Now a days we hear from many elderly people that they are undergoing knee replacement surgery. Find out why one has to undergo knee replacement, how it is carried out and how it can be prevented.

Bring ‘active dry yeast’ from the market. Mix a spoonful of yeast, two poonfuls sugar with «sufficient quantity of lukewarm water in a bottle. Fix a colourless, transparent balloon on the mouth of that bottle. Find out how to use the solution prepared in the above experiment, to make bread. Follow the recipe and make the bread. Find out and note down the reasons why the dough rises and makes the bread spongy.

Paragraph-based questions Read the paragraph and answer the questions given below: Disasters can be properly classified into three categories. viz. natural disasters, technological disasters and man-made disasters. The forces that cause natural disasters cannot be controlled. Moreover, they are becoming more frequent in the current years due to phenomena of climate change. On and off incidences of cyclones, cloud bursting, floods, etc. are creating havoc in the lives of people. Technological disasters are due to improper and callous behaviour at the different processes carried out in technical establishments. Man-made disasters are conflicts arising due to different religions, regions and terrorism. Which types of disasters can be controlled in order to lead happpy, peaceful and secured life? How?

There are 9 chairs in a room on which 6 persons are to be seated, out of which one is a guest with one specific chair. In how many ways can they sit

You may have seen how a drunken person struggles to maintain his body balance. An excess of alcohol in the body causes one to lose control over it. Why does this happen? Find out the reason with help of the internet.

There are instructions written near the arrows in the following diagram. From this information form suitable equations and write the boxes indicated by arrows. Select any two equations from these boxes and find their solutions Also verify the solutions. By taking one pair of equations at a time how many pairs can be formed? Discuss the solutions for these pairs.

The hourly energy requirements of an astronaut can be satisfied by the energy released when 34 grams of sucrose are "burnt" in his body. How many grams of oxygen would be needed to be carried in space capsule to meet his requirement for one day?

There are instructions written near the arrows in the following diagram. From this information form suitable equations and write in the boxes indicated by arrows. Select any two equations from these boxes and find their solutions. Also verify the solutions. By taking one pair of equations at a time, how many Pairs can he formed ? Discuss the solutions for these pairs.

Metals get attacked by substances around it such as moisture, acids, etc. Metal is said to 'corrode' due to this attack and the process is called corrosion. Many metals like iron, copper, silver, etc. get corroded. When iron is exposed to moist air, it undergoes corrosion and a reddish brown coloured solid layer is formed on its surface. Corrosion of iron, which is known as rusting, is a serious problem as enormous amount of money is spent every year to replace damaged iron. Similarly, copper reacts with moisture and. CO_(2) in air to form a green coloured coating of basic copper carbonate on its surface. Silver acquires a black colour when exposed to air containing H_(2)S due to the formation of silver sulphide on its surface. Based on the above paragraph, answer the following question. Why do we apply paint on iron articles?

Read the paragraph and answer the questions given below : Reproduction is the process by which the living Species continues its existence. Lower organisms carry out asexual reproduction while higher plants and animals always show sexual reproduction. Plants reproduce asexually by methods such as fragmentation, vegetative propagation, budding, Spore formation. For sexual reproduction they form gametes. In animal kingdom, budding, fission of different types and parthenogenesis are some of the methods that do not require both the sexes. Though regeneration also forms new individual, it is not considered to be a reproductive process because. basically it is a repair process. The ability to regenerate is lost in higher phyla. In human beings it is restricted only to wound healing. Sexual reproduction is also undergoing lots of experimentation such as cloning which may make females capable of producing their own baby without intervention of any male. Answer the follolwing question. How do living species continue their existence?