Glossary: Biological Classification | Biology for Grade 11 PDF Download

Domain: A domain is the highest rank of organisms. The three domains of life are Bacteria, Archaea, and Eukarya.

Kingdom: The Kingdom happens to be the highest classification after domain into which living organisms are grouped. At present, there are five known kingdoms till now.

In Linnaeus' time a Two Kingdom system of classification with Plantae and Animalia kingdoms was developed that included all plants and animals respectively.

Kingdom Monera

Bacteria are the sole members of the Kingdom Monera. They are the most abundant micro-organisms. 

• Archaebacteria: These bacteria are special since they live in some of the most harsh habitats. Archaebacteria differ from other bacteria in having a different cell wall structure and this feature is responsible for their survival in extreme conditions.
• Eubacteria: There are thousands of different eubacteria or ‘true bacteria’. They are characterised by the presence of a rigid cell wall, and if motile, a flagellum.
• Cyanobacteria: The cyanobacteria (also referred to as blue-green algae) have chlorophyll a similar to green plants and are photosynthetic autotrophs.
• Heterocysts: Some of the organisms can fix atmospheric nitrogen in specialised cells called heterocysts, e.g., Nostoc and Anabaena
• Chemosynthetic autotrophic:  Chemosynthetic autotrophic bacteria oxidise various inorganic substances such as nitrates, nitrites and ammonia and use the released energy for their ATP production. They play a great role in recycling nutrients like nitrogen, phosphorous, iron and sulphur.
• Heterotrophic Bacteria: Heterotrophic bacteria are most abundant in nature. The majority are important decomposers. They are helpful in making curd from milk, production of antibiotics, fixing nitrogen in legume roots, etc. Some are pathogens causing damage to human beings, crops, farm animals and pets.
• Mycoplasma: The Mycoplasma are organisms that completely lack a cell wall. They are the smallest living cells known and can survive without oxygen.

Kingdom Protista

All single-celled eukaryotes are placed under Protista, but the boundaries of this kingdom are not well defined that whether its a plant or photosynthetic protistan.

• Diatomaceous earth: Diatoms have left behind large amount of cell wall deposits in their habitat; this accumulation over billions of years is referred to as ‘diatomaceous earth’.
• Pellicle: Instead of a cell wall in Euglenoids, they have a protein rich layer called pellicle which makes their body flexible.
• Plasmodium: Under suitable conditions, slime moulds form an aggregation called plasmodium which may grow and spread over several feet.

Kingdom Fungi

• Hyphae:  fungi are filamentous. Their bodies consist of long, slender thread-like structures called hyphae. 
• Mycelium: The network of hyphae is known as mycelium.
• Coenocytic hyphae: Some hyphae are continuous tubes filled with multinucleated cytoplasm – these are called coenocytic hyphae.
• Saprophytes: Most fungi are heterotrophic and absorb soluble organic matter from dead substrates and hence are called saprophytes.
• Parasites: Fungi that depend on living plants and animals are called parasites.
• Plasmogamy: Fusion of protoplasms between two motile or non-motile gametes called plasmogamy.
• Karyogamy: Fusion of two nuclei called karyogamy.

Kingdom Plantae

• Conidiophores: The asexual spores are conidia produced exogenously on the special mycelium called conidiophores.
• Ascospores: Ascomycetes sexual spores are called ascospores which are produced endogenously in sac like asci (singular ascus).
• Ascocarps: These asci are arranged in different types of fruiting bodies called ascocarps.

Kingdom Animalia

• Imperfect Fungi: Deutromycetes are commonly known as imperfect fungi because only the asexual or vegetative phases of these fungi are known.
• Conidia: The deuteromycetes reproduce only by asexual spores known as conidia.

Viruses, Viroids and Lichens

• Virus: A virus is a nucleoprotein and the genetic material is infectious. In general, viruses that infect plants have single stranded RNA and viruses that infect animals have either single or double stranded RNA or double stranded DNA.
• Capsomere: The protein coat called capsid made of small subunits called capsomeres, protects the nucleic acid.
• Viroids: Infectious agent that was smaller than viruses and caused potato spindle tuber disease. It was found to be a free RNA; it lacked the protein coat that is found in viruses.
• Prions: It Consists of abnormally folded protein. The agent was similar in size to viruses. These agents were called prions.
• Lichens: Lichens are symbiotic associations i.e. mutually useful associations, between algae and fungi. The algal component is known as phycobiont and fungal component as mycobiont, which are autotrophic and heterotrophic, respectively.