Organisms and Population Test 8

A natural association of interdependent populations of different species inhabiting a common environment of habitat as a viable, self-contained unit is called a biotic community of biocoenosis.

An organism (or an individual is a living unit of nature and is the most basic unit of ecological hierarchy.

Ecology is the study of inter-relationship between organisms and their natural environment, both living and non-living. The study of ecological interactions provides important information about the nature and mechanisms of evolutionary change.

Coniferous forests occur just south of tundra across North America, Europe, Asia and are also found in Southern hemisphere. Precipitation in coniferous forests is 10-35cm in drier parts andd over 150 cm in wetter parts. It occurs both as rain as well as snow. The average temperature is less than 15°C. Temperate forests are found in both northern and southern hemispheres. Their annual precipitation lies between 75-250 cm and average temperature lies between 6-20°C.

The revolution of our planet around the sun and the tilt of its axis cause annual variations in the intensity and duration of temperature, resulting in distinct seasons. These variations together with annual variation in precipitation account for the formation of major biomes such as deserts, rain forest and tundra.

A biome is a large regional unit caracterized by a major vegetation type and associated fauna found in a specific climatic zone. Some examples of terrestrial biomes are desert, temperate deciduous forest, tropical rain forest, etc.

Environment is the sum of all biotic (living) and abiotic (non-living)  factors that surround and practically influence the organism. All components are inter-linked and inter-dependent. Biotic factors include organisms. Abiotic factors are non-living factors, substances and conditions of the environment which infuence survival, form, function, behaviour and reproduction of organism. There are manu abiotic factors. The four major abiotic factors are temperature, water light and soil.

Temperature is the most relevant environmental factor. The everage temperature varies seasonally. The physiological functions and the geographical distribution of many plants and animals is governed by temperature.

The geographical distribution of different species of organisms depends on their therma tolerance. Organisms which can tolerate a wide range of temperature variations, e.g., most mammals and birds, are called eurythermal organisms. The average temperature in tropical deserts in summer is more than 50°C. Thermal springs can sustain life, many microorganisms (e.g., some archaebacteria) live there.

Organisms with narrow range of temperature tolerance are called stenothermal organisms, e.g., polar bear, frog, lizards, coconut, etc. The organisms with wide range of temperature tolerance are called eurythermal organisms e.g., most mammals and birds.

Temperature has a direct effect on working of enzymes. Through enzymes, it influences basal metabolism, activity and other physiological functions of the organisms. Hence, mango trees cannot grow in temperate countries like Canada and Germany.

Water makes the major part of an organism's life next to temperature. It is an important factor which influences the life of organisms. The productivity and distribution of land plant are dependent upon availability of water. Water is required for growth and development of plants.

Protoplasm is the material comprising the living contents of a cell. It consists of 90% water alongwith the minerals, sugars, amino acids, proteins, enzymes, etc. The translocation of nutrients inside the body occurs via blood which also, majorly consists of water. In an environment with excesive heat, water loss in the form of sweating and transpiration keeps the body cool. Thus, water maintains body temperature.

The plants which grow in dry or xeric conditions or where availability of water is negligible, are known as xerophytes. Opuntia and Asparagus are succulents which store water in their stem and root respectively.

For aquatic organisms the quality (chemical composition pH) of water is very important. The salt concentration (measured as salinity in parts per thousand), is less than 5 per thousand parts in inland waters, 30-35 per thousand parts in the sea and more than 100 per thousand parts in some hypersaline lagoons. Many fresh water animals cannot live for long in sea water and vice versa because of the osmotic problems they would face.

An organism's physical environment includes temperature, light, humidity, etc. whereas its biological environment includes other organisms and its relationship with them.

Euryhaline organisms are able to tolerate a wide range of salt concentration (or salinities) e.g. Poecilia sphenops is a fish that can live in fresh water, brackish water of salt water.

In sea water, the surrounding water is salty and hence is hypertonic to body cells. Thus, water will move from its higher concentration (in body) to its lower concentration (sea water) leading to exosmosis.Therefore, many fresh water animals can not live for long in sea water and vice varsa.

Topography means the physical features of a place, such as hills, plains, slopes, rocks, valley, etc. The topography affects the distribution of organisms directly or indirectly by influencing other factors, such as light intensity, wind velocity, nature of soil, rainfall, water currents or wave action.

The red colour of red algae is due to abundant formation of phycoerythrin which is able to absorb blue green wavelengths of light. Being shorter, these wavelengths are able to reach the maimum depth in water. Therefore, red algae can be found in deepest ocean waters.