GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

   

Gujarat Board GSEB Textbook Solutions Class 12 Biology Chapter 14 Ecosystem Textbook Questions and Answers, Additional Important Questions, Notes Pdf.

Gujarat Board Textbook Solutions Class 12 Biology Chapter 14 Ecosystem

GSEB Class 12 Biology Ecosystem Text Book Questions and Answers

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

1. Fill in the blanks.

  1. Plants are called as ………………….. because they fix carbon dioxide.
  2. In an ecosystem dominated by trees, the pyramid (of numbers) is ……………… type.
  3. In aquatic ecosystems, the limiting factor for productivity is ……………….
  4. Common detritivores in our ecosystem are ……………………
  5. The major reservoir of carbon on earth is……………………….

Answer:

  1. Autotrophs
  2. Upright
  3. Light
  4. Bacteria and earthworms.
  5. Oceans

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

Question 2.
Which one of the following has the largest population in a food chain?
a. Producers
b. Primary consumers
c. Secondary consumers
d. Decomposers
Answer:
d. Decomposers

Question 3.
The second trophic level in a lake is
a. phytoplankton
b. zooplankton
c. benthos
d. fishes
Answer:
b. zooplankton

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

Question 4.
Secondary producers are
a. herbivores
b. producers
c. carnivores
d. None of the above
Answer:
d. None of the above

Question 5.
What is the percentage of photosynthetically active radiation (PAR), in incident solar radiation?
a. 100%
b. 50%
c. 1-5%
d. 2-10%
Answer:
b. 50 %

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

Question 6.
Distinguish between
a. Grazing food chain and detritus food chain
b. Production and decomposition
c. Upright and inverted pyramid
d. Food chain and Food web
e. Litter and detritus
f. Primary and secondary productivity
Answer:
a. Grazing food chain: The plant biomass is eaten by the herbivores which are subsequently consumed by a variety of carnivores. Detritus food chain: Here the food chain begins from dead bodies of animals and fallen leaves commonly termed as detritus.

b. Production refers to the process of synthesis of organic compounds from inorganic substances such as CO2, H2O, and minerals utilizing generally the sunlight. It is mainly done by plants. Decomposition: The process of breaking down a substance into its constituent parts. It is brought about by reducer organisms.

c. Upright pyramid: When the number of producer organisms or their biomass is maximum in an ecosystem and these decrease progressively at each trophic level in a food chain, we get an upright pyramid.
Inverted pyramid: When the number of individuals or their biomass at the producer level is minimum and it increases progressively at each trophic level in a food chain, then we get an inverted pyramid.

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

d. Food chain: The sequential inter-linking of organisms involving the transfer of food energy from the producers, through a series of organisms with repeated eating and being eaten is referred to as the food chain.
The Food web is a network of food chains which become inter-connected at various trophic levels so as to form a number of feeding connections amongst different organisms of a biotic community.

e. Detritus: Dead remains of plants and animals constitute the detritus. It is differentiated into litterfall and below-ground detritus.

Litter is above ground detritus. The dead remains of plants and dead remains of animals, their faecal matter that falls on the surface of the earth in the terrestrial ecosystem are litter.

f. Primary productivity refers to the rate of production of biomass or organic matter per unit area over a time period by the producers in an ecosystem. Secondary productivity refers to the rate of production of biomass or organic matter over a time period by the consumers.

Question 7.
Describe the components of an ecosystem.
Answer:
The components of ecosystem may be divided into two main types – biotic component comprising the various kinds of organisms and abiotic component consisting of environmental factors.

a. Biotic components: The living organisms present in an ecosystem form the biotic components. They are interconnected through food. Based on the mode of obtaining food, the organisms occurring in an ecosystem are classified into three main categories. They are producer, consumers and decomposers.

i. Producers: They produce food materials. These are of two types photoautotrophs and chemoautotrophs.
Photoautotrophs: These are green plants that having chlorophylls. They trap the light energy and change it into chemical energy.
Chemoautotrophs: Some bacteria such as sulphur bacteria, iron bacteria, etc. capture the energy released during chemical reactions and prepare organic food.

ii. Consumers: These are mainly animals which are unable to prepare their own food. So they utilize the materials and energy stored by the producers. Consumers are of 3 types. They are primary consumers, secondary consumers, tertiary consumers etc.

iii. Decomposers: These are the organisms which decompose the dead organic bodies of producers and consumers. These are mainly bacteria and fungi. They are also known as saprotrophs.

b. Abiotic factors: These include the non-living, physicochemical factors of the environment. These components affect the distribution, structure, behaviour, and relationship of organisms. Abiotic factors include inorganic substances, organic compounds, and climatic factors.

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

Question 8.
Define ecological pyramids and describe with examples, pyramids of number and biomass.
Answer:
An ecological pyramid may be defined as a graphical representation of the numbers or biomass or status of accumulated energy at different trophic levels in a food chain in an ecosystem.

a. Pyramid of numbers: A pyramid of numbers is the graphical representation depicting the arrangement of a number of individuals of different trophic levels in a food chain in an ecosystem. The pyramid of numbers is found in animal communities. The shape of the pyramids may be upright, e.g. Food chain in a grassland ecosystem or pond ecosystem and inverted, e.g. parasitive food chain.

b. Pyramid of biomass: Pyramid of biomass is a graphical representation of biomass present per unit area in different trophic levels, e.g. Grassland and forest ecosystem.

Question 9.
What is primary productivity? Give a brief description of the factors that affect primary productivity.
Answer:
Primary productivity refers to the rate of production of biomass or organic matter per unit area over a time period by the producers in an ecosystem.

Various factors which affect primary productivity include light, temperature, water, nutrients etc. In deserts, sunlight is abundant but water is scarce or nutrients are lacking. Therefore, in such areas water and nutrient supply become the limiting factor. Productivity increases from polar regions towards the tropics because of the increasing sunlight and temperature.

Question 10.
Define decomposition and describe the processes and products of decomposition.
Answer:
The process of physical and chemical breakdown of complex organic remains into inorganic raw materials (CO2, H2O, minerals) for recycling is called decomposition. It is carried out by organism remain are called detritus.
There are types of decomposition process that occur.

  • Fragmentation
  • leaching and
  • Catabolism

(a) Fragmentation of Detritus:- Small invertebrates animals called detritivores comes out in highly pulverised state in their faeces.

(b) Leaching:- Part of soluble substances present in the fragmented and decomposing detritus get leached to upper layers of soil by percolating water.

(c) Catabolism:- It is carried out by saprotrophic bacteria. They secrete digestive enzymes over the fragmented detritus. The enzymes change the complex organic compounds into simple compounds.

Catabolic action forms two types of products- humus and inorganic the process involved information of these products are respectively called humification and mineralization.

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

Question 11.
Give an account of energy flow in an ecosystem.
Answer:
The ultimate source of entire energy used by living things is sunlight. The radiant energy of sunlight is converted into the chemical energy of the bonds of organic substances prepared by the- green plants by photosynthesis. So they are the producers.

When an animal (primary consumer) eats a plant, the organic substances of the plant are oxidized in the animal’s body to liberate energy. Some of the energy released in the animal dissipates as heat and only a part is used in building up animal tissues. When a second animal (secondary consumer) eats the first, a further loss of energy as heat occurs as the second animal oxidizes the organic substances of the first.
When the organisms undergo death, the decomposers decompose the dead bodies and release chemical energy. So the energy flow is unidirectional i.e., from sunlight to plants and from plants to animals and then to decomposers.

Question 12.
Write the important features of a sedimentary cycle in an ecosystem.
Answer:
In the sedimentary cycle, the reservoir for the nutrient elements is in the sediments of the earth. Elements such as phosphorus, sulphur, potassium, and calcium have a sedimentary cycle. These cycles are slow and less perfect systems in that the elements may get locked in the reservoir pool and go out of circulation for long periods.

Important features:
(i) Input of Nutrients:- Nutrients enter the nutrient pool through weathering of rocks. In sites soil formation also occur through weathering of rocks. Nutrients present in the soil become available to plants. The wind carries nutrients from mining areas and industrial areas and deposited over the soil.

(ii) Internal nutrient cycling:- It is the cycling or circulation of nutrients within the ecosystem. Plants absorb nutrients from the soil and incorporate them into organic matter. In the form of organic matter, the nutrients pass from producers to herbivores and herbivores to carnivores. The process is called transfer. All trophic levels pass a part of organic matter as detritus.

Detritus acted upon by decomposers and releases the nutrients back into the cycling pool. In stable ecosystems, over 80% of the nutrient requirement of the biotic is met through internal nutrient cycling.

(iii) Output of Nutrients:- It is a movement of nutrients out of an ecosystem. Output reduces the availability of nutrients in the cycling pool. It occurs through soil erosion, runoff water, and economic output like harvesting of crops or removal of wood from forests. Crop fields are always under a negative nutrient budget.

Question 13.
Outline the salient features of carbon cycling in an ecosystem.
Answer:
All living organisms require nutrient elements in relatively large amounts. They get the nutrients from the biosphere components. The nutrient elements derived from the earth by the living organisms for use in their growth and metabolism are called biogeochemical or biogenetic nutrients. The movement of nutrient elements through the living and the nonliving components of the biosphere is called the biogeochemical cycle.

In the gaseous cycles the reservoir for nutrient elements is in the atmosphere. The four most abundant elements in the living systems – H, C,0, N – have predominantly gaseous cycles. The carbon cycle is quick and relatively perfect system in that the elements remain in circulation.

Carbon is generally considered as the basis of life. Carbon atom is acting as a back bone for complex organic molecules like carbohydrates, lipids, proteins and nucleic acids.

The main sources of carbon are air, water, fossil fuel and rocks. Carbon dioxide is obtained from the biosphere by

  • green plants for photosynthesis
  • corals for making calcareous skeletons.

Carbon is added to the biosphere by

  • respiration in organisms
  • decay of organic wastes and dead organisms.
  • burning of fuel.
  • weathering of rocks
  • volcanic activity.

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

GSEB Class 12 Biology Ecosystem Additional Important Questions and Answers

Question 1.
Mention the technical term for expressing an animal’s place of living in abiotic environment and its functional relationship with other organisms in an ecosystem.
Answer:
Trophic level and food chain

Question 2.
Give 2 man-made ecosystems.
Answer:
Pond, crop fields

Question 3.
In a particular climatic condition, which components of detritus determine its
a. slower decomposition
b. quicker decomposition?
Answer:
a. Decomposition rate is slower if detritus is rich in lignin and chitin.
b. Decomposition rate is quicker if detritus is rich in nitrogen and water-soluble substances like sugars.

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

Question 4.
Break down of complex organic matter into inorganic substances by decomposers is called decomposition. Some terms related to decomposition are given.
Detritus, detritivores, fragmentation, leaching, catabolism, humification, mineralisation.
Explain the above terms to give an outline of the decomposition process.
Answer:

  • Detritus: Includes dead plant remains such as leaves, bark, flowers, and dead remains of animals including faecal matter.
  • Detritivores: Organisms that break down detritus into smaller particles. Fragmentation: Break down of detritus into smaller particles.
  • Leaching: Process by which water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
  • Catabolism: Degradation of remaining detritus into simpler inorganic substances by bacterial and fungal enzymes.
  • Humification: This leads to the accumulation of a dark coloured amorphous substance called humus.
  • Mineralisation: Further degradation of the humus by some microbes and release of inorganic nutrients occur by this process.

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

Question 5.
Lindeman proposed law of 10%. How will you explain this law in relation to food chain?
Answer:
The transfer of energy from producer to consumer and from consumer >
to next consumer, at higher trophic level is accompanied by loss of energy i
all along the path. When plants are eaten by animal about 10% of energy in the food is fixed into animal flesh. When a carnivore consumes that animal only about 10% of energy is fixed. Producers -> Herbivores
GSEB Solutions Class 12 Biology Chapter 14 Ecosystem 1

Question 6.
The number of individuals in an ecosystem is given. Construct the pyramid of number and energy.
Producer – 1, Herbivores – 50, Carnivores – 75
Answer:
GSEB Solutions Class 12 Biology Chapter 14 Ecosystem 2

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

Question 7.
The mean net productivity of two biomes are given. Analyse them and answer the following questions.
Tropical rain forest – 450 kg/sq.km Desert – 15 kg/sq.km
a. Why does the productivity of deserts become less than that of the tropical rain forest?
b. From the above data analyse the importance of plants in the existence of life.
Answer:
a. In desert the annual rainfall is less than 10 inches. The day temperature ranges from 100°F to 135°F. It is the driest ecosystem in the environment. So the productivity of the desert becomes lesser.

b. In tropical rain forest the vegetation consists of a luxuriant mass of trees and other plants. Plants are the producers of an ecosystem. So the productivity of tropical rain forest is high.

Question 8.
Consider a pond ecosystem.
a. Draw a pyramid of energy in that ecosystem.
b. Compare three types of pyramidal relationships found among the organisms in the pond ecosystem.
c. Is there any difference between nutrient flow and energy flow in an ecosys¬tem? Substantiate.
Answer:
a.
GSEB Solutions Class 12 Biology Chapter 14 Ecosystem 3

b. Pyramid of number and energy is upright and pyramid of biomes is inverted in the pond.

c. Energy flow is unidirectional, but the nutrient flow is in a cyclic manner. The amount of energy flow decreases with successive trophic levels but no such variation in nutrient cycling.

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

Question 9.
Observe the figures given below and answer the following questions.
GSEB Solutions Class 12 Biology Chapter 14 Ecosystem 4
a. Identify the ecological concept converged through the given figures.
b. Name the group of organisms coming as a pioneer community in this ecological process.
c. Given any two characteristic features of climax community.
Answer:
a. Serai stages of hydrarch
b. Phytoplanktons
c.

  • Large-sized individual
  • Complex food chain and food web
  • High nutrient conservation.
  • The efficiency of energy use is high.

Question 10.
It is stated that the pyramid of energy is always upright. Justify (Delhi 2008)
Answer:

  • The base of the pyramid of energy is occupied by producers, which have the maximum amount of energy.
  • When energy flow from one trophic level only 10% is transferred, there is always a loss of some energy in the form of heat.
  • So, the amount of energy at a higher trophic level will always be less than the lower trophic levels, and the pyramid of energy will be upright and be inverted.

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

Question 11.
The products of ecosystem processes are named ecosystem services. Give any five services of the ecosystem.
Answer:

  • Purification of air and water
  • Mitigates drought and flood
  • Cycles nutrients
  • Maintains biodiversity
  • Provides wildlife habitat.

Question 12.
Why does secondary succession is faster than primary succession?
Answer:

  • Secondary succession occurs in an area or place where life had existed before but had been somehow wiped out.
  • some soil and organic sediments are already present, hence succession is faster Primary succession occurs in an area where no life existed before. It takes time for the formation of soil and so succession takes more time.

Question 13.
Cite an example of an inverted ecological pyramid. What kind of pyramid of energy would it have?
Answer:
Example: The pyramid of biomass in the sea.
Kind of pyramid: The energy of the pyramid is always upright.

GSEB Solutions Class 12 Biology Chapter 14 Ecosystem

Question 14.
Name the pioneer species on a bare rock. How do they help in establishing?
Answer:
Lichens are the pioneer species in succession on a bare rock. The lichens secrete certain acids to corrode the rock and help in weathering of rocks and soil formation; thus they pave the way to some plants like bryophytes. The climax community will be a mesic forest.

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