Class X CH – 8 How Do Organism Reproduce?
Syllabus of Reproduction: Reproduction in animal and plants (asexual and sexual) reproductive health-need for and methods of family planning. Safe sex vs. HIV/AIDS. Childbearing and women's health.
|
2. Asexual reproduction - Process of creating new individual using one parent organism. Example – Vegetative propagation, tissue culture, and spore formation.
3. Sexual reproduction: Process of creating new individuals using two individuals' parent organisms. Example: Bulls alone cannot produce new calves, nor can hens alone produce new chicks. In such cases, both sexes, males and females, are needed to produce new generations.
3. Three distinguishing features between sexual and asexual types of reproduction.
Asexual reproduction -
i. Process of creating new individual using one parent organism.
ii. It does not involve the fusion of gametes,
iii. It produces offspring that are identical to the parent.
Sexual reproduction-
i. Process of creating new individuals using two individuals' parent organisms. In such cases, both sexes, males and females, are needed to produce new generations.
ii. It involves the fusion of two gametes,
iii. It Produces offspring that are not identical to either of the two parents
4. Chromosomes- The chromosomes in the nucleus of a cell contain information for the inheritance of features from parents to the next generation in the form of DNA ( Deoxyribose Nucleic Acid) molecules.
5. DNA - The DNA in the cell nucleus is the information source for making proteins. If the information is changed, different proteins will be made. Different proteins will eventually lead to altered body designs.
6. A basic event in reproduction is the creation of a DNA copy.
i. Cells use chemical reactions to build copies of their DNA. This creates two copies of the DNA in a reproducing cell.
ii. Keeping one copy of DNA in the original cell and simply pushing the other one out would not work, because the copy pushed out would not have any organized cellular structure for maintaining life processes. Therefore, DNA copying is accompanied by the creation of an additional cellular apparatus, and then the DNA copies separate, each with its own cellular apparatus. Effectively, a cell divides to give rise to two cells.
iii. The process of copying the DNA will have some variations each time. As a result, the DNA copies generated will be similar, but may not be identical to the original.
iii. Some of these variations might be so drastic that the new DNA copy cannot work with the cellular apparatus it inherits. Such a newborn cell will simply die.
iv. The consistency of DNA copying during reproduction is important for the maintenance of body design features that allow the organism to use that particular niche. Reproduction is therefore linked to the stability of populations of species.
7. Variation is useful for the survival of species over time -
Temperatures on earth can go up or down, water levels can vary, or there could be meteorite hits if a population of reproducing organisms were suited to a particular niche and if the niche were drastically altered, the population could be wiped out. However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. Thus, if there were a population of bacteria living in temperate waters, and if the water temperature were to be increased by global warming, most of these bacteria would die, but the few variants resistant to heat would survive and grow further. Variation is thus useful for the survival of species over time.
8. Fission - Fission is the process of splitting of a cell into two or more cells during cell division. Each small cell is known as a daughter cell.
9. Binary fission is the process of splitting of a cell into two cells during cell division. Example of binary fission: Many bacteria and protozoa simply split into two equal halves during cell division. In organisms such as Amoeba, the splitting of the two cells. Leishmania (which causes kala-azar), which has a whip-like structure at one end of the cell. In such organisms, binary fission occurs in a definite orientation in relation.
10. Multiple fission: is the process of splitting of a cell into many cells during cell division.Example of multiple fission: Other single-celled organisms, such as the malarial parasite, Plasmodium, divide into many daughters cells simultaneously by multiple fission.
11. Fragmentation: Fragmentation is seen in multi-cellular organisms with relatively simple body organization. Here the body of the organism simply breaks up into smaller pieces during maturation. These fragments grow into new individuals. Example – Fragmentation in spirogyra, molds, annelid worms, etc.
12. Multi-cellular organisms, need to use more complex ways of reproduction - All multi-cellular organisms cannot simply divide cell-by-cell. The reason is that many multi-cellular organisms are not simply a random collection of cells. Specialized cells are organized as tissues, and tissues are organized into organs, which then have to be placed at definite positions in the body. In such a carefully organized situation, the cell-by-cell division would be impractical. Multi-cellular organisms, therefore, need to use more complex ways of reproduction.
In multi-cellular organisms different cell types perform different specialized functions. Therefore reproduction in such organisms is also the function of a specific cell type.
13. Regeneration : Many organisms have the ability to give rise to new individual organisms from their damaged or lost body parts. If the individual is somehow cut or broken up into many pieces, many of these pieces grow into separate individuals. This is known as regeneration. Example: Hydra and Planaria can be cut into any number of pieces and each piece grows into a complete organism.
14. Budding : In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals. This process is known as budding.
15. Regeneration- Regeneration is carried out by specialized cells. These cells proliferate and make large numbers of cells. From this mass of cells, different cells undergo changes to become various cell types and tissues. These changes take place in an organized sequence referred to as development.
16. Vegetative Propagation: In many plants in which parts like the root, stem, and leaves develop into new plants under appropriate conditions. This is known as vegetative propagation. Examples : Layering or grafting to grow many plants like sugarcane, roses, or grapes for agricultural purposes, buds produced in the notches along the leaf margin of Bryophyllum fall on the soil and develop into new plants
17. Advantages of vegetative propagation: Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds. Such methods also make possible the propagation of plants such as banana, orange, rose and jasmine that have lost the capacity to produce seeds. Another advantage of vegetative propagation is that all plants produced are genetically similar enough to the parent plant to have all its characteristics.
18. Tissue culture: In this process, new plants are grown by removing tissue or separating cells from the growing tip of a plant. The cells are then placed in an artificial medium where they divide rapidly to form a small group of cells or callus. The callus is transferred to another medium containing hormones for growth and differentiation. The plantlets are then placed in the soil so that they can grow into mature plants. Using tissue culture, many plants can be grown from one parent in disease-free conditions( advantage). This technique is commonly used for ornamental plants.
19. Spore formation: The thread-like structures that developed on the bread are the hyphae of the bread mould (Rhizopus). They are not reproductive parts. The tiny blob-on-a-stick structures are involved in reproduction. The blobs are sporangia, which contain cells, or spores, that can eventually develop into new Rhizopus individual’s .The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.
Reproduction, unlike other life processes, is not essential to maintain the life of an individual organism.
iii. It Produces offspring that are not identical to either of the two parents
4. Chromosomes- The chromosomes in the nucleus of a cell contain information for the inheritance of features from parents to the next generation in the form of DNA ( Deoxyribose Nucleic Acid) molecules.
5. DNA - The DNA in the cell nucleus is the information source for making proteins. If the information is changed, different proteins will be made. Different proteins will eventually lead to altered body designs.
6. A basic event in reproduction is the creation of a DNA copy.
i. Cells use chemical reactions to build copies of their DNA. This creates two copies of the DNA in a reproducing cell.
ii. Keeping one copy of DNA in the original cell and simply pushing the other one out would not work, because the copy pushed out would not have any organized cellular structure for maintaining life processes. Therefore, DNA copying is accompanied by the creation of an additional cellular apparatus, and then the DNA copies separate, each with its own cellular apparatus. Effectively, a cell divides to give rise to two cells.
iii. The process of copying the DNA will have some variations each time. As a result, the DNA copies generated will be similar, but may not be identical to the original.
iii. Some of these variations might be so drastic that the new DNA copy cannot work with the cellular apparatus it inherits. Such a newborn cell will simply die.
iv. The consistency of DNA copying during reproduction is important for the maintenance of body design features that allow the organism to use that particular niche. Reproduction is therefore linked to the stability of populations of species.
7. Variation is useful for the survival of species over time -
Temperatures on earth can go up or down, water levels can vary, or there could be meteorite hits if a population of reproducing organisms were suited to a particular niche and if the niche were drastically altered, the population could be wiped out. However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. Thus, if there were a population of bacteria living in temperate waters, and if the water temperature were to be increased by global warming, most of these bacteria would die, but the few variants resistant to heat would survive and grow further. Variation is thus useful for the survival of species over time.
8. Fission - Fission is the process of splitting of a cell into two or more cells during cell division. Each small cell is known as a daughter cell.
9. Binary fission is the process of splitting of a cell into two cells during cell division. Example of binary fission: Many bacteria and protozoa simply split into two equal halves during cell division. In organisms such as Amoeba, the splitting of the two cells. Leishmania (which causes kala-azar), which has a whip-like structure at one end of the cell. In such organisms, binary fission occurs in a definite orientation in relation.
10. Multiple fission: is the process of splitting of a cell into many cells during cell division.Example of multiple fission: Other single-celled organisms, such as the malarial parasite, Plasmodium, divide into many daughters cells simultaneously by multiple fission.
11. Fragmentation: Fragmentation is seen in multi-cellular organisms with relatively simple body organization. Here the body of the organism simply breaks up into smaller pieces during maturation. These fragments grow into new individuals. Example – Fragmentation in spirogyra, molds, annelid worms, etc.
12. Multi-cellular organisms, need to use more complex ways of reproduction - All multi-cellular organisms cannot simply divide cell-by-cell. The reason is that many multi-cellular organisms are not simply a random collection of cells. Specialized cells are organized as tissues, and tissues are organized into organs, which then have to be placed at definite positions in the body. In such a carefully organized situation, the cell-by-cell division would be impractical. Multi-cellular organisms, therefore, need to use more complex ways of reproduction.
In multi-cellular organisms different cell types perform different specialized functions. Therefore reproduction in such organisms is also the function of a specific cell type.
13. Regeneration : Many organisms have the ability to give rise to new individual organisms from their damaged or lost body parts. If the individual is somehow cut or broken up into many pieces, many of these pieces grow into separate individuals. This is known as regeneration. Example: Hydra and Planaria can be cut into any number of pieces and each piece grows into a complete organism.
14. Budding : In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals. This process is known as budding.
15. Regeneration- Regeneration is carried out by specialized cells. These cells proliferate and make large numbers of cells. From this mass of cells, different cells undergo changes to become various cell types and tissues. These changes take place in an organized sequence referred to as development.
16. Vegetative Propagation: In many plants in which parts like the root, stem, and leaves develop into new plants under appropriate conditions. This is known as vegetative propagation. Examples : Layering or grafting to grow many plants like sugarcane, roses, or grapes for agricultural purposes, buds produced in the notches along the leaf margin of Bryophyllum fall on the soil and develop into new plants
17. Advantages of vegetative propagation: Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds. Such methods also make possible the propagation of plants such as banana, orange, rose and jasmine that have lost the capacity to produce seeds. Another advantage of vegetative propagation is that all plants produced are genetically similar enough to the parent plant to have all its characteristics.
18. Tissue culture: In this process, new plants are grown by removing tissue or separating cells from the growing tip of a plant. The cells are then placed in an artificial medium where they divide rapidly to form a small group of cells or callus. The callus is transferred to another medium containing hormones for growth and differentiation. The plantlets are then placed in the soil so that they can grow into mature plants. Using tissue culture, many plants can be grown from one parent in disease-free conditions( advantage). This technique is commonly used for ornamental plants.
19. Spore formation: The thread-like structures that developed on the bread are the hyphae of the bread mould (Rhizopus). They are not reproductive parts. The tiny blob-on-a-stick structures are involved in reproduction. The blobs are sporangia, which contain cells, or spores, that can eventually develop into new Rhizopus individual’s .The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.
Reproduction, unlike other life processes, is not essential to maintain the life of an individual organism.
- The DNA copying the mechanism, cannot be absolutely accurate, and the resultant errors are a source of variations in populations of organisms.
- Every individual an organism cannot be protected by variations, but in a population, variations are useful for ensuring the survival of the species.
- DNA-copying mechanisms are not absolutely accurate, they are precise enough to make the generation of variation in a fairly slow process. If the DNA coping mechanisms were to be less accurate, many of the resultant DNA
- Combining variations from two or more individuals would thus create new combinations of variants.
- In multi-cellular organisms have special lineages of cells in specialized organs which have only half the number of chromosomes and half the amount of DNA as compared to the nonreproductive body cells. Thus, when these germ-cells from two individuals combine during sexual reproduction to form a new individual, it results in re-establishment of the number of chromosomes and the DNA content in the new generation.
- In very simple organisms, the two germ-cells are not very different from one another, or may even be similar. But as the body designs become more complex, the germ-cells also, specialize. 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.
- Angiosperms - The plants that have flowers
and produce seeds enclosed by fruits known as angiosperms,
the different parts of a flower – sepals, petals, stamens, and carpels. Stamens
and carpels are the reproductive parts of a flower which contain the
germ-cells.
- Unisexual flower – Unisexual the flower contains either stamens or carpels. Example: Papaya and watermelon
- Bisexual flower – Bisexual the flower contains both stamens and carpels. Example - Hibiscus, mustard
- Stamen - Stamen is the male reproductive part and it produces pollen grains, They are yellowish in colour.
- Carpels - Carpel is present in
the center of a flower and is the female reproductive part. The swollen bottom
part is the ovary, the middle elongated part is the style and the terminal part
which may be sticky is the stigma. The ovary contains ovules and each ovule has
an egg cell.
- Pollination:
The
transfer of pole grains from one flower to another is called pollination.
- Each pollen grain contains two male gametes but only one male gamete fuses with the egg while the other fuses with the polar nuclei to form the endosperm
- Fusion or fertilization - The male
germ-cell produced by pollen grain fuses with the female gamete present in the
ovule. This is called fusion or fertilization which gives us the zygote which is capable of growing into
a new plant.
- Self-pollination - If this transfer of
pollen occurs in the same flower, it is referred to as self-pollination.
- Cross
pollination - If the pollen is transferred from one
flower to another, it is known as cross-pollination.
- Germination
- Transfer of pollen from one flower to another is achieved by agents like
wind, water, or animals. After the pollen lands on a suitable stigma, it has to
reach the female germ-cells which are in the ovary. For this, a tube grows out
of the pollen grain and travels through the style to reach the ovary. After
fertilization, the zygote divides several times to form an embryo within the
ovule. The ovule develops a tough coat and is gradually converted into a seed.
The ovary grows rapidly and ripens to form a fruit. Meanwhile, the petals,
sepals, stamens, style, and stigma may shrivel and fall off. The seed contains
the future plant or embryo which develops into a seedling under appropriate
conditions. This process is known as germination.
- In multi-cellular bodies there are specialized cells to carry out specialized functions. The creation of germ-cells to participate in sexual reproduction is another specialized function, Human beings develop special tissues for this purpose. However, while the body of the individual organism is growing to its adult size, the resources of the body are mainly directed at achieving this growth. While that is happening, the maturation of the reproductive tissue is not likely to be a major priority. Thus, as the rate of general body growth begins to slow down, reproductive tissues begin to mature. This period during adolescence is called puberty.
- During puberty, new hair-growth patterns are signals that sexual maturation is taking place.
- The sexual mode of reproduction means that germ-cells from
two individuals have to join together. This can happen by the external release
of germ-cells from the bodies of individuals or by two
individuals joining their bodies together for internal transfer of germ-cells
for fusion.
- The formation of germ-cells or sperms takes place in the testes. Testes are located outside the abdominal cavity in scrotum because sperm formation requires a lower temperature than the normal body temperature.
- The roles of the testes - Roles are the secretion of the hormone testosterone that is brought about changes in appearance seen in boys at the time of puberty, and to regulate the formation of sperms.
- Vas deferens - The sperms formed from the testes are delivered through the vas deferens which unites with a tube coming from the urinary bladder. The urethra thus forms a common passage for both the sperms and urine.
- Roles of prostate and seminal vesicles that are present along the path of vas deferens – secretions of fluid so that the sperms can transport with fluid easily and this fluid also provides nutrition to the sperm.
- Sperms – Sperms are present in the male body which are tiny bodies that consist of mainly genetic material and a long tail that helps them to move towards the female germ-cell.
- The role of ovaries - Role of ovaries is the production of eggs for fertilization and production of reproductive hormones, estrogen, and progesterone.
- The role of the fallopian tube - It is the site of fertilization in a female. 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 called a fallopian tube. The sperms enter through the vaginal passage during sexual intercourse and travel upwards and reach the fallopian tube where they may encounter the egg and egg becomes fertilized.
- Egg
-
The female germ-cells are made in the ovaries and these germs cells are called eggs. They are responsible for the production of hormones.
- Role of the uterus - After fertilization of egg with sperm in the fallopian tube the fertilized egg, the zygote forms and gets implanted in the lining of the uterus and starts dividing. The uterus opens into the vagina through the cervix..
- Fertilization of eggs - The sperms enter through the vaginal passage during sexual intercourse. They travel upwards and reach the oviduct where they may encounter the egg and egg becomes fertilized. The fertilized egg, the zygote, gets implanted in the lining of the uterus and starts dividing.
- Placenta-
The embryo gets nutrition from the mother’s blood with the help of a special
tissue called the placenta. This is a
disc that is embedded in the uterine wall. It contains villi on the embryo’s
side of the tissue. On the mother’s side are blood spaces, which surround the
villi. This provides a large surface area for glucose and oxygen to pass from
the mother to the embryo. The developing embryo will also generate waste
substances which can be removed by transferring them into the mother’s blood
through the placenta.
- The development of a child inside the mother’s body takes approximately nine months.
- Menstruation
- The ovary releases one egg every month, the uterus also prepares itself every month
to receive a fertilized egg. Thus its lining becomes thick and spongy. This
would be required for nourishing the embryo if fertilization had taken place. If
the egg is not fertilized it lives for about one day and so the lining of the ovary is
not needed any longer. So, the lining slowly breaks and comes out through the
vagina as blood and mucous. This cycle takes place roughly
every month and is known as menstruation.
- Diseases
during the sexual act – Gonorrhoea, syphilis, and viral
infections such as warts and HIV-AIDS.
- To prevent the transmission of such diseases during the sexual act should use a covering, called a condom.
- Method of contraception - Many ways or contraceptive methods to avoid pregnancy are – using condoms, changing the hormonal balance by using pills, by using a loop or the copper-T in female, blocked the male and female vas deferens and fallopian tubes respectively.
- Reproduction involves creation of a DNA copy and additional cellular apparatus by the cell involved in the process.
- Various organisms use different modes of reproduction depending on their body design.
- In fission, many bacteria and protozoa simply divide into two or more daughter cells.
- Organisms such as hydra can regenerate if they are broken into pieces. They can also give out buds that mature into new individuals.
- Roots, stems, and leaves of some plants develop into new plants through vegetative propagation.
- These are examples of asexual reproduction where new generations are created from a single individual.
- Sexual reproduction involves two individuals for the creation of a new individual.
- DNA copying mechanisms create variations which are useful for ensuring the survival of the species. Modes of sexual reproduction allow for greater variation to be generated.
- Reproduction in flowering plants involves the transfer of pollen grains from the anther to the stigma which is referred to as pollination. This is followed by fertilization.
- Changes in the body at puberty, such as an increase in breast size in girls and new facial hair growth in boys are signs of sexual maturation.
- The male reproductive system in human beings consists of testes which produce sperms, vas deferens, seminal vesicles, prostate gland, urethra, and penis.
- The female reproductive system in human beings consists of ovaries, fallopian tubes, uterus, and vagina.
No comments:
Post a Comment