Ncert Exercises & Solutions

Q. 4 A Differentiate between

(a) oestrus and menstrual cycles;

(b) ovipary and vivipary. Give an example for each type.

The differences between oestrus and menstrual cycle are as follows

Oestrus cycle	Menstrual cycle
The cyclic changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase of non-primate mammais is called oesturs cycle.	The cyclic changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase of primate mammals is called menstrual cycle.
Females show strong irresistible sexual urge.	Females do not show irresistible sexual urge.
There is estrus/heat production at the time of ovulation and copulation occurs only at that period.	There is no heat period and copulation occurs during any time of the cycle.
The shedding of endometrium and bleeding do not occur. e..r., cows, sheep, rats, deers, dogs and tigers etc.	The shedding of endometrium and bleeding occurs. e.g., monkeys, apes and humags.

(b) The differences between oviparity and vivipary are as follows

Ovipary	Vivipary
In ovipary, animals lay eggs.	In vivipary, animals give birth to yound ones.
The eggs are covered by heard calcareous shell.	Ovum are not covered by calcareous shell.
The development of zygote takes place outside the female's body	The development of zygote takes place inside the female's body.
Females lay eggs in a safe place in the environment, but the chances of survival are less e.g., all birds, most of reptiles are egg laying mammals.	Females deliver young ones and the chances of survival are more. e.g., mammals except monotremes egg-laying mammals.