1 Pasteurized milk has more nourishment than the ordinary boiled milk. Give reasons.
Pasteurization is a process of heating food, usually liquid, to a specific temperature for a definite length of time and then cooling it immediately. This process slows microbial growth in food. The process was named after its creator, French chemist and microbiologist Louis Pasteur. The process was originally conceived as a way of preventing wine and beer from souring.

The Purpose of Pasteurization
a. To increase milk safety for the consumer by destroying disease causing microorganisms (pathogens especially Micro bacterium Tuberculosis) that may be present in milk.

b. To keep the quality of milk products by destroying spoilage microorganisms and enzymes that contribute to the reduced quality and shelf life of milk.

c. To maintain the taste and integrity of milk.

2. Why is it dangerous to touch a live wire with bare hands and feet?
Human body is a good conductor of electricity. If we touch a live wire with bare hands and feet, current will pass through the body giving it a severe shock. If the voltage is high, the shock can be fatal.

3. Gravity of all the objects is same, regardless of their mass at a given point on the earth's surface?
Gravity is the acceleration that an object experiences because of gravity when it falls freely on the surface of a massive body, such as a planet. The planets like the Earth have ability to attract bodies towards their surface.

Note: Resistance offered by air hinders the process of falling objects of different masses to the ground.

For the Earth, g = 9.8m/sec2
The value of “g” is constant almost all over the surface of the Earth and this is due to the almost spherical shape of the Earth. If the Earth had no atmosphere, an object dropped from a great height would keep accelerating at a rate of 9.8 m/s2 (32 ft/s2) until it hits the ground. If there were no atmosphere, all objects would fall at the same rate.

4. Goiter is common among people living in hilly areas. Why?
Goiter is a disease of the thyroid gland. An endocrine gland is located at the front of neck of every human. Goiter is caused by deficiency of iodine in a person's diet. The thyroid gland uses this mineral to synthesize thyroxin: a hormone needed for the normal growth and metabolism of human body.

When iodine is absent from the diet there is greater release of TSH i.e. thyroid stimulating hormone from the pituitary gland forcing the thyroid gland to produce more thyroxin. Due to absence of iodine, however, the gland is unable to produce thyroxin and in an attempt to do so the gland gets hypertrophied (enlarged).

5. Why a petrol fire cannot be extinguished by pouring water over it?
Water, being heavier, slips down and petrol will rise to the surface and continue to burn. Hence, water cannot be used for extinguishing petrol fire.

6. What would happen if the force of gravity disappears suddenly?
In the absence of force of gravity all living objects will be practically in a floating condition. They will be thrown away because of the centrifugal force caused by the rotation of the Earth. Thus one would not be able to eat, drink, move and continue to live.

7. Why does it take more time to cook food at hill stations than at plains?
The boiling point of water depends upon the pressure on its surface. It increases with the increase of pressure and decreases on lowering of pressure. At higher altitudes, the atmospheric pressure is low as compared to plains and water boils at less than 100 degree centigrade. Thus sufficient heat is not provided for cooking. This can be overcome by the use of pressure cooker which maintains the pressure on water surface and provides sufficient heat for cooking.

8. Why does your voice sound different to you on a recording?
When you hear yourself speak regularly, the sound waves emanate through the tissue, bone, and other materials which change its quality.

9. Why are copper rods preferred for making lightning conductors?

Copper rods are preferred because:
a) Copper is a better conductor than iron

b) Copper is not easily oxidized in the presence of oxygen and water molecules while iron gets rusted

c) Loss of energy is much less with copper rod than with iron rod, as copper is bad conductor of heat than iron.

10. Colour Blindness and Hemophilia are more common in men than in women. Give reasons.
Colour blindness and Hemophilia are genetic diseases related to "Sex Chromosomes". In humans, there are 46 chromosomes in 23 pairs in the nucleus of the cell. Twenty-two pairs are called “autosomes” while there is one pair of chromosome that is called "sex chromosome" as they determine the sex of a person. Males have "XY" chromosomes as a pair and females have "XX" chromosomes in a pair. The "Y" chromosome in "XY" Chromosome pair in male as a dummy and only "X" chromosome is functional in the "XY" pair. While in females, one of the "X" is fully functional just like in male, but the other "X" is partially functional.

Just as a chromosome has a pair, every gene has a pair in the other pairing chromosome and these genes control various traits of humans.

Recessive trait and Dominant Trait
A trait that requires a single gene to express itself is called Dominant trait while a trait that needs two or more genes to express itself is called Recessive trait.

For example in humans, gene for short height is dominant. Thus, if there is one gene for short height and the other for long height, the person would be short heighted. Conversely, if there are two genes for long height, the person would be tall.

What is a colour blind carrier?
When a female has one colourblind gene on one chromosome while the other chromosome is normal; then the female is said to be "Carrier". She is, however, not diseased with "Colourblindness".

Haemophilia and color blindness:
Hemophilia and colour blindness are hereditary diseases which mean that they are expressed on the sex chromosomes.

In humans, the genes for hemophilia and color blindness are recessive which means that they need to be present in pairs (that is on both chromosomes) to cause the disease.

For example:
A. A female may be a carrier of a colour blindness gene.
eg. CX
c = x chromosome carrying a colour blind gene
x = x chromosome carrying no colour blind gene
In that female, there will be no colour blindness.

Colour blindness gene present on the single 'x' chromosome, will be expressed in male because the chromosome 'y' is inert. i.e. x+y So the male children will be suffering from colour blindness.

B. When a colour blind female marries a colour blind male
Colour Blind Male (CY) Colour Blind Female (CX)
CC = Colour blind Female

CX = Carrier Female

YC = Colour Blind Male

XY = Normal Male



Result = CC, CX , CY , XY

i.e. half of the daughters will be colour blind and half will be carriers, while half of the sons will be colourblind and half normal.


C. When a colour blind man marries with a normal female
Colour Blind Male (CY) Normal Female (XX)

CX = Colour blind female
CX = Colour Blind female

XY= Normal male

XY = Normal male
Result = CX, CX, XY, XY

i.e. all the daughters will be carriers and all the sons will be normal.


Dr Najam us Sahar Butt (CSP)