Organisms and Population Test 9

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.

Temperature affects the absolute size of an animal and the relative proportions of various body parts. Birds and mammals attain greater body size in cold regions than in warm areas. But poikilotherms are smaller in cold region. This is Bergman's rule. This is true because small animals have little volume but larger surface area, so if they are in cold, they lose their body heat very fast. In cold climate, reduced surface area to volume ratio is ideal.

Adaptation is a quality of the organism (morphological physiological, behavioural) that enables it to survive and reproduce in its habitat. Adaptations allow organisms to live in different types of habitats. They develop due to natural selection of suitable variations appearing in living beings through mutations and recombinations.

Kangaroo and desert rat seldom drink water It has a thick coat to minimise evaporative desiccation. The animal seldom comes out of its comparatively humid and cool burrow during the day time 90% of its water requirement is met from metabolic water which is produced by respiratory breakdown of fats 10% is obtained from food. Loss of water is minimized by producing nearly solid urine and faeces.

Osmoconformers are the organisms that change the osmotic concentration of their body with the change in ambient conditions Their body fluids are inosmotic balance with the environment. For many marine invertebrates the osmolarrty and ionic concentrations of their body fluids are similar to those of the sea water in which they live.

Aestivation is a state of inactivity occurring in some animals, notably lungfish, during prolonged periods of drought or heat. Feeding, respiration, movement, and other bodily activities are considerably slowed down. Reptiles such as lizard hibernate in winters.

Xerophytes can withstand a prolonged period of drought, for this purpose they have certain peculiar adaptations. Thick cuticle is present in these plants. Stomata are generally sunken (deep seated) and open during night only. They have CAM pathway for photosynthesis. Leaves are generally small and scaly. Sometimes leaves are modified into spines to reduce water loss through transpiration. They generally have an extensive root system and a smaller shoot system. Stems may be modified to phyllodades or dadodes to carry out the function of photosynthesis.

When we go to high altitude places (>3500m) we experience altitude sickness. Its symptoms include nausea, fatigue and heart palpitations. It is due to the low atmospheric pressure of high altitudes due to which body does not get enough oxygen. The body compensates low oxygen availability by increasing red blood cell production, decreasing the binding capacity of haemoglobin and by increasing breathing rate.

Diving to depth can result in mechanical distortion and tissue compression, especially in gas-filled spaces of the body. Absorption of nitrogen into blood can cause high blood nitrogen levels which can exert a narcotic effect. Lungs of the deep-diver cannot serve as a source of oxygen during the dive.

Bats are nocturnal flying mammals which do not employ eyesight for location of thir path, food, place of rest, etc. They produce high-frequency sound which produces echoes after striking various objects on the principle of sonar. Echoes are then analysed by the bats to know their path.

Camouflage (cryptic appearance) is the fallibility to blend wiith the surrounding or background. It is the most common type of adaptation by animals to remain unnoticed for protection or aggression, e.g. many insects, reptiles and mammals.