Biological Classification

Since the earliest times, people have tried to classify living organisms. Aristotle classified plants as trees, shrubs and herbs. Linnaeus later used a two-kingdom system of Plantae and Animalia, which failed to separate prokaryotes from eukaryotes, unicellular from multicellular organisms, or photosynthetic from non-photosynthetic forms. In 1969, R.H. Whittaker proposed the five-kingdom classification: Monera, Protista, Fungi, Plantae and Animalia. Its main criteria were cell structure, body organisation, mode of nutrition, reproduction and phylogenetic relationships. This chapter studies the first three kingdoms in detail, beginning with Monera: archaebacteria such as methanogens and halophiles, and eubacteria, including cyanobacteria like Nostoc and Anabaena, and mycoplasma. You will then study kingdom Protista: chrysophytes (diatoms and desmids), dinoflagellates, euglenoids, slime moulds and protozoans such as Amoeba, Trypanosoma, Paramoecium and Plasmodium. In kingdom Fungi you will learn the features of Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes, with examples like Rhizopus, Penicillium, Agaricus and Puccinia. The chapter ends with acellular forms that do not fit the system: viruses, viroids and prions, and the symbiotic associations called lichens.

Detailed Worksheet: Biological Classification Section A - Definitions (10 marks) 1. Who proposed the five-kingdom classification? Name the five kingdoms. (2 marks) 2. What are heterocysts? Name an organism that has them. (2 marks) 3. What is diatomaceous earth? How is it formed? (2 marks) 4. What are viroids? Who discovered them? (2 marks) 5. What are lichens? Name the two partners. (2 marks) Section B - Calculations and Applications (15 marks) 6. A bacterium divides by binary fission every 20 minutes. Starting with one cell, calculate the number of cells after 3 hours. How many cells would there be after 4 hours if no limitation of food or space occurred? (3 marks) 7. A culture starts with 500 bacteria and the number doubles every 30 minutes. Calculate the number after 2.5 hours. Express your answer as 500 x 2^n. (3 marks) 8. A sample of 200 microorganisms contained 80 cyanobacteria, 50 diatoms, 40 protozoans and 30 fungal spores. Calculate the percentage of prokaryotes and eukaryotes in the sample. To which kingdoms do they belong? (3 marks) 9. Tabulate in words the kingdom, cell type, nutrition and one example for: Nostoc, Euglena, Penicillium, Plasmodium, Agaricus. (3 marks) 10. A slime mould plasmodium spreads over 10 square cm and doubles its area every 2 days. Calculate its area after 8 days. Under what conditions does it form fruiting bodies? (3 marks) Section C - Diagrams (10 marks) 11. Draw labelled diagrams of the different shapes of bacteria: coccus, bacillus, vibrio and spirillum. (4 marks) 12. Draw a labelled diagram of a bacteriophage. (3 marks) 13. Draw labelled diagrams of Euglena and Paramoecium. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Explain the limitations of the two-kingdom classification and how Whittaker's five-kingdom system overcame them. What are the limitations of the five-kingdom system? (5 marks) 15. Compare the four classes of fungi on the basis of mycelium, spores and sexual reproduction, with examples. Why are Deuteromycetes called imperfect fungi? (5 marks) 16. 'Viruses are not considered truly living.' Discuss this statement with reference to their structure and properties. How do viroids and prions differ from viruses? (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Draw diagrams neatly with labels. Show the steps of calculations.