Previous Year Question

Which of the following are detritivores?

Select the correct answer using the code given below.

1, 2 and 4

2, 3, 4 and 5

1, 3 and 5

1, 2, 3, 4 and 5

Correct Answer: C

Detailed Solution

1. Earthworms are detritivores.

Earthworms consume dead and decomposing plant material, microorganisms and other organic residues present in the soil.
They divide dead organic material into smaller particles and increase its surface area.
This makes the chemical decomposition of the material easier for decomposers such as bacteria and fungi.
The activities of earthworms increase soil aeration, water infiltration and the mixing of nutrients.
Their excreted casts may contain a greater quantity of plant-available nutrients than the surrounding soil.
Therefore, earthworms are regarded as important soil detritivores and ecosystem engineers.

2. Jellyfish are not detritivores.

Jellyfish are primarily carnivorous aquatic animals.
They use their tentacles and nematocysts to capture zooplankton, fish eggs, larvae and small aquatic organisms.
The stinging cells present in their tentacles help immobilise prey.
Dead and decomposing organic material is not their principal food.
Therefore, jellyfish are not generally considered detritivores.

3. Millipedes are detritivores.

Millipedes primarily feed upon fallen and decomposing leaves, rotting wood and other dead plant material on land.
They divide coarse plant litter into smaller fragments.
This increases microbial action upon the dead material and accelerates its decomposition.
Millipedes assist in humus formation and nutrient recycling on the forest floor.
Therefore, millipedes are important terrestrial detritivores.

4. Seahorses are not detritivores.

Seahorses are small marine fish belonging to the genus Hippocampus.
They mainly prey upon small crustaceans, copepods, amphipods and other minute aquatic organisms.
They rapidly draw prey inside through their long, tube-shaped snout.
Dead and decomposing organic material is not their usual principal food.
Therefore, seahorses are not considered detritivores.

5. Woodlice are detritivores.

Woodlice are terrestrial isopod crustaceans.
They feed upon fallen leaves, rotting wood, fungi and other decomposing organic material in moist and shaded places.
They increase microbial decomposition by fragmenting dead plant material.
Their activity helps return organic matter and nutrients to the soil.
Therefore, woodlice are important detritivores.

Difference between detritivores and decomposers

Detritivores ingest dead organic material and perform its physical fragmentation and digestion inside their bodies.
Earthworms, millipedes and woodlice are examples of detritivores.
Decomposers such as bacteria and fungi release enzymes outside their bodies and chemically decompose dead material externally.
Detritivores accelerate microbial decomposition by increasing the surface area of dead material.
Both detritivores and decomposers are important for nutrient recycling and the flow of energy through ecosystems.

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