Friday, February 1, 2013

class 9 biology exam solved questions sa2

1. What are pathogens?[1]
Ans. Disease-causing organisms are called pathogens

2. List any two human activities that lead to an increase in the carbon dioxide content of air.[1]
Ans: a. Combustion of wood. b. Deforestation. c. Respiration

3. (a) Name any two green house gases. (b) What causes global warming?[2]
Ans:  (a) Carbon dioxide (CO2), methane (CH4), ozone (O3) and water vapour (H2O) green house gases.

(b) The greenhouse gases do not allow heat rays to escape from the earth resulting in an increase of temperature of the earth. Hence, green house gases cause global warming.

4. Give two examples each of biodegradable and non-biodegradable pollutants.[2]
Ans: Biodegradable pollutants-cow dung and paper

Non-biodegradable pollutants-polythene, plastic and DDT

5. Write two points of difference between gymnosperms and angiosperms.[2]
Ans:   Gymnosperms 
(i) The seeds are naked.

(ii) The microspores and megaspores are produced by male and female cones.


(i) The seeds are enclosed by fruit wall.

(ii) The microspores are produced in anthers while the megaspores are produced in ovules of the ovary in flowers.

6. Why are bats not placed in birds (Two Points)? [2]
1. Bats are not placed in birds because bats possess mammary glands (milk producing glands).
2. Secondly cutaneous glands are absent in birds but present in bats.

7. (a) Write any two important features that are present in all chordates. (b) Mention one difference between triploblastic and diploblastic animals. [3]
(a) (i) Presence of a tubular, dorsal, hollow nerve cord. (ii) Triploblastic and coelomate

(b) An animal with a body wall composed only of two layers, ectoderm and endoderm are diplablastic.

An animal having a body composed of three embryonic cell layers – the ectoderm, mesoderm and endoderm are triploblastic.

8. List any two benefits of classification. Why bryophytes and pteridophytes grow in moist and shady places? [3]
(i) It makes study of organisms easy.
(ii) It gives inter-relationship amongst different groups of animal.
(iii) It gives us an idea about existing life forms.
(iv) Classification is the base for development of other branches of biological science.

(b) Bryophytes and pteridophytes grow in moist and shady places because they require water for fertilization.

9. Explain, how HIV-AIDS virus affects and damages our body? What is an antibiotic?[3]
(i) In HIV infection, the virus goes to the immune system and damages its function by attacking cells of immune system (T-cells). 

Gradual decrease in their number weakens our immune system. Our body can then no longer fight off the many minor infections that we face everyday.

Instead, every small cold can become pneumonia; minor gut infection can produce major diarrhoea with blood loss. Ultimately, these other infections kill the people suffering from HIV-AlDS.

(ii) Antibiotics are chemical substances obtained from some microbes such as bacteria and fungi, which stop the growth of specific kinds of microbes.

10. a) Describe with diagram the oxygen cycle operating in nature. b) How depletion of ozone layer takes place?[5]

Ans: a) Oxygen-cycle: Oxygen from the atmosphere is used up in combustion, respiration and in the formation of oxides of nitrogen. It is returned to the atmosphere through photosynthesis.

(b)Chlorofluorocarbons used as solvents, refrigerants, propellants and blowing agents for plastic foams are stable and persist in atmosphere for years.

These enter the upper layers of atmosphere where UV radiation causes CFCs to dissociate the ozone into oxygen.

11. a) Define the following terms: (i) Ammonification (ii) Nitrification (iii) Denitrification

      b) State any two applications of green house effect.[5]

Ans:  i) Ammonification is defined as the conversion of organic material of plants and animals into ammonia and amino acids by microorganisms.

ii) Nitrification is defined as the conversion of ammonia into nitrates by microorganisms.

iii) Denitrification is defined as the conversion of nitrate into ammonia and free nitrogen by microorganisms.

b) Applications of green house effect:
i) In cold climatic conditions, vegetables and plants are grown in glass house to protect them from cold.

ii) It is useful in increasing temperature in black box of solar cookers by covering it with plain glass sheet.

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