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Bihar Board Class 12th Biology Organisms and Populations Textbooks Solutions PDF
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BSEB Class 12th Biology Organisms and Populations Textbooks Solutions with Answer PDF Download
Find below the list of all BSEB Class 12th Biology Organisms and Populations Textbook Solutions for PDF’s for you to download and prepare for the upcoming exams:Bihar Board Class 12 Biology Organisms and Populations Text Book Questions and Answers
Question 1.
How is diapause different from hibernation?
Answer:
Diapause is a stage of suspended development. For example, under unfavourable conditions many zooplankton species in lakes and ponds are known to enter diapause. Hibernation refers to winter sleep. For example, bear go into hibernation during winter to protect themselves from the severe cold conditions.
Question 2.
If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why or why not?
Answer:
No, a marine fish placed in a fresh water aquarium will not survive due to osmotic problems. For aquatic animals the quality (chemical composition, pH) of water becomes important. The salt concentration is very high in sea water as compared to fresh water.
Question 3.
Define phenotypic adaption. Give one example.
Answer:
Phenotypic adaptation is a type of adaptation which allows some organisms to respond quickly to a stressful situation. For example, while going to a hill station we sometimes can get symptoms such as nausea, fatigue, and heart palpitations. This is because in the low atmospheric pressures of high altitudes, the body does not get enough oxygen. The body compensates low oxygen availability by increasing red blood cell production, decreasing the binding capacity of haemoglobin and by increasing breating rate.
Question 4.
Most living organisms cannot survive at temperatures above 45°C. How are some microbes able to live in habitats with temperatures exceeding 100°C.
Answer:
Some microbes are able to live in habitats with temperatures exceeding 100°C by showing an array of biochemical adaptation.
Question 5.
List the attributes that populations but not the individuals possess.
Answer:
Populations have attributes that an individual organism does not. An individual may have births and deaths, but a population has birth rates and death rates. In a population these rates refer to per capita births and deaths respectively. An individual is either a male or a female but a population has sex-ratio. The size of the population tells us a lot about its status in the habitat. A single individual cannot tell us about the particulars of a habitat.
Question 6.
If a population growing exponentially doubles in size in 3 years, what is the intrinsic rate of increase (r) of the population?
Answer:
The intrinsic rate of natural increase (r) is a measure of the inherent potential of a population to grow. To calculate the value of r we need to know the birth rates and death rates. By knowing the birth rates and death rates we can calculate r by the following formula :
𝑑𝑁𝑑𝑡 = rN
If the population has become three times the r factor becomes 3r.
Question 7.
Name important defence mechanisms in plants against herbivory.
Answer:
Plants have eolved an astonishing variety of morphological and chemical defences against herbivory. Thorns of cactus are the most common morphological means of defence. Many plants produce and store chemicals that make the herbivore sick when eaten, inhibit feeding or digestion, disrupt its reproduction or even kill it. The weed Calotropis produces highly poisonous cardiac glycosides.
For this reason cattle or goats are never seen browsing on this plant. In fact a wide variety of chemical substances we
extract from plants on a commercial scale (nicotine, quinine, opium etc.) are produced by the plants as defences against grazers and browsers.
Question 8.
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:
An orchid plant growing on the branch of mango tree is an interaction of commensalism. In this reaction one species benefits and the other is neither harmed or benefitted. In the above case the mango tree may not derive any apparent benefit from the orchid plant.
Question 9.
What is the ecological principle behind the biological control method of managing with pest insects?
Answer:
Biological control methods adopted for managing with pest insects are based on the prey-regulating ability of the predator.
Question 10.
Distinguish between the following :
(a) Hibernation and Aestivation
(b) Ectotherms and Endotherms.
Answer:
(a) Hibernation is winter sleep, in which some animals to save themselves from the severe cold conditions go to a deep slumber. Some organisms such as snails and fishes to avoid the heat of summer go into aestivation.
(b) Ectotherms feed on the external surface of the host organism whereas endotherms are those that live inside the host body at different sites.
Question 11.
Write a short note on :
(a) adaptations of desert plants and animals.
(b) adaptations of plants to water scarcity.
(c) behavioural adaptations in animals.
(d) importance of light to plants.
(e) effect of temperature or water scarcity and the adaptations of animals.
Answer:
(a) Adaptations of desert plants and animals –
– Desert plants have thick cutile on the leaf surfaces and have their stomata arranged in deep pits to minimise water loss through transpiration.
– In some desert plants, such as opuntia, the leaves are reduced to spines.
– The Kangaroo rat in North America deserts has internal fat oxidation through which it can meet all its water requirements. It can concentrate its urine so that minimal volume of water is used to remove excretory products.
– The camel has a hump to store water and food in the desert. It can last without water and food for several days.
– The long legs and padded toes of the camel can withstand the hot sand of the desert.
(b) Adaptations of plants to water scarcity –
– Many desert plants have thick cutile on the leaf surfaces and the stomata are arranged in deep pits to minimise water Loss through transpiration.
– There plants have a special photosynthetic pathway (CAM) that enables their stomata to remain closed during the day.
– In deserts plants like opuntia, the leaves are reduced to spines. The photosynthetic function is taken over by flattened stems.
(c) Behavioural adaptations in animals – Many birds from severe cold conditions migrate temporarily to a less stressful habitat. However, when the weather changes they once again migrate to their original home.
(d) Importance of light to plants –
All plants produce food through photosynthesis, a process which is only possible when sunlight is available as a source of energy. Thus, light is most important for plants to produce food.
(e) Effect of temperature or water scarcity and the adaptation of animals –
All physiological functions and geographical distribution of plants and animals is governed by temperature. Thus, temperature is the most ecologically reveiant environmental factor. For example, the’mango tree cannot grow in temperate countries like Canada and Germany or snow leopards cannot be found in Kerala forests.
Temperature affects the very kinetics of enzymes and through it the basal metabolism, activity and other physiological function of the organism. Some organisms can thrive in a wide, range of temperatures but a vast majority of organisms are restricted to a narrow range of temperature.
Question 12.
List the various abiotic environmental factors.
Answer:
The most important abiotic environmental factors are :
(a) Temperature,
(b) Water,
(c) Soil,
(d) Light.
Question 13.
Give an example for:
(a) An endothermic animal
(b) An ectothermic animal
(c) An organism of bentic zone.
Answer:
(a) Tapeworm,
(b) Lice,
(c) Squid.
Question 14.
Define population and community.
Answer:
Population – The total number of individuals of any species occupying in a particular geographic area at a given time, is termed as population.
Community-Populations of a variety of plants, animals and micro-organisms living together within a habitat. AH such populations together constitute the community.
Question 15.
Define the following terms and give one example for each :
(a) Commensalism
(b) Parasitism
(c) Camouflage
(d) Mutualism
(e) Interspecific competition
Answer:
(a) Commensalism: The interaction where one species is benefitted and the other is neither benefitted nor harmed is called commensalism.
For example, an orchid growing as an epiphyte on a mango branch, and barnacles growing on the back of a whale benefit while neither the mango tree nor the whale derives any apparent benefit.
(b) Parasitism: It is a process by which only one species benefits (parasite) and the interaction is determined to the other species (host). Most of the parasites, both ecto and endo, harm the host; they may reduce the survival, growth and reproduction of the host and reduce its population densely. They might render the host more vulnerable predation by making it physically weak. For example, tapeworm living in the stomach of animals.
(c) Camouflage: Some species of insects and frogs are cryptically- coloured (camouflaged) to avoid being detected easily by the predator. Thus, it is a process by which an animal changes its colour according to the surroundings, or has the same colour according to the surrounding.
(d) Mutualism: It is an interaction which confers benefits on both the interacting species. For example, lichens represent an intimate mutualistic relationship between a fungus and photosynthesising algae or cyanobacteria.
(e) Interspecific competition: It is the potent force in organic evolution. The feeding efficiency of one species might be reduced due to the interfering and inhibitory presence of the other species.
Or It is a process in which the fitness of one species (measured in terms of its V the intrinsic rate of increase) is significantly lower in the presence of another species.
For example, the Abingdon tortoise in Galapagos Islands become extinst within a decade after goats were introduced on the island, apparently due to the greater browsing efficiency of the goats.
Question 16.
With the help of suitable diagram describe the logistic population growth curve.
Answer:
No population of any species in nature has its disposal unlimited resources to permit exponential growth. This leads to competition between individuals for limited resources. Eventually, the fittest individual 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.
A population growing in a habitat with limited resources show a lag phase, which is followed by phases of acceleration and deceleration and finally, an asymptote when the population density reaches the carrying capacity. A plot of N in relation to time (t) results in a sigmoid curve. It is described by the following equation :
N=Popuiation density at time (t)
r = Intrinsic rate of natural increase
K = Carring capacity
Question 17.
Select the statement which explains best parasitism.
(a) One organ is benefited.
(b) Both the organisms are benefited.
(c) One organ is benefited, others is not affected.
(d) One organism is benefited, other is affected.
Answer:
(d) One organism is benefited, other is affected.
Question 18.
List any three important characteristics of a population and explain.
Answer:
Important characteristics of a population: A population is a group of individuals of a given species sharing or competing for similar resources, in a defined geographical area.
(a) Populations have attributes such as birth rates, death rates, sex ratio and distribution. An age pyramid indicates whether a population is stationary, growing or declining.
(b) Ecological effects of any factor on a population are generally reflected in its size (population density), which may be expressed in different ways (number, biomass, per cent cover, etc.) depending on the species.
(c) Population grow through births and immigration and decline through deaths and emigration. When resources are limited, the growth is usually exponential but when resources become progressively limiting, the growth pattern turns as logistic.
(d) In nature populations of different species in a habitat do not live in isolation but interact in many ways.
Bihar Board Class 12 Biology Organisms and Populations Additional Important Questions and Answers
Very Short Answer Type Questions
Question 1.
Name the biotic factors of the environment.
Answer:
Plants, animals, human beings and micro-organisms.
Question 2.
Name the abiotic factors of the environment.
Answer:
Temperature, water, light, soil, etc,
Question 3.
What is the ultimate source of energy on earth?
Answer:
Sun.
Question 4.
What is the term inter-breeding refer to?
Answer:
Sexual reproduction.
Question 5.
What does the size of the population tell us?
Answer:
The size of the population tells us a lot about its status in the habitat.
Question 6.
What does birth rates and death rates refer to?
Answer:
These rates refer to per capita birth and death.
Question 7.
What is an age pyramid?
Answer:
If the age distribution (per cent individuals of a given age or age group) is plotted for the population, the resulting structure is called an age pyramid.
Question 8.
What is population density? ‘
Answer:
Population size is referred to as population density.
Question 9.
What is natality?
Answer:
Natality refers to the number of birth during a given period in the population that are added to the initial density.
Question 10.
What is mortality?
Answer:
Mortality is the number of deaths in the population during a given period.
Question 11.
What is immigration?
Answer:
Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.
Question 12.
What is emigration?
Answer:
Emigration is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.
Question 13.
What is migration?
Answer:
Migration is the movement of organism temporarily from the stressful habitat to a more hospitable area and return when stressful period is over.
Question 14.
What is suspend?
Answer:
In bacteria, fungi and lower plants, various kinds of thick-walled spores are formed which help them to survive unfavourable conditions – there germinate on availability of suitable environment. This process is called suspend.
Question 15.
What is the equation of Verhulst-Pearl Logistic Growth?
Answer:
dNdt =rN[K−NK].
Question 16.
In which process both the species benefit?
Answer:
Mutualism.
Question 17.
In which process only one species benefit?
Answer:
Parasitism.
Question 18.
What is the interaction called where one species is benefitted and the other is neither benefitted nor harmed?
Answer:
Commensalism.
Question 19.
What is the interaction called in which one species is harmed whereas the other is unaffected?
Answer:
Amensalism.
Question 20.
Define ecology.
Answer:
Ecology is the study of the relationships of living organisms with the abiotic and biotic components.
Question 21.
Why is population ecology an important area of ecology?
Answer:
Population ecology is an important area of ecology became evolutionary changes through natural selection take place at the population level.
Short Answer Type Questions
Question 1.
How can age-sex structure of a population be deficted in a pyramid diagram?
Answer:
The age structure of a given population refers to the proportion of individuals of different ages within that population. Many functional aspects of the individuals are related to age. For example., infants, below one year of age, and the older people have higher mortality rates than individuals of other ages.
In addition, the proportion of reproductively active males and females in a population influences the population growth. The number of female individuals in active reproductive age (usually 15-44 years) influences the birth rates within a population.
Age-sex Structure of a population can be depicted in the form of a pyramid diagram by plotting the percentage of population of each sex in each age class.
The age-sex structure of the developed world gives a steeper pyramid, which represents a nearly stable population. A rapidly growing population, like that of India, is represented by a much less steep pyramid.
The population planning policies have succeeded only marginally.
Question 2.
Briefly outline the reasons for human population explosion.
Answer:
Population explosion refers to increase in human population at an alarming rate.
It is because :
- Agricultural production has increased and “starvation deaths have declined.
- Medical services have brought down mortality due to fatal diseases and epidemics.
Question 3.
Why is increasing food production considered only a temporary solution for a growing population?
Answer:
Malthus had stated that “population, when unchecked increases in geometrical ratio, while the food supply at the best increase in an arithmetical ratio, hence population tends to increase up to the limits of means of subsistence”. Advances in biotechnology has led to increase in food production but it is considered as temporary solution because the environment can support population up to a certain limit. If the current trend of growth counting, the other available natural resources will become too meagre to meet the needs. This will lead to number of socio-economic problems.
Question 4.
What do evolutionary biologists believe that the ‘success’ of mammals is largely due to their ability to maintain a constant body temperature and thrive whether they live in Antarctica or in the Sahara desert?
Answer:
The mechanisms used by most mammals to regulate their body temperature are similar to the ones that humans use. Human being maintain a constant body temperature of 37°C. In summer, when outside temperature is more than our body temperature, we sweat profusely.
The resulting evaporate cooling, similar to what happens with a desert cooler in operation, brings down the body temperature. In winter when the temperature is much lower than 37°C, we start, to shiver, a kind of exercise which produces heat and raises the body temperature.
Question 5.
Why is temperature regarded as the most ecologically relevant environmental factor?
Answer:
The average temperature on land varies seasonally, decreases progressively from the equator towards the poles and from plains to the mountain tops. It ranges from subzero levels in polar areas and high altitude to >50°C in tropical deserts in summer. Where average temperature exceed 100°C there are unique habitats such as thermal springs and deep-sea hydrothermal vents. Due to this variation in temperature mango trees cannot grow in temperate countries like Canada and Germany and snow leopards are not found in Kerala.
Question 6.
Name the major biomes of India.
Answer:
Major biomes of India :
(a) Tropical rain forests
(b) Deciduous forests
(c) Desert
(d) Sea coast.
Question 7.
What are the key elements that lead to variation in the physical and chemical conditions of different habitats?
Answer:
The most important key elements are temperature, water, light and soil. However, the physicochemical (abiotic) components alone do not characterise the habitat of an organism completely; the habitat includes biotic components also – pathogens, parasites, predators and competitor – of the organisms with which they interact constantly.
Question 8.
Explain in brief the importance of light.
Answer:
Plants produce through photosynthesis, which is possible only when sunlight is available as a source of energy. Many species of small plants, growing in forests are adopted to photosynthesis optionally under very low conditions because they are constantly overshadowed by tall, canopied trees. Many plants are also dependent on sunlight to meet their photoperiodic requirement for flowering. The availability of light on land is closely linked with that of temperature since the sun is the source for both.
Question 9.
What will happen if the predator is too efficient and overexploits its prey?
Answer:
If a predator is too efficient and over-exploits its prey, then the prey might become extinct and following it, the predator will also become extinct for lack of food.
Question 10.
In the following table of interspecific interactions, fill the blanks with ‘+’ sign for beneficient interaction, the’-‘ sign for detrimental and 0 for neutral interaction.
| Species A | Species B | Name of Interaction |
| + | Mutualism | |
| – | Competition | |
| – | Predation | |
| + | Parasitism | |
| + | Commensalism | |
| 0 | Amensalism |
Answer:
| Species A | Species B | Name of Interaction |
| + | + | Mutualism |
| – | – | Competition |
| + | – | Predation |
| + | – | Parasitism |
| + | 0 | Commensalism |
| – | 0 | Amensalism |
Long Answer Type Questions
Question 1.
Give a brief explanation of population growth pattern.
Answer:
There are mainly two primary reasons for increase in human population. These are:
(i) Decline in death rate,
(ii) Increase in longevity.
However, in the civilized world of today, it- is unfortunate that man himself is an enemy of man. He harms his fellow men through hoarding, adulteration, deprivation, exploitation, subjugation, violence and war.
World human population growth rate is about 2% on the basis of 1973 census. It was 0.8% per year for the developed countries and nearly 2.5% of developing countries. At this current rate of growth human population is doubling itself every 35 years.
If the 6.0 billion people in the world today (1997) continue to increase at the present rate, their combined mass of more than 338 million tonnes will exceed the mass of the earth (which is about 6.5 billion trillion tonnes) in a period of about 1550 years. Thus, the human population explosion as shown in Fig. has become a serious global concern.
Whether our earth planet will have the carrying capacity of such a large mass of human population is a big question. Earth will soon become severely overcrowded and uninhabitable. Will the human beings then take the extraterrestrial migration and colonise other planets? About 56% of the total world population resides in Asia alone.
Japan is the most thickly populated country and Australia is the most thinly populated country in the world. In India, Kerala is the most thickly populated state. According to 1991 census, population of India is 843 million. The sex ratio is 929females per 1,000 males. The literacy rate is 52.11%. Population growth rate in India is 2.14%.
Population beyond certain limit experiences acute food storage and many individuals face death from starvation or malnutrition. Accordingly, if the present trend of human population growth continues, all available natural resources will be too meagre to meet the needs. When all these sources fall far below the need of a common man, a severe competition is bound to ensue, which may lead to large number of socio-economic problems such as energy crisis, eco degradation, hunger, poverty, famine, soil erosion, floods, deforestation, unemployment, shortage of raw materials, medical aid, housing, drinking water, clothing and lack of educational facilities.
Danger of epidemic diseases will increase. These conditions may result into misery, poor health and increase of urban slums. Overpopulation is the main cause of economic backwardness in our country
Question 2.
How can be know whether a population is flourishing or declining?
Answer:
The size of a population keeps changing in time, depending on various factors including food availability, predation pressure and reduce weather. These changes in the population density can give us some idea what is happening to the population – whether it is flourishing or dealings. However, the density of a population in a given habitat during a given period fluctuates due to changes in four basic processes. These are as follows :
(a) Natality: number of births during a given period in the population that are added to the initial density. ‘
(b) Mortality: the number of deaths in the population during a
given period.
(c) Immigration: number of individuals of the same species that have come into from elsewhere during the time period under consideration.
(d) Emigration: number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.
One Word Type Questions
Question 1.
Name a plant of the desert region.
Answer:
Cactus.
Question 2.
Give an example of ectoparasite.
Answer:
Lice.
Question 3.
Give an example of endoparasite.
Answer:
Tapeworm.
Question 4.
Give an example of benthic zone.
Answer:
Squid.
Question 5.
The process by which plant manufacture their food.
Answer:
Photosynthesis.
Question 6.
What is the per cent of salt in inland water?
Answer:
5 per cent.
Question 7.
What is the per cent of salt in hypersaline lagoons?
Answer:
> 100.
Question 8.
What is the stage of suspended development called?
Answer:
Diapause.
Question 9.
Name a butterfly which is highly distasteful to its predator.
Answer:
Monarch butterfly.
Question 10.
Name a starfish which is an important predator in the rocky intertidal communities of the American Pacific Coast.
Answer:
Pisaster.
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