Directions : In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.
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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.
(a) : The normal temperature of the testes in the scrotum is about \(2^{\circ}-2.5^{\circ} \mathrm{C}\) 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 : The regions outside the seminiferous tubules are called interstitial spaces, which contain Leydig’s cells.
Reason : Leydig’s cells synthesise and secrete testicular hormones called androgens.
(b) : 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 : Wall of seminiferous tubule is formed of double layered germinal epithelium.
Reason : Majority of cells of germinal epithelium are germ cells and some are Sertoli cells.
(d) : Wall of each seminiferous tubule is formed by single layered germinal epithelium.
Assertion : Infundibulum is a funnel shaped part closer to ovary.
Reason: The edges of infundibulum helps in collection of the ovum after ovulation.
(b) : 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 shape of the uterus is like an inverted pear.
Reason: The inner glandular layer that lines the uterine cavity is called as myometrium.
(c) : The shane of the uterus is like an inverted pear. The wall of the uterus has three layers, external membranous perimetrium, middle layer of smooth myometrium and inner glandular layer of endometrium.
Assertion : The endometrium undergoes cyclical changes during menstrual cycle.
Reason : The myometrium exhibits strong contractions during delivery of the baby.
(b)
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.
(c) : The female external genitalia include mons pubis, labia majora, labia minora, hymen and clitoris. 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 : The type B spermatogonia are called primary spermatocytes.
Reason : Primary spermatocytes complete the first meiotic division leading to secondary spermatocytes.
(b)
Assertion : The middle piece is called as power house of the sperm.
Reason : The numerous mitochondria coiling around axial filament produce energy for the movement of the tail.
(a) : The middle piece of human sperm contains the mitochondria coiled around the axial filament called mitochondrial spiral. They provide energy for the movement of the sperm. So it is called as the ‘power house of the sperm’.
Assertion : Human male ejaculates about 50-100 million sperms during a coitus.
Reason : Semen has an alkaline pH to neutralise acidity of urethra.
(d) : Human male ejaculates about 200 to 300 million sperms during a coitus. Semen has a pH of \(7.35-7.5\), its alkalinity helps to neutralise the acidity of urethra left from passage of urine.
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.
(a) : 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 : The embryo with 8 to 16 blastomeres is called a morula.
Reason : The morula continues to divide and transforms into trophoblast.
(c): The embryo with 8 to 16 blastomeres is called a morula. The morula continues to divide and transforms into blastocyst as it moves further into the uterus. The blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast called the inner cell mass.
Assertion : After implantation, finger-like projections appear on the trophoblast called chorionic villi.
Reason : Chorionic villi are surrounded by the uterine tissue and maternal blood.
(b) : 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 (fetus) and maternal body called placenta.
Assertion : During pregnancy the levels of hormones like estrogens and progestrogens are increased.
Reason: The increased production of these hormones is essential for fetal growth.
(b)
Assertion : Vigorous contraction of the uterus at the end of pregnancy causes expulsion.
Reason : The stimulatory reflex between the uterine contraction and oxytocin secretion results in weakening contractions.
(c) : Vigorous contraction of the uterus at the end of pregnancy causes parturition. Parturition is induced by a complex neuroendocrine mechanism. Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates further secretion of oxytocin. The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger contractions.
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