Solutions-Class-12-Biology-Chapter-14-Ecosystems and Energy Flow-Maharashtra Board

Ecosystems and Energy Flow

Maharashtra Board-Class-12th-Biology-Chapter-14


Question 1. Multiple choice questions

(1) Which one of the following has the largest population in a food chain?

(a) Producers

(b) Primary consumers

(c) Secondary consumers

(d) Decomposers

Answer :

(a) Producers

(2) The second trophic level in a lake is ________________

(a) Phytoplankton

(b) Zooplankton

(c) Benthos

(d) Fishes

Answer :

(b) Zooplankton

(3) Secondary consumers are __________

(a) Herbivores

(b) Producers

(c) Carnivores

(d) Autotrophs

Answer :

(c) Carnivores

(4) What is the % of photosynthetically active radiation in the incident solar radiation?

(a) 100%

(b) 50 %

(c) 1-5%

(d) 2-10%

Answer :

(b) 50 %

(6) Give the term used to express a community in its final stage of succession?

(a) End community

(b) Final community

(c) Climax community

(d) Dark community

Answer :

(c) Climax community

(7) After landslide which of the following type of succession occurs?

(a) Primary

(b) Secondary

(c) Tertiary

(d) Climax

Answer :

(a) Primary

(8) Which of the following is most often a limiting factor of the primary productivity in any ecosystem.

(a) Carbon

(b) Nitrogen

(c) Phosphorus

(d) Sulphur

Answer :

(c) Phosphorus

Question 2. Very short answer question.

(1) Give an example of ecosystem which shows inverted pyramid of numbers.

Answer :

Number of insects dependent on a single tree, is an example of ecosystem having inverted pyramid of numbers.

(2) Give an example of ecosystem which shows inverted pyramid of biomass.

Answer :

Oceanic ecosystem has inverted pyramid of biomass.

(3) Which mineral acts as limiting factor for productivity in an aquatic ecosystem.

Answer :

Phosphorus acts as limiting factor for productivity in an aquatic ecosystem.

(4) Name the reservoir and sink of carbon in carbon cycle.

Answer :

Atmosphere is the reservoir of carbon cycle, while fossil fuels embedded in ocean and oceanic waters are the sink of carbon in carbon cycle.

Question 3. Short answer questions.

(1) Distinguish between upright and inverted pyramid of biomass

Answer :

Upright pyramid of biomass Inverted pyramid of biomass
In upright pyramid, the number and biomass of the organisms which are at first trophic level of producers is high. The inverted pyramid shows that the number and biomass of organisms at the first trophic levels of producers are the lowest.
Biomass decreases at each level. The biomass foes on increasing at each trophic level.
Base always contains large number of producers. The base of pyramid is always in small numbers of producers.
Pyramid is always upright. Pyramid is always inverted.

(2) Distinguish between Food chain and Food web.

Answer :

Food chain Food web
The food chain is a linear sequence of organisms that feeds on a single type of organism. Food web is interconnections between many small food chains.
Energy flows through a single pathway from lower to higher trophic levels. In food web, the energy flow is interconnected through numerous food chains in the ecosystem.
Higher trophic level members feed on only one type of organism. It allows one organism to feed on multiple types of organisms.
Energy flow can be easily calculated in the food chain. Energy flow is difficult to calculate in a food web.
Increased instability occurs due to the number of separate and confined food chains. The complexity of food chains increases stability and prevents disturbance from the removal of one group of organisms.
The food chain consists of 4-6 trophic levels of different species, and competition occurs between members of the same trophic level. The food web contains numerous trophic levels and diverse species populations, with competition observed in members of the same and different trophic levels.
Food chains are of two types :

1. Grazing food chain 2. Detritus food chain

In food web there are no types

Question 4. Long answer questions.

(1) Define ecological pyramids and describe with examples, pyramids of number and biomass.

Answer :

Ecological Pyramids : Ecological Pyramids are the representation of relationships between different components of ecosystem at successive trophic levels.

Pyramid of numbers :

  • The pyramid of numbers demonstrates the connection between producers, herbivores, and predators at each trophic level based on their numbers.
  • As we move up the trophic levels, the number of dependent creatures decreases.
  • For example, there are more grasses than animals who consume them. The amount of herbivores, such as rabbits, would be lower than grass but higher than predators, which rely on rabbit populations.
  • Thus, the producers would be more than primary consumers and primary consumers would be more than secondary consumers.
  • The top level consumers would be least in their numbers. This pyramid shows upright nature.

Pyramid of biomass :

  • Pyramid of biomass are constructed by taking into consideration the different biomass in every successive trophic level.
  • Pyramid of biomass in seas in inverted as the biomass of fishes is more than the biomass of phytoplankton.

(2) What is primary productivity? Give brief description of factors that affect primary productivity.

Answer :

Primary Productivity: Primary productivity refers to the rate of biomass generation in an ecosystem, measured in grams per square metre per day (g/m2/day), expressed in units of mass per unit surface per unit time.

  • Primary productivity is described as gross primary productivity (GPP) and net primary productivity (NPP).
  • The rate of production of organic matter during photosynthesis is called gross primary productivity of an ecosystem. Of this the amount of energy lost through respiration of plants is called respiratory losses.
  • It is calculated by subtracting the energy lost through respiration, resulting in net primary productivity (NPP), which is the available biomass for heterotrophs (herbivores, carnivores, and decomposers).

Factors affecting primary productivity:

Gross primary productivity (GPP) depends on the following factors :

  • Plant species inhabiting a particular area.
  • Variety of environmental factors such as temperature, sunlight, salinity,
  • oxygen and carbon dioxide content, etc.
  • Availability of nutrients.
  • Photosynthetic capacity of plants.

(3) Define decomposition and describe the processes and products of decomposition.

Answer :

  • Decomposition is a process carried out by decomposer organisms, including bacteria, actinomycetes, and fungi.
  • Detritus food chain initiates decomposition, starting from dead organic matter.
  • Detritivores break down detritus into smaller fragments, referred to as fragmentation.
  • Water-soluble inorganic nutrients seep into the soil, precipitated as salts, known as leaching.
  • Catabolism, a third step, involves enzymes degrading detritus into simple inorganic substances.
  • Humus, a dark-colored amorphous substance, is formed from partially decomposed organic matter.
  • Decomposition requires more oxygen and is influenced by temperature and humidity.

(4) Write important features of a sedimentary cycle in an ecosystem.

Answer :

  • Reservoir of sedimentary cycles is earth’s crust.
  • The nutrients such as phosphorus which show sedimentary cycle, moves through hydrosphere, lithosphere and biosphere.
  • There is no respiratory release of nutrients into the atmosphere which show sedimentary cycle.
  • Natural reservoir of such nutrients are usually in the form of rocks. The rocks upon weathering release such nutrients into circulation.
  • Sedimentary cycles are very slow in their reactions.

(5) Describe carbon cycle and add a note on the impact of human activities on carbon cycle.

Answer :

Carbon cycle :

  • The carbon cycle involves several processes, including photosynthesis, respiration, decomposition, sedimentation, and combustion.
  • Carbon, which makes up 49% of the dry weight of all organisms, is present in the oceans and fossil fuels, which serve as long-term storage places.
  • Carbon dioxide is stored in the carbon-carbon bonds of carbohydrates during photosynthesis, while respiration releases the same energy. Carbon dioxide is primarily found in oceans and rocks, where it forms mild carbonic acid upon dissolution. Corals and algae help build coral reefs made of limestone.
  • Carbon moves through food chains, with autotrophic green plants on land and in water taking up carbon dioxide and manufacturing carbohydrates through photosynthesis.
  • Carbon stored in plants can be released into the atmosphere, consumed by animals upon feeding, or stored until the plant dies. Animals obtain their carbon through their food, and carbon in animals can be released back into the atmosphere through respiration, decomposition, or conversion into fossil fuels.
  • Fossil fuels like coal, oil, and natural gas can be mined and burned for energy purposes, releasing carbon dioxide back into the atmosphere. Carbon from limestone can also be released if pushed to surfaces and slowly weathered away, and subducting and volcanic eruptions can release stored carbon from sediments.

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