MPSC 2025 Prelims Paper-I · Question 59 of 100

Correct — option (3), a, c and d (statements a, c and d). Spirogyra is a filamentous green alga (Chlorophyta) common in still or slow-moving freshwater bodies — ponds, ditches and lake margins — where its filaments form the slimy, bright-green floating mats popularly known as 'pond scum' or 'pond silk', which is exactly what statement a describes. Statement c is Spirogyra's single most distinctive diagnostic feature: each cylindrical cell contains one or more ribbon-like chloroplasts arranged in a spiral, helical path along the length of the cell, studded with pyrenoids (starch-storing bodies) — this spiral chloroplast is what gives the genus its name (from the Greek 'speira', a coil) and is the feature most exam questions use to identify it. Statement d is also correct: Spirogyra is classified in the family Zygnemataceae, order Zygnematales, within the class Charophyceae/Zygnematophyceae of green algae — a family defined by exactly this kind of filamentous, unbranched, sexually-reproducing-by-conjugation algal body plan. Statement b is the one false claim: Spirogyra is a strictly freshwater genus, not a marine one, and its cell walls and osmoregulation are adapted to freshwater conditions rather than the higher salinity of seawater.

• (1)a, b and c — This bundle keeps the false statement b (that Spirogyra grows in marine water) alongside the two true statements a and c, but drops the true statement d. Spirogyra is a freshwater alga, and any option that includes b as correct is including a factually wrong claim, while also incorrectly excluding its correct family classification.
• (2)b, c and d — This bundle again includes the false statement b (marine growth) while dropping the true statement a (the 'pond scum' common name). Spirogyra's freshwater, still-water habitat is exactly why it earns the popular name 'pond scum', so omitting a while including the false marine claim gets both parts of the option wrong.
• (4)a, b and d — This bundle keeps the two true statements a and d but again includes the false statement b, and in doing so drops the true statement c — Spirogyra's defining spiral chloroplast, the feature the genus is named for. An option that both admits a false claim and excludes the genus's single most diagnostic true feature cannot be the fully correct set.

Spirogyra is a genus of unbranched, filamentous freshwater green algae in the family Zygnemataceae (order Zygnematales), instantly recognisable under a microscope by its one or more ribbon-shaped, spirally coiled chloroplasts running the length of each cylindrical cell, each chloroplast bearing pyrenoids that store starch. It reproduces asexually by simple fragmentation of the filament and sexually by conjugation, in which two parallel filaments form connecting tubes and the protoplast of one cell migrates through the tube into a cell of the other filament to form a zygospore — a process with no motile gametes, unlike many other green algae. Because it thrives in nutrient-rich still or slow freshwater, dense Spirogyra mats are a common, visually obvious sign of a pond or ditch, giving rise to its everyday name, pond scum or pond silk.

MPSC's botany questions frequently list several plausible-sounding claims about a well-known organism and ask which subset is correct, testing whether a candidate can distinguish a genuinely diagnostic feature (the spiral chloroplast, defining the genus name) from a superficially plausible but wrong claim (marine habitat, when Spirogyra is strictly freshwater) and correctly recall taxonomic placement (family Zygnemataceae).

• Spirogyra is a filamentous freshwater green alga, commonly called 'pond scum' or 'pond silk', found in still or slow-moving water bodies.
• Its most diagnostic feature is one or more ribbon-shaped chloroplasts arranged in a spiral (helical) pattern along each cell, studded with pyrenoids — the source of the genus name.
• Spirogyra belongs to the family Zygnemataceae, order Zygnematales, and reproduces sexually by conjugation, forming zygospores without motile gametes.
• Spirogyra is not found in marine (seawater) environments; it is adapted specifically to freshwater conditions.

• Assuming any alga forming visible pond mats must be marine, when Spirogyra's characteristic mats are specifically a freshwater phenomenon
• Confusing Spirogyra's spiral chloroplast (the genus's defining feature) with the cup-shaped chloroplast of Chlamydomonas or the net-like chloroplast of Oedogonium, when a question mixes multiple algal genera
• Mixing up the family name Zygnemataceae with the order name Zygnematales, or with unrelated algal family names, when recalling exact taxonomic placement

MPSC's biology section frequently bundles four short factual claims about a common organism into an 'a, b, c, d' statement list and asks which subset is correct, rewarding candidates who can independently verify each claim rather than pattern-matching on how many statements 'sound right'.

No directly related past PYQ was found.

• practice — not a real PYQ

  The genus name 'Spirogyra' directly refers to which distinctive structural feature of the alga ?

  • (a)Its spirally coiled, ribbon-shaped chloroplast
  • (b)Its spiral-shaped cell wall
  • (c)Its coiled, spring-like filament structure
  • (d)Its spirally arranged flagella

  Answer(a) Its spirally coiled, ribbon-shaped chloroplast — the name derives from the Greek 'speira' (coil), referring specifically to the chloroplast's shape, not the cell wall, filament shape, or flagella (Spirogyra cells are non-motile and lack flagella).

• practice — not a real PYQ

  Spirogyra reproduces sexually through which process, which does not involve motile gametes ?

  • (a)Conjugation, forming a zygospore
  • (b)Isogamy, with two identical motile gametes
  • (c)Oogamy, with a large non-motile egg and small motile sperm
  • (d)Budding of the parent filament

  Answer(a) Conjugation, forming a zygospore — two parallel filaments form connecting tubes through which one cell's protoplast migrates into a cell of the other filament, with no motile gametes involved.