Which one of the following is the mechanism of action of oral contraceptive pills?
- A.They kill the egg.
- B.They kill the sperm.
- C.They kill the zygote.
- D.They inhibit the release of egg.
Correct answer
Explanation
The correct answer is D, They inhibit the release of egg.. Oral contraceptive pills prevent pregnancy mainly by stopping the ovary from releasing an egg.
The pills contain small doses of synthetic progesterone, often combined with oestrogen. These hormones signal the pituitary gland to cut down its release of follicle-stimulating hormone and luteinising hormone, so no follicle matures and ovulation does not take place. They also thicken the mucus at the cervix, which makes it harder for sperm to pass. Pills have to be taken daily, usually for 21 days with a gap of seven days; India's government brand of a once-a-week pill is Saheli.
A is wrong because the pills do not kill an egg; they stop one from being released at all.
B is wrong because killing sperm is the action of spermicides, a chemical method, not of the pill.
C is wrong because the pill acts before fertilisation, so there is no zygote to act on.
Exam tip: oral pills inhibit ovulation; Saheli is the non-steroidal once-a-week pill developed by CDRI Lucknow.
Practice Questions
View allWhich one of the following is the purest form of Carbon ?
- A.Charcoal
- B.Coke
- C.Fullerene
- D.Carbon black
Show answer
Fullerenes are made of carbon atoms alone, with no surface to trap other substances, so they are counted as the purest form of carbon.
Read the full explanation →A planet has a mass M₁ and radius R₁. The value of acceleration due to gravity on its surface is g₁. There is another planet 2, whose mass and radius both are two times that of the first planet. Which one of the following is the acceleration due to gravity on the surface of planet 2?
- A.g₁
- B.2g₁
- C.g₁/2
- D.g₁/4
Show answer
Surface gravity is g = GM/R², so doubling the mass doubles g while doubling the radius divides it by four, leaving g₁ × 2/4 = g₁/2.
Read the full explanation →Which one of the following is the major constituent of biogas ?
- A.Carbon dioxide
- B.Nitrous oxide
- C.Methane
- D.Oxygen
Show answer
Methane makes up the largest share of biogas, usually about 55 to 75 per cent, and it is the gas that burns.
Read the full explanation →A lemon kept in water in a glass tumbler appears to be larger than its actual size. It is because of
- A.reflection of light
- B.scattering of light
- C.refraction of light
- D.polarization of light
Show answer
The lemon looks bigger because light from it bends as it passes from water through the curved glass into air.
Read the full explanation →Which one of the following conclusions could not be derived from Rutherford's α-particle scattering experiment?
- A.Most of the space in the atom is empty.
- B.The radius of the atom is about 10⁵ times the radius of the nucleus.
- C.Electrons move in a circular path of fixed energy called orbits.
- D.Nearly all the mass of the atom resides in the nucleus.
Show answer
. Orbits of fixed energy were proposed by Niels Bohr in 1913; Rutherford's experiment said nothing about the energy of electrons.
Read the full explanation →