How can we prevent the following diseases?
Question: How can we prevent the following diseases? Cholera Typhoid Hepatitis-A Solution: Cholera An infectious disease caused by bacteria Vibrio cholerae. It occurs due to the consumption of contaminated or unhygienic food and water. It can be prevented by maintaining personal hygiene, good sanitation practice, consumption of clean drinking water, etc. Typhoid An acute illness caused by bacteria Salmonella typhi. It occurs by ingestion of typhoid bacterium through food, water, fomite, etc. Pre...
Read More →Give reasons for the following.
Question: Give reasons for the following. Fresh milk is boiled before consumption while processed milk is stored in packets and can be consumed without boiling. Raw vegetables and fruits are kept in refrigerators, whereas jams and pickles can be kept outside. Farmers prefer to grow beans and peas in nitrogen deficient soils. Mosquitoes can be controlled by preventing stagnation of water though they do not live in water. Why? Solution: Fresh milk is boiled before consumption to kill the micro org...
Read More →Express
Question: Express $0 . \overline{68}$ as a rational number. Solution: Let, x = 0.68686868 $\Rightarrow x=0.68+0.0068+0.000068+\ldots \infty$ $\Rightarrow x=68(0.01+0.0001+\ldots \infty)$ $\Rightarrow x=68\left(\frac{1}{10^{2}}+\frac{1}{10^{4}}+\frac{1}{10^{6}}+\frac{1}{10^{8}}+\ldots \infty\right)$ Here, $a=\frac{1}{10^{2}}$ and $r=\frac{1}{10^{2}}$ $\therefore$ Sum $=\frac{\mathrm{a}}{1-\mathrm{r}}=\frac{\frac{1}{10^{2}}}{1-\frac{1}{10^{2}}}=\frac{1 \times 100}{99 \times 100}=\frac{1}{99}$ $\Ri...
Read More →How do vaccines work?
Question: How do vaccines work? Solution: Vaccines contain dead or weakened microbial strains of a particular disease. When a vaccine is introduced into a heathy body. It produces specific cells against the pathogen. These cells, are called antibodies and they becomes active when the pathogen attack our body. The body fights and kills them by producing specific set of reactions. These antibodies remain in the body for life long and protect against the microbe when microbe enters the body again. ...
Read More →Each side of an equilateral triangle is increasing at the rate of 8 cm/hr.
Question: Each side of an equilateral triangle is increasing at the rate of 8 cm/hr. The rate of increase of its area when side is 2 cm, is (a) $8 \sqrt{3} \mathrm{~cm}^{2} / \mathrm{hr}$ (b) $4 \sqrt{3} \mathrm{~cm}^{2} / \mathrm{hr}$ (c) $\frac{\sqrt{3}}{8} \mathrm{~cm}^{2} / \mathrm{hr}$ (d) none of these Solution: (a) $8 \sqrt{3} \mathrm{~cm}^{2} / \mathrm{hr}$ Let $x$ be the side and $A$ be the area of the equilateral triangle at any time $t$. Then, $A=\frac{\sqrt{3}}{4} x^{2}$ $\Rightarrow...
Read More →Each side of an equilateral triangle is increasing at the rate of 8 cm/hr.
Question: Each side of an equilateral triangle is increasing at the rate of 8 cm/hr. The rate of increase of its area when side is 2 cm, is (a) $8 \sqrt{3} \mathrm{~cm}^{2} / \mathrm{hr}$ (b) $4 \sqrt{3} \mathrm{~cm}^{2} / \mathrm{hr}$ (c) $\frac{\sqrt{3}}{8} \mathrm{~cm}^{2} / \mathrm{hr}$ (d) none of these Solution: (a) $8 \sqrt{3} \mathrm{~cm}^{2} / \mathrm{hr}$ Let $x$ be the side and $A$ be the area of the equilateral triangle at any time $t$. Then, $A=\frac{\sqrt{3}}{4} x^{2}$ $\Rightarrow...
Read More →(a) Name two diseases that are caused by virus.
Question: (a) Name two diseases that are caused by virus. (b) Write one important characteristic of virus. Solution: (a) Influenza and chickenpox are two diseases caused by virus in humans. (b) Virus are dead when present in the environment. They can reproduce only inside the cells of an infected person (as host)....
Read More →What will happen to ‘pooris’ and ‘unused kneaded
Question: What will happen to pooris and unused kneaded flouri if they are left in the open for a day or two? Solution: The unused kneaded flour if left in warm conditions, gets infected by microbes which causes fermentation and spoils the flavour, texture, etc., of the flour. The pooris would remains in relatively good condition because these were deep fried in heated oil that kills microbes....
Read More →Express
Question: Express $0 . \overline{6}$ as a rational number. Solution: Let ,x = 0.6666 $\Rightarrow x=0.6+0.06+0.006+\ldots$ $\Rightarrow x=6(0.1+0.01+0.001+0.0001+\ldots \infty)$ $\Rightarrow x=6\left(\frac{1}{10}+\frac{1}{100}+\frac{1}{1000}+\frac{1}{10000}+\ldots \infty\right)$ This is an infinite geometric series. Here,a = 1/10 and r = 1/10 $\therefore$ Sum $=\frac{\mathrm{a}}{1-\mathrm{r}}=\frac{\frac{1}{10}}{1-\frac{1}{10}}=\frac{1 \times 10}{9 \times 10}=\frac{1}{9}$ $\therefore x=6 \times ...
Read More →While returning from the school,
Question: While returning from the school, Boojho ate chaat from a street hawker. When he reached home, he felt ill and complained of stomachache and fell ill. What could be the reason? Solution: The reason could be that the chaat was contaminated by pathogenic micro organisms. The unhygienic conditions present near the shop becomes the breeding place for microbes, flies, etc. The pathogens can be transmitted to places by flies and other vectors, even the utensil used for serving could have been...
Read More →If the rate of change of area of a circle is equal
Question: If the rate of change of area of a circle is equal to the rate of change of its diameter, then its radius is equal to (a) $\frac{2}{\pi}$ unit (b) $\frac{1}{\pi}$ unit (c) $\frac{\pi}{2}$ units (d) $\pi$ units Solution: (b) $\frac{1}{\pi}$ unit Let $r$ be the radius and $A$ be the area of the circle at any time $t$. Then, $A=\pi r^{2}$ $\Rightarrow A=\frac{\pi D^{2}}{4}$ $\left[\because r=\frac{D}{2}\right]$ $\Rightarrow \frac{d A}{d t}=\frac{\pi D}{2} \frac{d D}{d t}$ $\Rightarrow \fr...
Read More →If the rate of change of area of a circle is equal
Question: If the rate of change of area of a circle is equal to the rate of change of its diameter, then its radius is equal to (a) $\frac{2}{\pi}$ unit (b) $\frac{1}{\pi}$ unit (c) $\frac{\pi}{2}$ units (d) $\pi$ units Solution: (b) $\frac{1}{\pi}$ unit Let $r$ be the radius and $A$ be the area of the circle at any time $t$. Then, $A=\pi r^{2}$ $\Rightarrow A=\frac{\pi D^{2}}{4}$ $\left[\because r=\frac{D}{2}\right]$ $\Rightarrow \frac{d A}{d t}=\frac{\pi D}{2} \frac{d D}{d t}$ $\Rightarrow \fr...
Read More →Express
Question: Express $0 . \overline{123}$ as a rational number. Solution: Let, x = 0.123123123. $\Rightarrow x=0.123+0.000123+0.000000123+\ldots \infty$ $\Rightarrow x=123(0.001+0.000001+0.000000001+\ldots \infty)$ $\Rightarrow x=123\left(\frac{1}{10^{3}}+\frac{1}{10^{6}}+\frac{1}{10^{9}}+\frac{1}{10^{12}}+\ldots \infty\right)$ This is an infinite geometric series. Here, $a=\frac{1}{10^{3}}$ and $r=\frac{1}{10^{3}}$ $\therefore \operatorname{Sum}=\frac{\mathrm{a}}{1-\mathrm{r}}=\frac{\frac{1}{10^{3...
Read More →Paheli watched grandmother making mango pickle.
Question: Paheli watched grandmother making mango pickle. After she bottled the pickle, her grandmother poured oil on top of the pickle before closing the lid. Paheli wanted to know why oil was poured? Can you help her understand why? Solution: The oil poured on the pickle forms a barrier between the pickle and air. This prevents the bacteria present in air from entering jar and attacking the pickle and spoiling it. Thus, increasing the shelf life of pickles....
Read More →Polio drops are not given to children
Question: Polio drops are not given to children suffering from diarrhoea. Why? Solution: If the child is suffering from diarrhoea, the polio drops that is an oral vaccine for fighting against polio virus may be excreted out because of frequent motions. Thus, the child becomes susceptible to polio inaction as the vaccine becomes ineffective to fight against invading pathogen....
Read More →If the rate of change of volume of a sphere
Question: If the rate of change of volume of a sphere is equal to the rate of change of its radius, then its radius is equal to (a) 1 unit (b) $\sqrt{2 \pi}$ units (c) $\frac{1}{\sqrt{2 \pi}}$ unit (d) $\frac{1}{2 \sqrt{\pi}}$ unit Solution: (d) $\frac{1}{2 \sqrt{\pi}}$ unit Let $r$ be the radius and $V$ be the volume of the sphere at any time $t .$ Then, $V=\frac{4}{3} \pi r^{3}$ $\Rightarrow \frac{d V}{d t}=\frac{4}{3}\left(3 \pi r^{2}\right) \frac{d r}{d t}$ $\Rightarrow \frac{d V}{d t}=4 \pi...
Read More →Why should we avoid standing
Question: Why should we avoid standing dose to a tuberculosis patient while he/she is coughing? Solution: Tuberculosis is an air-borne disease, which is easily spreads when the infected person coughs. As coughing spreads germs in the air and these germs remain suspended in air until inhaled by person present in promixity of the patient who is suffering from the disease. That is why we should avoid standing close to a TB patient....
Read More →Prove that
Question: Prove that $\left(1-\frac{1}{3}+\frac{1}{3^{2}}-\frac{1}{3^{3}}+\frac{1}{3^{4}} \ldots \infty\right)=\frac{3}{4}$ Solution: It is Infinite Geometric Series. Here, a = 1, $r=\frac{\frac{-1}{3}}{1}=\frac{-1}{3}$ Formula used: Sum of an infinite Geometric series $=\frac{a}{1-r}$ $\therefore$ Sum $=\frac{1}{1-\frac{-1}{3}}=\frac{1 \times 3}{3+1}=\frac{3}{4}=$ R.H.S. Hence, Proved that $\left(1-\frac{1}{3}+\frac{1}{3^{2}}-\frac{1}{3^{3}}+\frac{1}{3^{4}} \ldots \infty\right)=\frac{3}{4}$...
Read More →Preservatives are used in kitchen on daily basis.
Question: Preservatives are used in kitchen on daily basis. List a few of them. Preservatives prevent the spoilage of food lives for a long time from microbial infestation. Solution: Vinegar common salt and oil are common preservatives used in kitchen....
Read More →Name the process in yeast
Question: Name the process in yeast that converts sugars into alcohol. Solution: Fermentation is the process by which yeast converts sugars into alcohol....
Read More →Name one commercial
Question: Name one commercial use of yeast. Solution: Baking bread/manufacturing of alcoholic drinks is the commercial use of yeast....
Read More →Suggest a suitable word for each of
Question: Suggest a suitable word for each of the following statements. (a) Chemicals added to food to prevent growth of micro organisms. (b) Nitrogen-fixing micro organism present in the root nodules of legumes. (c) Agent which spreads pathogens from one place to another. (d) Chemicals which kill or stop the growth of pathogens. Solution: (a) Preservatives are the chemicals added in food. They prevent microbial infection without altering the taste or appearance. (b) Rhizobium are the nitrogen f...
Read More →The volume of a sphere is increasing at the rate
Question: The volume of a sphere is increasing at the rate of $4 \pi \mathrm{cm}^{3} / \mathrm{sec}$. The rate of increase of the radius when the volume is $288 \pi \mathrm{cm}^{3}$, is (a) $1 / 4$ (b) $1 / 12$ (c) $1 / 36$ (d) $1 / 9$ Solution: (c) $1 / 36$ Let $r$ be the radius and $V$ be the volume of the sphere at any time $t$. Then, $V=\frac{4}{3} \pi r^{3}$ $\Rightarrow \frac{4}{3} \pi r^{3}=288 \pi$ $\Rightarrow r^{3}=\frac{288 \times 3}{4}$ $\Rightarrow r^{3}=216$ $\Rightarrow r=6$ $\Rig...
Read More →Unscramble the jumbled words underlined
Question: Unscramble the jumbled words underlined in the following statements. (a) Cells of our body produce santiidobe to fight pathogens. (b) Curbossulite is an air-borne disease caused by a bacterium. (c) Xanrhat is a dangerous bacterial disease. (d) Yeasts are used in the wine industry because of their property of meronettinaf. Solution: (a) Antibodies are specific molecules produced against invading microbes. (b) Tuberculosis is an infectious air-borne disease caused by Mycobacterium tuberc...
Read More →Paheli dug two pits, A and B, in her garden.
Question: Paheli dug two pits, A and B, in her garden. In pit A, she put a polythene bag packet with some agricultural waste. In pit B, she dumped the same kind of waste but without packing it in a polythene bag. She, then covered both the pits with soil. What did she observe after a month? (a) Waste in pit A degraded faster than that in pit B (b) Waste in pit 6 degraded faster than that in pit A (c) Waste in both pits degraded almost equally (d) Waste in both pits did not degrade at all Solutio...
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