Download CBSE Class 12 Biology Organisms And Populations Notes in PDF format. All Revision notes for Class 12 Biology have been designed as per the latest syllabus and updated chapters given in your textbook for Biology in Standard 12. Our teachers have designed these concept notes for the benefit of Grade 12 students. You should use these chapter wise notes for revision on daily basis. These study notes can also be used for learning each chapter and its important and difficult topics or revision just before your exams to help you get better scores in upcoming examinations, You can also use Printable notes for Class 12 Biology for faster revision of difficult topics and get higher rank. After reading these notes also refer to MCQ questions for Class 12 Biology given our website
Organisms And Populations Class 12 Biology Revision Notes
Class 12 Biology students should refer to the following concepts and notes for Organisms And Populations in standard 12. These exam notes for Grade 12 Biology will be very useful for upcoming class tests and examinations and help you to score good marks
Organisms And Populations Notes Class 12 Biology
ORGANISMS AND POPULATIONS
Ecology: It is a branch of biology which studies the interactions i) among organisms and ii) between the organism and its physical ( abiotic) environment.
Organism: Individual of a species.
Population: Population is a group of individuals of the same species which can interbreed among themselves and live in a localized area.
Biome: The largest ecological regions distinguishable by characteristic plants and animals. Eg. tundra, conifer, deciduous forest, grassland, tropical, and desert.
Alpine tundra: Alpine tundra is located on mountains throughout the world at high altitude where trees cannot grow. The growing season is approximately 180 days. The night time temperature is usually below freezing. Unlike the arctic tundra, the soil in the alpine is well drained.
Group of animals that live in Alpine tundra:
Mammals: mountain goats, sheep
Insects: beetles, grasshoppers, butterflies
Coniferous forests: Coniferous forests are made up mainly of cone-bearing or coniferous trees, such as spruces, hemlocks, pines and firs. The leaves of these trees are either small and needle-like or scale-like and most stay green all year around (evergreen). All are softwoods able to survive cold temperatures and acidic soil.
Temperate Forests: The term ‘temperate forest’ is very broad. It covers the forests found between the tropical and subtropical regions and the barren, treeless lands of the far north and extreme south.
Tropical forest: "Tropical forests" encompass the idyllic rainforest, the remote cloud forest, and the lesser-known but equally endangered dry forest, pine savanna and much, much more. They are not one ecosystem, but millions of unique ecosystems.
Deciduous forest: The average annual temperature in a deciduous forest is 50° F. The average rainfall is 30 to 60 inches a year. The deciduous forest has four distinct seasons, spring, summer, autumn, and winter. In the autumn the leaves change color. During the winter months the trees lose their leaves.
Temperature, water, light, soil.
• Average temperature varies seasonally
• Organisms may be Eurythermal or Stenothermal
• Eurythermal- wide range of temperature tolerence
• Stenothermal-Narrow range of temperature tolerance
• Influences life of organisms. No life without water.
• Productivity and distribution of plants are water dependent.
• Organisms may be Euryhaline or Stenohaline.
• Euryhaline:Wide range of salinity tolerance
• Stenohaline:Narrow range of salinity tolerance.
• Photosynthesis and release of oxygen light dependent.
• Sciophytes need to use diurnal and seasonal light intensity of forage, migration and reproduction.
• Nature and proportion of soil in a place depends on climate, weathering process and types of soil.
• Soil composition, grain size and aggregation determine percolation and water holding capacity of soil.
• Physical and chemical properties determine type of plants and Animals that survive in a habitat.
Response of organisms to environmental condition
• Organisms maintain homeostasis achieved by physiological and behavioral means
• Thermo regulation and osmoregulation.
• Cannot maintain constant internal Environment
• Body temperature and osmotic concentration of body changes with ambient temperature and concentration of medium.-Thermo confirmer and osmo-confirmer
• Organism moves away temporarily to another habitat in stressful condition. e.g.- Migratory birds like Siberian crane
• Organisms suspend their metabolic activities during stressful condition
• Resume their function at the return of favorable conditions.
E.g. Hibernation (winter sleep) of Frog, Reptiles, Polar Bear etc
• Aestivation (summer sleep) in Snail and Fish.
• Seed dormancy.
• Morphological, physiological and behavioral changes that enable organisms to adjust to the ever changing environment .
E.g. Kangaroo rat survives in desert conditions through internal oxidation of fat, removing concentrated urine of limited quantity.
• Allen‗s rule-cold climate mammals have shorter ears and limbs to minimize heat loss.
• Polar mammals like seals have blubber to prevent heat loss.
• Burrowing habit to escape from heat
• Higher count of RBC, Hb (haemoglobin) at high altitudes.
• Birth Rate – Number of individuals born per thousand per year.
• Death Rate – Number of individuals die per thousand per year.
• Sex Ratio – Ratio of male-female in the population.
• Population density. - the number of individual organisms per unit area (appropriate measure – total number-sometimes difficult to determine or meaningless because 4
factors N+I-M+E are concerned w.r.t habitat concerned )
• 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.
• Three ecological ages:
• Pre-reproductive, Reproductive and Post-Reproductive
• High proportion pre-reproductive individuals occur in Expanding population
• Pre-reproductive individuals are uniform in Stable population.
• Pre-reproductive individuals are less in Declining population.
Factors that affect the size of population
Density of population at any time at a given
place depends on Natality, Mortality, Emigration
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