AQA GCSE (9-1) Biology: Classification of Living Organisms

Key Takeaways for Classification of Living Organisms

1. Linnaeus’s Binomial System

• Definition: A two-part naming system for organisms (Genus + species).
  • Example: Homo sapiens (humans), Panthera leo (lion).
• Rules for Writing Binomial Names:
  • Genus: Capitalised and italicised (e.g., Panthera).
  • Species: Lowercase and italicised (e.g., leo).
  • Shortened form: After first mention, abbreviate the genus (e.g., P. leo).
  • ✘ Common Mistakes: Writing in plain text, incorrect capitalisation (e.g., panthera leo).

2. Hierarchical Classification System

• Order: Kingdom → Phylum → Class → Order → Family → Genus → Species.
  • Mnemonic: “Keeping Precious Creatures Organised For Grumpy Scientists”.
• Example Classification for Humans:
  • Kingdom: Animalia → Phylum: Chordata → Class: Mammalia → Order: Primates → Family: Hominidae → Genus: Homo → Species: sapiens.

3. Five Kingdoms vs. Three Domains

• Traditional Five Kingdoms:
  1. Animals (e.g., gorillas).
  2. Plants (e.g., orchids).
  3. Fungi (e.g., honey fungus).
  4. Protists (e.g., Plasmodium).
  5. Prokaryotes (e.g., E. coli).
• Carl Woese’s Three Domains (based on DNA/RNA):
  1. Eukaryota (animals, plants, fungi, protists).
  2. Bacteria (e.g., E. coli).
  3. Archaea (extremophiles, e.g., methanogens).
• Key Difference: Domains reflect evolutionary relationships, not just physical traits.

4. Species Definition & Exceptions

• Species: Group of organisms that can interbreed to produce fertile offspring.
  • Example: Lions (Panthera leo) and tigers (Panthera tigris) can mate but produce infertile ligers → different species.
  • Exception: Some hybrids (e.g., salamanders) can be fertile.

5. Evolutionary Trees & DNA Evidence

• Purpose: Show evolutionary relationships and common ancestry.
  • Example: Figure 17.4 shows humans share a common ancestor with chimpanzees.
• Why DNA > Anatomy?
  • DNA provides objective evidence (e.g., Boloceroides daphneae reclassified as Relicanthus after DNA analysis).

6. Common Exam Tips

• Interpreting Diagrams:
  • Closer branches = closer evolutionary relationships (e.g., wolves and dogs share the genus Canis).
• Answering “Why Use Binomial Names?”:
  • Avoid confusion from regional/common names (e.g., “daddy longlegs” refers to different species in the UK/US).
• Describing Classification Changes:
  • Mention technological advances (e.g., microscopes, genome sequencing) and new evidence.

7. Key Examples to Remember

• Linnaeus’s Errors: Classified whales as fish (now mammals).
• Extinct Homo Species: Homo erectus, Homo neanderthalensis.
• Panthera Genus: Lion (P. leo), Tiger (P. tigris), Jaguar (P. onca), Leopard (P. pardus), Snow Leopard (P. uncia).

8. Practice Question Tackling

• Example Question: “Why do scientists use DNA evidence over anatomy?”
  • Answer Structure:
    1. DNA is less subjective than physical traits.
    2. Reveals evolutionary links (e.g., Relicanthus reclassification).
    3. Anatomy can be misleading (e.g., convergent evolution).

Equation for Hierarchy:
Kingdom→Phylum→Class→Order→Family→Genus→SpeciesKingdom→Phylum→Class→Order→Family→Genus→Species

Revision Tip: Use flashcards to memorise hierarchy order and binomial rules!

50 GCSE Questions on Classification of Living Organisms

Section A: Linnaeus & Binomial Classification

1. Who developed the binomial classification system?
2. What are the two parts of a binomial name?
3. Write the binomial name for humans using correct formatting.
4. How should binomial names be written (italicised, capitalisation)?
5. Why is Panthera leo shortened to P. leo after its first mention?
6. Name the five species in the Panthera genus.
7. Which organism has the same common and binomial name?
8. What mistake did Linnaeus make regarding whales?
9. Name the book Linnaeus published in 1735.
10. What were Linnaeus’s original three kingdoms?

Section B: Hierarchical Classification

11. List the hierarchy of classification from kingdom to species.
12. What is the mnemonic for remembering this hierarchy?
13. To which order do humans belong?
14. Name the class that includes gorillas and dogs.
15. Which taxonomic level is broader: family or genus?
16. Classify a polar bear (Ursus maritimus) into its kingdom, phylum, and class.
17. What is the genus of the skunk (Mephitis mephitis)?
18. Which two species belong to the Canis genus in Figure 17.11?
19. What is the common name for Lutra lutra?
20. Which taxonomic level includes both mammals and reptiles?

Section C: Kingdoms & Domains

21. List the five kingdoms used in modern classification.
22. Which kingdom does Escherichia coli belong to?
23. Name a feature of plant cells that distinguishes them from animal cells.
24. What are the three domains proposed by Carl Woese?
25. Why are viruses not classified into any kingdom?
26. Which domain includes extremophiles like methanogens?
27. Give an example of a protist.
28. What technique did Woese use to develop his three-domain system?
29. Why did Woese’s system replace the five-kingdom model?
30. Which domain do humans belong to?

Section D: Species & Hybrids

31. Define the term “species”.
32. Explain why ligers (lion-tiger hybrids) do not contradict this definition.
33. Give an example of a hybrid that can produce fertile offspring.
34. Why was Boloceroides daphneae reclassified as Relicanthus daphneae?
35. What is the main problem with using anatomy alone to classify species?
36. Why might two organisms with similar anatomy belong to different species?
37. Name two extinct species in the Homo genus.
38. Are Neanderthals (Homo neanderthalensis) the same species as humans? Explain.

Section E: Evolutionary Trees & DNA Evidence

39. What does an evolutionary tree show?
40. In Figure 17.4, which primate shares the closest ancestor with humans?
41. How does DNA evidence improve classification accuracy?
42. What does “16S ribosomal RNA” refer to in Woese’s work?
43. Why might organisms in the same genus have different species names?
44. Interpret Figure 17.11: Which species is most closely related to the European otter?
45. Which species in Figure 17.11 is the most distantly related to the leopard?

Section F: Application & Analysis

46. A student writes “salmonella enterica”. Correct the formatting.
47. Gallus gallus is a binomial name. What type of organism is it?
48. Explain why binomial names avoid confusion compared to common names.
49. Design a binomial name for a toad with spiral markings using Table 17.3.
50. Why might classification systems change over time?

Detailed Answers

1. Carl Linnaeus.
2. Genus (capitalised) and species (lowercase).
3. Homo sapiens.
4. Italicised (or underlined if handwritten); genus capitalised, species lowercase.
5. To avoid repetition; genus is abbreviated after the first mention.
6. Lion (P. leo), Tiger (P. tigris), Jaguar (P. onca), Leopard (P. pardus), Snow Leopard (P. uncia).
7. Boa constrictor.
8. Classified whales as fish (they are mammals).
9. Systema Naturae.
10. Animal, Plant, Mineral (minerals no longer used).
11. Kingdom → Phylum → Class → Order → Family → Genus → Species
    Kingdom→Phylum→Class→Order→Family→Genus→SpeciesKingdom→Phylum→Class→Order→Family→Genus→Species
12. “Keeping Precious Creatures Organised For Grumpy Scientists”.
13. Primates.
14. Mammalia.
15. Family.
16. Kingdom: Animalia; Phylum: Chordata; Class: Mammalia.
17. Mephitis.
18. Wolf (Canis lupus) and Domestic dog (Canis familiaris).
19. European otter.
20. Phylum (e.g., Chordata).
21. Animals, Plants, Fungi, Protists, Prokaryotes.
22. Prokaryotes.
23. Cell walls (cellulose) and chloroplasts.
24. Eukaryota, Bacteria, Archaea.
25. Viruses are not considered living organisms.
26. Archaea.
27. Plasmodium falciparum (causes malaria).
28. 16S ribosomal RNA analysis.
29. DNA evidence showed deeper evolutionary relationships.
30. Eukaryota.
31. Group of organisms that can interbreed to produce fertile offspring.
32. Ligers are infertile → parents remain distinct species.
33. Some salamanders (e.g., Figure 17.6).
34. DNA analysis showed it was not a sea anemone.
35. Anatomy can be misleading due to convergent evolution.
36. They cannot interbreed to produce fertile offspring.
37. Homo erectus, Homo neanderthalensis.
38. No; they are a separate species (cannot produce fertile offspring with H. sapiens).
39. Evolutionary relationships and common ancestry.
40. Chimpanzees.
41. DNA provides objective, genetic evidence of relatedness.
42. A conserved RNA region used to compare evolutionary divergence.
43. They share a genus but have distinct traits preventing interbreeding.
44. B: Skunk (Mephitis mephitis) – same family (Mustelidae).
45. C: Dog (Canis familiaris) – different family (Canidae vs. Felidae).
46. Salmonella enterica (italicised, genus capitalised).
47. Chicken (Gallus gallus).
48. Common names vary regionally; binomial names are universal.
49. Bufo helix (genus Bufo + species helix for spiral).
50. New evidence (e.g., DNA) and technological advancements.