NCERT Class 10 Science Solutions: How do Organisms Reproduce

Question:

The female reproductive system in human beings is a complex network of organs responsible for reproduction. Key components include organs that produce eggs, facilitate fertilization, and support the development of a fetus. The male reproductive system has distinct organs responsible for producing sperm and delivering it for fertilization.


The question asks to identify which of the given options is NOT a part of the female reproductive system.
A. Ovary: Ovaries are the primary female reproductive organs, responsible for producing eggs (ova) and female hormones like estrogen and progesterone. Therefore, it IS a part of the female reproductive system.
B. Uterus: The uterus is a muscular organ where a fertilized egg implants and develops into a fetus. Therefore, it IS a part of the female reproductive system.
C. Vas deferens: The vas deferens (also known as the sperm duct) is a tube that carries sperm from the epididymis to the ejaculatory duct in the male reproductive system. It is not involved in the female reproductive system.
D. Fallopian tube: Fallopian tubes (also called oviducts) connect the ovaries to the uterus. Fertilization typically occurs in the fallopian tubes. Therefore, it IS a part of the female reproductive system.
Based on this, the vas deferens is the only organ listed that is not part of the female reproductive system.

Final Answer: The final answer is $\boxed{C}$

Question:

The question asks about the contents of an anther. To answer this, one needs to understand the structure of a flower and the reproductive parts of a plant, specifically the stamen. The stamen is the male reproductive organ of a flower and consists of the anther and the filament. The anther is the part of the stamen that produces and contains pollen.


The anther is the part of a stamen, which is the male reproductive organ of a flower. The primary function of the anther is to produce and hold pollen grains. Pollen grains contain the male gametes of the plant.
Option A, Sepals, are leaf-like structures that enclose and protect the bud before it opens.
Option B, Ovules, are structures found within the ovary of a flower and develop into seeds after fertilization. They are part of the female reproductive organ (pistil/carpel).
Option C, Carpel (or pistil), is the female reproductive organ of a flower, consisting of stigma, style, and ovary. The ovary contains ovules.
Option D, Pollen grains, are microscopic structures that carry the male gametes. They are produced and stored within the anther.

Therefore, the anther contains pollen grains.

The final answer is $\boxed{D}$.

Question:

Asexual reproduction is a mode of reproduction that involves a single parent and produces offspring that are genetically identical to the parent. Budding is a type of asexual reproduction where an outgrowth or bud develops from the parent organism, eventually detaching to form a new independent organism. Key examples of organisms that reproduce asexually through budding are important to recall.


The question asks to identify the organism that reproduces asexually through budding. Let’s examine the options:
A. Amoeba reproduces asexually primarily through binary fission, where the cell divides into two identical daughter cells.
B. Yeast is a fungus that commonly reproduces asexually through budding. A small bud-like outgrowth forms on the parent cell, grows, and then separates.
C. Plasmodium is a protozoan parasite that causes malaria. Its asexual reproduction involves multiple fission within host cells.
D. Leishmania is another protozoan parasite that reproduces asexually through binary fission.

Therefore, yeast is the organism that reproduces asexually through budding among the given options.

The correct answer is B.

Question:

Pollination is the transfer of pollen from the anther to the stigma. Fertilization is the fusion of the male gamete with the female gamete.


Pollination and fertilization are two distinct but sequential events in the sexual reproduction of flowering plants.

Pollination is the *transfer* of pollen grains from the anther (the male part of a flower that produces pollen) to the stigma (the receptive tip of a carpel, or of several carpels fused together, in the gynoecium of a flower). This transfer can occur through various agents like wind, water, insects, birds, or other animals. It is essentially a prerequisite for fertilization, ensuring that the male gametes reach the vicinity of the female gamete. There are different types of pollination, such as self-pollination (pollen transferred to the stigma of the same flower or another flower on the same plant) and cross-pollination (pollen transferred from a flower on one plant to a flower on another plant of the same species).

Fertilization, on the other hand, is the *fusion* of the male gamete (contained within the pollen grain) with the female gamete, also known as the ovum or egg cell (located within the ovule). After pollination, if the pollen is compatible, it germinates on the stigma and grows a pollen tube down through the style to reach the ovary. Inside the ovule, the male gamete fuses with the egg cell. This fusion results in the formation of a zygote, which is diploid (containing chromosomes from both parents). The zygote then develops into an embryo, and the ovule develops into a seed, while the ovary develops into a fruit.

In summary:
Pollination = Transfer of pollen.
Fertilization = Fusion of gametes.

Question:

Asexual reproduction, spores, advantages of spore reproduction, dispersal, survival.


An organism reproducing through spores benefits in several ways, primarily related to survival and dispersal.

1. Dispersal and Colonization: Spores are typically very small, lightweight, and often have protective outer layers. This allows them to be easily dispersed by wind, water, or animals over long distances. This wide dispersal increases the chances of the organism finding new, favorable environments to colonize and grow, leading to a wider geographical distribution.

2. Survival in Unfavorable Conditions: Many spores are highly resistant to harsh environmental conditions such as extreme temperatures, dryness, or lack of nutrients. They can remain dormant for extended periods, waiting for favorable conditions to arise before germinating. This resilience significantly enhances the organism’s survival rate.

3. Rapid Multiplication: Asexual reproduction through spores is a rapid process. A single organism can produce a vast number of spores, leading to quick population growth when conditions are suitable.

4. Genetic Uniformity (if desired): Since spore formation in many organisms is a form of asexual reproduction, the offspring are genetically identical to the parent. This can be advantageous if the parent organism is well-adapted to its current environment, as it ensures the continuation of those advantageous traits.

In summary, spore reproduction provides a powerful strategy for organisms to spread widely, survive challenging conditions, and multiply rapidly, ensuring the continuation and propagation of the species.

Question:

Puberty is the biological process of sexual maturation that occurs in adolescence. For girls, this involves the development of secondary sexual characteristics and the onset of menstruation, driven by hormonal changes.


At the time of puberty, girls experience several significant physical and physiological changes. These include:

1. Breast Development: The breasts begin to enlarge and develop, a process that starts with the budding of the nipples and areolas.

2. Growth Spurt: Girls typically experience a rapid increase in height and weight. This growth spurt often begins before that of boys.

3. Development of Pubic and Armpit Hair: Hair starts to grow in the pubic area (around the genitals) and in the armpits. This hair is typically coarser and curlier than body hair.

4. Changes in Body Shape: The body shape changes as fat is distributed more around the hips, thighs, and breasts, leading to a more rounded physique.

5. Menstruation (Menarche): The onset of the first menstrual period, known as menarche, is a key indicator of puberty. This occurs when the reproductive organs mature and the menstrual cycle begins.

6. Vaginal Lubrication: The vagina begins to produce natural lubrication.

7. Acne: Hormonal changes can lead to increased oil production in the skin, resulting in acne breakouts on the face, chest, and back.

8. Voice Changes: While less pronounced than in boys, some girls may experience a slight lowering of their voice.

Question:

The question is about the accessory glands of the male reproductive system. The key concept is understanding the function of these glands in producing seminal fluid and its role in sperm viability and transport.


The seminal vesicles and the prostate gland are accessory reproductive glands in males. Their primary role is to contribute to the seminal fluid, which is a mixture of secretions that nourishes, protects, and transports sperm.

The seminal vesicles produce a alkaline fluid that makes up about 70% of the semen volume. This fluid contains fructose (for sperm energy), prostaglandins (which stimulate smooth muscle contractions in the female reproductive tract to aid sperm movement), and clotting factors.

The prostate gland secretes a milky, slightly acidic fluid that constitutes about 25% of the semen volume. This fluid contains citrate (a nutrient for sperm), enzymes like prostate-specific antigen (PSA) which liquefies the semen after ejaculation, and other substances that contribute to sperm motility.

Together, the secretions from the seminal vesicles and the prostate gland, along with the contribution from the bulbourethral glands, form the semen. Semen not only transports sperm but also protects them from the acidic environment of the female reproductive tract and provides them with the necessary nutrients for survival and motility.

Question:

Heredity, Genes, DNA, Reproduction, Cell Division


DNA copying, also known as DNA replication, is absolutely essential for reproduction because it ensures that genetic information is accurately passed from one generation to the next. Organisms reproduce to create offspring that are similar to themselves. This similarity is due to the inheritance of specific traits, which are determined by genes. Genes are segments of DNA that carry the instructions for building and operating an organism.

During reproduction, especially asexual reproduction (like binary fission in bacteria or budding in yeast) or the production of gametes in sexual reproduction (sperm and egg cells), the cell needs to make an exact copy of its entire DNA. This copied DNA is then distributed to the new daughter cells or gametes. If DNA were not copied, the offspring would receive only half or none of the necessary genetic material, making them unable to survive or develop properly. In sexual reproduction, the fusion of two gametes (each with a copy of half the DNA) results in a new organism with a complete set of genetic information, half from each parent. Therefore, DNA copying is the fundamental process that allows for the faithful transmission of genetic traits and the continuation of life.

Question:

The embryo’s nourishment relies on a specialized organ called the placenta, which facilitates the exchange of nutrients, oxygen, and waste products between the mother and the developing fetus.


Inside the mother’s body, the developing embryo (and later, fetus) receives nourishment through a vital structure called the placenta. The placenta attaches to the uterine wall, and a cord, known as the umbilical cord, connects the placenta to the embryo.

The placenta acts as an interface between the mother’s circulatory system and the embryo’s circulatory system. Nutrients such as glucose, amino acids, vitamins, and minerals, along with oxygen, are transferred from the mother’s blood to the embryo’s blood through the placenta. This transfer occurs via diffusion and active transport across the placental membranes.

Simultaneously, waste products from the embryo, such as carbon dioxide and urea, are passed from the embryo’s blood into the mother’s blood to be eliminated by the mother’s body.

Therefore, the placenta plays a crucial role in providing the developing embryo with all the essential substances required for growth and development while removing waste, effectively sustaining it within the mother’s body.

Question:

Asexual reproduction in unicellular organisms involves the division of a single parent cell into multiple daughter cells. Binary fission and multiple fission are two distinct methods of asexual reproduction.


Binary fission is a type of asexual reproduction in which a single parent cell divides into two approximately equal daughter cells. The nucleus divides first, followed by the cytoplasm. This is commonly observed in organisms like Amoeba and Bacteria.

Multiple fission is a type of asexual reproduction in which a single parent cell divides to produce many daughter cells simultaneously. The nucleus divides multiple times, and then the cytoplasm divides around each nucleus, forming numerous small daughter cells. This process is often observed in unfavorable conditions, allowing the organism to produce many offspring when conditions become favorable. For example, Plasmodium (malaria parasite) exhibits multiple fission.

The key difference lies in the number of daughter cells produced at once. Binary fission yields two daughter cells, while multiple fission yields many daughter cells.

Question:

Cell differentiation, specialization, complexity of multicellular organisms, reproductive strategies


Regeneration is the process by which an organism regrows lost or damaged body parts or even creates an entirely new organism from a fragment. This ability is more common and efficient in simpler organisms like Hydra, starfish, and flatworms. More complex organisms, like humans and other mammals, have evolved highly specialized cells and tissues. These cells are so differentiated that they have lost the ability to revert to a less specialized state and divide to form entirely new, complex structures. The intricate network of interconnected systems and organs in complex organisms also makes it impossible for a simple fragment to develop into a complete, functional individual. Instead, complex organisms rely on sexual reproduction, which involves the fusion of specialized gametes (sperm and egg) to create a new genetically unique individual. While complex organisms can regenerate some tissues or organs (e.g., liver, skin), they typically cannot regenerate an entire new organism.

Question:

Evolution, Natural Selection, Adaptation, Survival of the Fittest, Genetic Variation, Environmental Change


Variation is beneficial to a species because it increases the chances of survival for the entire group when faced with environmental changes or new challenges. Different individuals within the species will have different traits due to variations. If the environment changes, some of these variations might be advantageous, allowing those individuals to survive and reproduce, passing on their beneficial traits. This ensures the species can adapt and persist over time. However, variation is not necessarily beneficial for an individual. An individual with a particular variation might be less suited to the current environment compared to others, making its survival less likely. For example, a variation that provides camouflage might be excellent in a forest but detrimental on a snowy plain. Therefore, while variation offers a survival advantage to the species as a whole by increasing its adaptability, it can sometimes put individual organisms at a disadvantage.

Question:

The menstrual cycle is a monthly series of changes a woman’s body goes through in preparation for the possibility of pregnancy. Each month, one of the ovaries releases an egg (ovulation). At the same time, hormonal changes prepare the uterus for pregnancy. If ovulation takes place and the egg is not fertilized, the lining of the uterus (endometrium) sheds, resulting in menstrual bleeding.


Menstruation occurs because of the cyclical changes in the female reproductive hormones, primarily estrogen and progesterone. After ovulation, if fertilization does not happen, the corpus luteum (which produces progesterone) degenerates. This decline in progesterone levels causes the uterine lining, which has thickened to receive a fertilized egg, to break down and shed. This shedding of the uterine lining, along with blood and mucus, is what we call menstruation or a period. It is a natural and healthy part of a woman’s reproductive life, indicating that pregnancy did not occur during that cycle.

Question:

Methods of Contraception and their functions.
Specifically, understanding the primary function of a Copper-T and its mechanism of action.
Understanding the definition and mode of transmission of Sexually Transmitted Diseases (STDs).


A Copper-T is a type of intrauterine device (IUD) used as a method of birth control. Its primary function is to prevent pregnancy by releasing copper ions that are toxic to sperm, thus preventing fertilization. It does not create a physical barrier that would prevent the transmission of pathogens (like bacteria or viruses) responsible for STDs. Therefore, while a Copper-T effectively prevents pregnancy, it offers no protection against sexually transmitted diseases. To protect against STDs, barrier methods like condoms are necessary.