Saturday, December 13, 2008

How do the physical features of the surroundings affect organisms? What are these physical factors?

  • How do the physical features of the surroundings affect organisms?
    The physical features of the surroundings and the nature of the soil determine the types of plants found in the region. Since animals rely directly or indirectly on plants for food, the animals that live in a region determined by the plants growing in that region. Organisms found in a region are usually adapted to the physical features of their environment.

    The physical factors are:

  • Light intensity - Light intensity affects the distribution and growth of both plants and animals. Green plants exist only where theere is an adequate suppl of sunlight. Some plants develop adaptations to reach the light. For example, climbing plants may twine around or grasp a support to pull themselves upwards. However, bright light causes plant stems to grow more slowly. This is why plants growing in the open usually end up shorter than those in the shade. Certain plants have develop adaptations to block or screen off excessive light. For example, some plants have a dense covering of hairs on the leaf epidermis or a thick-walled cells called the hypodermis just beneath the epidermis. These adaptations protect the plant by screening off excessive heat and reducing the rate of transpiration. Many animals need sunlight to see in order to catch their prey or to detect predators. However , some animals develop special adaptations for living in dark caves. they locate prey in the dark by bouncing sound waves off objects around them.

  • Temperature - Temperature affects the rate of reaction of enzymes, which control metabolic or physiological activities of plants and animals. Most organisms cannot tolerate extremes of temperatures. Temperatures that are too high or too low would kill an organism. Many flowering plants are adapted to changing seasons. Such plants are able to survive through a hot and dry seasons or through winter by storing food in underground storage organs, shedding leaves to reduce water loss, or foaming seeds which are resistant to heat, cold or drought, just before these seasons arrive.

  • Amount of water available - No organisms can live long without water. Hence, the amount of available water is one of the major factors affecting the number and location of the plants and animals in a region. The amount of available water depends on the amount of rain and pattern in which rain falls throughout the year. Some organisms are adapted to survive under the conditions where there is a limited supply of water. For example, camels are able to survive for many days in the desert without water because they can drink more than 100 litres of water because they when available, then they go for long periods without drinking. Some plants, known as xerophytes, are adapted to survive prolonged drought. They reduce their rate of transpiration by shedding their young leaves or by developing leaves reduce to spines, stems become fleshy(storing up much water) and green stems also take over the function of photosynthesis from the leaves. On the other hand, there are other plants that live in water or in very wet places. These are called hydrophytes. Hydrophytes may be completely submerged, for example, hydrilla; partially submerged, for example, water lily; or free floating, for example, water hyacinth. Mangrove plants, such as Avicennia, have their roots buried in oxygen-poor mud. Special breathing roots called pneumatophores project above the mud srface. Pneumatophores have openings through which oxygen passes downwards to the whole root system. Aquatic animals also show adaptive features for living in water, such as gills, for absorbing oxygen or special structures for swimming. For example, frogs have webbed toes and fish have fins for swimming.

  • Oxygen content - Most organisms are aerobic, that is, they require oxygen for respiration. They cannot survive in enviroments of low oxygen content. However, some aerobic organisms can survive in enviroments of low oxygen content. This is because they possess mangrove plants adaptations for obtaining sufficient oxygen, for example, oxygen content are usually air-breathers. They can come to the surface of the water to gulp air.

  • Salinity - The salinity or salt concentration of water is an important factor affecting aquatic organisms. Animals living in sea water tend to lose water by osmosis as seawater contains a higher salt concentration than the cytoplasm of animal cells. Saltwater or marine fishes have a waterproof coat consisting of closely-fitting scales covered by a slimy mucous material. This reduce the rate of water loss. The cytoplasm of the cells of freshwater organisms usually has a higher salt concentration than the surrounding water. Hence, water tends to enter this organisms by osmosis. The cells of freshwater plants have rigid cell walls that prevent them from bursting. Protozoa such as Amoeba have contractile vacuoles to remove the excess water that enters them by osmosis. Most freshwater fish possess slimy scaly skins which keep water from entering their cells.

  • pH - The term pH refers to the acidity or alkalinity of a solution. The pH of soil water or the water in freshwater ponds or the sea affects the types of organisms thet can live in such ebvironments. Aquatic organisms are sensitive to the pH of the water in which they live and may die if there are drastic or sudden changes in pH. Seawater is alkaline with a pH of about 8. The pH of seawater does not vary that much. In freshwater ponds and streams, the pH varies from one region to another. Changes in pH do occur, especially if the pH of the water depends on the amount of hydrogencarbonates present in it. For example, in strong daylight, photosynthesis in plants uses up the carbon dioxide in the water, making the water more alkaline. During the night, photosynthesis stops and the carbon dioxide produced in respiration makes the water more acidic. For most types of freshwater organisms, nuetral or nearly nuetral water provides optimum living conditions.

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