Part 5 – Energy Flow in Ecosystem
Part 5 – Energy Flow in Ecosystem (Food Chains, Food Webs, 10% Law)
(25 MCQs with answers and detailed explanations, NCERT Class 12 + NEET UG level)
Q1.
The primary source of energy for most ecosystems is:
a) Wind
b) Sunlight
c) Water
d) Soil
Answer: b) Sunlight
Explanation:
- (a) Wind → Affects environment, not energy base.
- (b) Correct → Solar energy captured by producers.
- (c, d) Provide abiotic support, not primary energy.
Q2.
Energy flow in an ecosystem is:
a) Unidirectional
b) Cyclic
c) Bidirectional
d) Reversible
Answer: a) Unidirectional
Explanation:
- Energy enters as sunlight → lost as heat → cannot be recycled.
Q3.
Which law explains the 10% energy transfer in a food chain?
a) Law of limiting factors
b) Lindeman’s 10% law
c) Competitive exclusion law
d) Hardy–Weinberg law
Answer: b) Lindeman’s 10% law
Explanation:
Raymond Lindeman (1942) → only 10% energy is transferred to next trophic level.
Q4.
In a grazing food chain, the first trophic level is occupied by:
a) Herbivores
b) Producers
c) Carnivores
d) Decomposers
Answer: b) Producers
Explanation:
Producers (plants, algae) capture sunlight → entry point of energy.
Q5.
In a terrestrial ecosystem, the primary consumers are mostly:
a) Carnivores
b) Herbivores
c) Decomposers
d) Omnivores
Answer: b) Herbivores
Explanation:
Herbivores eat plants, transferring energy to higher levels.
Q6.
Which of the following is a detritus-based food chain?
a) Grass → Rabbit → Fox
b) Dead leaves → Earthworm → Crow
c) Grass → Grasshopper → Frog → Snake
d) Phytoplankton → Zooplankton → Fish
Answer: b) Dead leaves → Earthworm → Crow
Explanation:
Detritus food chain starts with dead organic matter.
Q7.
Food webs are more stable than food chains because:
a) They involve fewer species
b) They are shorter
c) They have multiple feeding pathways
d) They involve no producers
Answer: c) They have multiple feeding pathways
Explanation:
Food webs distribute energy flow, prevent collapse if one chain is broken.
Q8.
Which of the following is NOT true about energy flow?
a) Energy flow is always unidirectional
b) Energy is recycled in ecosystems
c) Energy decreases at higher trophic levels
d) Energy flow follows the 10% law
Answer: b) Energy is recycled in ecosystems
Explanation:
Energy cannot be recycled, unlike nutrients.
Q9.
If producers in a grassland trap 1000 kcal energy, how much will be available to secondary consumers?
a) 100 kcal
b) 10 kcal
c) 1 kcal
d) 500 kcal
Answer: b) 10 kcal
Explanation:
1000 → 100 (primary consumers) → 10 (secondary consumers).
Q10.
In an aquatic food chain, phytoplankton are:
a) Primary consumers
b) Producers
c) Secondary consumers
d) Decomposers
Answer: b) Producers
Explanation:
They photosynthesize and form the energy base.
Q11.
Which of the following represents a grazing food chain?
a) Leaf litter → Earthworm → Hen
b) Grass → Grasshopper → Frog → Snake
c) Dead animals → Fungi → Bacteria
d) Cow dung → Beetles → Birds
Answer: b) Grass → Grasshopper → Frog → Snake
Explanation:
Starts with living plants → grazing.
Q12.
Detritus food chain is important because:
a) It recycles nutrients
b) It transfers solar energy directly
c) It has top carnivores
d) It lacks decomposers
Answer: a) It recycles nutrients
Explanation:
Decomposers and detritivores mineralize organic matter.
Q13.
Energy loss at each trophic level occurs mainly as:
a) Heat
b) Nutrients
c) Light
d) Water
Answer: a) Heat
Explanation:
Respiration releases heat, lost from system.
Q14.
Which of the following ecosystems has the shortest food chain?
a) Grassland
b) Forest
c) Ocean
d) Desert
Answer: d) Desert
Explanation:
Limited producers → shorter chains.
Q15.
Which ecosystem usually has the longest food chain?
a) Desert
b) Ocean
c) Tundra
d) Grassland
Answer: b) Ocean
Explanation:
Marine ecosystems have complex food webs with many levels.
Q16.
Which organism acts as both primary and secondary consumer in food webs?
a) Cow
b) Deer
c) Human
d) Earthworm
Answer: c) Human
Explanation:
Humans are omnivores → can eat plants (primary consumer role) or animals (secondary).
Q17.
If energy at producer level is 10,000 kcal, energy at tertiary consumer level will be:
a) 1000 kcal
b) 100 kcal
c) 10 kcal
d) 1 kcal
Answer: b) 100 kcal
Explanation:
10,000 → 1000 → 100 → 10 kcal (actually tertiary consumer = 10 kcal).
⚠ Correction → Tertiary consumer receives 10 kcal.
✅ Correct Answer: c) 10 kcal
Q18.
In terms of energy flow, decomposers are important because:
a) They produce food
b) They close the energy cycle
c) They recycle matter but not energy
d) They transfer 90% energy
Answer: c) They recycle matter but not energy
Explanation:
Energy is not recycled, matter is.
Q19.
Why are food chains generally short (4–5 trophic levels)?
a) Energy is lost at each transfer
b) Producers cannot fix much energy
c) Decomposers interfere
d) Consumers reproduce slowly
Answer: a) Energy is lost at each transfer
Explanation:
Only ~10% passed up → limits length of chains.
Q20.
Which of the following is the correct order of food chain in grassland ecosystem?
a) Grass → Tiger → Deer → Vulture
b) Grass → Deer → Tiger → Vulture
c) Grass → Grasshopper → Snake → Frog
d) Grass → Frog → Grasshopper → Tiger
Answer: b) Grass → Deer → Tiger → Vulture
Explanation:
Producers → herbivores → carnivores → decomposers/scavengers.
Q21.
In a forest ecosystem, the lion occupies which trophic level?
a) First
b) Second
c) Third
d) Fourth
Answer: d) Fourth
Explanation:
Plants (1) → deer (2) → tiger/leopard (3) → lion (top carnivore, 4).
Q22.
Food webs are more realistic than food chains because:
a) All species feed on only one type of food
b) Organisms often have multiple food sources
c) There are no decomposers in food webs
d) Energy transfer is 100% efficient
Answer: b) Organisms often have multiple food sources
Explanation:
Webs represent natural complexity.
Q23.
The length of a food chain in any ecosystem is limited by:
a) Number of producers
b) Availability of water
c) Loss of energy at each trophic level
d) Number of decomposers
Answer: c) Loss of energy at each trophic level
Explanation:
Energy loss restricts chain length to 4–5 levels.
Q24.
Which of the following is NOT part of grazing food chain?
a) Phytoplankton
b) Zooplankton
c) Carnivorous fish
d) Fungi
Answer: d) Fungi
Explanation:
Fungi belong to detritus food chain.
Q25.
Energy transfer from one trophic level to the next is usually about:
a) 5%
b) 10%
c) 25%
d) 50%
Answer: b) 10%
Explanation:
As per Lindeman’s 10% law.
- Ecosystem Class 12, NCERT Biology MCQs, Productivity and Decomposition, Energy Flow Ecosystem, Ecological Pyramids Notes, CBSE Class 12 Biology, NEET UG Biology Prep, Ecosystem Chapter MCQs, ecosystem class 12 biology mcqs for neet, ncert biology class 12 chapter 12 questions, productivity and decomposition class 12 notes, energy flow in ecosystem class 12 mcqs, ecological pyramids class 12 neet questions, ecosystem class 12 biology cbse mcqs online, ecosystem class 12 important questions for neet, class 12 biology ecosystem mcqs with answers