Directions : In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.
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Assertion: Prolonged intraspecific competition causes an increase in the size of the niche of a population.
Reason: In such a population, use of a new type of resource will increase through the generations.
(a) Prolonged intraspecific competition causes an increase in the size of the niche of a population. A population at its carrying capacity does not have enough of the limiting resources to go around and any individual who makes use of a new type of resource will experience less competition and so be able to produce more offsprings. Use of the new resource will increase through the generations and the niche thus will become larger.
Assertion : The community of an ecotone commonly contains the organisms of each of the overlapping communities and in addition the organisms which are restricted to the ecotone.
Reason: The tendency for increased variety and density at community junctions is known as the edge effect.
(b) An ecotone is a transition zone between two or more diverse communities as, for example, between forest and grassland. It is a junction zone which may have considerable linear extent but is narrower than the adjoining community areas themselves. The ecotonal community commonly contains many of the organisms of each of the overlapping communities and in addition, organisms which are characteristic of and often restricted to the ecotone. Often, both the number of species and the population density of some of the species are greater in the ecotone than in the communities flanking it. The tendency for increased variety and density at community junctions is known as the edge effect.
Assertion : Stomata generally open in light and close in dark.
Reason : Transpiration is enhanced by heating effect of light.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion
Assertion : The aquatic organisms in which the osmotic concentration and temperature of body change according to the ambient conditions of water are referred to as conformers.
Reason : Aquatic organisms are able to maintain homeostasis through thermoregulation and osmoregulation by physiological or behavioural means.
(c) The aquatic organisms in which the osmotic concentration and temperature of body change according to ambient conditions of water are called conformers. About 99 percent of animals and nearly all plants are included in the category of conformers, which do not have a mechanism to maintain a constant internal body environment. Their body temperature change with the surrounding temperature. On the other hand, some organisms (e.g., birds and mammals) are able to maintain a constant body temperature and constant osmotic concentration despite changes in the external environment. They are called as regulators. They perform homeostasis mostly through thermoregulation and osmoregulation by physiological or behavioural means.
Assertion: Small sized animals are rarely found in polar regions.
Reason: Small sized animals have larger surface area relative to their volume and they have to spend much energy to generate body heat through metabolism.
(a) Thermoregulation is an energetically expensive process for many organisms. Heat loss or heat gain is a function of surface area. Small sized animals (such as shrews, humming birds etc.), have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; thus they have to expend much energy to generate body heat through metabolism. This is the main reason why very small animals are rarely found in polar regions.
Assertion : At high altitude a person, from plain areas, may experience altitude sickness.
Reason : At high altitudes atmospheric pressure is generally high leading to symptoms like nausea, fatigue, etc.
(c) At high altitude, a person may experienced altitude sickness. Its symptoms include nausea, fatigue and heart palpitations. It is due to the low atmospheric pressure of high altitudes that the body does not get enough oxygen.
Assertion : Bell shaped age pyramid represents a stable population.
Reason : In a stable population, proportion of individuals in reproductive age group is higher than the individuals in pre-reproductive age group.
(c) In a bell-shaped age pyramid, the number of pre reproductive and reproductive individuals is almost equal. Post reproductive individuals are comparatively fewer. It represents a stable population.
Assertion : The rate at which a population can be expected to grow in the future can be assessed graphically by means of a population pyramid.
Reason : A triangular population pyramid is characteristic of a country whose population is stable, neither growing nor shrinking.
(c) The rate at which a population can be expected to grow in the future can be assessed graphically by means of a population pyramid-a bar graph displaying the number of people in each age category. Males are conventionally shown to the left of the vertical age axis and females to the right. A human population pyramid thus displays the age composition of a population by sex. In general, rectangular pyramids are characteristic of countries whose populations are stable, their numbers neither growing nor shrinking. A triangular pyramid is characteristic of a country that will exhibit rapid future growth, as most of its population has not yet entered the child-bearing years. Inverted triangles are characteristic of populations that are shrinking.
Assertion : A population growing in a habitat with limited resources shows initially a lag phase, followed by phases of acceleration and deceleration and finally an asymptote, when the population density reaches the carrying capacity.
Reason : In Verhulst-Pearl Logistic growth, plot of N (population density) at time (t) results in a sigmoid curve.
(b) A population growing in a habitat with limited resources shows 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 and is described by the following equation :
\(
\frac{d N}{d t}=r N\left(\frac{K-N}{K}\right)
\)
Where \(N=\) Population density at time \(t\)
\(r=\) Intrinsic rate of natural increase
and \(K=\) Carrying capacity.
Assertion : Predators maintain prey population under control.
Reason: Predators reduce the intensity of competition among competing prey species.
(a) Predation is an interaction between members of two species in which members of one species capture, kill and eat up members of other species. The former are called predators while the latter are spoken as preys. Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species.
Assertion : Elimination of a competitively inferior species in a closely related or otherwise similar group is known as competitive exclusion principle.
Reason : If two species compete for the same resource, they could avoid competition by choosing different times for feeding or different foraging patterns.
(b) Gause’s ‘Competitive Exclusion Principle’ states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one is eliminated eventually. This may be true if resources are limiting, but not otherwise. Mechanism of ‘Resource partitioning’ states that if two species compete. for the same resource, they could avoid competition by choosing, for instance, different times for feeding or different foraging patterns.
Assertion : Endoparasites live on the surface of the host.
Reason : The malarial parasite and Trypanosoma are examples of endoparasites.
(d)
Assertion : The epiphytes use the trees only for attachment and manufacture their own food by photosynthesis.
Reason : Commensalism results in negative effects on the growth and survival of one or both of the populations.
(c) Epiphytes which grow on the branches and in the forks of some trees, cite an example of commensalism. Commensalism is a type of positive interaction in which, two organisms (of different species) live together without any physiological dependence between them, and one gets the benefit from the association while the other is neither benefitted nor harmed.
Assertion: Mycorrhizae represent a mutually beneficial interspecific interaction of fungi with roots of higher plants.
Reason : In a mutualistic relationship, both the organisms enter into some sort of physiological exchange.
(b) Mycorrhizae refer to the symbiotic association of fungal hyphae with the roots of higher plants. In this association, the two symbionts are in close contact and are physiologically interdependent on each other. Mycorrhizae increase the ability of the plant to extract minerals from the soil. In return, fungi are provided with shelter and products of photosynthesis by the plant. Plants having such associations show other benefits also, such as resistance to root-borne pathogens, tolerance to salinity and drought and an overall increase in plant growth and development.
Assertion : Plant-animal interactions do not generally involve co-evolution of the mutualist organisms.
Reason : Evolution of the plants and animals go side by side.
(d) Plant-animal interactions often involve co-evolution of the mutualists, that is, the evolution of the flower and its pollinator species are closely linked with one another. This is because plants need the help of animals for pollinating their flowers and dispersing their seeds. Animals get rewards in the form of pollen and nectar for pollinators and juicy and nutritious fruits for seed dispersal.
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