Biology
Give scientific reasons for the following statements:
(i) Colour blindness is more common in men than in women.
(ii) Injury to medulla oblongata leads to death.
(iii) When an ovum gets fertilized, menstrual cycle stops temporarily in a woman.
(iv) Mature erythrocytes in humans lack nucleus and mitochondria.
(v) Blood flows in arteries in spurts and is under pressure.
Genetics
ICSE 2016
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Answer
(i) Colour blindness is more common in men than in women because the genes responsible for the color blindness are located on the X chromosome. Males have only one X chromosome whereas females have two X chromosomes. In males, only one defective X chromosome is enough to cause colour blindness. In females, two defective X chromosomes are required to cause colour blindness. This type of inheritance pattern is called X-linked inheritance and it primarily affects males.
(ii) It regulates involuntary movements such as breathing, respiration, circulation, the function of blood vessels etc. Thus, injury to medulla oblongata leads to death.
(iii) When ovum gets fertilized, the corpus luteum continues to release progesterone and so keeps the uterus in a state suitable for implantation. The endometrium gets thickened, and vascularized to house the embryo. The fertilised egg implants itself in the endometrial lining of the uterus and gets fixed in it. This causes the menstrual cycle to stop temporarily.
(iv) The presence of nucleus would occupy space and reduce the oxygen carrying capacity. The nucleus is also not required as a mature RBC does not divide. Mitochondria is absent so that oxygen is not utilised by the RBC and all the oxygen is transported to target areas.
(v) As the ventricles of the heart contracts, they push the blood into the small lumen of the arteries with a great force, thus making the blood in the arteries flow in spurts and under pressure.
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