Responses to Abiotic Factors
Organisms maintain a stable internal environment (homeostasis) despite varying external environmental conditions through various processes.
a. Regulate
- Regulation is the maintenance of homeostasis by physiological and behavioral means, ensuring constant body temperature (thermoregulation) and osmotic concentration (osmoregulation).
- Examples include all birds, mammals, and very few lower vertebrates and invertebrates.
- Thermoregulation in mammals: The success of mammals is mainly due to their ability to maintain a constant body temperature. In summer, when the outside temperature exceeds body temperature (37°C), sweating occurs, resulting in evaporative cooling to lower body temperature. In winter, when the temperature is below 37°C, shivering produces heat to raise body temperature.
- Most organisms are not regulators or are partial regulators because thermoregulation is energetically expensive, especially for small animals (e.g., shrews, hummingbirds). These animals have a larger surface area relative to their volume, losing body heat quickly in cold conditions and expending significant energy to generate heat. Consequently, very small animals are rare in polar regions.
b. Conform
- Approximately 99% of animals and nearly all plants cannot maintain a constant internal environment. Their body temperature or osmotic concentration changes with surrounding conditions. These are called conformers.
c. Migrate
- Many animals, such as birds, temporarily move from stressful habitats to more hospitable areas and return when the stressful period is over.
- For example, during winter, Keoladeo National Park (Bharatpur, Rajasthan) hosts migratory birds from Siberia and other extremely cold northern regions.
d. Suspend
- In bacteria, fungi, and lower plants, thick-walled spores help survive unfavorable conditions, germinating under suitable conditions.
- In higher plants, seeds and some vegetative reproductive structures reduce metabolic activity to tide over stress periods, germinating under favorable moisture and temperature.
In animals:
- Hibernation of bears during winter.
- Aestivation of some snails and fishes during summer.
- Diapause, a stage of suspended development in many zooplanktons in lakes and ponds.
Adaptations
Adaptation is the morphological, physiological, and behavioral attribute that enables an organism to survive and reproduce in its habitat. Many adaptations have evolved over long evolutionary time and are genetically fixed.
Adaptations of kangaroo rat in North American deserts:
- Internal fat oxidation produces water as a byproduct when no external water source is available.
- Ability to concentrate urine, minimizing water use for excretory products.
Adaptations of desert plants:
- Presence of a thick cuticle on leaf surfaces.
- Sunken stomata minimize water loss due to transpiration.
- CAM photosynthetic pathway
- enables stomata to remain closed during the day.
- Desert plants like Opuntia have no leaves (reduced to spines), with photosynthesis occurring in stems.
Adaptations of Mammals:
- Mammals in colder climates have shorter ears and limbs to reduce heat loss, known as Allen’s Rule.
- 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.
Physiological and Biochemical adaptations:
- Archaebacteria thrive in hot springs and deep-sea hydrothermal vents where temperatures exceed 100°C. Many fish survive in Antarctic waters at temperatures below 0°C.
- Many marine invertebrates and fish live at great ocean depths where pressure exceeds 100 times normal atmospheric pressure.
- At high altitudes (>3,500m), low atmospheric pressure causes altitude sickness (symptoms: nausea, heart palpitations, fatigue) due to insufficient oxygen. The body acclimatizes by increasing red blood cell production, breathing rate, and decreasing hemoglobin’s oxygen-binding capacity.
Behavioural adaptations:
- Desert lizards bask in the sun to absorb heat when their body temperature is low but move into shade when ambient temperatures rise.
- Some species burrow into the soil to hide and escape from above-ground heat.
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