Living World: diversity, adaptation, and organization of living things
This domain tests the organization of living things, cell structure, classification, and how adaptations help organisms survive. Expect questions comparing prokaryotic and eukaryotic cells, plant and animal cells, taxonomic groups, and structural, behavioural, or physiological adaptations.
Cells and organization
All living things are made of cells. Prokaryotic cells lack a membrane-bound nucleus; eukaryotic cells have a nucleus and organelles. Plant cells have a cellulose cell wall, chloroplasts, and a large central vacuole; animal cells lack a cell wall and chloroplasts. Levels of organization run from cell to tissue, organ, organ system, and organism. Organelles have specific roles: mitochondria release energy from glucose, chloroplasts carry out photosynthesis, and the nucleus contains DNA.
Diversity and classification
Taxonomy groups organisms by shared characteristics. The hierarchy is domain, kingdom, phylum, class, order, family, genus, species. A dichotomous key uses paired choices to identify organisms. Biodiversity includes variation within species, between species, and among ecosystems. Scientific names use genus and species, with the genus capitalized.
Adaptation and evolution
An adaptation is an inherited trait that improves survival or reproduction in a particular environment. Structural adaptations are body features, behavioural adaptations are actions, and physiological adaptations are internal processes. Natural selection acts on existing variation: individuals with advantageous traits reproduce more, and allele frequencies can change over generations. Acclimatization is a short-term adjustment, not an inherited adaptation.
Worked example
A cell has a nucleus, mitochondria, and a rigid outer layer but no chloroplasts. It is eukaryotic because it has a nucleus and mitochondria. The rigid layer is a cell wall, so the cell is not an animal cell; because it lacks chloroplasts, it is more likely a fungal cell than a typical plant cell. Reasoning from presence and absence of structures is safer than guessing from shape alone.
Traps
- Saying all eukaryotes are multicellular; many are unicellular.
- Placing cell wall or chloroplasts in animal cells.
- Confusing adaptation with acclimatization.
- Mixing up the order of taxonomic ranks.
- Treating a dichotomous key as a food web or classification tree.