Test: Organism & Its Environment - NEET MCQ

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.

The interaction among organisms is necessary for survival within their environment. Survival is the state of being alive. Organisms are inter-depending on one another of their well-being.

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.

Proteins, lipids, and carbohydrates are the abiotic components. They are the non-living factors present or used in an environment. Some other examples of abiotic factors are sunlight, water, air, etc.

An ecosystem involves interaction among communities and their physical environment. It is the functional unit of nature. It involves biotic and abiotic components. This ecosystem may be natural or artificial (man-made).

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.

The quantity of water that soil can retain after flowing down of the gravitational water is called its field capacity or water holding capacity. It depends on chemical composition of the soil which means types of ions present and hence pH of the soil. Size of soil particles and their aggregation form pores in soil. Large pores take part in percolation of water in the soil but small pores hold water by capillarity.

In tropical biome, the climate is warm with alternate wet dry periods. Rainfall is 90-160 cm. The climate in desert biome is hot and dry. The air, having little water vapour, is a poor insulator. The temperature rises considerably during the day and falls greatly at night because the ground radiates heat rapidly.

Animals with constant body temperature are called homoiotherms. They have insulating coat to check the loss of body heat. This coat consists of hair in most mammals, blubber(subcutaneous fat) in whales and seals, and feathers in birds. Shivering warms up the body and perspiration cools down the body of these animals when required. These are also termed endotherms as they regulate their body temperature by physiological means and maintain more or less constant internal temperature. Poikilotherms are cold-blooded animals which are unable to regulate their body temperature which changes with change in temperature of environment e.g., fish, frog, lizards. They are also called as ectottherms.

X-Conformers - These are the animals and plants in which the osmotic eoncentration and temperature of body changes according to ambient conditions of external environment e.g., Asterias.
Y-Regulators- These are able to maintain a constant body temperature and constant osmotic concentration despite changes in the external environment e.g. birds and mammals.
Z-Partial regulators- They have the ability to regulate body functions to a limited extent beyound which they become conformers.

Animals use seasonal variations in light intensity and photoperiod to time various activities. Birds of colder areas of northern hemisphere begin their southward migration as the day lengths begin to shorten. Reverse journey is undertaken with the increase in day length. Turkeys, ferrets and starlings breed in response to lengthening of days while goat, sheep and deer breed in response to shortening of days. Rabbits and guinea pigs are day neutral. In temperate and subtropical areas, cold blooded or ectothermic animals undertake hibernation as the day length begins to shorten.

The seasonal movement of complete populations of animals to a more favourable environment is called migration. It is usually in response to uneven precipitation and lower temperaturesresulting in a reduced food supply and is often triggered by a change in day length. Migration is common in mammals (e.g. porpoises), fish (e.g., eels and salmon) and some insects but is most marked in birds.

About 99 percent of animals and nearly all plants do not have a mechanism to maintain a constant internal body environment. Their body temperature changes with the surrounding temperature. They are called conformers. They change their body temperature according to the ambient temperature.

Some organisms show behavioural adaptations to cope with variations in their environment. A rhino covering itself in mud to keep cool and desert lizard basking in sun to keep warm are examples of behavioural means of homeostasis. Desert lizards lack the physiological ability to deal with the high temperature, fairly constant by behavioural means. They enjoy in the sun and absorb heat when their body temperature drops below the comfort zone, but move into shade when the surrounding temperature starts increasing. Some species are capable of burrowing into the soil to hide and escape from too much heat.

Maintainig homeostasis, especially thermoregulation is energetically expensive for many organisms. During the course of evolution, the costs and benefits of maintaining a constant internal environment were taken into consideration and thus some species preferred to be conformers.

Various organisms, if unable to migrate, might avoid the unfavourable environment by escaping in time. Polar bears go into hibernation during winter season to escape extreme cold. Some snails and fish undergo aestivation to avoid summer-related problems like heat and desiccation, etc.