Q22 of 26 Page 1

How has the use of Agrobacterium as vectors helped in controlling Meloidegyne incognitia infestation in tobacco plants? Explain in correct sequence.

A nematode, Meloidegyne incognitia infects the roots of tobacco plants. It feeds on root cells and causes them to grow into large knots. Its infection reduces the yield largely. The strategy adopted to protect tobacco plants is RNA interference, which is a naturally occurring mechanism in all eukaryotes as a method of cellular defence that leads to silencing of specific genes. This method involves silencing of specific mRNA due to formation of dsRNA molecule. This dsRNA molecule prevented the translation of the original mRNA.

The use of agrobacterium vectors has greatly helped in controlling Meloidegyne incognitia infestation in tobacco plants. The nematode specific genes, which were responsible for parasitism, were introduced in tobacco plants through agrobacterium vectors. The genes introduced in the host plant, produced both sense RNA and anti-sense RNA, which were complementary to each other. These two RNAs formed a dsRNA molecule, which initiated silencing of the specific mRNA in the nematode, when taken up by the parasite. As a result, the translation of mRNA in the parasite was prevented and it was unable to survive in the transgenic tobacco plant. Through RNA interference, the plant got itself protected from infestation.


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20

(a) Differentiate between analogous and homologous structures.

(b) Select and write analogous structures from the list given below:


(i) wings of butterfly and birds


(ii) vertebrate hearts


(iii) tendrils of bougainvillea and cucurbita


(iv) tubers of sweet potato and potato

 21

(a) ‘‘India has greater ecosystem diversity than Norway.’’ Do you agree with the statement? Give reasons in support of your answer.

(b) Write the difference between genetic biodiversity and species biodiversity that exists at all the levels of biological organization.


OR


Explain the effect on the characteristics of a river when urban sewage is discharged into it.

 23

Looking at the deteriorating air quality because of air pollution in many cities of the country, the citizens are very much worried and concerned about their health. The doctors have declared health emergency in the cities where the air quality is very severely poor.

(a) Mention any two major causes of air pollution.


(b) Write any two harmful effects of air pollution to plants and humans.


(c) As a captain of your school Eco-club, suggest any two programmes you would plan to organise in the school to bring awareness among the students on how to check air pollution in and around the school.

 24

(a) Describe any two devices in a flowering plant, which prevent both autogamy and geitonogamy.

(b) Explain the events up to double fertilisation after the pollen tube enters one of the synergids in an ovule of an angiosperm.


OR


(a) Explain menstrual cycle in human females.


(b) How can the scientific understanding of the menstrual cycle of human females help as a contraceptive measure?