Questions Related to Science

In humans, the mother always gives an X chromosome. The father can give either an X or a Y chromosome.
If the father gives X, the child is girl (XX).
If the father gives Y, the child is boy (XY).

So, the sex of the child is determined by the father.

No, this information is not enough to tell which blood group is dominant.
The father could be AA or AO, and the mother is OO, so the child can get O only if the father has an O gene (AO).

So we cannot decide dominance just from this one family — we need more crosses to be sure.

Mendel crossed plants with two different traits and found new combinations in the next generation.
Traits like seed shape and seed colour got mixed in different ways.
This showed that each trait is inherited independently of the other.

Mendel crossed a tall plant with a short plant. All the plants in the first generation were tall. This means the tall trait hides the short trait.
When these tall plants were crossed again, the short plants came back in the next generation.
This showed that:
Tall trait = dominant (shows itself)
Short trait = recessive (gets hidden but is not lost)
So Mendel proved that some traits hide others, which is why they are called dominant and recessive.

Variations help a species survive because they make some individuals better suited to changes in the environment.
If the climate changes, food becomes less, or a new disease appears, not all individuals will be affected in the same way.
Those with useful variations will survive and reproduce, while others may die.

So, variations increase the chances that at least some members of the species will survive, even when conditions change.

Trait B must have appeared earlier.
This is because in asexually reproducing organisms, traits spread very slowly. Since Trait B is found in 60% of the population and Trait A only in 10%, the trait that is present in more individuals must have been there for a longer time.

So, Trait B arose earlier than Trait A.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.