HOTS Questions: Journey of a River | Our Wondrous World Class 5 - New NCERT PDF Download

Q1: If deforestation occurs along a river's banks, how would this primarily affect the river's flow and ecosystem?
(a) It would enhance fish populations with more sunlight
(b) It would decrease flooding by absorbing more water
(c) It would make the river cleaner by reducing organic debris
(d) It would increase erosion, leading to sedimentation and habitat loss
Ans: (d)
Explanation: Cutting down trees along a river's banks removes the roots that hold soil in place, so rain washes dirt into the water easily, making the river muddy and shallow. 
This blocks sunlight and clogs fish gills, hurting animals and plants that live there. Over time, the ecosystem suffers with fewer homes for creatures, and the river might change its path. 

Q2: Evaluate why perennial rivers like the Godavari are more reliable for agriculture than seasonal rivers.
(a) They carry more saltwater for crops
(b) They provide year-round water flow for irrigation
(c) They flood more predictably
(d) They dry up in summer, conserving soil
Ans: (b)
Explanation: Perennial rivers like the Godavari keep flowing all year because they get water from steady sources like melting snow or underground springs, so farmers can always use them to water crops. 
Seasonal rivers only run during rainy times and dry up otherwise, making it hard to plan farming. This steady supply helps grow food without worrying about sudden dry spells.

Q3: In a delta like Godavari's, why do mangroves play a crucial role in protecting coastal areas?

(a) They increase sedimentation for new land
(b) They attract tourists, boosting the economy
(c) Their roots prevent erosion and buffer against storms
(d) They purify saltwater into freshwater
Ans: (c)
Explanation: Mangroves in deltas like the Godavari have tangled roots that grip the mud tightly, stopping waves and wind from washing away the land during big storms. 
They act like a natural wall, keeping coastal villages safe from floods and salty seawater sneaking in. 
Without them, the delta could shrink and lose its protection. 

Q4: If chemical fertilisers from farms wash into a river, predict the long-term impact on aquatic life.
(a) It would attract more birds to the river
(b) It would cause algal blooms, depleting oxygen and killing fish
(c) It would make the water clearer for better visibility
(d) It would enhance plant growth without issues
Ans: (b)
Explanation: Chemical fertilisers add too many nutrients to the river, making algae grow wildly like a thick green blanket on the surface. 
When the algae die, bacteria eat them up and use all the oxygen in the water, leaving none for fish to breathe. 
Over time, the water stays unhealthy and smelly.

Q5: Propose how building a dam on a river like the Godavari affects downstream biodiversity.
(a) It alters water flow, disrupting habitats and species
(b) It prevents any changes to biodiversity
(c) It increases fish migration upstream
(d) It purifies water for better ecosystems
Ans: (a)
Explanation: A dam on a river like the Godavari blocks the natural flow, so less water reaches downstream areas, changing the wet spots where animals and plants live. 
Fish can't swim up to lay eggs like before, and the slower water might make some places too dry or flooded weirdly. 
This confuses the ecosystem, with some species disappearing.

Q6: Analyse the consequences if a river's tributaries dry up due to low rainfall.
(a) It would benefit navigation with calmer waters
(b) Reduced water volume could lead to droughts and ecosystem collapse
(c) The main river would widen naturally
(d) It would increase salinity in the delta
Ans: (b)
Explanation: Tributaries are like little streams feeding the big river, so if they dry up from not enough rain, the main river gets way less water and might shrink. 
This can cause droughts where plants wilt and animals have no place to drink or live, leading to a big ecosystem crash. Fish populations drop, and the land around gets drier too. 

Q7: Why might pollution from factories along a river disproportionately affect delta regions?
(a) Deltas are upstream, away from factories
(b) Mangroves in deltas absorb all pollutants
(c) Slower flows in deltas allow pollutants to accumulate
(d) Deltas have faster currents to disperse pollutants
Ans: (c)
Explanation: In delta regions, the river slows down as it meets the sea, so dirty stuff from factories upstream doesn't rush away quickly and piles up in the mud and water. 
This builds up toxins that hurt fish, birds, and plants more than in faster parts of the river.
It makes the delta unhealthy for a long time. 
Slower flows in deltas allow pollutants to accumulate, affecting them disproportionately.

Q8: If plastic waste increases in a river, evaluate its impact on the food chain.
(a) It floats away to the oceans without local effects
(b) It dissolves harmlessly in water
(c) Animals ingest it, leading to blockages and toxin transfer up the chain
(d) It provides nesting materials for birds
Ans: (c)
Explanation: Plastic in a river doesn't break down, so animals like fish think it's food and swallow it, which blocks their stomachs and makes them sick or starve.  
It messes up the whole eating system in the river. 
Over time, fewer healthy animals survive.

Q9: Compare the ecological roles of a river's source in the mountains versus its delta at the sea.
(a) Deltas are sources of freshwater; sources are salty
(b) Sources have more biodiversity than deltas
(c) Sources provide clean, fast water; deltas support mangroves and estuaries
(d) Both are identical in function
Ans: (c)
Explanation: At the river's source in the mountains, the water starts fresh and fast, picking up clean minerals and supporting quick-swimming fish and rocky plants. 
Down at the delta by the sea, it slows and mixes with salt, creating rich spots for mangroves and bird-filled estuaries where baby fish grow.

Q10: Propose a community strategy to reduce river pollution from household waste.
(a) Promote waste segregation and treatment before discharge
(b) Divert waste to the oceans instead
(c) Increase plastic production for durability
(d) Ignore as rivers self-clean
Ans: (a)
Explanation: A good strategy is for everyone in the community to sort their trash at home, like separating plastics and organics, then treat dirty water before it goes into the river. 
This stops harmful stuff from flowing in and keeps the water clean for fish and people. 
It also helps the river stay healthy long-term. 
Waste segregation and treatment before discharge reduce pollution from household waste.

Q11: If a river floods frequently, analyse how reforestation upstream could mitigate this.
(a) It does not affect flooding
(b) Forests attract more rain, worsening floods
(c) Roots absorb water and stabilise soil, reducing runoff
(d) Trees increase water speed
Ans: (c)
Explanation: Planting trees upstream means their roots soak up rain like sponges and hold the soil tight, so less water rushes into the river all at once during storms. 
This slows down floods and keeps the water cleaner without extra dirt. 
Over time, it makes the river safer for nearby towns. 
That's why roots absorb water and stabilise soil, reducing runoff and mitigating frequent floods.

Q12: Why do perennial rivers support more stable human settlements than seasonal ones?
(a) They carry more sediment for building
(b) They dry up predictably for farming
(c) Consistent flow ensures a year-round water supply
(d) They freeze in winter, providing ice
Ans: (c)
Explanation: Perennial rivers flow steadily all year, giving people reliable water for drinking, farming, and daily needs without dry seasons interrupting life. 
Seasonal rivers vanish part of the year, making it hard to build lasting homes or grow food consistently. 
This stability helps communities thrive and plan better. 
That's why consistent flow ensures a year-round water supply, supporting more stable human settlements.

Q13: Evaluate the trade-offs of building dams on rivers for human benefit versus ecological cost.
(a) They provide water and power, but disrupt migration and habitats
(b) They have no ecological downsides
(c) They eliminate flooding entirely
(d) Dams always increase biodiversity
Ans: (a)
Explanation: Dams give people stored water for drinking and electricity from hydro power, which is great for cities and farms. 
But they block fish from swimming to breeding spots and change the river's natural flow, hurting downstream plants and animals.  
It's a balance where humans gain, but nature pays a price. That's why they provide water and power but disrupt migration and habitats.

Q14: If climate change reduces rainfall in a river basin, predict the effects on the delta mangroves.
(a) Expansion due to warmer temperatures
(b) Increased salinity harms salt-intolerant species
(c) More freshwater boosts growth
(d) No change as mangroves are resilient
Ans: (b)
Explanation: Less rainfall means the river brings less fresh water to the delta.
So salty sea water pushes in more, making the area too briny for some mangrove types that need a mix. 
This can kill off trees and the animals that live in them, shrinking the delta's green protection. 
Over time, the whole ecosystem weakens. 

Q15: Which initiative should be monitored to improve a local river's health.
(a) Track pollution levels, biodiversity, and flow rates
(b) Focus only on watercolour
(c) Measure only during floods
(d) Ignore community involvement
Ans: (a)
Explanation: An initiative could involve locals checking the river regularly by measuring how dirty the water is, counting types of fish and plants to see biodiversity, and tracking how fast it flows. 
This helps spot problems early, like too much trash or low water, and plan cleanups or protections. 
It keeps the river healthy for years. 
Tracking pollution levels, biodiversity, and flow rates improves local river health.