Questions of Assertion Reason Chapter 1 Human Reproduction biology CBSE Class 12 are very simple to understand as this chapter deals with Human Reproduction means reproduction in humans which every student is very much familiar with. To solve assertion reason type questions of biology, deeper understanding of concept about Sexual Reproduction in humans is required. In order to help the student in solving Assertion Reason type of questions, detailed process is explained.
How to solve Assertion Reason Type Questions?
In Assertion-Reason type of question, two statements are given, first is Assertion and second is called Reason. Student must have to think critically about both the statements in Assertion Reason Questions, since it combines multiple choice questions and true/false type of questions which requires a higher level of understanding.
How many types are there of Assertion Reason Type Questions?
Assertion-Reason type of questions can be asked either with four MCQ options or with five MCQ options. First four options are same in both the cases only one more options is being provided i.e. last one. One extra option increases the difficulty level of the questions.
In assertion reason type of questions, all 4 or 5 options are same for each question, which are as:
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
(e) Both Assertion and Reason are false.
Then a question haunts in every student’s mind, which option is correct and when?
This can be understood clearly with the following table:
|Assertion (A)||Reason (R)||MCQ Options (Fixed for all questions)|
|If True||True||(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).|
|If True||True||(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).|
|If True||False||(c) Assertion (A) is true but reason (R) is false.|
|If False||True||(d) Assertion (A) is false but reason (R) is true.|
|If False||False||(e) Both Assertion and Reason are false.|
Now, lets practice some Assertion Reason Questions of Biology Chapter : 2 Human Reproduction.
Read instructions carefully before answering the questions.
For question given below, two statements are given- one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both A and R are true and R is correct explanation of the assertion.
(b) Both A and R are true but R is not the correct explanation of the assertion.
(c) A is true but R is false.
(d) A is false but R is true.
Assertion: In human male, testis are extra abdominal and lie in scrotal sacs.
Reason: Scrotum acts as thermo-regulator and keeps testicular temperature lower by 2°C for normal spermatogenesis.
Scrotum is a place where testes begins to descend during the third month with a concomitant shortening of gubernaculum. Proper descend of testes is essential for complete fertility because sperms needs low temperature by about 2°C from normal body temperature (37°C) to mature. The scrotal sacs has dartos muscles which constantly contracts and relaxes the loose scrotal skin. The loose scrotal skin helps to keep the testicular temperature at 35°C. If the testes do not descend from the abdominal cavity to the scrotum, the high temperature will destroy the sperm producing seminiferous tubules which results in sterility. So, scrotum acts as a thermoregulator and helps in spermatogenesis.
Assertion: At puberty human male develops secondary sexual characters.
Reason: At puberty there is decreased secretion of testosterone in male.
Puberty is the period of life at which the ability to reproduce begins and reproductive organs become functional. In male, the puberty is the period between 13-16 years. Puberty in male is controlled by male sex hormone called testosterone, which is secreted by interstitial or Leydig’s cells of the testes under the stimulation of interstitial cells stimulating hormone (ICSH) secreted by anterior pituitary. After puberty the seminiferous tubules start producing sperms. The development of secondary sex organs like prostate, scrotum, penis, etc., starts and secondary sexual characters like growth of hair on face, chest, pubis and axillae, broadening of shoulders, deepening of voice due to enlargement of voice box occurs. In puberty (male), height increases due to rapid growth of muscles and bones.
Assertion: Cilia lining the fallopian tube helps to pick up and push the released ovum into the oviduct.
Reason: Cilia of fallopian tubes beat towards uterus.
Assertion: Clitoris of female is homologous to tip of penis.
Reason: Both have same origin and richly supplied with nerves and blood vessels.
Clitoris of female is the small, spongy and erectile structure which hangs freely from the front end of vulva. It represents the underdeveloped penis. Whereas penis is a finger-like cylindrical outgrowth of abdomen projecting in between the scrotal sacs. Clitoris and penis both originate from the same origin, that digest a portion of the endometrium. A blastocyst therefore are homologous.
Homologous organs are those organs which have the same origin and may or may not have the same function. Clitoris and penis both are the reproductive organs present in female and male respectively. They are originated from the mesoderm layer and both are supplied with the nerves and blood vessels.
Assertion: Corpus luteum secretes the female hormone progesterone.
Reason: After ovulation, a ruptured follicle turns into yellowish solid mass of cells called corpus albicans.
At about the 14 day of the menstrual cycle, the distended mature graafian follicle ruptures and the ovum or secondary oocyte is extruded into the abdominal cavity. This is the process of ovulation which is triggered by a surge in LH secretion. The follicle that ruptures at the time of ovulation promptly fills with blood forming a corpus haemorrhagicium. The granulosa cell and theca cells of the follicle lining promptly begins to proliferate and the clotted blood is rapidly replaced with yellowish, lipid rich in luteal cells forming the corpus luteum. This initiates the luteal phase of the menstrual cycle, during which the luteal cells secretes estrogen and progesterone. Progesterone is a steroid hormone that has functions in preparing the uterus for pregnancy. If pregnancy occurs, the corpus luteum persists and if there is no pregnancy the corpus luteum begins to degenerate about 4 days before the next menses (24th day of the cycle) and is eventually replaced by scar tissue, forming a corpus albicans.
Assertion: Epididymis is divided into three parts.
Reason: Epididymis is the organ that stores spermatozoa.
Epididymis lies along the top and side of testes and is divided into 3 parts – anterior caput epididymis; middle corpus epididymis and posterior cauda epididymis.
The epididymis, besides forming a part of tubular conducting system for sperm transport, in it serves as a storage reservoir for sperms.
Assertion: One oogonium produces one ovum and three polar bodies.
Reason: Polar bodies have small amount of cytoplasm.
Assertion: In morula stage, the cells divide without any increase in size.
Reason: Zona pellucida remains undivided till cleavage is complete.
In morula stage, the cells divide without any increase in size and becomes a solid mass of cells. Zona pellucida remains undivided till cleavage is complete. After damage it breaks down and morula formation starts.
Assertion: The second meiotic division of the developing ovarian follicles is completed just after conception.
Reason: Conception is the onset of pregnancy when the implantation of blastocyst take place.
Assertion: At the time of implantation, which takes place in 14 days, the human embryo is called blastocyst.
Reason: Implantation occurs in the gastrula stage.
Implantation is the attachment of the early embryo called blastocyst, to the lining of womb. It begins between the fifth and seventh day after the ovulation and is enabled by the secretion of enzymes that digest a portion of the endometrium. A blastocyst is composed of a hollow sphere of trophoblast cells, inside of which is a small cluster of cells called the inner cell mass. Trophoblast goes on to contribute to fetal membrane systems. While the inner cell mass is destined largely to become the embryo and fetus.
Assertion: If several spermatozoa hit the egg at the same time, all can enter the egg.
Reason: The above process is called amphimixis which can be prevented by fertilisation membrane.
If several spermatozoa hit the egg at the same time, even then only one can get entry into the egg because after the entry of one sperm cell, the egg cell becomes impervious (not able to be penetrated) to other sperm cells. This can be done by fertilizin- antifertilizin compatibility reaction. Fertilizin of egg interacts with antifertilizin of a sperm of the same species. This interaction makes the sperms stick to the egg surface. The process of penetrating the ovum by many sperms is called polyspermy. Once the sperm cell has penetrated the corona radiata and zona pellucida, its unit membrane fuses with the unit membrane surrounding the egg cytoplasm. Just after the entry of sperm in the egg, a fertilisation membrane is formed (by zona pellucida) in the egg. This membrane prevents polyspermic fertilisation. Amphimixis is the mixing up the chromosomes of a sperm and an ovum.
Assertion: Corpus luteum contains blood clot and fibrin.
Reason: Corpus luteum is formed by the germinal epithelium.
Corpus luteum is formed after the release of secondary oocyte from the Graafian follicle.
Assertion: Placenta acts as a major endocrine organ.
Reason: In mammals fetal components of the placenta derive initially from the chondroblast.
Placenta may be defined as the connection between the fetal membranes (amnion and chorion) and the uterine wall (decidua basalis, the portion of the decidua which is directly adjacent to conceptus at the implantation site) for physiological exchange between the fetus and the mother’s blood.
In mammals, the fetal components of the placenta derive initially from trophoblast, connected with embryonic blood stream, through its contact with yolk sac. Placenta also acts as a major endocrine organs as it secretes hormones such as estrogen, progesterone and hCG that are essential for maintaining a maternal physiological condition appropriate for continued development of the conceptus.
Assertion: In mammals the female secondary sexual characters are developed by gonadotropins.
Reason: Gonadotropins are secreted by Graafian follicle.
The female secondary sexual characters are developed by estrogen. Estrogens are steroid hormones secreted by growing ovarian follicles. This hormone is responsible for the development of female secondary sexual and accessory characters. In humans, it is also formed in the adrenal cortex, testis and fetoplacental unit.
Gonadotrophic hormones (LH and FSH) are secreted by the anterior lobe of pituitary gland. LH is responsible for ovulation and transforms Graafian follicle into corpus luteum and FSH stimulates spermatogenesis, maturation of Graafian follicle and secretion of estrogen in ovaries.
Assertion: Head of sperm consists of acrosome and mitochondria.
Reason: Acrosome contains spiral row of mitochondria.
Sperm is a microscopic thread like motile cell which is distinguishable into head, middle piece and tail. Head is the enlarged end of sperm which contain 2 components – nucleus capped by acrosome. Acrosome contains sperm lysins (hyaluronidase enzyme) and nucleus is a compact mass of DNA having some prolamines. Middle piece is the mitochondrial portion. In between the head and middle piece there is a small constricted neck part containing two centrioles. Tail is narrow vibratile long part with two regions – main and end piece.
Assertion: Ovulation is the release of egg.
Reason: Ovulation takes on 14 days after fertilisation.
Assertion: Man does not urinate and ejaculate at the same time.
Reason: Membranous and penile part of urethra forms the outflow pathway for the urine and for the seminal fluid.
Urethra leads from urinary bladder through the prostate gland and into the penis. It consists of four parts – urinary, prostatic, membranous and penile. The urethra (membranous and penile part) in the male forms the outflow pathway for the urine and for the seminal fluid. However, it is physically impossible for a man to urinate and ejaculate at the same time because just prior to ejaculation the internal sphincter closes off the opening of the urinary bladder. The sphincter does not relax until the ejaculation is completed. The closing of this internal sphincter prevents urine from entering the urethra and also prevents the backflow of ejaculatory fluid into the urinary bladder.
Assertion: Seminiferous tubule is related with spermatogenesis.
Reason: Spermatogenesis takes place under the influence of pituitary gonadotrophins and testosterone.
The process of development, differentiation and metamorphosis of spermatozoa is known as spermatogenesis. Spermatogenesis takes place within the seminiferous tubules under the influence of pituitary gonadotrophins (FSH and LH) and a male hormone, testosterone secreted by the interstitial cells of Leydig which represent the endocrine tissue of the testis.
Assertion: Mammary gland is a modified sweat gland.
Reason: Mammary gland is functional in both male and female.
Mammary glands are modified sweat glands that lie over the pectoral muscles. They are also present in male but in a rudimentary form. Essential function of mammary gland is milk production which has nutritive and immunologic functions. Presence of mammary gland in male is a condition called gynaecomastia.
Assertion: In blastulation, cell masses show morphogenetic movements.
Reason: A three layered blastocyst is formed during blastulation.
Assertion: A drop in temperature does not affect spermatogenesis.
Reason: During temperature drop the smooth muscles contracts and bring the testes closer to the pelvic cavity.
The normal temperature of the testes in the scrotum is about 2°-2.5°C lower than the internal body temperature. When the body is chilled, the smooth muscle contracts and brings the testes closer to the pelvic cavity. This movement towards the pelvic cavity allows the testes to absorb heat from the rest of the body so that the sperm cells do not become chilled and get optimum temperature for spermatogenesis.
Assertion: Each seminiferous tubule is lined on its inside by three types of cells.
Reason: These cells are male germ cells, Sertoli cells and Leydig’s cells.
Each seminiferous tubule is lined on its inside by two types of cells called male germ cells (spermatogonia) and Sertoli cells. The regions outside the seminiferous tubules called interstitial spaces, contain Leydig’s cells. Leydig’s cells synthesise and secrete testicular hormones called androgens.
Assertion: Infundibulum is a funnel shaped part closer to ovary.
Reason: The edges of infundibulum helps in collection of the ovum after ovulation.
In human females each Fallopian tube extends from the periphery of each ovary to the uterus, the part closer to the ovary is the funnel shaped infundibulum. The edges of the infundibulum possess finger-like projections called fimbriae, which help in collection of the ovum after ovulation.
Assertion: The endometrium undergoes cyclical changes during menstrual cycle.
Reason: The myometrium exhibits strong contractions during delivery of the baby.
Assertion: All copulations do not lead to the fertilisation and pregnancy.
Reason: Fertilisation can occur only if the ovum and sperms are transported simultaneously to the ampullary – isthmic junction.
Fertilisation can only occur if the ovum and sperms are transported simultaneously to the ampullary-isthmic junction and ovum is released only once a month. This is one of the reasons why all copulations do not lead to fertilisation and pregnancy.
Assertion: Testicular lobules are the compartments present in testes.
Reason: These lobules are involved in the process of fertilization.
Testicular lobules are the compartments present in the testes that are not involved in the process of fertilization as whole. Fusion of male and female gametes is called fertilization.
Assertion: Interstitial cell is present in the region outside the seminiferous tubule called interstitial spaces.
Reason: Interstitial cells provide nutrition to the sertoli cells.
Leydig cells, also known as interstitial cells, are found adjacent to the seminiferous tubules in the testicle. They produce testosterone in the presence of luteinizing hormone (LH).
Assertion: The testes are situated outside the abdominal cavity within the scrotum.
Reason: Muscles in scrotum helps to maintain low temperature of testes, necessary for spermatogenesis.
The testes are situated outside the abdominal cavity within a pouch called scrotum. The scrotum helps in maintaining low temperature of the testes (2-2.5 °C) lower than the normal internal body temperature which is necessary for spermatogenesis.
Assertion: The bulbourethral gland is a male accessory gland.
Reason: Its secretion helps in the lubrication of the penis, thereby facilitating reproduction.
Bulbourethral gland, also called Cowper’s Gland, either of two pea-shaped glands in the male are located beneath the prostate gland at the beginning of the internal portion of the penis. These are responsible for adding fluids to semen during the process of ejaculation, thereby facilitating the process of reproduction.
Assertion: In human male, there are perianal glands near the anus.
Reason: Perianal glands secretes sex-attractant pheromone which initiates sexual desire in human.
Perianal gland are found in rabbit not in human beings. These are a pair of dark elongated scent glands lying behind the cowper’s glands. These are sex attractant secreting glands, its smell serves as sex attractant for the female.
Assertion: Testes are located in the scrotum, outside the coelom.
Reason: A vaginal coelom partly surrounds the testes in the scrotum.
Vaginal coelom partly surrounds the testes in scrotum in a wrong statement because vagina is the part of external genitalia (vulva) in the female reproductive system and scrotum is a sac like structure in which testes are suspended.
Assertion: Fimbriae are finger-like projections of the infundibulum part of oviduct which is closest to ovary.
Reason: They are important for collection of ovum after ovulation from ovary.
The ends of the fallopian tubes close to the ovaries are covered with finger like projections called fimbriae. Each of these fimbriae are covered with tiny hair like projections called cilia. When an egg cell is released from the ovary, it is swept into the fallopian tube by the cilia of the fimbriae.
Assertion: Finger-like projections appear on the trophoblast called chorionic villi after implantation.
Reason: Chorionic villi are surrounded by the uterine tissue and maternal blood.
After implantation, finger-like projections appear on the trophoblast called chorionic villi which are surrounded by the uterine tissue and maternal blood. The chorionic villi and uterine tissue become interdigitated with each other and jointly form a structural and functional unit between developing embryo (foetus) and maternal body called placenta.
Assertion: The female external genitalia includes mons pubis, labia majora and labia minora.
Reason: The glandular tissue of each breast is divided into 5-10 mammary lobes.
The female external genitalia include mons pubis, labia majora, labia minora, hymen and clitoris. Mons pubis is a cushion of fatty tissue covered by skin and pubic hair. The labia majora are fleshy patches of tissue, which extend down the mons pubis and surrounds the vaginal opening. The labia minora are paired folds of tissue under the labia majora. A functional mammary gland is characteristic of all female mammals. The mammary glands are paired structures (breasts) that contain glandular tissue and variable amount of fat. The glandular tissue of each breast is divided into 15-20 mammary lobes containing clusters of cells called alveoli.
Assertion: Vagina acts as copulation canal and fertilization canal.
Reason: Both insemination and fusion of gametes occur in the vagina of female.
Vagina is the tubular female copulatory organ. Passageway for menstrual flow as well as birth canal. Vagina receives semen from male during mating but fertilization (fusion of gametes) occurs in fallopian tube.
Assertion: In the testis, spermatogenesis occurs in the seminiferous tubules and testosterone secretion takes place from the sertoli cells.
Reason: Testosterone brings growth and maturation of primany sex organs and also development of accessory sex characters.
In the testis, spermatogenesis occurs in the seminiferous tubules and testosterone secretion takes place in the interstitial cells. Testosterone brings growth and maturation of secondary sex organs. It also brings about development of secondary sex characters.
Assertion: Spermatogenesis starts at the age of puberty.
Reason: There is a significant increase in level of gonadotropin releasing hormone at puberty.
Spermatogenesis starts at the age of puberty due to significant increase in the Gonadotropin Releasing Hormone (GnRH).