QUESTION

 

 

 

ANSWER

 

1.1 Pass
1. a) A-Head
B-Middle piece
C-Tail
D-Nucleus
E-Acrosome
b) The function of acrosome is that it is filled with some enzymes which help in the ovum fertilisation.
c) Sperm cells usually contain numerous mitochondria (about 25-30) which produces energy for the movement of tail of the sperm which helps in providing motility to the sperm which is extremely important for fertilisation.

2)
Spermatogenesis Oogenesis
● Spermatogenesis is the process of production of sperms. The process of formation of a mature female gamete is known as oogenesis.
● It begins at puberty. It begins during the embryonic development.

3. (i) A-Primary follicle
B-Tertiary follicle
C-Graafian follicle
D-Ovum
E-Blood vessels
F-Ovary
G-Corpus luteum
H-Corpus albicans
ii) FEABCDGH
B. (i) A- Hormone secreted by primary follicle(A) is oestrogen
E- LH and FSH
(ii) A-The function of oestrogen is in the development of secondary sexual characters in females which further includes regulation of menstrual cycle,breasts formation, etc.and regulation and growth of entire female reproductive system.
E-LH and FSH plays a very important role during the menstruation cycle. It behind to receptors of ovary and by promoting the sex steroid production and gametogenesis these regulate gonadal functions.

1.1 Merit
There is an immense change in the concentrations of different hormones at different stages of pregnancy. HCGi.e. Human chorionic Gonadotropin hormone is normally released by the cells of the placenta during the pregnancy and it is an indicator of pregnancy as its level indicates whether a woman is pregnant or not as if the level of hcg is less than 5 mIU/ml then it indicates that the woman is not pregnant but if it is present in more than 25mIU/ml then it clearly indicates that the woman is pregnant.The concentration of HCG is high during the initial stage due to this above describes reason. HCG also plays an important role in maintenance of corpus luteum during the initial phase of pregnancy and it allows the corpus luteum to release progesterone which is very essential during pregnancy during the third trimester.Now discussing about the level of oestrogen and progesterone although progesterone dominates oestrogen throughout the pregnancy it is also important as progesterone secretion by the placenta is stimulated by oestrogen. As shown in the graph, initially the level of progesterone is comparatively lower this is due to the fact that initially corpus luteum secretes progesterone which is then sufficient enough to perform functions but later on the level of progesterone rises due to the fact that when placenta grows and it develops the ability to release hormones and the cell of placenta i.e. trophoblast takes over the function of secreting progesterone to fulfil its needs to perform various other functions. Placenta also aids in the production of oestrogen by the fetal-liver and adrenal gland. Level of oestrogen rises steadily until birth of the foetus as it is very crucial for the proper development of many fetal organs including liver, kidney, etc. It not only stimulate the growth of placenta but also stimulate the proper functioning of placenta. It is also very essential for proper growth of maternal breast tissues and also prepares the fetal mother for the process of lactation. Thus, oestrogen level rises during the last stages of pregnancy. All three above mentioned hormones in the graph are very essential for mother as well as fetal to sustain. There are changes in the concentration of these hormones on the basis of requirement and their functions.

 

1.1 Distinction
Mature female gametes are produced through a process known as oogenesis.
There are basically three stages involved in oogenesis namely:-
1. Multiplication Phase
2. Growth Phase
3. Maturation Phase

Multiplication Phase:-
Certain cells present in the germinal epithelium of the female ovary are bigger than the others during the fetal development.These cells hence divide by mitotic type of cell division and creates a couple of million of mother egg cells or oogonia in each ovary in the fetus. There is a fact that neither more oogonia are formed neither added after the birth.
Growth phase:-
The oogonium formed are transformed into bigger primary oocyte. Now this primary oocyte gets surrounded by a layer of granulosa cells and now known as primary follicle. A large number of primary follicles gets degenerated during the duration from birth to puberty. Due to this reason at the time of puberty only 60000-80000 primary follicles can be seen in each of the ovary.
Maturing Phase:-
In this phase, every primary oocyte undergoes two maturation divisions. In the first meiotic division, the primary oocyte segregates and form two haploid daughter cells which are uneven and are known as large secondary oocyte and the smaller one is known as polocyte. In the second maturation separation, the initial polar body splits and form two second polar bodies. And in this phase secondary oocyte once again divides to form unfit daughter cells.

1.2 Pass
1. Follicular phase
2. FSH(Follicle-Stimulating Hormone)
3. LH(Luteinizing Hormone)
4. Pituitary
5. Estrogens
6. Ovulation
7. LH
8. Progesterone
9. Progesterone
10. Corpus luteum
11. Progesterone
12. Fertilisation

1.2 Distinction

Process of oogenesis in human female:-
The process of production of mature female gamete is known as oogenesis which is initiated during the embryonic development stage. At this stage a couple of million of oogonia are formed within each fetal ovary. Neither more oogonia are formed nor added after birth of a human female. The oogonial cells starts dividing and enters the prophase-I of the meiotic division and then gets arrested temporarily at this stage and is known as primary oocyte and when each such formed primary oocytes gets surrounded by a layer of granulosa cells then it is known as primary follicle.With the onset of puberty primary follicles starts to mature with each and every ovarian cycle.the follicular cells divide by mitosis to form a stratified epithelium, the granulosa layer. When the primary follicle gets surrounded by many layers of granulosa cells and a new theca then it is known as secondary follicle.This secondary follicle soon transforms into a tertiary follicle which is characterised by a fluid filled cavity known as antrum. The primary oocyte present within the tertiary follicle grows in size and completes its first meiotic division at the stage of puberty. It is an example of unequal division in which a large haploid secondary oocyte and a small polar body is formed. Thus formed secondary oocyte retains the bulk of cytoplasm (which is nutrient rich) of the primary oocyte. Then the tertiary follicle changes into mature follicle known as graafian follicle.The secondary oocyte forms a new membrane which is called as zona pellucida around it. The granulosa cells lying in close proximity of the ovum and zona pellucida, becomes elongated and now forms a new structure known as corona radiata.The graafian follicle now ruptures in the presence of LH hormone and release the secondary oocyte developing from the ovary through ovulation. After ovulation the ruptured follicle left in the ovary is converted to corpus luteum which secretes a hormone namely progesterone.

 

1.2 Merit

A. Precautionary steps:-
1. Woman should have a balanced and healthy diet.
2. Woman should intake vitamins which have folic acid content.

B. It is very essential to maintain the corpus luteum during the early stage of pregnancy because corpus luteum secretes a hormone known as progesterone which is important for maintenance of endometrium lining of the uterus which plays an important role during pregnancy.Further it improves supply of oxygen and flow of blood.

2.1 Pass
(i) S-phase of Interphase
(ii)Prophase of M Phase
(iii)G2-phase of Interphase

2.1 Merit

Mitosis in onion cell:-
Mitosis is a process in which a parent cell divides into two identical daughter cells.
Mitosis is divided into four stages:-
1. Prophase
In this stage,the condensation of chromatin material occur and during condensation,the DNA strands get untangled to form compact mitotic chromosome and at this time each chromosome appears double and consists of two coiled sister chromatids joined by a centromere.It is also called as spireme stage.

2. Metaphase:-
At this stage, disintegration of nuclear envelope begins.Mitotic spindle formation is comolete.At this stage rh chromosome are thickest and shortest.
● Sister chromatids line up at the spindle equator.
● At the end of metaphase, centromere divides.

3. Anaphase:-
● It begins with the separation of the centromeres.
● By the contraction of spindle fibres,the sister chromatids are drawn to opposite poles of the cell.

4.Telophase:-
● It begins when the two sets of daughter chromosomes of the onion cells have reached the two poles of the cell.
● The spindle fibre disintegrates,the nuclear membrane forms around each set of daughter chromosomes and the nucleoli reappears.
● Later the chromosomes of the onion cell starts uncoiling and becomes less visible under the light microscope.

2.1 Distinction
Crossing over is a phenomenon which occurs during the pachytene stage of prophase I of meiosis I.
Crossing over is a term which refers to the exchange of genetic material ( D.N.A. in case of human) between the non-sister chromatids of the homologous chromosomes and this crossing over gives rise to recombination(which is a enzyme-mediated process) of genetic material which involves the mutual exchange of the corresponding segments of non-sister chromatids of homologous chromosomes. It occurs through breakage and reunion of chromatid segments.Thus crossing over leads to evolution and now when we talk about independent assortment which is a phenomenon in which during anaphase I of meiosis I when cells are dividing, the homologous chromosomes are distributed randomly and gets separated and segregated independently to each other resulting in gametes that have unique combinations of chromosomes. Both of these phenomenons lead to variation in gametes and leads to evolution.

2.2 Pass

Mitosis Meiosis
● Diploid (2n) ● Haploid (n)
● Produces identical cells. ● Produces non-identical cells.
● 1 cell division ● 2 cell division
● Produces two diploid cells. ● Produces four haploid cells.

2.2 Merit

Mitosis Meiosis
Mitosis is a process in which a parent cell divides into two identical daughter cells.
Meiosis is a process in which a single parent cell (diploid)forms four daughter cells(haploid)
Mitosis is divided into four stages:- It is divided in two parts namely meiosis-I and meiosis-II.
Meiosis-I is divided into 4 sub- stages.
Meiosis-II is same as mitosis.
2. Prophase Meiosis-I:
1.Prophase-I:- It is more prolonged, elaborate and complex than mitotic prophase.The long and complicated prophase-I is further subdivided into 5 stages:-

 

‘Pro’ means first and ‘phase’ means stage.
In this stage,the condensation of chromatin material occur and during condensation,the DNA strands get untangled to form compact mitotic chromosome and at this time each chromosome appears double and consists of two coiled sister chromatids joined by a centromere.It is also called as spireme stage.

● Leptotene:-condensation and coiling of chromatin fibres begin.The chromatin material condenses to form distinct chromosome which become visible under light microscope gradually.
● Zygotene :- Homologous chromosomes start pairing together.These homologous chromosomes come to lie side by side in pairs and this pairing is known as synapsis.
● Pachytene:- Crossing over occur at this substage.
● Diplotene:- Crossing over is completed and the two homologous chromosomes begin to separate from each other and later chiasmata formation is there.
● Diakinesis:- Terminalisation of chiasmata occur.Nucleolus disappears and the nuclear envelope disintegrates.

2. Metaphase 2. Metaphase-I
‘Meta’ means second and ‘phase’ means stage.
At this stage, disintegration of nuclear envelope begins.Mitotic spindle formation is comolete.At this stage rh chromosome are thickest and shortest.
Sister chromatids line up at the spindle equator.
At the end of metaphase, centromere divides.
The bivalent chromosomes align themselves on the equatorial plate.Double metaphasic plate is formed.

3. Anaphase:- 3.Anaphase-I:-
‘Ana’ means up and ‘phase’ means stage.
It begins with the separation of the centromeres.
By the contraction of spindle fibres,the sister chromatids are drawn to opposite poles of the cell.
The two homologous chromosomes separate from each other. They begin moving towards the poles.
The intact chromosomes containing two chromatids held together by a centromere separate and move towards the opposite poles due to spindle fibre attached to it.
The reduction in the number of chromosomes occurs during this anaphase-I stage.

4.Telophase:- 4.Telophase-I:-
It begins when the two sets of daughter chromosomes have reached the two poles of the cell.
The spindle fibre disintegrates,the nuclear membrane forms around each set of daughter chromosomes and the nucleoli reappears.
Later the chromosomes starts uncoiling and becomes less visible under the light microscope.

The chromosomes reach the opposite poles. The spindle fibres disappears completely.
The nucleolus and nuclear membrane reappear.
The chromosomes starts uncoiling and elongate but remains straight in this phase. They could not reach the extreme extended state of the interphase nucleus.

Then intermeiotic interphase is present and then Meiosis-II begins which is same as the mitotic type of cell division.

Meiosis-II

 

2.2 Distinctions
SIMILARITIES
● DNA replication occurs only once both in meiosis and mitosis
● Both involves multiple stages.
● Chromosome condensation follows the same mechanism in both mitosis and meiosis.

DIFFERENCES

Mitosis Meiosis
● Karyokinesis occurs only once. ● Karyokinesis occurs twice.
● Crossing over is absent. ● Crossing over is present.
● Chiasma formation is absent. ● Chiasmata formation is present.
● Chromosomes form a single plate during metaphase. ● Chromosomes form two parallel plates in metaphase I and only one one plate in metaphase II.
● The stage telophase occurs in all cases. ● The stage telophase I is omitted in some cases.
● Karyokinesis is usually followed by cytokinesis. ● Cytokinesis does not occur after telophase I or meiosis I sometimes but it always occurs after meiosis II or telophase II thus forms 4 cells.
● Prophase is short and without sub-stages. ● Prophase Iis long with further 5 sub-stages.
● Mitosis is responsible for healing, repair and growth. ● Meiosis is responsible for maintaining chromosome number constant from one generation to another.
● Produces identical cells. ● Non-identical cells are produced