Science [5 marks Questions]

Followed by fertilization, placenta is developed which serve to provide nutrition and oxygen to developing embryo from the mother's blood. It is a disc embedded in the uterine wall and contains villi on the embryo's side of the tissue while blood spaces surrounding the villi are present on mother’s side. The embryo is connected to the placenta by umbilical cord, a tube like structure.Placenta serves to fulfill all nutritional requirements of developing embryo by supplying food and oxygen from mother’s blood to the embryo. Waste products of developing embryo are removed by transferring them into the mother's blood through the placenta. Functions of placenta are facilitated by villi that provide large surface areas for passage of nutrition and oxygen to embryo from mother through blood.

Methods to avoid undesired pregnancy are called contraceptive methods. It includes:

1. Mechanical barrier that prevent arrival of sperm to the egg, e.g., condom.
2. Chemical Drugs or contraceptive pills-Small dosage of female hormones that prevent released of egg.
3. Loop or copper-T-physical devices to prevent pregnancy.
4. Surgical method-permanent contraception by vasectomy and tubectomy.

Surgical methods: Vasectomy refers to surgical method in which vasa deferentia in human males are cut and sealed to prevent pregnancy by making seminal fluid devoid of sperms. Tubectomy refers to surgical process in which oviducts in human females are cut and sealed to prevent pregnancy by inhibiting released of egg.

1. Differences between Pollination and Fertilization:

	Pollination	Fertilization
1.	Definition: It is transfer of pollen grains from anther to the stigma of a flower.	It is the fusion of male and female gametes.
2.	Step: Pollination precedes fertilization.	Fertilization occurs only after pollination when the pollen grain has germinated and male gametes are carried into ovule.
3.	Purpose: It carries the male gamete production pollen grains to the female sex organ.	It actually brings about fusion of gametes.
4.	Process: Pollination is a physical process.	Fertilization is a physico-chemical (biological) process.
5.	Occurrence: It occurs only in seed plants.	It occurs in both plants and animals of various types.

2.  

1. Site of Fertilization. Embryo sac in ovule.
2. Product of Fertilization. Zygote, Primary endosperm cell.

3.  

	Gamete	Zygote
1.	Formed after meiosis.	Formed after fusion of two gametes.
2.	Has haploid number of chromosomes.	Has diploid number of chromosomes.
3.	Produced by male and female parts.	Formation takes place in female part.
4.	Role in sexual reproduction: Gamete are necessary for sexual reproduction to take place, because zygote cannot be formed without gametes. Brings gene pool from two individuals.	Role in sexual reproduction: Zygote formation is a precursor of embryo formation.

Budding, fragmentation and regeneration are considered as asexual types of reproduction because none of them includes gamete formation and fertilization. All of these give rise to offspring from single parent only.
Regeneration in Planaria It exhibits regeneration i.e. ability to grow the broken body part again. If the body of Planaria is cut into any number of pieces, each piece grows into a complete organism i.e. reproduction through regeneration.
Regeneration is carried out by specialized cells which proliferate and produce large numbers of daughter cells. Different cells from the group of daughter cells then differentiate into various cell types and tissues.

1.  

2. Male gamete forming part: Pollen grain, produced in anther of stamen.

Female gamete forming part: Embryo sac developed inside ovule of ovary part of pistil.

Survival of an individual depends on many factors. An individual can survive if he/ she gets food and shelter. An individual can survive if he/ she is not killed by a predator. An individual can survive if he/ she is not killed by a competitor. In biological sense, an individual can survive if all the life processes continue in the body.
But reproduction creates a new individual and the new individual carries the lineage of the species even after the death of parents. Moreover, a good rate of reproduction ensures a large population which counterbalances mortality in the population. We know that a higher birth rate and lower mortality rate helps in growth of population. If mortality rate becomes more than birth rate, then a population can be wiped out. Thus, reproduction helps in maintaining the stability of a species.

1. Differences between Asexual and Sexual Reproduction:

	Asexual Reproduction	Sexual Reproduction
1.	Parents: It is monoparental.	It is generally biparental.
2.	Meiosis: Meiosis does not occur during asexual reproduction. There are no gametes and no fertilization.	Meiosis occur. Gametes are formed and fertilization occurs in sexual reproduction.
3.	Ex. Binary fission in Amoeba, Budding in yeast.	Ex. Offspring in Wheat, Human.

2. Development of Variation in Sexual Reproduction:

Sexual reproduction produces a number of variations in the population due to:

1. Chance separation of chromosomes at the time of meiosis.
2. Crossing over during meiosis.
3. Chance combination of chromosomes during fertilization. It produces a unique combination of variations already accumulated by each individual in its DNA obtained from its parents,
4. Mutations or defective DNA replication.

Sexualy transmitted diseases: Diseases which spread from one person to another through sexual act are called sexually transmitted diseases. he organisms that cause sexually transmitted diseases may pass from person to person in blood, semen, or vaginal and other bodily fluids.HIV, Gonorrhoea, Herpes, etc. are examples of STDs.
Ways to prevents STDs:

• Use of condoms or other physical barriers.
• Avoiding sexual contacts with unknown partners.
• Avoid sharing towels or underclothing.
• Get a vaccination for hepatitis B. This is a series of three shots.

Ejaculated sperms are the ones which are stored in epididymes. They are formed regularly in seminiferous tubules from where they pass through vasa efferentia into epididymes. At the time of ejaculation, the sperms are first pushed through vasa deferentia, enter ejaculatory duct where they receive secretion of seminal vesicles and then urinogenital duct where the secretion of prostate gland is poured to form semen. The urinogenital duct is lubricated by secretion of a pair of Cowper’s glands (bulbourethral glands).
Secretion of Seminal Vesicles. Nourishment, activation and providing fluid medium for sperm transport.
Secretion of Prostates Gland. Motility of Sperms.