Practice Question Paper -5
Class XII (044)
Unit x Ecology and Environment
Biology (2024-25)
Maximum Marks: 70 Time: 3 hours
General Instructions:
(i) All questions are compulsory.
(ii) The question paper has five sections and 33 questions.
(iii) Section–A has 16 questions of 1 mark each; Section–B has 5 questions of 2 marks each; Section–
C has 7 questions of 3 marks each; Section– D has 2 case-based questions of 4 marks each; and
Section–E has 3 questions of 5 marks each.
(iv) There is no overall choice. However, internal choices have been provided in some questions. A
student must attempt only one of the alternatives in such questions.
(v) Wherever necessary, neat, and properly labeled diagrams should be drawn.
Section – A
Q. No. 1 to 12 are multiple choice questions. Only one of the choices is correct. Select
and write the correct choice as well as the answer to these questions.
Q. No Questions Marks
1 The extinction of passenger pigeon was due to 1
(a) Increased number of predatory birds.
(b) Over exploitation by humans.
(c) Non-availability of the food
(d) Bird flu virus infection.
2 Which of the below mentioned regions exhibit less seasonal variations? 1
(a) Tropics
(b) Temperate
(c) Alpines
(d) Both (a) and (b)
3 Vertical distribution of different species occupying different levels 1
represents:
a. Productivity b. Standing crop c. Stratification, d. Trophic level
4 ------------- are not given any place in ecological pyramids even though 1
they play an important role in the ecosystem.
a. Saprophytes b. Producers c. Consumers d. Abiotic factors
5 The process of mineralization by microorganism helps in release of 1
a) Inorganic nutrients from humus
b) Both organic and inorganic nutrients from detritus
c) Organic nutrients from humus
d) Organic nutrients from detritus and formation of humus
6 Which of the following forests is known as the ‘lungs of the planet 1
Earth’?
(a) Taiga forest
(b) Tundra forest
(c) Amazon rainforest
(d) Rainforests of North East India
7 Which of the following is an example of ex- situ conservation 1
a) sacred groves
b) national park
c) biosphere reserve
d) seed bank
8 Cuckoo and crow are example of 1
a) competition
b) ecto parasite
c) brood parasitism
d)predation
9 A protozoan reproduces by binary fission. What will be the number of 1
protozoans in its population after the 5th generation?
a) 128 b)24 c)64 d)32
10 The birth and death rates of four countries are given below. Which one 1
will have the least population growth rate?
Country Birth rate/1000 Death rate/1000
A 48 41
B 15 5
C 25 10
D 35 18
a) A b)B c) C d) D
11 Sea anemone gets attached to the surface of the hermit crab. The kind of 1
population interaction exhibited in this case is
a) Amensalism
b) b) Commensalism
c) c) Mutualism
d) d) Parasitism
12 What is the percentage of photosynthetically active radiation (PER) in 1
the incident solar radiation
a)100% b)50%c) 1 to 5%c) 2 to10%
Question No. 13 to 16 consist of two statements – Assertion (A) and Reason (R).
Answer these questions selecting the appropriate option given below:
A. Both A and R are true and R is the correct explanation of A.
B. Both A and R are true and R is not the correct explanation of A.
C. A is true but R is false.
D. A is False but R is true.
13 Assertion: Maximum biodiversity occurs in temperate regions. 1
Reason: Tropical areas have favourable conditions for speciation
and for supporting a variety and
number of organisms.
14 1
Assertion: Interspecific competition is the only potent force in
organic evolution.
Reason: Unexceptionally two closely related species competing for
the same resources can not coexist indefinitely.
15 Assertion :Natality contributes to the increase in population density 1
Reason: Natality refers to the number of birth during a given
period in the population which is added to the initial density
16 Assertion: Pyramids of energy can be inverted or upright. 1
Reason: Energy flow is unidirectional and at each step of trophic
level it is lost as heat.
Section - B
17 The Tundra desert's gross primary productivity (GPP) is 800 2
kilocalories/m2 and respiration losses are about 200
kilocalories.(a) What is the net primary productivity of the desert?
Show calculations.(b) Why do deserts have the least NPP across
most ecosystems?
OR
Why is the number of trophic levels in an ecosystem limited?
18 Define’ Zero population growth ‘.Draw an age pyramid for the 2
same.
OR
Name the interaction in each of the following:
(i) Antibiotic secreted by certain fungi kill some bacteria in the
vicinity
(ii) Mycorrhizal association between fungi and plant roots
(iii) Koyal lays eggs in crow’s nest
(iv) An orchid plant growing on a mango tree
19 The Abingdon tortoise in Galapagos islands became extinct within 2
a decade on the introduction of goats in the island. Explain giving
reasons.
20 What is mutualism? Mention any two examples, where the 2
organisms involved are commercially exploited in agriculture.
21 (a) Draw a ‘pyramid of numbers’ of a situation where a large 2
population of insects feed upon a very big fruit tree. The insects in
turn, are eaten by small birds which in turn are fed upon by big
birds.
(b) Differentiate giving reason, between the pyramid of biomass of
the above situation and the pyramid of numbers that you have
drawn.
OR
(c) Differentiate between a detritivore and a decomposer.
(d) Construct a grazing food chain and detritus food chain using
the following, with 5 links each:
Earthworm, bird, snake, hawk, grass, grasshopper, frog, vulture
decaying plant matter.
Section - C
22 (a) Explain, giving one example, how co-extinction is one of the 3
causes of loss of biodiversity.
(b) What is common about Eichhornia, Lantana and Parthenium
with reference to the threat to our biodiversity?
(c) Lantana and Eichhornia are examples of two weeds. How do
they affect the ecosystem?
23 “The population of a metro city experiences fluctuations in its 3
population
density over a period of time.”
(a) When does the population in a metro city tend to increase?
(b) When does the population in metro city tend to decline?
(c) If ‘N’ is the population density at the time ‘t’, write the
population
density at the time ‘t + 1’.
24 Carefully observe the graph given below and answer the questions 3
that
follow.
a) Name the naturalist who made this observation. Add a note on
his findings.
b) When would the slope of ‘a’ become steeper?
c) Represent the relationship based on equations for ‘a’ and ‘b’.
25 a) Name the process that help in nutrient cycling. 3
b) Write the factors responsible for controlling the rate of this
process
c) Mention the factors, when the rate would be faster.
26 a) What is primary productivity? Why does it vary in different 3
types of ecosystems?
b) Why is the assimilation of energy at the herbivore level
called secondary productivity?
27 Study the graph given below and answer the questions that follow: 3
a) What does K stand for in this equation?
b) Which curve represents human population growth at present?
Do
you think such a curve is sustainable? Give reason in support of
your answer.
28 a) List any three ways of measuring population density of a habitat. 3
b) Mention the essential information that can be obtained by
studying the population density of an organism
Section - D
29 The following is a general graph of the interaction that happens 4
between deer and lions over time in the forest. The deer population
is represented as prey population and the lion population as
predator population.
a) Deer are herbivores. But they are also predators in a broad
ecological context .How?
b) How do predators help in maintaining biodiversity?
c) Bring out the key roles played by lion in this population
interaction
OR
Imagine deer population evolved adaptation that allowed them to
run faster and easily evade lions. What changes could this have on
deer population and lion population over many generations.
30 4
Why is Amazon’s Biodiversity Critical for the Globe?
This biodiversity is important globally. Every species in this
incredibly
A biodiverse system represents solutions to a set of biological
challenges, any one of which has transformative potential and
could generate global human benefits. For example, the discovery
of ACE (Angiotensin Converting Enzyme) inhibitors, inspired by
studies of Fer de Lance venom (a tropical viper found in the
Amazon), help hundreds of millions of people control hypertension
around the world. This rich wealth of species brims with promise,
awaiting discovery. Leaf cutting ants are an example. These ants
collect leaves as mulch for their fungus farms, deliberately
avoiding those with natural fungicides. Studying the species they
avoid might be a shortcut to identifying new natural fungicides.
Knowledge of indigenous populations have a large role to play in
uncovering this potential. Biodiversity is also important locally,
constituting a natural capital underpinning many human activities,
in particular livelihoods of the world’s poor. For example, the giant
catfish is an important local stapler. Amazon biodiversity also
plays a critical role as part of global systems, influencing the
global carbon cycle and thus climate change, as well as
hemispheric hydrological systems, serving as an important anchor
for South American climate and rainfall.
(a) Give two reasons that gives the credit for amazon forest as’
lungs of planet’
(b) What factors may lead to more species diversity in an
ecological area?
(c) What do you understand about the ‘Evil Quartet ‘of
biodiversity loss?
(d) what are the different types of biodiversity?
Section - E
31 5
a- Provide two examples each of natural ecosystems and artificial
ecosystems.
b- Zooplankton belongs to which level of the food chain.
c- Give one example which represents an inverted pyramid.
d- What is common to earthworm, soil mites and dung beetles in an
ecosystem?
e-who explained that stability of a community depends on a
species richness?
OR
a- Provide information on the limitations of ecological pyramids.
b- Observe the diagram given below and answer the given
questions-
i- Identify the situation where such a pyramid is possible.
ii- one which belongs to PC
iii- one on which PC depends
c- Define standing crop
32 Name the type of population interaction. 5
i) Ticks living on the skin of dogs.
ii) sucker fish attached to the back of a Whale.
iii)Cuscuta growing on a hedge plant
iv) Clown fish living among the tentacles of sea anemone.
v) Rhizobium in the root nodules of leguminous plants.
OR
Explain the defence mechanism evolved in praise to avoid
overpopulation of their predators.
33 What are the two types of desirable approaches to conserve 5
biodiversity? Explain with examples bringing out the difference
between the two types.
OR
Explain briefly the 'rivet popper hypothesis' of Paul Ehrlich.
Answer key and marking scheme
Practice Question Paper -5
Class XII (044)
Unit X: Ecology and Environment
Biology (2024-25)
Maximum Marks: 70 Time: 3 hours
Q.N Value Points Mark
o. s
1. 1
(b) Over exploitation by humans
2. (a) Tropics 1
3. (c) Stratification 1
4. (a) Saprophytes 1
5. (a) Inorganic nutrients from humus 1
6. (c) Amazon rainforest 1
7. (d) Seed bank 1
8. (c) Brood parasitism 1
9. (a) 32 1
10. (a) A 1
11. (b) Commensalism 1
12. (d) 2 to 10% 1
13. (D) A is false but R is true. 1
14. (C) A is true but R is false. 1
15. (A) Both A and R are true, and R is the correct explanation of A. 1
16. (D) A is false but R is true. 1
17. 1
(a) Net Primary Productivity (NPP) = Gross Primary Productivity (GPP) -
Respiration losses
= 800 kcal/m² - 200 kcal/m²
= 600 kcal/m²
(b) Reason for low NPP in deserts: Deserts have limited water, extreme
temperatures, and poor soil nutrients, which restrict plant growth, resulting in
lower Net Primary Productivity (NPP).
OR
Reason for limited trophic levels in an ecosystem: The number of trophic levels is
limited because energy decreases significantly at each trophic level due to energy
loss as heat, making it insufficient to support many levels.
18. 1+1
Zero Population Growth: A situation where the birth rate equals the death rate,
resulting in a stable population size.
Age pyramid for zero population growth: A rectangular shape, with relatively
equal proportions of age groups.
OR
Name the interactions: (i) Amensalism
(ii) Mutualism
(iii) Brood parasitism
(iv) Commensalism
19. The Abingdon tortoise in the Galapagos Islands became extinct due to the 2
introduction of goats, which led to competition for food. Goats quickly consumed
vegetation that was crucial for the tortoise’s survival, leading to a decline in food
availability and ultimately the extinction of the tortoise within a decade.
20. Mutualism is an interaction between two species where both benefit from the 1+1
relationship.
Examples of mutualism exploited in agriculture:
Rhizobium bacteria in root nodules of legumes, which help in nitrogen fixation.
Mycorrhizal fungi associated with plant roots to improve nutrient uptake.
21. 1 +1
(a) Pyramid of numbers:
A large fruit tree (1) → Many insects (hundreds) → Small birds (lesser in
number) → Big birds (few)
(b) Difference between the pyramid of biomass and pyramid of numbers:
In this scenario, the pyramid of biomass would be upright, as the biomass of the
large tree is much greater than the biomass of insects and birds. The pyramid of
numbers, however, is inverted due to the large population of insects feeding on a
single tree.
OR
(c) Difference between detritivores and decomposers:
Detritivores: Organisms like earthworms that physically break down detritus.
Decomposers: Microorganisms like bacteria that chemically decompose organic
matter into simpler substances.
(d) Grazing food chain:
Grass → Grasshopper → Frog → Snake → Hawk
Detritus food chain:
Decaying plant matter → Earthworm → Bird → Snake → Vulture
22. (a) Co-extinction example: When a host species goes extinct, its associated 1+1+1
parasite also goes extinct. For instance, if a specific flower species becomes
extinct, its specialized pollinator may also go extinct.
(b) Common threat with Eichhornia, Lantana, and Parthenium: They are invasive
species that threaten native biodiversity by outcompeting native plants and
disrupting ecosystems.
(c) Effects of Lantana and Eichhornia on ecosystems:
Lantana forms dense thickets, preventing growth of native plants.
Eichhornia (water hyacinth) clogs water bodies, depleting oxygen and harming
aquatic life.
23. 1+1+
(a) The population in a metro city tends to increase due to high birth rates, 1
immigration, and better employment opportunities.
(b) The population in a metro city tends to decline due to emigration, higher
death rates, and economic downturns.
(c) Population density at time (t+1) can be represented as:
N(t+1) = N(t) + (B + I) - (D + E)
where:
B = Births, I = Immigration, D = Deaths, E = Emigration
24. a) Alexander von Humboldt 1+
b) The slope of ‘a’ becomes steeper in smaller, isolated areas like islands or 1+1
specialized habitats. This is because these areas often have unique species
that adapt specifically to that environment, leading to a more rapid increase
in species richness per unit area.
c) The species-area relationship can be represented by the equation: S =
CA^Z,
where:
S = species richness
C = constant
A = area
Z = slope of the line (usually between 0.1 and 0.2 for continental areas;
higher in islands or isolated habitats).
25. 1+
a) The process that helps in nutrient cycling is decomposition. 1+1
b) Factors controlling the rate of decomposition include temperature,
moisture, oxygen availability, and the chemical composition of detritus
(e.g., lignin content).
c) Decomposition rate is faster in warm and moist conditions with
adequate oxygen and in simple organic matter that decomposes easily.
26. 1+
a) Primary productivity is the rate at which energy is converted by autotrophs 1+1
(producers) into organic substances.
It varies among ecosystems due to factors like light availability, temperature,
nutrient supply, and water availability.
b) The assimilation of energy at the herbivore level is called secondary
productivity because it represents the energy absorbed and converted by
herbivores (consumers) from the organic matter of producers.
27. a) Carrying capacity
b) The curve representing human population growth at
present is the exponential (J-shaped) growth curve. 1 +1+1
c) This curve is not sustainable in the long term because
resources like food, water, and space are limited, and
rapid population growth can lead to resource
depletion, environmental degradation, and a decrease
in the quality of life.
28. 1+1+1
a) Three ways to measure population density of a habitat:
Direct counting (census) of individuals.
Sampling techniques like quadrat or plot sampling.
Mark-recapture method for mobile animals.
b) Essential information obtained by studying population density includes:
Population size and distribution across the habitat.
Health and viability of the population.
Impact of environmental factors on population dynamics
29. 1+1+2
a) Deer are herbivores, but they are considered predators in a broad ecological
context because they consume plants, which are living organisms. By feeding
on vegetation, deer influence plant populations and community dynamics.
b) Predators help maintain biodiversity by controlling prey populations,
preventing any one species from dominating the ecosystem. This allows a
variety of species to coexist and promotes ecological balance.
c) Key roles played by lions in this interaction:
Population control: Lions help regulate deer populations, preventing
overgrazing and supporting vegetation.
Selective pressure: Lions target weaker or slower individuals, promoting a
healthier and more resilient deer population.
OR
If deer evolved to run faster and evade lions, the likely changes over
generations would be:
Increase in deer population, as fewer would be caught by predators.
Decline in lion population, as food availability decreases, leading to weaker or
fewer lions over time.
30 a) Two reasons that credit the Amazon rainforest as the "lungs of the planet": 1+1+2
Oxygen production: The Amazon rainforest produces a significant amount of
the world's oxygen through photosynthesis.
Carbon dioxide absorption: It absorbs large quantities of carbon dioxide,
helping to mitigate climate change.
(b) Factors that may lead to more species diversity in an ecological area:
Habitat heterogeneity: Diverse habitats and microclimates promote various
niches for different species.
Climate stability: Stable and favorable climatic conditions allow for the
establishment and survival of multiple species.
c) i) Habitat loss and fragmentation ii) over exploitation iii) invasion of alien
species iv) co-extinction
d) The three types of biodiversity are:
Genetic biodiversity: The variety of characteristics within a species
due to genetic differences
Species biodiversity: The variety of species and their numbers within
an ecosystem
Ecological biodiversity: The variety of life across different ecosystems
31 a) 5
Natural ecosystems: Forests, wetlands.
Artificial ecosystems: Agricultural fields, urban parks.
b) Zooplankton belongs to the second trophic level (primary consumers) of the
food chain.
c) An example that represents an inverted pyramid is the pyramid of numbers in
a forest where a large number of insects feed on a single tree.
d) Earthworms, soil mites, and dung beetles are all decomposers in an
ecosystem, helping recycle nutrients.
OR
a) Limitations of ecological pyramids include:
They do not account for the size of organisms.
They can be misleading when considering overlapping trophic levels.
b)
i) Such a pyramid is possible in a marine ecosystem (e.g., large fish feeding on
zooplankton).
ii) An organism that belongs to PC (Primary Consumer) could be zooplankton.
iii) An organism on which PC depends could be phytoplankton.
c) A standing crop is the total dried biomass of the living organisms present in a
given environment. It is the total amount or number of living things or of one
kind of living thing (as an uncut farm crop, the fish in a pond, or organisms in
an ecosystem) in a particular area at any given time.
32 Population Interactions: 1+1+1
+1+1
i) Parasitism (Ticks on dogs)
ii) Commensalism (Sucker fish on whale)
iii) Parasitism (Cuscuta on hedge plant)
iv) Mutualism (Clownfish and sea anemone)
v) Mutualism (Rhizobium in leguminous plants)
OR
Defense Mechanisms in Prey:
Prey species evolve various defense mechanisms such as camouflage, mimicry,
and warning coloration to avoid predation. These adaptations help them blend
into their environment, resemble toxic species, or signal potential danger to
predators, reducing their chances of being overpopulated by predators.
33 Desirable Approaches to Conserve Biodiversity: 3+2
In-situ Conservation:
Definition: Conservation of species in their natural habitats.
Example: National parks and wildlife reserves, such as the Sundarbans National
Park in India, where tigers and other species are protected in their natural
environment.
Ex-situ Conservation:
Definition: Conservation of species outside their natural habitats.
Example: Botanical gardens or zoos, such as the San Diego Zoo, which houses
endangered species for breeding and research.
Difference: In-situ focuses on protecting ecosystems and habitats, while ex-situ
involves preserving species in controlled environments.
The 'rivet popper hypothesis' of Paul Ehrlich
The 'rivet popper hypothesis' of Paul Ehrlich is an analogy where the ecosystem
is compared to an airplane and species are compared with the rivets. In an
aeroplane (ecosystem) various parts (components of an ecosystem) are joined
together by thousands of rivets (species).
Removal of rivets from the airplane
If every passenger travelling in it starts pulling out a rivet to take home, it may
not affect the safety of the flight initially. Hence, loss or extinction of a few
species from the ecosystem initially will not create any threat to the existing
species.
Removal of rivets from crucial parts
But as more and more rivets are removed, the plane becomes dangerously weak
over a period of time. Removal of rivets of a crucial part like wings (equivalent
to keystone species) will pose a serious threat to the safety of flight.
This means that the extinction of key species (rivets on the wings), which are
performing a major function in that ecosystem, will become a threat to the
safety of other species (flight safety compromised).
Example
For example, removing a predator like lions from an ecosystem will result in
the increase in the number of the prey species (deer, rabbits). This will result in
the competition between them (for the same food) and finally they will starve to
death.
