Biological Classification

This chapter covers classification systems, five kingdom classification, Monera, Protista, Fungi, Plantae, Animalia, viruses, viroids, lichens, tables, and flow diagrams.

Chapter overview

Biological classification is the scientific arrangement of organisms into groups based on similarities, differences, and evolutionary relationships.

1. Need for classification

Classification helps to:

• study enormous biodiversity,
• identify organisms,
• understand relationships,
• organise information,
• trace evolutionary history.

2. Early classification systems

Aristotle classified organisms into plants and animals.

Plants were grouped into:

• herbs,
• shrubs,
• trees.

Animals were grouped based on habitat:

• aquatic,
• terrestrial,
• aerial.

Limitation: artificial characters were used.

3. Two kingdom classification

Linnaeus proposed:

Limitations:

• Prokaryotes and eukaryotes were grouped together.
• Unicellular and multicellular organisms were grouped together.
• Photosynthetic and non-photosynthetic organisms were not properly separated.
• Fungi were placed with plants.

4. Five kingdom classification

R.H. Whittaker proposed five kingdom classification.

Criteria:

• cell structure,
• body organisation,
• mode of nutrition,
• reproduction,
• phylogenetic relationships.

5. Comparison of five kingdoms

6. Kingdom Monera

Monera includes bacteria and cyanobacteria.

Features:

• prokaryotic,
• unicellular,
• no true nucleus,
• no membrane-bound organelles,
• cell wall usually present.

Bacterial shapes:

Nutrition in bacteria:

• autotrophic,
• heterotrophic,
• chemosynthetic,
• photosynthetic.

7. Archaebacteria

Archaebacteria live in extreme environments.

Types:

Methanogens produce methane:

$$CO_2+4H_2\rightarrow CH_4+2H_2O$$

8. Kingdom Protista

Features:

• unicellular,
• eukaryotic,
• mostly aquatic,
• some have cilia or flagella.

Groups:

• chrysophytes,
• dinoflagellates,
• euglenoids,
• slime moulds,
• protozoans.

9. Kingdom Fungi

Features:

• eukaryotic,
• heterotrophic,
• absorptive nutrition,
• cell wall made of chitin,
• body made of hyphae,
• network of hyphae is mycelium.

$$\text{Hyphae} \rightarrow \text{Mycelium} \rightarrow \text{Fungal body}$$

Types:

10. Kingdom Plantae

Features:

• eukaryotic,
• multicellular,
• cell wall present,
• chlorophyll present,
• photosynthetic.

General photosynthesis equation:

$$6CO_2+6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6+6O_2$$

11. Kingdom Animalia

Features:

• eukaryotic,
• multicellular,
• no cell wall,
• heterotrophic,
• holozoic nutrition,
• usually motile.

12. Viruses

Viruses are acellular infectious agents.

They contain:

• nucleic acid,
• protein coat called capsid.

Genetic material may be:

$$DNA\quad\text{or}\quad RNA$$

Viruses are obligate parasites.

13. Viroids

Viroids are smaller than viruses and consist of free RNA without protein coat.

14. Lichens

Lichen is a symbiotic association between algae and fungi.

$$\text{Lichen} = \text{Algae} + \text{Fungus}$$

Algal partner:

$$\text{phycobiont}$$

Fungal partner:

$$\text{mycobiont}$$

15. Solved/example questions

Example 1

Why were fungi separated from plants?

Because fungi:

• lack chlorophyll,
• are heterotrophic,
• have chitinous cell wall,
• store food as glycogen.

Example 2

Why are viruses considered living and non-living?

Living character:

• reproduce inside host.

Non-living character:

• inert outside host,
• can be crystallised.

16. Common mistakes

• Placing fungi under plants.
• Confusing bacteria and viruses.
• Forgetting Monera is prokaryotic.
• Forgetting Protista is eukaryotic and mostly unicellular.
• Calling viruses cellular organisms.
• Confusing phycobiont and mycobiont.

17. Quick revision