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Describe sexually transmitted diseases and mention the ways to prevent them.

Ans.
Sexually transmitted diseases/venereal diseases/ reproductive tract infections. STDs are infectious diseases transmitted by sexual intercourse and bodily fluids such as semen, blood etc. Few STDs and their causative organisms

DISEASE                                                                                           CAUSATIVE ORGANISM
AIDS (acquired immune deficiency syndrome)                                  HIV (human immunodeficiency virus)
GONORRHOEA                                                                                 Neisseria gonorrhoea
SYPHILIS                                                                                           Treponema pallidum
GENITAL HERPES                                                                             Herpes simplex virus 

Preventive measures:
(I) avoid sex with multiple partners
(ii) avoid unprotected sexual activities and maintain personal hygiene.
(iii) stop sharing needles, as there are chances for the transition of bodily fluids.

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Reproduction is essentially a phenomenon that is not for survival of an individual but for the stability of a species. Justify.

Ans.

Reproduction is the process of production of organisms of its own kind and maintaining continuity generations after generations. Reproduction produces offspring's which are with some similarities and variations with parents due to genetic recombination occurred during gamete formation by crossing over and independent assortment and fertilization of male and female gametes. Such variation ensures them to overcome struggles such as competition for natural resources, habitation, predation etc.

Therefore, reproduction not only restores the number of individuals removed from the species by above mentioned natural forces but also maintain heredity of genetic characters and introduction of variations, as needed for continuity and stability of a species.   

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How does fertilization take place? Fertilization occurs once in a month. Comment.

Ans.

The sperms released during sexual intercourse enter through the vagina and travel upwards and reach the oviducts which is the site of fertilization, where they fuse with the egg forming zygote which gets implanted in the uterus. Millions of sperms are released during ejaculation at the sexual intercourse, but only one sperm gets to fuse with the ovum. Ovulation release of ovum from ovary occurs only once in a month on 14th day of the menstrual cycle. Hence fertilization can occur only once in a month.

 

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What are various ways to avoid pregnancy? Elaborate any one method.

Ans.

Various ways to avoid pregnancy:

Natural methods
(a) Periodic abstinence - abstain from sexual intercourse during the fertile period (10-17 day of the menstrual cycle)
(b) Lactational amenorrhea - ovulation generally will not occur during the period of intense lactation.

Barrier methods
(a) Condoms - made of thin rubber latex sheath, prevents ejaculated sperms from reaching the uterus.
(b) Other barrier methods are diaphragms, cervical caps, and vaults

Intrauterine devices – These are devices inserted into the uterus by doctors or trained nurses through the vagina. These are of different types such as non-medicated (lippes loop), copper releasing (Cu T, multi-load 375), hormone-releasing (Progestasert, LNG-20).

Oral contraceptive pills – Oral administration of small doses of progesterone – estrogen combination in the form of pills, eg. Saheli.

Surgical methods - Vasectomy (vas deference are cut and tied ensuring the absence of sperms in semen), tubectomy (fallopian tubes are cut and tied preventing ovum reaching uterus).

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What is placenta? Mention its role during pregnancy?

Ans.

The placenta is formed by outer layer trophoblast of embryo and endometrium. It starts to form after implantation of blastocyst around 12 weeks of pregnancy. It is a disc-like structure formed by interdigitation of maternal tissue and chorionic villi of embryonal tissue forming a structural unit referred to as placenta.

Placenta serves to provide nutrients and oxygen from the mother's blood to embryo and also removes waste generated by the embryo. The fetus and placenta are connected by the umbilical cord.

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Draw the diagram of a flower and label the four whorls. Write the names of gamete producing organs in the flower.

Ans

Four whorls of a flower are   

  • CALYX- Sepals
  • COROLLA- Petals
  • ANDROECIUM- male reproductive structure, stamens.
  • GYNOECIUM- female reproductive structure, pistil.

Gametes producing organs:

  • Anthers (Part of androecium) - male gametes   
  • Ovary (Part of gynoecium) - female gamete

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Distinguish between a gamete and zygote. Explain their roles in sexual reproduction.

Ans

ROLE OF GAMETES AND ZYGOTE IN SEXUAL REPRODUCTION:
Gametes are the product of meiosis and hence carry half the chromosome number as that of parent cells. This chromosome number is restored during fertilization and zygote formation. Hence, gamete and zygote are the two phases of sexually reproducing organisms that help maintain the constant chromosome number in each species.

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Distinguish between pollination and fertilization. Mention the site and product of fertilization in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule.

Ans

Site of fertilization is female gametophyte (embryo sac) inside an ovule. Products of fertilization are zygote formation, the transformation of ovule into seeds, ovary into fruits.

 

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Write two points of difference between asexual and sexual types of reproduction. Describe why variations are observed in the offspring formed by sexual reproduction.

Ans.

Variations are seen in sexual reproduction because of the fusion of genetically different gametes- fertilization. Gametes are formed by meiosis where there is an event termed crossing over which leads for genetic recombination. Even independent assortment of gametes is also responsible for variations in sexual reproduction.

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Why budding, fragmentation and regeneration all are considered as asexual types of reproduction? With neat diagrams explain the process of regeneration in Planaria.

Ans.

Asexual reproduction is uniparental and it does not involve gamete formation and fertilization. As fragmentation, budding and regeneration none of these involves gamete formation & fertilization, and all of them produce individuals from single parents only hence these are considered as asexual reproduction.

Regeneration is asexual reproduction in which organism has the ability to regenerate the lost (or) damaged body parts, for example, if a planarium is cut into small pieces then each piece develops into a new individual.

 

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