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Tiny creatures known to scientists as 'rhizobia' could become one of the most important means of boosting food production in the hungry regions of the third world, perhaps even averting the threat of global famine frequently predicted by demographers and economists. These highly industrious micro-organisms not only hold out the promise of providing farmers in developing nations with a much cheaper alternative to scarce and expensive chemical fertilizers, but unlike the nitrogenous fertilizers, present no threat to the environment. What they have in common with chemical fertilizers is their ability to provide nutrients for the soil. Rhizobia absorb nitrogen from the air, converting it and the organic matter in the soil into a valuable nutrient to improve the yield of various crops.

Plants themselves cannot use nitrogen straight from the atmosphere. Rhizobia and related bacteria are the only living organisms which can perform the miracle of converting it into a form which growing plants can use. For more than a decade, scientists have been working to find the most efficient strain, or culture of rhizobia, so that it can be isolated and used to increase food yields, in much the same way as chemical fertilizers do - but at a fraction of the cost, with the added advantage of being environmentally sound.

The vital role which these microorganisms can play was first discovered in the rice fields of the Philippines in 1962. Scientists at the International Rice Research Institute, near Manila, were mystified when a trial plot, where no chemical fertilizer was added, kept giving sustained yields of rice year after year with no decline in soil fertility. Research showed that millions of the tiny 'free living' bacteria were working with the rice plants, drawing atmospheric nitrogen down through the water, via the stems to revitalize the soil. It was observed that the rhizobia bacteria only performed the job of nitrogen fixation effectively when the paddy field was under water. This was because this particular strain of rhizobia reached the rice by way of the blue-green algae in the water.

The search for different rhizobia strains which would work effectively with other food crops, and without the need for water, soon spread to other countries and continents. Attention was concentrated on leguminous plants, since it was known that some rhizobia lived in symbiotic relationships with such vegetables as peas and beans. Many African peasant farmers, who have been cultivating their maize for generations in fields, also planted peas or beans. They are unaware of the scientific reason for this, but experience has taught them how to achieve better yields.

In the legume roots, the bacteria live in nodules -- each one a virtual 'fertilizer factory' no bigger than a peanut. Many varieties of peas and beans support effective rhizobia, but the most efficient strain yet identified lives in the roots of the cowpea, a twining plant of the bean family, widely used for food in Eastern Asia.

Even in countries where chemical fertilizers are available, they might be applied more sparingly if rhizobia were used. This would avoid the pollution of water supplies resulting from overuse of chemicals. It could also prevent damage to the ozone layer: some scientists fear that the intensive use of nitrogenous fertilizers may have even more serious effects than aerosols, or supersonic transport planes. 

  1. (a) Describe rhizobia.
    (b) Compare rhizobia with chemical fertilizers.
    (c) How were rhizobia discovered ?
  2. (a) How does water affect rhizobia ?
    (b) What are leguminous plants ?
  3.   How are rhizobia better for the environment than chemical fertilizers ?
  4.   For each of the following words give one word or short phrase ( not more than seven words ) which has the same meaning as it has in the passage.
      i.   industrious   v.   relationships
      ii.   nutrients   vi.   unaware
      iii.   converting   vii.   varieties
      iv.   sustained   viii.   damage
  5. Summarize in less than 160 words, the discovery and use of rhizobia.
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  1. (a) They are micro organisms which are able to convert atmospheric nitrogen into plant food.
    (b) Rhizobia are much cheaper than chemical fertilizers and are also friendlier to the environment.
    (c) Rhizobia were discovered in the Philippines. A field of rice yielded a good harvest year after year in spite of no fertilizer being used.
  2. (a) Rhizobia drew the nitrogen from the air through the water in the stems and revitalized the soil.
    (b) They are beans
  3.   Rhizobia are cheaper and do not affect the ozone layer, unlike chemical fertilizers. It is feared that chemical fertilizers could actually be causing more damage to the atmosphere than other known causes. Hence rhizobia could be used even in areas where the farmers can afford chemical fertilizers.
  4. i hard-working
    ii food
    iii changing
    iv consistent
    v connections
    vi unfamiliar
    vii species
    viii destruction
  5. Rhizobia were discovered in the rice fields Philippines. It was a chance discovery. a trial plot of rice plants in which no fertilizers were used produced sustained yields of rice year after year without the soil declining in fertility -- as it should have. Puzzled scientists researched and discovered the presence of the micro organisms. Millions of the bacteria were at work drawing atmospheric nitrogen through the plants and bringing it into the soil and then fixating it into food for the plants.

Rhizobia were found to be cheaper than the chemical fertilizers and had one more plus point -- they were environmentally much friendlier. Then began the search for different strains for different plants. Attention was concentrated on bean plants but soon to other plants. Each of the bacteria were actually like a fertilizer factory. they were introduced into Asia and Africa. Now, even in countries where chemical fertilizers are available, it has been concluded that rhizobia were more appropriate. ( 158 words )


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Comprehension 1


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