Notes of How do organisma reproduce? ( Sexual reproduction in Plants and humans)
Sexual
Reproduction
When
reproduction takes place as a result of fusion of two gametes, one
from
each parent, it is called sexual reproduction
The process of fusion of male and female gametes is called fertilization.
˜ The
formation of gametes involves exchange of chromosomal (genetic)
fragments between homologous chromosomes causing genetic
recombination
which leads to variation.
Gametes: Special Reproductive cells
are different from normal cells as they have half
the number of chromosomes.
the number of chromosomes.
e.g Human cells have 46 chromosomes but sperm and egg have 46/2=23
chromosomes.
So when sperm and egg fuse, zygote will have 23+23= 46 chromosome.
Male gamete : small in size and motile (has tail)
Female gamete: big in size ( because of stored food reserve) and
non motile.
Sexual Reproduction in Plants
It occurs mostly in flowering plants. In fact flowers are the
reproductive organ of plants.
FLOWERS
Bisexual Flowers
|
Unisexual Flowers
|
Both male and female reproductive part i.e., stamen &
carpel are present.
|
Either male or female reproductive part is present.
|
Eg. Hibiscus, mustard
|
Eg.
Papaya, Watermelon
|
A typical flower consists of four main whorls namely 1. Calyx
(Sepals),
2. Corolla (Petals),
3. Androceium (Stamens)
and
4. Gynoecium( Carpels).
Reproductive
Part of Flower
1. STAMENÃ Anther (2n) + Filament
Pollen grains
(Male gamete)
(n)
2. CARPEL-Ã Stigma +
Style + Ovary(2n)
Egg cell
(ovule)
(n)
Pollination:
Transfer of pollen grains from anther to stigma of carpel.
(Self-Pollination)
Pollen
grains transferred to the stigma of the carpel of the same flower (Cross-Pollination)
Pollen grains transferred to the stigma
of carpel of the another flower ˜ This
transfer of pollens is achieved by agents like wind, water or animals.
˜ After Pollination, a pollen
tube grows out of pollen grains, through which male
germ cell reaches the ovary and fusses
with the female germ cell.
˜Fertilization:The
fusion between the pollen grain and female egg cell.
- It occurs inside the ovary. Zygote is
produced in this process.
-Zygote divides several times to form an
embryo within the ovule.
-The ovule develops a tough coat and is
converted into a seed.
- Ovary grows rapidly and ripens to
forms a fruit, while the seed contains the future plant or embryo which develops into a
seedling under suitable condition. This process is known as Germination.
Reproduction
in Human Beings
˜ Humans use Sexual Mode
of reproduction.
˜ It needs sexual
maturation which includes creation of the germ cells
i.e., egg (ova) in the female and sperm in the
male .
This
period of attainment of sexual maturation is called Puberty.
Pubertal changes/Secondary
sexual characteristics:
(Common) Hair growth in armpits, genital
region,
Acne/ pimples(excessive oil production
by sebaceous glands in skin)
(Girls) : Breast
development, Menstruation
( Boys) : Facial hair i.e. beards,
moustaches, Adam’s apple (change in voice)
Penis enlargement..
˜ Human beings have a
well developed male and female
reproductive system.
Male Reproductive
System- Male
reproductive organ (Testis)
+ Other glands (Prostate Gland and seminal
vesicles)
+ Ducts
(Vas deferens, Ejaculatory duct…)
.
The
Testes
(male reproductive organ)
Function:
a) Formation of male germ cell (sperms)
takes place.
Location:
A pair of testes are located inside scrotum situated outside the
abdominal cavity. It is meant to keep
relatively a low temperature
needed for the production of sperms by
testes.
Function:
b) Testes release a male sex hormone
called testosterone whose
function is to:
1. Regulate the production of sperm
2. Brings about changes in appearance
seen in boys at the time of puberty.
The
sperms along with the secretion of prostate gland and seminal vesicle,
together constitute semen.
( Sperms + Secretions of
Prostate gland and seminal vesicles = Semen)
Secretions of Prostate gland and seminal vesicles-
1.Provide nourishment to sperms.
2.
Help sperms in their movement by lubricating the ducts.
The semen is released and made to enter into
the female genital tract during Copulation.
Female
Reproductive System- Female
reproductive organ (Ovary)
+ Ducts (Fallopian tube, Uterus, Vagina)
Ovary-Location: One ovary each on
both sides of abdomen.
Function: 1.The female germ
cells or eggs are produced in the ovaries.
(When a girl is born, the ovaries
already contain thousands of immature eggs.
At the puberty, some of these eggs
start maturing. One egg is produced
every
month by one of the ovaries.
2. Female sex hormones (oestrogen and progesterone) are produced
in ovary.
Fallopian tube:
Carries egg from ovary to the uterus (also known as womb)
Uterus:
is an elastic bag like structure in which development of embryo takes place.
˜ The Uterus opens into
the vagina through the cervix (birth canal).
Fertilisation
:
(Fusion of sperm and egg)
˜ Fertilization occurs in
the fallopian tube of female genital tract. (Internal fertilization)
˜ The fertilized egg also
called zygote (2n) starts dividing, reaches uterus and gets
embedded in the thick lining of the uterus, (which is richly supplied with blood to
nourish the growing embryo) . This process is known as Implantation.
embedded in the thick lining of the uterus, (which is richly supplied with blood to
nourish the growing embryo) . This process is known as Implantation.
˜ Placenta. The Embryo
gets nutrition from the mother's blood with the help of a
special tissue called Placenta.
special tissue called Placenta.
(Function) - It provides a large surface area for glucose and oxygen to
pass from the mother to the embryo.
pass from the mother to the embryo.
- Similarly the wastes from developing embryo
are removed
to mother's blood through placenta.
to mother's blood through placenta.
- Placenta
also produces hormones to support pregnancy.
˜ The child is born as a
result of rhythmic contractions of the muscles in the uterus. After nine months
(36 weeks) of development inside mother's womb. This is called Gestation
Period.
If no fertisation
occurs (i.e. sperms are not present in the female genital
tract) –
1. Zygote
is not formed,
2. The
inner wall of uterus breaks which causes bleeding through vagina. This process is called MENSTRUATION. It occurs at a
regular interval of 28 days.
˜ The sexual
cycle in a woman continues upto the age of 45 to 50 years.
After that the ovary do not
release egg. This stage is called Menopause.
It also marks the end of menstruation in the
woman.
Reproductive Health
˜ Reproductive
Health means a total well-being in all aspects of reproduction, i.e.,
physical emotional, social and behavioural.
˜ Contraception
: It is the avoidance of pregnancy.
It can be achieved by preventing the fertilization of ova.
Methods
of contraception
11. Physical
Barrier: To prevent union of
sperm & egg.
Use
of condoms, Diaphragm & cervical
caps.
22. Surgical
Method: Also called sterilization.
In vasectomy, the vas deferens of male is blocked to
prevent sperm transfer.
In tubectomy, the fallopian
tube of female is blocked to prevent egg to reach uterus.
3. Chemical Method : Oral contraceptive
(OCs) - changes the hormonal balance to
check the egg release in females.
OCs cause side effect.
4. IUDs: Intrauterine contraceptive device-
Copper-T or loop is placed in uterus to
prevent
pregnancy.
˜ Healthy
society needs a balanced sex ratio that can be achieved by educating the
people to avoid malpractices like female foeticide & prenatal sex determination.
people to avoid malpractices like female foeticide & prenatal sex determination.
Sexually
Transmitted diseases (STDs)
VIRAL STDs: Eg.
H.I.V. – AIDS, Warts
Bacterial STDs: Eg. Syphilis and Gonorrhoea
STDs
are communicated during unsafe sexual contact.
These
diseases (STDs) can be prevented by using physical barrier i.e.
condom.
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