Organisms and the Environment


  • Our world is teeming with diverse life forms, each contributing to the rich tapestry of existence. 
  • Exploring this diversity requires understanding processes at various levels of biological organization. 
  • These levels range from macromolecules and cells to tissues, organs, individual organisms, populations, communities, and ecosystems. 
  • At each level, we can inquire about mechanisms ("how-type" questions) or significance ("why-type" questions) of biological processes. 
  • Approaching nature with a scientific mindset unveils a plethora of intriguing phenomena waiting to be explored. 
  • Ecology, the study of interactions among organisms and their environment, provides insights into the interconnectedness of life. 
  • Through our exploration of biology, we uncover the intricate beauty and complexity of the living world. 
  • Ecology is concerned with four levels of biological organization: organisms, populations, communities, and biomes. 
  • Ecology at the organismic level focuses on physiological ecology, understanding how organisms adapt to their environments for survival and reproduction. 
  •  Annual variations in temperature and precipitation, influenced by Earth's rotation and tilt, lead to the formation of distinct seasons and major biomes like deserts, rainforests, and tundra. 
  • Regional and local variations within biomes create a wide array of habitats, fostering diverse life forms. 
  • India showcases various biomes, including deserts, forests, and grasslands. 
  • Life thrives not only in favorable habitats but also in extreme environments like deserts, forests, oceans, mountains, and even within the human intestine. 
  • Key elements contributing to habitat variation include temperature, water availability, light intensity, and soil composition. 
  •  Habitats encompass both abiotic components (physical and chemical conditions) and biotic components (interactions with pathogens, parasites, predators, and competitors). 
  • Organisms undergo natural selection, evolving adaptations over time to optimize their survival and reproduction within their habitats.



Major Abiotic Factor Temperature


  • Ecologically, temperature is highly significant, impacting the physiology and distribution of organisms. 
  • Average temperatures vary seasonally and geographically, decreasing from the equator to the poles and from lowlands to high altitudes. 
  • Extremes exist, from subzero levels in polar regions to over 50°C in tropical deserts, and even surpassing 1000°C in unique habitats like thermal springs and deep-sea hydrothermal vents. 
  • Examples illustrate temperature's influence: mango trees don't grow in Canada or Germany, snow leopards aren't found in Kerala, and tuna fish are rare beyond tropical latitudes. 
  • Temperature affects enzyme kinetics, basal metabolism, and physiological functions of organisms. 
  • Eurythermal organisms tolerate a wide temperature range, while stenothermal organisms thrive only within a narrow range. 
  • Geographical distribution of species is largely determined by their thermal tolerance levels. 
  • Concerns arise regarding increasing global temperatures and their potential impact on species distribution and ecosystems.


Major Abiotic Factor Water

  • Second only to temperature, water is crucial for supporting life. 
  • Life on Earth originated in water, and its presence is essential for sustaining life. 
  • Availability of water varies, with deserts having limited water, requiring special adaptations for survival.


Impact on Organisms:

  • Productivity and distribution of plants are heavily influenced by water availability. 
  • Aquatic organisms face challenges related to water quality, including chemical composition and pH. 
  • Salinity, measured in parts per thousand, varies in different water bodies, ranging from less than 5 in inland waters to over 100 in hypersaline lagoons.



  • Euryhaline organisms tolerate a wide range of salinities, while stenohaline organisms thrive only within a narrow range. 
  • Osmotic problems limit the ability of many freshwater animals to survive in seawater and vice versa.



  • Water plays a critical role in shaping ecosystems and influencing the distribution and behavior of organisms. 
  • Understanding water dynamics is essential for conservation efforts and managing freshwater and marine habitats.


Major Abiotic Factor-Light

  • Light is essential for photosynthesis, the process by which plants produce food. 
  • Autotrophs, such as plants, rely on sunlight as their primary source of energy for photosynthesis.


Adaptations in Plants:

  • Many forest-dwelling plants have adapted to low light conditions under dense tree canopies, optimizing their photosynthesis.
  • Sunlight also plays a crucial role in triggering the flowering process in many plant species, fulfilling their photoperiodic requirement.


Significance for Animals:

  • Animals use variations in light intensity and duration (photoperiod) as cues for timing activities like foraging, reproduction, and migration.


Relationship with Temperature:

  • On land, light availability is closely linked with temperature, as both are sourced from the sun. 
  • However, deep ocean environments (>500m) are perpetually dark, and inhabitants are not exposed to sunlight.


Energy Source in Deep Oceans:

  • In deep ocean environments, where sunlight doesn't penetrate, organisms rely on alternative energy sources such as chemosynthesis.


Spectral Quality:

  • Spectral quality of solar radiation, including harmful UV components, varies and impacts different organisms. 
  • Marine plants living at different depths of the ocean may not have access to all colors of the visible spectrum.


Adaptations of Algae:

  • Among red, green, and brown algae inhabiting the sea, brown algae are more likely to be found in the deepest waters. 
  • Brown algae have pigments that allow them to absorb available light more efficiently in low-light environments, making them suited for deep water habitats.


Major Abiotic Factor-Soil

  • Soil characteristics vary depending on factors like climate, weathering processes, transportation, and sedimentation. 
  • Soil development is influenced by these factors, resulting in diverse soil types across different regions.


Properties of Soil:

  • Soil composition, grain size, and aggregation influence its percolation and water holding capacity. 
  • Parameters such as pH, mineral composition, and topography further determine soil characteristics.


Impact on Vegetation:

  • Soil properties largely dictate the type of vegetation that can thrive in an area. 
  • Vegetation, in turn, influences the types of animals that can be supported in a particular habitat.


Aquatic Environment:

  • In aquatic environments, sediment characteristics play a crucial role in determining the types of benthic (bottom-dwelling) animals that can thrive.



  • The relationship between soil properties, vegetation, and animal life highlights the interconnectedness of ecosystems. 
  • Understanding soil characteristics is essential for ecosystem management and conservation efforts.


Responses to Abiotic Factors:


Variability in Habitat Conditions:

  • Habitats often experience drastic fluctuations in abiotic conditions over time. 
  • Organisms must cope with these stressful conditions to survive and thrive.


Importance of Maintaining Internal Environment:

  • Over millions of years, species have evolved mechanisms to maintain a relatively constant internal environment, optimizing biochemical reactions and physiological functions. 
  • This internal constancy, known as homeostasis, enhances the overall fitness of the species. 
  • Imagine a person who performs best at 25°C and desires to maintain this temperature regardless of external weather conditions. 
  • This can be achieved through artificial means like using air conditioners in summer and heaters in winter, ensuring optimal performance despite external variations.


Mechanisms of Coping:

  • Living organisms employ various strategies to cope with fluctuating environmental conditions:

- Physiological adaptations: Internal mechanisms to regulate body temperature, osmotic balance, etc. 

- Behavioral adaptations: Altering behaviors to seek shelter, adjust activity patterns, or migrate to more favorable habitats. 

- Evolutionary adaptations: Species evolve traits over time that enhance their ability to withstand and thrive in specific environmental conditions.


Interplay of Factors:

  • Responses to abiotic factors are often complex and involve a combination of physiological, behavioral, and evolutionary adaptations. 
  • Understanding these responses is crucial for comprehending how organisms interact with their environment and adapt to changing conditions.


Regulators and Conformers






  • Some organisms maintain homeostasis through physiological or behavioral means, ensuring constant body temperature and osmotic concentration. 
  • Examples:

- Birds, mammals, and a few lower vertebrate and invertebrate species can regulate their internal environment (thermoregulation and osmoregulation). 

- Mammals, including humans, excel in maintaining a constant body temperature, a trait believed to contribute to their evolutionary success. 

  • Mechanisms in Mammals:

Mammals regulate body temperature similar to humans:

- In hot conditions, sweating occurs, and evaporative cooling reduces body temperature. 

- In cold conditions, shivering generates heat to raise body temperature. 

  • Comparison with Plants:

- Unlike mammals, plants lack mechanisms to regulate internal temperatures. 

- Plants rely on external factors like sunlight and soil moisture for growth and survival. 

  • Significance:

- The ability to regulate internal conditions allows organisms to thrive in diverse environments, contributing to their ecological success. 

- Understanding regulatory mechanisms is essential for studying organismal physiology and adaptation to changing environmental conditions.



  • The majority of animals (99%) and most plants cannot maintain a constant internal environment and instead conform to changes in their surroundings. 
  • Characteristics:

- Body temperature of conformers fluctuates with ambient temperature, while osmotic concentration in aquatic animals changes with water osmotic concentration. 

  • Reasons for Conformity:

- Conformers have not evolved into regulators due to the energetic expense and evolutionary trade-offs involved. 

- Thermoregulation, especially, is energetically costly, particularly for small animals like shrews and hummingbirds, due to their high surface area to volume ratio. 

- Small animals lose body heat rapidly in cold environments and must expend energy to generate heat through metabolism. 

  • Limitations of Thermoregulation:

- Very small animals are rarely found in polar regions due to the high energetic cost of thermoregulation. 

  • Evolution balances the costs and benefits of maintaining a constant internal environment. 
  • Some species have evolved limited regulatory abilities, operating within a narrow range of environmental conditions. 
  • If external conditions are localized or short-lived, organisms have alternative strategies for coping.



  • Migration involves organisms temporarily moving away from stressful habitats to more hospitable areas and returning when conditions improve. 
  • Similar to a person relocating from a hot city like Delhi to a cooler hill station like Shimla during the summer months. 
  • Many animals, especially birds, undertake long-distance migrations to escape harsh conditions. 
  • Every winter, Keoladeo National Park in Rajasthan hosts thousands of migratory birds from Siberia and other cold northern regions. 
  • Migration allows organisms to avoid extreme conditions and find suitable habitats elsewhere. 
  • It ensures survival and enhances reproductive success by providing access to food, water, and nesting sites. 
  • Migratory species have evolved specialized physiological and behavioral adaptations for long-distance travel and navigation. 
  • Migration patterns and routes are crucial for conservation efforts, as they highlight the interconnectedness of ecosystems and the need for international cooperation in preserving habitats.



  • Suspend involves organisms adopting strategies to survive unfavorable conditions by temporarily halting their normal activities. 
  • Examples in Bacteria, Fungi, and Lower Plants:

- Thick-walled spores are formed in bacteria, fungi, and lower plants, enabling them to endure harsh conditions. 

- These spores germinate when suitable conditions return, allowing the organisms to resume normal growth and reproduction. 

  • Seeds and vegetative reproductive structures in higher plants aid in survival during stressful periods and facilitate dispersal. 
  • They enter a state of dormancy, reducing metabolic activity until favorable conditions return. 
  •  Examples in Animals:

- Animals may evade stress by escaping in time if unable to migrate. 

- Hibernation, observed in bears during winter, is an example of escaping unfavorable conditions. Hibernation is state of inactivity and metabolic depression in animals, characterized by low body temperature and slowed physiological processes, to conserve energy during harsh winter conditions. 

- Some snails and fish undergo aestivation to avoid heat and desiccation during summer. Aestivation is state of dormancy in animals during hot and dry periods, characterized by reduced metabolic activity and decreased water loss, to survive high temperatures and drought conditions (desiccation). 

- Zooplankton species in lakes and ponds enter diapause, a stage of suspended development, under unfavorable conditions.



  • Adaptation refers to any attribute of an organism (morphological, physiological, or behavioral) that enables it to survive and reproduce in its habitat. 
  • Kangaroo rats in North American deserts meet their water requirements through internal fat oxidation and concentrate urine to minimize water loss. 
  • Desert plants have thick cuticles, deep pit stomata, and CAM photosynthetic pathways to reduce water loss and survive in arid conditions. 
  • Mammals in colder climates have shorter ears and limbs to minimize heat loss (Allen's Rule). 
  • Aquatic mammals in polar seas have a thick layer of fat (blubber) for insulation. 
  • At high altitudes, the body compensates for low oxygen availability by increasing red blood cell production, decreasing hemoglobin's binding affinity, and increasing breathing rate. 
  • People living in high-altitude areas may have higher red blood cell counts or total hemoglobin levels. 
  • Microbes in hot springs and deep-sea hydrothermal vents flourish in temperatures exceeding 100°C due to specialized biochemical adaptations. 
  •  Fish in Antarctic waters prevent body fluids from freezing through antifreeze proteins and other mechanisms. 
  • Marine organisms living at great depths in the ocean withstand high pressures through physiological and biochemical adaptations, possibly including special enzymes. 
  • Desert lizards regulate body temperature behaviorally by basking in the sun to absorb heat and seeking shade when temperatures rise. 
  • Some species burrow into the soil to escape above-ground heat.