Key Concept: Adolescence and Puberty

b) Puberty

[Solution Description]

Boys and girls become capable of reproduction during puberty. Puberty marks the onset of reproductive maturity, which occurs during adolescence.

Key Concept: Adolescence and Puberty

c) Becoming capable of reproduction

[Solution Description]

The syllabus states that the most important change which marks puberty is that boys and girls become capable of reproduction. This change indicates reproductive maturity.

Key Concept: Adolescence and Puberty

b) Due to the onset of significant hormonal changes[Solution Description]Adolescence typically begins around the age of 11 because this is when the body starts to undergo significant hormonal changes. These changes are necessary for the physical and sexual maturation required to reach reproductive maturity. The onset of adolescence varies slightly between individuals, but it generally occurs between the ages of 10 and 12.

Key Concept: Hormonal Control

c) Pituitary gland

[Solution Description]

The pituitary gland controls the secretion of hormones from the testes and ovaries. It secretes various hormones, including those that stimulate the testes to produce testosterone and the ovaries to produce estrogen. The pituitary gland plays a crucial role in regulating reproductive functions and the onset of puberty.

Key Concept: Adolescence and Puberty

c) Secretion of testosterone by testes

[Solution Description]

The development of secondary sexual characteristics in boys during adolescence is primarily due to the secretion of the male hormone testosterone by the testes. Testosterone triggers changes such as the growth of facial hair, deepening of the voice, and development of muscles.

Key Concept: Secondary Sexual Characters

b) Growth of facial hair

[Solution Description]

Secondary sexual characteristics are features that help distinguish males from females. In boys, these include the growth of facial hair, such as moustaches and beards, as well as hair on the chest.

Key Concept: Adolescence, Puberty, Hormones

c) Luteinizing hormone

[Solution Description]

The pituitary gland secretes various hormones, one of which is the luteinizing hormone (LH). In males, LH stimulates the testes to produce testosterone. This hormone is essential for the development of male secondary sexual characteristics during puberty.

Key Concept: Adolescence, Puberty

d) 13 to 19

[Solution Description]

Adolescence for the boy starts at 12 and lasts until 19. The period from 13 to 18 or 19 years is considered the "teenage" years. Since he starts adolescence at 12, his teenage years would be from 13 to 19. However, since adolescence ends at 19, the upper limit of his teenage years is 19. Thus, the range of his teenage years is 13 to 19.

Key Concept: Adolescence, Puberty, Teenage Years

d) Adolescence

[Solution Description]

The girl is in the stage of adolescence, specifically puberty, where the body undergoes changes to reach reproductive maturity. Menstruation and the development of secondary sexual characteristics are key indicators of this stage. Adolescence typically spans from 11 to 18 or 19 years, covering the teenage years, hence this stage is referred to as adolescence or teenage years.

Key Concept: Individual variations in adolescence

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The syllabus states that all parts of the body do not grow at the same rate during adolescence, and sometimes adolescents may have oversized arms, legs, hands, or feet that appear out of proportion with the rest of their body. This is because different parts of the body grow at different rates. However, over time, the other parts catch up, resulting in a proportionate body. The Reason correctly explains the Assertion, as the disproportionate growth is indeed due to the varying growth rates of different body parts.

Key Concept: Puberty and Hormones

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that the onset of puberty is controlled by hormones, which is correct as per the syllabus. The reason explains that hormones are chemical substances secreted by endocrine glands that regulate body functions, which is also true. Additionally, the reason correctly explains the assertion because the hormones secreted by endocrine glands, such as the pituitary gland, control the onset of puberty. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Definition of Puberty

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that puberty is the stage when adolescents reach reproductive maturity, which is correct as per the syllabus. The reason explains that during puberty, the body undergoes changes that make boys and girls capable of reproduction, which is also correct. Moreover, the reason correctly explains why puberty leads to reproductive maturity, as it directly links the changes in the body to the capability of reproduction. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Adolescence and Puberty, Hormones, Secondary Sexual Characters

d) Assertion is false, but Reason is true.

[Solution Description] The assertion states that the development of secondary sexual characters in boys is primarily driven by the hormone estrogen. This is incorrect because estrogen is the female hormone responsible for the development of secondary sexual characters in girls, such as breast development and widening of the hips. In boys, the hormone testosterone is responsible for the development of secondary sexual characters, including the growth of facial hair, deepening of the voice, and muscle development. The reason claims that estrogen is responsible for the growth of facial hair and deepening of the voice in males, which is also incorrect. Therefore, the assertion is false, but the reason is true.

Key Concept: Menstrual Cycle

c) Menarche

[Solution Description]

The first menstrual flow that begins at puberty in girls is termed menarche. It marks the onset of the reproductive phase in females. Therefore, the correct answer is menarche.

Key Concept: Role of Hormones

b) Testosterone

[Solution Description]

The male hormone testosterone is released by the testes at the onset of puberty. This hormone is responsible for the development of male secondary sexual characteristics such as the growth of facial hair and deepening of the voice.

Key Concept: Growth Rate Comparison

a) The boy by 13.8 cm

[Solution Description]

First, we calculate the full height of the boy using the formula:

$\text{Full height}_{\text{boy}} = \frac{\text{Present height}}{\% \text{ of full height}} \times 100 = \frac{140}{81} \times 100$

Calculating this:

$\text{Full height}_{\text{boy}} = 172.84 \text{ cm}$

Next, we calculate the full height of the girl:

$\text{Full height}_{\text{girl}} = \frac{\text{Present height}}{\% \text{ of full height}} \times 100 = \frac{140}{88} \times 100$

Calculating this:

$\text{Full height}_{\text{girl}} = 159.09 \text{ cm}$

The boy is likely to be taller as an adult. The difference in their full heights is:

$172.84 - 159.09 = 13.75 \text{ cm}$

Therefore, the boy is likely to be approximately 13.8 cm taller than the girl.

Key Concept: Rate of growth, Percentage of full height

b) 95\%

[Solution Description]

From the growth chart, a 15-year-old boy has reached 95\% of his full height. Therefore, the boy has already achieved 95\% of his full height by the age of 15.

Key Concept: Growth patterns in boys vs. girls

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The syllabus states that girls grow faster than boys during the initial stages of puberty. This is a direct observation from the growth patterns discussed. Additionally, it mentions that the rate of growth in height varies among individuals, but it is specifically noted that girls grow faster than boys initially. This directly ties the Reason to the Assertion, making the Reason the correct explanation for the Assertion.

Key Concept: Genetic factors influencing height

a) Genes inherited from parents

[Solution Description]

The height of an individual during adolescence is largely determined by genetic factors, specifically the genes inherited from parents. Although nutrition and other environmental factors play a role in growth, the primary determinant of height is genetics.

Key Concept: Balanced Diet

a) Roti, dal, and vegetables

[Solution Description]

A balanced meal includes proteins, carbohydrates, fats, and vitamins in requisite proportions. Our Indian meal of roti/rice, dal (pulses), and vegetables is a balanced meal. Milk is also a balanced food in itself.

Key Concept: Change in Body Shape

c) Region below the waist

[Solution Description]

During puberty, girls experience significant changes in their body shape. One of the primary changes is the widening of the region below the waist. This is a natural development that occurs as part of the physical transformation during adolescence.

Key Concept: Changes at Puberty

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that boys develop broader shoulders during puberty due to increased muscle growth. This is true as the syllabus mentions that boys' shoulders broaden as a result of growth during puberty. The reason states that during puberty, boys experience more prominent muscle growth compared to girls. This is also true according to the syllabus, which highlights that boys' muscles grow more prominently than girls'. Additionally, the reason correctly explains why boys develop broader shoulders, as it directly links the broader shoulders to the increased muscle growth in boys.

Key Concept: Change in Body Shape

b) Broadening of shoulders and chest

[Solution Description]

During puberty, boys undergo significant physical changes, including the broadening of their shoulders and chest. This is due to the growth of bones and muscles in these areas, which is influenced by increased levels of testosterone during this stage of development.

Key Concept: Height Calculation

c) 178 cm

[Solution Description]

According to the growth chart, a 12-year-old boy has reached 84\% of his full height. To calculate his full height, we use the formula:

$\text{Full Height} = \frac{\text{Present Height}}{\% \text{ of Full Height at this Age}} \times 100$

Substituting the values:

$\text{Full Height} = \frac{150}{84} \times 100 = 178.57 \, \text{cm}$

Therefore, his likely full height is approximately 178.57 cm.

Key Concept: Voice Change, Adam’s Apple

c) The muscles of the growing voice box go out of control, causing hoarseness temporarily.

[Solution Description] At puberty, the voice box or larynx begins to grow. In boys, the larynx grows larger, which is visible as Adam’s apple. The muscles of the growing voice box sometimes go out of control, causing the voice to crack or become hoarse. After a few days or weeks, the muscles adjust, and the voice becomes deeper.

Key Concept: Growth of the larynx, Voice Change

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description]

During puberty, the larynx grows significantly in boys, leading to the formation of the Adam’s apple. This growth causes the vocal cords to lengthen and thicken, resulting in a deeper voice. However, as the larynx is growing, the muscles controlling the vocal cords may temporarily go out of control, causing the voice to crack or become hoarse. This is a normal part of the maturation process and usually resolves within a few days or weeks. Thus, both the assertion and the reason are true, but the reason does not directly explain why the voice cracks; it explains the overall change in voice pitch. Therefore, the correct answer is that both assertion and reason are true, but the reason is not the correct explanation of the assertion.

Key Concept: Formation of Adam’s Apple in Boys

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

During puberty, the larynx in boys undergoes significant growth, leading to the formation of the Adam’s apple. This growth is primarily driven by the increased production of testosterone, a male hormone that is responsible for the development of secondary sexual characteristics in boys. Therefore, the Assertion is true, and the Reason provides the correct explanation for the Assertion.

Key Concept: Voice Change during Puberty

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

During puberty, boys experience significant changes in their bodies, including the growth of the larynx (voice box). This growth leads to the development of a larger voice box, which can be observed as the Adam's apple. As the larynx grows, the muscles controlling it may temporarily go out of control, resulting in hoarseness or cracking of the voice. This hoarseness is a normal part of puberty and usually resolves within a few days or weeks. Therefore, the assertion that hoarseness in a boy's voice during puberty is due to the growth of the larynx is true. The reason provided, that the larynx grows rapidly during puberty causing the muscles to go out of control temporarily, is also true and correctly explains the assertion.

Key Concept: Development of Sex Organs, Ovaries, Egg Maturation

b) Enlargement and maturation of eggs

[Solution Description]

During puberty, the ovaries in females undergo several changes including enlargement and the maturation of eggs. The ovaries start releasing mature eggs as part of the menstrual cycle.

Key Concept: Development of Sex Organs

c) Pituitary gland

[Solution Description]

The pituitary gland, located at the base of the brain, secretes various hormones that regulate bodily functions. One of these hormones stimulates the testes to mature and produce sperm. Thus, the pituitary gland plays a crucial role in controlling the maturation of reproductive parts in males during puberty.

Key Concept: Role of pituitary gland

b) Pituitary gland

[Solution Description]

The pituitary gland secretes hormones that stimulate the ovaries to produce estrogen. This hormone plays a crucial role in initiating and regulating the reproductive function in girls.

Key Concept: Hormonal Control of Puberty

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that the production of sperms in boys begins at puberty due to the secretion of testosterone by the testes. This is true as testosterone, a male hormone, is responsible for the development of secondary sexual characteristics and the initiation of sperm production during puberty. The reason explains that testosterone is secreted by the testes under the stimulation of pituitary hormones, which also causes the development of male secondary sexual characteristics and sperm production. Both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Egg Maturation and Release

b) Begins at 10-12 years and ends at 45-50 years

[Solution Description]

According to the syllabus, the reproductive phase of life in females begins at puberty, typically between 10 to 12 years of age, and generally lasts until approximately 45 to 50 years of age.

Key Concept: Increased Activity of Sweat and Sebaceous Glands

c) As a result of increased activity of sweat glands

[Solution Description] During puberty, hormonal changes lead to increased activity of sweat glands, resulting in higher sweat production.

Key Concept: Increased Activity of Sweat and Sebaceous Glands

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that during puberty, the increased activity of sebaceous glands can lead to acne and pimples on the face. This is true because during puberty, hormonal changes cause these glands to produce more oil. The reason explains that the sebaceous glands produce more oil during puberty, which can clog pores and lead to skin issues like acne. This is also true and directly explains why the assertion is correct. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Sebaceous Glands and Acne

c) Acne

[Solution Description]

During puberty, the increased activity of sebaceous glands leads to excess oil production, which can clog pores and result in acne. Acne is a common skin condition experienced by many adolescents during this stage of development.

Key Concept: Increased Activity of Sweat and Sebaceous Glands

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

During puberty, hormonal changes occur in the body, which lead to increased activity of sweat glands. This results in more sweating. The Assertion correctly states that the activity of sweat glands increases during puberty. The Reason explains that this increase is due to hormonal changes, which is a correct and logical explanation. Therefore, both the Assertion and Reason are true, and the Reason is the correct explanation of the Assertion.

Key Concept: Sebaceous Glands and Acne

b) Increased activity of sebaceous glands

[Solution Description]

During puberty, the activity of sebaceous glands increases, leading to the production of more oil (sebum). This excess oil can clog hair follicles, trapping dirt and bacteria, which results in the formation of acne and pimples.

Key Concept: Formation of Acne

b) Increased activity of sebaceous glands

[Solution Description]

During puberty, the activity of sebaceous glands increases, leading to the overproduction of oil (sebum). This excess oil can clog pores, resulting in the formation of acne and pimples.

Key Concept: Intellectual Development

c) Intellectual development is at its peak

[Solution Description]

According to the syllabus, adolescence is a period when intellectual development takes place. Adolescents spend considerable time thinking and their brains have the greatest capacity for learning during this phase. Therefore, the most appropriate description of intellectual development during adolescence is that it is at its peak.

Key Concept: Reaching Mental, Intellectual, and Emotional Maturity

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] During adolescence, significant intellectual development occurs as adolescents spend considerable time thinking and learning. This is because the brain has its greatest capacity for learning during this period. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Emotional Maturity

b) Changes in body and mind

[Solution Description]

Adolescents may feel insecure due to the rapid changes occurring in their bodies and minds. These changes can be overwhelming as they try to adjust to their new selves, leading to feelings of insecurity. However, it's important to understand that these changes are a natural part of growing up.

Key Concept: Reaching Mental, Intellectual and Emotional Maturity

c) Their brain has the greatest capacity for learning

[Solution Description]

Adolescents undergo intellectual development, which leads to increased capacity for learning and spending more time thinking. This is a natural part of reaching mental maturity during this stage of life.

Key Concept: Intellectual Development in Adolescence

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

During adolescence, the brain undergoes significant development, which enhances thinking and reasoning skills. This period is marked by increased intellectual capacity, allowing adolescents to spend more time thinking deeply. The assertion is true because adolescents are known to engage in extensive thinking and reasoning. The reason is also true because scientific studies indicate that adolescence is the phase when the brain has the greatest capacity for learning. Furthermore, the reason correctly explains the assertion, as the brain's enhanced learning capacity during adolescence directly contributes to increased thinking and reasoning abilities.

Key Concept: Emotional maturity, Intellectual development

c) Acknowledge the changes and seek support from trusted individuals while practicing self-reflection.[Solution Description]Adolescents should acknowledge that physical and mental changes are a natural part of growing up. They should focus on developing emotional resilience by seeking support from trusted individuals, engaging in self-reflection, and understanding that everyone goes through similar experiences. This balanced approach helps in managing insecurities effectively.

Key Concept: Emotional changes and insecurities

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description]

The assertion states that adolescents often feel insecure due to rapid changes in their body and mind. This is true as adolescence is a period of significant physical, emotional, and mental changes, which can lead to feelings of insecurity. The reason claims that these feelings are a natural part of growing up and indicate intellectual development. While it is true that these feelings are natural, they do not directly indicate intellectual development. Intellectual development involves cognitive growth and learning capacity, not just emotional responses. Therefore, both the assertion and reason are true, but the reason does not correctly explain the assertion.

Key Concept: Emotional changes and insecurities

b) Adolescents develop greater independence and self-awareness

[Solution Description]

Emotional maturity during adolescence involves developing independence, self-awareness, and the ability to handle emotions effectively. The syllabus highlights that adolescents become more independent and self-conscious, which are key aspects of emotional growth. They also spend considerable time thinking and processing emotions, which contributes to their overall emotional development.

Key Concept: Hormones and Secondary Sexual Characteristics

c) Testosterone

[Solution Description]

Testosterone is the primary male hormone responsible for the development of secondary sexual characteristics such as facial hair, deep voice, and muscle growth. Estrogen is the female hormone responsible for the development of secondary sexual characteristics in females. Therefore, the correct answer is the option that mentions testosterone.

Key Concept: Secondary Sexual Characteristics

a) Growth of facial hair

[Solution Description]

Secondary sexual characteristics in boys include the growth of facial hair (moustache and beard), hair on the chest, and changes in the voice box leading to a hoarse voice. Breast development is a secondary sexual characteristic in girls, not boys.

Key Concept: Secondary Sexual Characteristics, Hormonal Control

c) Estrogen[Solution Description]The development of breasts in girls at puberty is primarily influenced by the hormone estrogen. This hormone is produced by the ovaries once puberty is reached. Estrogen is responsible for the development of secondary sexual characteristics in females, including breast development and the formation of milk-secreting glands (mammary glands) inside the breasts.

Key Concept: Hormones and Secondary Sexual Characters

b) Estrogen

[Solution Description]

The development of female secondary sexual characteristics, including breast development, is primarily due to the hormone estrogen. Estrogen is produced by the ovaries once puberty begins.

Key Concept: Secondary Sexual Characteristics, Testosterone

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that the growth of facial hair in boys during puberty is primarily due to the release of testosterone. This is true because testosterone, the male hormone, is released by the testes at the onset of puberty and is responsible for various secondary sexual characteristics, including the growth of facial hair. The reason states that testosterone is the male hormone responsible for the development of secondary sexual characteristics in males. This is also true as testosterone plays a crucial role in the development of secondary sexual characteristics such as facial hair, deepening of the voice, and growth of body hair. Moreover, the reason correctly explains the assertion because it directly links the role of testosterone to the development of facial hair.

Key Concept: Secondary Sexual Characteristics in Males

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that the growth of facial hair in boys during puberty is a secondary sexual characteristic, which is true as per the syllabus. Secondary sexual characteristics are features that help distinguish males from females, such as facial hair, chest hair, and voice changes. The reason given is that the male hormone testosterone, released by the testes at puberty, causes these changes. This is also true as testosterone is responsible for the development of secondary sexual characteristics in males. Moreover, the reason correctly explains the assertion since it links the hormonal change to the physical development.

Key Concept: Secondary Sexual Characteristics

b) Production of milk

[Solution Description]

The primary function of the mammary glands in females is to produce milk. These glands develop inside the breasts and are essential for breastfeeding.

Key Concept: Secondary Sexual Characteristics

c) Estrogen

[Solution Description]

The development of breasts in females during puberty is primarily controlled by the hormone estrogen. Estrogen is produced by the ovaries and plays a crucial role in the development of secondary sexual characteristics in females.

Key Concept: Role of Hormones

c) Pituitary gland

[Solution Description]

The pituitary gland secretes hormones that control the production of sex hormones in both males and females. These hormones regulate the maturation of ova in the ovaries and sperms in the testes.

Key Concept: Hormones, Pituitary Gland, Reproductive Function

c) Both delayed growth of facial hair in boys and underdevelopment of mammary glands in girls

[Solution Description] The pituitary gland controls the release of sex hormones from the testes and ovaries by secreting specific hormones. If the pituitary gland malfunctions, it can lead to insufficient production of testosterone or estrogen, causing delayed or incomplete development of secondary sexual characteristics during puberty.

Key Concept: Role of Hormones in Puberty

d) Pituitary gland

[Solution Description]

The pituitary gland is a key endocrine gland that controls the release of sex hormones in both males and females during puberty. It secretes hormones that stimulate the testes to produce testosterone in males and the ovaries to produce estrogen in females. These hormones are responsible for the development of secondary sexual characteristics during adolescence.

Key Concept: Role of Hormones in Initiating Reproductive Function, Endocrine Glands and Their Role

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that the onset of puberty is primarily controlled by the pituitary gland. This is true because the pituitary gland secretes hormones such as luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which stimulate the testes to produce testosterone and the ovaries to produce estrogen. These sex hormones are responsible for the development of secondary sexual characteristics during puberty.

The reason states that the pituitary gland secretes hormones that regulate the production of sex hormones in the testes and ovaries. This is also true because the pituitary gland's role in regulating the release of LH and FSH directly influences the production of testosterone and estrogen in the gonads.

Since both the assertion and reason are true, and the reason correctly explains the assertion, the correct answer is that both are true, and the reason is the correct explanation of the assertion.

Key Concept: Hormones and Puberty

c) Testosterone

[Solution Description]

The onset of puberty in boys is primarily controlled by the hormone testosterone. Testosterone is secreted by the testes and leads to the development of male secondary sexual characteristics such as facial hair growth, deepening of the voice, and muscle development.

Key Concept: Role of Hormones in Initiating Reproductive Function

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that the pituitary gland controls the secretion of testosterone and estrogen, which is true as per the syllabus. The reason explains that the pituitary gland secretes hormones that stimulate the testes and ovaries to produce their respective hormones, which is also true and directly explains the assertion. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Menstrual Cycle

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that menstruation occurs once in about 28 to 30 days due to hormonal changes. This is true as the menstrual cycle is regulated by hormones such as estrogen and progesterone. The reason explains that the menstrual cycle involves the maturation of the egg, its release, thickening of the uterine wall, and its breakdown if pregnancy does not occur. This is also true and directly explains why menstruation occurs at regular intervals. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Menopause

c) 45 to 50 years

[Solution Description]

Menopause, the cessation of the menstrual cycle, typically occurs between 45 to 50 years of age in females.

Key Concept: Reproductive Phase, Hormonal Regulation

d) Hormonal regulation in males ensures continuous sperm production throughout their lives

[Solution Description] In males, the reproductive phase begins at puberty and continues for a much longer period compared to females. This is because the testes continuously produce sperms under the regulation of hormones secreted by the pituitary gland. The pituitary gland releases hormones that stimulate the testes to produce testosterone, which in turn maintains sperm production. Unlike females, who experience menopause and stop producing eggs, males do not undergo a similar phase and continue to produce sperms until late adulthood, ensuring a prolonged reproductive phase.

Key Concept: Hormonal Control, Testosterone Function

c) Testosterone is responsible for both sperm production and the development of secondary sexual characteristics

[Solution Description] The hormone responsible for the development of secondary sexual characteristics in males during puberty is testosterone. This hormone is produced by the testes and is regulated by the pituitary gland. Testosterone not only stimulates the production of sperms but also leads to the development of secondary sexual characteristics such as facial hair growth, deepening of the voice, and enlargement of the male reproductive organs. The pituitary gland releases hormones that stimulate the testes to produce testosterone, which in turn ensures continuous sperm production throughout a male's life.

Key Concept: Menstrual Cycle and Hormonal Control

a) Both Assertion and Reason are true, and Reason is he correct explanation of Assertion.

[Solution Description]

The menstrual cycle in females is indeed regulated by hormones, which is a fundamental concept in reproductive biology. These hormones include estrogen and progesterone, which play crucial roles in the maturation of the egg, its release from the ovary, and the thickening of the uterine wall to prepare for potential pregnancy. Therefore, both the Assertion and Reason are true, and the Reason correctly explains the Assertion.

Key Concept: Menopause

b) 45 to 50 years

[Solution Description]

As per the syllabus, the menstrual cycle stops at around 45 to 50 years of age in females. This cessation of menstruation is termed menopause. Therefore, the correct age range for menopause is 45 to 50 years.

Key Concept: Menstrual Cycle, Menarche, Menopause

c) It signifies the start of her reproductive phase and the ability to produce mature ova.

[Solution Description]

The first menstrual flow, known as menarche, signifies the onset of puberty and the beginning of the reproductive phase in females. It indicates that the girl's body is now capable of producing mature ova and that her reproductive system is functioning. This event typically occurs between the ages of 10 to 12 years and marks the start of the menstrual cycle, which continues until menopause (around 45 to 50 years of age).

Key Concept: Sex Determination

b) Father

[Solution Description]

The mother always contributes an X chromosome, while the father can contribute either an X or a Y chromosome. Therefore, the sex of the baby is determined by whether the sperm that fertilizes the egg carries an X or a Y chromosome.

Key Concept: Sex Determination

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The sex of a baby is determined by the combination of sex chromosomes inherited from the parents. The egg always contains one X chromosome, whereas the sperm can carry either an X or a Y chromosome. If the sperm carrying an X chromosome fertilises the egg, the resulting zygote will have XX chromosomes, leading to the development of a female child. Conversely, if the sperm carrying a Y chromosome fertilises the egg, the resulting zygote will have XY chromosomes, leading to the development of a male child. Therefore, the assertion is true, and the reason correctly explains why the sex of the baby is determined by the sperm\'s contribution.

Key Concept: Sex Determination, Chromosomes

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] The sex of a baby is determined by the combination of sex chromosomes in the zygote. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The egg always contributes an X chromosome, whereas the sperm can contribute either an X or a Y chromosome. If a sperm carrying an X chromosome fertilizes the egg, the resulting zygote will be XX, leading to the development of a female child. Conversely, if a sperm carrying a Y chromosome fertilizes the egg, the resulting zygote will be XY, leading to the development of a male child. Therefore, the assertion is true because the sex of the baby is indeed determined by the type of chromosome contributed by the sperm. The reason is also true because the sperm can carry either an X or a Y chromosome, while the egg always carries an X chromosome. Moreover, the reason correctly explains the assertion since the variation in the sperm's chromosome determines the baby's sex.

Key Concept: Sex chromosomes, Zygote formation

b) XY, male

[Solution Description]

The egg always carries an X chromosome. If a sperm carrying a Y chromosome fuses with the egg, the resulting zygote will have one X chromosome and one Y chromosome (XY). This chromosomal composition determines the sex of the baby as male. Therefore, the zygote will have XY chromosomes, and the baby will be a boy.

Key Concept: Sex Determination, Chromosome Inheritance

c) 1/2

[Solution Description] The sex of each child is determined independently by the type of sperm that fertilizes the egg. There are two types of sperm: one with an X chromosome and one with a Y chromosome. The probability of a child being female is determined by the probability of an X-bearing sperm fertilizing the egg, which is 1/2. Since the outcome of previous children does not affect future outcomes, the probability that the next child will be female remains 1/2.

Key Concept: Sex Determination

c) The father's sperm determines the sex of the baby.

[Solution Description]

The sex of a baby is determined by the type of sperm that fertilizes the egg. The egg always contains an X chromosome, while the sperm can contain either an X or a Y chromosome. If the sperm contributes an X chromosome, the zygote will have two X chromosomes and develop into a female. If the sperm contributes a Y chromosome, the zygote will have one X and one Y chromosome and develop into a male. Therefore, the father's sperm determines the sex of the baby.

Key Concept: Hormonal Functions

c) Maintaining metabolic rate

[Solution Description]

The thyroid gland produces the hormone thyroxine, which plays a crucial role in regulating the body's metabolism. It helps in controlling how quickly the body uses energy, makes proteins, and responds to other hormones.

Key Concept: Thyroid Hormone and Iodine

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that thyroxine production in the thyroid gland requires the presence of iodine in water. This is true because iodine is a crucial component for the synthesis of thyroxine. The reason provided explains that iodine is essential for the synthesis of thyroxine, which regulates metabolism. Both statements are correct, and the reason accurately explains the assertion.

Key Concept: Pituitary Gland: Controls growth and other endocrine glands

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description]

The assertion states that the pituitary gland regulates the production of sex hormones in the testes and ovaries. This is true as the pituitary gland secretes hormones like Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH), which are essential for the maturation of ova and sperm production. The reason states that the pituitary gland controls the secretion of thyroid and adrenal hormones through its own hormones. This is also true because the pituitary gland secretes Thyroid Stimulating Hormone (TSH) and Adrenocorticotropic Hormone (ACTH), which regulate the thyroid and adrenal glands respectively. However, while both statements are true, the reason does not explain why the assertion is true. The regulation of sex hormones and thyroid/adrenal hormones are separate functions of the pituitary gland.

Key Concept: Thyroxine and Iodine

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The thyroid gland produces thyroxine, which is essential for regulating metabolism. The synthesis of thyroxine requires iodine. If there is insufficient iodine in the water, the thyroid gland cannot produce adequate thyroxine, leading to conditions like goitre. Therefore, the assertion that iodine deficiency leads to improper production of thyroxine is true. The reason that thyroxine is a hormone produced by the thyroid gland that requires iodine for its synthesis is also true and correctly explains the assertion.

Key Concept: Pancreas: Insulin Production

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The pancreas is responsible for producing insulin, a hormone that helps regulate blood sugar levels by allowing cells to absorb glucose for energy. If the pancreas does not produce enough insulin, the body cannot effectively metabolize glucose, resulting in elevated blood sugar levels and leading to diabetes. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Adrenal Glands and Adrenalin

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that adrenalin is produced by the adrenal glands, which is true as per the syllabus. The reason states that adrenalin helps the body to adjust to stress when one is very angry, embarrassed or worried, which is also true. Additionally, the reason correctly explains why adrenalin is produced by the adrenal glands.

Key Concept: Role of Thyroxine, Metamorphosis in Frogs

b) Tadpoles will remain in the larval stage indefinitely

[Solution Description]

Thyroxine is a hormone produced by the thyroid gland, and its production requires iodine. In frogs, thyroxine controls metamorphosis, the process by which tadpoles develop into adult frogs. If the water lacks iodine, thyroxine cannot be synthesized, leading to incomplete or failed metamorphosis. The tadpoles will remain in their larval stage and will not develop into adult frogs.

Key Concept: Hormones, Metamorphosis

d) Thyroxine controls metamorphosis.

[Solution Description]

The transformation from tadpole to frog is called metamorphosis, which is controlled by the hormone thyroxine produced by the thyroid gland. Thyroxine production requires iodine. If there is insufficient iodine in the water, thyroxine cannot be synthesized, and metamorphosis is hindered.

Key Concept: Role of thyroxine in metamorphosis

c) The tadpoles will not undergo metamorphosis.

[Solution Description]

Thyroxine is the hormone produced by the thyroid gland, which is essential for the metamorphosis of tadpoles into frogs. Thyroxine production requires iodine. If the water lacks sufficient iodine, thyroxine cannot be produced in adequate amounts, and the tadpoles will not undergo metamorphosis to become adult frogs.

Key Concept: Role of Hormones in Metamorphosis, Insect Hormones, Pituitary Hormones

b) Production of insect hormones for metamorphosis

[Solution Description]

The pituitary gland secretes hormones that regulate other endocrine glands, including those that produce insect hormones necessary for metamorphosis. If the pituitary gland is non-functional, the secretion of these regulatory hormones would be disrupted, directly affecting the production of insect hormones and thus the process of metamorphosis.

Key Concept: Reproductive Health, Myths and Taboos, HIV/AIDS

c) There is no scientific basis for the claim; it is a myth.

[Solution Description]

The given statement is a myth related to menstruation. There is no scientific evidence to support the claim that eating cold food during menstruation causes infertility. It is important to educate adolescents about such myths and encourage them to rely on scientifically validated information.

Key Concept: Reproductive Health, Menstrual Hygiene

c) Changing pads every 4–5 hours

[Solution Description]

Maintaining proper hygiene during menstruation is crucial to prevent bacterial infections. The most effective practices include using sanitary napkins or clean homemade pads, changing them every 4–5 hours, and washing the genital area with clean water. Using the same pad for an extended period can lead to bacterial growth, increasing the risk of infection. Therefore, the most effective practice is changing pads regularly.

Key Concept: Personal Hygiene

b) To prevent bacterial infections

[Solution Description]

Adolescents should maintain personal hygiene because increased activity of sweat glands can lead to body odor. Regular bathing helps remove dirt and bacteria, preventing infections. Girls especially need to maintain hygiene during menstruation to avoid bacterial infections. Thus, maintaining personal hygiene is crucial for overall health and well-being.

Key Concept: Personal Hygiene

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that adolescents should take a bath at least once every day due to the increased activity of sweat glands, which can lead to body odor. This is true because sweat glands are more active during adolescence, leading to a higher chance of body odor if not cleaned regularly. The reason given is that maintaining cleanliness helps prevent bacterial infections. This is also true, as poor hygiene can lead to bacterial infections on the skin. Moreover, the reason correctly explains why cleanliness is important for adolescents, as it directly relates to preventing infections caused by bacteria that thrive in unclean conditions. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Balanced Diet

b) Chapati, dal, and vegetables

[Solution Description]

A balanced meal for an adolescent should include proteins, carbohydrates, fats, and vitamins in proper proportions. Roti/rice provide carbohydrates, dal (pulses) provide proteins, and vegetables provide vitamins and minerals. Milk is a balanced food in itself, and fruits also provide nourishment. Therefore, a meal consisting of roti/rice, dal, and vegetables is balanced.

Key Concept: Balanced Diet

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

A balanced diet is crucial during adolescence as it supports rapid growth and development. The assertion correctly states that a balanced diet for adolescents must include proteins, carbohydrates, fats, and vitamins in the right proportions. The reason explains the roles of these nutrients: proteins are essential for growth, carbohydrates and fats provide energy, and vitamins protect the body from diseases. Both statements are true, and the reason correctly explains why a balanced diet is necessary.

Key Concept: Iron-rich foods

a) Leafy vegetables

[Solution Description]

Anemia is often caused by a deficiency of iron, which is essential for building blood. Foods rich in iron, such as leafy vegetables, jaggery, meat, citrus fruits, and Indian gooseberry (amla), help prevent anemia. Among these, leafy vegetables are particularly high in iron and are highly effective in preventing anemia.

Key Concept: Junk Food

c) They lack nutritional value

[Solution Description]

Junk food like chips and packed snacks should be avoided because they do not have adequate nutritional value. They lack essential nutrients like proteins, vitamins, and minerals required for proper growth and health.

Key Concept: Menstrual Hygiene

c) Every 4–5 hours

[Solution Description] During menstruation, it is recommended to change sanitary napkins or homemade pads every 4–5 hours to maintain hygiene and prevent bacterial infections. This practice ensures cleanliness and reduces the risk of infections caused by prolonged use of the same pad.

Key Concept: Personal Hygiene, Sweat Glands

c) Due to increased activity of sweat glands causing body odor

[Solution Description]

Teenagers have increased activity of sweat glands due to hormonal changes during puberty. This leads to more sweat production, which can mix with bacteria on the skin and cause body odor. Bathing daily helps remove sweat, bacteria, and dirt, reducing the risk of body odor and bacterial infections.

Key Concept: Menstrual Hygiene, Sanitary Products

c) 30

[Solution Description]

The girl changes her napkin every 4 hours. In a day, there are 24 hours, so she would change her napkin $\frac{24}{4} = 6$ times per day. Over 5 days, she would use $6 \times 5 = 30$ napkins.

Key Concept: Menstrual Hygiene

b) Every 4–5 hours

[Solution Description]

The syllabus specifies that sanitary napkins should be changed every 4–5 hours to ensure cleanliness and reduce the risk of bacterial infections.

Key Concept: Importance of Physical Exercise

b) They are generally healthier and more active

[Solution Description]

Children who exercise regularly tend to have better physical fitness, improved energy levels, and stronger immunity compared to those who do not exercise regularly. A common observation is that they are generally healthier and more active.

Key Concept: Physical Exercise

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that regular physical exercise is essential for maintaining overall health, which is true as exercise contributes to physical and mental well-being. The reason given is that physical exercise improves cardiovascular health, strengthens muscles, and enhances mental well-being, which is also true and directly explains why regular exercise is essential for overall health. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Physical exercise, Benefits of regular walking

b) Regular outdoor games improve cardiovascular and respiratory health.

[Solution Description]

The study clearly shows that regular participation in outdoor games has significant health benefits. A 20\% lower resting heart rate indicates better cardiovascular health. A 15\% higher lung capacity suggests improved respiratory function, and a 10\% lower BMI points to healthier weight management. These findings collectively support the conclusion that regular physical activity, such as playing outdoor games, leads to overall fitness improvement.

Key Concept: HIV Transmission

b) Through sharing syringes

[Solution Description]

HIV can be transmitted through sharing syringes used for injecting drugs, from an infected mother to her infant through breast milk, and through sexual contact with an infected person.