Download how do organisms reproduce

HOW DO ORGANISMS REPRODUCE
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Reproduction is also known as Procreation. It is a biological process in which a new
"offspring" is produced from their "parents".
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The production of new organisms from the existing organisms of the same species is
called as reproduction.
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Importance of reproduction :1. It produces similar kinds of individuals having similar characteristics as their
parents, generation after generation.
2. It is essential for the survival of a species on the earth.
3. It ensures continuity of life in various forms on earth.
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In reproduction, a DNA copy is created along with additional cellular apparatus required
by the cell during the process.
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Different organisms use different modes of reproduction depending on their body design.
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There are two main modes by which organisms reproduce.
1. Asexual reproduction
2. Sexual reproduction
 Asexual reproduction
 This involves production of a new organism from a single parent without the
involvement of sex cells or gametes.
 There are different modes of reproduction used by a single parent. They are:o Fission – In this process, a unicellular organism splits to form two or
more new organisms. Fission is of two types:1. Binary fission (parent organism splits to form two new
organisms).
2. Multiple fission (parent organism splits to form more than two
new organisms).
HOW DO ORGANISMS REPRODUCE
o Fragmentation – The process of breaking up of the body of a simple
multicellular organism into two or more pieces on maturing, each of
which subsequently grows into a new organism is called fragmentation.
o Regeneration – The process of getting back a full organism from its body
parts is called as regeneration.
o Budding – In this process, a small part of the body of the parent organism
grows out as a ‘bud’ which then detaches and becomes a new organism.
o Vegetative propagation – In this process, new plants are obtained from
the parts of old plants without the help of any reproductive organs.
o Spore formation – In this process, the parent organism breaks up into
several microscopic units called ‘spores’ each of which eventually
develops into an organism like the parent form.
 Sexual reproduction
1. Sexual reproduction in flowering plants.
 The reproductive parts of angiosperms are located in the flower.
 Stamens (in male) and carpels (in female) are the reproductive parts of a flower
which contain the germ-cells.
 Pollination is a process by which the pollen grains are transferred from the anther
to stigma of the carpel. Pollination if mainly of two types:
a) Self-pollination – When the pollens from the anther of a flower are
transferred to the stigma of the same flower (or another flower on the
same plant), it is called as self-pollination.
b) Cross-pollination – When the pollens from the anther of a flower on one
plant are transferred to the stigma of a flower on another similar plant, it is
called cross-pollination.
 In the fertilization process, primary endospermic nucleus is formed.
 After the fertilization process, the ovary develops into the fruit and ovules into
seed.
HOW DO ORGANISMS REPRODUCE
2. Sexual reproduction in animals.
 Reproduction resulting from the fusion of male and female sex cells is known as
sexual reproduction.
 These sex cells are special reproductive cells called as ‘gametes’.
 In sexual reproduction, a new offspring is formed from two parents of opposite
sexes: a male parent and a female parent.
 Each of the two parents have a different reproductive system.
 The male parent has male sex gametes which are called as ‘sperms’ and the
female parent contains female sex gametes which are called as ‘ovum’ or ‘egg’.
 The male reproductive system
 The human male reproductive system consists of a pair of testes, scrotum,
vas deferens, a pair of epididymis, seminal vesicles, prostate gland and
penis.
 It consists of portions which produce the germ-cells and other portions that
deliver the germ-cells to the site of fertilization.
 The germ cells or sperms are formed in the testes.
 Testes secrete the hormone testosterone that regulates the formation of
sperms. It also brings about changes in the appearance seen in boys at the
time of puberty.
 The female reproductive system
 The female reproductive system consists of the ovaries, oviduct (also called
as fallopian tubes), uterus and vagina.
 Ovaries are the primary reproductive organ in a female.
 Ovaries produce mature ova or eggs and also produce oestrogen and
progesterone which are female sex hormones.
 Fertilization
 Internal fertilization takes place in human beings.
 The sperms produced in the testes are introduced into the vagina through
penis during copulation.
 Only one sperm fuses with the ovum in the oviduct (fallopian tube) to form
a zygote.
 The zygote divides rapidly to form an embryo which gets embedded in the
uterus. This process is called as the implantation.
 The embryo gets nutrition from the mother’s blood with the help of a special
tissue called placenta.
HOW DO ORGANISMS REPRODUCE
 The development of the child inside the mother’s body takes approximately
nine months after which the child is born as a result of rhythmic
contractions of the muscles in the uterus. This process is known as
parturition.
 Menstruation
 The breakdown and removal of the inner, thick and soft lining of the uterus
along with its blood vessels in the form of vaginal bleeding is called as
menstrual flow or menstruation.
 Menstruation occurs if an ovum released by the ovary is not fertilised by the
sperm during ovulation.
 Menstruation begins when the girl reaches puberty at the age of about 10 to
12 years.
 It occurs after a fixed period of 28 days (to 30 days) due to which it is called
as menstrual cycle.
 After the age of 45 – 50, menses stop and the process is called as
menopause. It indicates the end of the reproductive phase of a woman.
 Reproductive Health.
 Many ways have been devised to avoid pregnancy. These contraceptive
methods fall in a number of categories. Some of these barrier methods are as
follows.
1) Mechanical barrier method – This method prevents conception by
preventing either the sperms from entering the uterus or by preventing
implantation if fertilization has occurred.
e.g. Condoms, cervical cap, diaphragm and ICDU method.
2) Hormonal method – This method is used by women to suppress the
production of ovum e.g. Oral pills.
3) Chemical contraception – These include creams, jellies and foaming
tablets which are placed in vagina for killing sperms.
4) Surgical techniques :a) Vasectomy – This involves blocking the vas deferens of the
male by cutting a small piece and tying the rest which blocks the
passage of sperms from the testes to semen.
b) Tubectomy – A portion of both the fallopian tubes is excised
and ligated to block the passage of ovum.