Hard Set - Cross-Group Synthesis & NEET Traps
Revise these high-yield discriminators before attempting the set.
Algae pigments & stored food: Chlorophyceae = chl a,b / starch; Phaeophyceae = chl a,c + fucoxanthin / laminarin, mannitol; Rhodophyceae = chl a,d + phycoerythrin / floridean starch. Agar = Gelidium, Gracilaria; carrageen = red algae; algin = brown algae.
Land-plant trends: algae -> bryophytes -> pteridophytes -> gymnosperms -> angiosperms shows increasing land adaptation: vascular tissue first appears in pteridophytes; the seed habit is foreshadowed by heterospory + megaspore retention in Selaginella/Salvinia; naked seeds in gymnosperms; seeds enclosed in fruit + double fertilisation in angiosperms.
Dominant phase: Bryophytes = gametophyte dominant (sporophyte dependent); Pteridophytes = sporophyte dominant (gametophyte = free prothallus); seed plants = sporophyte dominant, gametophyte reduced.
Life-cycle types: Haplontic = most algae; Diplontic = seed plants and Fucus; Haplo-diplontic = bryophytes & pteridophytes (and Ectocarpus, kelps, Polysiphonia). Spores by meiosis; gametes by mitosis.
Gymnosperm traps: xylem lacks vessels (except Gnetales); phloem lacks sieve tubes & companion cells; Cycas = coralloid roots (cyanobacteria); Pinus = mycorrhiza.
Angiosperm traps: embryo sac = 7-celled, 8-nucleate; syngamy -> 2n zygote; triple fusion -> 3n endosperm; double fertilisation is unique to angiosperms.
Assertion-Reason key: (a) Both true, R correct explanation; (b) Both true, R NOT the explanation; (c) A true, R false; (d) A false, R true.