Unity and Diversity: notes and practice questions
A. Unity and diversity (SL 19 h, HL 33 h). Why living things are alike and why they differ. Water and its hydrogen bonding, nucleic acid structure, cell structure and microscopy, then species, classification and evolution, closing on the biodiversity crisis. Three of the nine subtopics are HL only: origins of cells, viruses, and classification and cladistics. The hard parts are drawing conventions (nucleotides, DNA strands antiparallel but not helical, micrograph annotations with functions) and the difference between a species concept and a species. It is examined with drawing items, micrograph identification, cladogram reading at HL, and a reliable Paper 2 extended response on conservation.
Subtopics
- Practice questionsWater
This topic explores the essential physical and chemical properties of water for life and its role as a habitat. Water molecules are polar due to unequal electron sharing in covalent bonds.
- Practice questionsNucleic Acids
This topic covers the molecular structure of nucleic acids, DNA and RNA, and their fundamental roles in storing and transmitting genetic information. Nucleotides, the monomers of nucleic acids, consist of a phosphate group, a pentose sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base.
- Practice questionsOrigins of CellsHL only
This topic explores plausible hypotheses and evidence for the origin of life and the first cells on early Earth. Early Earth lacked free oxygen and ozone, with higher concentrations of carbon dioxide and methane, leading to spontaneous formation of carbon compounds.
- Practice questionsCell Structure
This topic covers cell theory, the structure of prokaryotic and eukaryotic cells, and microscopy techniques. Cells are the basic structural unit of all living organisms.
- Practice questionsDiversity of Organisms
This topic explores the variation among organisms, species concepts, binomial nomenclature, and genomic diversity. Species are defined as groups of organisms that can breed to produce fertile offspring (biological species concept).
- Practice questionsVirusesHL only
This topic covers the structural features, diversity, life cycles, origins, and rapid evolution of viruses. Viruses are obligate parasites, characterized by small, fixed size, nucleic acid (DNA or RNA) as genetic material, and a protein capsid.
- Practice questionsEvolution and Speciation
This topic covers the mechanisms of evolutionary change, including natural and sexual selection, and the process of speciation. Evolution is defined as a change in the heritable characteristics of a population over time.
- Practice questionsConservation of Biodiversity
This topic covers the definition of biodiversity, its current status, causes of its loss, and various conservation approaches. Biodiversity encompasses ecosystem diversity, species diversity, and genetic diversity.
- Practice questionsClassification and CladisticsHL only
This topic explores the classification of organisms, contrasting traditional taxonomy with cladistics for evolutionary relationships. Classification helps organize immense species diversity; traditional ranks are often arbitrary.
