NEET BIOLOGY BY SHASHI SIR

14.8 ECOSYSTEM SERVICES Healthy ecosystems are the base for a wide range of economic, environmental and aesthetic goods and services.  The products of ecosystem processes are named as ecosystem services, for example, healthy forest ecosystems purify air and water, mitigate droughts and floods, cycle nutrients, generate fertile soils, provide wildlife habitat, maintain biodiversity, pollinate crops, provide storage site for carbon and also provide aesthetic, cultural and spiritual values.  Though value of such services of biodiversity is difficult to determine, it seems reasonable to think that biodiversity should carry a hefty price tag.  Robert Constanza and his colleagues have very recently tried to put price tags on nature’s life-support services.   Researchers have put an average price tag of US $ 33 trillion a year on these fundamental ecosystems services, which are largely taken for granted because they are free.  This is nearly twice the value of ...

15.2.2 How do we conserve Biodiversity?  When we conserve and protect the whole ecosystem, its biodiversity at all levels are protected - we save the entire forest to save the tiger.  This approach is called in-situ (on-site) conservation.  However, when there are situations where an animal or plant is endangered or threatened and needs urgent measures to save it from extinction, ex-situ (off-site) conservation is the desirable approach.  In situ conservation–  Faced with the conflict between development and conservation, many nations find it unrealistic and economically not feasible to conserve all their biological wealth.  Invariably, the number of species waiting to be saved from extinction far exceeds the conservation resources available.  On a global basis, this problem has been addressed by eminent conservationists.  They identified for maximum protection certain ‘biodiversity hotspots’ regions with very high levels of species ...

15.2.1 Why Should We Conserve Biodiversity?  There are many reasons, some obvious and others not so obvious, but all equally important.  They can be grouped into three categories: narrowly utilitarian, broadly utilitarian, and ethical. The narrowly: The narrowly utilitarian arguments for conserving biodiversity are obvious; humans derive countless direct economic benefits from nature food (cereals, pulses, fruits), firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes ) and products of medicinal importance.  More than 25 per cent of the drugs currently sold in the market worldwide are derived from plants and 25,000 species of plants contribute to the traditional medicines used by native peoples around the world.  Nobody knows how many more medicinally useful plants there are in tropical rain forests waiting to be explored.  With increasing resources put into ‘ bioprospecting ’ (exploring molec...

16.2 DIGESTION OF FOOD: The process of digestion is accomplished by mechanical and chemical processes.  1. Digestion in buccal (oral) cavity: The buccal cavity performs two major functions, mastication of food and facilitation of swallowing.  The teeth and the tongue with the help of saliva masticate and mix up the food thoroughly.  Mucus in saliva helps in lubricating and adhering the masticated food particles into a bolus.  The bolus is then conveyed into the pharynx and then into the oesophagus by swallowing or deglutition.  The bolus further passes down through the oesophagus by successive waves of muscular contractions called peristalsis.  The gastro-oesophageal sphincter controls the passage of food into the stomach.  The saliva: The saliva secreted into the oral cavity contains electrolytes (Na+, K+, Cl–, HCO3–) and enzymes, salivary amylase and lysozyme.  The chemical process of digestion is initiated in the oral ca...

16.1.2 Digestive Glands The digestive glands associated with the alimentary canal include the salivary glands, the liver and the pancreas.  Salivary glands:  Saliva is mainly produced by three pairs of salivary glands, the parotids (cheek- Stenson's duct), the sub-maxillary/sub-mandibular (lower jaw- Wharton's duct) and the sublinguals (below the tongue- ducts Rivinus).  These glands situated just outside the buccal cavity secrete salivary juice into the buccal cavity. Parotid gland Submandibular submaxillary glands Sublingual glands Location Cheeks At the Junction of upper and lower jaw In lower jaw below the tongue Size Largest Medium Smallest Ducts Stenson’s Duct Wharton’s ducts Ducts of RIvinus % of secretion 20-25 % 70-75% 5% Nerve IX (glossopharyngial) VII (facial) VII (facial) Lacks mucin, mainly produces...

15.1.3 The importance of Species Diversity to the Ecosystem Does the number of species in a community really matter to the functioning of the ecosystem? This is a question for which ecologists have not been able to give a definitive answer.  For many decades, ecologists believed that communities with more species, generally, tend to be more stable than those with less species.  What exactly is stability for a biological community? A stable community should not show too much variation in productivity from year to year; it must be either resistant or resilient to occasional disturbances (natural or man-made), and it must also be resistant to invasions by alien species.  We don’t know how these attributes are linked to species richness in a community, but David Tilman’s long-term ecosystem experiments using outdoor plots provide some tentative answers.  Tilman found that plots with more species showed less year-to-year variation in total biomass.  ...

Causes of biodiversity losses ( ‘The Evil Quartet’ ): The accelerated rates of species extinctions that the world is facing now are largely due to human activities. There are four major causes (‘ The Evil Quartet’ is the sobriquet used to describe them). (i) Habitat loss and fragmentation: This is the most important cause driving animals and plants to extinction. The most dramatic examples of habitat loss come from tropical rain forests.  Once covering more than 14 per cent of the earth’s land surface, these rain forests now cover no more than 6 per cent.  They are being destroyed fast. By the time you finish reading this chapter, 1000 more hectares of rain forest would have been lost.  The Amazon rain forest (it is so huge that it is called the ‘lungs of the planet’ ) harbouring probably millions of species is being cut and cleared for cultivating soya beans or for conversion to grasslands for raising beef cattle.  Besides total loss, the degradation of...