Maharashtra Board Class 12 Biology Chapter 2- Reproduction in lower & higher Animals


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Q. 1 Multiple choice questions.
1. The number of nuclei present in a zygote 
is ……
a. two
b.one
c. four
d.eight

2. Which of these is the male reproductive organ in human?
a. sperm
b. seminal fluid
c. testes
d. ovary

3. Attachment of embryo to the wall of the uterus is known as……..
a. fertilization
b. gestation
c. cleavage
d. implantation

4. Rupturing of follicles and discharge of 
ova is known as ..............
a. capacitation
b. gestation
c. ovulation
d. copulation

5. In human female, the fertilized egg gets implanted in uterus ..................
a. After about7 days of fertilization
b. After about 30 days of fertilization
c. After about two months of fertilization
d. After about 3 weeks of fertilization

6. Test tube baby technique is called.........
a. In vivo fertilization
b. In situ fertilization
c. In vitro fertilization
d. Artificial insemination

7. The given figure shows a human sperm. Various parts of it are labelled as A, B, C, and D .Which labelled part represents acrosome ?

a. B
b. C
c. D
d. A

8. Presence of beard in boys is a ............
a. primary sex organ
b. secondary sexual character
c. secondary sex organ
d. primary sexual character


Q.2 : Answer in one sentence.

1. What is the difference between a foetus and an embryo?
Answer : A foetus is formed by the growth and development of embryo. while the embryo is formed by the repetitive cell division of Zygote.


2. Outline the path of sperm upto the urethra.
Answer Sperm then travels through the deferent duct through up the spermatic cord into the pelvic cavity, over the ureter to the prostate behind the bladder. Here, the vas deferens joins with the seminal vesicle to form the ejaculatory duct, which passes through the prostate and empties into the urethra.


3. Which glands contribute fluids to the semen?
Answer : It's made up from secretions from the three accessory glands. The seminal vesicles, the prostate and the bulbourethral glands all contribute to the production of semen. The seminal vesicles provide nutrients and mobility to previously immobile sperm.


4. Name the endocrine glands involved in maintaining the sex characteristics of males.
Answer : The gonads are additional types of endocrine glands. They are the sex organs and include the male testes. Their main role is the production of steroid hormones. The testes produce androgens, which allow for the development of secondary sex characteristics and the production of sperm cells.


5. Where does fertilization and implantation occur?
AnswerFertilization occurs in the fallopian tubes. Once fertilization takes place, this newly fertilized cell is called a zygote. From here, the zygote will move down the fallopian tube and into the uterus. The zygote then burrows into the uterus lining. This is called implantation.


6. Enlist the external genital organs in female.
AnswerThe external genital organs include the mons pubis, labia majora, labia minora, Bartholin glands, and clitoris. The area containing these organs is called the vulva.


7. Give two differences between blastula and gastrula.
AnswerBlastula develops from the morula in a process called blastulation. It comprises of an inner cell mass, which develops into the embryoblast. The outer cell layer is the trophoblast, which gives rise to the placenta. Gastrula develops from the blastula in a process called gastrulationMassive movements of cell masses in the blastula develop the three primary germ layers: endoderm, ectoderm, and mesoderm.


8. What is the difference between embryo and zygote?
Answer :  Embryo is multicellular, zygote is unicellular. The process of formation of embryo is known as embryogenesis. The process of formation of zygote is known as fertilization.



Q. 4 Short answer questions.


1. Write a note on budding in Hydra.
Answer : It is a simple method of asexual reproduction normally occuring in favourable conditions. It is seen in a variety of animals like coelenterates (Hydra and corals) and in some colonial ascidians. In Hydra, a small outgrowth is produced towards the basal end of the body. It develops as a bud which grows and forms tentacles and develops into a new individual. This process is called budding. The young Hydra gets detached from the parent and becomes an independent new organism.


Fig: Budding in Hydra

2. Explain the different methods of reproduction occuring in sponges.
AnswerSponges are able to reproduce both sexually using gametes and asexually by budding. Even though sponges are hermaphroditic, individuals will only make one type of gamete at a time. There are two forms of asexual reproduction that sponges can go through: external budding and internal budding.


3. Write a note on IVF.
Answer : IVF (In Vitro Fertization) :
It is a process of fertization where an egg is combined with sperm outside the body in a test tube or glass plate to form a zygote under simulated conditions in the laboratory. The zygote or early embryos (with up to 8 blastomeres) could be then transferred into the fallopian tube for further development.


4. Comment on any two mechanical contraceptive methods.
AnswerMechanical barriers are devices that provide a physical barrier between the sperm and the egg. Examples of mechanical barriers include the male condom, female condom, diaphragm, cervical cap, and sponge. The condom is the only contraceptive method that helps prevent sexually transmitted infections (STIs).


5. Write a note on tubectomy.
AnswerTubectomy is a major surgical procedure in which the fallopian tubes are cut open and clipped or tied up to block the passage of the egg into the uterus. A few small incisions are made around the belly button. A telescopic device known as a laparoscope is inserted through one of the cuts.


6. Give the name of causal organism of syphilis and write on its symptoms.
AnswerSyphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum subspecies pallidum. The signs and symptoms of syphilis vary depending in which of the four stages it presents (primary, secondary, latent, and tertiary). 
The symptoms of primary syphilis include one or more painless, firm, and round syphilitic sores, or chancres. Secondary syphilis symptoms include: sores that resemble oral, anal. a nonitchy, rough, red or red-brown rash that starts on the trunk and spreads to the entire body, including the palms and soles.


7. What is colostrum?
AnswerColostrum is the first form of milk produced by the mammary glands of mammals immediately following delivery of the newborn. Most species will generate colostrum just prior to giving birth. Colostrum contains antibodies to protect the newborn against disease.


Q. 5 Answer the following questions.


1. Describe the phases of menstrual cycle
and their hormonal control.
Answer : The menstrual cycle is complex and is controlled by many different glands and the hormones that these glands produce. A brain structure called the hypothalamus causes the nearby pituitary gland to produce certain chemicals, which prompt the ovaries to produce the sex hormones oestrogen and progesterone.
The four main phases of the menstrual cycle are: menstruation, the follicular phase, ovulation, the luteal phase.

Menstruation is the elimination of the thickened lining of the uterus (endometrium) from the body through the vagina. Menstrual fluid contains blood, cells from the lining of the uterus (endometrial cells) and mucus. The average length of a period is between three days and one week.

The follicular phase starts on the first day of menstruation and ends with ovulation. Prompted by the hypothalamus, the pituitary gland releases follicle stimulating hormone (FSH). This hormone stimulates the ovary to produce around five to 20 follicles (tiny nodules or cysts), which bead on the surface.
Ovulation is the release of a mature egg from the surface of the ovary. This usually occurs mid-cycle, around two weeks or so before menstruation starts. During the follicular phase, the developing follicle causes a rise in the level of oestrogen. The hypothalamus in the brain recognises these rising levels and releases a chemical called gonadotrophin-releasing hormone (GnRH). This hormone prompts the pituitary gland to produce raised levels of luteinising hormone (LH) and FSH.
During ovulation, the egg bursts from its follicle, but the ruptured follicle stays on the surface of the ovary. For the next two weeks or so, the follicle transforms into a structure known as the corpus luteum. This structure starts releasing progesterone, along with small amounts of oestrogen. This combination of hormones maintains the thickened lining of the uterus, waiting for a fertilised egg to stick (implant).


2. Explain the steps of parturition.
Answer : . Parturition is the process of giving birth to a baby. The physical activities involved in parturition like uterine and abdominal contractions, dilation of cervix and passage of baby are collectively called labour. Labour is accompanied by localised sensation of discomfort or agony called labour pains.


Fig : Parturition

It involves the following three steps :
1. Dilation stage : Uterine contractions begin from top, forcing the baby towards the cervix. Contractions are accompanied by pain caused by compression of blood vessels. Oxytocin induced uterine contractions become stronger and stronger due to stimulatory reflex. As the baby is pushed down in the uterus, its head comes to lie against cervix. Cervix gets dilated.

2. Expulsion stage : The uterine and abdominal contractions become stronger. In normal delivery, the foetus passes out through cervix and vagina with head in forward direction. It takes 20 to 60 min. The umbilical cord is tied and cut off close to the baby’s navel.


3. After birth : After the delivery of the baby the placenta separates from the uterus and is expelled out as “after birth”, due to severe contractions of the uterus. This process happens within 10 to 45 minutes of delivery.



3. Explain the histological structure of testis.
Answer : 
Fig : Testis Structure.

The testis is externally covered by a collagenous connective tissue layer called tunica albuginea. Outer to it is an incomplete peritoneal covering called tunica vaginalis, and inner to it is tunica vasculosa, a thin membranous and vascular layer. Fibers from tunica albuginea divide each testis into about 200-300 testicular lobules. Each with 1-4 highly coiled seminiferous tubules. Each seminiferous tubule is internally lined by cuboidal germinal epithelial cells (spermatogonia) and few large pyramidal cells called Sertoli or sustentacular cells. 

The germinal epithelial cells undergo gametogenesis to form the spermatozoa. Sertoli cells provide nutrition to the developing sperms. Various stages of spermatogenesis can be seen in the seminiferous tubules. The inner most spermatogonial cell (2n), primary spermatocyte (2n), secondary spermatocyte

(n), spermatids (n) and sperms (n). The Interstitial or Leydig’s cells lie in between the seminiferous tubules. They secrete the male hormone androgen or testosterone.


4. Describe the structure of blastula.

Answer
Fig: Cleavage & Blastula Formation

The development of multi-cellular organisms started from fertilization. Fertilization forms a single-celled zygote, which undergoes rapid cell division to form the blastula. The rapid, multiple rounds of cell division are termed cleavage. The cleavage has produced over 80-100 cells, the embryo is called a blastula. The blastula is usually a spherical layer of cells (the blastoderm) surrounding a fluid-filled or yolk-filled cavity (the blastocoel). Mammals at this stage form a structure called the blastocyst, characterized by an inner cell mass that is distinct from the surrounding blastula, 


During cleavage, the cells divide without an increase in mass; that is, one large single-celled zygote divides into multiple smaller cells. Each cell within the blastula is called a blastomere.


In mammals, the blastula forms the blastocyst in the next stage of development. Here the cells in the blastula arrange themselves in two layers: the inner cell mass, and an outer layer called the trophoblast. The inner cell mass is also known as the embryoblast and this mass of cells will go on to form the embryo. At this stage of development, the inner cell mass consists of embryonic stem cells that will differentiate into the different cell types needed by the organism. The trophoblast will contribute to the placenta and nourish the embryo.


5. Explain the histological structure of ovary in human.
Answer


The ovary is an organ found in the female reproductive system that produces an ovum. It is the primary female sex organ. Its main function is production of egg or ovum and the female reproductive hormones. It is solid, oval or almond shaped organ. It is 3.0 cm in length, 1.5 cm in breadth and 1.0 cm thick. It is located in the upper lateral part of the pelvis near the kidneys. Each ovary is a compact structure differentiated into a central part called medulla and the outer part called cortex.


The cortex consist of germinal epithelial cells. The outer cortex is more compact and granular. It has large number of tiny masses of cells called ovarion follicles. These are collectively formed from the immature ova originating from cells of the dorsal endoderm of the yolk sac. The cells migrate to the gonadal ridge during embryonic development and divide mitotically. Now these cells are called oogonia. As the oogonia continue to grow in size they are surrounded by a layer of granulosa cells and form the rudiments of the ovarian follicles. The process of oogenesis starts much before the birth of the female baby and by the end of twelve weeks the ovary is fully formed. It has more than two million primordial follicles in it.


6. Describe the various methods of birth
control to avoid pregnancy.
Answer : The birth control measures which prevent fertilization are referred to as contraceptives. The contraceptive methods help to prevent unwanted pregnancies. An ideal contraceptive should be easily available, user friendly, effective and with no or least side effects.
Contraceptive methods are of two main types :
A) Temporary and 
B) Permanent.

Temporary methods:

These are of following types :
1. Natural method/ Safe period / Rhythm method .
2. Coitus Interruptus or withdrawal.
3. Lactational amenorrhea (absence of menstruation).
4. Chemical means (spermicides).

5. Mechanical means / Barrier methods: In this method, with the help of barriers the ovum and sperm are prevented from physically meeting. These mechanical barriers are of three types.

i) Condom
ii) Diaphragm, cervical caps and vaults.
iii) Intra-uterine devices (IUDs)
6. Physiological (Oral) Devices : Physiological devices are used in the form of tablets and hence are popularly called pills. It is an oral contraceptive, used by the female.

B. Permanent Method:

The permanent birth control method in men is called vasectomy and in women it is called tubectomy.
These are surgical methods, also called sterilization. In vasectomy a small part of the vas deferens is tied and cut where as in tubectomy, a small part of the fallopian tube is tied and cut. This blocks, gamete transport and prevent pregnancy.

1. Medical Termination of Pregnancy (MTP) : An intentional or voluntary termination of pregnancy before full term is called Medical termination of Pregnancy (MTP) or induced abortion. MTP is essential in cases of unwanted pregnancies or in defective development of foetus. It is safe during the first trimester of pregnancy. The defective development of foetus is examined by amniocentesis.


7. What are the goals of RCH programme.
AnswerGoals of RCH Programmes:
1. To create awareness among people about various aspects related to reproduction.
2. To provide the facilities to people to understand and build up reproductive health.
3. To provide support for building up a reproductively healthy society.

4. To bring about a change mainly in three critical health indicators i.e. reducing total infertility rate, infant mortality rate and maternal mortality rate.


8. Which hormones are involved in parturition?
AnswerParturition is the process of giving birth to a baby as the development of the foetus gets completed in the mother’s womb. The hormones involved in this process are oxytocin and relaxin. Oxytocin leads to the contraction of smooth muscles of myometrium of the uterus, which directs the full term foetus towards the birth canal. On the other hand, relaxin hormone causes relaxation of the pelvic ligaments and prepares the uterus for child birth


9. Which as the function of male accessory glands?
AnswerThe male accessory ducts (vasa efferentia, epididymis, vas deferens, and rete testis) serve to temporarily store spermatozoa and to transport them outside urethra during ejaculation. 

Male accessory glands are seminal vesicles, prostate glands, and bulbourethral glands which contribute seminal plasma to semen. These glands secrete fluids that lubricate the reproductive system and sperms. The sperms get dispersed in the fluid which makes their transportation into the female body easier. The fluid is rich in fructose, ascorbic acid, and certain enzymes. They also provide nutrients and activate the sperm.


Seminal vesicle secretion accounts for 60% of seminal plasma and adds alkaline pH (to counteract acidic pH of the vagina), fructose (a nutrient), mucus and coagulating and local acting enzymes. Prostate gland secretions account for 30% of plasma and add citrate (a nutrient for sperm mitochondria), calcium and a proteolytic enzyme termed as prostate-specific antigen (to liquefy ejaculate just before release). Secretion from Cowper gland adds only small volume.


10. What is capacitation? Give it’s importance.
Answer : Sperm capacitation refers to the physiological changes spermatozoa must undergo in order to have the ability to penetrate and fertilize an egg. Recognition of the phenomenon was quite important to early in vitro fertilization experiments as well as to the fields of embryology and reproductive biology


Q. 6 Long answer questions.


1. Explain the following parts of male reproductive system along with labelled diagram showing these parts- Testis, vasa deferentia, epididymis, seminal vesicle, proastate gland and penis.
Answer : Male Reproductive System :


Fig : Male reproductive system

It consists of the primary male organ (gonad) called testes, the accessory ducts and glands which form internal and external genitalia.

Testis : A pair of testes, mesodermal in origin, are formed in lower abdominal cavity. They are located in a pouch called scrotum. During early foetal life, the testes develop in abdominal cavity and later they descend into the scrotal sac through a passage called inguinal canal. Each testis is oval in shape, 4 to 5cm long, 2 to 3cm wide and 3cm thick.

Seminal vesicles: It is a pair of glands lying on the posterior side of urinary bladder. It secretes an alkaline seminal fluid which contains fructose, fibrinogen and prostaglandins. It contributes about 60% of the total volume of the semen. Fructose provides energy for sperm movement while fibrinogen coagulates the semen into a bolus for quick propulsion in the vagina.

Prostate gland: It is a large and single gland made up of 20-30 lobes and is located underneath the urinary bladder. It surrounds the urethra and releases a milky white and slightly acidic prostatic fluid into the urethra. It forms about 30% of volume of semen. It contains citric acid, acid phosphatase and various other enzymes. The acid phosphatase protects the sperms from the acidic environment of vagina.

The accessory ducts include rete testis, vasa efferentia, epididymis, vas deferens, ejaculatory duct and urethra. All the seminiferous tubules of the testis at the posterior surface form a network of tubules called rete testis. 12-20 fine tubules arising from rete testis are vasa efferentia. They carry the sperms from the testis and open into the epididymis.


2. Describe female reproductive system of human.
AnswerFemale Reproductive System: The female reproductive system consist of the following parts :

1. Ovary : It is the primary female sex organ. Its main function is production of egg or ovum and the female reproductive hormones. It is solid, oval or almond shaped organ. It is 3.0 cm in length, 1.5 cm in breadth and 1.0 cm thick. It is located in the upper lateral part of the pelvis near the kidneys. Each ovary is held in position by ligaments by attaching it to the uterus and the abdominal wall. The ovary produces five hormones viz, estrogen, progesteron, relaxin, activin and inhibin. Each ovary is a compact structure differentiated into a central part called medulla and the outer part called cortex.



2. Oviduct / Fallopian tube / Uterine tube: These are a pair of muscular ducts lying horizontally over the peritoneal cavity. The proximal part of the tube lies close to the ovary, and distally it opens into the uterus. Each tube is 10 to 12 cm in length. It is internally lined by ciliated epithelium. It can be divided into three regions :


a. Infundibulum : The proximal funnel like part with an opening called ostium surrounded by many finger like processes called fimbriae (of these at least one is long and connected to the ovary). The cilia and the movement of fimbrae help in driving the ovulated egg to the ostium.


b. Ampulla : It is the middle, long and straight part of the oviduct. Fertilization of the ovum takes place in this region.


c. Isthmus / Cornua : The distal narrow part of the duct opening into the uterus.


3. Uterus : It is commonly also called the womb. It is a hollow, muscular, pear shaped organ, located above and behind the urinary bladder. It is about 7.5 cm long, 5 cm broad and 2.5 cm thick. The uterus can be divided into three regions :


a. Fundus : It is the upper dome shaped part. Normally implantation of the embryo occurs in the fundus.


b. Body : It is the broad part of the uterus which gradually tapers downwards.


c. Cervix : It is the narrow nec about 2.5 cm in length. It extends into the vagina. Its passage has two openings : an internal os towards the body, and an external os towards the vagina.


4. Vagina : It is a tubular, female copulatory organ, 7 to 9 cm in length. It lies between the cervix and the vestibule. The vaginal wall has an inner mucosal lining, the middle muscular layer and anouter adventitia layer. The mucosal epithelium is stratified and non-keratinised and stores glycogen. The opening of the vagina into the vestibule is called vaginal orifice. This opening is covered partially by a fold of mucus membrane called hymen. The vagina acts as a passage for menstrual flow as well as birth canal during parturition.


5. External genitalia : The external genital organs of female include parts external to the vagina and are collectively called ‘vulva’ (covering or wrapping), or pudendum.


6. Accessary glands / Vestibular glands / Bartholin’s glands : It is a pair of glands homologous to the Bulbourethral or Cowper’s glands of the male. They open into the vestibule and release a lubricating fluid.


3. Describe the process of fertilization.
Answer : Fertilization / Syngamy:
Sexual reproduction primarily involves formation and fusion of gametes. Fertilization is the later process which involves fusion of the haploid male and female gametes resulting in the formation of a diploid zygote (2n). Like in other mammals, in humans the process of fertilization is internal and it usually takes place in the ampulla of the fallopian / uterine tube. The fertilized egg or zygote will develop into an embryo and this process occurs within the uterus.


Fig : Process of Fertilization

Mechanism of fertilization :
Semen released during ejaculation has sperms and some secretions. The coagulated semen now undergoes liquification and sperms become active. The mechanism of fertilization is as follows :

Movement of sperm towards egg:
It involves capacitation of sperms reaching the vagina. Here as many as 50% are demotilised / broken / destroyed. Remaining sperms undergo capacitation. This process requires 5-6 hours. 

Due to the acrosomal reactions, the plasma membrane of the secondary oocyte and the sperm fuse together so that the contents of the sperms can enter. When the plasma membrane of the sperm binds with that of the secondary oocyte, the plasma membrane of the oocyte depolarizes. This prevents polyspermy.

Calcium ions play a significant role in the acrosomal reaction. The main factors essential for acrosomal reactions are optimum pH, temperature and calcium and magnesium concentration.

Cortical Reaction : Soon after the fusion of the plasma membranes, the oocyte shows cortical reactions. Cortical granules found under the plasma membrane of the oocyte, which fuses with the plasma membrane and releases cortical enzymes between the zona pellucida and plasma membrane. The zona pellucida is hardened by the cortical enzymes that prevent polyspermy.

Sperm Entry into the ovum /egg : A projection known as the cone of reception is formed by the secondary oocyte at the point of sperm contact. This cone of reception receives the sperm.

Karyogamy : After the entry of the sperm, the suspended second meiotic division is completed by the secondary oocyte. This gives rise to a haploid ovum and a second polar body. The head of the sperm containing the nucleus detaches from the entire sperm and is known as male pronucleus. The tail and the second polar body degenerates. The nucleus of the ovum is known as female pronuclei.

The male and female pronuclei fuse and their nuclear membranes degenerate. The fusion of the chromosomes of male and female gametes is called karyogamy. The ovum is now fertilized and is known as a zygote.

 Activation of Ovum / Eggs: The entry of sperm triggers the metabolism in the zygote. Consequently, protein synthesis and cellular respiration increase.

Fusion of egg and sperm : The coverings of male and female pronuclei degenerate allowing the chromosomal pairing. This results in the formation of a synkaryon by theprocess called syngamy or karyogamy. The zygote is thus formed.

Implantation : Once fertilization happens, the cell starts to divide and multiply within 24 hours in the fallopian tube. This detached multi-celled structure is called zygote. Later, after 3-4 days it travels to the uterus and now we call it as an embryo. The embryo develops and undergoes various stages and gets attached to the endometrial layer of the uterus. This process of attachment is known as implantation.