Sperm comes out from testis into the vas deferens and then passes through urethra before ejaculation. The secretions of seminal vesicle and prostrate glands provide nutrition to the sperms and also facilitate their transport.

 Following changes take place in uterus if fertilization does not occur:
• The extra lining of uterus degenerates.
• Fragments of the uterine lining are discharged through vagina.
• Unfertilized egg is also discharged.
• Menstruation take place. 

Following changes take place in uterus after implantation of young embryo:
• Uterine lining thickens to support to developing embryo.
• Uterine lining is richly supplied with blood vessels so that nutrition and oxygen could be supplied to the developing foetus. 

Following are the benefits of mechanical barriers during sexual act:
• Prevention of unwanted pregnancy.
• Prevention of STDs. 

(a) Production of egg
(b) Site of fertilisation
(c) Site of implantation
(d) Entry of the sperms 

The ratio of chromosome number between an egg and its zygote is 1:2. Sperm has Y chromosome as the 23rd chromosome, while egg has X chromosome as the 23rd chromosome. Moreover, the genetic makeup of sperm is similar to father and that of egg similar to mother.

A single parent is involved and gamete formation does not take place in reproduction through budding, fragmentation and regeneration. Hence, all of these are considered as asexual types of reproduction.

Regeneration in Planaria: The body of planaria may get divided into many pieces. Each piece has the ability to develop complementary portion to become a new individual. The given figure shows a planaria getting divided into three pieces. Subsequently, each piece develops into a new individual. 

Asexual reproduction	Sexual reproduction
(a) Involves only one parent	(i) Often involves two parents
(b) Gametes are not produced	(ii) Gametes are produced
(c) No fertilisation and zygote formation	(iii) Fertilisaton and zygote formation is observed.
(d) Meiosis does not occur at anytime during reproduction	(iv) Meiosis occurs at the time of gamete formation

Variations are observed in the offspring formed by sexual reproduction, because of
following reasons:
• Gene pool is contributed by two parents.
• Crossing over during meiosis results in variations.
• DNA replication also plays some role in variation.