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.