BIOLOGY Assertion (A) & Reason (B) MCQ

1. Both assertion and reason are true, and reason is the correct explanation of assertion.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

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 2ºC from normal body temperature (37ºC) 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 35ºC. 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 thennoregulator and helps in spermatogenesis.

2. Both assertion and reason are true, but reason is not the correct explanation of assertion.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

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.

2. Both assertion and reason are true, but reason is not the correct explanation of assertion.

Explanation:

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.

2. Both assertion and reason are true, but reason is not the correct explanation of assertion.

1. Both assertion and reason are true, and reason is the correct explanation of assertion.

​​​​​​​​​​​​​​​​​​​​​Explanation:

The normal temperature of the testes in the scrotum is about 2º-2.5ºC 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.

1. Both assertion and reason are true, and reason is the correct explanation of assertion.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

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.

4. Both assertion and reason are false.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

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 fanned (by zona pellucida) in the egg. This membrane prevents polyspermic fertilisation. Amphimixis is the mixing up the chromosomes of a sperm and an ovum.

3. Assertion is true, but reason is false.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

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 gynecomastia.

3. Assertion is true, but reason is false.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

Corpus luteum is formed after the release of secondary oocyte from the Graafian follicle.

2. Both assertion and reason are true, but reason is not the correct explanation of assertion.

4. Both assertion and reason are false.

Explanation:

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.

3. Assertion is true, but reason is false.

1. Both assertion and reason are true, and reason is the correct explanation of assertion.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

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, 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.

2. Both assertion and reason are true, but reason is not the correct explanation of assertion.

Explanation:

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.

3. Assertion is true, but reason is false.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

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.

2. Both assertion and reason are true, but reason is not the correct explanation of assertion.

4. Both assertion and reason are false.

Explanation:

In blastulation cells do not move. A single layered hollow blastocyst is formed.

1. Both assertion and reason are true, and reason is the correct explanation of assertion.

3. Assertion is true, but reason is false.

​​​​​​​​​​​​​​​​​​​​​Explanation:

Placenta may be defined as the connection between the fetal membranes (amnion and chorion) and the uterine wall (decidua basal is, 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.

2. Both assertion and reason are true, but reason is not the correct explanation of assertion.

Explanation:

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.

3. Assertion is true, but reason is false.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

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 Thea 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 (24^th day of the cycle) and is eventually replaced by scar tissue, forming a corpus albicans.

4. Both assertion and reason are false.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

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.

2. Both assertion and reason are true, but reason is not the correct explanation of assertion.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

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.

4. Both assertion and reason are false.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

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 fanned in the adrenal cortex, testis and fetoplacental unit. Gonadotrophic hormones (LH and FSH) are secreted by theanteriorlobe 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.

4. Both assertion and reason are false.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

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.