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Class 10 science chapter 7 how do organisms reproduce notes

                                                                                     CLASS 10

                                                                      How do organisms reproduce

Reproduction –

Reproduction is the biological process by which living organisms produce new individuals of the same species, ensuring the continuation of their species over generations.

It serves several important purposes:

Survival of the Species: Reproduction is necessary for the survival of a species. Without reproduction, a species would eventually become extinct because individuals die over time, and if no new individuals are born, the population would dwindle to zero.

Do organisms create exact copies of themselves?

Organisms do not typically create exact copies of themselves through reproduction. Instead, they produce offspring that inherit genetic information from their parents, resulting in similarities but not perfect copies.

Chromosomes in the cell contain the information for the inheritance of features which are passed from generation to generation in the form of DNA molecules. So reproduction involves copying of DNA and other cell apparatuses. The copies will be similar to the original and not identical.

This property is variation which is the basis and necessary for the evolution of living beings. Variations help the species to withstand drastic environmental changes, thus saving the species from becoming extinct and promoting its survival for a longer time.

There are two types of reproduction –

1. Asexual Reproduction –

       In this reproduction only a single parent is involved.

  • Typically results in genetically identical offspring, known as clones, because they inherit all their genetic material from a single parent.
  • Common in simple organisms such as bacteria, fungi, some plants, and some animals (e.g., certain species of insects and reptiles).
  • Asexual reproduction can occur through various mechanisms, including binary fission, budding, fragmentation, and vegetable propagation.

2. Sexual Reproduction

       In this reproduction, two parents male and female both are involved.

  •    Involves the fusion of specialized reproductive cells (gametes) from two parent organisms, typically a male and a female.
  • Common in complex multicellular organisms, including most animals and many plants.
  • Offspring are not genetically identical to their parents or each other, which can lead to variations in traits within a population.

Modes of Reproduction used by Asexual reproduction –

1. Fission –

Binary Fission – This is a common mode of asexual reproduction in single-celled organisms, such as bacteria and some protozoa. In binary fission, the parent cell divides into two genetically identical daughter cells. In organisms such as amoeba, the splitting of two cells during division can take place in any plane.

Binary Fission in Leishmania –

Multiple Fission –

The malarial parasite, Plasmodium, divides into many daughter cells by multiple fission.

Fragmentation –

Fragmentation is a mode of asexual reproduction in which a multicellular organism breaks into two or more parts, and each fragment can regenerate into a new individual. This process is common in organisms like flatworms, starfish, and some plants (e.g., certain species of algae and mosses).

 Ex- Fragmentation in Spyrogyra

Regeneration –

In some organisms, regeneration is a form of asexual reproduction. In this method, the cut parts of the body of an organism give rise to new individuals. Ex- Regeneration in planaria.

Budding –

Budding is a form of asexual reproduction seen in many multicellular organisms, including some animals (like hydra and yeast) and some plants (like certain fungi). In budding, a small outgrowth or bud forms on the parent organism and eventually detaches to become a new individual. The offspring is genetically identical to the parent.

Vegetative Propagation –

This is a type of vegetative reproduction carried out by humans in the fields and laboratories. The most common types of vegetative reproduction occurring artificially include:

 Cutting

In this, a part of a plant, specifically a stem or leaf is cut and planted in the soil. These cutting parts will grow in soil. The new plant is formed from the modified roots developing from the cutting. Ex – rose

Grafting

In this, the cutting from some other plant is attached to the stem of a plant rooted in the ground. The tissues of the graft become integrated with the tissues of the rooted plant and develop as a single plant over time. Ex – Mango

Layering

In this, the stem of the plant is bent to the ground and covered with soil. Adventitious roots emerge from the plant parts covered with the soil. This attached stem with developing roots is known as a layer. Ex – Jasmine

Tissue Culture

In this, the plant cells from different parts of a plant are cultured in the laboratory to develop a new plant. This technique is helpful in increasing the number of rare and endangered plant species that are unable to grow under natural conditions. Ex – Orchids, ornamental plants.

Benefits of Vegetative Propagation

  1. Plants can bear flowers, fruits earlier than those produced from seeds.
  2. Growing plants like banana, orange, rose, jasmine that have lost the capacity to produce seeds.
  3. Genetical similarity is maintained in the plants.
  4. Helps in growing seedless fruits.
  5. Cheaper and easier method of growing plants.

Spore Formation – In some simple multi-cellular organisms, specific reproductive parts are identified. The thread like structures that develop on bread are hyphae of the bread mould (Rhizopus). The tiny blob-on-a-stick structures are involved in the reproduction. The blobs are sporangia, which contain cells or spores that can develop into new individuals (Rhizopus). The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.

SEXUAL REPRODUCTION

When reproduction takes place as a result of the fusion of two gametes, one from each parent, it is called sexual reproduction.

If the zygote is to grow and develop into an organism which has highly specialized tissues and organs, then it has to have sufficient stores of energy for doing this. In very simple organisms, it is seen that the two germ cells are not very different from one another, or may even be similar. But as the body designs become more complex, germ cells also specialise. One germ cell is large and contains the food stores while the other is smaller and likely to be motile. Conventionally, the motile germ cell is called the male gamete and the germ cell containing the stored food is called the female gamete.

Sexual reproduction in flowering plants

Sexual reproduction in flowering plants, also known as angiosperms, involves the formation of new plants through the fusion of male and female gametes. The process begins with the development of flowers, which are the reproductive structures of angiosperms. Flowers can be unisexual (either male or female)(Papaya and watermelon) or bisexual (containing both male and female reproductive organs)(Hibiscus, mustard).

Flowers have different parts-

Sepals – Sepals are small, leaf-shaped, green-coloured and outermost part of the flower. Their main function is to protect the flower bud as it develops.

Petals – The parts of a flower that are often conspicuously colored.

Male Reproductive part

Stamen –

The stamen is the male reproductive organ of a flower and consists of two main parts:

  • Anther: The anther contains pollen sacs where pollen grains are produced.
    • Filament: The filament supports the anther.

Female Reproductive part –

Pistil or Carpel –

The pistil is the female reproductive organ, and it consists of three main parts:

  • Stigma: The stigma is the sticky, receptive surface at the top of the pistil, where pollen is received.
    • Style: The style is a slender tube-like structure that connects the stigma to the ovary.
    • Ovary: The ovary is located at the base of the pistil and contains one or more ovules.

Pollination: Pollination is the transfer of pollen from the anther of a stamen to the stigma of a pistil. This can occur through various mechanisms:

  • Self-pollination: When pollen from the same flower or a flower of the same plant fertilizes the ovules in the same flower.
    • Cross-pollination: When pollen is transferred from one flower to another, typically by wind, insects, birds, or other animals.

After successful pollination, the pollen grain germinates on the stigma and forms a pollen tube. The pollen tube grows down through the style and reaches the ovary.

Fertilization : Within the ovary, the male gametes (sperm cells) are released from the pollen tube and fertilize the female gametes (egg cells) inside the ovules.

Once fertilization occurs, the ovules develop into seeds, and the ovary matures into a fruit. The seeds contain the genetic information of both parent plants.

The mature fruit is often involved in seed dispersal, where the seeds are released and transported to new locations, ensuring the spread of the plant species.

Germination: When conditions are favorable, a seed can germinate, leading to the development of a new plant. This process begins with the emergence of a young seedling from the seed.

REPRODUCTION IN HUMAN BEINGS

Puberty – It is a natural and significant stage of human development that marks the transition from childhood to adulthood. It is a complex and gradual process during which a child’s body undergoes various physical and hormonal changes, leading to sexual maturity and the ability to reproduce. Puberty typically occurs during adolescence, between the ages of 8 and 13 in girls and between 9 and 14 in boys, although the exact timing can vary widely among individuals.

  1. Physical Changes: Puberty involves a range of physical changes, including the development of secondary sexual characteristics such as breast development in girls and the growth of facial hair in boys. Both genders may experience an increase in height and weight.
  2. Hormonal Changes: The onset of puberty is triggered by hormonal changes in the body. In girls, estrogen is the primary hormone responsible for many of the changes, while in boys, it’s testosterone.
  3. Growth Spurts: During puberty, adolescents often experience growth spurts, which can lead to rapid increases in height. This is because the growth plates in their bones are still open and can lengthen.
  4. Changes in the Reproductive System: Puberty also involves the maturation of the reproductive organs. In girls, the ovaries begin releasing eggs, and menstruation typically begins. In boys, the testes start producing sperm.
  5. Emotional and Psychological Changes: Along with the physical changes, adolescents may also experience emotional and psychological changes. These can include mood swings, increased self-awareness, and the development of a more mature sense of self.

Male Reproductive System –

The male reproductive system is a complex network of organs and structures that work together to produce and deliver sperm, as well as to facilitate the fertilization of an egg. Key components of the male reproductive system include:

  1. Testes: These are the primary male reproductive organs, responsible for producing sperm and the hormone testosterone. Sperm are produced in tiny tubules within the testes called seminiferous tubules.
  2. Vas Deferens: Also known as the ductus deferens, this is a long muscular tube that carries sperm to the urethra during ejaculation. The vas deferens also play a role in transporting seminal fluid.
  3. Seminal Vesicles: These are two small glands located near the base of the bladder. They produce a significant portion of the seminal fluid, which nourishes and protects sperm. The seminal fluid contains fructose and prostaglandins, among other substances.
  4. Prostate Gland: The prostate gland surrounds the urethra just below the bladder. It secretes a milky, alkaline fluid that makes up a portion of semen. The alkaline nature of this fluid helps neutralize the acidic environment of the female reproductive tract, increasing sperm viability.
  5. Urethra: The urethra is a tube that runs through the penis, serving as a conduit for both urine and semen. It connects the bladder to the outside of the body. During ejaculation, sperm and seminal fluid exit the body through the urethra.
  6. Penis: The penis is the external male organ that is used for both sexual intercourse and the passage of urine. It contains three columns of erectile tissue, which fill with blood during sexual arousal, causing an erection.

Female reproductive System –

The female reproductive system is a complex system responsible for the production of female gametes (eggs or ova), fertilization, gestation (pregnancy), and childbirth. It also plays a crucial role in regulating hormonal balance. Here are the key components of the female reproductive system:

  1. Ovaries: These are paired organs located in the pelvis, one on each side of the uterus. Ovaries produce and release eggs in a process known as ovulation. They also produce female sex hormones, primarily estrogen and progesterone.
  2. Fallopian Tubes: Also known as oviducts, these are thin, tube-like structures that extend from the ovaries to the uterus. The fallopian tubes are the site where fertilization typically occurs. They transport the egg from the ovary to the uterus.
  •  Uterus: The uterus is a muscular, pear-shaped organ where a fertilized egg can implant and develop into a fetus during pregnancy. The inner lining of the uterus, called the endometrium, thickens in preparation for pregnancy each month and is shed during menstruation if pregnancy does not occur.
  • Vagina: The vagina is a muscular, tube-like structure that connects the cervix to the external genitalia. It serves as a passage for menstrual blood to leave the body and as the birth canal during childbirth.

When a girl is born, the ovaries already contain thousands of immature eggs. On reaching puberty, some of these start maturing. One egg is produced every month by one of the ovaries. The egg is carried from the ovary to the womb through a thin oviduct or fallopian tube. The two oviducts unite into an elastic bag-like structure known as the uterus. The uterus opens into the vagina through cervix.

The sperms enter through the vaginal passage during sexual intercourse. They travel upwards and reach the oviduct where they may encounter the egg. The fertilised egg, the zygote, gets implanted in the lining of the uterus, and starts dividing. The lining thickens and is richly supplied with blood to nourish the growing embryo.

The embryo gets nutrition from mother’s blood with the help of a special tissue. The placenta is an organ that develops in the uterus during pregnancy. This structure provides oxygen and nutrients to a growing baby. It also removes waste products from the baby’s blood.

The time period from fertilization upto the birth of the baby is called Gestation Period. In humans, it is about nine months(36 weeks).

Female sex hormones are oestrogen and progesterone which produced by ovary.

Menstruation

Menstruation is the cyclic event of the release of the ovum from the ovary and its removal from the body when fertilization does not happen.

During menstruation, the blood-rich endometrium of the uterus also breaks down while the ovum is removed from the body.

In humans, the cycle repeats every 28 days.

REPRODUCTIVE HEALTH

Reproductive health means total well-being in all aspects of reproductive, physical emotional, social and behavioral.

There are some diseases can be transmitted sexually. These are –

Bacterial infections – Gonorrhoea and syphillis

Viral infections – Warts and HIV-AIDS

There are some methods for avoiding these diseases and unwanted pregnancy.

  • Physical barrier – Sperm does not reach the egg. Such as – use of Condom.
    •  Contraceptive pills – Oral contraceptive changes the hormonal balance of the body so that eggs are not released and fertilization cannot occur. The drugs can be taken orally as pills.
    • Contraceptive devices – Loop or Copper – T are placed in the uterus to prevent pregnency.
    •  Surgical methods – Vas deferens of male is blocked to prevent sperm transfer. Or the fallopian tube of female is blocked to prevent egg to reach uterus.

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