Definitions [1]
Define the following.
Bacteriophages
Bacteriophages are virus that infect bacterial cells, e.g. T4 bacteriophage.
Key Points
1. Meaning - All single-celled eukaryotes act as a link between plants, animals and fungi; mostly aquatic; have a nucleus and membrane-bound organelles.
2. Chrysophytes - Includes diatoms and golden algae; cell wall has silica; deposits form Diatomaceous Earth (used in polishing and filtration); chief producers in oceans.
3. Dinoflagellates - Mostly marine, photosynthetic; cell wall of cellulosic plates; have two flagella (one longitudinal, one transverse); rapid multiplication of red dinoflagellates (e.g. Gonyaulax) causes red tides.
4. Euglenoids - Have a pellicle instead of a cell wall; photosynthetic in sunlight but become heterotrophs in its absence. e.g. Euglena.
5. Slime Moulds - Saprophytic; feed on decaying matter; undergo syngamy to form a plasmodium that spreads over several feet.
6. Protozoans - 4 types:
- Amoeboid - move by pseudopodia. e.g. Amoeba, Entamoeba
- Flagellated - have flagella; cause sleeping sickness. e.g. Trypanosoma
- Ciliated - have cilia; have a gullet for feeding. e.g. Paramecium
- Sporozoans - no locomotory organelle; all parasitic. e.g. Plasmodium
1. Meaning - Heterotrophic organisms; body made of thread-like hyphae; network of hyphae = mycelium; cell wall made of chitin; grow in warm and humid places; except yeasts, all are multicellular.
2. Nutrition - Can be saprophytic (feed on dead matter), parasitic or symbiotic (as lichens and mycorrhiza).
3. Reproduction - Asexual by spores (conidia, zoospores, aplanospores); sexual reproduction involves 3 steps - plasmogamy → karyogamy → meiosis; Ascomycetes and Basidiomycetes undergo a dikaryotic stage.
4. 4 Classes of Fungi:
- Phycomycetes - Mycelium aseptate, coenocytic; spores endogenous in sporangium. e.g. Rhizopus, Albugo
- Ascomycetes (Sac fungi) - Asexual spores = conidia; sexual spores = ascospores in ascus. e.g. Aspergillus, Neurospora
- Basidiomycetes - No asexual spores; sexual spores = basidiospores (exogenous). e.g. Agaricus, Ustilago, Puccinia
- Deuteromycetes (Imperfect Fungi) - Sexual form unknown; saprophytic/parasitic. e.g. Alternaria, Colletotrichum
5. Classification basis - Based on morphology, mode of spore formation and fruiting bodies.
6. Important examples - Puccinia (wheat rust), Penicillium (antibiotic), Agaricus (mushroom), Neurospora (genetic research).
- Microbes are found everywhere - soil, water, air, and inside the bodies of humans, animals, and plants.
- They survive extreme conditions - thermal vents (100°C), deep soil, thick snow layers, and highly acidic environments.
- Types of microbes - protozoa, bacteria, fungi, microscopic plants, viruses, viroids, and prions (proteinaceous infectious agents).
- Bacteria and fungi grow on nutritive media to form visible colonies, essential for studying microorganisms.
- Microbes cause diseases in humans, animals, and plants, but many are also beneficial to human welfare.
