Organisms and Populations VBQs Class 12 Biology

VBQs for Class 12

VBQs Organisms and Populations Class 12 Biology with solutions has been provided below for standard students. We have provided chapter wise VBQ for Class 12 Biology with solutions. The following Organisms and Populations Class 12 Biology value based questions with answers will come in your exams. Students should understand the concepts and learn the solved cased based VBQs provided below. This will help you to get better marks in class 12 examinations.

Organisms and Populations VBQs Class 12 Biology

Very Short Answer Type Questions

Question. Define Diapause. 
Answer :
Diapause is a stage of suspended development in zooplanktons species under unfavourable conditions. 

Question. Mention how do bears escape from stressful time in winter ? 
Answer :
Bears undergo hibernation to get rid of the stressful time in winter. 

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

Question. Very small animals are rarely found in polar regions. Give two reasons.
Answer :
Small animals have larger surface area relative to their volume, loose heat very fast, due to small size, expend much energy to generate body heat through metabolism. 

Short Answer Type Questions

Question. Heat loss or heat gain depends upon the surface area of the organism’s body. Explain with the help of a suitable example.
Answer :
 Small animal like humming bird / shrew, have a larger surface area relative to their volume, they tend to loose heat when it is cold outside, hence spend much energy to generate body heat through metabolism. 

Question. Why do people suffer from altitude sickness after reaching the high altitude regions ? How does their body acclimatized after a couple of days ?
Answer :
 “Altitude sickness” is because of low atmospheric pressure at high altitude, the body does not get sufficient oxygen. The body compensates low oxygen availability by increasing RBCs production, decreasing the binding capacity of haemoglobin, by increasing breathing rate. 

Question. Many fresh water animals cannot survive in marine environment. Explain.
Answer : 
Fresh water animals are not able to maintain their osmotic concentration in marine conditions. If they are transferred in marine conditions, their body will shrink due to exosmosis. Hence, they cannot survive in marine environment. 

Question. Why do algae and fungi shift to sexual mode of reproduction just before the onset of adverse conditions ? 
Answer :
 For survival during unfavourable conditions / Fusion of gametes helps to pool their resources for survival (hunger theory of sex) / Zygote develops a thick wall that is resistant to dessication and damage, undergoes a period of rest before germination. 
Detailed Answer :
Organisms such as fungi and algae switch to sexual mode of reproduction during adverse conditions because sexual reproduction brings variation into the individuals, some of which might help the individuals to adapt to the changed conditions and survive. This ensures the continuity of species. 

Question. Why are some organisms called as eurythermals and some others stenohalines ? 
Answer : 
Eurythermals are the organisms which can tolerate and live in a wide range of temperature while stenohalines can tolerate only a narrow range of salinities. 

Question. In certain seasons we sweat profusely while in some other season we shiver. Explain.
Why do we experience shivering during winters when temperature is very low ?
Answer :
To regulate body temperature. 
In summer, outside temperature is higher than body temperature, sweating causes cooling by evaporation of sweat and thus lowering the body temperature.
In winter, outside temperature is much lower than body temperature, shivering is an (involuntary) exercise which produces heat and raises the body temperature in winter. 

Question. Why are certain organisms called regulators or conformers ? Explain with the help of one example of each. 
Answer :
Regulators maintain / regulate constant body temperature irrespective of external condition. 
Conformers changing / varying body temperature as per external condition. 
Regulators : Humans maintain a constant body temperature of 37°C. In summer when temperature is more outside we sweat, when evaporates causes cooling / in winter when outside temperature is much lower than 37°C, we start shivering / a kind of exercise which produce heat and raises body temperature (any other suitable appropriate example). 
Conformers : In aquatic animals, the osmotic concentration of body fluid changes with that of the ambient water osmotic concentration / Internal body temperature of reptiles, amphibians, fishes change with that of external temperature. (Any other suitable appropriate example.) 

Question. The graph given below shows the distribution of biomes:

Organisms and Populations VBQs Class 12 Biology

a) What do the ‘X’ and ‘Y’ axes represent?
b) Identify the ‘grassland’ and ‘coniferous forest’ biomes, from the above figure.
c) Why is ‘F’ located at the given position in the graph?
Answer :
(i) ‘X’ axis–Mean annual precipitation (cm)
‘Y’ axis–Mean annual temperature (0°C)
(ii) Grassland – B
Coniferous forest – E 
(iii) The mean annual temperature ranges from – 12 to 20°C (error accepted ± 2) and mean annual precipitation ranges from 10 – 125 cm, these are the optimum conditions in tundra biome. 

Question. How do kangaroo rats and desert plants adapt themselves to survive in their extreme habitat? Explain. 
Answer : Kangaroo rats :
Internal fat oxidation where water is a byproduct, excretes concentrated urine.
Desert Plants : Thick cuticle / sunken stomata / leaves reduced to spines / deep roots / Special photosynthetic pathway / CAM 
Detailed Answer :
Kangaroo rats fulfil the water requirement by internal oxidation of fat in the absence of water.
Desert plants have thick cuticle to prevent loss of water. CAM plants open their stomata during night to reduce the loss of water during photosynthesis.

Question. Explain with the help of suitable examples the three different ways by which organisms overcome their stressful conditions lasting for short duration. 
How do organisms cope with stressful external environmental conditions that are localized or of short duration ? 
Answer : (i) Migration :
The organisms (animals) can move away temporarily from stressful habitat to a more hospitable area and return when stressful period is over. 
e.g – Humans moving from Delhi to Shimla during summer / many animals or birds undertake long distance migration to hospitable area. (Any one example) 
(ii) Spore formation : Various kind of thick walled spores are formed which germinate on availability of suitable environment.
e.g – bacteria / fungi / lower plants. (Any one)
(iii) Dormancy : Seeds or vegetative reproductive structures help to tide over stress by reducing their metabolic activity.
e.g seeds or vegetative reproductive structures of higher plants.
(iv) Hibernation : It takes place during winter.
e.g bears or any other correct relevant example.
Aestivation : It takes place during summer to avoid heat and dessication in animals.
e.g snails / fish or any other correct relevant example. 
Diapause : Under unfavourable conditions zooplanktons enter a stage of suspended metabolic activity.
E.g. zooplankton. (Any two after migration)
Detailed Answer :
Three different ways by which organisms overcome their stressful conditions are :
(i) Migration : Birds like bar-headed geese temporarily move from the stressful environment to the more hospitable environment and may return when the period of stress is over. This phenomenon of moving from one place to another is commonly known as migration.
(ii) Hibernation (winter sleep) : It is period of long inactivity in which organism reduces all its metabolic activities and undergo a period of long sleep e.g. polar bear hibernates during winter.
(iii) Aestivation (Summer Sleep) : It is commonly seen in animals that live in hot and arid conditions. Frogs undergo aestivation.

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.
Answer : Plants :
Ephemeral mode (complete life cycle in short period) / Deep tap roots / Deciduous leaves / Waxy cuticle / Sunken stomata / Succulence to store water / C4 Pathway of photosynthesis. (Any three) 
Animals : No sweating / uricotelic / deposition of fat in sub-epidermal layer / burrowing nature / thick skin / body covered with scales.

Question. When you go for a trip to any high altitude places you are advised to take it easy and rest for first two days. Comment giving reasons.
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 :
At high altitude, the availability of oxygen is low.
Therefore, it is advised to take it easy and take rest during initial period of high altitude trip because during this period, the early rest of the body compensates the low O2 availability by increasing RBC production and increasing the breathing rate.

Long Answer Type Questions

Question. (a) The graph given below represents the organisms response to temperature as an environmental condition.

Organisms and Populations VBQs Class 12 Biology

(i) Which one of the two lines represents conformers and why ?
(ii) What does the other line in the graph represent and why ?
(b) Mention the different adaptations the parasites have evolved with, to be able to successfully complete their life cycles in their hosts.
Answer :
(a) (i) A is a conformer
Cannot maintain homeostasis / constancy of internal environment by physiological means / their body temperature and osmotic concentration of body fluids changes with the ambient temperature. 
(ii) Regulators
Maintain homeostasis by physiological means / capable of thermo regulation / maintain a constant body internal environment. 
(b) Loss of unnecessary sense organs, presence of adhesive organs / suckers to cling on to the host, loss of digestive system, high reproductive capacity.