NCERT Solutions for Class 10th Science Chapter 7 How do Organisms Reproduce?

DNA copying is important because it passes the parent's traits to the offspring.  OR  DNA copying is important because it gives the new baby the same instructions as the parents.

It helps the new cell or organism know how to grow and work.
Small changes during copying also create differences between individuals

Variation is useful for a species because it gives different members different qualities, so if the environment changes, some of them can still survive.
But a single individual doesn’t always benefit from the variation it has — it might help, or it might not make any difference.
So variation helps the species continue, even if it doesn’t always help each individual.

In binary fission, one organism splits into two equal parts, each becoming a new organism (like in amoeba).
In multiple fission, one organism divides into many daughter cells at the same time (like in Plasmodium).

So, binary fission produces two offspring, while multiple fission produces many in one go.

An organism benefits from spore formation because spores can survive harsh conditions like heat, dryness, or lack of food.
They are light and easily spread by wind or water, helping the organism spread to new places.
When conditions become favourable again, the spores grow into new organisms.

More complex organisms cannot reproduce by regeneration because their bodies are made of many specialised cells and organs that depend on each other.
If a big part is cut, the body cannot rebuild all those complex organs again.

Regeneration in such organisms only helps in healing wounds, not making a whole new individual.

Vegetative propagation is used because it produces new plants quickly and without seeds. The new plants are exactly like the parent plant, so good qualities are preserved.
It also helps grow plants that don’t produce viable seeds or take too long to grow from seeds.

DNA copying is essential because it passes the parent’s information and traits to the offspring.  It makes sure the new cell knows how to grow, function, and develop properly.

Without DNA copying, the new organism would not get the instructions it needs to live.

Pollination is the transfer of pollen from the anther to the stigma of a flower.  Fertilisation happens after pollination, when the male cell in the pollen fuses with the female egg cell inside the ovule.

So, pollination is about pollen reaching the stigma, while fertilisation is about fusion of male and female gametes.

The seminal vesicles and prostate gland produce fluids that mix with sperm to form semen.
These fluids give energy to the sperm and help them move smoothly.
They also protect the sperm and make it easier for them to travel through the female body.

Girls become taller, their breasts start to grow, and their hips get wider. Hair appears under the arms and in the private parts.
They also start their periods, showing that their body is becoming mature.

Inside the mother’s body, the embryo receives nourishment through a special organ called the placenta.
The placenta is attached to the wall of the uterus and connected to the embryo by the umbilical cord.
Food, oxygen, and other nutrients from the mother’s blood pass through the placenta and enter the baby’s blood without the two bloods mixing.
At the same time, waste materials from the embryo are carried back through the placenta to the mother’s blood for removal.
This exchange keeps the embryo healthy and helps it grow properly until birth.

No, a copper-T cannot protect a woman from sexually transmitted diseases. It only prevents pregnancy. To avoid STDs, using condoms is necessary because they block the transfer of germs during sex.

Sexual reproduction is better because it mixes the traits of two parents, so the offspring are all a little different from each other. These differences help the species survive if the environment changes, because some individuals may be better adapted.

In asexual reproduction, all offspring look the same, so if conditions become bad, the whole group can be affected.

The testis produces sperm, which are the male reproductive cells.
It also makes the male sex hormone testosterone, which controls changes at puberty and the development of male features.

So, the testis is responsible for making sperm and producing hormones.

Menstruation happens when the egg is not fertilised.
The thick wall inside the uterus is not needed, so it breaks and comes out as blood. This monthly bleeding is called menstruation.

Different methods of contraception include:

1. Barrier methods – like condoms, which stop sperm from reaching the egg.
2. Hormonal methods – like birth control pills, which prevent the release of an egg.
3. Intrauterine devices (IUDs) – like copper-T, which prevent fertilisation inside the uterus.
4. Surgical methods – like vasectomy in men and tubectomy in women, which permanently block the reproductive tubes.

These methods help prevent pregnancy in different ways.

In  unicellular organisms, reproduction is usually done by simple methods like binary fission or budding, where one cell divides to form a new organism.
In multicellular organisms, reproduction is more complex and usually involves special reproductive organs and cells (like sperm and egg).

So, unicellular organisms reproduce by simple cell division, while multicellular organisms use organised reproductive systems.

Reproduction helps keep a species stable because it makes new individuals to replace the ones that die. It also passes on the species’ traits from one generation to the next, so the group continues to survive.
By producing more members, reproduction keeps the population from disappearing.

People adopt contraceptive methods to avoid unwanted pregnancy and plan their family.
They help couples decide when they want to have children.
Contraceptives also protect the health of the mother by spacing births and, in some cases like condoms, help reduce the risk of sexually transmitted diseases.