Notes for how do organisms reproduce chapter of class 10 science. Dronstudy provides free comprehensive chapter-wise class 10 Science notes with proper images & diagrams.
Want to learn by Video Lectures? CLICK HERE to watch them
Reproduction is the process by which living organisms produce more living organisms of their own kind. The offspring grows, matures, and in turn, produces new offspring, Thus, there is a cycle of birth, growth, and death. Reproduction, therefore, ensures the continuity of life of a species on earth.
There are two main types of reproduction in living organisms. They are asexual reproduction and sexual reproduction.
(a) Asexual Reproduction: The process of reproduction in which new individuals are produced from a single parent. E.g., microorganisms.
Occurrence: Asexual reproduction is found in single-celled organisms such as the archaebacteria, eubacteria, and protists. Many plants and fungi reproduce asexually as well.
(b) Sexual Reproduction: The process of reproduction in which two individuals are involved to produce a new individual, E.g., Human, tiger.
Types of Asexual reproduction:
i) The word 'fission' means dividing, so binary fission is literally dividing in two. Fission is an asexual reproduction by which a unicellular organism divides and forms two or more new individuals. Fission is of two types.
a) Binary Fission:- In this method, an organism divides and forms two daughter cells. First, the nucleus divides and forms two daughter nuclei, Then the cytoplasm in the mother cell divides into two daughter cells. This leads to the formation of the two daughter cells each having a nucleus and its own cell organelles which then develop into a fully formed adult. E.g.:- Amoeba, Paramecium, leishmania, etc.
(b) Multiple fission: In multiple fission, the nucleus of the parent cell undergoes repeated divisions to produce many daughter nuclei. The cytoplasm also divides and cleaves around each nucleus forming several daughter cells in the parent cell. In favorable conditions when the parent cell membrane raptures all the daughter individuals are released. E.g.: Plasmodium (Malarial parasite).
Types:
On the basis of the plane of cytokinesis ( the process in which the cytoplasm of a single eukaryotic cell is divided to form two daughter cells), binary fission is of three types:
(i) Irregular or simple binary fission:
place along any plane
(ii) Longitudinal binary fission:
Some unicellular organisms show somewhat morn organization of their bodies, such as is seen in Leis mania (which cause kala-azar, Euglena etc which have a whip-like stricture at one end of the cell. In such organisms, binary fission occurs in along longitudinal axis in relation to these structures.
(iii) Transverse binary fission:
Here cytokinesis takes place along transverse axis e.g., in ciliate protozoan (Paramecium).
(ii) Fragmentation- Another type of asexual reproduction is called fragmentation. With this process, we see that an organism break up. into many pieces upon maturation. Each of those fragments develops into mature, grown up individuals that are a replica of the original organism. The splitting might or might not be deliberate. Fragmentation occurs in multi
cellular organisms with simple body organization.
E:g.: Spirogyra
Difference between binary and fragmentation:
Unicellular organisms yeast also reproduces by budding. The most common mode of vegetative growth in yeast is asexual reproduction by budding. Here, a small bud, or daughter cell, is formed on the parent cell. This nucleus of the parent cell splits into a daughter nucleus and migrates into the daughter cell. The bud continues to grow until it separates from the parent cell, forming a new cell. The daughter cell produced during the budding process is generally smaller than the mother cell.
(iv) Regeneration:
Many fully differentiated organisms have the ability to give rise to new individual organisms form their body parts. That is. 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.
In regeneration, if a piece of a parent is detached, it can grow and develop into a completely new individual. For example, simple animals like Hydra and Planarian can be cut into any number of pieces and each piece grows into a complete organism.
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. However, regeneration is not the same as reproduction, since most organisms would not normally depend on being cut up to be able to reproduce.
Regeneration in Planarian:
Planarians are masters of regeneration where an amputated fragment as small as 1/279th of the original worm can regenerate an entire adult. When a planarian is cut, cells move to the wound site and form a blastema (a mass of cells capable of growth and regeneration into organs or body parts) that will begin to form new tissues. Over time, these cells will divide, more and more of them will differentiate, and the form of the missing body part will take shape.
Complex organisms like dogs, humans, etc cannot reproduce by regeneration because their body is highly complicated as complex organisms have organ-system level of organization. All the organ systems of their body work together as an interconnected unit. Here, specialized cells form tissues, tissues form organs, organs form an organ systems, and the organ system continues to form an organism. Specific organs do the specific function and there is a division of labour in the body of the complex organisms
In a complex multicellular organism, the process of regeneration lakes place but only to a small extent. Under this process, a new organism cannot be produced but they can regenerate their lost body parts such as skin, muscles, blood, etc.
But. Regeneration cannot be considered as reproduction because reproduction is creating a new life form. Regeneration is repairing or healing. An entire organism is developed from its fragmented body.
(v) Vegetative Propagation— It is a method of reproduction in which a vegetative plant part (i.e., a non-reproductive part or a non-flowering part namely bulb of onion, runners of strawberry, tuber of potato, rhizome of ginger etc) produces a new plant. Such type of vegetative growth is natural vegetative propagation. Only one plant is involved and the new plant is genetically identical to the parent.
(a) Tuber of potato: The potato tuber is a modified stem. Many notches can be seen on the surface of potato. These are called ‘eyes’ of potato. Each ‘eye’ of a potato can give rise to a new potato plant under suitable conditions.
(b) Modified roots of carrot and sweet potato: Carrot and sweet potato are examples of modifications of roots; for food storage. These roots can give rise to new plants; when kept under the soil.
(c) Rhizomes of Ginger and Turmeric: Rhizomes are examples of modified underground sterns for food storage. These contain nodes, internodes and scaly leaves. When buried under the soil, the rhizomes produce new plants.
(d) Leaf of Bryophyllum: Leaves of bryophyllum have notches on the margin. If a leaf is put under the soil, small saplings grow from the notches on the leaf margin.
(e) Runners of Strawberry: Runners are also horizontal stems growing from the parent plant, but they grow above ground. When their terminal buds touch the ground they take root and produce new plants.
Vegetative reproduction can also be done artificially, Artificial Propagation includes growing plants by man-made methods and the commonly used methods are:
Advantages of Vegetative Propagation:
It allows for quick and easy propagation.
Better qualities of the plants can be maintained and the quality can even be enhanced as in seedless oranges.
Plants raised by vegetative propagation bear fruits and flowers earlier as compared to those produced from seeds.
Makes possible propagation of such plants that have lost the capacity to produce seeds.
Spore formation: Spore formation is the method of developing new individuals by forming reproductive structures called spores. Some types of mould reproduce through sporulation. They produce reproductive cells called spores. Spores are very minute unicellular asexual reproductive bodies that are stored in special spore cases until they are ready to be released. Spores are formed in special spot-being organ called sporangia. When spores mature; the sporangium bursts open to release them. After they are released, each spore germinates and grows into new individual organisms. Some organisms like ferns, mosses, some groups of fungi reproduce by spore formation. Bread mould reproduces by sporulation.
(vii) Tissue Culture: It is a method of cultivation of plants where in 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 (containing nutrients and auxins) where they divide rapidly to form a small group of cells or callus. The callus is transferred to another medium combining 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. This technique is commonly used for ornamental plants. Oil palm, date palm, begonia, tomato, banana, apple, etc. are produced by this method.
Advantages of tissue culture:
Sexual reproduction:
This is the most evolved process of reproduction. It involves two sexes, namely male and female in the form of gametes produced by two different parents.
Sexual reproduction occurs nearly in all animals including those which reproduce asexually. In most animals there are two sexes male and female, and the differences between them are genetically determined.
Males have male sex cells/male gametes/male germ cells. Similarly, females have female sex cell/ female gametes / female germ cell.
Sex Cells- Gametes, also known as sex cells or germ cells, are the cells that come together during fertilization or conception in organisms that reproduce sexually. Their genetic complement consists of a single set of unpaired chromosomes.
Sexual Reproduction in flowering plants:
Angiosperms - Angiosperms are seed-bearing vascular plants. Their reproductive structures are flowers in which the ovules are enclosed in an ovary.
In angiosperms (flowering plants) reproductive organs are located in the flower. A flower is a part of the shoot modified for sexual reproduction. Flower parts are arranged in rings or circles called as whorls. The different parts of a flower are— sepals, petals, stamens and carpets.
(a) Sepals: They resemble like small leaved and they protect the flower in the bud.
(b) Petals are the coloured and scented part of the flower. Petals attract insects and birds.
Petals also protect other delicate parts of the flower-like the anther.
(c) Stamen is the male reproductive part and it produces pollen grains that are yellowish in colour. Pollen grains produce male germ cells. The stamen also has a filament, the stalk that holds the anther.
(d) Carpel is present in the centre of a flower and is the female reproductive part. It is made of three parts. The swollen bottom part is the ovary, 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/ovum.
The flower may be unisexual (papaya, watermelon) when it contains either stamens or carpets or bisexual (Hibiscus, mustard) when it contains both stamens and carpals.
Pollination: Pollination is the transfer of pollen grains from the authors of the stamens to the stigma of a carpet. There are two methods of pollination namely-
1) Self-pollination
2) Cross-pollination
If the transfer of pollen grains from the anthem to the stigma occurs in the same flower or another flower of the same plant, it is referred to as self-pollination.
If the pollen is transferred from one flower to another, it is known as cross-pollination. This transfer of pollen from one flower to another is achieved by agents like wind, water, or animals.
Fertilization:
The fusion of male and female gametes is called fertilization. The product of fertilization is
called a zygote. The zygote undergoes several rounds of mitosis and develops into an embryo. Subsequently, the embryo develops into a new individual.
The main events leading to fertilization are:
The changes that take place in a flower after fertilization:
Germination:
Seed germination is the basic stage of the growth of any plant. A seed contains the essence of a plant in a resting, embryonic condition. Whenever a seed gets a favorable environment, the stages of germination start taking place. A dormant seed lying in the ground needs warmth, oxygen, and water to develop into a plant.
The seed coat is the outer covering of a seed which protects the embryo from any kind of damage, caused by the natural elements or due to the invasion of parasites, and prevents it from drying. The endosperm inside the seed coat contains a temporary nutritional reserve, which is packed around embryo in the form of cotyledons or seed leaves. Germination is the process which involves the emergence of a plant from the seed when proper temperature, humidity, and sunlight are provided.
Various Stages of germination:
Germination starts with the rapid uptake of water by the send through its micropyle. The first visible indication of germination is the swelling of the seed with a resultant increase in weight. It is also accompanied by the softening of the seed coat. Absorption of water causes a number of physiological changes in the seed. Germinating seeds exhibit increased respiratory activity. The embryo produces enzymes which convert the food material stored in the cotyledons or endosperm into soluble form usable by the growing embryo. Once the food is made available, cell division activity starts in the growing embryo, i.e. radical and plumule. The growth of the embryonic tissue ruptures the seed coat.
The growing plant emerges out. The part of the plant that first emerges from the seed is the embryonic root known as the radicle. The radicle allows the seedling to anchor itself to the ground and start absorbing minerals and water mom the soil.
After the root starts absorbing water, an embryonic shoot emerges from the seed. This shoot comprises of three main parts- the cotyledons (seed leaves}, the hypocotyl (section of shoot below the cotyledons), and the epicotyls (section of shoot above the cotyledons).
Sexual reproduction-Human:
Organisms that reproduce sexually do so via the production of sex cells called gametes, In humans, male sex cells or spermatozoa (sperm cells), are relatively motile. Female sex cells, called ova or eggs, are non-motile and much larger in comparison to the male gamete. When these cells fuse in a process called fertilization, the resulting cell (zygote) contains a mix of inherited genes from the father and mother.
Human sex cells are produced in reproductive system organs called gonads. Gonads produce sex hormones needed for the growth and development of primary and secondary reproductive organs and structures.
Puberty is the age or period, when the reproductive organs of a child start functioning and the child attains sexual maturity. In girls, puberty is achieved at the age of 10-12 yrs of age. In boys, puberty is achieved at the age of l3-14 yrs of age.
Both the male and the female reproductive systems do not perform their function continuously from birth onwards in the same way as, for instance, the respiratory system, nervous system, or digestive system. In fact, the reproductive organs do not start to function until puberty. When this happens, the reproductive system also has effects on other systems, all round the body. Secondary sexual characteristics. Obviously, these changes are different in the two sexes, but there are some similarities.
Changes are seen in boys at the time of puberty:
These changes are caused by the male sex hormone known as testosterone.
Changes are seen in girls at the time of puberty:
These changes are caused in girls by the female sex hormone known as Oestrogen and Progesterone.
Primary sex organ- The sex organs which produce the germ cells or gametes are called primary sex organs. They are — testis in males and ovaries in females.
Secondary sex organs- The sex organs which conduct and nourish the gametes are known as secondary sex organs.
Primary sex characters- Characters which distinguish a male from a female at the time of birth are called primary sex characters.
Secondary Sex Characters- Characters which develop later on during puberty are known as secondary sexual characters. E.g., breasts in females, beard in males.
The reproductive phase is the phase in the life of every individual which makes the individual capable of reproducing the offspring. In the early reproductive phase, individuals acquire changes in the body which result in the formation of germ cells. Sperms are male germ cells and eggs are female germ cells. The reproductive phase (puberty) involves the changes in the appearance and size of the bodily organs.
Male reproductive system:
It is active and functional only after puberty (13-14 yrs)
Male reproductive system: This system includes a pair of the testis, vas deferens and a
muscular organ, the penis.
(a) Testes: Testis is the main reproductive organ in males. A pair of the testis is placed in a structure called the scrotum which is located outside the abdominal cavity because sperm formation requires a lower temperature than the normal body temperature. The sperms are tiny bodies that consist of mainly genetic material and a long tail that helps them to move towards the female germ-cell. Testes also secrete male sex hormones like testosterone to regulate the development of sperms and the secondary sexual characteristics leading to puberty.
(b) Vas deferens: The sperm duct is also known as vas deferens. They are two in number, each one arising from testis played on either side. They transport sperms into the penis. They also collect fluids secreted by different glands. These secretions are rich in proteins to enrich the sperms. Sperms along with these secretions form a thick liquid called semen. Semen is conveyed to the urethra through which it is discharged outside. The prostate gland and seminal vesicles secrete semen to make the movement of sperms easier.
(c) Urethra: Urethra forms a common passage for both the sperm and urine as it is just one tube that connects both the glands — urinary bladder and vas deferens.
(d) Penis: It is a part of the male reproductive system. The penis is a muscular organ which transfers semen into the female reproductive tract. Penis receives both urinary tube and sperm duct and serves as a common transporting organ for urine and semen. It opens out through a small tube called the urethra. The penis is underlined by thin blood vessels which give it a continuous supply of blood.
Female reproductive system: This system includes a pair of ovaries, a pair of oviducts, uterus, and vagina opening out through the urethra.
(a) Ovary: A pair of ovaries forms the gonads in females. They are oval-shaped and are close to the kidney. Ovaries are the female sex organs that lie one on either side of the abdominal cavity. Ovaries by the process of oogenesis four eggs or ova which are released as one per month. Ovaries produce two hormones, namely, estrogen and progesterone. Ovaries have thousands of follicles. After puberty, these follicles develop into eggs. Estrogen controls the changes that occur during puberty, like feminine voice, soft skin and development of mammary glands, growth of pubic hair and controls the release of mature eggs. Progesterone controls the uterine changes during the menstrual cycle and helps in the maintenance of pregnancy.
(b) Oviducts: A tube-like structure arising from each ovary on either side is called as an oviduct. This is also called a fallopian tube. The egg is carried from the ovary to the uterus through a thin oviduct also known as the fallopian tube. The two oviducts combine and open into an elastic bag-like stricture known as the uterus.
(c) Uterus: Uterus is a hollow muscular organ which has the capacity to bear the child. It is otherwise called as womb. The zygote formed after fertilization in the fallopian tube travels
downward by dividing itself continuously to form an embryo. Embryo as it reaches the uterus gets implanted into the wall of the uterus. After fertilization, female reproductive hormones bring in many changes to the uterus, so as to bear the growing embryo. As the embryo grows, it transforms into foetus. The uterus is the organ which bears the foetus.
(d) Cervix is located at the top of the vagina - it is the junction between the vagina and
uterus.
(e) Vagina: It is the reproductive part situated at the end of the uterus in female reproductive tract.
It is also called the birth canal and it opens outside the body. It connects the uterus to the outside world. The vagina secretes mucous to keep the track wet. It opens out through the vulva.
Eggs, the female gametes develop inside the ovaries, One mature egg is released by either of the ovaries per month. Ovaries secrete two hormones namely estrogen and progesterone which bring about secondary sexual characters in females. The egg is carried from the ovary to the uterus through a thin oviduct also known as the fallopian tube. The two oviducts combine and open into an elastic bag-like structure known as the uterus. The uterus opens into the vagina through the cervix. The uterus helps in the development of the foetus.
Process of reproduction:
(i) Fertilization- During copulation, millions of sperms are released into the vagina. Sperms are highly active and motile. They move up to the female body through the cervix, uterus and finally reach the fallopian tube. As they move up, most of the sperms are destroyed by the female secretions. The few sperms that have survived make it to the ovum present in the fallopian tube. Only one sperm and one egg are involved in fertilisation. Once one sperm enters the egg, the egg forms a membrane that prevents other sperm from entering. Once the sperm fuses with the ovum, it fertilises it and a zygote is formed (fertilised ovum).
(ii) Implantation: About 6-9 days after fertilisation, the fertilised egg (zygote) descends from the fallopian tube into the uterus. During its movement towards the uterus, the division of the zygote starts.
On contact, the zygote will attach itself to the uterine wall, usually in the upper pan of the uterus. The inner wall of the uterus develops and partially envelops the embryo. This process is called implantation. The fertilised egg (zygote) is called an embryo as soon as it implants which is around 7 to 10 days after fertilization. It continues to be called an embryo until the week.
The lining of the uterus becomes thick and is richly supplied with blood to nourish the growing embryo. The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. This is a disc which 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.
A woman with an embryo or foetus developing her uterus is called pregnant and the physical condition of the woman is called pregnancy.
(iii) Gestation period- The period during which the embryo development takes place in the uterus is called the gestation period. The development of the child inside the mother’s body takes approximately nine months (36 weeks).
(iv) Birth- Few days before birth, the foetus moves in the uterus until its head points towards the cervix. The child is born as a result of rhythmic contractions of the muscles in the uterus. Contractions of the muscular uterine wall force the fully-grown foetus through the cervix into the vagina. Contractions of the uterine and the abdominal muscles at regular intervals are called labour. The cervix dilates, the head of the foetus passes through and the amnion bursts discharging the amniotic fluid through the vagina. The repeated contractions of the uterus along with the contractions of the abdominal muscles forces the child out of the uterus through the vagina and the infant is thus born. The umbilical cord remains attached which is later cut off and tied up. The remaining cord on the infant shrivels and becomes its navel.
After the baby is born, the placenta and the uterine lining are discharged through menstruation.
Ovulation in females:
At about the age of 10 to 13 years, the ovaries of females are stimulated by the follicle-stimulating hormone (PSH) of the pituitary. This is called the onset of puberty and is accompanied by the release of hormones oestrogen and progesterone. These hormones control the production of ova or eggs and the appearance of secondary sexual characteristics. Unlike males where sperms can be produced throughout the life of man. in females, the reproductive phase only lasts till the age of 45-50 years. This phase is characterized by the presence of the menstrual cycle.
The oval has thousands of follicles in it. These follicles are present right from the birth of the girl child. But they remain inactive till puberty. After puberty, the follicles become eggs, The process of making of eggs from follicles is called ovulation.
After puberty, the body of the females has some periodic activity.
The ovary produces one egg every 28th and the uterus prepares to receive the fertilised egg. Its wall becomes thick and spongy with blood vessels for nourishing the embryo. If fertilisation does not take place then the uterus wall breaks and comes out of the
vagina as blood and mucous. This cycle takes place once every month and is called menstruation. It occurs in response to the low level of estrogen and progesterone hormone.
The menstrual cycle is the series of changes a woman's body goes through to prepare for a pregnancy. Menstruation (menstrual phase) lasts for the first 3-4 days. During this phase, the inner lining of the uterus is shed which causes the blood vessels to rupture. This causes bleeding and is called menstruation. The first occurrence of menstruation is termed menarche. It stops by the age of 45-50 years and is called menopause.
Most women ovulate on the 14th day but 14 is an average, and most women will actually ovulate on a different day of the menstrual cycle. The day of ovulation will vary from cycle to cycle.
After ovulation:
Once the egg (or ovum) has been released, it moves along the fallopian tube towards the womb. The egg can live for up to 24 hours. Sperm survival is more variable, but typically 3-5 days, so the days leading up to ovulation and the day of ovulation itself are the most ferrite — when a roman is most likely to get pregnant. As soon as ovulation has started, the follicle starts producing another hormone: progesterone.
Progesterone causes further build up the lining of the womb in preparation for a fertilized egg. Meanwhile, the empty follicle within the ovary starts to shrink, but carries on producing progesterone.
Preparing for the next period:
As the empty follicle shrinks, if the egg is not fertilized, levels of estrogen and progesterone decrease. Without the high levels of hormones to help maintain it, the thick womb lining that has been built up starts to break down, and the female body sheds the lining. This is the start of the period and the beginning of the next menstrual cycle.
If the egg has been fertilised, the menstrual cycle may temporarily stop till the birth of the child.
Birth Control:
Contraceptive methods are adopted to present unwanted conception and to have a sufficient gap between successive births.
A number of methods have been developed to parent and regulate childbirth. Some of them are-
(i) The creation of a mechanical barrier so that sperm does not reach the egg. Condoms on the penis or similar coverings worm in the vagina can serve this purpose.
(ii) Ovulation and fertilisation can be prevented by changing the hormonal balance of the body. It can be done by taking oral pills. Ora1 pills used by women contain hormones which alter the ovulatory cycle.
(iii) Use of Intrauterine Contraceptive Device (IUCD) such as the loop or the copper-T are placed in the uterus to prevent pregnancy. The drawbacks with these devices are bleeding and discomfort.
(iv) Surgical methods - lf the vas deferens in the male is blocked, sperm transfer will be prevented. The procedure is called vasectomy (males). lf the fallopian tube in the female is blocked, the egg will not be able to reach the uterus. The procedure is called tubectomy (female), In both cases, fertilisation will not take place. Surgical methods can be used to create such blocks
Sexually Transmitted Diseases (STD's):
During the process of reproduction, some diseases can be transmitted between males and females. The diseases which are spread by sexual contact from an infected person to a healthy person are called sexually transmitted diseases or STDS.
(i) AIDS (Acquired Immune Deficiency Syndrome)
(ii) Gonorrhea
(iii) Syphilis
(iv) Genital herpes
’AIDS’ — damages the immune system of the human body
Do Organisms Create Exact Copies of Themselves?
Organisms took similar because their body designs are similar. If body designs are to be similar, the blueprints for these designs should be similar. Thus, reproduction involves making copies of the blueprints of body design.
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 (Deoxyribo Nucleic Acid) molecules. The DNA molecule present in the chromosome defines the characteristics of organisms. 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 more the difference in DNA, the more the difference between organisms.
Therefore, DNA is responsible for inheritance. During reproduction, there is the formation of new cells which must carry the same amount and type of hereditary information.
as present in the parent cell. This is accomplished by DNA copying, prior to each cell division. As a result, DNA division takes place; very often the DNA does not divide to form exact copies. The process of copying DNA will have some variations each time. The DNA copies generated will be similar but may not be identical to the original.
This is because DNA division is a biochemical reaction. When a cell divides, the two copies of the cell may be similar but not identical. When DNA of a cell is changed, it will behave in a slightly different manner. Such differences that take place during the division of DNA are called variation and this is the reason why organisms cannot make identical copies of themselves.
lf a cell makes an exact copy of itself, then it is engaging in asexual reproduction. Asexual reproduction uses genetic material from a single parent. During asexual reproduction, the genetic material is copied and passed to the forming daughter cell. When replication is complete, the daughter cell divides away from the parent and becomes an EXACT replica or clones. Sexual reproduction uses genetic material from two different individual parents. During the process of reproduction, the genetic material (DNA) Horn both the parents are taken. This results in offspring’s having similarities to both parents but are not an exact copy of either one.
The Importance of Variation:
The consistency of DNA copying during reproduction is important, which leads to the stability of population species. Changes in the ecological system, which are beyond our control like varying temperature, varying water levels, and natural calamities, can wipe out the population species. So, if there are some variations that are present in some individuals of the population species then there is a chance for the survival of these species over time. The process of reproduction results in the production of offspring’s which are exactly similar to parents.
This is so useful and amazing for me
Please sir mak
e it to short
this chapter notes is very very lengthy diversity chapter notes short than this .... but its too lengthy and it just like book not like dron style so please provide us your style notes that makes easier for our study.. thnks
Nice
Amazing
It is fantastic
It is fantastic and Outstanding class
Give me a numberI
Gud
Very very good!!
Thank you Sir for notes
Superb
thanks for my study helper
good for revision
very nice for revision
Its really good fr revision 🙂
It's really helpful for me
Thanks ...for helping
It is really very useful and easy
Thanks. It contains all necessary points.
Great job ,nice notes really helpful for revision
Very Useful for us
Thank you sir for your notes it is very helpful
Thank u and better notes for a student
Very good notes
Superb just an exact study material I was finding
Was useful
fair
Very helpful and informative notes....so easy language. Thank you so much Sir.
thanks for help and very very nice for note's
you always explain the content in a very simple way
thanks!!
Nice good notes
Nice good notes for students
What about variation...?but the notes are good.
very gud notes and thanks alot to post these helpful notes
Nice
nice
Not bad
Thanksss a lot
It's really reaally very helpful for me
Really nice and useful notes
U r too gd..thnxx for help..
they r reallly good
It's to good and helpful for me
Thanks
Perfect notesss thankkssss
Awesome
Helfull . Good job
Awesome
Helfull
fabulous
Thanks a lot
Good those who made this information collected from class12
thank u for ur guidance
This notes are brilliant and it is 2 useful for me.....
one of the best and easy learning site
really informative n helpful...
It is really amazing
Thankyou very much
good better best
Awesome
Brilliant it is very auwesome
Thanks it is very usefull
nice
Its osssssssmmmmm
supperr.....
Bawallllllllll
Easy to understand
Very very thanks
awesome and extraordinary
How to download
thanks a lot
Thank you
Thank
Nice notes ....
Thnxxx for help me.....
This is really good for the instant exam preparation
Awesome
So good
Notes are awesome but do something to magnify the notes these are very small resulting in eye strain
It is the best notes for exam
It is amazing
good
nice and very helpful
Nice
Very nice
Very nice
Very helpful
Nice notes thanks
wow.. Fantastic
You provide notes with proper diagram.
Really, it's amazing.
Very good concept sir.
Thank You so much....
Very nice abd helful
Very helpful
It helped me alot
yes this is amazing
These were awesome n helped a lot for a quick revision of chapter.
Thanks I score 76 out of 80 in exam because of these notes
Thanks once again
Thanx best notes
very helpful
They are the best notes, it helps me a lot.THANKS*
it was best notes and easy to read and understand it. THANKS*
It is too long
Better than book study
Good than book study
Very nice notes
SIR, PLEASE PROVIDE CHAPTER NOTES OF SST (SOCIAL SCIENCE) , PLEASE , FOR CLASS 10
ossummm notes.. i love it ......thnks...this website
it is a veerry essential for me n every people...thnks...this website
useful and everything is mentioned
thanks
Thank you so much for this. It is very helpful for me. Thanxxxxxx
Very helpful
These notes are acute and good but don't zoom in plz help
Good and excellent
very helpful
NIce facility provided by Drone Study.
The notes are good and better to understand.
Keep it up!! Drone Study
really very nice
thanx this is realy helpful for us
It is very interesting to read I am feeling...
nice note
Very good, nyc helpful .....
please keep a download option or keep it as a pdf file
Awesome.this page made me so curious . thank you so much
These notes are really great
Gud.....
Very good, helpful
Thanks Google.....
v nice and precised notes
spellbound and required precised notes
TNKS
NICE
it was really helpful to me. THANKS A LOT
It's very easy to learn and understand
Good is not is not enough for this notes
Very good app.thanks for making the notes for learning
Tysm sir for such detailed notes.......helped me a lot while preparing for exams...
Amazing notes
Amazing and helpful notes
msttt jhakkassss
mstt
It's very helpful
How can I download and Print them
Great job!!!
Very nice and helped a lot!!!!
Very nice and helped me a lot......
Thank you so much sir
solid description
thanks
nice description ,of all in this chapter
It is really very good.it is very helpful and
easy to learn
tooo gud
Really good
Cool thanks
Good
I just impressed with this type of notes I just saw in cardovaang ur explanatory in study material is awesome
Best notes
Nice notes
Very nice and useful
somewhat helpful
good notes all topics are well defined
This note are really help full
very nice
Very helpful
I thanks to droon study for helping students
nice and esay notes..... really love #dronstudy.com
Nice
✌ like
very gud
nice notes for copy completion and revision also
Great post, my name is ron spinabella and i run a great blog and twitter account. I'm going to repost it for my followers.
gud information
it is very nice and use and useful to study
it is easy to study
very helpful nice
Message *Good, very helpfull.
nice for all in exams
Too much easy
Too good and very very useful for the examination
Mostly useful and really it's too good for examination
Easy to understand...
Nice notes
This is the best way of revising ! Thanks
Mazzzzzzzzzzzzzz......superb 🙂
Vry nice thanxx a lot
Fantastic
Very nice, it is vry helpful for all students
its arranged according to its importance .it helped me very well .thank you
Clarity of words is not good. Work on that.
Cool notes☺☺☺☺☺
its very easy n helpful.. thanx
VERY HELPFUL.....
thanks the notes are awesome
very niceeee
hats off to u 4 giving us this wonderful notes
its really very helpful
It is very detailly explained Ithat is very helpful
Very nice and helpful for exams
Very good and helpful for exams
fabulous explanation of every topic
nice
very useful notes... amazing....
Awesome contents given above ...its very helpful for the students of × ...
awesome
very helpful when one doesn t get notes at school
i like it
uesful
Really good notes.... Easy language & proper way is used for understanding.... In fact extra information is given..... I liked it... 🙂
Thank you
it's very nice n useful, n it help me alot for my preboards
Thank you
Its good
Its good for revision.. We can gain more marks from this.
awesome life saver dronstudy 🙂
It is a very good notes
Very helpful 4 study and easy
Nice?
Thank you Nehu
its reaallllllllyy helpfullll
Thank you bbli dixit
Thank you...it was really an easy method for learning and was really helpful!?
thank you vidhi
its help lot
Thnxss
Thnxsss...vry helpful notes
gud n clear explanation......
Good
its good in explaination
this notes are completely satisfying.
Amazing
Vry helpful for preparing the chapter ........THNQ FOR THE NOTES ITS AMAZING NOTES
Vry helpful for preparing the chapter ........THNQ FOR THE NOTES ITS AMAZING NOTES
Wonderful Notes. Very Helpful
Outstanding
good for quick leanings
good for quick leanings
Really ..it is very helpful to me....
THANX....
osm.......
thy r useful easy for exams
thanks for helping students its much easier than we thought. its really nice
Very very nice notes
Thanks for helping in my revision......
Awesomeeee superbbbb amazinggggg
Fantabulous
THANK YOU
It's good from this website can easily revise
Good!!
so nice and helpful
Nice ??
Nice
Thanks fr the notes... Are helpful a lot!!?
Message *;-)VERY GOOD.IT'S A GOOD NOTS B-)
It's really helpful for me
It's really awesome notes and are really helpful
It's really awesome notes and are really helpful for exams
Hope ... it will help me for exam
...
Amazing
THIS NOTES IS TOO USEFUL
Good and easy to understand???
very good
i see improvement in my study after reading this notes???
Very good sir
nice notes
Verrry veerrry useful guide
Thank you sir
Thanks it help a lot
Thankhuu
Thanks it provide all info
Very good sir you are brilliant sir
Awesome....
It really helped me a lot
Thanks for helping us . it's very helpful
This note is very useful. I really like it....
This note is very useful.I really like it.....
its really awsm and easy to learn for exams
GOOD NOTES...................................................
Very helpfull,and good.
VERY HELPFUL
Very much helpful to me!
Thank you.............
nice and helpfull
very good
Message *very well
really very helpful 🙂
very easy to understand and helpful
Very useful thank you ????
Message it's good and easy to understand....
it is very helpful website
this is very use ful my studies ism score A1 in all
Thank u so much
I don't like it
These r very beneficial to all. Thankyou to upload this material
very helpfull in revision
Very nice
Very nice ma
So thanks full to u
Superbbbbb
gud fr lst min preparation
Message *यू कहें तो ज्ञान का समुन्दर
it is easy to notes to preparations
for exams
it is really good and easy
AWESOME NOTES...very helpful
niceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
Good and very useful but long also
This website is very nice and it helped me so much.I got many extra questions.thank uuu!!!!
helpful
Good thnku
It is very good forvdistance student
It is very useful for the distance students
nice
its very easy and very helful also
super se upar
super se upaar
bst help
fantastic notes..helped lot
bst
Niceeeeeeee...........
Very helpful
Awesome , really very nice
Very useful thanq for preparing this page...?
Really superb notes....
thnxcc...
nice one
these notes help me in my FAs..
It is so useful & helpful
I like this , it' s very helpful
These r very easy to read n full of info thanx for making it this useful for us ??
Thanks. Awesome notes
They really helped me a lot to complete my notes.
Good
very easy to understand and helpful for every student
very very helpful
very useful for us
good but i want to download it
the best notes u can ever get
excellent
This is very good notes for study
Good
It's easy to understand
Awesome nots
Actually it is a very gud thing to learn through notes and by these it's amazing!!!!!!
Thnx ! It really proved vry helpful to me...
And it's gud ....
Good
THANK IN EXAMS MY FACE IS LIKE THIS 🙂
thaks for notes it are helpful for exams
helpful
really good...!!!!!
nyc
Good
thank u
thank u so much
good
Very easy and understandable..
good
Very easy and helpful
sweet notes
wonderful.......
Message *it is nyc for good student
Wonderful and very helpful
Amazing and very useful
Very good...
I really appreciate...i loved it...
It has very nice explanation of every particular topic...thank u..
Very goot notes....really helpful
Nice notes for examination
thnku so much
Fantastic
This notes Good for me becouse it help for doing my h. Work
Extremely helpful
Something different
nice notes
nice
it is very helpfull
Excellent notes , really helpful and soooo gooood
Excellent notes , really helpful
Auspicious notes
It is easy as well as very helpful
very helpfull notes
good
nice
nice thans dron study
Nice
It really helped me a lot
Really good!
wonderful. praiseworthy.
Awesome notes
It's really awesome. Very easy and helpfull
fantastic
nice
Us it is so nice
its very good
Wonderful!
it is eazy and contain all important information...
Good,short nd easy
Fantstic
its toooooooo longgggggggg
So nice
So easy and so nice
Ty soo much
It helped me a lot
Nice its very helpful....
very good notes.
nice explanation
very useful.....
very useful....
nice and interesting for class 10
good
Good
Excellent....
And very much helpful
good
no need of written notes really a good shorcut
its use ful for me
Very nice
very nicce notes
its good and helpfull
its good and helpfull
Excellent
Very helpful
very good
awesome and this made me score high.
lovely keep it up .
Wow! Amazing
its good
very nice
awesome
it is very nice
super
awsome
Thnkzz for dizz
Notes were really very helpful
Notes were really very good..
outstanding very helpful
This is really to study . Thank you .
Its good
Yrr....I love DronStudy
This is Great! Thank You!
i think this is really good but i want too short and this is very long.
very nice but i was not able to download these
Dear Hardik,If u want to download the chapter then u need to buy them.thanks 🙂
very easy notes
superb, great, awesome, excellent, fantastic, mind blowing
..........even these words are less for this site and for teachers who explains
i found these notes and explanation is very useful for our examinations
really I mean seriously hats off to you...........
thank you very much dronstudy
Nice notes
nice
awesome
Very helpful notes
It was very very very helpful for me with the diagrams....really understood this lesson
Thnxxxx it is very useful.......
very nice for all students
Super notes with topic wise. Good and easy to understand.
It is very superb notes and we should follow this notes
THIS ONE IS SO GOOD.AMAZING.
THANK YOU. 🙂
this is vry helpful for me nd my frnds...thanx
Bestt notes as well as useful
Nice extra knowledge
These were really helpful thankyou
good
very good really nice
really i love it
nyc
niceee gud nd useful fr studies...........
nice 1
NYC & required good info.
Its really good
really helpful for me. thank you so much
really helpful. thank you so much
I think it is nice and i have got many information about chapter. Can i get ppt of chapter Heredity and evolution
You can watch the video of Heredity and Evolution going to our site.
really nice
101% Complete notes, thanks alot !
101% Complete notes, thanks alot !
supeb
awsm
Explaination is very well and it also covers all the topics.....
this is going to help many of us and had already helped me to understand me this chapter
its awesome and very helpful
superb.!
I love it
telented
badiya hai
mast
maja agaya bhaiiii
niceeeee
owsmmmmmmm....... i like it 🙂
these were superb
Good
NICE very helpful
fantastic work thanxx
It is reallyyyyyyyy good for exam preparation
very helpful and intrusting notes......
Nice
thanks a lot for this note
this notes give me marks 20/20 in paper
NICE
NICE
Really helpful,short & sweet study notes..
GOOD...!!!
This is proved very useful for me
superb
Message *THANKS
good
GOOD
It is good notes for revision
good
This is really nice and contains all the required information for exams....
thanks these are very helpful for every student
nice&these r good.........
These are very usefull for me
Very useful
Awsm guide way
Awesome ☺☻♥♦♣♠
niceee☺☺
soo gud..
Awesome
Helped me fr my fa
Very helpful and thanks a lot
easy
its easy to learn and understand
These are really helpful
thanksssssssss......
so helpfull
Gud...
thanks for your support
Helpfull
Nice is really helpful
Very very thanks
really very nice, thanks
thanx
thanks for helping me
Very easy and helpfull
It's really very helpful and easy.
amazing