UPSC Prelims 2018 GS Paper I · Q99 of 100 General Science medium

Consider the following : 1. Birds 2. Dust blowing 3. Rain 4. Wind blowing Which of the above spread plant diseases ?

  1. (a) 1 and 3 only
  2. (b) 3 and 4 only
  3. (c) 1, 2 and 4 only
  4. (d) 1, 2, 3 and 4 ✓ UPSC's answer

Why the answer is (d)

• Plant pathogens (fungi, bacteria, viruses) spread by many agents.

• Wind (4) carries fungal spores over long distances — wheat rust spores travel hundreds of kilometres; dust blowing (2) carries spores and bacteria on soil particles.

• Rain (3) splashes spores and bacteria from soil and infected leaves onto healthy plants and spreads them through run-off.

• Birds (1) carry pathogens on feathers, beaks and in droppings, and spread parasitic seeds and infected fruit.

• Hence 1, 2, 3 and 4, option (d).

Why the other options are wrong

(a) 1 and 3 only
Dust and wind also spread pathogens.
(b) 3 and 4 only
Birds and dust also spread pathogens.
(c) 1, 2 and 4 only
Rain also spreads pathogens by splash dispersal.

Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2018, held on 3 June 2018. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.

Reading the answer is not the same as getting it right under a clock. Practise this question with UPSC's negative marking, and anything you miss goes into an error notebook until you get it right twice.

Practise this paper free