Question: Pteridophytes — characteristics, life cycle dominance, heterospory, and evolutionary significance as precursors to seed plants
Introduction
Pteridophytes occupy a pivotal position in plant evolution, representing the first vascular land plants and bridging the gap between bryophytes and the more advanced seed-bearing gymnosperms and angiosperms.
Body
1. First Vascular Land Colonisers
Pteridophytes — encompassing ferns, horsetails (Equisetum), and club mosses (Lycopodium) — were the earliest plants to develop vascular tissue (xylem and phloem). This adaptation enabled efficient water and nutrient transport, allowing colonisation of terrestrial habitats far beyond what non-vascular bryophytes could achieve.
2. Sporophyte Dominance and Free-Living Gametophyte
Unlike bryophytes where the gametophyte dominates, in pteridophytes the diploid sporophyte is the conspicuous, dominant generation. The haploid gametophyte, called the prothallus, is small, free-living, and photosynthetically independent, though short-lived and dependent on moist conditions for fertilisation.
3. Absence of Seeds — A Key Limitation
Pteridophytes reproduce via spores, not seeds. This absence of a protective seed coat and endosperm restricts their dispersal efficiency and survival in drier environments, distinguishing them fundamentally from spermatophytes (seed plants).
4. Heterospory as an Evolutionary Precursor
Certain pteridophytes such as Selaginella and Salvinia exhibit heterospory — producing distinct megaspores (female) and microspores (male). This differentiation is considered an evolutionary precursor to the seed habit, as the megaspore retained within the sporangium mirrors the condition seen in early seed plants.
Conclusion
Pteridophytes thus represent a critical evolutionary grade — vascularised yet seedless. Understanding heterospory within this group illuminates the stepwise transition toward seed plants, which ultimately enabled vegetation to dominate diverse terrestrial ecosystems.
Word count: 213
PYQ 2025
Consider the following pairs:
Plant — Description
I. Cassava : Woody shrub
II. Ginger : Pseudo-stem herb
III. Malabar spinach : Herbaceous climber
IV. Mint : Annual shrub
V. Papaya : Woody shrub
How many of the above pairs are correctly matched?
PYQ 2025
Consider the following pairs:
Plant : Description
I. Cassava : Woody shrub
II. Ginger : Herb with pseudostem
III. Malabar spinach : Herbaceous climber
IV. Mint : Annual shrub
V. Papaya : Woody shrub
How many of the above pairs are correctly matched?
PYQ
Consider the following statements regarding C4 plants:
1. In C4 plants, the first stable product of carbon fixation is oxaloacetate (OAA), a 4-carbon compound.
2. C4 plants have Kranz anatomy with bundle sheath cells having abundant chloroplasts.
3. C4 plants show higher photorespiration than C3 plants.
4. Sugarcane, maize and sorghum are examples of C4 plants.
Which of the statements given above are correct?
PYQ
With reference to Polyploidy in plants, consider the following statements:
1. Allopolyploidy involves chromosome doubling within a single species.
2. Bread wheat (Triticum aestivum) is a hexaploid, having 2n = 42 chromosomes.
3. Banana (Musa) cultivars consumed widely are triploid and sterile.
4. Colchicine is commonly used to induce polyploidy by inhibiting spindle formation during cell division.
Which of the statements given above are correct?
PYQ
Consider the following statements about secondary metabolites in plants:
1. Alkaloids such as caffeine, morphine and quinine are nitrogen-containing compounds derived from amino acid metabolism.
2. Terpenes and terpenoids form the largest class of secondary metabolites and include essential oils, carotenoids and rubber.
3. Tannins are phenolic compounds that act as feeding deterrents against herbivores.
4. Glucosinolates found in Brassica plants are sulphur-containing compounds that release toxic products upon hydrolysis.
Which of the statements given above are correct?