Q. Mention two uses of isotopes in the field of medicine.


(i) An isotope of cobalt is used in the treatment of cancer.

(ii) An isotope of iodine is used in the treatment of goitre.

Q. Who discovered vaccine for the first time?


Edward Jenner discovered vaccine for the first time.

Q. Why do fish go in deep waters during day light?

During day time, the shallow water is warmer and hence contains less dissolved oxygen. Therefore fish tend to go in deep water during day time.
Q. (a) Name two properties of a substance to check its purity?

(b) Alloys cannot be separated by physical means, though it is considered mixture, Why?


(a) A pure substance has a fixed melting point or boiling point at constant pressure. The purity of a substance can be tested by checking its melting point or boiling point. If a substance is impure i.e. it contains traces of another substance, the melting and boiling point of that substance will change.

(b) Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods. But still, an alloy is considered as a mixture because it shows the properties of its constituents and can have variable composition.

Q. Is it possible that an object is in the state of accelerated motion due to external force acting on it, but no work is being done by the force? Explain it with an example.


Yes, it is possible, if an object is moving in a circular path because in that case the centripetal force always acts perpendicular to the direction of displacement.

For example: Consider the motion of earth around sun. The earth is constantly moving in a direction perpendicular to the gravitation pull of sun, hence work done by the gravitational force is zero.

Q. (a) List any four properties of a colloid and mention any two properties in which colloids differ from suspension.

(b) State what is Tyndall effect ? Which of the following solutions will show Tyndall effect ? Starch solution, sodium chloride solution, Tincture iodine, air


(a)  Properties of a colloid (any four)
(i) A colloid is a heterogeneous mixture.
(ii) The size of particles of a colloid is too small to be individually seen by naked eyes. 
(iii) Colloids are big enough to scatter a beam of light passing through it and make its path visible. 
(iv) They do not settle down when left undisturbed, that is, a colloid is quite stable.
(v) They cannot be separated from the mixture by the process of filtration. But, a special technique of separation known as centrifugation can be used to separate the colloidal particles.

Two properties in which colloids differ from suspension are (ii) and (iii) as the particles of a suspension are large enough to be observed with a naked eye and these particles settle down well when the mixture is left undisturbed.

(b) Tyndall effect is the phenomenon of scattering of a beam of light by the particles of a colloid.

Starch solution and tincture iodine are colloid and thus will show Tyndall effect.

Q. (a) What is immunisation ?

(b) Define immunity and vaccination.

(c) Define vaccine.

(d) What type of diseases can be prevented through vaccination?


(a) Immunisation: It is a process of inoculation (injecting) of substance (vaccine) into a healthy person in order to develop immunity against the disease.

(b) Immunity: Immunity is the ability of a body to recognize, destroy, and eliminate external disease-causing agents.

Vaccination: Vaccination is the administration of antigenic material (a vaccine) to stimulate an individual's immune system to develop immunity to a pathogen.

(c) Vaccine: A vaccine is a solution containing the disease-causing organisms in a diluted or weakened form. It may have organisms in living or even dead form. This does not actually cause the disease but this would prevent any subsequent exposure to the infecting microbe from turning into actual disease.

(d) Protection against diseases like smallpox, rabies, polio, diphtheria, chickenpox and hepatitis is provided through vaccination. It has been possible to eradicate smallpox from all regions of the world through a massive vaccination program.