BIOLOGY 3 Marks Question

All human beings have 23 pairs of chromosomes. Human males have 22 pairs of autosomes and contain one or two types of sex chromosome. They are either X or Y. On the contrary, human females have 22 pairs of autosomes and contain only the X sex chromosome. The sex of an individual is determined by the type of the male gamete (X or Y), which fuses with the X chromosome of the female. If the fertilizing sperm is X, then the baby will be a girl and if it is Y, then the baby will be a boy.
Hence, it is incorrect to blame a woman for the gender of the child.

The process of delivery of the foetus (childbirth) at the end of pregnancy is called parturition.
The hormones involved in induction of parturition are:

• Oxytocin hormone from maternal pituitary stimulates strong uterine contractions that lead to expulsion of the baby from the uterus.
• Relaxing hormone from ovary widens the vagina to facilitate birth.

The seminiferous tubule is a structural unit in the adult testis. The seminiferous tubules are situated in testicular lobules. Seminiferous tubule consists of two types of cells – Sertoli or supporting cells & spermatogenic cellsl Sertoli cells, are elongated and pyramidal & partially envelop the spermatogenic cells. The cells provide nourishment to the developing spermatogenic cells. Spermatogenic cells are stacked in 4-8 layers. These cells divide several times & differentiate to produce spermatozoa. Between seminiferous tubules lie the interstitial cells or leydig cells which produces testosterone hormone.

One egg is released by human ovary in a month:Identical twins:
Identical twins are formed when a single fertilized egg splits into two genetically identical parts. The twins share the same DNA set, thus they may share many similar attributes. However, since physical appearance is influenced by environmental factors and not just genetics, identical twins can actually look very different.
Fraternal twins:
These twins are formed when two fertilized eggs are formed. The twins share the different DNA set, thus they may share different attributes (dizygotic embryo).

On the sperm head, has enzymes to dissolve the follicles of ovum/facilitate entry of sperm nucleus for fertilisation/help the sperm enter into the cytoplasm of the ovum.

Blastocyst/Blastula.

Fallopian tubes/ (ampulla of) oviduct.

In the seminiferous tubules/testes, nourishes sperms/germ cells.

Meiosis.

Colostrum has abundant antibodies/IgA to develop resistance in newborn babies.

Cervix helps in regulating the passage of sperms into the uterus and forms the birth canal to facilitate parturition.

1. 30
2. 15

It is a cap-like structure present in the anterior of the head of a sperm.

Gametogenesis, Insemination, Fertilisation, Implantation, Gestation, Parturition.

Second meiotic division.

Middle of cycle (14th day).

Spermiogenesis.

Gametogenesis → Insemination → Fertilisation → Implantation → Gestation → Parturition.

60,000-80,000

It forms the foetal part of placenta.

Halving of chromosomal number takes place during gametogenesis by meosis and regaining the 2n number occur as a result of fertilisation by fusion of male and female gametes.

Middle myometrium.

A-Fertilisation.
B-Uterus.

Provide energy for the movement of sperm tail.

Uterus.

Zona pellucida.

Ampullary-isthmic junction of the fallopian tube.

Oogenesis starts during embryonic developmental stages of the female foetus while, spermatogenesis starts at puberty.

The outer layer of blastocyst is referred to as trophoectoderm or trophoblast.

They produce male androgen (testosterone).

LH surge is essential for the events leading to ovulation.

Blastomeres.

Spermatids are produced by meiosis during spermatogenesis. Thus, they possess haploid number of chromosomes.

Umbilical cord transports nutrients and respiratory gases and metabolic wastes to and from mother and foetus.

During fertilisation a sperm head comes in contact with zona pellucida layer of ovum and induces changes in the membrane that block the entry of additional sperms.

Before birth at five months of foetal life, oogonia reach their maximum number.

Six eggs were released by the ovary of a female dog which gave birth to six puppies.

Seminal plasma (secreted by the male reproductive glands) along with the spermatozoa, constitute semen.

Fertilisation takes place in Fallopian tube (W) and implantation takes place in uterus (Y).

The first sign of growing foetus is noticed by listening to the heart sounds through a stethoscope.

In this phase, progesterone stimulates the endometrial glands of the uterus to secrete a nutrient fluid for the foetus hence, also called the secretory phase.

S. No.	Column I	S. No.	Column II
A.	Acrosome	4.	Contains enzymes to dissolve egg envelopes.
B.	Head	3.	Contains the genetic material.
C.	Tail	1.	Motility of sperm towards the egg.
D.	Middle piece	2.	Powerhouse of the sperm; contains a number of mitochondria.

Colostrum.

Perimetrium, Myometrium and Endometrium.

40 chromosomes.

Ciliated epithelial tissue.

If the testes fail to descend to the scrotum, gametogenesis could be inhibited. The process of spermatogenesis requires a marginally lesser ambient temperature than that in the abdominal cavity.

Trophoblast is the outer layer of blastocyst which helps in the attachment of blastocyst to the endometrium of the uterus.

Chorionic villi appear after implantation on the trophoblast. It becomes interdigitated with uterine tissue to form the placenta and increases the surface area for exchange of materials between the mother and the embryo.

First cleavage division of zygote occurs in the ampullary-isthmic junction in the female reproductive tract.

During the production of secondary oocyte and ovum.

These are mild uterine contraction induced by the signals for parturition originated from fully developed foetus and placenta.

The primary oocyte within the tertiary follicle grows in size and completes its first meiotic division to form secondary oocyte and first polar body.

Yes. For example, the external reproductive organ penis in males and clitoris in females.

Endometrium.

During pregnancy, placenta produces hormones like human chorionic gonadotropin and human placental lactogen and ovary produces relaxin.

Sertoli cells. They are found on the inner lining of seminiferous tubule.

Because eggs are non-motile (stationary) and sperms have to travel up to eggs.

1. Isthmus.
2. Ampulla.

Leydig cells are present in the regions called interstitial spaces outside the seminiferous tubules. They synthesise and secrete androgens (testosterone).

Sperms swim by vibrating their tail in the fluid while eggs do not require it.

The follicle cells that envelope the egg outside zona pellucida are called corona radiata.

Luteal phase/ Secretory phase.

Blastocyst stage.

It is the innermost glandular layer of uterus which lines the uterine cavity. Here, implantation of blastocyst takes place. It undergoes cyclical changes during menstrual cycle.

Spermiogenesis: It is the transformation of spermatids into spermatozoa or sperms.
Spermiation: It is the release of sperms from seminiferous tubules.

The secretions of the bulbourethral glands help in the lubrication of the penis.

400 sperms and 100 ova.

Ovulation.

60,000-80,000 primary follicles are left in each ovary.

Labia minora.

Amniotic fluid.

Testosterone.

Endometrium.

Luteinizing hormone.

S. No.	Column I	S. No.	Column II
A.	Cleavage	2.	Mitotic divisions of the zygote in quick succession.
B.	Implantation	3.	Embedding of the blastocyst in the endometrium of uterus.
C.	Inner cell mass	5.	Group of cells attached to one end of trophoblast that differentiate into embryo proper.
D.	Trophoblast	1.	Outer layer of the blastocyst that attaches to the endometrium during implantation.

200 sperms.

The correct order is Mammary tubules → Mammary duct Mammary ampulla Lactiferous duct.

Oogenesis in human females initiate at the foetal/ embryonic stage.
Spermatogenesis in human males starts at puberty.

It is the remaining part of Graafian follicle after ovulation in the luteal phase which acts as an endocrine gland.

Spermiation.

Ampulla.

Epididymis.

Colostrum contains necessary antibodies (IgA and IgG) that provide protection against diseases to newborn infants.

Inner cell mass.

1. Mesoderm.
2. Endoderm.

Cervix can hold about 7kg of foetus and fluid in the uterus against the pull of gravity for several days during pregnancy. Thus, it contains the largest and strongest sphincter.

High level of progesterone and estrogens during pregnancy suppress the gonadotropins which is required for the development of new follicles. Therefore, a new cycle cannot be initiated.

It is a mature ovarian follicle in the ovary.

23.

The acrosome of the sperm contains sperm lysin (hyaluronidase) which dissolve the mucopolysaccharide, hyaluronic acid by which the cells of corona radiata glued together.

Seminiferous tubule.

The signals for parturition arise from the fully-developed foetus and the placenta.

Lactation is the process of feeding the new born baby with the milk secreted by the mammary glands.
Endometrium is the inner most glandular layer of the uterine wall that undergoes cyclical changes during menstrual cycle, where implantation occurs; it also forms a part of the placenta.

Cervix helps in regulating the passage of sperms into the uterus and forms the birth canal to facilitate parturition.

Stem cells.

One ova is produced by one fully grown primary oocyte.

1. A primary spermatocyte is diploid and has 46 chromosomes; it undergoes meiosis I and forms two secondary spermatocytes.
2. A secondary spermatocyte is haploid and has 23 chromosomes; it undergoes meiosis II and forms two spermatids.

Colostrum.

1. A - Pelvic wall.
2. B - Clitoris.
3. C - Ova.

The urethra originates from the urinary bladder and extends through penis to its external opening called urethral meatus.

Progesterone.

The sperm penetrates through zona pellucida with the help of secretions from acrosome.

Zona pellucida.

Trophoblast forms chorionic villi, which become part of the placenta.

It is a mammalian blastocyst.
A is trophoblast.

Spermiogenesis is the formation of haploid, microscopic and functional spermatozoa (male gametes) from the spermatids. It takes place in the testes (male reproductive organ).

Acrosome contains hydrolytic enzymes used to penetrate the egg during fertilisation.

Trophoblast.

Cleavage refers to the rapid mitotic divisions that occur in the zygote.

Spermatic cords.

The basal parts of endometrium remain intact as they form the source of new endometrial lining and glands for the next cycle.

Ootid.

The time period between implantation and parturition, when the embryo completes its growth and development, is called gestation period.

ICM (Inner Cell Mass).

Menopause, i.e. stoppage of menstrual cycles occurs around 50 years of age; since no ovulation occurs, the woman cannot conceive after this age.

Relaxin and human chorionic gonadotropin.

Placenta is connected to embryo through umbilical cord and helps in transport of substance to and from the embryo.

Trophoblast is cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta. They are formed during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg.

Chorionic villi are the finger-like projections formed by the trophoblast immediately after implantation; they form the foetal part of the placenta.

Rete testis. It leads to vas deference.