Organisms and Populations - Notes | Class 12 | Part 1: Organisms and its Environment

Organism and Its Environment

Ecology is the study of interactions among organisms and between organisms and their physical (abiotic) environment.
Ecology is concerned with four levels of biological organization: Organisms, Populations, Communities, and Biomes.

Organism and Its Environment

Physiological ecology (ecology at the organismic level) is the study of an organism’s adaptation to environments in terms of survival and reproduction.
The rotation of Earth and the tilt of its axis cause annual variations in temperature and seasons. Major biomes (desert, rainforest, tundra, etc.) are formed due to these variations and precipitation (rain and snow).

Life exists even in extreme and harsh habitats, such as Rajasthan desert, rain-soaked Meghalaya forests, deep ocean trenches, torrential streams, permafrost polar regions, high mountain tops, thermal springs, and compost pits.
Our intestine is a habitat for many microbes.
The physico-chemical (abiotic) components (water, light, temperature, soil, etc.) and biotic components (pathogens, parasites, predators, competitors, etc.) lead to variation in different habitats.
The distinct role and position of an organism in its environment is called its niche. By this, each organism tolerates various conditions, utilizes various resources, etc.

Temperature is the most ecologically relevant environmental factor.
Temperature on land varies seasonally, gradually decreasing from the equator to the poles and from plains to mountain tops. It ranges from subzero levels (in polar areas and high altitudes) to over 500°C (in tropical deserts).
Average temperature in thermal springs and deep-sea hydrothermal vents is above 100°C.
Mango trees cannot grow in temperate countries (e.g., Canada, Germany). Snow leopards are not found in Kerala forests. Tuna fish are rare beyond tropical latitudes in the ocean.
Temperature affects the kinetics of enzymes, basal metabolism, and other physiological functions of organisms.
Based on range of thermal tolerance, organisms are 2 types:

Eurythermal: Organisms that can tolerate a wide range of temperatures.
Stenothermal: Organisms that can tolerate only a narrow range of temperatures.

Water is the second most important factor.
Desert organisms have special adaptations to limited water.
Productivity and distribution of plants depend on water.
For aquatic organisms, water quality (pH, chemical composition) is important. Salt concentration (salinity in parts per thousand) is less than 5 in inland waters, 30–35 in the sea, and over 100 in some hypersaline lagoons.

Many freshwater animals cannot live for long in seawater, and vice versa, due to osmotic problems.

Plants need sunlight for photosynthesis.
Small forest plants (herbs and shrubs) are adapted to photosynthesize optimally under very low light because they are overshadowed by tall, canopied trees.
Many plants depend on sunlight for photoperiodism (e.g., flowering). Many animals use diurnal and seasonal variations in light intensity and photoperiod for timing their foraging, reproductive, and migratory activities.
The sun is the ultimate source of light and temperature on land. In deep oceans (>500m), the environment is dark, and no energy is available from the sun.
The spectral quality of solar radiation is important for life. The UV spectrum is harmful to many organisms. Not all color components of the visible spectrum are available for marine plants.

The nature and properties of soil differ due to climate, weathering, sedimentation, and soil development methods.
Soil composition, grain size, and aggregation determine the percolation and water-holding capacity of soils.
These characteristics, along with parameters like pH, mineral composition, and topography, determine the vegetation and animals in an area.
In aquatic environments, sediment characteristics determine the type of benthic animals.

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