Biology · 2nd Puc Science
Ch 12Ecosystem — 2nd PUC Biology, concept-first.
An ecosystem is best understood as a functional unit of nature — living organisms interacting with each other and with their physical surroundings. Ecosystems vary hugely in size, from a small pond to an entire forest or sea; some ecologists even treat the whole biosphere as one global ecosystem, made up of every local…
Key concepts
Hover a concept to preview it and jump to its most relevant Q&A.
Ecological Concepts
Point a camera at a single deer grazing in a forest, and you are looking at an organism. Zoom out a little and you see the whole herd of deer sharing that forest — a population.
Most relevant Q&A
- Fill in the blanks. (a) Plants are called as ______ because they fix carbon dioxide. (b) In an ecosystem dominated by trees, the pyramid (of…Free
- The process of mineralisation by micro organisms helps in the release of: (a) inorganic nutrients from humus (b) both organic and inorganic…Free
- The reservoir for the gaseous type of bio-geo chemical cycle exists in (a) stratosphere (b) atmosphere (c) ionosphere (d) lithospherePreview
- Which of the following is an ecosystem service provided by a natural ecosystem? (a) Cycling of nutrients (b) Prevention of soil erosion (c)…Preview
- What is a biogeochemical cycle. What is the role of the reservoir in a biogeochemical cycle. Give an example of a sedimentary cycle with res…Preview
In previous exams
How often this chapter’s concepts have been examined — real appearance data, never estimated.
Chapter contents
The NCERT structure, section by section. Open a section to see its questions, then read the concept-first solution.
Introduction
An ecosystem is best understood as a functional unit of nature — living organisms interacting with each other and with their physical surroundings.
Ecosystem–Structure and Function
In earlier classes, you looked at the abiotic and biotic components of the environment individually — how they affect each other and their surroundings.
Productivity
Productivity is the rate at which biomass is produced in an ecosystem. It tells us how fast energy is being captured and stored by organisms, and it is the foundation on which the entire food web rest…
Decomposition
Decomposition is the process by which the complex organic matter in dead plants and animals — leaves, roots, animal bodies, waste — is broken down into simpler inorganic substances.
Energy Flow
The flow of energy is the single most important process that makes an ecosystem work. Every living organism needs energy to survive, grow, and reproduce, and that energy ultimately comes from one sour…
Ecological Pyramids
The relationship between organisms at different trophic levels — whether expressed in terms of number, biomass, or energy — takes the shape of a pyramid.
Summary
- Ecosystem structure: Every ecosystem has two interacting components — abiotic (physical factors like light, temperature, water, soil) and biotic (living organisms).
Exercises
+−Show 11 questionsHide questions11 questions
- 12.1Fill in the blanks. (a) Plants are called as ______ because they fix carbon dioxide. (b) In an ecosystem dominated by trees, the pyramid (of…Free
- 12.2Which one of the following has the largest population in a food chain? (a) Producers (b) Primary consumers (c) Secondary consumers (d) Decom…Free
- 12.3The second trophic level in a lake is (a) Phytoplankton (b) Zooplankton (c) Benthos (d) FishesFree
- 12.4Secondary producers are (a) Herbivores (b) Producers (c) Carnivores (d) None of the abovePreview
- 12.5What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation? (a) 100% (b) 50 % (c) 1-5% (d) 2-10%Preview
- 12.6Distinguish between (a) Grazing food chain and detritus food chain (b) Production and decomposition (c) Upright and inverted pyramid (d) Foo…Preview
- 12.7Describe the components of an ecosystem.Preview
- 12.8Define ecological pyramids and describe with examples, pyramids of number and biomass.Preview
- 12.9What is primary productivity? Give brief description of factors that affect primary productivity.Preview
- 12.10Define decomposition and describe the processes and products of decomposition.Preview
- 12.11Give an account of energy flow in an ecosystem.Preview
Exemplar Problems
Higher-order thinking / exemplar-style practice problems.
+−Show 54 questionsHide questions54 questions
- Q1Decomposers like fungi and bacteria are: i. autotrophs ii. heterotrophs iii. saprotrophs iv. chemo-autotrophs. Choose the correct answer: (a…Free
- Q2The process of mineralisation by micro organisms helps in the release of: (a) inorganic nutrients from humus (b) both organic and inorganic…Free
- Q3Productivity is the rate of production of biomass expressed in terms of: i. (kcal m^-3) yr^-1 ii. g^-2 yr^-1 iii. g^-1 yr^-1 iv. (kcal m^-2)…Free
- Q4An inverted pyramid of biomass can be found in which ecosystem? (a) Forest (b) Marine (c) Grass land (d) TundraPreview
- Q5Which of the following is not a producer? (a) Spirogyra (b) Agaricus (c) Volvox (d) NostocPreview
- Q6Which of the following ecosystems is most productive in terms of net primary production? (a) Deserts (b) Tropical rain forests (c) Oceans (d…Preview
- Q7Pyramid of numbers is: (a) Always upright (b) Always inverted (c) Either upright or inverted (d) Neither upright nor inverted.Preview
- Q8Approximately how much of the solar energy that falls on the leaves of a plant is converted to chemical energy by photosynthesis? (a) Less t…Preview
- Q9Among the following, where do you think the process of decomposition would be the fastest? (a) Tropical rain forest (b) Antarctic (c) Dry ar…Preview
- Q10How much of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores? (a) 1% (b) 10% (c) 40% (d) 90%Preview
- Q11The reservoir for the gaseous type of bio-geo chemical cycle exists in (a) stratosphere (b) atmosphere (c) ionosphere (d) lithospherePreview
- Q12If the carbon atoms fixed by producers already have passed through three species, the trophic level of the last species would be. (a) scaven…Preview
- Q13Which of the following type of ecosystem is expected in an area where evaporation exceeds precipitation, and mean annual rainfall is below 1…Preview
- Q14The zone at the edge of a lake or ocean which is alternatively exposed to air and immersed in water is called: (a) Pelagic zone (b) Benthic…Preview
- Q15Edaphic factor refers to: (a) Water (b) Soil (c) Relative humidity (d) AltitudePreview
- Q16Which of the following is an ecosystem service provided by a natural ecosystem? (a) Cycling of nutrients (b) Prevention of soil erosion (c)…Preview
- Q17Name an organism found as secondary carnivore in an aquatic ecosystem.Preview
- Q18What does the base tier of the ecological pyramid represent?Preview
- Q19Arrange the following as observed in vertical stratification of a forest: Grass, Shrubby plants, Teak, Amaranths.Preview
- Q20Name an omnivore which occurs in both grazing food chain and the decomposer food chain.Preview
- Q21Justify the pitcher plant as a producer.Preview
- Q22Name any two organisms which can occupy more than one trophic level in an ecosystem.Preview
- Q23What is the ultimate source of energy for the ecosystems?Preview
- Q24Is the common edible mushroom an autotroph or a heterotroph?Preview
- Q25Why are oceans least productive?Preview
- Q26Why is the rate of assimilation of energy at the herbivore level called secondary productivity?Preview
- Q27Why are nutrient cycles in nature called biogeochemical cyles?Preview
- Q28Define self sustainability.Preview
- Q29A photograph shows a natural landscape with a broad, bare stretch of pale sandy soil in the foreground, dotted only with a few scattered tuf…Preview
- Q30What is common to earthworm, mushroom, soil mites and dung beetle in an ecosystem.Preview
- Q31Organisms at a higher trophic level have less energy available. Comment.Preview
- Q32The number of trophic levels in an ecosystem are limited. Comment.Preview
- Q33Is an aquarium a complete ecosystem?Preview
- Q34What could be the reason for the faster rate of decomposition in the tropics?Preview
- Q35Flow of energy through various trophic levels in an ecosystem is unidirectional and non-cyclic. Explain.Preview
- Q36Apart from plants and animals, microbes form a permanent biotic component in an ecosystem. While plants have been referred to as autotrophs…Preview
- Q37Poaching of tiger is a burning issue in today's world. What implication would this activity have on the functioning of the ecosystem of whic…Preview
- Q38In relation to energy transfer in ecosystem, explain the statement "10kg of deer's meat is equivalent to 1 kg of lion's flesh".Preview
- Q39Primary productivity varies from ecosystem to ecosystem. Explain?Preview
- Q40What is an incomplete ecosystem? Explain with the help of suitable example.Preview
- Q41What are the shortcomings of ecological pyramids in the study of ecosystem?Preview
- Q42How do you distinguish between humification and mineralisation?Preview
- Q43An energy-flow diagram traces a grazing food chain, with each organism drawn in a box numbered 1 to 4 and a "Heat" bubble showing energy los…Preview
- Q44The rate of decomposition of detritus is affected by the abiotic factors like availability of oxygen, pH of the soil substratum, temperature…Preview
- Q45A farmer harvests his crop and expresses his harvest in three different ways. a. I have harvested 10 quintals of wheat. b. I have harvested…Preview
- Q46Justify the following statement in terms of ecosystem dynamics. "Nature tends to increase the gross primary productivity, while man tends to…Preview
- Q47Which of the following ecosystems will be more productive in terms of primary productivity? Justify your answer. A young forest, a natural o…Preview
- Q48What are the three types of ecological pyramids. What information is conveyed by each pyramid with regard to structure, function and energy…Preview
- Q49Write a short note on pyramid of numbers and pyramid of biomass.Preview
- Q50Given below is a list of autotrophs and heterotrophs. With your knowledge about food chain, establish various linkages between the organisms…Preview
- Q51"The energy flow in the ecosystem follows the second law of thermodynamics." Explain.Preview
- Q52What will happen to an ecosystem if: a. All producers are removed; b. All organisms of herbivore level are eliminated; and c. All top carniv…Preview
- Q53Give two examples of artificial or man made ecosystems. List the salient features by which they differ from natural ecosystems.Preview
- Q54What is a biogeochemical cycle. What is the role of the reservoir in a biogeochemical cycle. Give an example of a sedimentary cycle with res…Preview