Organisms and Populations Important Questions for CBSE Class 12 Biology Organisms and Its Environment

1.Ecology is the branch of biology, which studies the interactions among organisms  and their physical (abiotic) environment.

2.The subject ecology is basically concerned with four levels of biological organisation.
These are given below:
(i)Organism Living component of the environment at individual level and is basic unit of ecological hierarchy.
(ii)Population The sum total of all individuals of a species in a specific geographical area.
(iii)Communities Assemblage of all the populations of different species present in an area that interact among themselves.
(iv)Biome It is a large unit, which consists of a major vegetation type, associated fauna in a particular climatic zone. Tropical rainforest, deciduous forest, sea coast, deserts, etc., are the major biomes of India.
NOTE Other important terms used in ecology are:
Ecosystem Represents, the organisms and their environment in a particular area.
Habitat It refers to a specific place or locality delimited by a combination of factors, physical features and barriers where a community dwells.
Niche The ecological niche of an organism represents the physical space occupied by it, the resources it utilises and its functional role in the ecological system.
Biosphere The surface of earth with all life forms, i.e. union of all ecosystems. It is a highly ordered system.

3.Environment Ecology at organism level deals with how different organisms are adapted to their environment in terms of their survival and reproduction.
(i)Different biomes are formed due to:                                                                                                                                     .

  • annual variations in the intensity and duration of temperature.
  • annual variations in precipitation.

The major biomes of the world are desert, grassland, rainforest and tundra.
important-questions-for-class-12-biology-cbse-organisms-and-its-environment-t-13-1
(ii)Regional and local variations within each biome lead to the formation of a wide variety of habitats.
(iii) Life on earth exists in favourable habitats as well as in extreme and harsh habitats like scorching Rajasthan desert, rain-soaked Meghalaya forests, deep ocean trenches, torrential streams, permafrost polar regions, high mountain tops, boiling thermal springs and stinking compost pits and even in our intestine.
(iv) The biotic components of a habitat are pathogens, parasites, predators and competitors of the organism with which they interact constantly.
(v)The key abiotic elements that lead to variations in habitats are:
(a)Temperature  (b) Water
(c)Light                (d) Soil.

4.Major abiotic factors are:
(i)Temperature is the major abiotic factor, which is most ecologically relevant.

  • There is seasonal variation in average temperature of land.
  • It decreases progressively from the equator to the poles and from plain areas to the mountains.
  • The range of temperature varies from sub-zero levels in polar areas to >50 °C at high altitude in tropical deserts during summer.
  • The temperature affects the kinetics of body enzymes and thus, the basal metabolism and other physiological functions of the organism.
  • Based on tolerance of temperature range, organisms can be divided as:

Euiythennal These can tolerate a wide range of temperature.
Stenothermal These can tolerate a narrow range of temperature
(ii)Water is the next major important factor without which life cannot exist.

  • The productivity and distribution of plants in an environment depends on amount of water available.
  • For aquatic organisms, the quality (chemical composition and pH) of water is important.
  • Salinity refers to salt concentration (measured in parts per thousand) of water. Salt concentration is less than 5 in land water, 30-35 in sea and more than 100 in some hyper saline lagoons.
  • Based on tolerance of range of salinity, organisms can be grouped as:

Euryhaline Organisms, which can tolerate a narrow range of salinity.
Stenohaline Organisms, which can tolerate a narrow range of salinity.

  • Many freshwater animals cannot live for long in seawater and vice versa because of the osmotic problems they would face.

(iii)Light is an essential factor for the process of photosynthesis performed by autotrophs.

  • Oxygen is released during photosynthesis.
  • Many small plants like herbs and shrubs can perform photosynthesis under very low light conditions because they are overshadowed by tall, canopied trees.
  • Most of the plants also depend on sunlight to meet their photoperiodic requirement for flowering.
  • Light is also important for many animals as they use the diurnal and seasonal variations in light intensity and difration (photoperiod) as cues for timing their foraging, migratory and reproductive activities.
  • The UV component of solar radiation is harmful to many organisms. All the colour components of the visible spectrum are not available for marine plants living at different depths of the ocean.

(iv)Soil The nature and properties of soil vary from place to place. It depends on climate, weathering process and whether soil is transported or sedimentary and how its development occurred.

  • The soil composition, grain size and aggregation determine the percolation and water holding capacity of the soils.
  • The characteristics like pH, mineral composition and topography determine the vegetation of an area.
  • This in turn dictates the type of animals supported.

5.Responses to abiotic factors determines how organisms can cope or manage with stressful conditions of the habitat.
(i)During the course of millions of years of their existence, many species would have evolved a relatively constant internal (within the body) environment that permits all biochemical reactions and physiological functions to proceed with maximal efficiency and thus, enhance the overall fitness of the species.
(ii)The organisms should try to maintain the constancy of its internal environment,i.e.homeostasis, despite of varying external environmental conditions that tend to upset its homeostasis.
(iii)Human beings can maintain their homeostasis by using artificial means
(air conditioner in summer and heater in winter).
(iv)Ways by which other organisms can cope up with environmental changes are  given below:
Regulate

  • Some organisms maintain homeostasis by physiological and sometimes behavioural means.
  • All birds and mammals and few lower vertebrates and invertebrates are capable of thermoregulation and osmoregulation.
  • In mammals, during summer, sweating occurs profusely and the evaporation brings down temperature of the body.
  • In mammals, during winter, shivering occurs which is a kind of exercise that produces heat and raises the body temperature.
  • Plants, on the other hand, do not have such mechanisms to maintain their internal temperature.

Conform

  • About 99% of animals and almost all plants cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature.
  • In aquatic organisms, the osmotic concentration of the body fluids change with that of the osmotic concentration of the ambient water. These animals and plants are called
  • Thermoregulation is energetically expensive for many organisms. This is specially true for small animals like shrews and humming birds.Heat loss or gain is a function of surface area. Since, smal^animals have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; they have to expend much energy to generate body heat through metabolism. This is the reason that very small animals are rarely found in polar regions.
  • It can be concluded that during the course of evolution, some species have evolved the ability to regulate but only over a limited range of environmental conditions, beyond which they simply conform.

Migrate
It is the temporary movement from a stressful habitat to a more hospitable area and
return, when the stressful period is over.

  • Many animals, particularly birds, during winter undertake long-distance migrations to more hospitable areas.
  • Every winter the famous Keolado National Park in Bharatpur (Rajasthan) hosts, thousands of migratory birds coming from Siberia and other extremely cold Northern regions every winter.

Suspend

  • Under unfavourable conditions bacteria, fungi and lower plants slow down their metabolic rate and forms a thick-walled spore to overcome stressful conditions. These spores germinate under onset of suitable environment.
  • In higher plants, seeds and some other reproductive structures serve as means to tide over periods of stress. They reduce their metabolic activity and undergo dormancy.
  • Some animals, which fail to migrate might avoid the stress by escaping in time. For example, Bear undergoes hibernation during winter.
  • Some snails and fish undergo aestivation to avoid summer related problems.
  • During unfavourable conditions, many zooplanktons in lakes and ponds enter diapause (a stage of suspended development)

important-questions-for-class-12-biology-cbse-organisms-and-its-environment-t-13-2

6.Adaptation is any attribute of an organism, i.e. morphological, physiological or behavioural, that enables the organism to survive and reproduce in its habitat. Many adaptations have evolved over a long evolutionary time and are genetically fixed.
Some examples of adaptations are:
(i)Adaptations in kangaroo rat

  • The kangaroo rat in North American deserts is capable of meeting all its water requirements by internal oxidation of fat (water is a byproduct) in the absence of water.
  • It can concentrate its urine, so that minimal volume of water is used to expel excretory products.

(ii)Adaptations in desert plants

  • Many desert plants have a thick cuticle on their leaf surfaces and have their stomata arranged in deep pits to minimise water loss through transpiration.
  • They have special photosynthetic pathway (CAM) that enables their stomata to remain closed during day time.
  • Some desert plants like Opuntia, have no leaves. They are reduced to spines and photosynthesis occurs in flattened stems.

(iii)Adaptations in mammals

  • Mammals from colder climates generally have shorter ears and limbs to minimise heat loss. This is called Allen’s rule.
  • In polar seas, aquatic mammals like seals have a thick layer of fat (blubber) below their skin that acts as an insulator and reduces loss of body heat

(iv)Adaptations at high altitudes in humans
(a)At high altitude places like Rohtang Pass near Manali (> 3500 m) and Mansarovar, in China occupied Tibet, people suffer from altitude sickness.
(b)Its symptoms are nausea, fatigue and heart palpitations.
(c)This is because at low atmospheric pressure of high altitudes, body does not get enough oxygen.
(d)The relief occurs gradually due to acclimatisation.
(e)The body cope up with this low oxygen stress by

  • Increasing red blood cells production.
  • Decreasing the binding affinity of haemoglobin.
  • Increasing the breathing rate.

(v) Adaptations in desert lizards (Behavioural response)

  • They absorb heat from the sun when their body temperature drops below the comfort zone.
  • They move into shade when the ambient temperature starts increasing.
  • Some species burrow into the soil and escape from the above ground heat.

Previous Year  Examination Questions

1 Mark Questions

1.Give an example of an organism that enters ‘diapause’ and why?[Delhi 2014]
Ans.Many zooplanktons in lakes and ponds  enter diapause. They enter diapause to escape unfavourable environmental conditions and to delay the overall development.

2.Mention how do bears escape from stressful time in winter. [Delhi 2013c]
Ans.Bears escape from stressful time in winter  by going into hibernation

3.Write the basis on which an organism occupies a space in its community/natural surroundings.[All India 2013]
Ans.An organism occupies individual or species  level in its community. This level is occupied on the basis of ecological level of organisation or ecological hierarchy. Individual-> Population -> Biotic community -> Biome

4.Why are some organisms called as  eurythermals and some other as stenohaline? [Foreign 2011]
Ans.Organisms, which can tolerate and thrive  in a wide range of temperatures are called as eurythermal while organisms, which can tolerate and thrive in a narrow range of salinities are stenohaline

5.Why are green plants not found  beyond a certain depth in the ocean? [HOTS; Delhi 2011]
Ans.Beyond a certain depth, green plants are  not found, because light is unavailable in that zone.

6.Mention any two activities of  animals, which get cues from diurnal and seasonal variations in light intensity, [Delhi 2011 c]
Ans.The two activities of animals which get cues from diurnal and seasonal variations in light intensity are:
(i) Timing their foraging
(ii) Migratory activities
(iii) Reproduction (any two)

7.How do animals like fishs and snails  avoid summer related unfavourable conditions? [Delhi 2010]
Ans.Fish migrate and snails go into aestivation  or summer sleep to avoid summer-related problems.

8.How do prickles help cactus survive in desert? Give two methods.[All India 2010 C]
Ans.The two methods by which prickles help cactus survive in desert are:
(i) By reducing and altering outer surface to reduce evaporation of water.
(ii) By providing defense against grazing animals.

9.Which one of the two, stenothermals or eurythermals shows wide range of distribution on earth and why?[HOTS; Delhi 2008]
Ans.Eurythermals show a wide range of distribution on earth, as they can tolerate and thrive in a wide range of temperatures

10.When and why do some animals like snails go into aestivation?[All India 2008]
Ans.During stressful conditions of the habitat and  inability to migrate, animals like snails undergo aestivation and protect themselves

11.Why is the polar region not a suitable habitat for tiny humming birds? [HOTS; All India 2008]
Ans.Humming birds have a larger surface area  compared to body volume. They tend to lose body heat very fast, when it is cold outside. Due to this, they need to spend more energy to generate body heat. Hence, polar region being a cold habitat is not suitable for tiny hummingbirds

12.When and why do some animals go  into hibernation?  [Foreign 2008]
Ans.When unfavourable conditions are for a short  time and if the animals could not migrate, they undergo hibernation to avoid stressful winter conditions.

13.List any two physiological responses that help you to gradually get acclimatised to high altitudes when you go from the plains. [Delhi 2008 C]
Ans.The physiological condition or responses in order to get accl imatised to high attitudes are:
(i) To compensate low oxygen, the production  of red blood cells is increased.
(ii) High haemoglobin content and its decreased binding capacity.
(iii) Faster breathing rate (any two).

14.Define homeostasis. [All India 2008 C]
Ans.The process to maintain the constancy of  internal environment of the body, despite varying external environmental conditions is called homeostasis

15.When and why do some animals like frogs hibernate? [Delhi 2008]
Ans.When unfavourable conditions are for a short  time period and animals are unable to migrate, they hibernate to avoid the stres winter.

16.Between amphibians and birds, which will be stable to cope with global warming? Give reason.[HOTS; All India 2008]
Ans.Birds will be stable to cope with global warming because they can tolerate a wide range of temperatures (eurythermals).

17.How do herbs and shrubs survive  under the shadow of big canopied trees in forests?     [Delhi 2008C]
Ans.The herbs and shrubs are adapted to perform  photosynthesis optimally under very low light conditions due to growing in the forests under the shadow’ of big canopied trees

18.Why many of the freshwater animals cannot live for long in seawater or vice versa?[HOTS; Delhi; All India 2008 C]
Ans.Seawater contains high quantity of salt that is  not favourable for freshwater animals. They face osmotic problems, hence they cannot survive in seawater for long.

2 Marks Questions

19.Some organisms suspend their metabolic activities to survive in unfavourable condition. Explain with the help of any four examples.[Delhi 2012]
Ans.Examples of organisms that suspend their metabolic activities in unfavourable condition.
(i) Bacteria, fungi and lower plants They form thick-walled spores, which help them to survive in unfavourable conditions. Spores germinate on  return of favourable conditions.
(ii) Higher plants Seeds and some other vegetative reproductive structures serve as means to tide over periods of stress. They reduce their metabolic activity and undergo dormancy.
(iii) Animals They undergo hibernation or aestivation, if unable to migrate. For example, some snails and fishes.
(iv) Zooplanktons They enter diapause (suspended development) under unfavourable conditions.

20.Explain the response of all  communities to environment over time.   [All India 2011]
Ans.Response of communities to environment:
(i) Some organisms maintain homeostasis by physiological or behavioural means (regulate).
(ii)The internal environment in majority of animals and nearly all plants change with the change of external environment (conform).
(iii)Some organisms leave their habitats temporarily during unfavourable conditions and return back when conditions become favourable (migrate).
(iv)Some organisms suspend their  metabolic activities to avoid stress by timely escaping, e.g. hibernation and aestivation.

21.Bear hibernates, whereas some species of zooplanktons enter diapause to avoid stressful external conditions. How are these two ways different from each other?[Foreign 2011]
Ans.Difference between diapause and hibernation:
important-questions-for-class-12-biology-cbse-organisms-and-its-environment-t-13-4

22.How does our body adapt to low oxygen availability at high altitudes?[Foreign 2011]
Ans.Body adaptations at high altitudes are:
The physiological condition or responses in order to get accl imatised to high attitudes are:
(i) To compensate low oxygen, the production  of red blood cells is increased.
(ii) High haemoglobin content and its decreased binding capacity.
(iii) Faster breathing rate (any two).

23.Why are small animals rarely found in the polar regions? Explain.[HOTS; Foreign 2010]
Ans.Small animals have a large surface area  relative to their volume. So, they tend to lose body heat very fast during cold conditions. They need to spend more energy to generate body heat. Due to this smaller animals are rarely found in polar regions.

24.How do seals adapt to their natural  habitat? Explain.  [Foreign 2010]
Ans.Seals adapt to the natural habitat  (cold climate) by developing a thick layer of fat (blubber) below their skin that acts as an insulator and reduce excess loss of body heat.

25.Humming birds v live among the  bushes in tropics, while penguins live on icebergs. They cannot survive if their habitats are reversed. Justify.    [HOTS; Delhi 2010 C]
Ans.Humming birds are natural habitats of  tropics. They have large surface area relative to their volume. So, they tend to lose heat very fast, even when it is cold outside.Penguins live on icebergs (natural habitat). They have less surface area to volume ratio. The lesser the ratio, more effective will be the thermoregulation. Also, they hide in group to escape from cold conditions. Therefore, both of them will not survive if their habitats are reversed

26.How does human body maintain constant temperature both in summers and winters? Explain.[Delhi 2009 C]
Ans.Human body maintains constant body temperature (37 °C) as follows:
In summers, the outside temperature is very high than our body temperature. Due to this, profuse sweating occurs. This causes evaporation and cooling effect on the body.
In winters, the outside temperature is much lower than our body temperature. This causes shivering, a kind of exercise that produces heat and raises the body temperature.

3 Marks Questions

27.(i)State how the constant internal  environment is beneficial to organisms.
(ii)Explain any two alternatives by which orgnaisms can overcome stressful external conditions.[All India 2014]
Ans.(i)Constant internal environment is  beneficial to organisms as it permits all biochemical reactions and physiological functions to proceed with maximal efficiency, thereby enhancing the overall efficiency of organism.
(ii) The two alternatives by which organisms can overcome stressful external conditions are

  • Migration-organisms move temporarily to a favourable area under stressful conditions and return back when the period is over.
  • Hibernation and aestivation are ways  to escape the stress during winters and summers respectively.

28.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?   [ah India 2011]
Ans.Adaptation in plants
(i) Thick cuticle on their leaf surface.
(ii) Stomata are arranged in deep pits (sunken) to minimise water loss through transpiration.
(iii) Leaves are reduced to spines. The  photosynthetic function is carried out by thick, fleshy flattened stems.
Adaptation in animals
(i) Kangaroo rat meets the water requirement through internal oxidation of  fat.  They concentrate their urine, so that minimum volume of water is excreted.
(ii) Snails undergo aestivation during  summers.
Organisms either migrate or suspend their metabolic activities when conditions are stressful for short duration.In such conditions, organisms are as follow:
(i) Moving away from stressful habitat to more favourable area and return to their habitat when stressful period is over. For example, birds from Siberia and other cold countries migrate to Bharatpur Sanctuary of Rajasthan.
(ii) Hibernating (frogs) or aestivating (snails) or undergo diapause (zooplanktons).
(iii) Thick-walled spores are formed in stressful conditions and germinate under suitable conditions, e.g. bacteria, fungi and lower groups of plants.

29.How do organisms like fungi, zooplanktons and bears overcome the temporary short-lived climatic stressful conditions? Explain.[All India 2010; Delhi 2008]
Ans.(i)Fungi They produce various kinds of  thick-walled spores to survive under unfavourable conditions, which germinate on return of favourable conditions.
(ii) Zooplanktons They enter diapause, a stage of suspended development under unfavourable conditions.
(iii)Bears They hibernate during winter to  escape the time of unfavourable  conditions.

30.The following graph represents the organismic response to certain environmental condition (e.g. temperature)
important-questions-for-class-12-biology-cbse-organisms-and-its-environment-t-13-3
(i)Which one of these A or B depicts conformers?
(ii)What does the other line graph depict?
(iii)How do these organisms differ from each other with reference to homeostasis?
(iv)Mention the category to which  human belong.   [All India 2009]
Ans.(i)A depicts conformers.
(ii) The other line B depicts regulators.
(iii) Differences between conformer and regulator are:
important-questions-for-class-12-biology-cbse-organisms-and-its-environment-t-13-5
(iv) Humans are regulators.

5 Marks Questions

31.(i) 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.
(ii) It is impossible to find small animals in the polar regions. Give reasons.     [All India 2012]
Ans.(i)Tourists visiting to Rohtang Pass near  Manali (> 3500 m) may suffer from altitude sickness. They resume normal active life only after a week because in low atmospheric pressure at high altitudes, the body does not get enough oxygen. Gradually, the body compensates low oxygen availability by
(a)Increasing red blood cell production.
(b)Decreasing the binding affinity of  haemoglobin.
(c)Increasing the breathing rate.
(ii)Small animals have a large surface area  relative to their volume. So, they tend to lose body heat very fast during cold conditions. They need to spend more energy to generate body heat. Due to this smaller animals are rarely found in polar regions.

32.list the different ways by which  organisms cope or manage with abiotic stresses in nature. Explain any three ways.         [All India 2009c]
Ans.Organisms cope up with abiotic stress by:
(i)Regulating Some organisms maintain  homeostasis by physiological and behavioural means. They are called regulators, e.g.

  • In summers, when outside temperature is more, we sweat profusely that results in evaporative cooling to bring down the body temperature.
  • In winters, when temperature is low, we shiver (a kind of exercise) that produces heat and raise the body temperature.

(ii) Conformating Organisms that cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature. Such animals are called conformers. For example, small animals have larger surface area relative to their volume. They lose body heat very fast in low temperature. So, they expend energy to generate body heat through metabolism for adjusting.
(iii) Migrating The temporary movement of organisms from the stressful habitat to a  more hospitable area and return when favourable conditions reappear is called migration. The long distance migration is very common in birds.

33.(i) List any four abiotic components  that lead to variations in the physical and chemical conditions of habitats.
(ii) Explain the impact of these components on the distribution of organisms in different habitats.
[All India 2009 C]
Ans.(i)Temperature, water, light and soil.
(ii) (a) Temperature influences the kinetics of enzymes and thereby the metabolism and other physiological functions of the organisms.
Organisms may be eurythermal and can tolerate a wide range of temperature and stenothermal that can tolerate only a narrow range of temperature.
(b)Water is important to sustain life and productivity and distribution of plants is dependent on water.
Freshwater forms cannot thrive in sea water and vice versa.
(c)Light influences photosynthesis of plants. Light also influences the flowering in plants and timing of foraging, reproduction and migratory activities of animals.
Aquatic plants occupy different depths depending on their pigments and the light available.
(d)Soil influences vegetation by the  water holding capacity, topography and its composition.
Important Questions for Class 12 BiologyClass 12 BiologyNCERT Solutions Home Page