Topic 5.4 – Cladistics
Essential idea: The ancestry of groups of species can be deduced by comparing their base or amino acid sequences.
Nature of science:
Falsification of theories with one theory being superseded by another—plant families have been reclassified as a result of evidence from cladistics. (1.9)
∑ - A clade is a group of organisms that have evolved from a common ancestor.
∑ - Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.
DNA Base sequences
Amino Acid Sequence of Certain Proteins
Another example comes from immunological studies, which is an way to detect differences in specific proteins of species, indirectly showing how closely two species are related
|Species||% Precipitation with human serum||% Difference from human|
∑ - Sequence differences accumulate gradually so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor.
∑ - Traits can be analogous or homologous.
Example different types of wings or the fins between sharks and dolphins
∑ - Cladograms are tree diagrams that show the most probable sequence of divergence in clades.
β - Application: Cladograms including humans and other primates.
Draw a cladogram containing humans and other primates based on the order listed in the immunological study table above in the previous understanding
∑ - Evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group or species.
β - Application: Reclassification of the figwort family using evidence from cladistics.
Below is a picture of some of the groupings now
β - Skill: Analysis of cladograms to deduce evolutionary relationships.
These are some pictures outlining which part of a cladogram is a clade and another picture I created on ancestry using a cladogram. The red dots are called nodes, and represent the time when two species are estimated to have split.
One thing to note, just because a species like C split earlier than from B, it does not mean that B has evolved more. All the species at the top are present D species. The ones that have died out or changed would be at the nodes.
****Create your own cladogram that contains at least 8 organisms using biochemical evidence such as DNA, Protein similarities or immunological studies. ****
5.2 Natural selection
Essential idea: The diversity of life has evolved and continues to evolve by natural selection.
Nature of science:
Use theories to explain natural phenomena—the theory of evolution by natural selection can explain the development of antibiotic resistance in bacteria. (2.1)
∑ - Natural selection can only occur if there is variation among members of the same species.
∑ - Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
∑ - Adaptations are characteristics that make an individual suited to its environment and way of life.
Adaptations develop over time through natural selection
25 cool adaptations https://www.youtube.com/watch?v=wNqiclBUxdY
Animals in extremes - Mimic Octopus
∑ - Species tend to produce more offspring than the environment can support.
∑ - Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
∑ - Individuals that reproduce pass on characteristics to their offspring.
∑ - Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species.
Video on natural selection https://www.youtube.com/watch?v=aTftyFboC_M
Watch episode 2 of The Cosmos on Natural Selection (Evolution of Dogs)
***Do the data-based questions on page 253***
Applications and skills:
β - Application: Changes in beaks of finches on Daphne Major.
Watch the short film on changes in beak size of the Galapagos finches
Do the evolution in action data analysis and graphing
http://www.hhmi.org/biointeractive/evolution-action-data-analysis from the HHMI
The handout for the data analysis will be handed out in class. (Manage Bac)
β - Application: Evolution of antibiotic resistance in bacteria.
Antibiotic Resistance in Bacteria
***Also do the data-based question on page 255***
• Students should be clear that characteristics acquired during the lifetime of an individual are not heritable. The term Lamarckism is not required.
Theory of knowledge:
• Natural Selection is a theory. How much evidence is required to support a theory and what sort of counter-evidence is required to refute it?
5.1 Evidence for evolution
Essential idea: There is overwhelming evidence for the evolution of life on Earth.
Nature of science
Looking for patterns, trends and discrepancies—there are common features in the bone structure of vertebrate limbs despite their varied use. (3.1)
∑ - Evolution occurs when heritable characteristics of a species change.
∑ - The fossil record provides evidence for evolution.
*** Do data-based questions on page 243***
∑ - Selective breeding of domesticated animals shows that artificial selection can cause evolution.
Some good videos on artificial selection
Belgium Blue cow https://www.youtube.com/watch?v=Nmkj5gq1cQU
Russian domesticated foxes https://www.youtube.com/watch?v=-L58NPPQ5eI
∑ - Evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function.
*** Do data-based questions on page 244***
Woolly Mammoth Cloned? http://dailym.ai/1GQ7hWR
β - Application: Comparison of the pentadactyl limb of mammals, birds, amphibians and reptiles with different methods of locomotion.
Draw and compare the pentadactyl limb for a mammal, bird, amphibian, and a reptile.
|Mammal _______________||Bird _______________||Amphibian _______________||Reptile ______________|
∑ - Populations of a species can gradually diverge into separate species by evolution.
∑ - Continuous variation across the geographical range of related populations matches the concept of gradual divergence.
β - Application: Development of melanistic insects in polluted areas.
Do the peppered moth simulation
***Do data-based questions on page 248-249***
Theory of knowledge:
• Evolutionary history is an especially challenging area of science because experiments cannot be performed to establish past events or their causes.
There are nonetheless scientific methods of establishing beyond a reasonable doubt what happened in some cases. How do these methods compare to those used by historians to reconstruct the past?
5.3 Classification of biodiversity
Nature of science:
Cooperation and collaboration between groups of scientists—scientists use the binomial system to identify a species rather than the many different local names. (4.3)
∑ - The binomial system of names for species is universal among biologists and has been agreed and developed at a series of congresses
The main objectives with regards to using the binomial nomenclature system developed are to:
∑ - When species are discovered they are given scientific names using the binomial system.
Taxonomy - https://www.youtube.com/watch?v=F38BmgPcZ_I
∑ - Taxonomists classify species using a hierarchy of taxa.
∑ - All organisms are classified into three domains.
∑ - The principal taxa for classifying eukaryotes are kingdom, phylum, class, order, family, genus and species.
∑ - In a natural classification, the genus and accompanying higher taxa consist of all the species that have evolved from one common ancestral species.
β - Application: Classification of one plant and one animal species from domain to species level.
Research one plant and one animal example and fill out the table below.
|Taxa||Plant example (__________________)||Animal example (___________________)|
∑ - Taxonomists sometimes reclassify groups of species when new evidence shows that a previous taxon contains species that have evolved from different ancestral species.
Orangutan, as seen in this classification chart on the left, are now in a sub-family of Pongidae. All apes used to belong to the family Pongidae
∑ - Natural classifications help in identification of species and allow the prediction of characteristics shared by species within a group.
Applications and skills:
β - Application: Recognition features of bryophyta, filicinophyta, coniferophyta and angiospermophyta.
|Bryophyta||Mosses/small soft plants/no roots/simple stems and leaves||Non-vascular/no flowers or seeds/produce spores|
|Filicinophyta||Ferns and horsetails/large flat leaves/have stems and roots||Seedless / vascular plant/produce spores|
Conifers/leaves are needles or scale-like leaves/woody stems
|Vascular plants/produce seed cones and seed scales|
|Angiospermophyta||Flowering plants, flowers and fruits with seeds have roots/stems and leaves||Vascular plants/develop ovaries (eggs) and anthers (pollen)|
β - Application: Recognition features of porifera, cnidaria, platylhelmintha, annelida, mollusca, arthropoda and chordata.
|Porifera||Sponges/no mouth or anus||Pores on the surface that suck in water for filter feeding/ no symmetry|
One opening for food and waste
Generally soft accept species of hard corals/ radial symmetry/Tentacles arranged around the mouth (some with stinging cells)
|Platyhelminthes||Soft/no skeleton/flat thin ribbon-like shape/ bilateral symmetry|
Segmented worms such as earthworms and leeches/ segmented internal cavity with the same organs in each segment/mouth and anus
|Mollusca||Snails, bivalves and squid/most have calcium carbonate (CaCO3) shell||Mantle secretes shell/bilateral symmetry/most have radula (hard rasping tongue-like structure) for feeding|
|Arthropoda||Insects and crustaceans/mouth and anus/have a head, thorax and abdomen||Hard exoskeleton made of chitin/bilateral symmetry/ segmented bodies with jointed appendages |
|Chordata|| All the vertebrates and a few non-vertebrate (such as the tunicates - sea squirts) groups, have a mouth and an anus and have a dorsal strengthening structure called a notochord for at least some stage of their lives.||Have a nerve cord lying above the notochord and have a series of pharyngeal slits that open up between the mouth and esophagus|
**Please note that Chordata has a sub-phylum called vertebrata (have a vertebral column) **
β - Application: Recognition of features of birds, mammals, amphibians, reptiles and fish.
|Skin covered in feathers made out of Keratin||Skin has follicles with hair made out of Keratin|
Moist skin, permeable to water
Impermeable skin covered in scales of keratin
|Scales made |
out of bony plates in the
|Lungs ventilated using air sacs, with para-bronchial tubes||Lungs with alveoli, ventilated with ribs and a diaphragm||Simple lungs and moist skin for gas exchange||Lungs with extensive folding (increase SA)||Gills covered by an operculum|
|Pentadactyl Limbs||Pentadactyl Limbs||Pentadactyl Limbs||Pentadactyl Limbs||No limbs|
|Two wings and two legs||Four legs for many, some have two arms/wings and two legs||Adults have four legs||Four legs in most species (some have none)||Fins|
|Internal fertilisation (sperm and egg)||Internal fertilisation (sperm and egg)||External fertilisation with sperm and eggs||Internal fertilisation (sperm and egg)||External fertilisation with sperm and eggs|
|Females lay eggs with hard shells|
Most have live birth and feed young with milk from mammary glands
|Larval stage in water, adult usually on land||Females lay eggs with soft shells||Remain in |
|Beak and no teeth|
Different types of teeth, living core
Eggs coated in protective jelly
|Same type of teeth with no living parts||Swim bladder for buoyancy|
|Maintain constant internal temperature (warm-blooded)||Maintain constant internal temperature (warm-blooded)||Do not maintain an internal body |
|Do not maintain an internal body |
|Do not maintain an internal body |
β - Skill: Construction of dichotomous keys for use in identifying specimens.
Example for the Kingdom Animalia (using some of the characteristics from the above table)
Has bilateral symmetry go to 2
Has radial symmetry go to 3
Has mouth and anus go to 4
Has only one opening for mouth and anus go to 5
Secretes hard exoskeleton made from CaCO3 Stony corals
Soft exoskeleton go to 6
Has segmented body go to 7
No segmentation with mantle Octopus
Has suckers and hooks for attachment Tapeworm
No suckers or hooks Planaria
Move on surface beneath it by an adhesive foot Sea Anemone
Move by propulsion of water Jellyfish
Hard exoskeleton with jointed appendages Scorpion
Soft outer skeleton with bristles Earthworm
• Archaea, eubacteria and eukaryote should be used for the three domains.
• Members of these domains should be referred to as archaeans, bacteria and eukaryotes.
• Students should know which plant phyla have vascular tissue, but other internal details are not required.
• Recognition features expected for the selected animal phyla are those that are most useful in distinguishing the groups from each other and full descriptions of the characteristics of each phylum are not needed.
• Viruses are not classified as living organisms.
• There are international codes of nomenclature and agreements as to the principles to be followed in the classification of living organisms.
Theory of knowledge:
• The adoption of a system of binomial nomenclature is largely due to Swedish botanist and physician Carolus Linnaeus (1707–1778). Linnaeus also defined four groups of humans, and the divisions were based on both physical and social traits. By 21st-century standards, his descriptions can be regarded as racist. How does the social context of scientific work affect the methods and findings of research? Is it necessary to consider the social context when evaluating ethical aspects of knowledge claims?
IB Biology - Curriculum Notes