frequency of advantageous traits and decreases the frequency of less advantageous ones, leading to changes within a species.
Occurrences of Natural Selection
Natural selection operates when there is genetic variation within a species.
If there were no variation, there would be no selective advantage for one individual over another, and natural selection would not occur.
Genetic Variation
Sexual reproduction introduces variation through the combination of genetic material from two parents.
Meiosis and crossing over contribute to genetic diversity.
Mutations can also introduce new alleles.
Struggle for Survival
Populations produce more offspring than their environment can support.
Competition for limited resources leads to the survival of individuals with advantageous traits.
Over generations, these traits accumulate, resulting in evolutionary changes.
Antibiotic Resistance
Antibiotics kill or weaken bacteria, but some bacteria may survive due to genetic changes.
Incomplete antibiotic courses or inadequate dosage can contribute to resistance.
Resistant bacteria can multiply and cause recurrent infections.
Resistance genes can be transferred to other bacteria, further increasing antibiotic resistance.
Beak Changes in Finches on Daphne Major
The shape of finch beaks changes in response to environmental food availability, illustrating the role of natural selection in adaptation.
5.3 Classification of Biodiversity
Binomial Nomenclature
The binomial system names species universally among biologists.
Each species is given a unique scientific name with two parts: genus (capitalized) and species (lowercase), both italicized.
Subspecies may interbreed if barriers are removed.
Taxonomy
Taxonomists classify species into a hierarchical system of taxa.
All organisms are categorized into three domains: Eukaryota, Bacteria, and Archaea.
Key taxa for eukaryotes include kingdom, phylum, class, order, family, genus, and species.
Identification of Species
Natural classification organizes species into similar groups based on shared characteristics.
Homologous structures, shared traits resulting from common ancestry, aid in classification.
A dichotomous key is used to identify organisms based on observable characteristics.
Plantae Classification
Bryophytes (e.g., mosses) lack vascular tissue and reproduce using spores.
Filicinophytes (e.g., ferns) have vascular tissue and reproduce via spores.
Coniferophytes (e.g., pines) have vascular tissue and use naked seeds for reproduction.
Angiospermophytes (e.g., peach trees) have vascular tissue, produce flowers, and exhibit a variety of leaves and stems.
Animalia Classification
Porifera (sponges), Cnidaria (jellies), Platyhelminthes (flatworms), Annelida (segmented worms), Mollusca (e.g., squid), and Arthropoda (e.g., insects) are classified based on characteristics like symmetry, segmentation, and presence of mouth and anus.
5.4 Cladistics
Cladograms
Cladograms are tree diagrams illustrating the evolutionary relationships among species.
Clades are groups of organisms that share a common ancestor.
Cladistics uses evidence from genetic sequences to determine clade membership.
Time Correlation
Genetic differences accumulate over time, making molecular clocks for estimating divergence times possible.
Differences in DNA sequences can be used to deduce when species diverged from a common ancestor.
Analogous and Homologous Structures
Analogous structures are superficially similar structures in different groups due to similar functions and habitats.
Homologous structures are similar structures in different organisms resulting from common ancestry.
Reclassification
Cladistics has prompted the reclassification of some species or groups based on molecular evidence.
It has revealed that some morphological classifications do not accurately reflect evolutionary relationships.
IB BIOLOGY Topic 5: Evolution and Biodiversity
5.1 Evolution and Biodiversity
Evolution: Evolution is the gradual and cumulative change in the heritable characteristics of a population over many generations. These heritable characteristics are governed by genes and cannot be acquired during an individual's lifetime. They are traits or alleles encoded in an organism's DNA.
Evidence of Evolution:
Fossil Records: Fossils are the preserved remains of organisms from the past, showing the gradual changes in species over time. The timeline of fossil appearance aligns with scientific expectations, with older fossils of bacteria and algae followed by shelled animals, trilobites, dinosaurs, early reptiles, birds, and mammals.
Selective Breeding: Humans have selectively bred plants and animals to enhance specific genetic traits. This process has demonstrated observable changes in genetic characteristics over a few generations, such as chickens producing more eggs or cows producing more milk.
Homologous Structures: These are common internal structures that appear in seemingly dissimilar animals due to their shared ancestry. A classic example is the pentadactyl limb found in humans, dolphins, bats, and dogs, where the underlying bone structure remains the same despite variations in shape and function.
Vestigial Structures: These are remnants of structures that no longer serve a purpose in modern organisms, like the human appendix.
Comparative DNA Analysis: By comparing the DNA of different species, scientists can identify genetic similarities and differences, further supporting evolutionary relationships.
Observable Change: The observation of species adapting to their environment or exhibiting changes over time is a testament to evolution in action.
Gradual Divergence:
Genetic variation exists within populations.
When two populations of the same species become geographically separated, natural selection acts differently on each group.
Over time, these populations change and may no longer interbreed, leading to speciation.
5.2 Natural Selection
Principles of Natural Selection:
Variation: Natural selection can only occur if there is genetic variation among individuals within a species.
Sources of Variation: Genetic variation arises from mutations, meiosis, and sexual reproduction.
Adaptations: Adaptations are characteristics that enhance an individual's suitability to its environment and way of life.
Overproduction: Species tend to produce more offspring than their environment can support.
Survival of the Fittest: Individuals with better adaptations are more likely to survive and reproduce, passing on their advantageous traits.
Reproduction: Individuals that reproduce pass on their characteristics to their offspring.
Natural Selection: Natural selection increases the frequency of advantageous traits and decreases the frequency of less advantageous ones, leading to changes within a species.
Occurrences of Natural Selection
Natural selection operates when there is genetic variation within a species.
If there were no variation, there would be no selective advantage for one individual over another, and natural selection would not occur.
Genetic Variation
Sexual reproduction introduces variation through the combination of genetic material from two parents.
Meiosis and crossing over contribute to genetic diversity.
Mutations can also introduce new alleles.
Struggle for Survival
Populations produce more offspring than their environment can support.
Competition for limited resources leads to the survival of individuals with advantageous traits.
Over generations, these traits accumulate, resulting in evolutionary changes.
Antibiotic Resistance
Antibiotics kill or weaken bacteria, but some bacteria may survive due to genetic changes.
Incomplete antibiotic courses or inadequate dosage can contribute to resistance.
Resistant bacteria can multiply and cause recurrent infections.
Resistance genes can be transferred to other bacteria, further increasing antibiotic resistance.
Beak Changes in Finches on Daphne Major
The shape of finch beaks changes in response to environmental food availability, illustrating the role of natural selection in adaptation.
5.3 Classification of Biodiversity
Binomial Nomenclature
The binomial system names species universally among biologists.
Each species is given a unique scientific name with two parts: genus (capitalized) and species (lowercase), both italicized.
Subspecies may interbreed if barriers are removed.
Taxonomy
Taxonomists classify species into a hierarchical system of taxa.
All organisms are categorized into three domains: Eukaryota, Bacteria, and Archaea.
Key taxa for eukaryotes include kingdom, phylum, class, order, family, genus, and species.
Identification of Species
Natural classification organizes species into similar groups based on shared characteristics.
Homologous structures, shared traits resulting from common ancestry, aid in classification.
A dichotomous key is used to identify organisms based on observable characteristics.
Plantae Classification
Bryophytes (e.g., mosses) lack vascular tissue and reproduce using spores.
Filicinophytes (e.g., ferns) have vascular tissue and reproduce via spores.
Coniferophytes (e.g., pines) have vascular tissue and use naked seeds for reproduction.
Angiospermophytes (e.g., peach trees) have vascular tissue, produce flowers, and exhibit a variety of leaves and stems.
Animalia Classification
Porifera (sponges), Cnidaria (jellies), Platyhelminthes (flatworms), Annelida (segmented worms), Mollusca (e.g., squid), and Arthropoda (e.g., insects) are classified based on characteristics like symmetry, segmentation, and presence of mouth and anus.
5.4 Cladistics
Cladograms
Cladograms are tree diagrams illustrating the evolutionary relationships among species.
Clades are groups of organisms that share a common ancestor.
Cladistics uses evidence from genetic sequences to determine clade membership.
Time Correlation
Genetic differences accumulate over time, making molecular clocks for estimating divergence times possible.
Differences in DNA sequences can be used to deduce when species diverged from a common ancestor.
Analogous and Homologous Structures
Analogous structures are superficially similar structures in different groups due to similar functions and habitats.
Homologous structures are similar structures in different organisms resulting from common ancestry.
Reclassification
Cladistics has prompted the reclassification of some species or groups based on molecular evidence.
It has revealed that some morphological classifications do not accurately reflect evolutionary relationships.
