NCTB Class 9-10 Science Chapter 2 “Water for Life” Solution
Bangladesh Board Class 9-10 Science Solution Chapter 2 Water for Life Solution Exercises Question and Answer by Experienced Teacher.
NCTB Solution Class 9-10 Chapter 2 “Water for Life”:
|NCTB Bangladesh Board|
9 – 10 (Nine – Ten Classes)
Water for Life
Chapter 2 “Water for Life”
Multiple choice questions
1) Which of the following plant grows both in water and land?
a) Algae b) Bindweed
c) Waternut d) Duckweed
Answer:- b) Bindweed
2) Extreme decrease in PH of water results in aquatic fauna
i)Improper growth of different organ
ii) Lacking of mineral in the bodies
iii) attacked with various diseases
Which one is correct?
a)i and ii b) i and iii
c)ii and iii d) i, ii, and iii
Answer:- d) i,ii and iii
Read the following paragraph and answer the question 3 and 4
Onik and Tushar culture the fish in two separate ponds. The fish growth in onik’s pond is satisfactory where as in tushar’s pond the fishes are weak and their organs are not grown properly.
3) What is the type of water in onik’s pond?
a) acidic b) alkaline
c) neutral d) enriched with calcium
Answer:- b) alkaline
4) Which of the following should be used in Tushar’s pond?
a) acid b) alkali
c) calcium d) phosphorus
Que. 1] See the following picture and answer the questions.
A) which dissolved gas undergoes chemical reaction with glucose?
Answer:- Dissolved oxygen undergoes chemical reaction with glucose. As a result of this reaction the dissolved oxygen level of the water decreases and even it could be decreased at zero.
B) what do you mean by recycling of water ?
Answer:- Earth is covered with 75 % of water among that 97% of water is saline, and thus it cannot be utilised directly for various purposes. Only 1% of water resources we have is fresh and the major portion of it is present in the river ,lakes etc, and it is being “polluted” even ground water being used for various purposes including drinking get contaminated by toxic chemical substances like arsenic and thus become unsuitable for drinking and cooking.
Hence we need to recycle water and it is very important.
Water can also be recycled naturall, as the water vapour forms due to the sunlight and enters into the atmosphere and condense to become cloud and then finally come back as rain water this is naturally recycling of water .
C) To what kind the river will be converted ? Explain.
Answer:- due to diversion in flow of water many rivers have been water depleted converting those areas into almost a desert. Role water In the development and day to day life is very essential. We cannot think our life without water but due to threads due to flood and soil erosion rivers may die, the sedimentationin the river bed occur.
D) Do you think that it is possible to spring back the rivers to sustain the aquatic animals? Justify your answer.
Answer:-yes, it can be possible if all the citizens take the responsibility of preventing water form pollution. spring back the rivers can sustain aquatic animals. Aquatic animals are dying due to water pollution and many hazardous waste mixed in the water from many industrial and chemical sources as well as household work, this can be prevented only if the water quality is maintained to the aquatic life.
Que.2] mrs. Jamila makes turbid water of nearby pond suitable for cooking by the special process. On the other hand mr. Ratan use his water both in bottled water manufacturing plant and Pharmaceutical industry after disinfecting.
- a) What is meant by the term ‘boiling point of water’?
Answer:- At atmospheric pressure the temperature at which the liquid boils is called ‘boiling point’. Boiling point of water is 99.98°c which is very close to 100°c thus we generally say that boiling point of water is 100°c.
b)why do the aquatic plants not break down by water current?
Answer:- stems And other parts of the aquatic plants are so soft that they are suitable for adapting with water current and movement of aquatic fauna. If they grew on land instead of water they would breakdown and would not grow and not even survive.
c) How does mrs. Jamila make pond water suitable for cooking? Explain.
Answer:-mrs. Jamila make pond water suitable for cooking using the technique boiling. It is possible to kill the Germs present in water. After starting heating for additional 15-20 mincan disinfect water completely. It is simple and economical process for purifying drinking water at home.
d) Does Mr.Ratan disinfect water for both plant in the same method? Justify your answer.
Answer:-No,mr. Ratan does not use same process for disinfect water in both plants. He use chlorination for bottled water factory, he use sodium hypochlorite (NaOcl). Chlorine present in it kills the germs in the water. Other than chlorine germs can also be destroyed by ozone gas (O3) or ultraviolet radiation.
And for the pharmaceutical industry mr. Ratan use distillation process. When very pure water is needed water is purified by distillation method. For manufacturing medicine or to carry out chemical reaction 100% pure water is needed. In this method basically water taken in container is heated to vapour, Which is condensed and collected on another container. The possibility of having a substance in the water purified by this method is very low.