The shape of the lesson
By the end of the lesson, learners can
- What counts as a species?: Switch between the biological, morphological and ecological concepts.
- Three domains and a hierarchy: Click Bacteria, Archaea and Eukarya in turn and read how they differ.
- Four kingdoms, and the viruses: On the kingdoms chip, click each organism to read its kingdom's features.
- Biological species: interbreed to give fertile offspring.
- Archaea vs Bacteria: membrane lipids, rRNA, cell walls (no peptidoglycan in Archaea).
- Ranks: kingdom, phylum, class, order, family, genus, species.
- Viruses: DNA or RNA, single- or double-stranded; no domain.
One picture every idea returns to
A species can be defined in more than one way: by the ability to interbreed to produce fertile offspring (biological), by shared physical features (morphological) or by a shared ecological niche (ecological). All cellular life is placed in three domains: Bacteria and Archaea, which are both prokaryotes but differ in their membrane lipids, ribosomal RNA and cell wall composition, and Eukarya. Eukaryotes are classified into a hierarchy of kingdom, phylum, class, order, family, genus and species, with four kingdoms: Protoctista, Fungi, Plantae and Animalia. Viruses are not in any domain; they are classified by whether their nucleic acid is DNA or RNA and whether it is single-stranded or double-stranded.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Putting every organism in its place.. Before you can count biodiversity you need to know what counts as a species and where it belongs. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: What counts as a species? | Switch between the biological, morphological and ecological concepts. Project tab 1 of the lab (Biodiversity lab, species concepts) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Three domains and a hierarchy | Click Bacteria, Archaea and Eukarya in turn and read how they differ. Project tab 2 of the lab (Biodiversity lab, domains and the taxonomic hierarchy) and let a student drive it while the class predicts. | Pairs |
| 21 to 30 min | Teach and check: Four kingdoms, and the viruses | On the kingdoms chip, click each organism to read its kingdom's features. Project tab 3 of the lab (Biodiversity lab, kingdoms and viruses) and let a student drive it while the class predicts. | Rally Robin |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 16 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Four kingdoms, and the viruses, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Rally Robin
Pairs take turns to say one item each, back and forth: a definition, a unit, a step of the method. Keep it fast and oral; the point is retrieval, not writing.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Producing offspring is not enough for the biological species concept: the offspring must be fertile. | A horse and a donkey produce a mule, but the mule is infertile, so they are two species. |
| Archaea are not a kind of bacteria, even though both are prokaryotes. | They are a separate domain with different membrane lipids, different rRNA and no peptidoglycan in their cell walls. |
Species, domains and kingdoms: worksheet
6 questions, 16 marks. Written in the style of the papers; no past paper question is reproduced.
Discuss the meaning of the term species, comparing the biological and morphological species concepts.
State three differences between organisms in the domain Archaea and organisms in the domain Bacteria.
The bottlenose dolphin is Tursiops truncatus. It is in the family Delphinidae, the order Cetacea and the class Mammalia. Name the two ranks above class in its classification, and the rank shown by Tursiops.
An organism is multicellular, has cell walls, no chloroplasts, stores glycogen and is made of thread-like structures. Identify its kingdom and explain how two of these features rule out the kingdoms Plantae and Animalia.
Explain why viruses are not classified into one of the three domains, and outline how they are classified.
Outline the characteristic features of the kingdom Protoctista and give two examples.
Answer key and marking notes
- Biological: a group of organisms that can interbreed to produce fertile offspring and is reproductively isolated from other groups.
- Morphological: a group of organisms sharing the same observable physical / anatomical features; can be used for fossils and asexual organisms.
- Limitation of biological: cannot be applied to fossils, asexual organisms or populations that never meet; limitation of morphological: look-alike species, or great variation within one species (for example male and female).
- Membrane lipids: Archaea have branched chains joined by ether bonds; Bacteria have unbranched fatty acids joined by ester bonds.
- Ribosomal RNA: the base sequences of rRNA differ (archaeal rRNA is more similar to eukaryotic rRNA).
- Cell walls: Bacteria contain peptidoglycan; Archaea do not.
- Above class: phylum (Chordata), then kingdom (Animalia); the domain is Eukarya.
- Tursiops is the genus.
- Kingdom Fungi (hyphae / mycelium).
- It has cell walls, so it is not in Animalia (animal cells have no cell walls).
- It has no chloroplasts and stores glycogen rather than starch, so it is not in Plantae.
- Viruses are not cells: they have no cytoplasm, ribosomes or metabolism of their own, so they do not fit any domain of cellular life.
- They are classified by their nucleic acid: DNA or RNA, and whether it is single-stranded or double-stranded (for example HIV has single-stranded RNA).
- Eukaryotic organisms that do not fit into Fungi, Plantae or Animalia.
- Mostly unicellular, some multicellular (for example seaweeds), with no differentiated tissues; some photosynthesise, others are heterotrophic.
- Examples: Amoeba, Plasmodium, Paramecium, algae such as Chlorella.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which statement is the ecological species concept?
- Aa species is a group of organisms that share the same ecological niche
- Ba species is a group of organisms that interbreed to produce fertile offspring
- Ca species is a group of organisms that share the same observable features
- Da species is a group of organisms that live in the same habitat
Which rank in the taxonomic hierarchy lies directly between order and genus?
- Afamily
- Bclass
- Cphylum
- Dspecies
Organisms in which kingdom have cell walls made of chitin and feed by secreting enzymes and absorbing the products?
- AFungi
- BPlantae
- CProtoctista
- DAnimalia
A virus has a genome of one strand of RNA. How is it classified?
- Aas a single-stranded RNA virus, outside the three domains
- Bas a single-stranded RNA virus in the domain Bacteria
- Cas a prokaryote in the domain Archaea
- Das a member of the kingdom Protoctista
Which feature is shared by organisms in the domains Bacteria and Archaea?
- Athey are prokaryotes with no nucleus
- Btheir cell walls contain peptidoglycan
- Ctheir membrane lipids have ether bonds
- Dtheir rRNA sequences are identical
Use the description of organism X to decide where it should be classified.
- Adomain Archaea
- Bdomain Bacteria
- Cdomain Eukarya
- Dkingdom Protoctista
Two populations of frogs look identical. When they are brought together they mate, but the eggs never develop. What does this show?
- Athey are separate biological species despite being morphologically the same
- Bthey are one species, because they look the same and can mate
- Cthey are one species under the biological concept but two under the morphological
- Dthey are separate species because they share the same ecological niche
Sequencing shows that the rRNA of Archaea is more similar to that of eukaryotes than to that of Bacteria. Which conclusion is best supported?
- AArchaea share a more recent common ancestor with Eukarya than with Bacteria
- BArchaea evolved from eukaryotes by losing their nucleus
- CArchaea should be placed in the kingdom Protoctista
- DArchaea and Bacteria should be combined into one domain
Quiz key
The ecological species concept defines a species by its niche: its role, food, habitat and interactions. Interbreeding to give fertile offspring is the biological concept, and shared observable features is the morphological concept. Living in the same habitat is not enough: many species share a habitat but occupy different niches.
The order is kingdom, phylum, class, order, family, genus, species, so family lies between order and genus. Class and phylum are above order, and species is below genus.
Fungi have chitin walls and are heterotrophs that digest food outside their hyphae and absorb it. Plants have cellulose walls and photosynthesise. Protoctists are a varied group, many without chitin walls. Animals have no cell walls and usually ingest food.
Viruses are classified by the type of nucleic acid (DNA or RNA) and whether it is single- or double-stranded, so this is a single-stranded RNA virus. Viruses are not cells, so they are not placed in any domain or kingdom; Bacteria, Archaea and Protoctista all contain cellular organisms.
Both domains are prokaryotes, without a nucleus or membrane-bound organelles. Only Bacteria have peptidoglycan walls; only Archaea have ether-linked membrane lipids; and their rRNA sequences differ, which is one of the main reasons they are separate domains.
No nucleus and 70S ribosomes make X a prokaryote, ruling out Eukarya and the kingdom Protoctista, which is part of Eukarya. Ether-linked, branched membrane lipids and a wall without peptidoglycan are features of Archaea, not Bacteria. Many Archaea also live in extreme habitats such as very salty lakes, but the habitat alone would not decide it.
The biological concept needs fertile offspring; here no offspring develop, so the populations are reproductively isolated and are separate species. The morphological concept would wrongly group them because they look identical, so the third option has the concepts reversed. Mating alone is not enough, and sharing a niche would not make them separate species.
The more similar the rRNA sequences, the more recently the groups diverged, so Archaea and Eukarya share a more recent common ancestor. That does not mean Archaea evolved from eukaryotes. They remain prokaryotes, so they are not protoctists, and the rRNA difference is a reason to keep them separate from Bacteria, not to combine them.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.