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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 kind and maintaining continuity generations after generations. Reproduction produces offspring which are some similarities and variations with parents due to genetic recombination occurring during gamete formation by crossing over and independent assortment and fertilization of male and female gametes. Such variation ensures they 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 maintains the heredity of genetic characters and the introduction of variations, as needed for the continuity and stability of a species.   

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

Ans.

The sperm 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 sperm are released during ejaculation during sexual intercourse, but only one sperm gets to fuse with the ovum. Ovulation release of ovum from the ovary occurs only once a month on the 14th day of the menstrual cycle. Hence fertilization can occur only once a month.

 

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

Ans.

Various ways to avoid pregnancy:

Natural methods
(a) Periodic abstinence - abstain from sexual intercourse during the fertile period (10-17 days 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, prevent 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 (lippies loop), copper-releasing (Cu T, multi-load 375), and 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 deferens are cut and tied ensuring the absence of sperms in semen), tubectomy (fallopian tubes are cut and tied preventing ovum from reaching the uterus).

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What is placenta? Mention its role during pregnancy?

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

The placenta serves to provide nutrients and oxygen from the mother's blood to the 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

Gamete Zygote
Formed post meiosis. Formed due to the fusion of two gametes.
The gamete produced comprises the haploid number of chromosomes. The zygote produced comprises the diploid number of chromosomes.
Gametes are produced in both male and female bodies. In males as sperm, and in females as an egg. Generally, the formation of a zygote occurs within the bodies of females, like in mammals.
   

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.

Draw the diagram of the longitudinal section of a flower showing growth of pollen tube. Label the parts of the embryo sac. [2 marks]

Labelled diagram of pistil showing pollen tube growth and its entry into the ovule

The site of fertilization is the female gametophyte (embryo sac) inside an ovule. Products of fertilization are zygote formation, the transformation of the 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.

Asexual Reproduction Sexual Reproduction
Occurs in certain eukaryotic unicellular and multicellular creatures, lower invertebrates, plants, and prokaryotic microbes. Occurs almost in all types of multicellular organisms including humans, animals, and higher plants.
Uniparental. It is usually bi-parental.
Gametes are not formed. Gametes are formed.

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 to genetic recombination. Even an independent assortment of gametes is also responsible for variations in sexual reproduction.

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

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

Regeneration is asexual reproduction in which an organism can 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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