Biological Classification

Classification systems have evolved from simple morphological observations to complex phylogenetic studies:

• Aristotle’s Classification: The earliest scientific attempt. He classified plants into herbs, shrubs, and trees; and animals into those with red blood and those without.
• Two-Kingdom System (Linnaeus): Divided organisms into Plantae and Animalia based on cell walls. It failed to distinguish between eukaryotes/prokaryotes, unicellular/multicellular, and photosynthetic/non-photosynthetic organisms.
• Three & Four Kingdom Systems: Later, kingdoms like Protista and Monera were added to address the limitations of the two-kingdom system.
• Five-Kingdom System (R.H. Whittaker, 1969): Classifiction based on cell structure, body organization, mode of nutrition, reproduction, and phylogenetic relationships. The kingdoms are Monera, Protista, Fungi, Plantae, and Animalia.

(a) Heterotrophic Bacteria:

• Curd Production: Lactobacillus converts milk into curd.
• Antibiotics: Many bacteria like Streptomyces are used to produce antibiotics (e.g., Streptomycin).
• Nitrogen Fixation: Rhizobium in legume roots fixes atmospheric nitrogen.

(b) Archaebacteria:

• Biogas Production: Methanogens (found in the gut of ruminants) produce methane (biogas) from dung.
• Bio-leaching: Some are used in the extraction of metals from ores.

In diatoms, the cell walls form two thin overlapping shells, which fit together as in a soap box. The walls are embedded with silica and thus the walls are indestructible. This accumulation over billions of years creates “Diatomaceous Earth”.

Algal Bloom: It refers to the rapid increase in the population of algae in water bodies, often due to nutrient enrichment. It creates a green or colored layer on the water surface, depleting oxygen and killing aquatic life.

Red Tides: Caused by the rapid multiplication of red Dinoflagellates (e.g., Gonyaulax). The sea appears red due to their pigments. They may release toxins that can kill marine animals like fishes.

All protozoans are heterotrophs (predators or parasites). They are grouped into:

1. Amoeboid Protozoans: Move and capture prey using pseudopodia (false feet). E.g., Amoeba, Entamoeba (parasite). Marine forms have silica shells.
2. Flagellated Protozoans: Possess flagella for movement. Can be free-living or parasitic. E.g., Trypanosoma (causes Sleeping Sickness).
3. Ciliated Protozoans: Aquatic, actively moving organisms with thousands of cilia. Have a gullet. E.g., Paramecium.
4. Sporozoans: Include organisms that have an infectious spore-like stage in their life cycle. E.g., Plasmodium (Malarial parasite).

Yes, some plants are partially heterotrophic:

• Insectivorous Plants: They trap insects for nitrogen requirements but photosynthesize for food. Examples: Bladderwort and Venus flytrap.
• Parasitic Plants: They derive nutrition from host plants. Example: Cuscuta (Amarbel).

These terms refer to the two components of a Lichen (a symbiotic association):

• Phycobiont: The algal component. It is autotrophic and prepares food for the fungi.
• Mycobiont: The fungal component. It is heterotrophic; it provides shelter and absorbs mineral nutrients and water for its partner.

• Habitat: Mostly fresh water organisms found in stagnant water.
• Cell Wall: Absent. They have a protein-rich layer called pellicle which makes their body flexible.
• Flagella: They have two flagella, a short and a long one.
• Nutrition: They are photosynthetic in the presence of sunlight. When deprived of sunlight, they behave like heterotrophs (predating on smaller organisms).
• Example: Euglena.

Structure: Viruses are non-cellular organisms characterized by an inert crystalline structure outside the living cell. They consist of a protein coat called capsid (made of capsomeres) enclosing genetic material.

Genetic Material: Can be RNA or DNA (never both).
– Plant viruses: Usually single-stranded RNA.
– Animal viruses: Single/Double-stranded RNA or Double-stranded DNA.
– Bacteriophages: Usually double-stranded DNA.

Common Diseases: Mumps, Smallpox, Herpes, Influenza, AIDS (in humans).

Arguments for Living:
1. They possess genetic material (DNA/RNA).
2. They can reproduce (inside a host).
3. They can undergo mutation.

Arguments for Non-Living:
1. They have no cellular structure (protoplasm, organelles).
2. They are inert (crystalline) outside a host.
3. They lack autonomous metabolism (cannot generate energy).