IGCSE Biology Paper-4: Specimen Questions with Answers 141 - 142 of 279

Passage

Cotton, Gossypium hirsutum, is grown for the fibers that form within the fruits after fertilization, as shown in Fig.

Fibers from the fruits of cotton plants are used in the textile industry.

The Fibres
  • Cotton plants have been genetically engineered to produce a protein that is toxic to the caterpillars of several insect pests. This gives the cotton plants resistance to the pests.
  • The cry gene for pest resistance was isolated from the bacterium Bacillus thuringiensis and inserted into the cells of cotton plants as shown in Fig.
Bacterial DNA

Question 141 (4 of 5 Based on Passage)

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Outline the advantages to farmers of growing genetically engineered cotton plants that contain the toxic protein.

Explanation

  • It improves production and raise farmer՚s income. Farmers are still practicing traditional process of seeding and cultivation, which required scientific moves for raising their production. Hence, it is one of the moves to enhance the farm production.
  • It reduces the use of pesticide and insecticide during farming that might be great moves for the betterment of the food supply.
  • It can feed a rapidly increasing population because it shows dramatically increased yields.
  • It can produce more in small area of land.
  • BT cotton greatly reduced the use of toxic pesticides. BT cotton produces a common soil bacterium, Bacillus thuringiensis (BT) . It is a natural pest repelling bacterium that is toxic to many worms and pests that can harm the crop but is not hazardous to humans. BT is widely sprayed on crops by organic farmers as a pesticide.

Question 142 (5 of 5 Based on Passage)

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An enzyme cuts the cry gene from the DNA of B. thuringiensis.

(i) State the name of the enzyme that cuts DNA.

Explanation

Restriction Endonucleases

  • They cut the DNA strands at specific base sequence in palindrome site. Thus, they function as ‘molecular scissors’ or chemical scalpels. The restriction endonuclease inspects the length of a DNA sequence. Once it recognizes specific sequence, it binds to the DNA and cuts each of the two strands of the double helix at specific points in their sugar phosphate back bones. Special sequence in the DNA recognized by restriction endonuclease is called palindromic nucleotide sequence.
  • The palindromes are groups of letters that form the same words when read in both directions forward and backward. Ex:

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