Human Reproduction - Class 12 Biology - Chapter 2 - Notes, NCERT Solutions & Extra Questions
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Extra Questions - Human Reproduction | NCERT | Biology | Class 12
Give two examples each of sample, population, and variable.
Sample:
First example: Out of all the students in a university, a group of 200 students selected for a survey about online learning preferences.
Second example: From a city’s entire population, 500 residents selected at random to test a new municipal water filtering system.
Population:
First example: All the students enrolled in a high school.
Second example: The entire number of birds residing in a specific national park.
Variable:
First example: Age of patients in a hospital.
Second example: Temperature readings taken hourly at different locations in a greenhouse.
The smallest animal egg is that of:
A. Ostrich
B. Human female
C. Duck
D. Hen
The correct answer is Option B: Human female. The smallest animal egg is found in human females.
Write the function of the following hormones.
Oestrogen
Progesterone
Testosterone
LH
FSH
Each hormone plays a critical role in the human body, ranging from reproductive functions to the development of secondary sexual characteristics. Below are the primary functions of each hormone, with each point carrying equal marks:
Oestrogen: This hormone is instrumental in the development of female secondary sexual characteristics, such as the growth of breasts and the maturation of the endometrium. It also plays a key role in regulating the menstrual cycle.
Progesterone: Mainly involved in preparing and maintaining the lining of the uterus for pregnancy each month, ensuring it is suitable for a fertilized egg to implant.
Testosterone: Critical for the development of male reproductive tissues such as the testes and prostate. It also promotes secondary sexual characteristics including muscle mass, bone density, and the growth of body hair.
LH (Luteinizing Hormone): Essential for reproductive health, LH triggers ovulation in females and supports the development of the corpus luteum.
FSH (Follicle-Stimulating Hormone): Plays a vital role in reproductive health by aiding in the development of eggs in ovaries and the maturation of sperms in testes.
Estrogen and Progesterone are the female sex hormones produced by the ovary.
A) Estrogen; Progesterone
B) Testosterone; cortisol
C) Insulin; glucagon
D) FSH and LH
Correct Answer: A) Estrogen; Progesterone
The ovary is an organ that possesses both endocrine and exocrine functions, importantly producing hormones. The primary hormones synthesized by the ovaries are Estrogen and Progesterone. These hormones are integral for the development of secondary sexual characteristics and the maintenance of the reproductive cycle.
Which of the following statements is correct about the male reproductive system in humans?
A. Its main function is to produce urine.
B. Its main function is to produce semen.
C. The heart is the main organ in the male reproductive system.
D. If the reproductive system fails, the organism dies.
The correct answer is B: Its main function is to produce semen.
The male reproductive system is primarily responsible for the production of semen, which includes the male gamete known as sperm. This system plays a crucial role in sexual reproduction, which is important for the propagation of species, though not vital for the individual's survival. Key organs in the male system include the testes, which produce sperm and sex hormones crucial for the development of male sexual characteristics.
While the reproductive system is significant for reproductive functions, it is not directly related to life sustenance in the way that organs like the heart or lungs are. Note that the production of urine is primarily the function of the kidneys, although urine does pass through a part of the male reproductive system, the urethra, during excretion. The penis serves a dual role in excretion and as a copulatory organ during sexual intercourse.
Which hormone(s) is/are secreted by the ovaries in girls during puberty?
A) Estrogen
B) Progesterone
C) Both A & B
D) Ovulation hormone
The ovaries are responsible for secreting two primary hormones during puberty in girls, which are:
Estrogen
Progesterone
Estrogen plays a critical role in facilitating changes within the ovaries that lead to ovulation, and it also contributes to the development of secondary sexual characteristics.
Progesterone is essential for the growth and maintenance of the uterine lining, providing a suitable environment for an embryo if pregnancy occurs.
Therefore, the correct answer to the question is:
C) Both A & B
Uterus prepares itself every month to receive a _______ by making its _______ thick.
A. fertilized egg; inner lining
B. unfertilized egg; outer lining
C. egg; wall
D. fallopian tube; middle lining
The correct answer is A. fertilized egg; inner lining.
Each month, the uterus prepares for a potential pregnancy by thickening its inner lining, also known as the endometrium. This thickened lining provides necessary support and nutrition to a fertilized egg if implantation occurs.
What is the name given to the 23rd pair of chromosomes in humans?
A) Alleles B) Autosomes C) Sex Chromosomes D) Allosomes
The correct answers are:
C) Sex Chromosomes
D) Allosomes
The 23rd pair of chromosomes in humans is referred to as sex chromosomes or allosomes, distinguishing them through their role in determining the genetic sex of an individual.
Haploid cells in males and females are known as _____ and ______, respectively.
A sperm
B ovum
C embryo
D zygote
The correct answers are:
A sperm
B ovum
In reproductive biology, the haploid cells in males are referred to as sperm, and in females, they are called ovum or egg. Both types of gametes contain only half the number of chromosomes compared to other cells in the body. This reduced chromosome number is characteristic of haploid cells, ensuring that when they combine during fertilization, the resulting zygote has a complete set of chromosomes.
Inner lining of the uterine wall is called:
A) amnion
B) placenta
C) endometrium
D) perimetrium
The correct answer is C) endometrium.
The uterine wall comprises three distinct layers:
The perimetrium is the outermost layer.
The myometrium forms the middle muscular layer.
The endometrium is the innermost layer, which lines the inside of the uterus.
Additionally, the placenta is a structure that develops within the uterus and supports fetal development by facilitating nutrient and gas exchange between the mother and the fetus. The amnion is the membrane that encloses the amniotic cavity, surrounding and protecting the fetus.
"What is a test tube baby? What is parturition?" [3 MARKS]
Test tube baby: This term refers to a baby developed from an egg that was fertilized outside the body and then implanted in the uterus of the biological or surrogate mother. The egg is fertilized in an environment outside the human body, typically in a laboratory setting.
In-vitro Fertilization: The process of fertilization occurs 'in-vitro' (which means in glass) usually in glass test tubes or other lab equipment made from similar materials. This is the reason why the resulting babies are called test tube babies.
Parturition: This biological term refers to the expulsion of the fetus from the mother's womb. It marks the end of a pregnancy and the beginning of neonatal life.
(a) Name the respective part of the human female reproductive system: (i) that produces eggs, (ii) where fusion of eggs and sperm takes place, and (iii) where the zygote gets implanted. (b) Describe briefly what happens to the zygote after it gets implanted.
(a) Specific Parts of the Human Female Reproductive System:
(i) Ovary: This is the site where eggs are produced.
(ii) Fallopian Tube: The location where the fusion of eggs and sperm occurs.
(iii) Uterus: This is where the zygote gets implanted.
Female Reproductive System Diagram
(b) Development Post-Implantation:
After the zygote is implanted in the uterus, it undergoes multiple divisions to form an embryo. This embryo adheres to the endometrium, the inner lining of the uterus, which thickens each month and is rich in blood, providing necessary nourishment for the developing embryo. Subsequently, the embryo is enveloped by rapidly dividing uterine cells, initiating the state of pregnancy.
Over the months, the embryo evolves, forming limbs and resembling a miniature human. Upon full development of all body structures, the embryo is termed as a foetus. When the foetus is completely developed, childbirth occurs, resulting in the birth of a baby.
Which of the following is not a part of the human male reproductive system? (a) testes (b) oviducts (c) seminal vesicles (d) epididymis
The correct answer is (b) oviducts. Oviducts are not a part of the human male reproductive system. These structures, also known as fallopian tubes, function as the pathway through which an ovum or egg travels from the ovary in females. Thus, they are exclusively a component of the female reproductive system.
(a) Write the function of the following parts in the human female reproductive system: (i) Ovary (ii) Oviduct (iii) Uterus. (b) Describe briefly the structure and function of the placenta.
(a) Functions of specific parts in the human female reproductive system:
(i) Ovary: The ovary is primarily responsible for producing eggs for fertilization, as well as secreting hormones like estrogen and progesterone. Estrogen is crucial for regulating secondary sexual characteristics, while progesterone helps maintain the thickness of the uterine lining, crucial for pregnancy support.
(ii) Oviduct: Also known as the fallopian tube, the oviduct is the site of fertilization where the egg meets the sperm. It transports the egg or the fertilized ovum (zygote) to the uterus.
(iii) Uterus: The uterus provides a nurturing environment for the fertilized ovum to develop into a fetus. It also protects and nourishes the embryo until the baby is ready for birth.
(b) Structure and Function of the Placenta:
The placenta is a disc-shaped structure located on the uterine wall. It forms before the implantation of the embryo and plays multiple critical roles. The placenta facilitates the transfer of oxygen and nutrients from mother to fetus, alongside the removal of waste products from fetal blood. It is composed of maternal tissues and tissues derived from the embryo.
An embryonic component of the placenta includes the chorion, which partakes in forming structures called chorionic villi. These are composed of fetal blood vessels and trophoblastic cells, enhancing nutrient and gas exchange between the maternal and fetal bloodstreams. The efficient structure and function of the placenta are vital for a successful pregnancy.
What determines the XY combination of a baby?
A) Ovum
B) Sperm
C) 23rd pair
D) 22 pairs
The correct answer is B) Sperm.
Sperm is the male "gamete" or sex cell. It carries half of the genetic material necessary to form a baby. When a sperm cell combines with an ovum (the female gamete), it contributes either an X or a Y chromosome. The combination of these chromosomes determines the biological sex of the future baby. If the sperm contributes an X chromosome, paired with the X chromosome from the ovum, the result is a female (XX). If it contributes a Y chromosome, paired with the X from the ovum, the result is a male (XY). Thus, the determination of a baby having an XY chromosome combination primarily depends on the chromosome provided by the sperm.
The two glands $A$ and $B$, which occur in pairs, are present in the endocrine system of humans. The pair of glands $A$ is found only in females, whereas the pair of glands $B$ occurs only in males. The glands $A$ make and secrete two hormones $C$ and $D$, whereas glands $B$ make and secrete only one hormone, $E$. In addition to hormones, glands $A$ make gametes $\mathrm{F}$, whereas glands $\mathrm{B}$ make gametes $\mathrm{G}$. (a) What are glands $A$? (b) What are hormones $C$ and $D$? (c) What are glands $B$? Name the hormone $E$. (d) What are gametes (i) $\mathrm{F}$, and (ii) $\mathrm{G}$? (e) Which event in the life of males and females is associated with the secretion of hormones $C$, $D$, and $E?
Glands $A$: The glands referred to as $A$ in the description are the ovaries in females.
Hormones $C$ and $D$: The hormones produced and secreted by the ovaries are:
Hormone $C$: Oestrogen
Hormone $D$: Progesterone
Glands $B$ and Hormone $E$:
Glands $B$ are the testes found in males.
Hormone $E$ secreted by the testes is testosterone.
Gametes:
(i) Gamete $F$: This is the ovum or egg, produced by the ovaries.
(ii) Gamete $G$: This refers to the sperm, produced by the testes.
Associated Life Event:
The secretion of hormones oestrogen (C) and progesterone (D) in females, and testosterone (E) in males, is linked with the onset of puberty.
"Is the human egg microlecithal, alecithal, or both?"
The human egg is classified as microlecithal. This means it contains a small amount of yolk. Importantly, the concept of an alecithal egg, which would imply an absence of yolk, does not exist in reality. All animal eggs contain some yolk, making the idea of an alecithal egg entirely hypothetical. Thus, no egg is truly alecithal.
Secondary sexual characteristics in females are promoted by:
A) androgen
B) progesterone
C) oestrogen
D) testosterone
The correct answer is C) oestrogen.
Oestrogen, primarily produced by the ovaries, plays a critical role in female physiology. It stimulates the growth and activities of female secondary sex organs and aids in the development of growing ovarian follicles. Moreover, oestrogen is pivotal in the development of female secondary sexual characteristics and also regulates female sexual behavior.
In humans, male and female gametes fuse together during $\qquad$ to form a zygote.
A. Imbibition
B. Fertilization
C. Implantation
D. Breeding
The correct answer is B. Fertilization.
Fertilization is the process where a sperm cell and an egg cell (ovum) combine. During fertilization, a sperm penetrates an egg, resulting in the release of the sperm’s genetic material into the ovum. This event allows for the fusion of genetic material from both parents, ultimately leading to the creation of a new single-celled entity known as the zygote. This zygote then begins the process of developing into an embryo.
Antrum is the cavity of:
A) Graafian follicle
B) Gastrula C) Blastula
D) Ovary
The correct answer is A) Graafian follicle.
The antrum is a distinguishing structural feature specifically found in the Graafian follicle. It is a fluid-filled cavity that plays a critical role in the maturation of the oocyte within the follicle.
What will be the number of bivalents present in a typical human meiocyte?
In a typical human meiocyte, the number of bivalents present is 23 pairs. Each bivalent consists of a pair of homologous chromosomes that come together during meiosis.
Which of the following statements is incorrect about gonads?
(A) The Leydig cells or interstitial cells, which are present in the intertubular spaces in the testis, produce a group of hormones called androgens, mainly testosterone.
(B) After ovulation, the ruptured ovarian follicle is converted to a structure called corpus luteum, which secretes mainly estrogen.
(C) Androgens regulate the development, maturation, and functions of the male accessory sex organs like epididymis, vas deferens, seminal vesicles, prostate gland, urethra, etc.
(D) Progesterone supports pregnancy and acts on the mammary glands and stimulates the formation of alveoli and milk secretion.
The incorrect statement among the given options is (B). After ovulation, the ruptured ovarian follicle transforms into an entity called the corpus luteum, which primarily secretes progesterone, not estrogen.
Key Points:
Gonads refer to reproductive organs that produce sperms in males and ova in females, comprising the testes and ovaries, respectively.
Progesterone is the dominant hormone secreted by the corpus luteum post-ovulation, crucial for preparing the uterine lining for pregnancy. It also facilitates the development of milk-secretory tissues.
Although estrogen is secreted during the follicular phase (pre-ovulation) and to some extent post-ovulation, its secretion post-ovulation is less predominant compared to progesterone.
Testicular structure and function: The testes consist of seminiferous tubules surrounded by Leydig cells or interstitial cells in the intertubular spaces, which produce androgens including testosterone. These hormones are vital for the development of male secondary sexual characteristics and the maturation of male reproductive tracts such as the epididymis, vas deferens, and others.
This highlights that the focus of the corpus luteum's hormone secretion post-ovulation is primarily on progesterone, not estrogen, making option (B) the incorrect choice.
In bryophytes, diploid chromosome number occurs in:
A. Spore mother cells
B. Gamete nuclei
C. Gametophyte
D. Spore
The correct answer is A. Spore mother cells.
In bryophytes, the sporophyte stage is diploid, denoted as $2n$. This stage includes the spore mother cells, which are diploid. These cells undergo meiosis to produce haploid spores, transitioning from the diploid (2n) to the haploid ($n$) state.
Explain in vitro fertilization. [2 MARKS]
Explanation:
In vitro fertilization (IVF) is a technique where an egg is fertilized by sperm outside the body, referred to as "in vitro." IVF is primarily used as a treatment for infertility when other assisted reproductive technologies are unsuccessful.
The IVF process includes monitoring and stimulating a woman's ovulatory process, removing one or more eggs from the ovaries, and allowing sperm to fertilize the eggs in a laboratory setting using a fluid medium.
Which of the following is the site of fertilisation in humans?
A. Uterus
B. Oviduct
C. Ovary
D. Vagina
The question at hand asks about the specific site in the human body where fertilization takes place. Fertilization is essentially the process where male and female gametes (sperm and egg respectively) meet and fuse together, leading to the formation of an embryo.
In the human female reproductive system, the site of fertilization is the oviduct, also known as the Fallopian tube. This tube connects the ovary, where the eggs are produced, to the uterus. During the process of fertilization, the sperm travels from the site of intercourse (vagina) through the cervix and uterus, reaching the oviduct. It is in the oviduct where the sperm encounters the egg, and fertilization occurs.
Given the options:
A. Uterus
B. Oviduct
C. Ovary
D. Vagina
The correct answer is:
B. Oviduct
To elaborate further on the other options:
Uterus: This is often referred to as the womb where the embryo grows into a fetus during pregnancy, not the site of fertilization.
Ovary: This is the organ where eggs are produced, but fertilization does not occur here.
Vagina: It serves as the passage through which sperm enters the female body, but it is not the site of fertilization.
Thus, option B. Oviduct is the accurate answer to the question regarding the site of fertilization in humans.
One of the following is not associated with gametogenesis: A. Formation of Ova B. Formation of sperm C. Change of spermatids to spermatozoa D. Release of ova
Answer: D. Release of ova
Explanation
Gametogenesis is the process involved in the formation of gametes. Gametes are specialized cells (ova in females and sperm in males) that are designed for sexual reproduction. This process involves various stages through which precursor cells undergo division and differentiation to finally form mature gametes.
The formation of ova, known as oogenesis, is part of gametogenesis occurring in females.
The formation of sperm involves a process termed spermatogenesis in males.
Conversion of spermatids to spermatozoa is a crucial phase within spermatogenesis, where spermatids, the immature male gametes, transform into fully mature and motile spermatozoa ready for fertilization.
However, the option "Release of ova" (option D) does not fall under the category of gametogenesis. This event is known as ovulation, which is a separate process wherein the mature ovum is released from the ovary into the fallopian tube for potential fertilization. Ovulation is part of the menstrual cycle, distinct from the fundamental process of forming gametes. Thus, the correct answer is:
D. Release of ova is not associated with gametogenesis.
Human growth hormone is produced in:
A. thyroid
B. adrenal
C. pancreas
D. pituitary
Human growth hormone (HGH) is produced by the pituitary gland, which is often referred to as the "master gland" because it controls various other hormone glands in the body. This gland is located at the base of the brain and plays a crucial role in regulating growth and development, metabolism, and reproduction.
The process of HGH production starts from the hypothalamus, a region of the brain that releases Growth Hormone Releasing Hormone (GHRH). GHRH then stimulates the anterior part of the pituitary gland to release growth hormone. This hormone has various functions, including promoting the secretion of insulin-like growth factors that facilitate the development and strengthening of bones and muscles.
To clarify the options related to the question:
Thyroid gland: Produces thyroxine which primarily affects metabolism.
Adrenal gland: Secretes adrenaline, important for the body’s stress response.
Pancreas: Produces insulin and glucagon, regulating blood sugar levels.
Therefore, the correct answer to the question of where the human growth hormone is produced is:
D. Pituitary gland
The phenomenon of normal breathing in a human being comprises:
A) an active inspiratory and a passive expiratory phase. B) a passive inspiratory and an active expiratory phase. C) both active inspiratory and expiratory phases. D) both passive inspiratory and expiratory phases.
Normal breathing, or respiration, in human beings involves two primary phases: inspiration (inhaling) and expiration (exhaling). Each of these phases has distinct characteristics regarding muscle activity and energy usage.
Inspiratory Phase
During the inspiratory phase, the diaphragm, a major muscle located below the lungs, actively contracts. This contraction pulls the diaphragm downward, increasing the volume of the chest cavity. As the chest cavity's volume increases, it creates a vacuum inside the lungs. Due to this vacuum, the pressure inside the lungs becomes lower than the atmospheric pressure, causing air to flow into the lungs. Given that this process requires muscular effort and energy consumption, it is termed as an active process.
Expiratory Phase
Conversely, the expiratory phase primarily involves the relaxation of the diaphragm. As the diaphragm relaxes, the chest cavity's volume decreases, which pushes the air out of the lungs. This phase generally does not require muscular effort or energy expenditure (in the context of normal breathing), making it a passive process.
Given this explanation, the correct answer to the phenomenon of normal breathing in a human being is:
A) an active inspiratory and a passive expiratory phase.
This implies that inhalation is an active process requiring energy, while exhalation is generally passive, occurring with minimal energy expenditure under normal respiratory conditions.
In human females, immature eggs are first seen in the ovary:
A. at puberty, B. before birth, at the fetus stage, C. during the first menstrual cycle, or D. after the first year of birth.
In human females, immature eggs are first developed and visible inside the ovaries during the fetal stage before birth. This happens much before any external sexual development is noticeable.
Detailed Explanation:
Development Location: The immature eggs, known as oocytes, are located within the ovaries.
Formation Process:
During fetal development, oocytes begin to form and are contained within structures called follicles.
These follicles range from primary follicles and further develop into Graafian follicles as they mature.
Quantity:
Initially, during the early months of fetal development, approximately 6 to 7 million oocytes are present.
By the time the fetus reaches around nine months (at the time of birth), this number decreases to about 1 to 2 million due to a process known as atresia where many oocytes degenerate.
Release at Ovulation:
Over time, these immature eggs mature within the ovaries.
During each menstrual cycle starting from puberty, a Graafian follicle releases one mature egg during ovulation.
Hence, the correct answer to when human females first have immature eggs in their ovaries is:
B. before birth, at the fetus stage
The human embryo gets nutrition from the mother's blood with the help of a special organ called:
A. Zygote
B. Ovary
C. Oviduct
D. Placenta
The correct answer to the question regarding the special organ through which the human embryo gets nutrition from the mother's blood is Option D: Placenta.
Detailed Explanation:
The placenta is a crucial organ that forms in the uterus during pregnancy. It plays a central role in the development of the embryo for about 9 months. The primary function of the placenta is to connect the mother’s blood supply to the embryo, facilitating the transfer of oxygen and nutrients necessary for fetal growth. This connection is made through the umbilical cord, which acts as a conduit between the mother and the fetus.
Additionally, the placenta also handles the removal of waste materials produced by the fetus. These waste materials are transferred back to the mother's bloodstream via the placenta and the umbilical cord, from where they are excreted by the mother's body.
Thus, the answer is D. Placenta, as it is the vital organ responsible for the nutrition and overall support of the embryo by linking to the mother’s circulatory system. The other options listed (A. Zygote, B. Ovary, C. Oviduct) do not perform this function.
Positions of endocrine glands are labeled $A$-$E$ in the given diagram. Match the symbols of glands in column I with the type of hormone it secretes given in column 2.
Column I | I |
---|---|
A | I. Progesterone |
B | II. Insulin |
C | III. Parathyroid hormone |
D | IV. Melatonin |
E | V. Follicle stimulating hormone |
VI. Thyroxine | |
VII. Aldosterone |
Choose the correct combination from the following: A $\quad A$-$I, B$-$II, C$-$VII, D$-$III, E$-$V$ B $\quad A$-$I, B$-$IV, C$-$III, D$-$III, E$-$VI$ C $\quad A$-$V, B$-$II, C$-$IV, D$-$III, E$-$VII$ D $\quad A$-$V, B$-$IV, C$-$III, D$-$III, E$-$II$
To solve the given problem, we need to correctly match each endocrine gland labeled $A$-$E$ in the diagram with its respective hormone from Column 2. Let's analyze each one:
Label A: This is located where the ovaries are found, hence it should secrete Progesterone.
Correct match: $A$-$I$
Label B: This is situated at the pancreas, primarily known for secreting Insulin.
Correct match: $B$-$II$
Label C: Positioned at the adrenal glands which are responsible for secreting Aldosterone.
Correct match: $C$-$VII$
Label D: This labels the thyroid gland, known for producing Thyroxine (Label D seems to wrongly mentioned the parathyroid hormone in the transcript but based on its position, thyroxine is the correct hormone).
Correct match: $D$-$VI$
Label E: Appears at the pituitary gland, which secretes numerous hormones including Follicle Stimulating Hormone (FSH).
Correct match: $E$-$V$
Given the correct matches from our analysis, the most suitable option from the choices is: Option A: $A$-$I, B$-$II, C$-$VII, D$-$VI, E$-$V$
This is the correct configuration based on the hormonal functions of the glands at each corresponding label in the diagram.
Which of the following is also known as the Master gland? A. Thyroid gland B. Parathyroid gland C. Adrenal gland D. Pituitary gland
The correct answer to the question, "Which of the following is also known as the Master gland?" is D. Pituitary gland.
Here’s why:
Thyroid Gland - Located in the neck, the thyroid gland produces hormones such as thyroxine. However, it doesn’t regulate other glands in the body, which disqualifies it as the master gland.
Parathyroid Gland - This gland is responsible for secreting parathyroid hormone, which helps maintain calcium levels in the body. Like the thyroid, it doesn't control other glands.
Adrenal Gland - Situated above the kidneys, the adrenal gland releases hormones that influence emotions and stress levels, such as adrenaline. Despite its crucial role, it does not regulate the activity of other endocrine glands.
Pituitary Gland (The Master Gland) - Found at the base of the brain, the pituitary gland is termed the Master Gland because it controls several other endocrine glands. It plays a pivotal role in regulating vital bodily functions and hormone secretion across the body.
Thus, option D, the Pituitary Gland, is the correct answer as it oversees the functioning of other endocrine glands, hence earning the title Master Gland.
Which of the following is not a part of the female reproductive system in human beings? A Ovary B Uterus C Fallopian tube D Vas deferens
The question asks which option among the given choices is not a part of the female reproductive system in human beings.
Option A: Ovary
The ovaries produce and release eggs (ova), which are essential for fertilization. Therefore, ovaries are indeed a part of the female reproductive system.Option B: Uterus
The uterus is where the embryo implants and develops during pregnancy, making it a critical component of the female reproductive system.Option C: Fallopian Tube
Also known as the oviduct, the fallopian tube is where fertilization typically occurs when the egg meets the sperm. This too is a part of the female reproductive system.Option D: Vas Deferens
Unlike the previous options, the vas deferens is actually a part of the male reproductive system. It is responsible for transporting sperm from the testes, where they are produced, to the urethra.
Thus, the correct answer is: $$ \text{D: Vas deferens} $$ This is not a part of the female reproductive system.
Testosterone hormone is produced in:
A) Leydig cell
B) Kupffer cell
C) Granulosa cell
D) None of the above
Testosterone is often referred to as a male hormone because it induces male characteristics. It is produced in the testis, specifically within structures known as the Leydig cells, which are found in the interstitial space surrounding the seminiferous tubules. Inside these tubules, the Leydig cells play a vital role in releasing androgens, a key group of male hormones.
Given the options:
A) Leydig cell
B) Kupffer cell
C) Granulosa cell
D) None of the above
Option A - Leydig cell is the correct answer, as this is where testosterone is produced.
Kupffer cells, mentioned in the options, are actually macrophages located in the liver, involved in protection against bacteria, rather than in hormone production. Granulosa cells, also listed, are found in the ovaries where they are involved in releasing female hormones. Therefore, for the production of testosterone, Leydig cells are where this crucial hormone synthesis takes place.
Number of sex chromosomes in human beings are:
A. 23
B. 46
C. 1
D. 2
Humans possess 23 pairs of chromosomes in total, with each pair comprising two individual chromosomes. This includes autosomes and sex chromosomes. Autosomes are chromosomes that determine various biological functions and physical characteristics, except for sex determination. The chromosomes concerned with determining one's sex are specifically known as sex chromosomes.
Each individual, whether male or female, generally has two sex chromosomes. Among these two chromosomes:
Females have two X chromosomes (XX).
Males have one X and one Y chromosome (XY).
These genetic structures have a paramount role in determining the sexual characteristics of an individual. Therefore, the correct answer to the question, "Number of sex chromosomes in human beings," is:
D. 2
Which endocrine gland is called the master gland?
A. Thyroid B. Adrenal C. Thymus D. Pituitary
The endocrine gland referred to as the master gland is the pituitary gland. This gland, despite its small size, comparable to a pea, plays a crucial role in controlling the functions of many other endocrine glands. It is located at the base of the brain.
Among the options provided:
A. Thyroid
B. Adrenal
C. Thymus
D. Pituitary
The correct choice is D. Pituitary. This gland effectively regulates various vital body functions by releasing hormones that influence other glands, highlighting its central role in the endocrine system. Therefore, the pituitary gland is rightfully called the master gland.
When pregnancy does not occur, the life of corpus luteum is about:
(a) 4 days
(b) 10 days
(c) 14 days
(d) 28 days
The correct answer is (d) 28 days.
The life of the corpus luteum, when pregnancy does not occur, typically lasts for about 28 days.
So, the correct option is (d) 28 days.
Match the following and choose the correct options.
Column I | Column II |
---|---|
A. Trophoblast | 1. Embedding of blastocyst in the endometrium |
B. Cleavage | 2. Group of cells that would differentiate as embryo |
C. Inner cell mass | 3. Outer layer of blastocyst attached to the endometrium |
D. Implantation | 4. Mitotic division of zygote |
(A) $A-2$ B-1 C-3 $D-4$
(B) $A-3 \quad B-4 \quad C-2 \quad D-1$
C $A-3 \quad B-1 \quad C-2 \quad D-4$
(D) A-2 $B-4 \quad C-3 \quad D-1$
The correct option is B: ( A-3, B-4, C-2, D-1 ).
Here is the detailed alignment between the terms and their correct meanings:
Column I | Column II |
---|---|
A. Trophoblast | Outer layer of blastocyst attached to the endometrium |
B. Cleavage | Mitotic division of zygote |
C. Inner cell mass | Group of cells that would differentiate as embryo |
D. Implantation | Embedding of blastocyst in the endometrium |
To summarize:
Trophoblast (A) matches with 3, as it is the outer layer of the blastocyst that attaches to the endometrium.
Cleavage (B) matches with 4, referring to the mitotic division of the zygote.
Inner cell mass (C) matches with 2, as it is the group of cells that differentiate into the embryo.
Implantation (D) matches with 1, which is the embedding of the blastocyst in the endometrium.
In human beings, the sex chromosomes are denoted as:
Option 1) X and Y
Option 2) X and O
Option 3) Z and W
Option 4) Z and O
The correct answer is Option 1: X and Y.
In human beings, the chromosomes determining sex are referred to as sex chromosomes and are represented by the letters X and Y.
Males have non-identical sex chromosomes, denoted as X and Y.
Females have identical sex chromosomes, denoted as X and X.
These distinctive chromosomes play a crucial role in determining an individual's sex.
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Ask Chatterbot AINCERT Solutions - Human Reproduction | NCERT | Biology | Class 12
Fill in the blanks:
(a) Humans reproduce _______. (asexually/sexually)
(b) Humans are _______ (oviparous, viviparous, ovoviviparous)
(c) Fertilisation is _______ in humans (external/internal)
(d) Male and female gametes are _______ (diploid/haploid)
(e) Zygote is _______ (diploid/haploid)
(f) The process of release of ovum from a mature follicle is called _______.
(g) Ovulation is induced by a hormone called _______.
(h) The fusion of male and female gametes is called _______.
(i) Fertilisation takes place in _______.
(j) Zygote divides to form _______ which is implanted in uterus.
(k) The structure which provides vascular connection between foetus and uterus is called _______.
(a) Humans reproduce sexually (asexually/sexually)
(b) Humans are viviparous (oviparous, viviparous, ovoviviparous)
(c) Fertilisation is internal in humans (external/internal)
(d) Male and female gametes are haploid (diploid/haploid)
(e) Zygote is diploid (diploid/haploid)
(f) The process of release of ovum from a mature follicle is called ovulation
(g) Ovulation is induced by a hormone called luteinising hormone (LH)
(h) The fusion of male and female gametes is called fertilisation
(i) Fertilisation takes place in the ampullary region of the fallopian tube
(j) Zygote divides to form blastocyst which is implanted in uterus.
(k) The structure which provides vascular connection between foetus and uterus is called placenta
Draw a labelled diagram of male reproductive system.
The labelled diagram of the male reproductive system as described in the chapter:
Diagram of the Male Reproductive System
Labels:
Testis: Primary male sex organs responsible for producing sperm and androgens.
Epididymis: Stores sperm and allows them to mature.
Vas deferens: Transports mature sperm to the urethra.
Seminal vesicle: Produces a significant proportion of the fluid that becomes semen.
Prostate gland: Secretes prostate fluid, a component of semen.
Bulbourethral glands: Secretes a fluid that lubricates the urethra.
Penis: Male external genitalia involved in sexual intercourse and urination.
Urethra: Conducts urine and semen out of the body.
Scrotum: Sac that holds the testes and regulates their temperature.
Rete testis: Network of tubules that carry sperm from the seminiferous tubules to the vasa efferentia.
Vasa efferentia: Transports sperm from the rete testis to the epididymis.
This comprehensive anatomical layout helps in understanding the functions and connections of the male reproductive system.
Draw a labelled diagram of female reproductive system.
The labelled diagram of the female reproductive system:
Figure 2.3 (a) Diagrammatic sectional view of female pelvis showing reproductive system
Labels:
Ovaries
Oviducts (Fallopian tubes)
Uterus
Cervix
Vagina
External Genitalia (including labia majora, labia minora, and clitoris)
Mons Pubis
Hymen
Write two major functions each of testis and ovary.
Two major functions for both the testis and ovary:
Functions of Testis
Sperm Production (Spermatogenesis): The testis is responsible for producing male gametes called sperms. This process occurs in the seminiferous tubules, where germ cells undergo division and differentiation.
Hormone Secretion: The Leydig cells in the testis secrete androgens, mainly testosterone, which play crucial roles in the development of male secondary sexual characteristics, regulation of libido, and maintenance of male reproductive functions.
Functions of Ovary
Ovum Production (Oogenesis): The ovary produces female gametes called ova or eggs. This occurs through the process of oogenesis, where oogonia develop into mature eggs ready for fertilization.
Hormone Secretion: The ovary secretes steroid hormones, including estrogens and progesterone. These hormones regulate the menstrual cycle, support pregnancy, and contribute to the development of female secondary sexual characteristics.
By understanding these functions, we can appreciate the essential roles these organs play in human reproduction and hormonal regulation.
Describe the structure of a seminiferous tubule.
The seminiferous tubules are highly coiled structures located within the testicular lobules of the testes. Here's a detailed description of their structure:
Lining Cells:
Male Germ Cells (Spermatogonia): These cells are located on the inner side of the seminiferous tubule. They undergo meiotic divisions to form sperms.
Sertoli Cells: These are supportive cells that provide nutrition to the developing germ cells.
Interstitial Spaces:
The regions outside the seminiferous tubules contain small blood vessels and Leydig cells.
Leydig Cells: Also known as interstitial cells, these secrete testicular hormones called androgens.
The seminiferous tubules function as the site for the production and early development of sperms. The structure is key for maintaining the right conditions for spermatogenesis, including temperature regulation and nutrient supply by Sertoli cells.
Here's an illustrated diagram from the text for better visualization:
In summary, the seminiferous tubules are critical for the process of spermatogenesis, with the germ cells undergoing division and development and Sertoli cells providing necessary support and nutrition.
What is spermatogenesis? Briefly describe the process of spermatogenesis.
Spermatogenesis is the process by which sperms are produced in the testes of male individuals. Let's break down the process into key stages:
Stages of Spermatogenesis
Initiation:
Spermatogenesis begins at puberty.
It starts with the immature male germ cells known as spermatogonia, which are diploid, meaning they contain 46 chromosomes.
Mitotic Division:
The spermatogonia undergo mitotic divisions to increase in number. Some of these spermatogonia differentiate to form primary spermatocytes.
Meiotic Division:
Primary spermatocytes (still diploid) undergo the first meiotic division (meiosis I), resulting in two haploid cells called secondary spermatocytes (each with 23 chromosomes).
The secondary spermatocytes undergo the second meiotic division (meiosis II) to produce four haploid cells called spermatids.
Spermiogenesis:
The spermatids undergo a transformation process called spermiogenesis, where they develop into mature spermatozoa (sperms).
During this process, the spermatid elongates, develops a tail (for motility), and forms a head (containing the nucleus) and a middle piece packed with mitochondria (for energy).
Spermiation:
The mature sperms are then released from the Sertoli cells into the lumen of the seminiferous tubules in a process called spermiation.
Hormonal Regulation
The process of spermatogenesis is regulated by hormonal signals:
Gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the anterior pituitary gland to secrete luteinising hormone (LH) and follicle-stimulating hormone (FSH).
LH stimulates Leydig cells in the testes to secrete androgens (testosterone), which in turn stimulates spermatogenesis.
FSH acts on the Sertoli cells to support the developing germ cells and to secrete factors essential for spermatogenesis and spermiogenesis.
Diagram
Below is a simplified flow of the stages of spermatogenesis:
Spermatogonia (46 chromosomes) → Primary spermatocytes (46 chromosomes) → Secondary spermatocytes (23 chromosomes) → Spermatids (23 chromosomes) → Spermatozoa (23 chromosomes)
Structure of a Sperm
A sperm consists of:
Head: Contains the haploid nucleus and is capped by the acrosome which contains enzymes.
Middle piece: Packed with mitochondria to provide energy for motility.
Tail: Propels the sperm forward and is essential for its motility.
Spermatogenesis ensures the continuous production of sperm necessary for male fertility. The entire process from spermatogonia to mature spermatozoa takes approximately 64 days.
Name the hormones involved in regulation of spermatogenesis.
The hormones involved in the regulation of spermatogenesis are:
Gonadotropin-releasing hormone (GnRH): Secreted by the hypothalamus, it stimulates the anterior pituitary gland.
Luteinising hormone (LH): Secreted by the anterior pituitary gland, it acts on Leydig cells to stimulate the synthesis and secretion of androgens.
Follicle-stimulating hormone (FSH): Also secreted by the anterior pituitary gland, it acts on Sertoli cells to stimulate the secretion of factors that aid in spermiogenesis.
Androgens: Primarily testosterone, produced by the Leydig cells, which stimulate spermatogenesis.
These hormones work in concert to ensure the proper development and maturation of sperms from the spermatogonia in the seminiferous tubules.
Define spermiogenesis and spermiation.
Spermiogenesis and spermiation are key processes in the development of male gametes (sperms) within the male reproductive system.
Spermiogenesis:
Definition: Spermiogenesis is the process by which spermatids are transformed into mature spermatozoa (sperms).
Details: During spermiogenesis, the spermatids undergo significant morphological changes, including the condensation of nuclear material, development of the acrosome, formation of the flagella (tail), and reorganization of the mitochondria in the middle piece. This transformation is crucial for the sperms to gain the motility and ability to fertilize an ovum.
Spermiation:
Definition: Spermiation is the process by which mature spermatozoa are released from the Sertoli cells into the lumen of the seminiferous tubules.
Details: After spermiogenesis, the mature sperm heads become embedded in Sertoli cells, which provide nourishment. Spermiation is the final step where the mature sperms are released into the lumen from where they are transported out of the testes and through the male reproductive tract for eventual ejaculation.
These processes ensure that functional and motile sperms are produced and made available for fertilization.
Draw a labelled diagram of sperm.
Labelled Diagram of a Sperm
Here is a labelled diagram of a human sperm based on the chapter's description:
Description
Head:
Contains an elongated haploid nucleus.
The anterior portion is covered by acrosome, a cap-like structure filled with enzymes that help in fertilization.
Neck:
Connects the head to the middle piece.
Middle Piece:
Contains numerous mitochondria that produce energy needed for the movement of the tail.
Tail:
Responsible for the motility of the sperm, enabling it to swim towards the ovum for fertilization.
This structure facilitates the sperm's primary function of reaching and fertilizing the ovum.
What are the major components of seminal plasma?
The seminal plasma is rich in:
Fructose
Calcium
Certain enzymes
These components are secreted by the male accessory glands, which include the paired seminal vesicles, a prostate gland, and paired bulbourethral glands.
What are the major functions of male accessory ducts and glands?
The major functions of male accessory ducts and glands include:
Accessory Ducts:
Rete Testis, Vasa Efferentia, Epididymis, and Vas Deferens:
Storage and Transport of Sperms: These ducts transport sperms from the testis to the outside of the body through the urethra.
Sperm Maturation and Motility: The epididymis stores and matures sperms, enabling them to acquire motility and fertilizing ability.
Accessory Glands:
Seminal Vesicles:
Secretion of Seminal Plasma: Contributes to the formation of the seminal plasma which provides nutrients like fructose, calcium, and enzymes, aiding in the survival and motility of sperms.
Prostate Gland:
Secretion of Milky Fluid: Adds a slightly alkaline fluid to the semen, which enhances sperm motility and longevity.
Bulbourethral (Cowper's) Glands:
Secretion of Lubricating Fluid: Produces a pre-ejaculatory mucus that neutralizes any residual acidity in the urethra and lubricates the penis.
Summarised Function:
Support Sperm Function: The ducts and glands work together to ensure that sperms are well-nourished, mature, motile, and efficiently transported to the female reproductive tract.
What is oogenesis? Give a brief account of oogenesis.
Oogenesis is the process of formation and development of the female gametes (ova) in the ovaries. Here is a brief account of oogenesis:
Phases of Oogenesis
Embryonic Development:
Oogonia Formation: During the embryonic stage, a large number of gamete mother cells (oogonia) are formed within the fetal ovary. By birth, no new oogonia are added.
Primary Oocytes: The oogonia divide mitotically to form primary oocytes, which begin the initial stages of meiosis but arrest at prophase I until puberty.
From Birth to Puberty:
Primary Follicles: Each primary oocyte becomes encased in a layer of granulosa cells, forming primary follicles. Many of these follicles degenerate over time, leaving about 60,000 to 80,000 at puberty.
Puberty to Menopause:
Secondary Follicle Development:
The granulosa cells proliferate, and a theca layer forms around the primary oocyte, developing into secondary follicles.
The secondary follicle transforms into a tertiary follicle characterized by a fluid-filled cavity called the antrum.
Ovulation:
First Meiotic Division: The primary oocyte within the tertiary follicle completes the first meiotic division, resulting in a secondary oocyte and a first polar body.
Graafian Follicle Formation: The tertiary follicle matures into a Graafian follicle, which ruptures to release the secondary oocyte (known as ovulation).
Post-Ovulation:
Second Meiotic Division: The secondary oocyte undergoes the second meiotic division if fertilization occurs, producing an ovum and a second polar body. The mature ovum is then ready for fertilization.
Oogenesis vs Spermatogenesis
Oogenesis results in the formation of one functional ovum and smaller polar bodies, while spermatogenesis produces four functional spermatozoa.
Oogenesis starts at the embryonic stage and has long resting periods, unlike spermatogenesis which continues throughout the male's reproductive life.
Here is a schematic representation provided in the chapter:
In summary, oogenesis is a highly regulated and phased process that ensures the creation of a viable female gamete ready for fertilization, contributing to sexual reproduction in humans.
Draw a labelled diagram of a section through ovary.
A labelled diagram of a section through an ovary:
Labelled parts:
Primary follicles - These are follicles containing primary oocytes surrounded by granulosa cells.
Secondary follicle - It is a more advanced stage of follicular development with more layers of granulosa cells.
Tertiary follicle - Characterized by the formation of a fluid-filled cavity called antrum.
Graafian follicle (Mature follicle) - This follicle releases the oocyte during ovulation.
Zona pellucida - A glycoprotein layer surrounding the oocyte.
Theca interna and externa - Layers of cells surrounding the follicle.
Ovarian stroma - The connective tissue of the ovary which is divided into the peripheral cortex and inner medulla.
This labelled diagram corresponds to the different stages and structures found in the ovary necessary for gametogenesis and ovulation.
Draw a labelled diagram of a Graafian follicle?
A labelled diagram of a Graafian follicle:
Name the functions of the following:
(a) Corpus luteum
(b) Endometrium
(c) Acrosome
(d) Sperm tail
(e) Fimbriae
(a) Corpus luteum
The corpus luteum is a temporary endocrine structure involved in female reproduction. It secretes hormones, primarily progesterone, and to a lesser extent estradiol and inhibin A, which are essential for:
Maintaining the endometrium for implantation of the embryo.
Supporting early pregnancy by preventing menstruation.
(b) Endometrium
The endometrium is the inner lining of the uterus and has several key roles:
Support for Embryo Implantation: It thickens and becomes vascularized during the menstrual cycle to prepare for potential embryo implantation.
Nourishment: Provides nutrients to the developing embryo before the placenta forms.
Menstruation: Sheds during menstruation if no pregnancy occurs, marking the menstrual cycle.
(c) Acrosome
The acrosome is a cap-like structure covering the anterior part of the head of a spermatozoon. Its functions are:
Releasing Enzymes: Contains hydrolytic enzymes that help the sperm penetrate the zona pellucida of the ovum during fertilization.
Facilitating Fusion: Assists in the sperm-oocyte membrane fusion process, enabling fertilization.
(d) Sperm tail
The sperm tail, also known as the flagellum, is crucial for:
Mobility: Propels the sperm forward, enabling it to swim through the female reproductive tract to reach the ovum for fertilization.
Direction: Helps the sperm navigate, ensuring it moves in the correct direction towards the egg.
(e) Fimbriae
The fimbriae are finger-like projections at the end of the fallopian tubes:
Ovum Capture: Sweep over the ovary to capture the released ovum during ovulation.
Transport Facilitation: Help guide the ovum into the fallopian tube, where it can meet sperm for fertilization.
Identify True/False statements. Correct each false statement to make it true.
(a) Androgens are produced by Sertoli cells. (True/False)
(b) Spermatozoa get nutrition from Sertoli cells. (True/False)
(c) Leydig cells are found in ovary. (True/False)
(d) Leydig cells synthesise androgens. (True/False)
(e) Oogenesis takes place in corpus luteum. (True/False)
(f) Menstrual cycle ceases during pregnancy. (True/False)
(g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience. (True/False)
(a) Androgens are produced by Sertoli cells.
False. Correction: Androgens are produced by Leydig cells.
(b) Spermatozoa get nutrition from Sertoli cells.
True.
(c) Leydig cells are found in ovary.
False. Correction: Leydig cells are found in the testis.
(d) Leydig cells synthesise androgens.
True.
(e) Oogenesis takes place in corpus luteum.
False. Correction: Oogenesis takes place in the ovary.
(f) Menstrual cycle ceases during pregnancy.
True.
(g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience.
True.
What is menstrual cycle? Which hormones regulate menstrual cycle?
The menstrual cycle is the reproductive cycle in female primates, including humans, which is marked by periodic changes in the female reproductive system that prepares it for the possibility of fertilization and pregnancy. It typically begins at puberty, called menarche, and continues until menopause, occurring roughly every 28/29 days.
Hormones that regulate the menstrual cycle:
Gonadotropin-Releasing Hormone (GnRH):
Secreted by the hypothalamus.
Stimulates the pituitary gland to release its hormones.
Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH):
Secreted by the anterior pituitary gland.
FSH promotes the growth and maturation of ovarian follicles.
LH triggers ovulation and stimulates the formation of the corpus luteum.
Estrogens:
Produced mainly by the developing ovarian follicles.
Promote the thickening of the endometrium (the lining of the uterus).
Progesterone:
Secreted by the corpus luteum after ovulation.
Essential for maintaining the endometrial lining for potential implantation of an embryo.
Together, these hormones control the cyclic changes in the ovaries and the uterus. The menstrual cycle can be divided into three phases: the follicular phase, ovulation phase, and the luteal phase.
What is parturition? Which hormones are involved in induction of parturition?
Parturition is the process of delivery or childbirth that occurs at the end of pregnancy. It involves the expulsion of the fully developed fetus from the uterus through the birth canal.
Hormones Involved in the Induction of Parturition:
Oxytocin:
Secreted by the maternal pituitary gland.
It stimulates strong uterine contractions, which play a crucial role in the delivery of the baby.
Estrogens:
Levels increase towards the end of pregnancy.
Aid in the preparation of the uterus for labor.
Cortisol:
Produced by the fetal adrenal gland.
Helps in the maturation of fetal organs.
These hormones create a neuroendocrine mechanism that triggers parturition:
Foetal Ejection Reflex: Signals from the fully developed fetus and placenta initiate mild uterine contractions.
Oxytocin Release: These mild contractions promote the release of oxytocin, which causes stronger contractions.
This stimulatory feedback loop between uterine contractions and oxytocin secretion continues, resulting in the baby's expulsion.
This complex interplay ensures successful childbirth.
In our society the women are often blamed for giving birth to daughters. Can you explain why this is not correct?
The sex of a baby is determined by the combination of sex chromosomes (X and Y) from the parents. Specifically, the sperm from the father carries either an X or a Y chromosome, while the ovum from the mother always carries an X chromosome.
Here's how it works:
If the sperm carrying an X chromosome fertilizes the ovum (X), the baby will have two X chromosomes (XX), resulting in a female.
If the sperm carrying a Y chromosome fertilizes the ovum (X), the baby will have one X and one Y chromosome (XY), resulting in a male.
Thus, the sex of the baby is determined by the type of sperm (X or Y) that fertilizes the ovum. This means that the father’s sperm decides whether the baby will be a boy or a girl.
Summary
Females have XX chromosomes.
Males have XY chromosomes.
All ovum from the mother carry the X chromosome.
Sperm from the father carry either an X or a Y chromosome.
The combination XX results in a female (girl).
The combination XY results in a male (boy).
Conclusion
It is scientifically incorrect to blame women for giving birth to daughters. The father’s sperm is responsible for determining the sex of the baby.
How many eggs are released by a human ovary in a month? How many eggs do you think would have been released if the mother gave birth to identical twins? Would your answer change if the twins born were fraternal?
Number of Eggs Released by a Human Ovary in a Month
One ovum is released by a human ovary in a month during the process of ovulation, which is part of the menstrual cycle.
Identical Twins (Monozygotic Twins)
If a mother gave birth to identical twins, they originated from a single ovum that was fertilized by one sperm and then split into two embryos. Therefore, in the case of identical twins, one egg would have been released.
Fraternal Twins (Dizygotic Twins)
If the twins were fraternal twins, they developed from two separate ova that were fertilized by two different sperms. In this situation, two eggs were released by the ovaries.
Summary
Number of eggs released per month: One
For identical twins: One egg was released.
For fraternal twins: Two eggs were released.
How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?
In dogs, each fertilized egg typically develops into a single puppy. Therefore, if a female dog gave birth to 6 puppies, it most likely means that 6 eggs were released by the ovary and successfully fertilized, leading to the development of the 6 puppies.
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Ask Chatterbot AINotes - Flashcards - Human Reproduction | Class 12 NCERT | Biology
Notes - Human Reproduction | Class 12 NCERT | Biology
Comprehensive Human Reproduction Class 12 Notes
Human reproduction is a remarkable process that ensures the continuation of our species. This article delves into the various facets of human reproduction, meant to assist Class 12 students in grasping the subject thoroughly.
Introduction to Human Reproduction
Humans are sexually reproducing organisms, meaning they produce offspring through the fusion of male and female gametes. The key events in human reproduction include gametogenesis, insemination, fertilisation, implantation, gestation, and parturition. Let's delve deeper into these processes.
The Male Reproductive System
Structure of the Male Reproductive System
The male reproductive system is located in the pelvic region and consists of the testes, accessory ducts, glands, and external genitalia. The main components are:
Testes: The primary male reproductive organs responsible for spermatogenesis and hormone secretion.
Scrotum: A pouch that maintains the testes at a temperature 2–2.5°C lower than the body temperature, crucial for sperm production.
Function of the Scrotum and Testes
The scrotum hosts the testes, which are divided into approximately 250 compartments called testicular lobules. Each lobule contains highly coiled seminiferous tubules where sperms are produced.
Sertoli cells provide nutrition to developing sperms, while Leydig cells situated outside the seminiferous tubules secrete androgens, the male sex hormones.
Accessory Ducts and Glands in Males
The male accessory ducts include the rete testis, vasa efferentia, epididymis, and vas deferens. These ducts are responsible for storing and transporting sperms from the testes to the outside through the urethra.
The male accessory glands like the seminal vesicles, prostate, and bulbourethral glands secrete seminal plasma, rich in fructose, calcium, and enzymes.
The Female Reproductive System
Structure of the Female Reproductive System
The female reproductive system is complex, consisting of the ovaries, oviducts, uterus, cervix, vagina, and external genitalia. These components are integral to ovulation, fertilisation, pregnancy, birth, and child care.
Function of Ovaries
The ovaries are responsible for producing ova and secreting several steroid hormones. Each ovary is connected to the pelvic wall and the uterus by ligaments. The ovaries house follicles at different stages of development, aiding in the maturation of ova.
Accessory Ducts in Females
The female accessory ducts include oviducts (fallopian tubes), uterus, and vagina. Oviducts transport the ova from the ovaries to the uterus. The uterus, also known as the womb, is where the embryo implants and develops.
Female External Genitalia
The female external genitalia include the mons pubis, labia majora, labia minora, hymen, and clitoris, providing protective and sensory functions.
Gametogenesis
Spermatogenesis
Spermatogenesis occurs in the seminiferous tubules of the testes and involves the transformation of spermatogonia into mature sperms. It begins at puberty and is regulated by hormones like LH and FSH.
Oogenesis
Oogenesis involves the formation of a mature ovum and begins during embryonic development. Unlike spermatogenesis, oogenesis is marked by a limited number of primary oocytes at birth, which later develop into mature ova.
graph TD;
Spermatogonium -->|Mitosis| Primary_Spermatocyte;
Primary_Spermatocyte -->|Meiosis_I| Secondary_Spermatocyte;
Secondary_Spermatocyte -->|Meiosis_II| Spermatids;
Spermatids --> Spermatozoa;
Oogonium -->|Mitosis| Primary_Oocyte;
Primary_Oocyte -->|Meiosis_I| Secondary_Oocyte & Polar_Body;
Secondary_Oocyte -->|Meiosis_II| Ovum;
Menstrual Cycle
The menstrual cycle in females is a roughly 28-day cycle divided into the follicular phase, ovulation, and luteal phase. Hormones like LH, FSH, oestrogen, and progesterone play pivotal roles in regulating this cycle.
Fertilisation and Implantation
During intercourse, sperms are released into the female genital tract, swim through the cervix, and enter the ampullary region of the fallopian tube where fertilisation occurs. The fusion of sperm and ovum creates a zygote that subsequently implants into the uterine wall.
Pregnancy and Embryonic Development
Pregnancy progresses through three trimesters, each marked by significant embryonic and foetal development. The placenta, a vital organ formed during pregnancy, facilitates nutrient and gas exchange between the mother and the foetus.
graph LR;
Zygote --> Morula;
Morula --> Blastocyst;
Blastocyst --> Implantation;
Implantation --> Embryo;
Embryo --> Foetus;
Foetus --> Birth;
Parturition and Lactation
Parturition is the process of childbirth, induced by hormonal and physical signals from the foetus and placenta, leading to strong uterine contractions. Postpartum, the mother undergoes lactation, producing milk essential for the newborn's nutrition and immunity during the initial months.
Summary and Key Points
Understanding human reproduction equips us with the knowledge of how life begins and progresses in the womb. This article covered the male and female reproductive systems, gametogenesis, the menstrual cycle, fertilisation, embryonic development, parturition, and lactation. This holistic view is essential for Class 12 students and provides a solid foundation for further learning in reproductive biology.
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