Biological Classification

Biological classification is the scientific process of grouping organisms into groups and subgroups based on their similarities and differences.

Historical Classification Systems:

• Aristotle’s Classification: Divided organisms into plants (herbs, shrubs, trees) and animals (with or without red blood).
• Linnaeus’ Two-Kingdom System: Classified organisms into Plantae (plants) and Animalia (animals).

Modern Classification Systems:

• Whittaker’s Five-Kingdom System: Divided organisms into Monera (prokaryotes), Protista (unicellular eukaryotes), Fungi, Plantae (plants), and Animalia (animals).
• Carl Woese’s Three-Domain System: Classified organisms into Bacteria, Archaea (extremophiles), and Eukarya (eukaryotes).

Taxonomic Hierarchy:

The hierarchical arrangement of taxonomic categories is as follows:

• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

Characteristics Used for Classification:

• Cell structure: Prokaryotes vs. eukaryotes
• Mode of nutrition: Autotrophic vs. heterotrophic
• Body organization: Unicellular vs. multicellular
• Mode of reproduction: Asexual vs. sexual

Key Terms:

• Taxonomy: The science of classification.
• Binomial nomenclature: The system of naming organisms using a two-word Latin name (genus and species).
• Taxonomic key: A tool used to identify organisms based on their characteristics.

Exercise

1. Discuss how classification systems have undergone several changes over a period of time? 

Ans : 

Classification systems have evolved due to:

• Technological advancements (microscopes, DNA sequencing)
• New discoveries of species
• Changing understanding of evolution
• International collaboration

Historical highlights:

• Aristotle’s two-kingdom system
• Linnaeus’ two-kingdom system
• Whittaker’s five-kingdom system
• Woese’s three-domain system

Modern trends:

• Cladistics
• Molecular phylogeny
• Phylogenomic analysis

2. State two economically important uses of: 

(a) heterotrophic bacteria (b) archaebacteria

Ans : 

(a) Heterotrophic Bacteria

1. Bioremediation: Heterotrophic bacteria can degrade pollutants like oil spills, heavy metals, and organic contaminants, making them valuable in environmental cleanup efforts.
2. Food Production: Bacteria are essential in food production, such as:
   • Fermentation of dairy products (yogurt, cheese)
   • Production of fermented foods (pickles, sauerkraut)
   • Production of fermented beverages (beer, wine)

(b) Archaebacteria

1. Extremophiles in Biotechnology: Archaebacteria that thrive in extreme conditions (e.g., high temperatures, salinity, pH) are useful in biotechnology applications, such as:
   • Production of enzymes for industrial processes
   • Development of biofuels
   • Production of pharmaceuticals
2. Mineral Extraction: Archaebacteria can be used to extract minerals from low-grade ores, contributing to the mining industry.

3. What is the nature of cell-walls in diatoms?

Ans : 

Diatoms have cell walls composed of silica. This silica-rich wall is known as a frustule. The frustule is intricately patterned and provides structural support, protection, and a unique shape to diatoms.

The frustule is divided into two halves, called valves, that fit together like a petri dish. The patterns on the frustule can vary widely among different species of diatoms, making them a popular subject for microscopy and identification.

4. Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.

Ans : 

Algal Bloom and Red-Tides are terms used to describe excessive growth of algae in aquatic environments.

• Algal Bloom: This refers to a rapid increase in the population of algae in a body of water. Algal blooms can occur in various aquatic environments, including oceans, lakes, and ponds. While many algal blooms are harmless, some can produce toxins that are harmful to aquatic life and humans.
• Red-Tide: This is a specific type of algal bloom caused by dinoflagellates, a type of microscopic algae. Red-tides are often characterized by a reddish discoloration of the water due to the presence of these algae. Red-tides can also produce toxins that can harm marine life and humans.

5. How are viroids different from viruses?

Ans : 

Viroids and viruses are both extremely small infectious agents, but they differ in several key ways:

1. Genetic Material:
   • Viroids: Consist solely of a single-stranded RNA molecule, devoid of any protein coat.
   • Viruses: Typically composed of a protein coat (capsid) surrounding a genetic core, which can be either DNA or RNA.
2. Size:
   • Viroids: Are significantly smaller than most viruses, often measuring only a few hundred nucleotides in length.
   • Viruses: Can vary in size, but are generally larger than viroids.
3. Replication:
   • Viroids: Replicate independently within their host cells, utilizing the host’s machinery.
   • Viruses: Require the host cell’s machinery to replicate their genetic material and assemble new virus particles.
4. Diseases:
   • Viroids: Primarily cause plant diseases, such as potato spindle tuber disease and citrus exocortis disease.
   • Viruses: Can infect a wide range of organisms, including plants, animals, fungi, and bacteria, causing a variety of diseases.

6. . Describe briefly the four major groups of Protozoa

Ans : 

Amoeboid Protozoa:

• Move using pseudopodia (temporary extensions of cytoplasm)
• Examples: Amoeba, Entamoeba histolytica (causes amoebic dysentery)

Flagellate Protozoa:

• Move using flagella (whip-like structures)
• Examples: Trypanosoma (causes African trypanosomiasis or sleeping sickness), Leishmania (causes leishmaniasis)

Ciliate Protozoa:

• Move using cilia (hair-like structures)
• Examples: Paramecium, Balantidium coli (causes balantidiasis)

Sporozoan Protozoa:

• Do not have any locomotory organelles
• Form spores during their life cycle
• Examples: Plasmodium (causes malaria), Toxoplasma gondii (causes toxoplasmosis)

7. Plants are autotrophic. Can you think of some plants that are partially heterotrophic?

Ans : 

Yes, there are some plants that are partially heterotrophic. These plants are known as mixotrophs. They can produce their own food through photosynthesis (autotrophy), but they also obtain nutrients by consuming other organisms (heterotrophy).

Here are a few examples of mixotrophic plants:

• Venus Flytrap: This carnivorous plant traps and digests insects to supplement the nutrients it obtains from photosynthesis.
• Sundew: Another carnivorous plant that uses sticky tentacles to capture and digest insects.
• Parasitic Plants: Plants that obtain nutrients from a host plant, such as mistletoe and dodder.

8. What do the terms phycobiont and mycobiont signify?

Ans : 

Phycobiont and mycobiont are terms used to describe the two components of a lichen.

• Phycobiont: This is the photosynthetic partner in a lichen. It is usually an alga or cyanobacterium. The phycobiont provides the lichen with organic nutrients through photosynthesis.
• Mycobiont: This is the fungal partner in a lichen. It provides the lichen with a protective structure, absorbs water and minerals, and helps to anchor the lichen to its substrate.

9. Give a comparative account of the classes of Kingdom Fungi under the following: (i) mode of nutrition (ii) mode of reproduction

Ans : 

Class	Mode of Nutrition	Mode of Reproduction
Ascomycetes	Mostly saprophytes (decomposers), some parasites	Asexual reproduction: budding, conidia formation; Sexual reproduction: ascospore formation
Basidiomycetes	Mostly saprophytes, some parasites and mycorrhizal symbionts	Asexual reproduction: budding, fragmentation; Sexual reproduction: basidiospore formation
Deuteromycetes	Mostly saprophytes, some parasites	Asexual reproduction only (imperfect fungi)
Myxomycetes	Heterotrophs, engulfing food particles	Asexual reproduction: plasmodial stage, spore formation; Sexual reproduction: not well understood
Oomycetes	Heterotrophs, absorbing nutrients from decaying matter or living hosts	Asexual reproduction: zoospores, conidia; Sexual reproduction: oogamy (fusion of male and female gametes)

10. What are the characteristic features of Euglenoids?

Ans : 

Euglenoids are a group of unicellular eukaryotes that exhibit characteristics of both plants and animals. 

• Flagellum: They have a single flagellum for locomotion.
• Photosynthesis: Many euglenoids are capable of photosynthesis, containing chloroplasts like plants.
• Heterotrophy: In the absence of light, they can also obtain nutrients by ingesting food particles, similar to animals.
• Pellicle: They have a flexible outer covering called a pellicle that allows them to change shape.
• Eyespot: Some euglenoids have an eyespot, a pigment-containing organelle that helps them detect light and orient themselves towards it.
• Lack of Cell Wall: Unlike plants, euglenoids do not have a rigid cell wall.

11. Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.

Ans : 

Viruses are obligate intracellular parasites, which means they can only reproduce inside a host cell. They consist fundamental components:

1. Capsid: The capsid protects the genetic material and facilitates the attachment of the virus to the host cell. Some viruses may also have an outer envelope, composed of lipids and proteins, surrounding the capsid.

Common Viral Diseases:

1. Influenza: A respiratory illness caused by the influenza virus.
2. HIV/AIDS: A chronic and potentially fatal disease caused by the human immunodeficiency virus (HIV).
3. Common Cold: A mild respiratory illness caused by a variety of viruses.
4. Measles: A highly contagious viral infection that can cause fever, rash, and other symptoms.

12. Organise a discussion in your class on the topic – Are viruses living or nonliving?

Ans : 

Discussion Topic: Are Viruses Living or Nonliving?

Introduction: Viruses are microscopic entities that can infect living cells and replicate within them. Their nature has been debated for decades, raising the question: Are viruses living or nonliving?

Arguments for Viruses Being Living:

• Replication: Viruses can replicate within host cells, a characteristic often associated with living organisms.
• Evolution: Viruses can evolve over time, adapting to changes in their environment.
• Genetic Material: Viruses possess genetic material, a fundamental component of life.

Arguments for Viruses Being Nonliving:

• Lack of Cellular Structure: Viruses do not have the complex cellular structure found in living organisms.
• Incapable of Independent Metabolism: Viruses cannot carry out metabolic processes on their own.
• Obligate Intracellular Parasites: Viruses can only replicate within a host cell, suggesting a dependence on living organisms.