NEET Biology Ecosystem MCQs Set 17

Answer: (d) Productivity, decomposition, energy flow and nutrient cycling

Explanation:
1. The components of the ecosystem function as a unit through productivity, decomposition, energy flow and nutrient cycling.

Teacher's Note:
1. Ecosystem functions include productivity, decomposition, energy flow and nutrient cycling.
2. GPP minus respiratory loss gives NPP; the annual NPP of the biosphere is about 170 billion tons of dry matter, of which oceans contribute about 55 billion tons.

Answer: (b) Predation

Explanation:
1. Primary productivity depends on plant species, environmental factors and photosynthetic capacity, not on predation.

Teacher's Note:
1. Decomposition steps: fragmentation, leaching, catabolism, humification and mineralisation; it is faster in warm, moist conditions, with nitrogen and sugar rich detritus, and slower with lignin, chitin and in cold.
2. Humus is dark, amorphous, colloidal and highly resistant to microbial action.

Answer: (a) 170 billion tons

Explanation:
1. The annual net primary productivity of the whole biosphere is about 170 billion tons of dry matter.

Teacher's Note:
1. In aquatic ecosystems the grazing food chain is the major conduit of energy flow, whereas the detritus food chain dominates on land; only about 10 per cent of energy passes to the next trophic level.
2. Succession proceeds from pioneers to a climax; hydrosere and xerosere both end in a mesic climax.

Answer: (d) 55

Explanation:
1. The oceans contribute about 55 billion tons of the 170 billion tons of NPP.

Teacher's Note:
1. Ecosystem functions include productivity, decomposition, energy flow and nutrient cycling.
2. GPP minus respiratory loss gives NPP; the annual NPP of the biosphere is about 170 billion tons of dry matter, of which oceans contribute about 55 billion tons.

Answer: (b) Increasing surface area of detritus

Explanation:
1. Fragmentation of detritus increases the surface area for microbial action.

Teacher's Note:
1. Decomposition steps: fragmentation, leaching, catabolism, humification and mineralisation; it is faster in warm, moist conditions, with nitrogen and sugar rich detritus, and slower with lignin, chitin and in cold.
2. Humus is dark, amorphous, colloidal and highly resistant to microbial action.

Answer: (c) Colloidal in nature

Explanation:
1. Humus is a dark, amorphous and colloidal substance that is highly resistant to microbial action.

Teacher's Note:
1. In aquatic ecosystems the grazing food chain is the major conduit of energy flow, whereas the detritus food chain dominates on land; only about 10 per cent of energy passes to the next trophic level.
2. Succession proceeds from pioneers to a climax; hydrosere and xerosere both end in a mesic climax.

Answer: (d) Sugars

Explanation:
1. Lignin, chitin and cutin slow decomposition, whereas sugars and nitrogen rich substances speed it up.

Teacher's Note:
1. Ecosystem functions include productivity, decomposition, energy flow and nutrient cycling.
2. GPP minus respiratory loss gives NPP; the annual NPP of the biosphere is about 170 billion tons of dry matter, of which oceans contribute about 55 billion tons.

Answer: (a) Temp & soil moisture

Explanation:
1. Temperature and soil moisture are the most important climatic factors regulating decomposition.

Teacher's Note:
1. Decomposition steps: fragmentation, leaching, catabolism, humification and mineralisation; it is faster in warm, moist conditions, with nitrogen and sugar rich detritus, and slower with lignin, chitin and in cold.
2. Humus is dark, amorphous, colloidal and highly resistant to microbial action.

Answer: (c) Low temperature and anaerobiosis favours decomposition

Explanation:
1. Low temperature and anaerobiosis inhibit decomposition, so statement 3 is not correct.

Teacher's Note:
1. In aquatic ecosystems the grazing food chain is the major conduit of energy flow, whereas the detritus food chain dominates on land; only about 10 per cent of energy passes to the next trophic level.
2. Succession proceeds from pioneers to a climax; hydrosere and xerosere both end in a mesic climax.

Answer: (a) 1–5% and 2–10%

Explanation:
1. Plants capture about 1-5 per cent of incident solar radiation, which is 2-10 per cent of the PAR.

Teacher's Note:
1. Ecosystem functions include productivity, decomposition, energy flow and nutrient cycling.
2. GPP minus respiratory loss gives NPP; the annual NPP of the biosphere is about 170 billion tons of dry matter, of which oceans contribute about 55 billion tons.

Answer: (a) GFC

Explanation:
1. In aquatic ecosystems the grazing food chain is the major conduit for energy flow.

Teacher's Note:
1. Decomposition steps: fragmentation, leaching, catabolism, humification and mineralisation; it is faster in warm, moist conditions, with nitrogen and sugar rich detritus, and slower with lignin, chitin and in cold.
2. Humus is dark, amorphous, colloidal and highly resistant to microbial action.

Answer: (d) DFC can never be connected with GFC

Explanation:
1. The detritus food chain is connected to the grazing food chain, so statement 4 is incorrect.

Teacher's Note:
1. In aquatic ecosystems the grazing food chain is the major conduit of energy flow, whereas the detritus food chain dominates on land; only about 10 per cent of energy passes to the next trophic level.
2. Succession proceeds from pioneers to a climax; hydrosere and xerosere both end in a mesic climax.

Answer: (b) Dry weight

Explanation:
1. Biomass expressed as dry weight is more accurate because fresh weight varies with water content.

Teacher's Note:
1. Ecosystem functions include productivity, decomposition, energy flow and nutrient cycling.
2. GPP minus respiratory loss gives NPP; the annual NPP of the biosphere is about 170 billion tons of dry matter, of which oceans contribute about 55 billion tons.

Answer: (c) 3

Explanation:
1. From the standard pyramid of numbers, about 6 million producers support only about 3 top consumers.

Teacher's Note:
1. Decomposition steps: fragmentation, leaching, catabolism, humification and mineralisation; it is faster in warm, moist conditions, with nitrogen and sugar rich detritus, and slower with lignin, chitin and in cold.
2. Humus is dark, amorphous, colloidal and highly resistant to microbial action.

Answer: (d) 1.5 kgm–2

Explanation:
1. In the pyramid of biomass, 809 kg per square metre of producers supports about 1.5 kg per square metre of tertiary consumers.

Teacher's Note:
1. In aquatic ecosystems the grazing food chain is the major conduit of energy flow, whereas the detritus food chain dominates on land; only about 10 per cent of energy passes to the next trophic level.
2. Succession proceeds from pioneers to a climax; hydrosere and xerosere both end in a mesic climax.

Answer: (d) All the above

Explanation:
1. Ecological pyramids ignore species at more than one trophic level, do not fit food webs and exclude saprophytes.

Teacher's Note:
1. Ecosystem functions include productivity, decomposition, energy flow and nutrient cycling.
2. GPP minus respiratory loss gives NPP; the annual NPP of the biosphere is about 170 billion tons of dry matter, of which oceans contribute about 55 billion tons.

Answer: (c) Ecological succession

Explanation:
1. Gradual and fairly predictable changes in species composition of an area is ecological succession.

Teacher's Note:
1. Decomposition steps: fragmentation, leaching, catabolism, humification and mineralisation; it is faster in warm, moist conditions, with nitrogen and sugar rich detritus, and slower with lignin, chitin and in cold.
2. Humus is dark, amorphous, colloidal and highly resistant to microbial action.

Answer: (d) Decrease in niche specialisation

Explanation:
1. Succession is accompanied by increasing niche specialisation, so a decrease is not a feature.

Teacher's Note:
1. In aquatic ecosystems the grazing food chain is the major conduit of energy flow, whereas the detritus food chain dominates on land; only about 10 per cent of energy passes to the next trophic level.
2. Succession proceeds from pioneers to a climax; hydrosere and xerosere both end in a mesic climax.

Answer: (c) In hydrosere, hydric environment progress to mesic conditions

Explanation:
1. In hydrosere, a hydric environment progresses to a mesic one.

Teacher's Note:
1. Ecosystem functions include productivity, decomposition, energy flow and nutrient cycling.
2. GPP minus respiratory loss gives NPP; the annual NPP of the biosphere is about 170 billion tons of dry matter, of which oceans contribute about 55 billion tons.

Answer: (c) Mesic

Explanation:
1. All successions, in water or on land, proceed towards a mesic climax community.

Teacher's Note:
1. Decomposition steps: fragmentation, leaching, catabolism, humification and mineralisation; it is faster in warm, moist conditions, with nitrogen and sugar rich detritus, and slower with lignin, chitin and in cold.
2. Humus is dark, amorphous, colloidal and highly resistant to microbial action.

Answer: (d) All the above

Explanation:
1. Soil, moisture, pH and temperature regulate the rate of release of nutrients.

Teacher's Note:
1. In aquatic ecosystems the grazing food chain is the major conduit of energy flow, whereas the detritus food chain dominates on land; only about 10 per cent of energy passes to the next trophic level.
2. Succession proceeds from pioneers to a climax; hydrosere and xerosere both end in a mesic climax.

Answer: (a) 49 %

Explanation:
1. Carbon constitutes about 49 per cent of the dry weight of organisms.

Teacher's Note:
1. Ecosystem functions include productivity, decomposition, energy flow and nutrient cycling.
2. GPP minus respiratory loss gives NPP; the annual NPP of the biosphere is about 170 billion tons of dry matter, of which oceans contribute about 55 billion tons.

Answer: (b) 4 x 1013 kg

Explanation:
1. About \(4 \times 10^{13}\) kg of carbon is fixed in the biosphere through photosynthesis annually.

Teacher's Note:
1. Decomposition steps: fragmentation, leaching, catabolism, humification and mineralisation; it is faster in warm, moist conditions, with nitrogen and sugar rich detritus, and slower with lignin, chitin and in cold.
2. Humus is dark, amorphous, colloidal and highly resistant to microbial action.

Answer: (c) Products of antibiotics

Explanation:
1. Production of antibiotics is a product, not an ecosystem service; soil generation, habitat and pollination are services.

Teacher's Note:
1. In aquatic ecosystems the grazing food chain is the major conduit of energy flow, whereas the detritus food chain dominates on land; only about 10 per cent of energy passes to the next trophic level.
2. Succession proceeds from pioneers to a climax; hydrosere and xerosere both end in a mesic climax.

Answer: (d) Climate regulation = 5 trillion US dollars

Explanation:
1. Climate regulation was valued at only about 2 trillion dollars, so the statement of 5 trillion dollars is not true.

Teacher's Note:
1. Ecosystem functions include productivity, decomposition, energy flow and nutrient cycling.
2. GPP minus respiratory loss gives NPP; the annual NPP of the biosphere is about 170 billion tons of dry matter, of which oceans contribute about 55 billion tons.