Shankar IAS MCQs Marine Organisms - Famous Books for UPSC Exam (Summary

Q1: Statement 1: Sea grasses are unique as they are the only group of higher plants adapted to life in saltwater.
Statement 2: Major sea grass meadows in India are found primarily along the west coast of Maharashtra.
(a) Both statements are true
(b) Statement 1 is true, Statement 2 is false
(c) Statement 1 is false, Statement 2 is true
(d) Both statements are false
Ans: (b)
Explanation: Statement 1 is correct-seagrasses are the only marine flowering plants (higher plants) adapted to life in saline waters. Statement 2 is incorrect; major seagrass meadows in India occur along the south-east coast (for example, Tamil Nadu and the Gulf of Mannar), and in island groups such as the Lakshadweep Islands, rather than being concentrated mainly off the west coast of Maharashtra.

Q2: Match the following sea grass functions with their correct descriptions:

(a) 1 - B, 2 - D, 3 - C, 4 -A
(b) 1 - A, 2 - B, 3 - C, 4 -D
(c) 1 - D, 2 - C, 3 - B, 4 -A
(d) 1 - C, 2 - A, 3 - B, 4 -D
Ans: (a)
Explanation: Seagrass functions typically include reducing wave and current energy and stabilising bottom sediments, both of which help control coastal erosion; providing food and shelter (enhancing fish populations, especially in lagoon areas); and acting as nutrient sinks that buffer nutrient and chemical inputs. The matched option (a) correctly pairs these functions with their descriptions.

Q3: Assertion (a): Seaweeds are important for human consumption, animal feed, and as plant fertilizers.
Reason (R): Seaweeds are macroscopic algae known as thalloid plants and lack true tissues.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) A is false, but R is true
Ans: (b)
Explanation: The assertion is true-seaweeds are used as human food (e.g., edible red and green algae), as animal feed supplements and as organic fertilizers. The reason is also true from a biological perspective: seaweeds are macroscopic algae (thalloid) that lack differentiated vascular tissues. However, the biological structure (lack of true vascular tissues) is not the direct reason for their use in food and fertilizer, so R does not explain A.

Q4: Statement 1: Seaweeds are classified into different classes based on the color of their pigmentation.
Statement 2: The main classes of seaweeds are blue-green, green, yellow, and red.
(a) Both statements are true
(b) Statement 1 is true, Statement 2 is false
(c) Statement 1 is false, Statement 2 is true
(d) Both statements are false
Ans: (b)
Explanation: Statement 1 is correct-seaweed classification is largely based on dominant pigments. Statement 2 is incorrect because the commonly accepted major groups are blue-green (Cyanophyceae), green (Chlorophyta), brown (Phaeophyceae), and red (Rhodophyta); "yellow" is not a primary class used in standard algal classification.

Q5: Assertion (a): Rotting seaweed is a source of hydrogen sulfide, a toxic gas.
Reason (R): Seaweeds are used as potential indicators of pollution in coastal ecosystems.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) A is false, but R is true
Ans: (b)
Explanation: Both statements are true. Decomposition (rotting) of large amounts of seaweed under anaerobic conditions can produce hydrogen sulfide (H2S), which is toxic. Seaweeds are also used as bioindicators because many species accumulate pollutants such as heavy metals. However, the use of seaweeds as indicators of pollution does not directly explain why rotting produces hydrogen sulfide, so R is not the explanation of A.

Q6: Dugong, a mammal dependent on sea grass for food, is not considered at risk of extinction.
(a) True
(b) False
Ans: (b) False
Explanation: The statement is false. The dugong (Dugong dugon) relies on seagrass beds for food and is considered at risk due to habitat loss, degradation of seagrass beds, accidental capture, and other threats. It is listed by conservation organisations as vulnerable/endangered in many parts of its range.

Q7: Arrange the following species of turtles nesting on the Indian coast in the order of their mention in the provided information:
1. Olive Ridley
2. Green turtle
3. Leatherback sea turtle
4. Hawksbill
5. Loggerhead turtle
(a) 3, 2, 1, 4, 5
(b) 1, 2, 3, 4, 5
(c) 2, 3, 4, 1, 5
(d) 5, 4, 3, 2, 1
Ans: (a) 3, 2, 1, 4, 5
Explanation: The order given corresponds to Leatherback sea turtle, Green turtle, Olive Ridley, Hawksbill, and Loggerhead turtle.

Q8: Which of the following is a unique characteristic of sea grasses?
(a) They are microscopic organisms.
(b) They are the only group of higher plants adapted to life in saltwater.
(c) They thrive in deep oceanic waters.
(d) They lack root systems.
Ans: (b)
Explanation: Seagrasses are marine flowering plants adapted to live submerged in saline coastal waters; this makes them the only group of higher (vascular) plants fully adapted to marine conditions. They are not microscopic, they possess root and rhizome systems, and they inhabit shallow coastal waters rather than deep oceanic zones.

Q9: Seaweeds play a role in the biodegradation process, producing gases like methane.
(a) True
(b) False
Ans: (a) True
Explanation: During decomposition under anaerobic conditions, seaweed biomass can be broken down by microbes to produce gases such as methane (CH4) and hydrogen sulfide (H2S). This is part of the natural biodegradation of organic matter in coastal sediments and stranded algae.

Q10: Statement 1: Seaweeds are commonly distributed from inter-tidal to sub-tidal regions down to a depth of 15m.
Statement 2: IUCN prioritizes the conservation of sea grass.
(a) Both statements are true
(b) Statement 1 is true, Statement 2 is false
(c) Statement 1 is false, Statement 2 is true
(d) Both statements are false
Ans: (c) Statement 1 is false, Statement 2 is true
Explanation: Statement 1 is inaccurate as stated. Seaweeds occur from the intertidal zone to various subtidal depths depending on species and light penetration; some species may extend beyond 15 m where light permits, while others are restricted to shallower zones. Thus a blanket depth limit of 15 m is not universally correct. Statement 2 is correct-international conservation bodies and organisations, including IUCN, highlight the importance of conserving seagrass habitats because of their ecological roles and vulnerability.

Q11: Seagrass beds enhance fish and migratory bird populations by offering food and shelter.
(a) True
(b) False
Ans: (a)
Explanation: True. Seagrass beds provide structural habitat, food resources and nursery grounds for many fish and invertebrate species; they also support foraging by migratory birds, thereby enhancing local biodiversity and fisheries productivity.

Q12: Match the following seaweed pigmentation classes with their colors:

(a) 1 - B, 2 - C, 3 - A, 4 - D
(b) 1 - A, 2 - B, 3 - C, 4 -D
(c) 1 - D, 2 - C, 3 - B, 4 -A
(d) 1 - C, 2 - D, 3 - A, 4 -B
Ans: (a)
Explanation: The correct matching is: Chlorophyta (green), Phaeophyceae (brown), Rhodophyta (red), and Cyanophyceae (blue-green).

Q13: Assertion (a): Eutrophication leads to algal blooms, which can harm seagrass beds.
Reason (R): Algal blooms reduce sunlight penetration, essential for the growth of seagrass.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) A is false, but R is true
Ans: (a)
Explanation: Both statements are true and R correctly explains A. Nutrient enrichment (eutrophication) promotes phytoplankton and macroalgal blooms, which increase turbidity and surface shading, reducing the light available to submerged seagrasses and impairing their photosynthesis and growth.

Q14: Statement 1: Seaweeds are used as a drug for goiter treatment and intestinal disorders.
Statement 2: Seaweeds are a significant source of freshwater.
(a) Only Statement 1 is true
(b) Only Statement 2 is true
(c) Both statements are true
(d) Both statements are false
Ans: (a)
Explanation: Statement 1 is true: certain seaweeds are rich in iodine and have been used in traditional medicines (for example, in goitre management) and in treatments of some intestinal disorders; seaweed extracts also have pharmaceutical applications. Statement 2 is false: seaweeds are marine organisms and are not a source of freshwater.

Q15: Trawling and overexploitation for commerce are major threats to both seagrass beds and seaweeds.
(a) True
(b) False
Ans: (a)
Explanation: True. Bottom trawling physically damages seagrass beds and benthic algal communities; overharvesting of seaweeds for commercial purposes can deplete populations and degrade habitats. Both activities reduce habitat complexity and resilience.

Q16: Seaweeds are broadly classified into different classes based on the color of their pigmentation, such as blue-green, green, brown, and ______.
(a) Yellow
(b) Orange
(c) Red
(d) Purple
Ans: (c) Red
Explanation: The main pigment-based classes include blue-green (Cyanophyceae), green (Chlorophyta), brown (Phaeophyceae) and red (Rhodophyta).

Q17: Assertion (a): Seaweeds serve as important indicators of pollution in coastal ecosystems.
Reason (R): They have a high capacity to bind and accumulate heavy metals.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) A is false, but R is true
Ans: (a)
Explanation: Both A and R are true, and R explains A. Many seaweeds accumulate heavy metals and other contaminants in their tissues, making them useful bioindicators for monitoring coastal pollution levels.

Q18: Statement 1: Seagrass beds filter suspended sediments from the water.
Statement 2: Seagrass beds are predominantly found in deep oceanic waters.
(a) Only Statement 1 is true
(b) Only Statement 2 is true
(c) Both statements are true
(d) Both statements are false
Ans: (a) Only Statement 1 is true
Explanation: Statement 1 is correct-seagrass beds trap and stabilise suspended sediments, improving water clarity and reducing erosion. Statement 2 is false-seagrasses predominantly occur in shallow coastal waters where sufficient light reaches the seabed for photosynthesis.

Q19: Seagrass beds are major contributors to oxygen production in marine ecosystems.
(a) True
(b) False
Ans:  (a) True
Explanation: True. Through photosynthesis, seagrasses produce oxygen and contribute to primary production in coastal ecosystems. Their productivity supports food webs and helps maintain water quality.

Q20: What functions do sea grass beds perform in marine ecosystems?
I. Reduce wave and current energy.
II. Act as nutrient sinks on reef flats.
III. Provide habitat for terrestrial mammals.
(a) I only
(b) I and II only
(c) II and III only
(d) I, II, and III
Ans:  (b)
Explanation: Sea grass beds reduce wave and current energy and act as nutrient sinks, especially on reef flats and in lagoons. They do not provide habitat for terrestrial mammals; they are marine habitats supporting aquatic organisms and some shore-foraging species such as birds.