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BIOLOGY 2 Marks Questions

Ecosystems · Gujarat Board (GSEB) STD 12 Science (GSEB - English Medium). 72 questions.

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2 Marks Questions

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Question 12 Marks
Distinguish between
Grazing food chain and detritus food chain.
Answer
Grazing food chain and detritus food chain:
  Grazing food chain Detritus food chain
1 In this food chain, energy is derived from the Sun. In this food chain, energy comes from organic matter (or detritus) generated in trophic levels of the grazing food chain.
2 It begins with producers, present at the first trophic level. It begins with detritus such as dead bodies of animals or fallen leaves, which are then eaten by decomposers or detritivores.
3 This food chain is usually large. It is usually smaller as compared to the grazing food chain.
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Question 22 Marks
What is primary productivity? Give brief description of factors that affect primary productivity.
Answer
It is defined as the amount of organic matter or biomass produced by producers per unit area over a period of time. Primary productivity of an ecosystem depends on the variety of environmental factors such as light, temperature, water, precipitation, etc. It also depends on the availability of nutrients and the availability of plants to carry out photosynthesis.
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Question 32 Marks
Distinguish between
Primary and secondary productivity.
Answer
Primary and secondary productivity:
  Primary productivity Secondary productivity
1 Rate of amount of production of organic matter by producers over a period of time. Rate of amount of production of organic matter by consumers over a period of time.
2 It is due to photosynthesis. It is due to herbivory and predation.
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Question 42 Marks
Distinguish between
Food chain and Food web.
Answer
Food chain and Food web:
  Food chain Food web
1 Food chain is single pathway of energy transfer from upper to lower. Food web is made of several interconnecting pathways.
2 One individual occupies one trophic level at a time. One individual occupies many trophic level at a time.
3 It decreases stability of the ecological system and less adaptive. It increases stability of the ecological system and more adaptive.
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Question 52 Marks
Distinguish between
Production and decomposition.
Answer
Production and decomposition:
  Production Decomposition
1 It is the rate of producing organic matter (food) by producers It is the process of breaking down of complex organic matter or biomass from the body of dead plants and animals with the help of decomposers into organic raw materials.
2 It depends on the photosynthetic capacity of the producers. It occurs with the help of decomposers.
3 Sunlight is required by plants for primary production Sunlight is not required for decomposition by decomposers.
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Question 62 Marks
Distinguish between
Litter and detritus.
Answer
Litter and detritus:
  Litter Detritus
1 Litter contains all kinds of waste materials above the surface of the earth. Detritus contains dead animals and plants below and above the surface of the earth.
2 It contains both biodegradable as well as non-biodegradable wastes. It contains only biodegradable wastes.
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Question 72 Marks
Distinguish between
Upright and inverted pyramid.
Answer
Upright and inverted pyramid:
  Upright pyramid Inverted pyramid
1 The pyramid of energy is always upright. The pyramid of biomass and the pyramid of numbers can be inverted.
2 The number and biomass of organisms in the producer level of an ecosystem is the highest, which keeps on decreasing at each trophic level in a food chain. The number and biomass of organisms in the producer level of an ecosystem is the lowest, which keeps on increasing at each tropic level. Light is not required for decomposition by decomposers.
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Question 82 Marks
“It is possible that a species may occupy more than one trophic level in the same ecosystem at the same time.” Explain with the help of one example.
Answer
The trophic level represents a functional level, not a species as such. A given species may occupy more than one trophic level in the same ecosystem at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms.
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Question 92 Marks
Explain brood parasitism with the help of an example.
Answer
Koel is a parasitic bird (which has lost the instinct to make its own nest to lay eggs) has evolved the technique of layings eggs in the nest of a crow, Its eggs bear resemblences to those of crow.
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Question 102 Marks
Identify the type of the given ecological pyramid and give one example each of pyramid of number and pyramid of biomass in such cases.
Answer
Inverted pyramid.
Inverted pyramid of biomass in a lake-phytoplankton$\rightarrow$Zooplankton$\rightarrow$fishes.
Inverted pyramid of number-tree$\rightarrow$insects$\rightarrow$birds.
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Question 112 Marks
State the difference between the first trophic levels of detritus food chain and grazing food chain.
Answer
DFC - Dead and decaying organic matter/Dead remains of plants and animals.

GFC - Living green plants/producers.

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Question 122 Marks
How are productivity, gross productivity, net primary productivity and secondary productivity interrelated?
Answer
Productivity is rate of biomass production.
GPP - R = NPP.
NPP - is biomass available to consumers for secondary productivity.
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Question 132 Marks
Why the pyramid of energy is always upright? Explain.
Answer
Pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step. Each bar in the energy Pyramid indicate the amount of energy present at each trophic level in a given time or annually per unit area.
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Question 142 Marks
Name the type of food chains responsible for the flow of larger fraction of energy in an aquatic and a terrestrial ecosystem respectively. Mention one difference between the two food chains.
Answer
Aquatic ecosystem - Grazing Food Chain/GFC.
Terrestrial ecosystem - Detritus Food Chain/DFC.
Difference : GFC begins with phytoplanktons/producers whereas DFC begins with dead organisms/detritus.
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Question 152 Marks
Differentiate between a detritivore and a decomposer giving an example of each.
Answer
Detrivore feeds on dead plants and animals/detritus.

Example: Earthworm/Nematodes.

Decomposer breaks down complex (organic) matter in (inorganic) matter.

Example: Fungus/Bacteria.

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Question 162 Marks
What does secondary productivity in an ecosystem indicate? List any two factors by which productivity is limited in aquatic ecosystems.
Answer
The secondary productivity indicates the rate at which food energy is assimilated at the trophic level of consumers, Light, oxygen, temperature, nitrogen.
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Question 172 Marks
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.
Answer
Gradual decrease of energy at successive trophic levels.

Decrease in light/ nutrients/ oxygen.

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Question 182 Marks
Mention four significant services that a healthy forest ecosystem provide.
Answer
Ecosystem services are the products of ecosystem processes. Healthy forest ecosystem provides the following ecosystem services:
  1. Purification of air and water.
  2. Cycling of nutrients.
  3. Generation of fertile soil.
  4. Provision of habitat to wildlife.
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Question 192 Marks
How are primrry consumers dlfferent from primary carnivores?
Answer
S.No.
Primary consumers
Primary carnivores
(i)
These are the animals which depend on plants for their food.
These are the animals which feed on the herbivorous animals.
(ii)
They occupy the second trophic level; they are herbivores.
They occupy the third trophic level; they are secoundary consumers.
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Question 202 Marks
Give two examples of artificial or man made ecosystems. List the salient features by which they differ from natural ecosystems.
Answer
Crop fields and an aquarium considered as man-made ecosystems. In artificial ecosystems the biotic and abiotic components of ecosystems are maintained artificially by regular feeding and clearing of aquarium and regular irrigation and sowing of seeds in crop field ecosystem. Natural ecosystem self sustains biotic and abiotic components of an ecosystem.
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Question 212 Marks
  1. What is primary productivity? In what units could you express productivity?
  2. Explain the differences between net primary productivity and gross primary productivity.
Answer
  1. The rate at which solar radiation is trapped by producers for the synthesis of organic compound through photosynthesis is called primary productivity. It is expressed as g m-2 y-1 or kcal m-2 year-1.
  2.  

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Question 222 Marks
What does secondary productivity in an ecosystem indicate? List any two factors by which productivity is limited in an aquatic ecosystem.
Answer
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:

  1. Nitrogen in marine ecosystem.
  2. Light, which decreases with increasing depth of water.
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Question 232 Marks
What will happen to an ecosystem if:
All top carnivore population is removed.
Answer
If all the top carnivores are eliminated, then population of herbivores will become manifold. This will put the existence of green plants in danger because of overgrazing. Loss of green plants will force the herbivores to die because of starvation.
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Question 242 Marks
Mention the role of pioneer species in primary succession on rocks.
Answer
Lichens are pioneer species in primary succession on rocks. They secrete organic acids, which withers the rock and help in soil formation. Lichens by forming soil pave way for the next community, i.e. bryophytes.
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Question 252 Marks
Due to uncontrolled excessive hunting, the population of tiger in a forest becomes zero. Discuss the long-term effects of this situation in the population of deer in that forest.
Answer
The reduction in population of tiger (predator) will result in an increase in deer (prey) population. The increased deer population will give more pressure on vegetation due to overgrazing. As a result, the plant population will decrease and lead to decreased deer population due to starvation, death and migration. As a result, the ecological balance will be disturbed, but in the long run these relationships stabilise the prey and predator population in a community.
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Question 262 Marks
Discuss the relationship between detritus food chain and grazing food chain in a terrestrial ecosystem.
Answer
The producers occupy the first trophic level in terrestrial ecosystem and thus, make base of food chain. These producers (plants) are grazed upon by the grazers (herbivores) so herbivores are primary consumers. Primary carnivores prey upon herbivores and are eaten up by secondary carnivores.
This way the top carnivores are ferocious and are not eaten up by any other animal. The decomposers act on all dead animals/plants and return nutrients stored in them to the soil. These nutrients are again used up by the plants and cycle goes on. This way the grazing food chain and detritus food chains are linked up.
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Question 272 Marks
What is natural ecosystem? Explain with the help of suitable example.
Answer
Natural ecosystem These are capable of maintaining and operating themselves, without interference of man.

They are further classified as:

  1. Terrestrial ecosystem Forest, grassland, desert, etc.
  2. Aquatic ecosystem Pond, lake, river, wetland, estuary, etc.
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Question 282 Marks
What would happen to the successive trophic levels in the pyramid of energy, if the rate of reproduction of phytoplanktons was slowed down? Suggest two factors which could cause such a reduction in phytoplankton reproduction.
Answer
If the rate of reproduction of phytoplanktons slows down then the net primary productivity decrease. As a result, flow of energy will also decrease in the successive trophic level.

The following two factors cause reduction in phytoplankton reproduction:

  1. Less water availability.
  2. Less nutrient availability.
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Question 292 Marks
Fill in the missing stages in the given primary hydrarch succession. Phytoplankton-A B C Submerged free-floating → D-Forest plant stage.
Answer
A-Reed-swamp stage B-Submerged plant stage
C-Marsh meadow stage D-Shrub stage.
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Question 302 Marks
In the picture provided, what is the relationship between (1) and (2) with respect to population interaction and between (3) and (4) with respect to trophic levels.

Answer
(1) and (2) are predator and prey respectively.
(3) is a primary consumer (second trophic level).
(4) is a producer (first trophic level).
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Question 312 Marks
Compare the two ecological pyramids of biomass given below and explain the situations in which this is possible. Also, construct an ideal pyramid of energy, if 200,000 joules of sunlight is available.

Answer
The first pyramid of biomass corresponds to a terrestrial ecosystem. Second pyramid refers to a small standing crop of phytoplankton supporting a large standing crop of zooplankton or an aquatic ecosystem.

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Question 322 Marks
The diagram shows the flow of energy through an ecosystem.

Which arrows represent the smallest amount of energy transferred between organisms and the largest amount of energy lost to the ecosystem?
Answer
The smallest amount of energy transferred is represented by arrow 2 and largest energy loss by arrow 3.
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Question 332 Marks
Sometimes due to biotic/ abiotic factor the climax remain in a particular seral stage (preclimax) without reaching the climax. Do you agree with this statement. If yes, give a suitable example.
Answer
It is true that any change in the abiotic/ biotic factor will arrest a particular seral stage leading to a pre-climax condition before the climax stage is achieved. This can happen in cases of forest fires, landslide, change in soil characteristics, increase in herbivore population leading to overgrazing.
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Question 342 Marks
Construct a grazing food chain and a detritus food chain using the following, with five links in each:
Earthworm, bird, snake, vulture, grass, grasshopper, frog, decaying plant matter.
Answer
Grazing food chain:
Grass → Grasshopper → Frog → Snake → Vulture.
Detritus food chain:
Decaying plant matter → Earthworm → Bird Snake → Vulture.
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Question 352 Marks
Expand GPP and NPP. Differentiate between the two.
Answer
GPP stands for Gross Primary Productivity. It is the rate of production of organic matter during photosynthesis in an ecosystem.
NPP stands for Net Primary Productivity. It is defined as GPP-Respiratory loss.
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Question 362 Marks
Why is the rate of assimilation of energy at the herbivore level called secondary productivity?
Answer
It is because the biomass available to the consumer for consumption is a resultant of the primary productivity from plants.
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Question 372 Marks
Primary productivity varies from ecosystem to ecosystem. Explain.
Answer
Primary productivity varies from ecosystem to ecosystem because it depends on the plant species inhabiting the area and their photosynthetic activity. It also depends on various environmental factors, which vary in different ecosystems.
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Question 382 Marks
Explain 'standing crop' in an ecosystem. Draw a pyramid of biomass, where a small standing crop of phytoplanktons supports a large standing crop of zooplanktons in the sea.
Answer
The amount of living matter present at every trophic level at any given time, is called standing crop.

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Question 392 Marks
Why is secondary succession faster than the primary succession?
Answer
Secondary succession is faster than the primary succession because of presence of:
  1. Soil for growth, which also results in quick attainment of climax.
  2. Water, the environment and the seeds or other propagules which are easily available.
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Question 402 Marks
Human activities interfere with carbon cycle. List any two such activities.
Answer
Following are the two activities which interfere with carbon cycle:
  1. Clearing of forests: Reduced green cover hampers carbonification and thus interferes with carbon cycle.
  2. Burning of Fossil Fuels: Burning of fossil fuels adds carbon to the atmosphere and increases the percentage of carbon dioxide in the atmosphere. It also interferes with the carbon cycle.
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Question 412 Marks
What could be the reason for the faster rate of decomposition in the tropics?
Answer
The rate of decomposition is regulated by climatic factors like temperature and soil moisture as they have an effect on the activities of soil microbes. The tropics with its hot and humid climatic condition provides an environment which is ideal for the microbes to speed up the process of decomposition.
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Question 422 Marks
In the North East region of India, during the process of jhum cultivation, forests are cleared by burning and left for regrowth after a year of cultivation. How would you explain the regrowth of forest in ecological term?
Answer
In this case, regrowth of forests is an example of ecological succession. After clearing of forests, the conditions become xerarch which proceeds to mesarch condition after the growth of forests.
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Question 432 Marks
"The energy flow in an ecosystem is unidirectional'. Justify the statement.
Answer
Energy in an ecosystem flows from producers to primary consumers, then from primary consumers to secondary consumers and so on. There is never a back flow of energy, i.e. energy cannot come back to a trophic it has already passed. Therefore, the energy flow is unidirectional in an ecosystem.
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Question 442 Marks
How does the dead organic matter get decomposed in nature? Explain.
Answer
In nature, the decomposer organisms like bacteria and fungi act on the dead organic matter and decompose it. Decomposition is a process of breaking down of complex organic matter into inorganic substances like CO, water and nutrients.
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Question 452 Marks
Name any two organisms which can occupy more than one trophic level in an ecosystem.
Answer
Sparrow: It is a primary consumer when it feeds on grans but becomes a secondary consumer when it feeds on worms and insects.
Human: It is a primary consumer when it feeds on grains and pulses but becomes a secondary consumer when it feeds on lamb.
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Question 462 Marks
Explain the function of reservoir'in nutrient cycle. List the two types of nutrient cycles in nature.
Answer
Reservoir in an ecosystem meets the deficit that arises due to the imbalance in the rate of influx and efflux of nutrients. 

The two types of nutrient cycles are:

  1. Gaseous cycle.
  2. Sedimentary cycle.
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Question 472 Marks
What are saprotrophs? How do they obtain their nutrition?
Answer
Saprotrophs are those organisms, which meet their energy requirements by degrading the organic molecules.
They release enzymes which degrade/ decompose the organic matter outside their body and absorb the digested nutrients.
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Question 482 Marks
Why are oceans least productive?
Answer
Availability of solar radiation is least in oceans; especially in deep oceans. Due to this, oceans are least productive.
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Question 492 Marks
Mention the factors that regulate the rate of function of the entire pond.
Answer
  1. Solar input.
  2. Day length.
  3. Cycle of temperature.
  4. Other climatic factors.
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Question 502 Marks
List the three parameters used for constructing ecological pyramids. Describe any one instance where the pyramid may look inverted.
Answer
The three parameters used are:

  1. Number of individuals in a trophic level.
  2. Biomass of individuals in a trophic level.
  3. Rate of flow of energy in a trophic level.

The pyramid may look inverted in a tree ecosystem where the number of consumers are numerous depending on a single producer.

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2 Marks Questions - BIOLOGY STD 12 Science Questions - Vidyadip