UPPSC 2023 Prelims GS Paper-I · Question 22 of 150

Correct — B, Rivers. Freshwater ecosystems are split into two types by water movement: LOTIC (from Latin lotus, 'washed/flowing') systems have running water — rivers, streams, springs and brooks — while LENTIC systems have standing/still water. A river's continuous flow is the defining feature of a lotic ecosystem, so it is the only running-water option here. The current keeps the water well-oxygenated and shapes specialised communities (organisms adapted to cling on, such as riffle-dwelling insects).

• (a)Ponds — A pond is standing water — a classic LENTIC (still-water) ecosystem, the opposite of lotic.
• (c)Marshy area — A marsh is a wetland with stagnant or very slow-moving water; it belongs to the lentic/wetland category, not flowing (lotic) water.
• (d)Swamps — A swamp is a waterlogged wetland with essentially still water; like ponds and marshes it is lentic, not lotic.

Inland freshwater ecosystems are classified by whether the water flows. Lotic ecosystems (rivers, streams, springs) have moving water; lentic ecosystems (lakes, ponds, pools, marshes, swamps) have standing water. Flow controls oxygen levels, nutrient transport and which organisms can survive, so the two habitats support very different life.

Three of the four options (ponds, marshy area, swamps) are still-water habitats; only 'rivers' has moving water. Recognise the odd-one-out by the single distinguishing property — flow. Mnemonic: lOtic = flOwing; lentic = 'lent'/lingering/still.

• Lotic = flowing water: rivers, streams, springs, brooks (Latin lotus = washed/flowing).
• Lentic = standing water: lakes, ponds, pools, marshes, swamps (Latin lentus = slow/motionless).
• Flowing water is generally better oxygenated than stagnant water, favouring current-adapted organisms.
• Both are freshwater (inland) ecosystems, distinct from marine/estuarine systems.

• Treating all wetlands (marsh, swamp) as 'flowing' — they are still-water lentic systems.
• Confusing the terms: lotic = flowing, lentic = still (the spellings look alike).

UPPSC/UPSC test ecology definitions as odd-one-out or match-the-type items — fix the lotic/lentic pair firmly and classify each water body by whether it flows.

No directly related past PYQ was found.

• practice — not a real PYQ

  Which one of the following is a lentic ecosystem?

  • (a)Stream
  • (b)Spring
  • (c)Lake
  • (d)River

  Answer(c) Lake — a lake is standing water (lentic); streams, springs and rivers are flowing (lotic).

• practice — not a real PYQ

  The terms 'lotic' and 'lentic' are used to classify which of the following?

  • (a)Marine ecosystems by depth
  • (b)Freshwater ecosystems by water movement
  • (c)Forests by canopy layers
  • (d)Deserts by rainfall

  Answer(b) Freshwater ecosystems by water movement — lotic = flowing water, lentic = standing water.