Q25 of 50 Page 1

How did the process of RNA interference help to control the nematode from infecting roots of tobacco plants? Explain.

• RNA interference is a gene silencing process that block the expression of genes in the parasite when it enters the host’s body.


• Plant parasitic nematodes cause severe damage and yield loss in major crops all over the world.


• RNAi is a method adopted to prevent infestation of roots of tobacco plants by a nematode Meloidegyne incognitia.


• In this RNA expression is blocked by RNA interference because RNAi bind to its one of the RNA strand and hence stop the transcription.


• In this nematode-specific DNA is introduced and this introduction produce both sense and anti-sense RNA which are complementary to each other and form double stranded RNA and thus silenced the specific mRNA.


• This process control the tobacco plant from infection.


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(a) Name the tropical sugar cane variety grown in South India. How has it helped in improving the sugar cane quality grown in North India ?

(b) Identify ‘a’, ‘b’ and ‘c’ in the following table:



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Why are beehives kept in crop field during flowering period ? Name any two crop fields where this is practiced.

 26

Study the graph given below and answer the questions that follow :


(i) Write the status of food and space in the curves (a) and (b).


(ii) In the absence of predators, which one of the two curves would appropriately depict the prey population?


(iii) Time has been shown on X-axis and there is a parallel dotted line above it. Give the significance of this dotted line.


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(i) What is the primary productivity? Why does it vary in different types of eco-systems?

(ii) State the relation between gross and net primary productivity.