Key Points
Key Points: Kingdom Animalia
- Meaning - Heterotrophic, multicellular eukaryotes; cells lack a cell wall; cannot produce their own food.
- Nutrition - Mode of nutrition is holozoic (food obtained by ingestion); food is digested in an internal cavity; food is stored as glycogen or fat.
- Reproduction - By sexual reproduction - copulation of male and female followed by embryological development.
- Other features - Follow a definite growth pattern; higher forms have elaborate sensory and neuromotor mechanisms (nervous system and sensory organs); most are capable of locomotion.
- Cell structure - Has a nucleus and membrane-bound organelles; no chloroplasts (hence cannot photosynthesise); no cell wall (unlike plants and fungi).
Key Points: Viruses, Viroids, Prions and Lichens
Viruses
- Viruses are non-living outside a host, but become active inside living cells.
- They are nucleoproteins with a protein coat (capsid) and genetic material (DNA or RNA).
- They can have different structures, like helical or polyhedral.
- Cause diseases like influenza, AIDS, mumps, smallpox in humans and mosaic disease in plants.
- They can form crystalline structures outside the host and do not fit in the Whittaker classification.
Viroids
- Viroids are the smallest infectious agents, discovered by T.O. Diener (1971).
- They consist of only RNA, without a protein coat.
- Cause plant diseases like potato spindle tuber disease.
- Have low molecular weight and a simple structure.
- Can replicate independently inside host plants.
Prions
- Prions are infectious proteins without DNA or RNA.
- They cause neurodegenerative diseases in humans and animals.
- Examples include CJD, mad cow disease (BSE), and scrapie.
- Disease occurs due to the misfolding of normal proteins.
- Lead to brain damage and death.
Lichens
- Lichens are a symbiotic association between algae and fungi.
- Algae prepare food, while fungi provide shelter and nutrients.
- Lichens act as pollution indicators and are absent in polluted areas.
- Based on structure, lichens are of three types: crustose (crust-like and tightly attached), foliose (leaf-like and loosely attached), and fruticose (branched or bushy).
- Examples include Lecanora (crustose), Peltigera (foliose), and Ramalina (fruticose).
