(a) Explain with the help of schematic diagrams haplontic, diplontic, isomorphic, heteromorphic and triphasic types of life…

(a) Life Cycles in Algae

1. Haplontic: only the zygote is diploid, and meiosis is zygotic. Flow: haploid thallus → gametes (n) → fusion → zygote (2n) → meiosis → haploid spores (n) → new thallus. Example: Chlamydomonas, Spirogyra, Ulothrix.

2. Diplontic: the thallus is diploid, and only gametes are haploid, produced by gametic meiosis. Flow: diploid thallus (2n) → meiosis in gametangia → gametes (n) → zygote (2n) → diploid thallus. Example: Fucus, Sargassum (and diatoms).

3. Isomorphic (haplo-diplontic, with alternation of similar generations): haploid gametophyte and diploid sporophyte look identical. Flow: gametophyte (n) → gametes → zygote (2n) → sporophyte (2n) → meiosis in sporangia → spores (n) → gametophyte. Example: Ulva, Cladophora, Dictyota.

4. Heteromorphic: the generations differ in form. In Laminaria the large kelp sporophyte (2n) bears zoosporangia, where meiosis gives zoospores (n) that grow into microscopic male and female filamentous gametophytes; the egg is fertilised on the female gametophyte, and the zygote grows into the sporophyte. Example: Laminaria, Saccharina.

5. Triphasic (haplo-diplontic with three phases): gametophyte (n), carposporophyte (2n) and tetrasporophyte (2n). In Polysiphonia the fertilised carpogonium on the female gametophyte forms the carposporophyte, whose carpospores (2n) grow into independent tetrasporophytes that undergo meiosis to produce tetraspores (n) which become male and female gametophytes. Example: Polysiphonia, Gracilaria.

(b) Stelar Diversity in Vascular Cryptogams The stele is the central vascular cylinder: xylem, phloem, pericycle and sometimes pith. Vascular cryptogams (pteridophytes) show several types.

Protostele (no pith): haplostele, with a solid xylem core surrounded by phloem (Rhynia, Selaginella species); actinostele, a star-shaped xylem core (Lycopodium serratum); plectostele, xylem in plates (Lycopodium clavatum).

Siphonostele (pith present): ectophloic, with phloem only outside (Osmunda, Equisetum); amphiphloic, with phloem on both sides of xylem (Adiantum, Marsilea, Pteridium in part). Leaf gaps are present in ferns.

Solenostele: a siphonostele with leaf gaps that do not overlap (Pteridium, Adiantum).

Dictyostele: leaf gaps overlap, so the stele breaks into separate meristeles, as in Dryopteris and Pteris. Polycyclic forms with several concentric steles occur in Pteridium.

Eustele: vascular bundles around a pith, as in Equisetum and seed plants.

Evolutionary importance (Jeffrey's stelar theory): protostele is primitive (Psilophytales, e.g., Rhynia, and early lycopods), and evolved to siphonostele, then dictyostele and eustele. Increase in the xylem surface and conducting capacity, and the pith, supported larger bodies with large leaves (megaphylls); leaf gaps allow supply to leaves. Steles help show phylogeny and affinities, and the sequence supports adaptation to land.

(c) Microbes in Bioremediation of Soil and Water Bioremediation uses microbes (bacteria, fungi, algae), or their enzymes, to degrade or immobilise pollutants by biodegradation, biotransformation or biosorption.

Soil: hydrocarbons and oil are degraded by Pseudomonas putida, Alcanivorax and Bacillus; polycyclic aromatic hydrocarbons, pesticides and dyes by the white-rot fungus Phanerochaete chrysosporium; heavy metals by Cupriavidus metallidurans, and uranium reduced by Geobacter. Plants with rhizosphere microbes (rhizoremediation) and mycorrhizae assist. In-situ methods are bioventing and biostimulation, and bioaugmentation; ex-situ methods include biopiles and landfarming.

Water: Alcanivorax borkumensis degrades oil spills; nitrifiers and denitrifiers (Nitrosomonas, Paracoccus) remove nitrogen; activated sludge treats sewage; Chlorella and cyanobacteria take up metals, and fungal biomass (Rhizopus) biosorbs metals. Genetically engineered Pseudomonas (Chakrabarty) degrades oil components.

Advantages: low cost, ecologically friendly. Limitations: slow, incomplete degradation, and effect depends on conditions.