|
11 |
REPRODUCTION: HOW LIFE CONTINUES? |
Reproduction is a process by which living beings produce new
individuals of their own kind.
It is 2 types: Asexual (by a single parent) and Sexual (by
two parents).
ASEXUAL REPRODUCTION
·
It involves only one
parent and hence, produces genetically identical offspring (clones).
·
Asexual reproduction is
fast and increases population quickly in favourable conditions.
·
It is seen in unicellular
organisms like bacteria, amoeba, yeast and simple multicellular organisms
(hydra, sponge). It is also seen in many plants.
·
Many plants arise new plants
from their existing growing parts (vegetative parts). It is called vegetative
propagation. E.g.,
o Plants with underground stems (potato, ginger etc.), sprout new
plants.
o Money plant stem, sugarcane stem cuttings grow into a new plant.
o Bryophyllum leaves sprout tiny plantlets which grow into
new plants.
How is vegetative propagation in
plants helpful in agriculture?
·
Scientists &
horticulturists developed several methods of vegetative propagation, such as cutting,
grafting, layering and tissue culture.
· These are used to propagate plants and have improved
agricultural and horticultural practices. They help cultivate desirable crops
on a large scale.
Cutting
It is a method of asexual reproduction where a plant part (usually a
shoot) is used to grow a new plant.
Steps:
o Collect shoot cuttings in the morning for planting.
o Remove leaves from the lower half of the cutting.
o Insert the cutting about halfway into soil mixed with compost at
an angle of about 45-60° from soil surface.
o Water regularly.
Important:
รผ
Cut the overgrown branches
of a plant at the end of its growing season. It encourages dormant buds to
grow.
รผ
Average length of cuttings
is 15–30 cm.
รผ
A cutting should have at
least 2–3 nodes.
Grafting
o Take a healthy rooted plant (Plant A) (E.g., a wild rose
variety) and a healthy stem piece from another plant (Plant B) of other varieties (E.g., yellow or pink rose plant).
o Make a wound or a slit on stem of Plant A.
o Insert the stem cutting of Plant B into the slit of Plant A.
o Protect the slit with a cotton or by wrapping film to avoid
pests entering the graft until it heals.
o Cut the other branches of Plant A.
o Water regularly and observe growth.
Steps of grafting
Layering
o Select a flexible, thin twig of a tree or a shrub (e.g., lemon)
and bury its middle part in soil.
o Water regularly. New leaves are grown on the twig.
o Roots develop from the buried part after 10–15 days.
o Cut the rooted twig from the parent plant to grow as a new
plant.
Bridging Science and Society
· Krishi
Vigyan Kendras (KVKs)
under the Indian Council of Agricultural Research (ICAR) train farmers
in modern grafting techniques to grow high-yield fruits, and boost income.
·
Tissue culture has revolutionised farming practices like banana
farming.
·
Farmers are provided healthy plantlets from shoot tips
(apical meristem) of several plants. It helps eliminate virus-infected
plants and increases yields.
Asexual reproduction in other organisms
Budding
In this, a genetically identical organism develops as an outgrowth (bud)
on the parent body due to cell division at a specific site.
Activity:
o Take 20 mL of sugar solution (1g in 10 mL) in a test tube.
o Add some yeast granules and close the test tube with a cotton
plug.
o Keep it in a warm place so the yeast becomes active.
o After 1-2 hours, place a drop of yeast mixture from the test
tube on a slide and mount it with a coverslip.
o Observe under a compound microscope.
o Small, round outgrowths (buds) appear on parent yeast cells. It
is the reproduction of yeast by budding.
Yeast with outgrowths
Budding
in hydra
·
Budding in Hydra: The
parent body produces a small bud which enlarges and separates from the
parent to live independently. Many buds grow on the parent's body at the same
time.
Spore formation
·
In this, microbes such as
fungi release tiny round structures called spores. They grow into new
fungi.
·
Thus, Fungi cause rotting
of foods. In warm weather, cooked food starts
to smell and grow fuzzy patches due to fungi. They also form black
patches on damp wall.
·
Earlier, people thought living things arose spontaneously from
non-living matter. Louis Pasteur proved that new life always comes from
pre-existing life. He found the germ theory of disease, strengthened the
cell theory, and led to practices
like food & instrument sterilisation.
Activity:
o Moisten a slice of bread or roti with a few water drops.
o Prepare a moist chamber using a plastic box or steel dabba.
Place a thin layer of cotton in it, cover it with tissue paper. Moisten it with
pre-boiled water.
o On this, put the slice of bread.
o Keep the moist chamber in a warm and dark.
o After 3 days, observe mould (Rhizopus) growth using a
magnifying glass.
o With a needle, transfer a little mould on a slide. Add cotton
blue stain. Observe under a microscope.
Observation:
·
Thread-like structures (Hyphae)
of mould with a round sac at the tip. Inside the sac, there are spores.
· The fungi growing on rotten fruits or manure also have spores
which are released in air.
· Similarly, the spores of bread mould in air settles on the moist
bread and reproduce rapidly.
Fungi
·
Spores are formed in
a sac-like structure (swollen vesicle) on a long strip of fungal hyphae.
·
One mould colony can
produce millions of spores.
·
Spores are lightweight,
usually single-celled and float in air currents. Under suitable conditions (moisture,
nutrients etc.) germinate quickly into a new individual.
Bridging Science and Society
Benefits of fungi:
·
They degrade organic wastes and pollutants.
· Help remove
heavy metals from industrial wastes.
· To derive antibiotics
like penicillin and amoxicillin.
· Some fungi
can degrade plastic.
Threads of Curiosity
· Warm (25-35°C)
and moist conditions help mould spores grow.
· Lower
temperatures slow or stop their reproduction. Hence, refrigeration prevents
food spoilage by moulds and bacteria. It also improved food storage and
year-round availability of foods.
SEXUAL REPRODUCTION
·
It involves two parents
contributing genetic material in chromosomes to the offspring.
· If offspring received the full set of chromosomes from both
parents, chromosome number would double in each generation. This biological
problem is solved by a cell division called meiosis.
How does meiosis help create
variations in sexual reproduction?
·
Each species has a fixed
number of chromosomes in cells. E.g. Humans have 23 pairs (46) of chromosomes. One
chromosome of each pair comes from each parent.
·
In meiosis, the chromosome
number of a parent cell (diploid) is reduced to half (haploid) in
daughter cells. These cells (gametes) are used only for reproduction.
·
During meiosis, the
chromosomes of each pair separate so that each gamete receives only one
chromosome from each pair. i.e., human
gamete has 23 chromosomes.
·
In animals, male gametes
are called sperm and female gametes are called eggs.
· In plants, the pollen grain contains male gametes and ovule
contains female gametes (eggs).
Activity:
·
Take 3 pairs of coloured beads.
Each pair represents two contrasting characters on different chromatids of
different chromosomes.
o Pair 1 (green): Light green & Dark green. Represent
blonde & black hair colours on chromosome 1.
o Pair 2 (blue): Light blue & Dark blue. Represent
straight and curly hairs on chromosome 2.
o Pair 3 (red): Light red & Dark red. Represent brown &
black eye colour on chromosome 3.
·
Randomly pick one bead from
each pair to make a combination. E.g., 'light green, light blue, light red'.
·
Thus, with three pairs of
characters, eight combinations are possible. So, with 23 chromosome pairs,
enormous genetic variation is possible.
Understanding the segregation of characters during the
formation of gamete by meiosis
· Random mixing creates many chromosome combinations. Thus,
children differ genetically from parents and siblings.
·
Each individual receives a
unique combination of chromosomes creating variation. This is important for the
survival of a species.
· Variation helps individuals adapt better to changing
environments. Over time, this contributes to evolution. E.g., some people can
tolerate low oxygen at high altitudes, or digest milk in adulthood.
Sexual
reproduction in flowering plants
·
Reproductive organs of flowering
plants (angiosperms) are flowers.
·
Non-flowering plants like
pines also reproduce sexually.
· Flowers attract pollinators such as insects with their colour
and fragrance.
Longitudinal section of a flower
A flower has 4 parts—sepals, petals, stamens and pistil.
o
Sepals: The green
structures that form the outermost whorl of
the flower. They protect the coloured parts of the flowers in the bud stage.
o
Petals: Most
attractive coloured projections of flowers. It attracts pollinators such as
insects for pollination.
Most of the flowers have sepals and
petals. In grasses, these structures are absent.
In some flowers, both sepals and
petals are fused.
o
Stamen: Male
reproductive part. It consists of a filament and an anther, which
produces pollen grains containing male gametes.
o
Pistil: Female
reproductive part. It has 3 subparts-
§ Stigma: Located at the tip. May be flat and/or sticky.
§ Style: A thin long tube which connects the stigma to
ovary.
§ Ovary: Swollen base of the pistil. Contains ovules.
Each ovule has an egg cell (female gamete). The transfer of pollen from stamen
to stigma is essential for the formation of fruits.
Activity: Observation table to study the parts of a
flower
|
S. No. |
Flower parts |
Presence
of floral parts in flowers |
Other feature(s) |
Guess the function of
flower part |
|||
|
A Papaya |
B Hibiscus |
C Mustard |
D Pumpkin |
||||
|
1. |
Sepal |
Yes |
Yes |
Yes |
Yes |
Usually green; forms the outermost whorl. |
Protects the flower during the bud stage. |
|
2. |
Petal |
Yes |
Yes |
Yes |
Yes |
Brightly colored; often scented. |
Attracts insects and pollinators for pollination. |
|
3. |
Stamen |
No |
Yes |
Yes |
Yes |
Male reproductive part. |
Produces pollen grains containing male gametes. |
|
4. |
Pistil |
Yes |
Yes |
Yes |
No |
Female reproductive part. |
Receives pollen. |
Activity:
o Select two juvenile flower bud and three freshly blossomed
flowers on the same sweet pea (matar) or garden pea plant.
o Remove stamens from one bud and one flower.
o Cover the selected buds and flowers with muslin cloth bags.
Leave one blossomed flower uncovered.
o Observe fruit development in uncovered flowers.
o After pods develop, remove the cloth bags.
·
Observation: Fruits
are formed in all treatments except the one in which the stamens were removed
from the flower bud.
·
Inference: Pollination
is necessary for fruit formation.
·
The transfer of pollen
grains from the anther to the stigma of a flower is called pollination.
Observation table
to study pollination in a pea plant
|
Treatments |
Flower bud |
Flower bud with |
Flower with removed stamens
(wrapped) |
Flower (wrapped with muslin
cloth bag) |
Flower (without muslin cloth
bag) |
|
Fruit
formation |
Yes |
No |
Yes |
Yes |
Yes |
How does the process of pollination occur in
flowers?
· Transfer of pollen to the stigma of the same flower or another
flower of same plant is called self-pollination.
· Transfer of pollen from the anther of a flower of one plant to
the stigma of a flower of another plant of the same type is called cross-pollination.
· Pollination is necessary for fruit and seed formation. Otherwise,
fertilisation cannot occur and the flower withers and falls without producing
offspring.
Self-pollination
Cross
pollination
Pollination strategies and reproductive
success
Pollination depends on external agents called pollinators.
E.g., wind, water, insects, birds etc.
o Pollination by wind: It is seen in wheat, maize, rice etc.
Pollen grains are light and small, produced in large numbers. Stigma is long
and feathery to trap them.
o Pollination by water: It is seen in aquatic plants, such
as Vallisneria and Hydrilla. Water currents carry the pollen from
one flower to another.
o Pollination by insects (like bees and butterflies): It is
seen in many plants like sunflower, hibiscus & marigold.
Flowers are brightly coloured,
fragrant, and produce nectar to attract insects.
Pollen grains
are large, sticky or spiny to attach to the insect's body. The stigma is also
sticky to receive pollen.
o Pollination by birds (like Indian white-eye &
sunbirds): It is seen in coral tree and hibiscus plant.
Fertilisation and seed formation
·
On reaching a compatible
stigma, pollen grains produce pollen
tubes that grow down through the
style into ovary.
·
The male gamete moves
through this tube to the ovule, and fuses with the egg cell. This fusion of
gametes is called fertilisation. It is the beginning of a new life.
·
The fertilised egg is
called a zygote. It develops into an embryo. During this, the ovary
enlarges and develops into a fruit. The ovules develop into seeds.
·
Seed dispersal occurs
by wind or water and animals.
Transformation of an ovary to a fruit
· Under favourable conditions of water, air, and temperature, the
seed germinates into a new plant.
Activity:
Studies of pollen production and seed formation by two different
pollination strategies in different flowers show the following approximate
trends:
|
Pollination strategy |
Approximate pollen grains
released per flower |
Estimated average number of
seeds formed |
|
Wind-pollinated grasses (e.g.,
maize, wheat) |
5,00,000 – 10,00,000 |
50
– 200 |
|
Insect-pollinated
plants (e.g., sunflower) |
20,000 – 40,000 |
800
– 1,000 |
·
Compare and analyse the two
strategies in terms of
o Pollen to seed ratio.
o Efficiency of pollination and seed formation.
Answer:
|
Feature |
Wind-Pollinated |
Insect-Pollinated |
|
Pollen to
Seed Ratio |
5,000 - 10,000
pollen grains for one seed. |
25 - 40 pollen
grains for one seed. |
|
Efficiency
of |
Low
Efficiency. |
High
Efficiency. Pollinators deliver pollen directly. |
· Explain why producing a very large number of pollen grains can
still be an effective pollination strategy.
Answer: Wind
pollination requires large amounts of pollen because dispersal is random. This
increases the chance of pollen reaching a stigma. It is energy-efficient since
plants produce simple, lightweight pollen instead of nectar or colourful
petals.
Meet a Scientist
· P.
Maheshwari (Father
of Indian Embryology) worked in plant
embryology (study of plant reproductive organs).
· He developed in-vitro
fertilisation technique in flowering plants by fusing an egg and male gamete in
a test tube to create new hybrid plants.
· He also grew
plant embryos on artificial nutrient media.
· His book, An
Introduction to the Embryology of Angiosperms (1950), became a classic reference.
Bridging Science and Society
·
Sexual reproduction is important in plant
breeding. It includes methods such as selective breeding, artificial
hybridisation, genetically engineered crops, etc.
·
In selective breeding, plants with desirable characters
are chosen for reproduction.
·
Artificial hybridisation involves removal of stamens,
bagging flowers to prevent self-pollination, and transfer of the selected pollens.
·
Genetic engineering introduces desired genes into plant DNA. This
helps develop high-yielding and disease-resistant crops.
Pause
and Ponder
1.
In a China-rose (hibiscus or
gudhal), a pollen tube grows and continues through the style after pollen
lands on the stigma.
Which process is about to happen next?
Answer: Fertilization is the process.
Male gamete travels down the tube to fuse with female gamete.
2. Look at the
pictures of Calotropis (madar) seeds and dandelion seeds. Can you guess
what kind of seed dispersal these seeds are adapted for?
Answer: Both are adapted for wind
dispersal. They possess light, hair-like structures allowing to be carried long
distances by the wind.
3.
A farmer plants two varieties of maize side by side,
but notices that seeds form only when pollen from one variety reaches the
stigma of the other. What type of pollination is this?
Answer: This is cross-pollination. Plants
exchange genetic material between separate individuals.
SEXUAL REPRODUCTION IN ANIMALS
In animals, there are 2 types of fertilization:
1. External
fertilization:
·
It is the fertilisation
outside the body.
·
The female releases eggs
into the water, and the male releases sperm over eggs for fertilisation to take
place.
·
E.g., Aquatic animals such
as frogs and most fish.
· Although a large number of eggs are laid, many are destroyed by
water currents or eaten by other animals.
2. Internal
fertilization:
·
It is the fertilisation inside
the female body.
·
E.g., reptiles, birds and
mammals.
·
Here, the survival chances
of the young ones are higher because the fertilised egg or embryo is protected
more.
Pause and Ponder
4.
Why do animals with external fertilisation generally
produce more eggs than animals with internal fertilisation?
Answer: It compensates for losses due to
predators, environmental hazards, and flowing water, increasing the chances of
survival and fertilisation.
5.
In animals, which fertilisation method the gametes
are more protected?
Answer: Gametes are more protected in internal
fertilization. It protects them from predators and harsh environmental
conditions.
Variation in
reproductive strategies among animals
|
Animal |
Habitat |
Mode of
fertilisation |
Number of eggs
produced |
Estimated
survival of young ones |
|
Fish |
Water |
External |
100s-1000s at a time |
Low |
|
Frog |
Water/land |
External |
5,000-50,000 at a time |
Low |
|
Lizard |
Land |
Internal |
2-20 at a time |
Moderate |
|
Bird |
Water/land |
Internal |
1-15 at a time |
Moderate to High |
VARIATIONS
IN REPRODUCTION IN ANIMALS
·
Animals must ensure meeting
of male and female gametes and survival of the young ones.
·
Fish, amphibians, and
insects produce hundreds to thousands of yolk-rich eggs to nourish
developing embryos. Since the mother cannot provide large amounts of yolk to
all eggs, the yolk is sufficient only to form a larva, which hatches from the
egg.
·
The larva, then gets
nutrition by eating organic wastes (rotten food, manures etc.). This is an
intermediate stage in its development (feeding stage).
·
After enough nutrition, the
larva transforms into an adult, as in butterflies and frogs.
·
In reptiles & birds,
egg contains enough yolk to nourish the embryo until it hatches into young one.
·
In mammals, zygote develops
inside the female body.
·
In some species, young ones
can find food immediately after birth or hatching. Others need an extended
period of post-hatching or post-birth feeding and care. This depends on the
duration of embryonic development.
· Mammals feed their young with breast milk.
REPRODUCTION IN HUMAN BEINGS
Reproductive maturity
When a child grows into adult, physical and emotional changes occur,
reproductive organs mature and begin producing gametes (sperms or eggs).
What are the parts of the male
reproductive system?
It includes a pair of testes, vas deferens, glands etc.
o Testes (singular: testis): Oval-shaped organs that
produce sperm (male germ cells). They also produce a hormone. It
controls sperm production and causes the physical changes in boys during
puberty.
Testes are present in a pouch of skin
called scrotum. It keeps the testes slightly cooler than normal body
temperature for proper sperm formation.
o Vas deferens: A long tube from the testes through which sperm
travel. It opens into urethra (a common passage for urine and sperm).
o
Glands (seminal vesicles &
prostate): They add fluids to nourish sperm, and help them remain active
and move.
o A sperm has a head containing genetic material and a long
tail to swim towards the egg.
What are the parts of the female
reproductive system?
It includes a pair of ovaries, oviducts (fallopian tubes),
a uterus, and a vagina.
o Ovaries: Produce eggs (female germ cells) and
release hormones that cause changes during puberty.
o Oviducts: Connect each ovary to the uterus.
o Uterus: A bag-like structure where a foetus develops.
The uterus opens
into the vagina through a narrow passage called the cervix.
Female reproductive system
How are reproductive cells made?
·
Gametogenesis is the
process of formation of gametes.
·
Human body cells have 46
chromosomes, but sperms and eggs have only 23, so that after fertilisation the
zygote restores the normal chromosome number of 46.
· In males, gametogenesis occurs in testes that produce sperms.
In females, gametogenesis occurs in ovaries that produce a single egg.
Structure, size, and number of male and female gametes
|
Feature |
Sperm |
Egg |
|
Size |
Very small |
Large |
|
Number produced |
Millions |
Few |
|
Stored nutrients |
Absent |
Present |
|
Motility |
Actively motile |
Non-motile |
What happens when a sperm meets an
egg?
·
At birth, a girl's ovaries
have millions of immature eggs.
·
From puberty onwards, one
mature egg is released every month from one ovary. This is called ovulation.
·
Before ovulation, the
uterine inner lining starts to thicken. After ovulation, the egg travels to the
oviduct.
·
During sexual intercourse,
millions of sperm enter through the vagina. They swim through reproductive
tract and may reach the egg in the oviduct. If a sperm encounters and fuse with
an egg, a zygote is formed.
Process of fertilization
·
The uterine lining becomes
thicker and richer in blood vessels.
· As the zygote moves to the uterus, it undergoes a series of
mitotic divisions. Then it implants into the uterine lining to receive
nourishment for development. This implantation marks the beginning of pregnancy.
Meet a
Scientist
·
In-vitro Fertilisation (IVF) is a technique in which egg and
sperm are fused outside the female body in a laboratory dish.
·
The fertilised egg is implanted into the uterus. A
baby born through this method is called test tube baby (it actually
occurs in a culture dish, not in a test tube).
· In 1978, Subhash
Mukhopadhyay of Kolkata pioneered India's first test tube baby, Kanupriya
Agarwal (nickname: Durga).
What happens when an egg is not
fertilised?
·
If an egg is not
fertilised, it remains viable for about a day and then it degenerates.
·
The thickened uterine
lining is no longer needed. So, it sheds and along with some blood, leaves
through the vagina. This is called menstruation (period). It lasts
3 to 7 days.
·
The cycle of ovulation,
preparation of the uterus and menstruation repeats every 21-35 days (often 28
days). This cycle begins at puberty (ages of 10-14) and continues till menopause
i.e., around age 50.
Key
stages of the menstrual cycle across a typical 28-day period
Threads of Curiosity
·
Human has two sex chromosomes – XX in females
and XY in males.
· The mother
contributes an X chromosome to a baby and the father contributes X (Female: XX)
or Y (Male: XY). Thus, male determines the biological sex of a baby.
Bridging Science and Society
Hygiene practices
during menstruation:
รผ Use menstrual
products like sanitary pads, tampons, menstrual cups, etc.
รผ Wash
regularly — clean genital area. Avoid soap, as this can disrupt the natural
bacterial balance.
รผ Wash hands with
soap, before and after changing sanitary pad.
รผ Proper
disposal— wrap used pads before disposing them in a bin. Do not flush them down
the toilet.
รผ Follow the
manufacturer's instructions for cleaning reusable products. Ensure reusable
pads are completely dry before their next use.
รผ
Change menstrual products regularly — change pads in
4-6 hours, or more often if the flow is heavy.
Period is your pride: Menstruation is a sign of a
healthy reproductive system, not something to be ashamed of.
Pregnancy and childbirth
·
Human pregnancy lasts about
9 months. It is divided into 3 stages called trimesters. The
uterus protects and nourishes the baby throughout this time.
·
First trimester: Fertilised
egg develops into an embryo during the first
2 months and major organs start forming. From 9th week, the
developing embryo is called a foetus.
·
Second trimester: The
foetus grows bigger and stronger. The mother can feel its movements.
·
Third trimester: The
baby grows rapidly and gets ready for the life outside the womb.
·
During childbirth, strong
contractions of the uterine muscles help push the foetus out through birth
canal.
·
If a normal vaginal birth
is not possible or safe for the mother or the foetus, doctors may use medical
or surgical procedures to help deliver the baby safely.
·
After birth, breastfeeding
is essential because mother's milk provides complete nutrition and protects the
infant from many diseases.
·
Newborns must be kept warm,
vaccinated on time and
handled gently.
·
The mother requires
nutritious food and adequate rest,
and avoid
harmful habits, such as smoking, alcohol, or taking any medicines without
medical advice.
|
Pause and Ponder
6.
Ravi suddenly notices that he is growing taller
rapidly, his shoulders are broadening, and his voice cracks. What stage of life
is he entering?
Answer: Ravi is entering puberty
(adolescence).
7.
Rina's period occurs every 28 days. Her last period
was on the 5th of March. On which day is she most likely to get her
next period?
Answer: April 2nd.
8.
A human zygote has just formed. How many chromosomes
does it have?
Answer:
46 chromosomes (23 pairs).
Mother's health during pregnancy
It is important for the baby's growth and safety.
o Eat balanced diet rich in proteins, vitamins & minerals.
o Attend regular medical check-ups.
o Follow doctor's advice regarding light exercise and rest.
o Emotional well-being. Support from family members helps her
remain healthy and stress-free.
Threads of Curiosity
·
Some mothers may experience anxiety and fatigue after
childbirth, called post-partum depression.
·
They should seek help from healthcare workers if they
feel low or overwhelmed.
Bridging Science and Society
·
Over 10 lakh ASHA workers across India promote
hygiene, immunisation, family planning, maternal care, safe deliveries, and
contraceptive awareness, under the National Health Mission, especially
in rural areas.
What does it mean
to be sexually mature?
·
During adolescence, the
body gradually attains sexual maturity (sperm production, menstrual
cycle etc.) and becomes capable of reproduction, but emotional maturity and
social maturity develop more slowly.
·
Emotional maturity involves
handling feelings, clear communication, and thoughtful decisions.
How can unwanted pregnancies and
infections be prevented?
·
Readiness for sexual
activity involves thoughtful and responsible decision-making to prevent
unplanned pregnancies, sexually transmitted infections, and support healthy
relationships.
·
Infections transmitted
through sexual contact from an infected person to another are called Sexually
Transmitted Infections (STIs). E.g., gonorrhoea, herpes, syphilis, genital warts, and HIV (leads
to AIDS).
·
Some of these are not
curable.
·
Condoms can prevent
their transmission and also help prevent pregnancy.
Contraceptive methods to prevent unwanted pregnancy
o Barriers: They stop sperm from reaching the egg. E.g.,
condoms or vaginal covers.
o Medicines (oral pills): They change the release of eggs
by altering hormones. They have some side effects.
o Intra-Uterine Devices (IUDs): These are placed in uterus
to avoid pregnancy. E.g., copper-T. They may irritate the uterus.
o Surgical methods: Used to stop unwanted pregnancies.
These include blocking the vas deferens in males or the fallopian
tubes in females, so that the sperm and the egg cannot meet.
·
Unwanted pregnancies can be
removed by surgery during the first trimester (embryo is very small).
This procedure is called abortion.
·
Sex-selective abortion
disturbs the societal sex ratio, so prenatal sex determination is legally
prohibited in India to maintain a balanced society.
Bridging Science and Society
·
Central Drug Research Institute, Lucknow, developed the world's
first non-steroidal and non-hormonal oral contraceptive pill. Taken once
weekly, it avoids side effects like weight gain, nausea, or headaches.
·
It is safe, convenient, and effective. It is provided
free through the National Family Planning Programme.
Pause and Ponder
9.
What protective devices can be used during sexual
activity to reduce the spread of STIs?
Answer: Condoms
10.
If a couple uses oral contraceptive pills but not
condoms, which risks remain and why?
Answer: Pills prevent pregnancy but do
not reduce the risk of STIs because they do not block bodily fluid exchange or
skin-to-skin contact.
11.
In many animals,
the young ones can walk or find food soon after birth but human babies are completely
dependent for a long time. What might be some advantages and disadvantages of
this for humans as a species?
Answer:
Advantages: It supports better brain development,
learning, language skills, and strong social bonding.
Disadvantages: It requires
high parental investment and is highly vulnerable without constant protection.