Test: Organisms and Population - NEET MCQ

 Tropical rain forests have disappeared mainly due to man’s activities. Due to over population in countries like India, rain forests are cut to make place available for man to live and build houses. To build buildings and factories man has incessantly cut down trees. This has caused the depletion of rain forests. 

 Flora contains the actual account of habitat and distribution of plants of a given area. It provides the index to the plant species found in particular area. 

 A group of individuals resembling each other in morphological, physiological, biochemical and behavioural characters constitute a species. Such individuals can breed among themselves but cannot breed with members other than their own to produce fertile offsprings. New species are formed mainly due to reproductive isolation. 

 Ernst Mayr proposed the biological species concept, which defines species as groups of actually or potentially inter-breeding natural populations which are reproductively isolated from other such groups. 

 Desert can be cold (e.g., Tibet, Gobi) and hot (e.g., Thar, Sahara). The true desert is a place that has a rainfall of less than 12 cm/ yr while in extreme desert is less than 7 cm/ yr. 

 The organisms of all the species that live in a particular area and interact in various ways with one another form biotic community. Biotic community is a grouping that is higher than population. It is an assemblage of all the populations of different organisms occurring in an area. The different populations of a community do not remain isolated. They show interactions and inter-dependence. 

 Soils of Indo-Gangetic plains and the Indus valley are highly fertile and suitable for agriculture, so these areas have high population density. Favourable climate increases population density of a geographical area because it favours increase in population growth. High soil fertility favours population density. 

Living organisms are regarded as open system as they can gain or loose energy from external environment. All living organisms restore their energy either directly from sunlight or indirectly from food. 

Organisms occupying similar ecological niches but living in different regions are called ecological equivalents. Ecological equivalents possess similar types of adaptations but belong to different taxonomic groups. For example; succulents of American deserts are cacti while those of African desert are euphorbias. 

Plants have special traits that help them to enlarge their tolerance limits to light regimes. Heliophytes are the sun adapted plants which are adapted to high intensity of light, and have higher temperature optima for photosynthesis, as well as have high rate of respiration. On the other hand, shade adapted plants also called as sciophytes generally have low photosynthetic, respiratory and metabolic activities. Plants such as ferns and several herbaceous plants growing on the ground under the dense canopy of trees, are shade tolerant plants. 

 Leaf butterfly is green in colour and stick insect also mimics in order to escape from the enemies and also to catch prey. The camouflaging mechanism helps the organism to get adapted to its surroundings. The Leaf butterfly is seen more near the leaves while the stick insect camouflages with its surroundings by living on the branches. 

Animals blend with the surroundings or back ground to remain unnoticed for protection and aggression. 

 Disease resistant plants possess thick cuticle. Infectious organisms can not grow or invade cuticle. 

 In Daphnia the cyclomorphosis (cyclic change in morphology) is seen. The morphology depends upon the temperature variation in water. So at different seasons of the year the Daphnia shows different morphology. 

 The introduction and spread of exotic plant and animal species in Australia has impacted on the environment, native biodiversity and local communities, transforming the landscape. The most widespread invasive weed in Queensland was a group of cactus species from the Americas, collectively known as prickly pear. 

 Pollination is the act of transferring pollen grains from the male anther of a flower to the female stigma. The goal of every living organism, including plants, is to create offspring for the next generation. Flowers must rely on vectors to move pollen. These vectors can include wind, water, birds, insects, butterflies, bats, and other animals that visit flowers called "pollinators". However, in general, plants that rely on pollen vectors tend to be adapted to their particular type of vector, for example day-pollinated species tend to be brightly coloured, but if they are pollinated largely by birds or specialist mammals, they tend to be larger and have larger nectar rewards than species that are strictly insect-pollinated. 

The aquatic organisms in which the osmotic concentration and temperature of body change according to the ambient conditions of water are called conformers.About 99 percent of animals and nearly all plants are included in the category of conformers, which do not have a mechanism to maintain a constant internal body environment. Their body temperature changes with the surrounding temperature. Some organisms (e.g., birds and mammals) on the other hand, are able to maintain a constant body temperature and constant osmotic concentration despite changes in the external environment. They are called as regulators. They perform homeostasis mostly through thermoregulation and osmoregulation by physiological or behavioural means.

 Thermoregulation is an energetically expensive process for many organisms. Heat loss or heat gain is a function of surface area. Small sized animals (such as shrews, humming birds etc.), have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; thus they have to expand much energy to generate body heat through metabolism. This is the main reason why very small animals are rarely found in polar regions. 

An ecotone is a transition between two or more diverse communities as, for example, between forest and grassland or between a soft bottom and hard bottom marine community. It is a junction zone or tension belt which may have considerable linear extent but is narrower than the adjoining community areas themselves. The ecotonal community commonly contains many of the organisms of each of the overlapping communities and, in addition, organisms which are characteristic of and often restricted to the ecotone. Often, both the number of species and the population density of some of the species are greater in the ecotone than in the communities flanking it. The tendency for increased variety and density at community junctions is known as the edge effect. 

 In deep water bodies, variations in temperature of water at different depths result in thermal stratification. There are three thermal strata -Epilimnion (upper stratum of water), Metalimnion (middle stratum of water) and the Hypolimnion (lower stratum of water). During summer, temperature of the surface water is higher and is separated from the cooler hypolimnion zone by a thermocline. During winter season, temperature of surface water is at freezing temperature in the temperate lake whereas hypolimnion stratum of the lake has a temperature of about 4°(, In temperate lakes, cooling of surface water during autumn and warming of it during spring results in circulation of nutrients as well as oxygen twice a year.