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1. Chapter 13
Organisms and Populations
Q. 1 Multiple choice questions.
1. Which factor of an ecosystem includes plants, animals and microorganisms?
a. Biotic factor b. Abiotic factor c. Direct factor d. Indirect factor
2. An assembladge of individuals of different species living in the same habitat and having
functional interactions is ................
a. Biotic community b. Ecological niche c. Population d. Ecosystem
3. Association between sea anemone and Hermit crab in gastropod shell is that of ................
a. Mutualism b. Commensalism c. Parasitism d. Amensalism
4. Select the statement which explains best parasitism.
a. One species is benefited. b. Both the species are benefited.
c. One species is benefited, other is not affected. d. One species is benefited, other is harmed.
5. Growth of bacteria in a newly inoculated agar plate shows ................
a. exponential growth b. logistic growth c. Verhulst-Pearl logistic growth d. zero growth
Q. 2 Very short answer questions.
1. Define the following terms :
a. Commensalism :
an association between two organisms in which one benefits and the other derives neither
benefit nor harm.
b. Parasitism :
Parasitism describes a relationship between two organisms where one benefits, and the
other is harmed.
c. Camouflage :
Camouflage, also called cryptic coloration, is a defense or tactic that organisms use to
disguise their appearance, usually to blend in with their surroundings.
2. Give one example for each :
a. Mutualism :
Sharks and Remora Fish.Lichens, Nitrogen-Fixing Bacteria and Legumes
b. Interspecific competition:
interspecific competition is between lions and tigers that vie for similar prey. Another example is a farm of
rice paddies with weeds growing in the field.
3. Name the type of association:
a. Clown fish and sea anemone
- mutualism
b. Crow feeding the hatchling of Koel
- Brood parasitism
c. Humming birds and host flowering
plants - mutualism
4. What is the ecological process behind the biological control method of managing with pest
insects?
Answer : The basis of various biological control methods is on the concept of predation. Predation is a
biological interaction between the predator and the prey, whereby the predator feeds on the prey. Hence,
the predators regulate the population of preys in a habitat, thereby helping in the management of pest
insects.
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2. Q. 3 Short answer questions.
1. How is the dormancy of seeds different from hibernation in animals?
Answer : Dormancy is a period of inactivity, either in winter or summer. Both plants and animals have
dormant periods. Hibernation is a unique form of dormancy.
2. If a marine fish is placed in a fresh water aquarium, will it be able to survive? Give reason.
Answer : If a marine fish is placed in a fresh water aquarium, then its chances of survival will diminish.
This is because their bodies are adapted to high salt concentrations of the marine environment. In fresh
water conditions, they are unable to regulate the water entering their body (through osmosis)
3. Name important defense mechanisms in plants against herbivores.
Answer : The first line of defense in plants is an intact and impenetrable barrier composed of bark and a
waxy cuticle. Both protect plants against herbivores. Other adaptations against herbivores include hard
shells, thorns (modified branches), and spines (modified leaves).
4. An orchid plant is growing on the branch of mango tree. How do you describe this interaction
between the orchid and the mango tree?
Answer : The orchid grows as an epiphyte on branch of mango tree. The interaction between orchid and
the mango tree is termed commensalism where in orchid derives benefit of interaction while mango tree is
neither harmed nor benefited.
5. Distinguish between the following:
a. Hibernation and Aestivation
Answer : The state of inactivity and a low metabolic process performed by the animals during the winters
is known as Hibernation. It is also known as winter sleep. On the contrary, when animals take rest in
shady and moist place during summer, it is called Aestivation or Estivation. Aestivation is also known as
summer sleep.
b. Ectotherms and Endotherms
Answer : Ectotherms, including reptiles and amphibians, are organisms that don't possess the ability to
generate sufficient heat to keep themselves warm. As such, they are dependent on environmental
sources of heat, such as sunlight. This explains why most ectotherms are confined to warmer parts of the
world, and why snakes in particular can often be seen basking on roadsides in many countries.
Endotherms, in contrast, do possess the ability to generate their own body heat. Mammals and
birds are the only endothermic classes of organisms. Because of this trait, many mammal and bird
species have been able to colonies some of the coldest parts of the planet.
c. Parasitism and Mutualism
Answer :
Mutualism is a symbiotic relationship in which both species benefit. Commensalism is a symbiotic
relationship in which one species benefits while the other species is not affected. Parasitism is a symbiotic
relationship in which one species (the parasite) benefits while the other species (the host) is harmed.
6. Write a short note on
a. Adaptations of desert animals
Answer : Mammals from colder climates generally have shorter snout, ears, tail and limbs to minimize the
loss of body heat (Allen’s Rule.) In the polar seas, aquatic mammals like seals have a thick layer of fat
(blubber) below their skin acting as an insulator to reduce loss of body heat.
b. Adaptations of plants to water scarcity
Answer : Many desert plants have a thick cuticle on their leaf surfaces and have their stomata in deep
pits to minimize loss of water through transpiration. They also have a special photosynthetic pathway
(CAM - Crassulacean acid metabolism) that enables their stomata to remain closed during daytime. Some
desert plants like Opuntia, have their leaves reduced (modified) to spines and the photosynthetic function
is taken over by the flattened stems.
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3. c. Behavioural adaptations in animals
Answer : Some organisms show behavioural responses to cope with variations in their environment.
Desert lizards manage to keep their body temperature fairly constant by behavioural adaptations. They
bask in the sun and absorb heat, when their body temperature drops below the comfort zone, but move
into shade, when the ambient temperature starts increasing. Some species burrow into the sand to hide
and escape from the heat.
7. Define Population and Community.
Answer :
Population - a group of organisms of the same species who live in the same area at the same time.
Community - a group of populations living and interacting with each other in an area.
Q. 4 Long answer questions.
1. With the help of suitable diagram describe the logistic population growth curve.
Answer :
Logistic growth: competition between individuals for limited resources will weed out the ‘weaker’
ones. Only the ‘fittest’ individuals will survive and reproduce. In nature, a given habitat has enough
resources to support a maximum possible number, beyond which no further growth is possible.
Let us call this limit as nature’s carrying capacity (K) for that species in that habitat.
A population growing in a habitat with limited resources show initially a lag phase,
followed by phases of acceleration and deceleration and finally an asymptote, when the population
density reaches the carrying capacity. A plot of population density (N) in relation to time (t) results
in a sigmoid curve. This type of population growth is called Verhulst-Pearl Logistic Growth. Since
resources for growth for most animal populations, are finite and become limiting sooner or later,
the logistic growth model is considered a more realistic one.
2. Enlist and explain the important characteristics of a population.
Answer : The population has the following characteristics:
Population Size and Density:
Population dispersion or spatial distribution:
Age structure:
Natality (birth rate):
Mortality (death rate):
Vital index and survivorship curves:
Biotic Potential:
Life tables:
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