81: Which one of the following is the best description of the term 'ecosystem'?
(a) A community of organisms interacting with one another.
(b) That part of the Earth which is inhabited by living organisms.
(c) A community of organisms together with the environment in which they live
(d) The flora and fauna of a geographical area
Explanation:
Here statement C clearly define the ecosystem.
82: In many developing countries, three major causes of death and disease are
(a) lack of safe drinking water, increasing use of pesticides and thinning of the ozone layer
(b) contaminated food, global warming and industrial chloro-fluoro-carbons
(c) polluted air, greenhouse effect and soil erosion
(d) dirty water, contaminated food and polluted air
83: Sir J. C. Bose was a great scientist because he showed the:
(a) Sensitivity in plants
(b) Pigments in plants
(c) Growth in plants
(d) Relations between plants and animals
84: Which feature of some, species of blue-green algae helps promote them as bio-fertilizers?
(a) They convert atmospheric methane into ammonia which the crop plants can absorb readily
(b) The induce the crop plants to produce the enzymes which help convert atmospheric nitrogen to nitrates
(c) They have the mechanism to convert atmospheric nitrogen into a form that crop can absorb readily
(d) The induce the roots of the crop plants to absorb the soil nitrates in larger quantities
Explanation:
Cyanobacteria, also known as blue-green algea, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. Cyanobacteria include unicellular and colonial species. Colonies may form filaments, sheets or even hollow balls. Some filamentous colonies show the ability to differentiate into several different cell types: vegetative cells, the normal, photosynthetic cells that are formed under favorable growing conditions; akinetes, the climate-resistant spores that may form when environmental conditions become harsh; and thick-walled heterocysts, which contain the enzyme nitrogenase, vital for nitrogen fixation.
85: Match List I (Diseases) with List II (Types of disease) and select the correct answer using the codes given below the Lists :
List I
I. Haemophilia
II. Diabetes
II. Diabetes
IV. Ringworm
List II
(A) Deficiency disease
(B) Genetic disease
(C) Hormonal disorder
(D) Fungal infection
Codes:
(a) I-B, II-C, III-D, IV-A
(b) I-B, II-C, III-A, IV-D
(c) I-C, II-B, III-A, IV-D
(d) I-C, II-B, III-D, IV-A
Explanation:
Haemophilia is X-linked recessive genetic disease.
Dibetesis due to the low hormone (Insulin) levels in the blood which leads to high blood sugar levels.
Rickets is due to the deficiency of Vitamin D in children.
Ringworm is due to the fungal infections belong to a group called 'Dermatophytes'. (Microsporum, Trichophyton).