Reproduction in Plants and Animals Online Test 10th Science Lesson 17 Questions in English

“Living organisms cannot survive for an indefinite period on earth. All living organisms have the ability to produce more of its own kind by the process called reproduction. Reproduction is the unfolding of life forms where new individuals are formed. It ensures continuity and survival of the species. This process is to preserve individual species and it is called as self-perpetuation.

In sexual reproduction off springs are produced by the union of male and female gametes (sperm and egg). The male and female gametes contain the genetic material or genes present on the chromosomes which transmit the characteristic traits to the next generation.

There are three types of reproduction in plants namely i) Vegetative ii) Asexual and iii) Sexual reproduction.

In this type, new plantlets are formed from vegetative (somatic) cells, buds or organs of plant. The vegetative part of plant (root, stem, leaf or bud) gets detached from the parent body and grows into an independent daughter plant. It has only mitotic division, no gametic fusion and daughter plants are genetically similar to the parent plant.

Vegetative reproduction may take place through leaves, stems, roots and bulbils.

Leaves: In Bryophyllum small plants grow at the leaf notches.

Stems: In strawberry aerial weak stems touch the ground and give off adventitious roots and buds. When the connections with the parent plant are broken, the offspring become independent.

Root: Tuberous roots (Asparagus and Sweet potato) can be used for vegetative propagation.

Bulbils: In some plants the flower buds modified into globose which are called as bulbils, when these falls on the ground they grow into new plants. e.g. Agave.

Other types of Vegetative Reproduction: Fragmentation, Fission, Budding and Regeneration.

Fragmentation: In filamentous algae breaking of the filament into many fragments is called fragmentation. Each fragment having at least one cell, may give rise to a new filament of the algae by cell division e.g. Spirogyra.

Fission: In this type the parent cell divides into two daughter cells and each cell develops into a new adult organism e.g. Amoeba. Budding: Formation of a daughter individual from a small projection, the bud, arising on the parent body is called budding. e.g. Yeast.Regeneration: The ability of the lost body parts of an individual organism to give rise to an whole new organism is called regeneration. It takes place by specialized mass of cells e.g Hydra and Planaria.

Fission: In this type the parent cell divides into two daughter cells and each cell develops into a new adult organism e.g. Amoeba.

Production of an offspring by a single parent without the formation and fusion of gametes is called asexual reproduction. It involves only mitotic cell divisions and meiosis does not occur. Offspring produced by asexual reproduction are not only identical to parents but are also exact copies of their parent.

Asexual reproduction occurs by spore formation. This is the most common method of asexual reproduction in fungi and bacteria.

Asexual reproduction occurs by spore formation. During spore formation a structure called sporangium develops from the fungal hypha. The nucleus divides several times within the sporangium and each nucleus with small amount of cytoplasm develops into a spore. The spores are liberated and they develop into new hypha after reaching the ground or substratum.

Sexual reproduction is the process in which two gametes (male and female) are fused to produce offspring of their own kind. In such cases both sexes, male and female sex organs are needed to produce gametes.

A flower is a modified shoot with limited growth to carry out sexual reproduction. A flower consists of four whorls borne on a thalamus. These whorls are from outside Calyx – consisting of sepals Corolla – consisting of petals Androecium – consisting of stamens Gynoecium or pistil – consisting of carpels

The two outermost whorls calyx and corolla are non–essential or accessory whorls as they do not directly take part in the reproduction. The other two whorls androecium and gynoecium are known as the essential whorls, because both take part directly in reproduction.

Androecium: Androecium, the male part of flower is composed of stamens. Each stamen consists of a stalk called the filament and a small bag like structure called anther at the tip. The pollen grains are produced in the anther within the pollen sac.

Pollen grain: Pollen grains are usually spherical in shape. It has two layered wall. The hard outer layer is known as exine. It has prominent apertures called germpore. The inner thin layer is known as intine. It is a thin and continuous layer made up of cellulose and pectin.

Mature pollen grains contain two cells, the vegetative and the generative cell. Vegetative cell contains a large nucleus. The generative cell divides mitotically to form two male gametes.

Gynoecium: Gynoecium is the female part of the flower and is made up of carpels. It has three parts: Ovary, Style and Stigma

Androecium, the male part of flower is composed of stamens. Gynoecium is the female part of the flower and is made up of carpels.

The main part of the ovule is the nucellus which is enclosed by two integuments leaving an opening called as micropyle. The ovule is attached to the ovary wall by a stalk known as funiculus. Chalaza is the basal part.

The embryo sac contains seven cells and the eighth nuclei located within the nucellus.

Three cells at the micropylar end form the egg apparatus and the three cells at the chalaza end are the antipodal cells. The remaining two nuclei are called polar nuclei found in the center. In the egg apparatus one is the egg cell (female gamete) and the remaining two cells are the synergids.

Process of sexual reproduction in flowering plants involves: Pollination and Fertilization

The transfer of pollen grains from anther to stigma of a flower is called as pollination.

Importance of Pollination: It results in fertilization which leads to the formation of fruits and seed. New varieties of plants are formed through new combination of genes in case of cross pollination.

Self-pollination (Autogamy): Self-pollination is also known as autogamy. The transfer of pollen grains from the anther to the stigma of same flower or another flower borne on the same plant is known as self-pollination. e.g. Hibiscus.

Advantages of self-pollination: Self-pollination is possible in bisexual flowers. Flowers do not depend on agents for pollination. There is no wastage of pollen grains.

Disadvantages of self-pollination: The seeds are less in numbers. The endosperm is minute. Therefore, the seeds produce weak plants. New varieties of plants cannot be produced.

Cross-pollination is the transfer of pollen from the anthers of a flower to the stigma of a flower on another plant of the same species e.g. apples, grapes, plum, etc.

Advantages of cross pollination: The seeds produced as a result of cross pollination, develop and germinate properly and grow into better plants, cross pollination leads to the production of new varieties. More viable seeds are produced.

Disadvantages of cross-pollination: Pollination may fail due to distance barrier. More wastage of pollen grains. It may introduce some unwanted characters Flowers depend on the external agencies for pollination.

In order to bring about cross pollination, it is necessary that the pollen should be carried from one flower to another of a different plant. This takes place through the agency of animals, insects, wind and water.

The pollination with the help of wind is called anemophily. The anemophilous flowers produce enormous amount of pollen grains. The pollen grains are small, smooth, dry and light in weight. Pollen of such plants is blown off at a distance of more than 1,000 km. The stigmas are comparatively large, protruding and sometimes hairy to trap the pollen grains. e.g. Grasses and some cacti.

Pollination with the help of insects like honey bees, flies are called entomophily. To attract insects these flowers are brightly colored, have smell and nectar. The pollen grains are larger in size, the exine is pitted, spiny etc., so they can be adhered firmly on the sticky stigma.

Approximately, 80% of the pollination done by the insects is carried by honey bees.

Pollination by water: The pollination with the help of water is called hydrophily. This takes place in aquatic plants. Pollen grains are produced in large numbers. Pollen grains float on surface of water till they land on the stigma of female flowers e.g. Hydrilla, Vallisneria.

Pollination by Animals: When pollination takes place with the help of animals, it is called Zoophily. Flowers of such plants attract animals by their bright color, size, scent etc. e.g. sun bird pollinates flowers of Canna, Gladioli etc., Squirrels pollinate flowers of silk cotton tree.

The pollination with the help of wind is called anemophily. E.g. Grasses and some cacti. Pollination with the help of insects like honey bees, flies are called entomophily. The pollination with the help of water is called hydrophily. E.g. Hydrilla, Vallisneria. When pollination takes place with the help of animals, it is called Zoophily. E.g. sun bird pollinates flowers of Canna, Gladioli etc., Squirrels pollinate flowers of silk cotton tree.

One sperm fuses with the egg (syngamy) and forms a diploid zygote. The other sperm fuses with the secondary nucleus (Triple fusion) to form the primary endosperm nucleus which is triploid in nature. Since two types of fusion syngamy and triple fusion take place in an embryo sac the process is termed as double fertilization.

Post fertilization changes: The ovule develops into a seed. The integuments of the ovule develop into the seed coat. The ovary enlarges and develops into a fruit.

The seed contains the future plant or embryo which develops into a seedling under appropriate conditions.

Sexual reproduction involves the fusion of two haploid gametes (male and the female gametes) to form a diploid individual (zygote). Organs of the reproductive system are divided into primary and secondary (accessory) sex organs.

Primary reproductive organs include the gonads (Testes in male and Ovaries in female). Accessory sex organs Male: Vas deferens, epididymis, seminal, vesicle, prostate gland and penis. Female: Fallopian tubes, uterus, cervix and vagina.

The secondary (accessory) sex organs include those structures which are involved in the Process of ovulation, Fusion of the male and female gametes (fertilization), Division of the fertilized egg up to the formation of embryo, Pregnancy, Development of foetus and Child birth.

Testes are the reproductive glands of the male that are oval shaped organs which lie outside the abdominal cavity of a man in a sac like structure called scrotum.

Each testis is covered with a layer of fibrous tissue called tunica albuginea. Many septa from this layer divide the testes into pyramidal lobules, in which lie seminiferous tubules, cells of Sertoli, and the Leydig cells (interstitial cells).

The process of spermatogenesis takes place in the seminiferous tubules. The Sertoli cells are the supporting cells and provide nutrients to the developing sperms.

The Leydig cells are polyhedral in shape and lie between the seminiferous tubules and secrete testosterone. It initiates the process of spermatogenesis.

The ovaries are located on either side of the lower abdomen composed of two almond shaped bodies each lying near the lateral end of fallopian tube. Each ovary is a compact structure consisting of an outer cortex and an inner medulla.

The cortex is composed of a network of connective tissue called as stroma and is lined by the germinal epithelium. The epithelial cells called the granulosa cells surround each ovum in the ovary together forming the primary follicle.

As the egg grows larger, the follicle also enlarges and gets filled with the fluid and is called the Graafian follicle.

The formation of the sperm in male and the ovum in female is called gametogenesis. It involves spermatogenesis (formation of spermatozoa) and oogenesis (the formation of ova). Gametes with haploid cells are produced through gametogenesis.

The spermatozoa consist of head a middle piece and tail. The sperm head is elongated and formed by the condensation of nucleus.

The anterior portion of spermatozoan has a cap like structure called acrosome. It contains hyaluronidase an enzyme that helps the sperm to enter the ovum during fertilization.

The spermatozoan has a short neck connects the head and middle piece which comprises the centrioles. The middle piece contains the mitochondria provides energy for the movement of tail. It brings about sperm motility which is essential for fertilization.

The mature ovum or egg is spherical in shape. The ovum is almost free of yolk. It contains abundant cytoplasm and the nucleus.

The ovum is surrounded by three membranes. The plasma membrane is surrounded by inner thin zona pellucida and an outer thick corona radiata. The corona radiata is formed of follicle cells.

The membrane forming the surface layer of the ovum is called vitelline membrane. The fluid-filled space between zona pellucida and the surface of the egg is called Perivitelline space.

Puberty: The reproductive system in both males and females becomes functional and an increase in sex hormone production resulting in puberty. This phenomenon tends to start earlier in females than in males. Generally boys attain puberty between the ages of 13 to 14 years, while girls reach puberty between 11 to 13 years. In male, the onset of puberty is triggered by the secretion of the hormone testosterone in the testes, in female the secretion of estrogens and progesterone from the ovary.

The secretion of both male and female hormones is under the control of the pituitary gonadotropins luteinizing hormone (LH) and follicle stimulating hormone (FSH).

The cyclic events that take place in a rhythmic fashion during the reproductive period of a woman’s life is called menstrual cycle. In human females the menstrual cycle starts at the age of 11-13 years which marks the onset of puberty and is called menarche, and ceases around 48-50 years of age and this stage is termed menopause.

The reproductive period is marked by characteristic events repeated almost every month in physiologically normal women (28 days with minor variation) in the form of a menstrual flow.

The menstrual cycle consists of 4 phases: Menstrual or Destructive Phase, Follicular or Proliferative Phase, Ovulatory Phase and Luteal or Secretory Phase.

Significance of Fertilization: It stimulates the ovary to develop into fruit. It helps in development of new characters from two different individuals.

Events of Menstrual Cycle and the Role of Hormones

Changes in the ovary and the uterus are induced by the pituitary hormones (LH and FSH) and ovarian hormones (estrogen and progesterone).

Fertilization in human is internal and occurs in the oviduct of the female genital tract. It takes place usually in the ampulla of the fallopian tube. An oocyte is alive for about 24 hours after it is released from the follicle. Fertilization must take place within 24 hours.

The sperm enters into the ovum and fuses with it, resulting in the formation of a ‘zygote’. This process is called fertilization. The zygote is a fertilized ovum.

The first cleavage takes place about 30 hours after fertilization. Cleavage is a series of rapid mitotic divisions of the zygote to form many celled blastula (Blastocyst) which comprises an outer layer of smaller cells and inner mass of larger cells.

Implantation: The blastocyst (fertilized egg) reaches the uterus and gets implanted in the uterus. The process of attachment of the blastocyst to the uterine wall (endometrium) is called implantation.

The fertilized egg becomes implanted in about 6 to 7 days after fertilization.

Gastrulation: The transformation of blastula into gastrula and the formation of primary germ layers (ectoderm, mesoderm and endoderm) by rearrangement of the cells is called gastrulation. This takes place after the process of implantation.

The establishment of the germ layers namely ectoderm, mesoderm and endoderm initiates the final phase of embryonic development.

Organogenesis: During organogenesis the various organs of the foetus are established from the different germ layers attaining a functional state.

Formation of Placenta: The placenta is a disc shaped structure attached to the uterine wall and is a temporary association between the developing embryo and maternal tissues.

Placenta allows the exchange of food materials, diffusion of oxygen, excretion of nitrogenous wastes and elimination of carbon dioxide.

A cord containing blood vessels that connects the placenta with the foetus is called the umbilical cord.

Pregnancy (Gestation): It is the time period during which the embryo attains its development in the uterus.

Normally gestation period of human last for about 280 days. During pregnancy the uterus expands up to 500 times of its normal size.

Parturition (Child Birth): Parturition is the expulsion of young one from the mother’s uterus at the end of gestation. Oxytocin from the posterior pituitary stimulates the uterine contractions and provides force to expel the baby from the uterus, causing birth.

Sometimes ovaries releases two eggs and each is fertilized by a different sperm, resulting in Non-Identical Twins (Fraternal Twins). If single egg is fertilized and then divides into two fetuses, Identical Twins develop.

Lactation: The process of milk production after child birth from mammary glands of the mother is called lactation. The first fluid which is released from the mammary gland after child birth is called as colostrum. Milk production from alveoli of mammary glands is stimulated by prolactin secreted from the anterior pituitary. The ejection of milk is stimulated by posterior pituitary hormone oxytocin.

The milk produced from the breast during the first 2 to 3 days after child birth is called colostrum. It contains immune substances and provides immunity to the new born which is essential for the body.

According to World Health Organization (WHO) reproductive health means a total well-being in all aspects of reproduction, ability to reproduce and regulate fertility, women's ability to undergo pregnancy and safe child birth, maternal and infant survival and well-being.

Family welfare program: The National Family Welfare Programme is a comprehensive scheme which includes: Maternal and child health care (MCH) Immunization of mothers, infants and children. Nutritional supplement to pregnant women and children. Contraception with health education, to motivate couples to accept contraceptive methods and to have small family norms which improve economic status, living status and the quality of life.

Reproductive and Child Health Care (RCH) Programme: It has integrated all services which include Pregnancy and child birth , Postnatal care of the mother and child, Importance of breast feeding and Prevention of reproductive tract infections and sexually transmitted diseases.

Population explosion defined as the sudden and rapid rise in the size of population especially human population. Realizing the dangers inherent in population growth, the Government of India has taken several measures to check population growth and introduced family planning. India has been one of the first countries in the world to launch the nation-wide family planning program in 1952.

Contraception is one of the best birth control measures. A number of techniques or methods have been developed to prevent pregnancies in women. The devices used for contraception are called contraceptive devices.

Barrier Methods: This method prevents sperms from meeting the ovum. Its entry into the female reproductive tract is prevented by barrier. Condom: Condom prevents deposition of sperms in the vagina. Condoms are made of thin rubber or latex sheath. Condom also protect against sexually transmitted diseases (STD) like syphilis, AIDS. Diaphragm (Cervical cap): Vaginal diaphragm fitting into the vagina or a cervical cap fitting over the cervix. This prevents the entry of sperms into the uterus.

Hormonal Methods: Hormonal preparations are in the form of pills or tablets (contraceptive pills). These hormones stop (interfere with ovulation) the release of egg from the ovary.

Intra-Uterine Devices (IUDs): The intrauterine device (IUD) is contraceptive devices inserted into the uterus. There are two synthetic devices commonly used in India are Lippe’s Loop and Copper-T made of copper and plastic (non-irritant). This can remain for a period of 3 years. This reduces the sperm fertilizing capacity and prevents implantation. This also helps to give adequate time interval between pregnancies.

Surgical contraception or sterilization techniques are terminal methods to prevent any pregnancy. This procedure in males is vasectomy (ligation of vas deferens) and in females it is tubectomy (ligation of fallopian tube). These are methods of permanent birth control.

Many diseases affect both women and men, but a few diseases occur at a higher frequency in woman. Women are susceptible to UTI from the bacteria that are present on skin, rectum or vagina. This will enter the urethra, before moving upwards. The types of UTI are: Cystitis or Bladder infection, Kidney Infection and Asymptomatic Bacteriuria.

Hygiene is the practice of healthy living and personal cleanliness. Personal hygiene is caring of one’s own body and health. Social hygiene is proper care of the surrounding environment. The main aspect of hygiene is body hygiene, food hygiene, sanitary hygiene and hygienic environment.

The following measures can ensure toilet hygiene: The floors of the toilet should be maintained clean and dry. This helps to reduce the bad odor and also infection. Toilet flush handles, door knobs, faucets, paper towel dispensers, light switches and walls should be cleaned with disinfectants to kill harmful germs and bacteria. Hands should be washed thoroughly with soap before and after toilet use.

Every year May 28 is observed as Menstrual Hygiene day to make girls and women aware of maintaining menstrual hygiene and importance of menstrual hygiene for good health. By way of awareness through films discussions and campaigns menstrual hygiene has taken quite the center stage in recent days.

The menstrual hygiene scheme to provide subsidized sanitary napkins was launched by the Health ministry in 2011. In Tamil Nadu, UNICEF has developed an affordable incinerator that uses firewood to handle sanitary napkin waste at schools and special wells are equipped where sanitary napkins are composted.