Following are Organisms and Populations Notes for Class 12 Biology. These revision notes have been prepared by expert teachers of Class 12 Biology as per the latest NCERT, CBSE, KVS books released for the current academic year. Students should go through Chater 13 Organisms and Populations concepts and notes as these will help you to revise all important topics and help you to score more marks. We have provided Class 12 Biology notes for all chapters in your book. You can access it all free and download Pdf.

Chapter 13 Organisms and Populations Notes Class 12 Biology

Important Questions Organisms and Populations Class 12 Biology

Question. Will the distribution level of species be affected by gradual increase in temperature? Say briefly 
Answer : Yes the pattern of distribution will shift towards the poles with increase in temperature

Question. Define population and population density. How is it estimated? What are the attributes that determine the population characteristics?
Answer : The organisms of the same species at a given time in a specific area.
Number of organisms is a measure of population density, or the biomass cover, ii) attributes are natality, mortality, immigration emigration, sex ratio and age distribution

Question. Predators are prudent. Why? 
Answer : They keep the prey population in check without causing their extinction

Question. How does water affect aquatic animals? Explain. 
Answer : pH of water salt concentration Salinity,

Question. What is brood parasitism? 
Answer : One species lays eggs in the nest of another bird, let the host incubate them E.g. Cuckoo lays eggs in the nest of a crow

Question. How is liver fluke adapted to parasitism? 
Answer : Flat body, suckers for adhering to the host

Question. What adaptation have parasites evolved? 
Answer : Loss of unnecessary sense organs, presence of adhesive organs, suckers , loss of digestive system, high reproductive capacity

Question. Gause’s competitive exclusion principle, where does this apply? 
Answer : Organisms living closely related and in case if resources are limiting

Question. Give example of adaptation to desert condition shown by organisms.
Answer : Spines in place of leaves in cactus, deeply seated stomata, thick cuticle covering leaves, CAM photosynthetic pathway ,minimum loss of water in excretion,flattened green photosynthetic stems in place of leaves.

Question. How is competition avoided in Nature? Give example. 
Answer : Resource partitioning, two species adopt to have different grazing time to avoid competition.

Question. How have prey reduced impact of predation? 
Answer : Various defences-distasteful ,cryptically coloured to avoid detection

Question. Why is female mosquito not considered a parasite? 
Answer : It does not live in/on the body of the host

Question. What factors contribute to growth in population. In what way logistic growth differs from exponential growth?
Answer : Increase Natality and Immigration .decrease mortality and emigration. 
exponential growth takes place when resources are unlimited and therefore the reproductive potential is highest., logistic growth shows that the population cannot grow beyond the carrying capacity of the environment.(Depict graphically)

Question. How have plants developed defence against predators? 
Answer : Morphological-thorns and chemical-cardiac glycosides defences

Question. How are the four levels of biological organisations in ecology interrelated? 
Answer : -Similar organisms make Populations -make communities make Biomes

Question. How is orchid ophrys pollinated by sexual deceit? 
Answer : Sexual deceit

Question. What is the importance of light for organisms? How do deep sea organisms get their energy? 
Answer : Quality of light, photoperiod affect photosynthesis, affect reproductive, for aging activities, ii)scavenging and predation

Question. Which is the deepest dwelling algae- red, green or brown, why? 
Answer : Red-has longest wavelength

Question. What characteristic of solid etermine the vegetation? How are these different at different places? 
Answer : Soil composition, grainsize, percolation and water holding capacity-different based on climate and the weathering process

Question. What do you mean by competitive release? 
Answer : A species whose distribution is restricted because of the presence of a competitively superior species, expands its distribution when the superior competitor is removed

Question. The following graph represents the organismic response to certain environmental condition (e.g. temperature)
Which one of these,’ a’ or ‘b’ depicts conformers?
What does the other line graph depict?
How do these organisms differ from each other with reference to homeostasis?
Mention the category to which humans belong.
Answer :

i) a = conformers = ½
ii)response of the regulators =1/2
iii)maintain homeostasis by physiological means, others either migrate, or suspend
activities = 1/2×3
iv)regulators =1/2

Question. Lions are natural predators. Can you compare this act with that of indiscriminate killing of animals by humans for their leather horns etc .Comment.
Answer : No predators are prudent and with decrease in prey population the predator population also decreases. This is a Natural chain that helps in keeping a check on population size. Humans on the other hand kill for greed and not for basic needs. It should be realized that every species has a significant role in Nature.

Question. What are the roles of predators? 
Answer : Conduits of energy, checks prey population, maintains species diversity

QuestionGive three example of mutualistic relationship. 
Answer : Lichens-algae and fungi, bird and cattle, wasp and fig tree,

Question. Name the major biomes and the factors by which they vary. 
Answer : Desert, forest and grasslands-Precipitation, temperature, soil

Question. What are the factors that lead to the variation in the conditions of the habitat? 
Answer : Soil, temperature, water, light and biotic components like pathogens, parasites, predators and competitors.

Question. How does sconstancy in the internal environment help an organism? How do organisms achieve it with regard to temperature? Give example.
Answer : Constant internal environment permits all biochemical reactions to proceed with maximal efficiency, ii)regulate by physiological means eg sweating to reduce temperature when the external temperature increases.

Question. What is the relationship between egret and grazing cattle? Why? 
Answer : Commensalism-egret benefits while the cattle are not affected

Question. What alternatives do organisms take it stressful external conditions are localized? Give examples. 
Answer : Suspend activities for a brief period till the stressful conditions go(Hibernate or aestivate),migrate–move away to a far off place and return when stressful period is over-birds

Question. What is altitude sickness? How does the body overcome this? 
Answer : At higher altitudes the body shows symptoms like nausea, fatigue, heart palpitations, due to insufficient oxygen in the body. The body increases RBC production, decreases oxygen binding capacity of haemoglobin and Increases breathing rate.

Question. Give example of biochemical adaption shown by organisms. What are the behavioral adaptations shown by organisms?
Answer : Presence of thermos table enzymes in thermophiles, presence of antifreeze proteins in cold water fishes, presence of molecules that can withstand high pressure conditions in the deep sea .Lizards bask in the sun when temperature of their body drops and move to shade, burrows when the temperature around starts increasing

Question. How does temperature affect distribution of animals? Name two types based on their temperature tolerance.
Answer : Enzymes activity and therefore metabolic activities ,Eurythermal,stenothermal

Question. Define adaptation. What is the adaptation shown by –a) whales, b) kangaroo rat, c) polar bear. Why do cold regions not have small animals?
Answer : Adaptation is any attribute of an organism that allows the organism to survive and reproduce in its habitat. i)Blubber a layer of fat to prevent heat loss from the body ii)the animal needs only the metabolic water to survive iii) hibernation in polar bears iv)they lose heat faster than the rate of production as their surface area is large compared to its volume.