Life Processes in Living Organisms Part - 2

 

Life Processes in Living Organisms Part - 2

Ä Formation of new organisms of same species by earlier existing organism is called as reproduction.

Ä Reproduction is one of the various important characters of living organisms.

Ä It is one of the reasons for evolution of species.

Ä Reproduction occurs mainly by two methods : Asexual reproduction and Sexual reproduction.

Ä Asexual Reproduction:

o   Process of formation of new organism by an organism of same species without involvement of gametes is called as asexual reproduction.

o   Absence of genetic recombination is a disadvantage, whereas fast process is advantage of this reproductive method.

Ä Asexual reproduction in unicellular organisms:

Ä Binary fission

o   In this process, the parent cell divides to form two similar daughter cells.

o   Binary fission occurs either by mitosis or amitosis.

o   Axis of fission/division is different in different protists.

Ä Multiple Fission

o   Asexual reproduction by multiple fission is performed by Amoeba and other similar protists.

o   Many nuclei are formed by repeated nuclear division in the cyst.

o   It is followed by cytoplasmic division and thus many amoebulae are formed.

o   Cyst breaks open on arrival of favourable condition and many amoebulae are released.

Ä Budding

o   Asexual reproduction occurs by budding in yeast - unicellular fungus.

o   Yeast reproduces by mitotic division.

o   A small bulge appears on the surface of the parent cell.

o   This bulge is actually a bud. One of the two daughter nuclei enters this bud.

o   After sufficient growth, bud separates from the parent cell and starts to live independently as a daughter yeast cell.

Ä Asexual reproduction in multicellular organisms:

Ä Fragmentation

o   In this type of reproduction, the body of parent organism breaks into many fragments and each fragment starts to live as an independent new organism.

·        e.g. Spirogyra and Sycon

Ä Regeneration

o   Under certain situation, an animal- Planaria breaks up its body into two parts and thereafter each part

Ä regenerates remaining part of the body. Thus, two new Planaria are formed. This is called as Regeneration.

Ä Budding:

o   Hydra reproduces with this process under specific conditions.

o   An outgrowth is formed by repeated division of regenerative cells of body wall.

o   This bud formed grows progressively and finally forms small Hydra.

Ä Vegetative Propagation:

o   Reproduction in plants with the help of vegetative parts like root, stem, leaf and bud is called as vegetative reproduction. e.g. Bryophyllum, carrots and raddish.

Ä Spore formation:

o   Fungi like mucor have filamentous body. They have sporangia.

o   Once spores are formed sporangia bursts and spores are released.

o   Spores germinate in moist and warm place and new fungal colony is formed.

Ä Sexual Reproduction - Sexual reproduction always occur with the help of two germ cells : female gamete and male gamete.

Ä Two main processes occur in the sexual reproduction

o   Gamete formation - Haploid gametes are formed by meiosis.

o   Fertilization - A diploid zygote is formed in this process by union of haploid male and female gametes. This zygote divides by mitosis and embryo is formed. The embryo develops to form new individual.

Ä Sexual reproduction in plants:

o   A flower is the structural unit of sexual reproduction in plants.

o   A flower consists of four floral whorls as calyx, corolla, androecium and gynoecium.

o   Androecium and gynoecium are called as essential whorls.

o   Calyx and corolla are accessory whorls.

o   Androecium is male whorl and its members are called as stamens.

o   Gynoecium is female whorl and its members are called as carpels.

o   Ovary is present at the basal end of carpel.

o   A hollow style comes up from the ovary.

o   Stigma is present at the tip of style.

o   Ovary contains one or many ovules.

o   Embryo sac formed in each ovule consists of a haploid egg cell and two haploid polar nuclei.

Ä Transfer of pollen grains from anther to stigma is called as Pollination.

Ä Pollination occurs with the help of biotic and abiotic agents.

Ä Pollen grains germinate and fall on sticky stigma.

Ä Pollen tube carries male gametes which reaches the embryo sac via style.

Ä One male gamate unites with egg cell to form Zygote.

Ä This process is called fertilization.

Ä Second male gamate unites with two polar nuclei and endosperm is formed. This process is called double fertilization.

     Ä Sexual reproduction in human beings:

     Ä Human male reproductive system:

§  Male reproductive system of human consists of testes, various ducts and glands.

§  Testes present in the scrotum outside the abdominal cavity, contains numerous seminiferous tubules.

§  Germinal epithelium present in tubules divide by meiosis to produce sperms.

§  Sperms travel through sequence from testes, vas eferens, epididymis, vas deferens, ejaculatory duct and lastly to urinogenital duct.

§  Seminal vesicles secrete their secretion in ejaculatory duct and prostate gland and cowper’s glands secrete their secretion in urinogenital duct.

§  Semen is a mixture of sperms and these secretions.

§  Semen is ejaculated through penis.

o   Human female reproductive system

§  Female reproductive system includes a pair of ovaries, a pair of oviducts, single uterus and a vagina.

§  A pair of bulbo-urethral gland is present.

§  An ovum is released every month in the abdominal cavity alternately from each ovary.

§  The oviduct which is funnel shape has a free end through which the oocyte enters it.

§  Cilia present on the inner surface of the oviduct push the oocyte towards the uterus.

o   Gamete formation

§  Both gametes i.e. sperm and ovum are formed by meiosis.

§  Sperms are produced in testes of men from beginning of maturation till death.

§  2 - 4 million immature oocytes are present in the ovary from the time of birth.

§  An oocyte matures and is released every month and stops at the age of menopause (i.e. 45 years)

o   Fertilization

§  Formation of zygote by union of sperm and ovum is called as fertilization.

§  It is internal in humans.

§  Semen is ejaculated in vagina during copulation and sperms start their journey from vagina-uterus- oviduct.

§  One of the few million sperms fertilize the only ovum present in the oviduct.

§  From the age of puberty upto menopause, an ovum is released every month.

§  Only 400 oocytes are released and rest undergo degeneration.

Ä Development and Birth

Ä The zygote formed after fertilization in the oviduct, undergoes repeated mitotic divisions and embryo

·        is formed.

Ä Embryo is then implanted in uterus for further development.

Ä Placenta is formed for supply of food material from mother to the body.

Ä Embryonic development is completed approximately within nine months after the fertilization.

Ä Menstrual cycle

Ä Female reproduction system undergoes some changes at puberty and those changes repeat at the interval of every 28 - 30 days. This repetitive changes are called as menstrual cycle.

Ä It is controlled by four hormones : follicle stimulating hormone (FSH), luteinizing hormone [LH], estrogen and progesterone.

Ä One of the follicles in the ovary starts to develop along with oocyte in presence of FSH.

Ä This developing follicle secretes estrogen.

Ä Endometrium of uterus starts to develops in presence of estrogen.

Ä Developed follicle bursts in presence of LH and oocyte is released. This is called as ovulation.

Ä Remaining tissue of follicle forms the corpus luteum.

Ä Corpus luteum secrets Progesterone.

Ä Endometrial glands secrete their secretion in presence of progesterone and such endometrium is ready for implantation.

Ä If oocyte is not fertilized within 24 hours, corpus luteum becomes inactive and transforms into corpus albicans and secretion of estrogen and progesterone stops.

Ä Endometrium degenerates in absence of these hormones.

Ä Tissues of endometrium and unfertilized ovum are discarded through vagina accompanied with

·        continuous bleeding. This is called menstruation and continues for five days.

Ä Menstrual cycle is a natural process.

Ä Reproduction and modern technology

Ä Many couples cannot have child due to various reasons.

Ä But now with the help of advanced medical techniques like IVF, Surrogacy, Sperm bank, the childless couples can have a child.

Ä In IVF, fertilization is brought about in a test tube and embryo formed is implanted in uterus of woman at appropriate time.

Ä In surrogacy, oocyte is collected from woman having problem in implantation and sperms are collected from her husband and fertilized in the test tube.

Ä The embryo thus formed is implanted in uterus of some other woman having normal uterus. Such a woman is called as a surrogate mother.

Ä Just as women, men also face issue with sperm production.

Ä A new concept of sperm bank has been introduced.

Ä Semen is collected from desired men and stored in the sperm bank

Ä Twins.

Ä When two embryos develop simultaneously in the same uterus and thus two offsprings are delivered simultaneously. Such offsprings are called as Twins.

Ä They are of two types: monozygotic twins and dizygotic twins.

Ä Monozygotic twins are exactly similar to each other and their gender is also same.

Ä Dizygotic twins are formed from two separate oocytes and sperms so they are genetically different and may be of same or different gender.

Ä Reproductive Health

Ä A person’s state of being physical, mental and social strength is called health.

Ä Occurrence of menstrual cycle is related with reproductive and overall health of women.

Ä Some problems regarding reproductive health may arise in men too.

Ä Therefore, it is essential to maintain cleanliness of their genitals in order to protect themselves from various sexual diseases, syphilis and gonorrhea which are caused by bacteria.