VBQs Class 12 Biology Organisms and Populations

Please refer to VBQs for Class 12 Biology Organisms and Populations. All value based questions for Biology Class 12 have been provided with solutions. We have provided below important values questions and answers. Students should learn these solved VBQs for Class 12 Biology as these will help them to gain more marks and help improve understanding of important topics.

Organisms and Populations VBQs Class 12 Biology with Answers

Organism and Its Environment

Very Short Answer Type Questions

Question. Which one of the two, stenothermals or eurythermals, show wide range of distribution of earth and why? 
Answer.Eurythermal organisms are those organisms which can tolerate wide range of temperature variations and thus show wide distribution on earth.

Question. Mention how do bears escape from stressful time in winter. 
Answer.Bears undergo hibernation to escape from stressful time in winter. In hibernation, they seek a warm shelter and remain dormant, their respiration rate turns low and they consume stored food.

Question. How do seed bearing plants tide over dry and hot weather conditions?
Answer. Mesophytic seed bearing plants sometimes have to face hot and dry weather conditions. They survive such adverse conditions by forming underground perennating structures such as corms, rhizomes, tubers, etc. Xerophytic plants on the other hand have to face hot and dry conditions throughout the year. They show various adaptations like sunken stomata, Theshy organs, leaves reduced to spines, extensive root system, etc.

Question. How are ephemeral plants adapted to withstand hot and dry environment? Explain.
Answer. Ephemerals are xerophytic plants of hot and dry habitat where environment favours higher rate of transpiration than the rate of absorption. Ephemerals live for a brief period during the rains and rest of the year is passed in form of seeds.

Question. How do snails escape from stressful time in summers? 
Answer. Snails undergo aestivation to escape from stressful time in summers.

Question. Why are green algae not likely to be found in the deepest strata of the ocean? 
Answer. Green algae are photosynthetic in nature. In the deepest strata of the ocean i.e., benthic zone, light does not penetrate therefore, this zone is in perpetual darkness and photosynthetic organisms such as green algae cannot survive in this region.

Question. Why green plants are not found beyond a certain depth in the ocean? 
Answer. Green plants are photosynthetic and show autotrophic mode of nutrition. They require sunlight to photosynthesise. Light does not penetrate beyond a certain depth in oceans and hence very deep layers remain in perpetual darkness. In the absence of sunlight green plants cannot manufacture their food and hence cannot survive. Therefore, they are found in those regions of the ocean where sunlight is available.

Question. Why is the polar region not a suitable habitat for tiny humming birds? 
Answer. Polar region is not a suitable habitat for humming bird. Because of larger surface area relative to volume it tends to lose heat very fast in comparision to large sized animals hence it will have to spend more energy in maintaining its body temperature.

Question. Mention any two activities of animals which get cues from diurnal and seasonal variations in light intensity. 
Answer. Most animals are active during a particular period of the day, e.g., butterflies and most birds are active during day time hence called diurnal whereas few animals like rat, cockroaches and birds like owl are active during night hence called nocturnal. Various activities like flowering in plants and migration in birds and animlas are affected by seasonal variations.

Question.What does ecological niche of an organism represent? 
Answer. The ecological niche of an organism represents the status or role of the organism in its environment.Niche is defined by the types of food it consumes, its predators, temperature tolerance, etc.

Question. How does camouflage help an insect?
Answer. Camouflage is the ability of an organism to blend with the surroundings or background. It is the most common type of adaptation in animals. It is advantageous to insects whether they act as prey or predator. Prey insects can easily hide from their predators and escape from them whereas predator insects can also hide from their prey and remain unnoticed so that easily attack their prey.

Question. Give example of an organism that enters ‘diapause’ and why. 
Answer. Bombyx mori (silk moth) is an insect that enters diapause due to some adverse environmental conditions such as drought, extreme temperature, reduced food availability; which, in turn, delays the overall development. The physiological and metabolic activities diminish at this particular time.

Question. When and why do some animals like frogs hibernate? 
Answer. Hibernation or winter sleep is quite common in ectothermal (cold blooded) animals like frog. This is because they are unable to regulate their body temperature which changes with the fluctuating external environment. Such animals pass the winter period in dormant condition, resting in warm places. Hibernation is necessary for these animals to prevent their metabolic rate from slowing down to levels which could be harmful to them.

Question. List two advantages that a mycorrhizal association provides to the plant.
Answer. Mycorrhizal association is mutualistic interaction between fungus and roots of higher plant.
Two advantages of this association to the plant are :
(i) Fungus solubilises the minerals present in soil and helps the plant in absorption of minerals.
(ii) It protects plant against pathogenic fungi.

Question. When and why do some animals like snails go into aestivation? 
Answer.When animals like snails are exposed to very high temperatures, they go into aestivation to avoid the heat of summer.

Question. Between amphibians and birds, which will be able to cope with global warming? Give reason.
Answer.  Birds are better able to cope with global warming then amphibians because birds are eurythermal and can tolerate wide range of temperature whereas amphibians are stenothermal and cannot tolerate much fluctuation in the ambient temperature.

Question. Why are some organisms called as eurythermals and some others as stenohaline?
Answer. Some organisms can tolerate a wide range of temperature variations, e.g., most mammals and birds. They are called eurythermals while other organisms live within narrow range of temperature because of their requirement of nearly constant tempeture throughout the year e.g., polar bear, lizards, amphibians, and are called stenothermals.

Question. How do herbs and shrubs survive under the shadow of big canopied trees in forests?
Answer.Herbs and shrubs survive under the shadow of big canopied trees in forests as they are perfect shade tolerant plants showing better growth in lower level of light intensity and are arranged in different strata according to their shade tolerance.

Question. List any two physiological responses that help you to gradually get acclimatised to high altitudes when you go from the planes.
Answer.(i) Enhancement in RBCs production to compensate low oxygen availability
(ii) Increase in breathing rate.

Short Answer Type Questions

Question. A student on a school trip started sneezing and wheezing soon after reaching the hill station for no explained reasons. But, on return to the plains, the symptoms disappeard. What is such a response called? How does the body produce it? 
Answer.Atmospheric pressure is low at higher altitudes as compared to plains. When we go for a trek/trip on high altitude, then due to low atmospheric pressure our body does not get enough oxygen, as a result of which we experience nausea, fatigue and heart palpitation (altitude sickness). But by taking rest for first two days, body gets acclimatised to high altitude conditions. The body compensates low oxygen availability by increasing red blood cell production, decreasing binding capacity of haemoglobin and increasing breathing rate. Hence, we automatically stop experiencing altitude sickness.

Question. Plants that inhabit a rainforest are not found in a wetland. Explain. 
Answer. Plants that inhabit rainforest are not able to germinate in wetland due to presence of excess water and anaerobic conditions (due to water logging). Wetlands are marshy areas and plants growing there have negatively geotropic roots, called pneumatophores which help in gaseous exchange. Pneumatophores are not present in plants inhabiting rainforests.

Question. When you go for a trek/trip to any high altitude places, you are advised to take it easy and rest for the first two days. Comment, giving reasons.
Answer. Atmospheric pressure is low at higher altitudes as compared to plains. When we go for a trek/trip on high altitude, then due to low atmospheric pressure our body does not get enough oxygen, as a result of which we experience nausea, fatigue and heart palpitation (altitude sickness). But by taking rest for first two days, body gets acclimatised to high altitude conditions. The body compensates low oxygen availability by increasing red blood cell production, decreasing binding capacity of haemoglobin and increasing breathing rate. Hence, we automatically stop experiencing altitude sickness.

Question. During a school trip to ‘Rohtang Pass’, one of your classmates suddenly developed ‘altitude sickness’. But, she recovered after sometime.
(a) Mention one symptom to diagnose the sickness.
(b) What caused the sickness?
(c) How could she recover by herself after sometime? 
Answer.(a) Heart palpitation
(b) Sickness is due to low atmospheric pressure of high altitudes, as body does not get enough oxygen.
(c) After sometimes, body compensates for low oxygen availabilty by increasing red blood cell production, decreasing binding capacity of haemoglobin and by increasing breathing rate.

Question. How does a desert plant adapt to the dry,warmer environmental conditions?
Answer. Desert plants or xerophytes have various adaptations to cope with dry, hot environmental conditions such as leaves with thick waxy, hairy coating to reduce transpiration, leaves reduced to spines and photosynthetic stems, Theshy organs to store water, sunken stomata that open only during night and deep penetrating roots that reach water table.

Question. Why do we experience shivering during winters when the temperature is very low?
Answer.When the ambient temperature is very low, our body starts shivering. It is an exercise that raises body temperature and helps to maintain constant internal body temperature at about 37°C, by mechanism of homeostasis.

Question. Shark is eurythermal while polar bear is stenothermal. What is the advantage the former has and what is the constraint the later has?
Answer. Sharks being eurythermal can tolerate wide range of temperature variations and thus have wider distribution on earth, on the other hand, polar bear being stenothermal can tolerate only narrow range of temperature and is restricted to specific regions only.

Question. Write the normal body temperature of humans.How is it maintained during summers?
Answer. Normal body temperature of humans is about 37°C. Humans maintain constant body temperature by homeostasis. During summer, when external temperature rises, we begin to sweat profusely. As sweat evaporates, cooling of body occurs.

Question. How are mammals living in colder regions and seals living in polar regions able to reduce the loss of their body heat?
Answer.Animals inhabiting cold areas possess thick coat of hairs, feathers and subcutaneous fat to reduce loss of body heat.

Question. Why the plants that inhabit a desert are not found in a mangrove? Give reasons.
Answer.  Plants inhabiting desert (xerophytes) are not found in mangroves, because xerophytic plants are adapted to dry and hot environment. They possess various physical modifications to tolerate extreme water scarcity and heat, like extensive root system, succulent organs, leaf reduced to spine, etc. Mangrove swamp is a region of vegetation where soil is highly saline and water logged. Only halophytes can survive in such regions as they possess aerial roots called pneumatophores through which gaseous exchange occurs. Roots of xerophytes are positively geotropic and will sufocate and die in such badly aerated soil ultimately leading the whole plant to death.

Question. Explain why very small animals are rarely found in polar region. 
Answer. Small animals have large surface area relative to volume, so they tend to lose body heat very fast in cold environment as compared to large animals. They have to spend more energy to generate body heat through metabolism. Thus, considering the dificulty of maintaining constant internal temperature, small animals are rarely found in polar regions.

Question. Bear hibernates whereas some species of zooplanktons enters diapause to avoid stressful external conditions. How are these two ways different from each other? 
Answer. Bears undergo hibernation during winters to escape extreme cold. It is characterised by low body temperature, slow breathing and heart rate and low metabolic rate. However, diapause is a stage of suspended development or growth occurring in many insects and other invertebrates during which metabolism is greatly decreased. Diapause is oen triggered by seasonal changes and regulated by inborn rhythm.

Question. Some organisms suspend their metabolic activities to survive in unfavourable conditions.
Explain with the help of any four examples.
Answer.To tide over unfavourable conditions, some organisms suspend their metabolic activities. These are discussed as follows :
(i) Bacteria, fungi and lower plants develop thick walled spores, which germinate during suitable conditions.
(ii) Polar bears go into hibernation during winter season to escape cold.
(iii) Some snails and fish undergo aestivation to avoid summer related problems like heat and dessication.
(iv) During unfavourable conditions, zooplanktons in lakes and ponds are known to enter diapause, i.e., stage of suspended development.

Question. When an organism is called a ‘conformer’? Explain with the help of an example.
Answer. The organism in which osmotic concentration of body fluids and body temperature changes according to ambient conditions is called conformer. E.g. in aquatic animal Asterias, the osmotic concentration of body fluids changes according to the osmotic concentration of the surrounding water.

Question. How does the human body maintain constant temperature both in summers and winters?
Explain. Normal body temperature of humans is about 37°C. Humans maintain constant body temperature by homeostasis. During summer, when external temperature rises, we begin to sweat profusely. As sweat evaporates, cooling of body occurs.
When the ambient temperature is very low, our body starts shivering. It is an exercise that raises body temperature and helps to maintain constant internal body temperature at about 37°C, by mechanism of homeostasis.

Question. How do desert lizards cope with temperature variations in their environment? Explain.
Answer. Desert lizards lack the physiological ability that mammals have to deal with the high temperature. They keep their body temperature fairly constant by behavioural means. They enjoy in the sun and absorb heat when their body temperature drops below the comfort zone, but move into shade when the surrounding temperature starts increasing. Some species are capable of burrowing into the soil to hide and escape from too much heat.

Question. Many freshwater animals cannot survive in marine environment. Explain.
Answer. If a freshwater animal is placed in marine environment, then it will not be able to survive because of osmoregulation problem. The freshwater animal is adapted to live in fresh environment, so, if it is kept in saline water, it will not be able to cope with outside hypertonic environment and it would face death.

Question. Humming birds live among the bushes in tropics while penguins live on icebergs. They cannot survive if their habitats are reversed.Justify. 
Answer. Hummingbird is a small animal that has large surface area as compared to volume. In colder environment, it will lose heat very fast and will have to spend more energy in maintaining internal body temperature as compared to large sized animals. It is because of this reason small sized animals like humming bird do not occur in polar regions. Penguins found in polar regions have narrow and acuminate wings as compared to broader wings of birds of warmer areas and possess thick fur, subcutaneous fat and small extremities which help in conservation of heat so if they inhabit warm tropical areas they won’t be able to dessipate extra heat and will suffocate and die.

Short Answer Type Questions

Question. (a) State how the constant internal environment is beneficial to organisms.
(b) Explain any two alternatives by which organisms can overcome stressful external conditions.
Answer. 
(a) Regulators are organisms which maintain constant internal environment despite changes in external conditions through thermoregulation and osmoregulation. Such organisms generally have wide range of distribution.
(b) Organisms can overcome stressful external conditions by following adaptation :
(i) Migration – Birds of colder areas of northern hemisphere begin their southward migration as the day length begins to shorten.
(ii) Aestivation – Ground squirrels undergo aestivation to avoid heat by spending dry hot period in burrows.

Question. Water is very essential for life. Write any three features both for plants and animals which enable them to survive in water scarce environment.
OR
How do organisms cope with stressful external environmental conditions which are localised or of short duration? 
Answer. Water is very essential for life. Plants and animals show various adaptations to cope up with water scarcity in the area where they are found. Some of the adaptations seen in plants which enable them to survive in water scarce environment are as follows:
– Some plants have deep tap root system which is capable of absorbing water from deep soil e.g., Prosopis, Acacia etc.
– Cacti and succulents, have fleshy leaves and stems to store water.
– Many tropical plants, which grow in hot and arid climates possess C4 pathway of photosynthesis. So, these plants perform better in low soil water environments. Such plants, use less water to achieve higher rates of photosynthesis. Some of the adaptations seen in animals which enable them to survive in water scarce environment are as follows:
– Desert lizards keep their body temperature fairly constant by behavioural means. They enjoy in the sun and absorb heat when their body temperature drops below the comfort zone but move into shade when the surrounding temperature starts increasing.
– The Kangaroo rat conserves water by excreting nearly solid urine and can live from birth to death without even drinking water.
– The camels shows tolerance to wide fluctuations in body temperature and are able to maintain blood stream moisture even during extreme heat stress.
OR
Living organisms cope with stressful conditions by any of the following methods:
(i) Migration : The organism can migrate temporarily from the unfavourable habitat to more favourable area and return when unfavourable period is over e.g., Siberian birds migrate from Siberia to other parts every winter.
(ii) Hibernation : The phenomenon of spending extreme cold period of the year in an inactive stage by an animal, e.g., polar bears undergo hibernation during winter season to escape extreme cold.
(iii) Aestivation : The phenomenon of spending dry hot period of the year in an inactive stage by an animal e.g., snails and fish.
(iv) Diapause : It is a dormant stage of suspended development of an organism. During this period there is reduction in the amount of free water.

Question. Why do tribes who live in high altitude of Himalayas experience discomfort in respiration? How do they get adapted to survive in such a situation? 
Answer.Atmospheric pressure is low at higher altitudes as compared to plains. When we go for a trek/trip on high altitude, then due to low atmospheric pressure our body does not get enough oxygen, as a result of which we experience nausea, fatigue and heart palpitation (altitude sickness). But by taking rest for first two days, body gets acclimatised to high altitude conditions. The body compensates low oxygen availability by increasing red blood cell production, decreasing binding capacity of haemoglobin and increasing breathing rate. Hence, we automatically stop experiencing altitude sickness.

Question. Explain with the help of suitable examples the three different ways by which organisms overcome their stressful conditions lasting for short duration. 
Answer. Physiological and behavioural adaptations help organisms to manage stressful conditions. These include migration, hibernation, aestivation, camouflage, mimicry etc. Caribou migrate during winter to warmer places for search of food. Some animals undergo hibernation during winter to avoid low temperature whereas others undergo aestivation to avoid extreme heat. Viceroy butterfly mimics unpalatable toxic monarch butterfly in order to get protection against predator.

Question. The following graph represents the organismic response to certain environmental condition (e.g., temperature) :

conformers?
(b) What does the other line graph depict?
(c) How do these organisms differ from each other with reference to homeostasis?
(d) Mention the category to which humans belong. 
Answer.(a) The line graph, ‘A’ depicts conformers.
(b) The line graph ‘B’ depicts regulators.
(c) Regulators are able to maintain homeostasis by physiological means which ensures constant body temperatures. On the contrary, conformers do not have the ability to maintain homeostasis, instead their body temperature changes with ambient temperature.
(d) Humans belong to the category of regulators.

Question. How do snails, seeds, bears, zooplanktons, fungi and bacteria adapt to conditions unfavourable for their survival? 
Answer. Ecological adaptations are special characteristics evolved or developed by organisms in order to live comfortably and successfully under a prevailing set of environmental conditions. Adaptations may be morphological, physiological or behavioural or a combination of them. The ultimate aim of all adaptations is to make the individual fit to obtain food and space for its survival, opportunities for its reproduction and rearing of young ones.
Various kinds of thick walled spores are formed in bacteria, fungi and lower plants which help them survive under unfavourable conditions. These germinate on return of suitable conditions. Some organisms retard their metabolic activities under stress conditions and undergo hibernation or aestivation. For example, polar bears go into hibernation during winter season to escape extreme cold. Some snails and fish undergo aestivation to avoid summer-related problems like heat and dessication. Under unfavourable conditions many zooplanktons in lakes and ponds are known to enter diapause i.e., a stage of suspended growth and development. Seeds remain dormant in unfavourable conditions. They break dormancy and germinate in favourable environmental conditions.

Long Answer Type Questions

Question. (a) Explain giving reasons why the tourists visiting Rohtang pass or Mansarovar are advised to resume normal ‘active life’ only after a few days of reaching there.
(b) It is impossible to find small animals in the polar regions. Give reasons.
Answer. 
(a) Tourists visiting high altitude areas such as Rohtang Pass or Mansarovar, experience altitude sickness. Its symptoms include nausea, fatigue and heart palpitations. This is because in the low atmospheric pressure of high altitudes, the body does not get enough oxygen. But, gradually it gets acclimatised and stops experiencing altitude sickness. The body compensates low oxygen availability by increasing red blood cell production, decreasing the binding afinity of haemoglobin and increasing breathing rate. Thus, the visitors are advised to resume their normal active life involving heavy works only after few days because for doing heavy tasks our body needs energy and this energy is obtained by the oxidation of glucose. This oxygen is carried to the cells by haemoglobin present in RBCs. As oxygen is the limiting factor in high altitudes, more carrier molecules i.e., haemoglobins are needed to provided suficient amount of oxygen to cells. Thus, increased RBC production that starts in a few days after reaching altitudes prepares the tourist to lead a normal active life.
(b) According to Bergman’s rule, temperature affects the absolute size of an animal and the relative proportion of various body parts. Birds and mammals attain greater body size in cold regions than in warm areas . Thus, smaller animals are rarely found in polar regions. It can be explained as that small animals have a larger surface area relative to their volume and they tend to loose body heat very fast when it is cold outside. Due to higher heat loss they have to spend much energy to generate body heat through metabolism. Greater body size reduces surface area to volume ratio and decreases heat loss which is very essential for surviving in cold polar regions.