Biology notes, chapter 8
Biodiversity
Textbook Biology Form 5 (DLP), pages 142–167
What this chapter covers
- Explain why organisms need a classification system and scientific names (8.1.1)
- Classify organisms into the six kingdoms and state the main features of each (8.1.2, 8.1.3)
- Describe the Linnaeus taxonomic hierarchy and write scientific names using binomial nomenclature (8.1.3, 8.1.4)
- Use a dichotomous key to identify organisms (8.1.5)
- Describe genetic, species and ecosystem diversity (8.2.1)
- Explain what a phylogenetic tree shows and why biodiversity is important and must be conserved (8.2.2, 8.2.3)
- State the main characteristics of bacteria, protozoa, algae, fungi and viruses (8.3.1)
- Describe the roles of microorganisms in the nitrogen cycle, as producers, decomposers, parasites and symbionts (8.3.2, 8.3.3)
- Define pathogens and vectors and explain how pathogens affect human health (8.3.4, 8.3.5)
8.1Classification system and naming of organisms
Biodiversity is the variety of living organisms, such as microorganisms, animals and plants, that interact with one another. Taxonomy is the field of biology that deals with the classification, identification and naming of organisms in an organised way.
| Part of taxonomy | Tool used |
|---|---|
| Classification | Taxonomic hierarchy (based on physical features) |
| Identification | Dichotomous key |
| Naming | Binomial nomenclature system |
A common system lets scientists around the world study and discuss organisms in a systematic way. Carolus Linnaeus is known as the father of taxonomy.
The six kingdoms
Organisms are placed in six kingdoms using three clues: the type of cell, the number of cells and the type of nutrition.
| Kingdom | Cell type | Number of cells | Nutrition | Key features and examples |
|---|---|---|---|---|
| Archaebacteria | Prokaryote | Unicellular | Autotroph or heterotroph | Cell wall without peptidoglycan; lives in very hot, acidic, salty or oxygen-free places (methanogens, halophiles, thermophiles). Halobacterium salinarum |
| Eubacteria | Prokaryote | Unicellular, often in colonies | Autotroph or heterotroph | "True" bacteria; cell wall of peptidoglycan; ribosomes and plasmids but no membrane-bound organelles. Vibrio cholerae |
| Protista | Eukaryote | Unicellular or multicellular | Autotroph, heterotroph or both | Simple cell organisation, no specialised tissue; protozoa, algae and slime mould. Amoeba, Spirogyra |
| Fungi | Eukaryote | Unicellular or multicellular | Heterotroph (saprophyte or parasite) | Cell wall of chitin; body is a mycelium of hyphae. Yeast, mushroom |
| Plantae | Eukaryote | Multicellular | Autotroph (photosynthesis) | Have chlorophyll; sexual or asexual reproduction. Ferns, flowering plants |
| Animalia | Eukaryote | Multicellular | Heterotroph | Most can move and reproduce sexually. Starfish, elephant |
A prokaryote has no membrane-bound nucleus or organelles. A eukaryote has a nucleus and membrane-enclosed organelles. An autotroph makes its own food; a heterotroph obtains food by eating other organisms.
Only Archaebacteria and Eubacteria are prokaryotes. Everything else (Protista, Fungi, Plantae, Animalia) is eukaryotic.
Peptidoglycan (murein) is in the cell wall of Eubacteria. Archaebacteria have cell walls without peptidoglycan.
Whittaker (1969) proposed five kingdoms with Monera as one kingdom. Woese (1990) split Monera into bacteria and archaebacteria, giving six kingdoms, because RNA differs between the two groups.
The Linnaeus hierarchy
From the biggest group to the smallest: domain, kingdom, phylum, class, order, family, genus, species. Going down the hierarchy, the number of organisms in each group decreases and the organisms are more closely related genetically. A species is the smallest group; its members can interbreed to produce viable, fertile offspring.
Memory aid: Do Kings Play Chess On Fine Green Silk.
Example: the brown bearDomain Eukarya, Kingdom Animalia, Phylum Chordata, Class Mammalia, Order Carnivora, Family Ursidae, Genus Ursus, Species Ursus arctos.
Binomial nomenclature
- The scientific name has two words: the genus first, then the species.
- The genus starts with a capital letter; the species starts with a small letter.
- Printed names are in italics. Handwritten, underline each word separately.
ExamplesCommon kingfisher: Alcedo atthis. Paddy: Oryza sativa. Sacred lotus: Nelumbo nucifera. Malayan tiger: Panthera tigris jacksoni (a subspecies).
Writing Oryza Sativa or underlining the whole name as one line. Only the genus has a capital, and each word is underlined separately when handwritten.
Dichotomous key
A dichotomous key identifies organisms using couplets: two contrasting statements at every step. Use features that are obvious, observable and do not overlap. A key can be written as numbered statements or drawn as a branching diagram.
| Couplet | Statement | Go to / answer |
|---|---|---|
| 1a | Animals | 2 |
| 1b | Plants | 6 |
| 6a | Has seeds | 7 |
| 6b | Does not have seeds | Fern |
| 7a | Flowering plant | Hibiscus |
| 7b | Non-flowering plant | Pine tree |
Part of the sample key in textbook Figure 8.4, p. 151.
Using the key above, how is a pine tree identified?
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1b (a plant), then 6a (has seeds), then 7b (non-flowering plant): pine tree.
8.2Biodiversity
| Type | Meaning | Example |
|---|---|---|
| Genetic diversity | Variation of genes within a population and between populations of the same species | Many varieties of cultivated rice |
| Species diversity | Number of species in a community (species richness) and how evenly they are spread (species evenness) | Tropical rainforest: millions of insect species |
| Ecosystem diversity | Variety of biotic communities and ecological processes on land, in the sea and in other aquatic habitats | Ocean, desert, swamp |
No two individuals of the same species are genetically identical. That variation is genetic diversity.
Phylogenetic tree
Phylogeny is the evolutionary history of a group of organisms that are genetically linked. A phylogenetic tree is a diagram of hypotheses about how organisms are related; each branch shows a group diverging from a common ancestor.
Phylogenetic classification often uses homologous structures: body parts with the same basic structure because the animals share an ancestor, even if their functions differ (the limbs of a human, cat, whale and bat have the same bones).
Textbook Figure 8.7, p. 154.
Importance and conservation of biodiversity
- Biodiversity is a source of food, medicine and education, keeps nature in balance, and is used for recreation and scientific research.
- In situ conservation keeps species in their natural habitat, e.g. national parks, permanent forest reserves, the Sepilok orangutan rehabilitation centre.
- Ex situ conservation keeps species outside their natural habitat, e.g. zoos and botanical gardens.
- Threats to biodiversity: deforestation, illegal hunting, water pollution, and tourism that exploits biodiversity.
A tiger is kept in a zoo and another lives in a national park. Which one is in situ conservation?
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The tiger in the national park, because it stays in its natural habitat. The zoo is ex situ.
8.3Microorganisms and viruses
Microorganisms are too small to see with the naked eye. They include bacteria, protozoa, algae, fungi and viruses.
| Group | Main characteristics |
|---|---|
| Bacteria | No nucleus; DNA free in the cytoplasm as a nucleoid; some have plasmids. 1 to 10 µm long. Shapes: coccus (sphere), vibrio (comma), bacillus (rod), spirillum (spiral) |
| Protozoa | Animal-like and unicellular; move by pseudopodia (Amoeba), cilia (Paramecium) or flagellum (Euglena); mostly aquatic; free-living or parasitic; Euglena has chloroplasts |
| Algae | Unicellular (Chlamydomonas) or multicellular (Fucus); have chloroplasts so are autotrophs; no true roots, stems or leaves; live in ponds, lakes and the sea |
| Fungi | No chlorophyll, so heterotrophs (parasites or saprophytes); chitin cell wall; hyphae form a mycelium; found in dark, moist places and on dead organisms. Yeast is unicellular, Mucor is multicellular |
| Viruses | Not cellular and not in any kingdom; nucleic acid (DNA or RNA) in a protein capsid; 20 to 400 nm, seen only with an electron microscope; reproduce only inside host cells. Examples: tobacco mosaic virus, T4 bacteriophage, HIV |
Saying a virus is a bacterium or a "small cell". A virus has no cell structure and carries out no life processes outside a host cell.
Roles of microorganisms
Nitrogen cycle
Textbook Figure 8.14, p. 159.
| Process | What happens | Microorganism |
|---|---|---|
| Nitrogen fixation | N2 from the air becomes ammonium ions (NH4+) | Rhizobium (legume root nodules), Azotobacter (free-living) |
| Ammonification | Protein in dead organisms and waste becomes ammonium ions | Decomposers (bacteria, saprophytic fungi) |
| Nitrification (1) | Ammonium to nitrite (NO2−) | Nitrosomonas |
| Nitrification (2) | Nitrite to nitrate (NO3−) | Nitrobacter |
| Denitrification | Nitrate to nitrogen gas | Denitrifying bacteria |
Lightning and industrial fertilisers also add usable nitrogen to the soil. Plants absorb nitrates to make protein; animals get nitrogen by eating plants.
Other roles
- Producers: phytoplankton (green algae, cyanobacteria, dinoflagellates, diatoms) photosynthesise and start aquatic food chains.
- Decomposers: saprophytic fungi and bacteria secrete digestive enzymes onto dead matter and absorb the products, returning carbon, nitrogen and sulphur to the soil.
- Parasites: the parasite benefits while the host is harmed. Most parasites do not kill the host, because they depend on it. Plasmodium causes malaria.
- Symbionts: live in close association with a host. An ectosymbiont lives outside host cells (ectomycorrhiza on roots); an endosymbiont lives inside (Trichonympha in termites).
Pathogens and vectors
A pathogen is an organism that causes disease (viruses, bacteria, protozoa, fungi). A vector is an organism that transmits a pathogen.
| Vector | Pathogen | Disease |
|---|---|---|
| Housefly (Musca domestica) | Bacterium Vibrio cholerae | Cholera |
| Aedes aegypti mosquito | Dengue virus | Dengue |
| Cockroach (Periplaneta americana) | Bacterium Salmonella typhi | Typhoid |
| Pathogen | Example of disease | Symptoms |
|---|---|---|
| Virus | Hepatitis B | Liver inflammation, skin and eyes turn yellowish, may be fatal |
| Bacteria | Tuberculosis | Weight loss, coughing blood, shortness of breath |
| Protozoa | Dysentery | Stomach ache, diarrhoea, vomiting |
| Fungi | Tinea versicolour | Whitish or pinkish patches on the skin |
Pathogens harm health by damaging cells, disturbing cell functions or releasing toxins.
In Malaysia, scientists inject Wolbachia bacteria into the eggs of Aedes aegypti to curb the growth of the dengue virus in the mosquitoes.
Name the vector and the pathogen for dengue.
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Vector: Aedes aegypti mosquito. Pathogen: dengue virus.