Notes-Class 10-Science & Technology-2-Chapter-3-Life Processes In Living Organisms-2-Mah. Board

Topics to be learn : Reproduction: Asexual and Sexual reproduction Reproduction and modern technology. Reproductive health. Population Explosion.

Introduction :

Important life processes in living organisms:

All those life processes i.e. nutrition, respiration, excretion, sensation & response (control & co-ordination), etc. are essential to each living organism to remain alive.

• Reproduction is also a one more life process but it does not help the organism to remain alive but it helps to maintain the continuity of the species of that organism.

Essential life processes for production of energy required by body :

• Respiration, circulation and nutrition are the life processes that are essential for production of energy required by body.
• Oxygen is supplied to cells by respiratory and circulatory system.
• The oxidation of nutrients that are absorbed in body is done because of oxygen supplied to cells.
• This helps in liberation of energy.

Mitosis and meiosis :

• Mitosis and meiosis are the main types of cell division.
• In mitosis, the chromosome number remains the same. Two daughter cells are obtained from one cell.
• In meiosis, the chromosome number is reduced to half. From one cell, four daughter cells are obtained.

Role of chromosomes in cell division :

Due to chromosomes, the DNA from parental cells enter into daughter cells. The hereditary characters are transmitted to next generation by cell division.

• In picture ‘a’ vegetative propagation is shown. The twig is planted and it is showing rootlets. This indicates that new plant is being produced.
• In picture ‘b’ hen is laying eggs.
• In picture ‘c’ the seed is germinating and has produced radicle and plumule.
• In picture ‘d’ cell division or binary fission similar to mitosis is shown.
• All the pictures, show different types of reproduction.

Reproduction : Asexual and Sexual :

• Reproduction is formation of new offspring of same species by earlier existing parent organism.
• Reproduction is important character of living organisms.
• Evolution of every species occurs due to reproduction.

Maintenance of species : Maintenance of species means a species undertakes successful reproduction and produces individuals of its own kind. This keeps the species existing on the earth, The new organism produced from the old one is not genetically exactly similar to the parents. In meiotic cell division there is crossing over in the homologous Chromosomes, This produces genetic recombination. Thus the new organism is different from the earlier one, However, if the reproduction its of asexual type, then the young one Is exactly similar to the parents. The type of reproduction, whether it is Asexual or sexual, the type of crossing over, the extent of genetic recombination, etc. determine the similarity among the parent organisms and their offspring. Based on this genetic recombination the two organisms of a species do not show exact similarity. However, In case of monozygotic twins there is exact similarity, In asexual reproduction too there is similarity, Relationship between the cell division and formation of new organism of same species by earlier existing organism : In the process of reproduction, there is division of chromosomes, Due to cell division, the gametes are formed. The union of gametes produce new offspring. In sexual reproduction, all these processes take place due to cell division. In asexual reproduction too there is cell division. Growth of new organism also occurs due to cell divison.

Two main types of reproduction: Asexual reproduction and sexual reproduction.

Asexual reproduction :

Asexual reproduction is uniparental reproduction in which there is no formation of gametes.

• New organism is formed without the fusion of the gametes.
• The offspring produced is exactly similar to the parent organisms.
• It takes place by mitotic cell division.
• Demerit of asexual reproduction : Absence of genetic recombination.
• Merit of asexual reproduction : Rapid process of reproduction.

Sexual Reproduction :

Reproduction with the help of male and female gametes is called sexual reproduction. It has two main processes, viz. gamete formation and fertilization.

• Gamete formation: By meiosis the gametes are formed. The diploid germ cells give rise to haploid gametes.
• Fertilization : From union of haploid male and a female gamete a diploid zygote is formed during fertilization. Subsequent mitotic divisions of zygote form embryo which then develops into new individual.

Two parents i.e. male parent and female parent are involved in this type of reproduction.

• Male parent produces male gamete or sperm and the female parent produces female gamete or ovum.
• The fusion of these forms zygote.
• Zygote has recombined genes of both the parents. Hence, the offspring shows some Similarities and some differences in the parental characters.
• Genetic variation gives rise to diversity in living organisms. Those genetic variations that are helpful for adapting to the environment are retained. Such individuals exist and do not become extinct.

Know This : If meiosis does not happen the gametes produced will be diploid. Diploid (2n) gametes if united, they will form 4n, i.e. tetraploid variety. Such zygote will show severe abnormality. The chromosome number will not be maintained.

Sexual reproduction in plants :

Flower is structural unit of sexual reproduction in plants

• There are total four floral whorls. Of these two are accessory floral whorls while two are essential floral whorls.
• Calyx and corolla are accessory whorls. They are protective in nature.
• Members of calyx are known as sepals. They are usually green in colour. They protect the inner whorls.
• The members of corolla are called petals. They can be of different colours.
• Androecium and gynoecium are essential whorls as they participate in sexual reproduction.
• The male whorl androecium is made up of stamens. Each stamen has a filament with anther located at the upper end. In the anther there are four locules. Inside the locules the meiosis takes place forming pollen grains. During suitable time, the pollen grains are released from anther lobes.
• Gynoecium is made up of carpels, either in separate form or are united. Each carpel is formed of ovary at the basal end, hollow ‘style’ and the stigma at the tip of style. There are one or many ovules inside the ovary.

Bisexual flowers : In bisexual flowers both androecium and gynoecium are located in the same flower. e.g. Hibiscus.

Unisexual flowers : In unisexual flowers, androecium is present in male flowers and gynoecium is present in the female flowers, e.g. Papaya.

Pollination : Transfer of pollen grains from anther to stigma is called pollination.

Agents of pollination :

• Abiotic agents : Wind, water.
• Biotic agents : Insects, birds or other animals.

Types of pollination :

• Self-pollination : Pollination involves only one flower or two flowers borne on same plant.
• Cross-pollination : Involves two flowers borne on two plants of same species.

In artificial pollination for forming new high yielding and resistant varieties of plants, the pollination with the help of brush, is done by scientists.

Fertilization :

• Pollens fall upon sticky stigma and germinate.
• A long pollen tube and two male gametes are formed upon germination.
• The pollen tube carrying male gametes travels through style and reaches the embryo sac.
• In embryo sac, tip of the pollen tube bursts releasing two male gametes.
• Here fertilization occurs by union of one male gamete and egg cell.
• Second male gamete unites with two polar nuclei. This union forms endosperm.
• Since two nuclei take part in the process, it is called double fertilization.

Germination :

• The development of new plantlet from zygote after fertilization is called germination.

• After fertilization ovule develops into seed and ovary into fruit.
• Seeds from broken fruits fallen upon the ground start germinating if they get favourable conditions.
• Development takes place due to food stored in endosperm of seed.

Sexual reproduction in human being :.

Sex determination:

• Sex is determined according to the sex chromosomes,
• Human males have 44 somatic chromosomes and XY sex chromosomes.
• Human females have 44 somatic chromosomes and XX sex-chromosomes.
• Due to particular sex chromosomal complement, the masculine reproductive system or feminine reproductive system is developed.

Hormones :

• Pituitary gland secretes FSH and LH. LH is known as ICSH in males, as its function in the male body is different.
• From the gonads of male and female, hormones are secreted which are essential for male and female reproductive functions respectively.
• These hormones are testosterone secreted from testis in males and estrogen and progesterone secreted from the ovaries in females.
• Testosterone is essential for masculinity as well as for sperm production
• Female hormones estrogen are essential for changes in the female body leading to motherhood.

Why has the Government of India enacted the law to fix the minimum age of marriage as 18 in girls and 21 in boys?

Formation of gametes :

• Sperm from father and ovum from mother are haploid gametes formed by meiosis.
• Man can produce sperms from puberty till death.
• But in a woman the function of reproductive system stops at menopause.
• In mature woman a single matured oocyte is released from ovary every month.
• In woman’s body from birth, there are 2 – 4 million immature oocytes in the ovary of female foetus. Till the age of 45 years woman can produce ova.
• Later she attains menopause due to lessened secretion of female hormones. The reproductive functions then completely stop.

Fertilization :              

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

• There is internal fertilization in humans in which semen is deposited in vagina during intercourse. In the semen there are few millions of sperms. They swim from vagina through uterus and reach fallopian ducts. Only one sperm is required for fertilizing a single ovum that female produces.
• Women with advanced age have Strong chance of conceiving abnormal child. The ova that develop around menopausal age are 45-50 years old and hence they can be abnormal due to faulty meiosis. If such ovum is fertilized there are increased chances of getting genetically abnormal child. e.g. Down’s syndrome or Turner's syndrome.

Development and Birth :

• The fertilization takes place in fallopian duct. The zygote thus formed undergoes rapid and repeated mitotic divisions to develop embryo.
• It travels from fallopian tubes to uterus. In uterus it gets implanted and grows for next 40 weeks or 9 months.
• The nutrition during this period is provided by placenta which is an organ developed in pregnant mother.
• After completion of embryonic development for 9 months the pregnant mother gives birth to a baby.

Hormone oxytocin : The hormone oxytocin is released from the posterior pituitary of mother once the foetal, development is completed. Due to oxytocin, uterus contracts involuntarily and the baby is expelled out. Thus initiation of birth process is possible due to contractions of uterus.

Sex determination in human beings:

• The gametes develop from germ cells which are diploid (2n).
• Each diploid cell has 22 pairs of autosomes and 1 pair of sex-chromosomes i.e. (44 + XX or 44 + XY).
• Germ cells undergo meiosis forming haploid (n) gametes having chromosomal combination of 22+ X or 22+ Y.
• Sperms produced are of two types viz. (22 + X) or (22 + Y) but ova/oocytes are all (22 + X) types.
• Sperms complete process of meiosis before they leave male reproductive tract. But the oocytes complete meiosis after ovulation, i.e. only if they are fertilized.
• Type of sperm of father decides the sex of the child. If X bearing sperm fertilises the oocyte, the girl is born and if Y bearing sperm fertilises oocyte, it’s a boy. Mother has all X bearing oocytes, hence she is neutral in sex determination of the child. Thus mother is not responsible for the sex of child.

Girls are equal to boys in every aspect, therefore, female foeticide should be stopped. It is a crime to kill the unborn girls.

Reproduction and Modern Technology :

Some couples want a child but they are not able to bear one due to various problems either in mother or in father. In such cases modern techniques such as IVF, surrogacy and sperm bank are useful in conceiving a child.

Causes of sterility :

• Causes of sterility in females : In Woman if there are problems like irregularity in menstrual cycle, difficulties in oocyte production or implantation in uterus, obstacles in the oviduct, etc. then she can resort to any one technique of the above.
• Causes of sterility in males :  In man if there are no sperms in the semen, slow movement of sperms, or anomalies in the sperms then he becomes sterile.

Modern reproductive technologies :

(i) In Vitro Fertilization : This is the technique in the modern medical field where childless couples can be blessed by their own child.

• IVF technique is used for childless couples who are faced with problems such as less sperm count, obstacles in oviduct, etc.
• The IVF technique is done by removing the oocyte from the mother and artificially fertilizing by the sperms collected from father. This fertilization is done in a test-tube. Thus it is also called test tube baby. The embryo formed is implanted in uterus of real mother or a surrogate mother at appropriate time.

(ii) Surrogacy :

• In Woman if there is problem regarding the implantation of embryo in uterus, then help of another women is taken. This women is called surrogate mother.
• Oocyte from real mother is taken out and fertilized with sperms collected from her husband. These gametes are fertilized outside in a test-tube and then the fertilized zygote is implanted in the surrogate mother.

(iii) Sperm Bank / (IVF) Semen Bank :

If man has problems with the sperm production, then the sperms are collected from the sperm bank. Sperm bank is the place where the donor’s donate the sperms and such sperms are kept stored. The donor’s identity is kept secret and he should also be physically and medically fit person.

Reproductive health :

• The physical, mental and social well-being is called health.
• In India, there is lack of awareness about reproductive health. Social customs, traditions, illiteracy, shyness, etc. keep the society under pressure. There is always indifference towards the reproductive health of women.
• Reproductive health can be achieved by keeping genitals clean.
• Syphilis and gonorrhoea are sexually transmitted or bacterial venereal diseases which affect people on a large scale.
• Symptoms of syphilis : Occurrence of chancre (patches) on various parts of body including genitals, rash, fever, inflammation of joints. alopecia, etc.
• Symptoms of gonorrhoea : Painful and burning sensation during urination, oozing of pus through penis and vagina, inflammation of urinary tract, anus, throat, eyes, etc.

Population Explosion :

• Within a short duration if there had been excessive growth of population, then it is called population explosion.
• Population is growing by leaps and bounds in India. The problems due to population explosion are unemployment, decreasing per capita income and increasing loan, stress on natural resources, etc.
• For population control, therefore in India, family planning is a must.