Q1. The common nitrogen-fixer in paddy fields is
Solution
Azospirillum is the common nitrogen-fixer in paddy fields.
Q2. The pyramid of energy in an aquatic ecosystem is
Solution
The pyramid of energy in an aquatic ecosystem is always upright because at each transfer about 80-90% of the energy available at a lower trophic level is used up to overcome its entropy and to perform metabolic activities. Only 10% of the energy is available to the next trophic level.
Q3. The loss of energy as one proceeds from one trophic level to the next trophic level is approximately
Solution
Nearly 90% of energy is lost when it moves from one trophic level to the next because there is a decrease in the content and flow of energy with the rise in trophic level.
Q4. In
an ocean, the aphotic zone lies in the
Solution
Based
on the availability of light, oceans are divided into three vertical regions—the
photic zone (the well lit, upper region of 200 metres of the ocean), the
aphotic zone (the dimly lit region of 200-2000 metres) and the abyssal zone
(the permanently dark region below 2000 metres).
Q5. The
composition of the atmosphere is somewhat stable up to a height of ____ above
the Earth’s surface.
Solution
The
composition of the atmosphere is somewhat stable up to a height of 80 km
above the Earth’s surface.
Q6. The ‘10 Percent Law’ is related to
Solution
The ‘10 Percent Law’ implies that exactly 90% of the energy is lost in the transfer at each trophic level, and that only 10% is passed on as biological energy. According to this law, during the transfer of energy from organic food from one trophic level to the next, only 10% of energy from organic matter is stored as flesh. The remaining is lost during transfer, broken down in respiration or lost to incomplete digestion by higher trophic levels.
Q7. Primary succession occurs in
Solution
The natural development of a biotic community which occurs on a previously sterile or bare area is called primary succession. Some examples of primary succession include dunes and igneous rocks.
Q8. Explain
the response of all communities to environment over time.
Solution
Environmental factors like temperature,
water and light may influence the members of communities in varying degrees.
Organisms, in response to these factors, try to adapt according to their
capacities. In this process, they may try to maintain a constant internal
environment through homeostasis or migrate to a less stressful environment or
may even suspend activities till favourable conditions return.
Q9. The sequence
of species through which the organic molecules in a community process is
Solution
The sequence of populations or organisms of an ecosystem through which
the food and energy pass with each member becoming the food of a later member
of the sequence is called a food chain.
Q10. If
Pn is net primary
productivity, Pg is
gross primary productivity, R is respiration and E is excretion, then net
primary productivity is given by the formula
Solution
Net
primary productivity is given by the formula
Pn
= Pg − R, where
Pn
is net primary productivity, Pg
is gross primary productivity and R is respiration.
Q11. The
layer of the atmosphere which is present between the altitude of 50-85 km is
known as
Solution
Troposphere:
Up to 16 km altitude
Stratosphere:
16-50 km altitude
Mesosphere:
50-85 km altitude
Thermosphere:
85 km and beyond
Q12. What are primary consumers?
Solution
The herbivores which depend on plants for their food are called primary consumers.
Q13. The
10% law of energy was proposed by
Solution
The
10% law of energy was proposed by Lindemann. The law states that during
energy transfer from one tropic level to the other in the form of food, only
10% is stored in the higher tropic level and the rest is lost due to
respiration, wastage and decomposition.
Q14. Most
food chains are composed of how many trophic levels?
Solution
The maximum number
of trophic levels is hardly 3 to 5 in terrestrial ecosystems and 4 to 6 in
aquatic ecosystems. The lesser number of trophic levels is due to consumption
of lot of energy through respiration.
Q15. Biosphere means
Solution
Biosphere is the sum of all ecosystems and comprises atmosphere,
lithosphere and hydrosphere.
Q16. A
natural reservoir of phosphorus is
Solution
The reservoir for a nutrient element such as phosphorus is present in the
sediments of the Earth such as bare rocks.
Q17. Which
one of the following statements for pyramid of energy is incorrect, whereas
the remaining three are correct?
Solution
The pyramid of energy can never be inverted. It is always upright
because at each transfer about 80-90% of the energy available at the lower
trophic level is used up to overcome its entropy and to perform metabolic
activities. Only 10% of the energy is available to the next trophic level.
Q18. Which
of the following is a characteristic of a food web?
Solution
Characteristics
of a food web:
They are made of interlinking food chains.
They provide alternative pathways for food
availability.
They help check overpopulation as organisms
depend on each other for food.
They help in ecosystem development.
Q19. What does secondary productivity in an ecosystem
indicate? List any two factors by which productivity is limited in an aquatic
ecosystem.
Solution
The rate of assimilation and formation of
new organic matter by consumers is called secondary productivity. The factors
which affect productivity in an aquatic ecosystem are
(a) Nitrogen in a marine ecosystem
(b) Light, which decreases with increasing
depth of water
Q20. This is an inverted pyramid:
Solution
An inverted pyramid is formed when the number of individuals or biomass is minimum and increases at each trophic level. The pyramid of biomass in a pond ecosystem is an example of an inverted pyramid because the biomass of phytoplankton may be smaller than that of zooplankton.
Q21. Which of
the following is a pioneer in xerarch succession?
Solution
In xerarch succession, the pioneer community is the lichen stage which
brings about slow weathering of rocks and formation of soil leading to
secretion of lichen acids. The lichen acids slowly corrode the rock surface and
release minerals required for the proper growth of lichens.
Q22. The gradual and predictable change in the species composition of a given area is called ecological succession. What do you understand with the pioneer and climax communities in this context?
Solution
The first community invading the habitat and starting ecological succession is called a pioneer community. Examples: Phytoplankton in hydrosere and lichens in lithosere
The most stable community developed at the end of ecological succession is called a climax community. Example: Forest stage
Q23. In an ecosystem, the
cycling of nutrients is known as
Solution
The exchange or circulation of
biogenetic nutrients between living and non-living components of the biosphere
is said to be a biogeochemical cycle.
Q24. An inverted pyramid of numbers and an inverted pyramid of biomass are respectively seen in
Solution
In a tree ecosystem, the pyramid of numbers is inverted because the number or biomass at the producer level is minimum and increases at each trophic level and is similar in the case of sea ecosystem.
Q25. In an aquatic ecosystem, the trophic level equivalent to cows in a grassland is
Solution
The cows in a terrestrial ecosystem are herbivores or primary consumers. Similarly, in an aquatic system, the zooplankton are the herbivores.
Q26. Which
of the following pyramid of numbers is not upright?
Solution
The pyramid of numbers is always upside down because a tree will
support a huge number of insects, or a flea-infested dog will support a large
number of fleas.
The biomass of the insects is smaller than the biomass of their food,
but the numbers of insects are greater.
Q27. State two differences between the first trophic levels of the detritus food chain and the grazing food chain.
Solution
First trophic level of detritus food chain
First trophic level of grazing food chain
(i) Decomposers are the first trophic level.
(i) Producers are the first trophic level.
(ii) They break down complex organic matter into a simpler form by secreting enzymes.
(ii) They prepare complex organic molecules from simple organic material by using sunlight.
Q28. What is the role of plants, animals and bacteria in an ecosystem?
Solution
Plants, animals and bacteria are producers, consumers and decomposers in an ecosystem.
Q29. The biomass available for consumption to heterotrophs and the rate of formation of new organic matter by consumers are defined as
Solution
The amount of organic matter stored by the producers and is available for the heterotrophs is called net primary productivity (NPP), and the rate of resynthesis of organic matter by the consumers is known as secondary productivity.
Q30. (i) Explain
primary productivity and the factors which influence it.
(ii)
Describe how do oxygen and chemical composition of detritus control
decomposition.
Solution
(i) Primary
productivity is defined as the amount of biomass or organic matter produced
per unit area over a time period by plants during photosynthesis. It varies
in different types of ecosystems. It is expressed in terms of weight or
energy. It depends on the following factors:
(a) Plant
species inhabiting a particular area
(b)
Environmental factors
(c)
Availability of nutrients
(d)
Photosynthetic capacity of plants
(ii)
Decomposition of detritus is slow if it contains lignin, chitin, tannins and
cellulose, whereas it is quick if detritus is made up of nitrogenous
compounds and water-soluble substances like sugars. This is because the
latter are easy to degrade. Oxygen is required for the activity of
decomposers and detritivores. Therefore a reduced oxygen amount will slow
down the process of decomposition.
Q31. Approximately
what amount of energy is available to one trophic level from one trophic
level lower to it?
Solution
In the transfer of food energy from one trophic level to the other,
only about 10% is stored at a higher trophic level and the remaining 90% is
lost in respiration, decomposition and waste.
Q32. A
normal food chain consists of how many trophic
levels?
Solution
Normally
a food chain contains 4-5 trophic levels, wherein
the organisms are producers, primary consumers, secondary consumers, tertiary
consumers and decomposers.
Q33. Azotobacter and Beijerinckia
are examples of
Solution
Azotobacter and
Beijerinckia are free-living species (non-symbiotic) of bacteria which can
fix nitrogen in the rhizosphere of several plants.
Q34. The decomposition of organic matter is brought about by
Solution
The microorganisms are responsible for decomposition of organic matter because they break down the complex compounds and release simple substances.
Q35. Some of
the nutrient cycles are labelled as below:
Sulphur
cycle (A), Phosphorus cycle (B), Carbon cycle (C) and Nitrogen cycle (D). Of
these, the sedimentary cycle is represented by
Solution
In the sedimentary cycle, the material involved in circulation between
biotic and abiotic components is present in the sediments of the Earth. The
sedimentary cycles are the sulphur cycle and phosphorus cycle.
Q36. The functional aspect of a species with reference to the place of occurrence is called
Solution
The physical habitat of both plants and animal species is called an ecological niche. All the adaptations help the organisms survive in their ecological niche.
Q37. The statement ‘Tiger is the apex of the food chain’ indicates:
Solution
Nothing eats the tiger and that is why it is known as ‘the apex of the food chain’, indicating that the tiger is a carnivore.
Q38. Which one of the following statements is correct for secondary succession?
Solution
Secondary succession occurs in a forest area due to deforestation which may be due to a forest fire or severe drought.
Q39. Which
of the following forms the starting point of a detritus food chain?
Solution
In
a detritus food chain, fallen leaves form the start of the food chain. The
fallen leaves are eaten by detritivores, which in turn are eaten by smaller
insects, which become food for the lizard.
Q40. Which types of the following pyramids are never inverted?
Solution
The pyramid of energy is never inverted because the maximum amount of the energy available at the lower trophic level is used up to overcome its entropy and to perform metabolic activities.
Q41. The climax stage is achieved quickly in secondary succession as compared to primary succession. Why?
Solution
The rate of succession is much faster in secondary succession as the soil is already present as compared to primary succession where the process starts from a bare area.
Q42. The
final stable community in ecological succession is
Solution
The last stage in ecological succession is the climax community which comprises
hardy and light-demanding trees which grow in the area occupied by shrubs.
Q43. The important steps in the process of decomposition are
Solution
Decomposition is the physical and chemical breakdown of complex organic remains by the decomposers. Various processes include fragmentation, mineralisation, leaching, catabolism and humification.
The smaller fragments from a particular body are immobilised as a part of the detritus comes out undigested and are called fragmentation.
Mineralisation is the release of inorganic substances, both non-mineral and mineral, from organic matter.
Soluble substances formed during decomposition are subjected to leaching or passage to deep layers of soil/ground water by percolating water.
The decomposers change insoluble complex organic substances into simple and soluble organic compounds and inorganic substances which is called catabolism.
Humification is the process of formation of humus from detritus or organic remains.
Q44. Explain
how does
(i) A primary succession starts on a bare rock and reaches
a climax community.
(ii) The
algal bloom eventually chokes the water body in an industrial area.
Solution
(i) The
bare rock is invaded by pioneer species called lichens. Lichens secrete acids
to dissolve rock, helping in weathering and soil formation which pave the way
for the bryophytes, which hold in a small amount of soil. The bryophytes are
succeeded by the bigger plants, leading to forests. Forests are the climax
community in this succession.
(ii) An algal bloom is a rapid increase or
accumulation in the population of algae (typically microscopic) in an aquatic
system. Algal blooms may occur in freshwater or marine environments. The fertility
of a lake in an industrial area increases with inorganic chemicals and sewage,
causing an increase of primary productivity and leading to an increased
growth of algae. The decomposition of algae leads to reduction in oxygen
quantity and death of aquatic life. This excessive richness of nutrients in a
lake or other body of water, frequently due to run-off from the land, causes
a dense growth of plant life called eutrophication.
Q45. Acclimatisation is
Solution
The process of adapting to a new environment in an ecosystem is called acclimatisation. For example, an organism adapts to a reduced oxygen environment which results due to the decrease in oxygen concentration at a specific altitude.
Q46. Name the type of food chains responsible for the
flow of a larger fraction of energy in an aquatic and a terrestrial
ecosystem, respectively. Mention one difference between the two food chains.
Solution
The detritus food chain in an aquatic ecosystem and the
grazing food chain in a terrestrial ecosystem are responsible for the flow of
a larger fraction of energy.
The major difference between the food chains is that
the grazing food chain starts with green plants called producers as the first
trophic level, whereas the detritus food chain begins with dead organic
matter called saprophytes as the first trophic level.
Q47. Pond is
an example of
Solution
A pond ecosystem is a natural ecosystem which is a fragile balance of
organisms such as fish, plants and other animals. The ecosystem starts with
solar energy, which is utilised by plants which are then consumed by fish or
other primary producers, and the process may end up at the dining table.
Q48. Which one of the following is not a gaseous biogeochemical cycle in an ecosystem?
Solution
In gaseous cycles, the reservoir for elements like oxygen, carbon and nitrogen is in the atmosphere. Phosphorus is an element which is present in the sediments of the Earth. Therefore, the phosphorus cycle is called a sedimentary cycle.
Q49. Germplasm conservation at liquid N2 temperature is
Solution
The preservation of germplasm in liquid nitrogen at −198°C is called cryopreservation.
Stratification is the formation of vertical layers where vegetation is dense.
Scarification is a different term for skin etching or scratching.
Q50. Which
of the following components are decomposed slowly?
Solution
Components
such as cellulose, lignin and chitin found in bone and hair are decomposed
slowly.
Q51. What
are seral communities?
Solution
The whole series of changes in
community characteristics from the pioneer stage to the climax stage
constitute a sere.
Q52. The pyramid of
energy is always
Solution
The pyramid of energy is always upright because at each transfer about
80-90% of the energy available at a lower trophic level is used up to
overcome its entropy and to perform metabolic activities. Only 10% of the
energy is available to the next trophic level.
Q53. In
primary succession on rocks, the pioneer species are usually
Solution
In primary succession on rocks, the pioneer community is the
lichen stage which brings about slow weathering of rocks and formation of
soil leading to secretion of lichen acids. The lichen acids slowly corrode the
rock surface and release minerals required for the proper growth of lichens.
Q54. Maximum CO2 fixation is done by
Solution
First, carbon dioxide is fixed by the producers, which include the phytoplankton in an aquatic food chain. It then passes to zooplankton (herbivores) and so on.
Q55. The
universal Y-shaped energy flow model was proposed by
Solution
The
generalised or universal Y-shaped energy flow model was put forth by E. P.
Odum. This model is applicable to both terrestrial and aquatic ecosystems.
Q56. The first stable product of fixation of atmospheric nitrogen in leguminous plants is
Solution
Biological nitrogen fixation occurs when atmospheric nitrogen is converted to ammonia by an enzyme called nitrogenase.
Q57. In a
pyramid of numbers, in a grassland ecosystem, the largest population is that
of
Solution
The maximum number
of individuals occurs at the producer level in a grassland ecosystem.
Q58. Select the
correct match:
A.
Sedimentary nutrient cycle - Nitrogen cycle
B.
Pioneer species - Lichens
C.
Secondary succession - Burnt forests
D.
Pyramid of biomass in sea - Upright
Solution
In primary succession on rocks, the pioneer community is the lichen
stage which brings about slow weathering of rocks and formation of soil
leading to secretion of lichen acids. The lichen acids slowly corrode the rock
surface and release minerals required for the proper growth of lichens.
Secondary succession occurs in a forest area due to deforestation which
may be due to a forest fire or severe drought.
Q59. Explain with the help of two examples, how the
pyramid of numbers and the pyramid of biomass can look inverted.
Solution
The pyramid of biomass in a pond is generally
inverted because the biomass of fish exceeds that of phytoplankton and the
number of big fish eating the small fish is also greater than the small ones.
Also, in the pyramid of numbers, the number of
insects feeding on a big tree is far greater than the tree. Now the number of
small birds depending on the insects and the number of larger birds eating
the smaller ones also increases in the order.
Q60. Which one of the following is a sedimentary cycle?
Solution
In a sedimentary cycle, the material involved in the circulation between biotic and abiotic components is present in the sediments of the Earth. The best example is the phosphorus cycle.
Q61. Which one of the following is not used for construction of ecological pyramids?
Solution
Ecological pyramids are usually prepared considering three ecological parameters - number of individuals, rate of energy flow and dry weight.
Q62. Which
of the following is a transducer?
Solution
A
transducer is an organism which has the ability to convert energy from one
form to the other. Because producers can convert solar energy to chemical
energy, they are also referred to as transducers. Because grass is a producer,
it is also a transducer.
Q63. Ecological
pyramids were developed for the first time by
Solution
Charles
Elton developed ecological pyramids, and hence, they are also known as
Eltonian pyramids.
Q64. In a
food chain, the total amount of living material is depicted by
Solution
The amount of living organic matter is called biomass. The pyramid of
biomass is a graphic representation of biomass present sequence-wise per unit
area of different trophic levels with producers at the base and top
carnivores at the top.
Q65. An inverted pyramid is found in
Solution
An inverted pyramid is formed when the number of individuals or biomass is minimum and increases at each trophic level. The pyramid of biomass in aquatic ecosystem is an example of an inverted pyramid because the biomass of phytoplankton may be smaller than that of zooplankton.
Q66. Which one of the following is a denitrifying bacterium?
Solution
Nitrites and nitrates are converted by the denitrifying bacteria Pseudomonas into nitrogen, which escapes into the atmosphere and is lost from the cycle.
Q67. Detritivores break down
the detritus by the process called
Solution
When the detritivores feed on large fragments, small fragments are
left undigested. The part digested by detritivores is immobilised. Due to
fragmentation, left-over detritus comes out.
Q68. Why is a food web formed in nature?
Solution
Many organisms occupy positions in different food
chains, and several food chains become interconnected to form a food web.
Q69. Describe the basic requirements of an ecosystem.
Solution
The basic requirements of an ecosystem are
(a) Inorganic nutrients such as carbon dioxide and water.
(b) Autotrophs or producers such as plants.
(c) Micro-consumers or decomposers such as bacteria and fungi.
(d) A source of continuous supply of energy, i.e. Sun.
Q70. Ecosystem is
Solution
Ecosystem is open because materials move from one ecosystem to another. For example, the wind flows from forest to lake and the animals move from pond to land.
Q71. Secondary
productivity is the rate of formation of new organic matter by
Solution
The rate of resynthesis of organic matter by consumers is known as
secondary productivity. It depends on the loss while transferring energy-containing
organic matter from the previous trophic level in addition with consumption
due to respiration and predation.
Q72. Decomposers are
Solution
Decomposition is the chemical breakdown of complex organic remains by decomposers brought about by bacteria and fungi.
Q73. Which one of the
following is considered as a pioneer community in xerarch?
Solution
The sequence of successional stages which occur on dry land is called
xerarch. In dry land, the pioneer community is the lichen stage which brings about
slow weathering of rocks and formation of soil leading to secretion of lichen
acids. The lichen acids slowly corrode the rock surface and release minerals which
are required for the proper growth of lichens.
Q74. Ecosystem creates
Solution
In an ecosystem, all the living organisms are linked in a systematic chain for feeding habits called a food chain and also for interlocking food chains called a food web.
Q75. Changes in the body form of some planktonic animals with seasonal changes in temperature are called:
Solution
Cyclic recurrent polymorphism in certain planktonic fauna in response to seasonal temperature or salinity changes is said to be cyclomorphosis.
Q76. The
amount of carbon fixed in a year through photosynthesis produces about
Solution
The
amount of carbon fixed in a year through photosynthesis is about 7 × 1013
kg.
Q77. The boundary or transition between two or more communities is called:
Solution
The transitional area between two different plant communities such as forest and grassland is called an ecotone.
Q78. The flow of energy among various trophic levels of an ecosystem is
Solution
Energy flow in an ecosystem is always unidirectional because an energy pyramid's shape shows how the amount of useful energy, which enters each level is the chemical energy in the form of food, decreases as it is used by the organisms in that level.
Q79. When the number of organisms at successive levels is plotted, they assume the shape of a pyramid. This is called the pyramid of
Solution
The graphical representation of individuals at successive higher trophic level (stepwise) with producers kept at the base and top carnivores kept at the top is called a pyramid of numbers.
Q80. Explain
the function of ‘reservoir’ in a nutrient cycle. List the two types of
nutrient cycles in nature.
Solution
The function of the ‘reservoir’ is to meet
the deficit which occurs due to an imbalance in the rate of influx and
efflux.
Two types of nutrient cycles are gaseous
cycles (nitrogen and oxygen cycles) and sedimentary cycles (sulphur and phosphorus
cycles).
Q81. (i) What are the shortcomings of ecological pyramids
in the study of an ecosystem?
(ii) ‘Pyramid of energy is always upright’. Explain.
(iii) What is meant by saying that the energy flow
in an ecosystem is unidirectional?
Solution
(i) The ecological pyramid is like a simple food
chain and does not accommodate food webs. Thus, it does not take into account
the fact that species may belong to two or more trophic levels at a time.
Also, the saprophytes in an ecosystem are given no place in the ecological
pyramids despite their vital role.
(ii) Pyramid of energy is always upright because
when energy flows from a particular trophic level to the next trophic level,
some energy is always lost as heat at each step.
(iii) The Sun is an ultimate source of all energy.
The energy passes from producers to primary consumers, secondary consumers,
tertiary consumers and ultimately to the quaternary consumers, and the flow is
in one direction, i.e. energy cannot pass back in a reverse direction.
Q82. Which
of the following can convert sulphates to hydrogen sulphide?
Solution
Aerobacterand Desulphovibrio can convert
sulphate to H2S, while Beggiatoa,
Thiobacillus thiooxidansand Neurospora
oxidise sulphide to sulphate.
Q83. Why is secondary
succession faster than primary succession?
Solution
Secondary succession is faster than primary
succession because of the presence of
(a) Soil for growth, which also results in
quick attainment of climax.
(b) Water, environment and the seeds or
other propagules.
Q84. Mention one similarity between hydrarch
and xerarch successions.
Solution
Both hydrarch and xerarch
successions result in medium water conditions.
Q85. Why nutrient cycles in nature are called biogeochemical cycles?
Solution
Nutrient cycles in nature are called biogeochemical cycles because the elements move cyclically from the environment to living organisms and back to the environment.
Q86. What
is primary productivity? How is it different from net primary productivity?
Solution
Primary productivity is referred to as the
amount of biomass or organic matter produced per unit area over a time period
by the plants during photosynthesis. It is the weight of the organic matter
stored by the producers in a unit area volume per unit time. Net primary
productivity is equal to the rate of organic matter produced by photosynthesis
minus the rate of respiration and other losses.
It is represented as
NPP = GPP − R
Q87. The
Y-shaped energy flow model was pioneered by
Solution
The
Y-shaped energy flow model was pioneered by H. T. Odum.
Q88. A biome
is
Solution
The biome is a complex biotic community characterised by plant and
animal species and maintained under climatic conditions of the region. It is
the total of all ecosystems.
Q89. What is stratification in an ecosystem? Explain with an example.
Solution
The vertical distribution of different species occupying different levels in an ecosystem is called stratification. Trees occupy the topmost vertical layer of a forest, shrubs occupy the second layer and herbs and grasses occupy the bottommost or base layers.
Q90. During the
food chain, the maximum energy is stored in
Solution
The maximum amount of energy is used by the producers as solar energy which
uses 1000 Kcal because 90% of energy is lost when it moves from one trophic
level to the next.
Q91. Why is the length of a food chain in an ecosystem
generally limited to 3 to 4 trophic levels?
Solution
The amount of energy flow decreases with successive
trophic levels as only 10% of energy is transferred from one trophic level to
the other. The energy is lost in the form of respiration and other vital
activities to maintain life. If more trophic levels are present, then the
residual energy will be limited and decreases to such an extent that it
cannot further support any trophic level by the flow of energy.
Q92. What will happen to an ecosystem if
(i) All producers are removed.
(ii) All organisms of the herbivore level are
eliminated.
(iii) All top carnivore population is removed.
Solution
(i) If all producers are removed, then there will be
reduction in primary productivity and there will be no biomass available for
consumption by higher trophic levels or heterotrophs.
(ii) If all organisms of the herbivore level are
eliminated, there will be increase in primary productivity and biomass of
producers. The carnivore population will subsequently dwindle due to food
shortage.
(iii) If all top carnivore population is removed, then
there will be an increase in the number of herbivores which leads to
over-grazing by herbivores, resulting in desertification.
Q93. Why is the rate of assimilation of energy at the herbivore level called secondary productivity?
Solution
The rate of assimilation of energy at the herbivore level is called secondary productivity because the biomass available to the consumer for consumption is a resultant of the primary productivity from plants.
Q94. What would happen to the successive trophic levels in the pyramid of energy, if the rate of reproduction of phytoplankton was slowed down? Suggest two factors which could cause such a reduction in phytoplankton reproduction.
Solution
If the rate of reproduction of phytoplankton slows down, then the net primary productivity decreases. As a result, the flow of energy will also decrease in the successive trophic level.
The two factors which cause a reduction in phytoplankton reproduction are
(a) Less water availability
(b) Less nutrient availability
Q95. Write
the important features of a sedimentary cycle in an ecosystem.
Solution
The sedimentary cycle is the circulation of
non-gaseous biogeochemical nutrients between abiotic
and biotic components of an ecosystem with the reservoir pool being the lithosphere
or sediments of earth.
The important features of a sedimentary
cycle in an ecosystem are
(a) Input: Weathering of rocks, industrial
processing and mining add the nutrient to the cycling pool.
(b) Internal cycling: Nutrients contained in
the cycling pool are picked up by producers and the process is called uptake.
Organic matter with nutrients is then passed to the next trophic
levels.
(c) It is the loss of nutrients from the cycling
pool. It occurs through soil erosion and run-off water.
Q96. Name the pioneer and the climax species in a water
body. Mention the changes observed in the biomass and biodiversity of the
successive seral communities developing in the
water body.
Solution
Pioneer species in a hydrosere
in a water body is formed of plankton like diatoms, phytoplankton, cyanobacteria etc., while the climax community in it is
forest trees depending on the nature of the climate. In a hydrosere,
there is successive increase in biomass as well as biodiversity in the seral communities.
Q97. What are starting points of a grazing food chain and
a detritus food chain respectively?
Solution
Producers are the starting point of a grazing food
chain, and detritus is the starting point of a detritus food chain.
Q98. Mention the role of pioneer species in primary succession on rocks.
Solution
In primary succession on rocks, the pioneer species invade a bare area and give way for other species to grow.
Q99. Name
the dominant producers in a deep aquatic ecosystem. What other name could you
give to a primary consumer?
Solution
Phytoplankton
are the dominant producers in an aquatic ecosystem. Primary consumers are
also known as herbivores.
Q100. A food chain has only a few trophic levels. Justify.
Solution
In a food chain, about 80-90% of energy available with a trophic level is lost during its transfer from one trophic level to the next, so the amount of energy available decreases.
Q101. (i) Name the kind of organisms which constitute the
pioneer community of xerarch and hydrarch succession.
(ii)
Differentiate between pioneer community and climax community.
Solution
(i) Xerarch succession is seen in lichens and hydrarch succession is seen in phytoplankton.
(ii)
Pioneer Community
Climax Community
(a) The species which
invade a bare land is called pioneer community.
(a) The final stage
in a succession constitutes the climax community.
(b) The pioneer
species have high reproductive rate.
(b) The climax
species have low reproductive rate.
(c) Pioneer community
is replaceable.
(c) It is stable and
not replaced.
Q102. All the primary productivity is not available to a
herbivore. Give one reason.
Solution
All the primary productivity is not
available to a herbivore because a considerable amount is utilised by the
plant in respiration.
Q103. The
rate of decomposition of detritus is affected by the abiotic factors like
availability of oxygen, pH of the soil substratum, temperature etc. Discuss.
Solution
The decomposition of detritus is due to
activities of microbes. The rate of growth of microbes is affected by
temperature. The pH of the substratum affects the composition of microbes
which degrade dead organic matter. If oxygen is present, then aerobic degradation
occurs. In the absence of oxygen, anaerobiosis sets in and there will be
incomplete degradation. Also, the degradation is due to the activity of
exoenzymes secreted by microbes, and the activity of enzymes is affected by
factors such as temperature.
Q104. List the three parameters used for constructing ecological pyramids. Describe any one instance where the pyramid may look inverted.
Solution
The three parameters used for constructing ecological pyramids are
(i) Number of individuals in a trophic level.
(ii) Biomass of individuals in a trophic level.
(iii) Rate of flow of energy in a trophic level.
The pyramid may look inverted in a tree ecosystem where the numbers of consumers are numerous depending on a single producer.
Q105. Why is the pyramid of biomass inverted in a pond ecosystem?
Solution
The pyramid of biomass is inverted in a pond ecosystem because the biomass of fish is higher as compared to producers.
Q106. What could be the reason for the faster rate of
decomposition in the tropics?
Solution
The rate of decomposition is regulated by
climatic factors such as temperature and soil moisture as they have an effect
on the activities of soil microbes. The tropics with its hot and humid
climatic conditions provide an environment which is ideal for the microbes to
speed up the process of decomposition.
Q107. (i) Define mineralisation.
(ii) Justify the pitcher plant as a producer.
Solution
(i) Mineralisation is the process in which the humus is degraded by certain microbes and thus inorganic nutrients are released.
(ii) The pitcher plant is chlorophyllous and is thus capable of photosynthesis and acts as a producer.
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