13

Q1. Egrets are often seen along with grazing cattle. How do you refer to this interaction? Give a reason for this association.

Solution

The interaction in egrets and grazing cattle is called commensalism. (i) In this association, egrets are found close to the grazing cattle. (ii) During movement, the cattle flush out various insects which may be difficult for the egrets to catch. (iii) The egrets are benefitted, but the cattle are neither benefitted nor harmed.

Q2. Excessive aerenchyma is a characteristic feature of

• 1) Mesophytes
• 2) Hydrophytes
• 3) Xerophytes
• 4) Heliophytes

Solution

The presence of excessive aerenchyma in hydrophytes helps to transport oxygen produced during photosynthesis to various parts of the plant, including roots. So, the hydrophytes have inflated organs to store air.

Q3. A set of local populations connected by dispersing individuals is known as

• 1) Demes
• 2) Metapopulation
• 3) Sister population
• 4) Intrapopulation

Solution

A set of local populations connected by dispersing individuals is called a metapopulation.

Q4. The relationship between the alga Cladophora and the snail shell on which it grows corresponds to

• 1) Neutralism
• 2) Mutualism
• 3) Predation
• 4) Commensalism

Solution

Cladophora grows on snail shell in which the snail derives food from the algae, but the algae is neither affected nor benefitted. It is an example of commensalism.

Q5. The plants of this group are adapted to live partly in water and partly above the substratum and free from water:

• 1) Helophytes
• 2) Xerophytes
• 3) Thallophytes
• 4) Hydrophytes

Solution

Plants which grow in marshes, are partly submerged in water and regrow from the substratum are called helophytes.

Q6. Which of the following would necessarily decrease the density of a population in a given habitat?

• 1) Natality and immigration
• 2) Natality > mortality
• 3) Mortality and emigration
• 4) Immigration > emigration

Solution

The decrease of population in a habitat depends on two factors - mortality rate and emigration. Mortality rate or death rate is the average number of individuals which die per unit time. Emigration is similar to mortality, but there is no death; it is the permanent departure of some persons from an existing population to another state or country.

Q7. Animals undergo an inactive stage during the winter known as

• 1) Hibernation
• 2) Adaptation
• 3) Acclimatisation
• 4) Aestivation

Solution

Due to cold in winter, some animals like insects and molluscs escape from the cold by hiding in caves, burrows and mud. Hibernation also includes a warm shelter, and the animal consumes stored food.

Q8. Which of the following is a migratory animal?

• 1) Anguilla (eel)
• 2) All of the above
• 3) Siberian crane
• 4) Fur seal

Solution

Migration is the two-way movement of organisms of a population for adjusting to seasonal changes. Some organisms which show migration are Siberian crane, fur seal, elk and Anguilla (eel).

Q9. If in a population, natality is balanced by mortality, then there will be

• 1) Increase in population growth
• 2) Overpopulation
• 3) Zero population growth
• 4) Decrease in population growth

Solution

The density of a population in a given habitat changes due to four basic processes - natality and immigration contribute to an increase in population density and mortality and emigration contribute to a decrease in population density. In zero population growth, natality is balanced by mortality.

Q10. Rapid decline in the population due to high mortality rate is called

• 1) All of the above
• 2) Population density
• 3) Population crash
• 4) Population explosion

Solution

The sudden decrease in the number of people found in a given area as a result of shortage or the lack of environmental resources for survival and growth of the population is called population crash.

Q11. The population limited to a particular geographical area is called

• 1) Natural
• 2) Pandemic
• 3) Endemic
• 4) Alien

Solution

The population limited to a particular geographical area is called an endemic population.

Q12. Human population follows the

• 1) S-shaped growth curve
• 2) Z-shaped growth curve
• 3) J-shaped growth curve
• 4) All of the above

Solution

The human population shows an S-shaped growth curve because the phases of the S-shaped growth curve show steadiness, exponential increase and equilibrium stages for the growth of the individual.

Q13. In a population curve, the rate of growth becomes steady towards the end of the exponential curve due to

• 1) Environmental stress
• 2) Migration
• 3) All of the above
• 4) Reproductive power is reduced

Solution

The growth rate slows down from the exponential phase due to an increase in environmental stress. Environmental stress is due to many factors such as high competition for food, less space and greater mortality.

Q14. The study of the relation of an organism with its environment is called

• 1) Bionomics
• 2) Synecology
• 3) Autecology
• 4) Herpetology

Solution

The comprehensive study of an organism and its relation to its environment is called bionomics. The study of interactions between species in communities is called synecology. The branch of ecology dealing with the biological relationship between an individual organism or an individual species and its environment is called autecology. The study of amphibians and reptiles is called herpetology. 

Q15. Cold-blooded animals fall under the category of

• 1) Endotherms
• 2) Ectotherms
• 3) Psychotherms
• 4) Thermophiles

Solution

Ectothermic animals, sometimes called 'cold blooded' animals, are poorly insulated and produce metabolic heat at a low rate. They also lose heat to cooler surroundings quickly.

Q16. Cuscuta is an example of

• 1) Ectoparasitism
• 2) Predation
• 3) Endoparasitism
• 4) Brood parasitism

Solution

Cuscuta penetrates the tissues of the host by haustoria which extract nutrients, thus showing ectoparasitism.

Q17. In a population, unrestricted reproductive capacity is called

• 1) Carrying capacity
• 2) Biotic potential
• 3) Birth rate
• 4) Fertility

Solution

Biotic potential is when the reproductive capacity of a population increases at its maximum rate under ideal environmental conditions. For example, a single bacterium can divide after every 20 minutes under ideal laboratory conditions and can reproduce in just 36 hours, covering the entire Earth.

Q18. Orchid growing on a mango branch is example of

• 1) Mutualism
• 2) Predation
• 3) Competition
• 4) Commensalism

Solution

Orchids grow on a mango branch to get some space to grow and it does not harm the mango tree. The mango tree is benefitted from the orchid. This is an example of commensalism.

Q19. If the stronger partner is benefitted and the weaker partner is harmed, it is known as

• 1) Allelopathy
• 2) Predation
• 3) Symbiosis
• 4) Commensalism

Solution

The stronger partner kills the weaker partner and when the stronger partner is benefitted, it is said to be predation. For example, a hawk being the stronger bird kills and eats a rat which is a weak animal.

Q20. Which one of the following is most appropriately defined?

• 1) Host is an organism which provides food to another organism.
• 2) Predator is an organism which catches and kills other organisms for food.
• 3) Parasite is an organism which always lives inside the body of other organisms and may kill it.
• 4) Amensalism is a relationship in which one species is benefitted and the other is unaffected.

Solution

The most clear and appropriate phrase is Predator is an organism which catches and kills other organisms for food. This association among the species is called predation, and the species which is caught is called prey.

Q21. Write four characteristics of a biotic community. 

Solution

Four characteristics of a biotic community are species diversity, stratification, dominance and succession.

Q22. The protist Chlorella vulgaris has a mutualism relation with

• 1) Silk moth
• 2) Hermit crab
• 3) Hydra
• 4) Sea anemone

Solution

The protist Chlorella vulgaris has a mutualistic relation with the green hydra Chlorohydra. It lives in the gastrodermal cells of the hydra.

Q23. Bombykol is a pheromone secreted by

• 1) Male silk moth
• 2) Male ant
• 3) Female ant
• 4) Female silk moth

Solution

Bombykol is a pheromone secreted by the female silk moth to attract male silk moths for mating.

Q24. Which of the following is a partial root parasite?

• 1) Orobanche
• 2) Ganoderma
• 3) Sandal wood
• 4) Mistletoe

Solution

Partial root parasites are plants which grow on the roots of other plants. The roots of the plant attack the roots of host trees and nutrients are absorbed from them. Example: Sandal wood tree grows on the roots of Eucalyptus deriving nutrition from it.

Q25. Amensalism is an association between two species where

• 1) One species is harmed and other is unaffected
• 2) Both the species are harmed
• 3) One species is harmed and other is benefitted
• 4) One species is benefitted and other is unaffected

Solution

Amensalism is an association in which one species is intentionally harmed and the other species in not affected. For example, the interaction between grasses and cattle. The hooves of the cattle destroy the grass without causing any harm to the hooves.

Q26. (i) What is ‘r’ in the population equation? (ii) How does the increase and decrease in the value of ‘r’ affect the population size?

Solution

(i) ‘r’ in the population equation is the intrinsic rate of natural increase in the population. (ii) An increase in the value of ‘r’ will increase the population size. When ‘r’ decreases, the population size also decreases.

Q27. Given below is a graph drawn on the parameters of growth versus time. A, B and C respectively represent  

• 1) Lag phase, steady state phase and log phase
• 2) Steady state phase, lag phase and log phase
• 3) Exponential phase, lag phase and steady state phase
• 4) Slow growing phase, lag phase and steady state phase

Solution

Point A represents the steady state phase, point B represents the lag phase and point C represents the log phase. Point B begins with a small population of cells in which there is no increase in population. So, it is called the lag phase. Point C is the exponential phase in which the increase in population becomes rapid and the curve rises steeply upward. Point A is the last phase which is called steady state phase because the population of cells becomes stable.

Q28. The zone of the atmosphere near the earth’s surface is

• 1) Stratosphere
• 2) Mesosphere
• 3) Troposphere
• 4) Thermosphere

Solution

Troposphere is the layer of atmosphere which is closest to our planet. Temperature and water vapour content in the troposphere decrease. Troposphere contains 99% of water vapour in the atmosphere.

Q29. Which of the following population growth curves has only two phases?

• 1) All of the above
• 2) S-shaped growth curve
• 3) J-shaped growth curve
• 4) Bell-shaped growth

Solution

A population growth curve is of two types—S-shaped growth curve and J-shaped growth curve. The S-shaped growth curve has 5 phases—lag phase, positive acceleration phase, exponential phase, negative acceleration phase and stationary phase. The J-shaped growth curve on the other hand has only two phases—the lag phase and the exponential phase.

Q30. Bear hibernates whereas some species of zooplankton enter diapause to avoid stressful external conditions. How are these two ways different from each other?  

Solution

Hibernation is the winter sleep in cold-blooded animals in polar regions. During hibernation, these animals suspend their metabolic activities when the external temperature becomes unfavourable. Diapause is the phenomenon seen in insects during their developmental stages. During diapause, the metabolic activities are suspended due to unfavourable conditions.

Q31. Microorganisms having optimum temperature for growth below 15°C and cannot grow above 20°C are called

• 1) Mesophiles
• 2) Thermophiles
• 3) Psychrophiles
• 4) None of the above

Solution

Microorganisms which can survive in extreme cold conditions are called psychrophiles. They can grow below 15°C but cannot grow above 20°C.

Q32. Which of the following is a hyperparasite?

• 1) Amoeba
• 2) Cuscuta
• 3) Mosquito
• 4) Plasmodium

Solution

A hyperparasite is a parasitic organism which lives on another parasite. Plasmodium is a parasite which lives in the female Anopheles mosquito, which itself is a parasitic organism.

Q33. Explain why very small animals are rarely found in polar regions. 

Solution

Small animals have a larger surface area relative to their volume, and they tend to lose body heat fast when it is cold outside. They have to expend much energy to generate body heat through metabolism. So, small animals are rarely found in polar regions.

Q34. Broad-leaved oak forests are found in

• 1) Tropical deciduous forest
• 2) North coniferous forest
• 3) Temperate deciduous forest
• 4) Mediterranean evergreen forest

Solution

Broad-leaved oak trees are dominant vegetation in the temperate deciduous forests which are found in Eastern America and New Zealand.

Q35. The rate of individuals born per 1,000 individuals per year is called

• 1) Mortality rate
• 2) Growth rate
• 3) Vital rate
• 4) Natality rate

Solution

The birth rate is expressed as the number of births per 1,000 individuals in the population per year. It is also called the natality rate.

Q36. Who is considered as the Father of Ecology in India?

• 1) M. S. Swaminathan
• 2) Ramdeo Misra
• 3) P. Maheshwari
• 4) S. L. Mehta

Solution

Ramdeo Misra was the Father of Ecology in India. He was the founder of the National Institute of Ecology.

Q37. Xerophytes are mostly

• 1) None of the above
• 2) Mesophytes
• 3) Succulents
• 4) Water related

Solution

Xerophytes grow in water-deficient regions and dry climate. Succulents are fleshy xerophytes which absorb large quantities of water during the rainy season and store it in different body parts of the plant. Examples: Opuntia and Aloe

Q38. The formula for exponential population growth is

• 1) dt/dN = r N
• 2) r N/dN = dt
• 3) dN/dt = r N
• 4) dN/rN = dt

Solution

Exponential growth of population is denoted by the formula: dN/dt = r N, where N represents the total population, r represents the rate of increase of population and dN/dt is the increase or decrease in the total population over a certain period.

Q39. The temperate zone falls in the latitude range of

• 1) 60-80°
• 2) 40-60°
• 3) 20-40°
• 4) 0-20°

Solution

The latitude range of 0-20° is that of the tropical zone, 20-40° is that of the subtropical zone, 40-60° is that of the temperate zone and the arctic zone falls in the latitude range of 60-80°. The temperate zone has an average temperature range of 7-17°C.

Q40. Photosynthetically active radiation (PAR) represents the following range of wavelength:

• 1) 340-450 nm
• 2) 400-700 nm
• 3) 500-600 nm
• 4) 450-950 nm

Solution

Photosynthetically active radiation is the normal light or the visible spectrum which is effective in photosynthesis. It falls in the wavelength range of 400-700 nm.

Q41. What is aerenchyma? Mention any two specific functions of this tissue in hydrophytes. 

Solution

Aerenchyma is a modified parenchyma, where the cells are arranged with regular air spaces or air chambers to facilitate diffusion of gases to provide buoyancy to aquatic plants such as lotus and water hyacinth. Two functions of hydrophytes are (i) It helps in the diffusion of oxygen, both in and out. (ii) It provides buoyancy to aquatic plants.

Q42. Name the animal which finds its path using echolocation phenomenon.

Solution

The echolocation phenomenon is shown by horseshoe bat.

Q43. The velocity of a hurricane is about

• 1) 6-50 km/hr
• 2) 51-102 km/hr
• 3) 115 km/hr and above
• 4) 103-115 km/hr

Solution

The velocity with which the wind in a hurricane moves is above 115 km/hr. 

Q44. Define population and community. 

Solution

A population can be defined as a group of individuals of the same species residing in a particular geographical area at a particular time and functioning as a unit. A community is defined as a group of individuals of different species, living within a certain geographical area.

Q45. Study of trends of human population is

• 1) Demography
• 2) Psychology
• 3) Kalography
• 4) Biography

Solution

The study of structure and distribution of human population is called demography.

Q46. Describe habitat and ecological niche.

Solution

A habitat is the living place of an organism; for example, coastal areas of sea by Scoliodon. An ecological niche indicates not only the habitat of a species but also the functional role of a species in the community. 

Q47. An interaction favourable to both the populations, but not obligatory to either is

• 1) Commensalism
• 2) Mutualism
• 3) Proto-cooperation
• 4) Parasitism

Solution

The association between individuals of two species in which both are mutually benefitted but they can live without each other is called proto-cooperation.

Q48. Species can be identified on the basis of

• 1) Interbreeding
• 2) Reproductive isolation
• 3) None of these
• 4) Species diversity

Solution

The biological species can be identified as groups of actually interbreeding natural populations which are reproductively isolated from other groups.

Q49. State one difference between biotic community and ecosystem.

Solution

A biotic community represents only the populations of different species of an era, while an ecosystem represents both abiotic and biotic components of an area.

Q50. What is adaptation? Describe the adaptations of plants and animals in the desert.

Solution

Adaptation is the quality of the organism which enables the organism to survive and reproduce in its habitat. It helps organisms to live in different types of habitats. The adaptation of desert plants are (i) Desert plants have a cuticle to minimise transpiration. (ii) In some desert plants, the leaves modify into spines to minimise loss of water. (iii) They have long roots and adaptations to reduce transpiration. Example: Acacia The adaptations of desert animals are (i) Urine of desert animals is concentrated for minimum loss of water. Example: Kangaroo rat (ii) Desert animals absorb heat from the Sun when the body temperature drops below the comfort zone. (iii) They live in burrows during the hot season and have little water requirement.

Q51. Biological species concept is mainly based on

• 1) Morphological features only
• 2) Morphology and methods of reproduction
• 3) Methods of reproduction only
• 4) Reproductive isolation

Solution

The biological species concept is based on groups of actually interbreeding natural populations which are reproductively isolated from other groups.

Q52. Population was defined by

• 1) Hohn
• 2) Clarke
• 3) Charles
• 4) Weismann

Solution

The term population was defined by Clarke in 1954. Population is the total number of individuals of the same species occupying a particular geographical area at a given time.

Q53. When the number of immigration and births is more than emigration and deaths, the growth curve of the population will show

• 1) Declining phase
• 2) Exponential phase
• 3) Lag phase
• 4) Steady phase

Solution

From the above statement, it is clear that if the number of immigration and births is more than emigration and death, the rate of population increases and attains full potential rate.

Q54. An orchid plant is growing on the branch of a mango tree. How do you describe the interaction between the orchid and mango tree? 

Solution

The interaction between an orchid and the mango tree is commensalism because the orchid is benefitted by getting shelter from the mango tree, whereas the mango tree is neither harmed nor benefitted.

Q55. Biological organisation starts with

• 1) Atomic level
• 2) Organismic level
• 3) Submicroscopic molecular level
• 4) Cellular level

Solution

Hierarchy in organisation from the level of biomolecules to the organismic level is called biological hierarchy or biological organisation. At the entry level, biological organisation starts at the cellular level.

Q56. Organisms capable of maintaining constant body temperature are

• 1) Stenothermal
• 2) Homeothermal
• 3) Poikilothermal
• 4) Conformers

Solution

Animals with constant body temperature are called homeotherms. They have an insulating coat to check the loss of body heat.

Q57. Animals have the innate ability to escape from predation. Examples for the same are given below. Select the incorrect example.

• 1) Enlargement of body size by swallowing air in puffer fish
• 2) Poison fangs in snakes
• 3) Colour change in chameleon
• 4) Melanism in moths

Solution

Predation is the ability to kill and eat other species. There are various animals which escape from predation. Colour change in chameleon and melanism in moths help them escape from being eaten. Fangs in snakes is not an innate ability to escape from predation.

Q58. Which one is the edaphic factor in biosphere?

• 1) Light
• 2) Water
• 3) Soil
• 4) Temperature

Solution

The edaphic factor represents the amount of soil, a major abiotic factor of the environment. It influences survival, behaviour and reproduction of organisms. The study of soil is called edaphology.

Q59. The relationship between a commensal and the host corresponds to

• 1) Neutralism
• 2) Parasitism
• 3) Commensalism
• 4) Mutualism

Solution

The relationship between the commensal and the host is called commensalism. It involves the association of two species of which one is benefitted and the other is not affected. The species which is benefitted is called commensal, and the other species is termed host.

Q60. Mention any two significant roles which predation plays in nature.

Solution

(i) Predation transfers energy from plants to a higher trophic level. (ii) Predation keeps prey population under control.

Q61. Which of the following organisms live in troops?

• 1) Antelopes
• 2) Locusts
• 3) Monkeys
• 4) Lions

Solution

Apes and monkeys live in troops. Locusts live in swarms. Lion and antelopes live in herds.

Q62. What are the two types of population growth curves? What are the phases involved in both types of curves?

Solution

The two types of growth curve of a population are S-shaped and J-shaped. The phases of the S-shaped growth curve are lag phase, exponential phase and stationary phase. In the J-shaped growth curve, there are only two phases - the lag phase and exponential phase. 

Q63. Adamsia palliata is the scientific name for

• 1) Sea anemone
• 2) Termite
• 3) Lichen
• 4) Hermit crab

Solution

Adamsia palliata is the scientific name for sea anemone. It lives in a mutualistic relation with the hermit crab Pagurus prideaux.

Q64. The basic unit of study in ecology is

• 1) Population
• 2) Organism
• 3) Species
• 4) Community

Solution

An organism is the foremost unit of study in ecology, followed by population, community, ecosystem and biosphere. Without an organism, ecological interaction is not possible in the environment.

Q65. The praying mantis is a good example of

• 1) Warning colouration
• 2) Mullerian mimicry
• 3) Camouflage
• 4) Social insects

Solution

The praying mantis is a predatory insect which feeds on other insects. Its shape and colour is a good example of camouflage by mimicry. It changes its colour according to the surrounding environment thus escaping from the predators.

Q66. The main factor for the growth of human population in India is

• 1) High birth rate
• 2) All of the above
• 3) Low death rate
• 4) Lack of education

Solution

The growth of human population in India is a major concern which relies on many factors like high birth rate, low death rate and lack of education.

Q67. A large regional unit characterised by a major vegetation type and associated fauna found in a specific climate zone constitutes

• 1) Biome
• 2) Habitat
• 3) Ecosystem
• 4) Biological community

Solution

A large regional unit delimited by a specific climatic zone and having a particular major vegetation zone and associated fauna is called biome. Examples: Tundra, desert and tropical rainforest

Q68. An association between two individuals or populations where both are benefitted and where neither can survive without the other is

• 1) Mutualism
• 2) Commensalism
• 3) Amensalism
• 4) Protocooperation

Solution

Mutualism is when two individuals are benefitted from each other. One obtains food and the other provides protection.

Q69. Population growth curve is sigmoid if the growth pattern is 

• 1) Accretionary
• 2) Logistic
• 3) Geometric
• 4) Exponential

Solution

The sigmoid growth curve is also called a logistic curve because it undergoes several phases in which there is a zero growth phase. The population adapts to a particular condition and there is exponential growth so that the curve rises steeply upward.

Q70. Natality is balanced by mortality. There will be

• 1) Increase in population growth
• 2) Zero population growth
• 3) Overpopulation
• 4) Decrease in population growth

Solution

Natality is the birth rate of a population which is expressed as the number of births per 1,000 individuals in the population per year. Similarly, mortality is the death rate of a population which is expressed as the number of deaths per 1,000 persons in a population per year. So, there is zero population growth when natality equals mortality.

Q71.  equation is applicable to ___________ population growth.

• 1) Not related to population
• 2) Logistic
• 3) Exponential
• 4) Stationary

Solution

is the equation for the exponential growth of the growth curve which represents the rate of change in population size with respect to the population size and environmental resistance.

Q72. Small fish get stuck near the bottom of a shark and derive their nutrition from it? This kind of association is called

• 1) Symbiosis
• 2) Commensalism
• 3) Parasitism
• 4) Predation

Solution

Small fish attach to the underside of a shark getting nutrition from the dorsal fin of the shark. Here, the small fish are benefitted from the shark, but the shark is neither benefitted nor harmed. This association between the individuals is called commensalism.

Q73. Write short notes on (i) Mutualism, (ii) Competition, (iii) Predation and (iv) Parasitism

Solution

(i) Mutualism: It is a positive interaction in which both the interacting species favour the growth and survival of each other. It is of two types: (1) Protocooperation, in which both the species are mutually beneficial but association is facultative so that the partners can live separately. Example: Hermit crab and sea anemone association (2) Symbiosis, in which both the species are mutually beneficial but the association is obligatory. Example: Lichens, a symbiotic relationship of fungus with alga (ii) Competition: It is a type of interaction in which both the interacting species decrease the chances of growth and survival of each other as these compete for common resources. Example: Visiting flamingos and resident fish compete for zooplankton in the lakes of South America (iii) Predation: It is a type of interaction in which larger species (predator) attacks smaller species (prey) and kills for food. Example: All carnivorous animals are predators. (iv) Parasitism: It is a type of interaction in which smaller species (parasite) is benefitted, but the larger species (host) is harmed. Different types of parasites include ectoparasites (lice, bed bugs), endoparasites (malarial parasite), holoparasites (Cuscuta), partial parasites and brood parasites (cuckoo).

Q74. Maximum growth rate occurs in the

• 1) Stationary phase
• 2) Lag phase
• 3) Senescent phase
• 4) Exponential phase

Solution

Each species takes advantage of the availability of food and other requirements of life in plenty, and there is an increase in population at the maximum rate which is called exponential phase.

Q75. Genetic drift operates in

• 1) Fast reproductive population
• 2) Large isolated population
• 3) Small isolated population
• 4) Slow reproductive population

Solution

The difference in the relative frequency of different genotypes in a small population, leading to the chance of disappearance of particular genes, is said to be a genetic drift. All populations experience drift, but the smaller the population, the sooner the drift will have a drastic effect.

Q76. The logistic population growth is expressed by the equation:

• 1) dN/dt = r N
• 2) dt/dN = N r
• 3) dN/dt = r N
• 4) dN/dt = r N

Solution

The population growth is represented by an S-shaped growth curve (sigmoid) and a J-shaped growth curve. The logistic population growth curve is the S-shaped curve which is divided into lag phase, exponential phase and stationary phase. So, the sigmoid curve is represented by the equation: dN/dt = N r where dN/dt - rate of change in population size r - rate of increase in population N - population size  _{- environmental resistance}  

Q77. Give an example where percentage cover is a more meaningful measure of the population size.

Solution

In an area if there are 200 Parthenium plants but only a single huge banyan tree with a large canopy, the population density of banyan is low relative to that of Parthenium. The banyan tree plays an enormous role in that community. In such cases, the percent cover or biomass is a measure of the population size.

Q78. When one population is harmed and the other remains unaffected, the relationship is called

• 1) Amensalism
• 2) Protocooperation
• 3) Parasitism
• 4) Predation

Solution

The relationship in which one species is intentionally harmed and the other species in not affected is called amensalism. For example, the interaction between grasses and cattle. The hooves of cattle destroy the grass without causing any harm to the hooves.

Q79. How do organisms cope with stressful external conditions which are localised or of short duration?

Solution

To cope with stressful conditions, organisms (i) Migrate temporarily from the stressful habitat to a hospitable area (ii) Aestivate during summer (iii) Hibernate during winter (iv) Form thick-walled spores

Q80. How do protocooperation and mutualism resemble and differ?  

Solution

In protocooperation and mutualism, the two species are benefitted. However, the difference is that in protocooperation, the two species can live equally well without association, but this does not happen in mutualism.

Q81. Which one of the following in one of the characteristics of a biological community?

• 1) Sex-ratio
• 2) Mortality
• 3) Stratification
• 4) Natality

Solution

Sex ratio, natality and mortality are characteristics of population. Stratification, on the other hand, is a structural component of biological community.

Q82. While walking in the garden, Amit got hurt by a thorn present on a twig bearing beautiful rose flowers. He started analysing the role of different parts of the rose plant such as leaves, flowers etc. but was not able to understand the need of thorns on the rose plant. Read the above passage and answer the following questions: (i) Why plants produce thorn/spine-like structures on their body? (ii) What is meant by adaptation? (iii) What are other methods of adaptations of organisms in specific environments?

Solution

(i) Many plants have thorns or spines to protect themselves from the attack of grazing animals. (ii) Adaptation refers to the ability of a species to survive in a particular ecological niche, especially because of alterations of form or behaviour brought about through natural selection. (iii) Other methods of adaptations of organisms are some of the anatomical changes which include mimicry, hibernation and aestivation.

Q83. Why are mammals the most successful animals on Earth? 

Solution

The mammals are the most successful animals on Earth because they can maintain a constant body temperature with high range of tolerance whether in Antarctica or in the Sahara desert.

Q84. (i) What is carrying capacity? (ii) Write any four population attributes.

Solution

(i) Carrying capacity is the uppermost limit of population size beyond which no major increase can occur, so there is zero growth rate. (ii) The attributes which populations possess are population density, population growth, mortality rate, natality rate, sex ratio and age distribution. (Any four) 

Q85. How does the human body maintain constant temperature both in summers and winters? Explain.

Solution

Human beings maintain a constant temperature of 37°C. In summers, the outside temperature is much higher than our body temperature. Therefore, we sweat profusely. This results in evaporative cooling, and our body temperature is reduced to normal. In winters, the outside temperature is much lower than our body temperature. Therefore, we shiver, which is a kind of exercise, which produces heat and raises the body temperature.

Q86. What does the sigmoid growth curve of a population mean? 

Solution

The sigmoid growth curve indicates rapid multiplication and then equilibrium of population.

Q87. Growth of the population of an area depends on 

• 1) Environmental resistance
• 2) All of the above
• 3) Immigration
• 4) Natality rate

Solution

The growth of a population is due to variation in population size and density. So, the population size and density depend on factors such as natality rate, immigration, emigration and environmental factors.

Q88. Of the total amount of freshwater available on Earth, what is the amount that is found in the form of icecaps and glaciers?

• 1) 27.2%
• 2) 67.2%
• 3) 57.2%
• 4) 77.2%

Solution

Of the total freshwater available on Earth, 77.2% is found in the form of ice caps and glaciers, 22.4% in the form of underground pools and moisture in the soil and 0.36% in lakes, swamps, streams and rivers collectively.

Q89. Eichhornia crassipes is an alien hydrophyte introduced in India. Mention the problems posed by this plant.

Solution

Eichhornia crassipes is a water hyacinth which was introduced unintentionally to the aquatic ecosystem, which lead to the extinction of native species and caused a decline in phytoplankton.

Q90. With respect to breeding cycles, which of the following is a day-neutral animal?

• 1) Deer
• 2) Guinea pig
• 3) Sheep
• 4) Goat

Solution

With respect to breeding cycles, guinea pigs and ground squirrels are examples of day-neutral animals.

Q91. In the electromagnetic spectrum, what is the relation between energy of radiation and its wavelength?

• 1) Directly proportional
• 2) Indirectly proportional
• 3) Share no relation
• 4) Directly proportional only in the region of visible light

Solution

The energy of radiation is indirectly proportional to the wavelength of the radiation, i.e. with an increase in the wavelength of the radiation, the energy associated with the radiation decreases.

Q92. A sedentary sea anaemone gets attached to the shell lining of hermit crab. The association is

• 1) Ectoparasitism
• 2) Symbiosis
• 3) Amensalism
• 4) Commensalism

Solution

Sea anaemone, when attached to the hermit crab, lives in an association and both are helped by each other. This is  called symbiosis or mutualism. The sea anaemone protects the hermit crab from the enemies, and in turn, the sea anaemone receives pieces of food dropped by the crab.

Q93. Write adaptations of submerged, rooted hydrophytes.

Solution

To withstand movement of water, submerged, rooted hydrophytes have ribbon-shaped or greatly dissected leaves. The stems are soft, spongy and with long internodes.

Q94. In the formula for population density, D = N/S, ‘S’ represents

• 1) Number of individuals of a species
• 2) Number of individuals
• 3) Number of individuals of a sub-population
• 4) Number of units of space

Solution

In the formula D = N/S, D is the population density, N is the total number of individuals and S is the number of units of space.

Q95. List any two adaptive features evolved in parasites enabling them to live successfully on their hosts.

Solution

(i) Most parasites fit closely to the body of the host. (ii) They lay a large number of eggs.

Q96. Which one is exclusively a xerophytic adaptation?

• 1) Long tap root system
• 2) Absence of stomata
• 3) Stipular leaves
• 4) Spines

Solution

Xerophytic adaptations are found among the most drought-resistant plants on the planet. The leaves are reduced to spines to check transpiration.

Q97. Why in a natural environment with plenty of food but no predation, a population shows J-shaped growth curve? 

Solution

A population shows J-shaped growth curve because it shows rapid growth, but there is a corresponding decrease in the availability of food, which is finally exhausted and causes mass starvation and mortality.

Q98. According to Allen's rule, mammals in cold regions have ____________ to conserve body heat.

• 1) Smaller body mass
• 2) Longer extremities
• 3) Larger body mass
• 4) Smaller extremities (legs, tails and ears)

Solution

To minimise heat loss, mammals in colder regions possess smaller extremities (legs, tails and ears). This is called Allen’s Rule as it was proposed by Allen.

Q99. (i) Write the importance of measuring the size of a population in a habitat or an ecosystem. (ii) Explain how age structure plays an important role in population growth.

Solution

(i) The size of the population depends on its state in the habitat. The impact of a predator or the effect of a pesticide application can be determined by evaluating the size of the population. (ii) The age structure of a population is the percentage of individuals of different ages such as young, adult and old. The ratio of various age groups in a population determines the current reproductive status of the population. The age groups are classified as pre-reproductive, reproductive and post-reproductive.

Q100. Explain three types of interspecific interactions. 

Solution

Three types of interspecific interactions are (i) Competition: It is a type of interaction in which both the species suffer due to limited resources. Example: Carnivorous animals compete for prey (ii) Parasitism: It is a type of interaction in which one species is benefitted and the other species is harmed. Example: Malarial parasite inside the female Anopheles mosquito causes malaria in humans. (iii) Mutualism: In this type of interaction, both the species are benefitted. Example: The sea anemone and hermit crab stay in mutual relationship with each other.

Q101. What is the most important factor for the success of animal population?

• 1) Natality
• 2) Unlimited food
• 3) Interspecific activity
• 4) Adaptability

Solution

Animal population adjusts their surrounding according to the conditions of their environment. So, they have the ability to change in order to fit according to the change in environment. So, animals increase their population due to adaptability.

Q102. Differentiate between S-shaped and J-shaped growth curve.

Solution

 S-shaped curve   J-shaped curve (i) It comprises the lag phase, exponential phase and stationary phase. (i) It comprises only two phases - lag phase and exponential phase. (ii) Population becomes stable with zero growth rate and the curve levels. (ii) Population faces mass mortality, and the curve stops. (iii) It is observed by most species including humans. (iii) It is observed in few organisms such as reindeer and annual plants.  

Q103. Why cannot a population live alone by itself in nature? 

Solution

No population can live alone in nature. It is dependent on other populations for various requirements. Animals get food, shelter and oxygen from plants. Plants depend on animals for carbon dioxide, pollination etc.

Q104. Explain brood parasitism with the help of an example.

Solution

Brood parasitism is a method in which the parasitic bird lays its eggs in the nest of its host and the host incubates them. The eggs of the parasites resemble the eggs of the host bird and these eggs are raised by the host. Example: The cuckoo bird lays its eggs in the nest of a crow. The eggs of the cuckoo are incubated by the crow.

Q105. List the different population attributes which an individual does not possess. Explain any three.

Solution

The different population attributes which an individual does not possess are population density, population growth, mortality rate, natality rate, sex ratio and age distribution. (i) Population density: It is the number of individuals of a species per unit area or volume. (ii) Population growth: Increase in the number of population which resides in a particular geographical area. (iii) Mortality rate: It is expressed as the number of deaths per 1000 individuals of a population per year. (iv) Natality rate: It is expressed as the number of births per 1000 individuals of a population per year. (v) Sex ratio: The ratio of males to females in a population. (vi) Age distribution: The proportionate numbers of persons in different age categories in a given population. (Any three)

Q106. How do organisms which cannot migrate tend to overcome adverse environmental conditions? Explain taking one example each from vertebrates and angiosperms, respectively.

Solution

Organisms which cannot migrate tend to overcome adverse environmental conditions by developing several methods. For example, some vertebrates escape the stress caused by unfavourable environmental conditions by escaping in time, like bears go into hibernation during the winters. In angiosperms, seeds and some other vegetative reproductive structures serve as means to tide over periods of stress. They reduce their metabolic activity and go into a dormant state. They germinate to form new plants when favourable conditions return.

Q107. Name the organisms which form lichens.

Solution

Lichens are formed by the association between alga and fungus. This association is called symbiosis. 

Q108. What are ectoparasites and endoparasites? Give two examples of each. 

Solution

Parasites which live on the body surface of the host are called ectoparasites. Examples: Lice, bed bug Parasites which live inside the body of the host are called endoparasites. Examples: Malarial parasite, Ascaris