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Thursday 27 May 2021

Mathematics - For Class SSC - Part 2 (Science Group) - Solved Model papers 2020 - 2021- AS PER CONDENSED SYLLABUS

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Mathematics
For Class X Or SSC - Part 2 (Science Groups)
Solved Model papers 2020 - 2021
As Per condensed Syllabus





SECTION "B"


Q.2 (i) If A = {1, 2, 3, 4} and B = {2, 4, 6, 8} then
Prove that A∆B = (AUB) - (A∩B)
Solution:
Taking R.H.S:
AΔB = {1, 2, 3, 4} Δ {2, 4, 6, 8}
(By selecting uncommon members among both sets)
We get AΔB = {1, 3, 6, 8} ....... (1)

Taking L.H.S:
AUB = {1, 2, 3, 4} U {2, 4, 6, 8}
AUB = (1, 2, 3, 4, 6, 8)

A∩B = {1, 2, 3, 4} ∩ {2, 4, 6, 8}
A∩B = (2, 4)
AUB - A∩B = (1, 2, 3, 4, 6, 8) - (2, 4)
We get AUB - A∩B = {1, 3, 6, 8} ....... (2)
By (1) and (2)
AΔB = AUB - A∩B Hence Proved

Q.2 (ii) Simplify


Q.3 (i): Find the value of 85.7 x 2.47 / 8.89 with the help of logarithmic table.

Q.3 (ii) If y - z = , yz = -5, then find the value of y3 - z3
Solution:
Data:
y3 - z3 = ?
yz = -5
y - z = 4

Calculation:
⇒ y - z = 4
Taking cube on both side
⇒ (y -z)3 = (4)3

Using Formula
(a - b)3 = a3 - 3a2b + 3ab2 - b3

⇒ y3 - 3y2z + 3yz2 - z3 = 64
⇒ y3 - 3yz(y - z) - z3 = 64
⇒ y3 - 3(-5)(4) - z3 = 64
⇒ y3 - (-60) - z3 = 64
⇒ y3 + 60 - z3 = 64
⇒ y3 - z3 = 64 -60
⇒ y3 - z3 = 4 Ans

Q.4 (i): For what value of "p", 4a4 + 4a3 - 3a2 - pa + 1 will be a perfect square?

Q.4(ii): Find The solution set of x+5 / 10 < 25-4x / 5 , ∀ x ∈ N

Q.5(i) Solve the equation with the help of Cramer's rule:
5x - 2y = 1,
2x - y = 0

Q.5(ii) Find relation independent of "x" from the following equation:
x - 1/x = 2a
x2 + 1/x2 = b2

Q.6(i): Prove that:

Q.6(ii): Solve the following equation by using quadratic formula:
3a2 - 12a - 15 = 0

Q.7(i) Find the solution set of:

Q.7(ii): Find all the Values of the trigonometric ratios of 45°.


SECTION "C"


Q.8: If a side of a triangle is extended, the exterior angle so formed is, in measure, greater than either of the two interior opposite angles.

Q.9: Factorization
Sequence to apply formula for factorization
1) Try Common
2) Perfect square (a + b)2 = a2 + 2ab + b2
3) a2 - b2 = (a-b)(a+b)
4) Middle term breaking
5) (a + b + c)2 = a2 + b2 + c2 + 2ab + 2bc + 2ac
6) (a3 + b3) = (a + b)(a2 + ab + b2)
7) a3 + b3 + c3 - 3abc = (a + b + c)(a2 + b2 + c2 - ab - bc -ac)
I) a4 +2 b4
Solution:
By applying perfect square formula
(a + b)2 = a2 + 2ab + b2
⇒ [(a2)2 + 2(a2)(2b2) + (2b2)2 - 4a2b2]
⇒(a2 + 2b2)2 - (2ab)2
By applying Formula
a2 - b2 = (a-b)(a+b)
⇒ (a2 + 2b2 - 2ab) (a2 + 2b2 + 2ab)
⇒ Or (a2 -2ab + 2b2) (a2 + 2ab + 2b2) Ans.

II) x2 + 11x + 10
By applying formula
Middle term breaking
⇒ x2 + x + 10x + 10
⇒ x(x + 1) + 10(x + 1)
⇒ (x + 10)(x + 1) Ans.

III) a3 - a2 + 2
⇒ a3 - a2 + 1 + 1
⇒ a3 + 1 - a2 + 1
⇒ a3 + 1 - (a2 - 1)
⇒ Or (a3 + 13) - (a2 - 12)
By applying formula
(a3 + b3) = (a + b)(a2 + ab + b2)
and a2 - b2 = (a-b)(a+b)
⇒ {(a)3 + (1)3} - {(a)2 - (1)2}
⇒ {(a + 1)[(a)2 - (a)(1) + (1)2]} - {(a + 1)(a - 1)}
⇒ {(a + 1) (a2 - a + 1} - {(a + 1)(a - 1)}
By applying formula
Try Common
⇒ (a + 1) (a2 - a + 1) - (a - 1)
⇒ (a + 1) (a2 - a + 1 - a + 1)
⇒ (a + 1) (a2 - 2a + 2) Ans.

IV) 27x3 + 8y6 - 1 + 18xy2
By applying formula
a3 + b3 + c3 - 3abc = (a + b + c)(a2 + b2 + c2 - ab - bc -ac)
⇒ (3x)3 + (2y2)3 + (-1) - 3(3x)(2y2)(-1)
⇒ {(3x) + (2y2) + (-1)}{(3x)2 + (2y2)2 + (-1)2 -(3x)(2y2) - (2y2)(-1) - (-1)(3x)}
⇒ (3x + 2y2 -1)(9x2 + 4y4 + 1 -6xy2 + 2y2 + 3x) Ans.

(V) a2 + 6ac + 9c2 - b2
Solution:
⇒ a2 + 6ac + 9c2 - b2
⇒ (a)2 + 2(a)(3c) + (3c)2 - (b)2
By applying perfect square formula
(a + b)2 = a2 + 2ab + b2
⇒ (a + 3c)2 - (b)2
By applying formula
a2 - b2 = (a - b)(a + b)
⇒ (a + 3c + b) (a + 3c -b)
⇒ (a + b + 3c) (a -b + 3c)Ans.

VI) x3 + 64
By applying formula
(a3 + b3) = (a + b)(a2 + ab + b2)
⇒ (x)3 + (4)3
⇒ (x + 4) {(x)2 + (x)(4) + (4)2}
⇒ (x + 4) (x2 + 4x + 16)Ans.

Q.10: Construct a ∆PQR in which mPR = 5cm, mQR = 4.5cm, and m ∠Q = 65° and write down the steps of construction.
Solution:

Steps of Construction:
  1. Draw a line segment mQR = 4.5cm.
  2. At point Q draw an angle ∠RQX of measure 65°.
  3. With centre R draw an arc of length 5cm which cuts Qx at point P.
  4. Join R to P. such that mPR = 5cm.
  5. So, we get ∆PQR.


Q 11: The sum of the measures of the angles of a triangle is 180°.

Special Thanks To Sir Sajjad Akber Chandio


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Wednesday 26 May 2021

General Mathematics جنرل ریاضی - For Class SSC - Part 1 (Arts / General Group) - Model papers 2020 -2021- AS PER CONDENSED SLLABUS

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General Mathematics جنرل ریاضی
For Class SSC - Part 1 (Arts / General Groups)
Solved Model papers 2020 - 2021
As Per condensed Syllabus






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General Mathematics - For Class SSC - Part 1 (Arts / General Group) - Solved Model papers 2020 -2021- AS PER CONDENSED SYLLABUS

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General Mathematics
For Class SSC - Part 1 (Arts / General Groups)
Solved Model papers 2020-2021
As Per condensed Syllabus






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Tuesday 25 May 2021

General Science (Urdu) جنرل سائنس - For Class SSC - Part 1 (Arts / General Group) - Solved Model papers 2020 -2021- AS PER CONDENSED SYLLABUS

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General Science (Urdu) جنرل سائنس
For Class SSC - Part 1 (Arts / General Groups)
Solved Model papers 2020 - 2021
As Per condensed Syllabus







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General Science - For Class SSC - Part 1 (Arts / General Group) - Solved Model papers 2020 -2021- AS PER CONDENSED SYLLABUS

GO TO INDEX
General Science
For Class SSC - Part 1 (Arts / General Groups)
Solved Model papers 2020-2021
As Per condensed Syllabus








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Biology For Class IX - Chapter No.5 - CELL CYCLE - Review Questions From Text Book

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CHAPTER 5
CELL CYCLE
Review Questions From Text Book

1. Encircle the correct Answer:
1. Which processes involve mitosis?
(a) Growth, reduction division and asexual reproduction
(b) Growth, repair and asexual reproduction ✓
(c) Growth, repair and semi conservative replication
(d) Growth, reduction division and repair

2. What occurs in metaphase of mitosis?
(a) Chromosome line up on the equator of the cell ✓
(b) Chromatids reach the poles of the spindle
(c) Chromatids separate and move to opposite poles
(d) Chromosomes start to coil up and become visible

3. Select the mismatched:
(a) Anaphase 4 Chromatids move
(b) Prophase 4 Centriole move
(c) Telophase 4 Nuclear membrane disappear ✓
(d) Metaphase 4 Chromosome line up

4. Which process occurs during prophase of mitosis in an animal cell?
(a) Division of centromeres
(b) Formation of chromosomes ✓
(c) Replication of DNA
(d) Separation of centrioles

5. Sequence of physiological changes by which cell commit suicide.
(a) Apoptosis
(b) Necrosis
(c) Autophagy
(d) Both "a" and "c" ✓

6. Choose the Incorrect statement regarding meiosis.
(a) Maintain chromosome number from generation to generation
(b) Reduces the diploid number of chromosomes to half
(c) Takes place in germ cell to produce gametes
(d) Production of new somatic cells from germ cells ✓

7. A type of cell division in which spore mother cell produce spores
(a) Amitosis
(b) Mitosis
(c) Meiosis ✓
(d) Both "a" and "c"

8. Stage of mitosis in which chromatids reach the poles and their movement ceases.
(a) Prophase
(b) Metaphase
(c) Anaphase
(d) Telophase ✓

9. Stage of meiosis in which centromeres shorten and the paired chromatids are pulled away from one another.
(a) Anaphase-II ✓
(b) Metaphase-II
(c) Telophase-Il
(d) Prophase-II

10. Phenomenon in which pair of homologous chromosomes fails to separate called:
(a) Non-disjunction ✓
(b) Terminalization
(c) Synapsisjo j
(d) Linkage

2. Fill in the blanks:
(i) Chromosomes are thread like structures appear at the time of cell division.
(ii) Sequence of changes which occurs between one cell division and the next is called cell cycle.
(iii) The two chromatids are attached to each other at centromere.
(iv) Chromosomes in the cell which are similar to each other in shape and size are called homologous pair.
(v) Chromosomes with one arm very small and other very long called Acrocentric.
(vi) Chromosomes consist of two genetically identical copies of thread called chromatids.
(vii) Period of extensive metabolic activity, in which cell grow, enzymes are synthesizes G1 phase.
(viii) In animal meiosis produces gametes.
(ix) During metaphase homologous chromosomes arrange themselves on the equator of the spindle.
(x) Cell death which is caused by external factor called necrosis.

3. Define the following terms:
  1. Pachytene
  2. Cytokinesis
  3. Bivalent
  4. Chaismata
  5. Chromatids
  6. Diakinesis
  7. Terminalization
  8. Necrosis
  9. Crossing over
  10. Centromere
 Ans: i. Pachytene:
  • It is the third sub-stage of Propahse I of meiosis I, followed by Zygotene.
  • The synaptic forces of attraction between each bivalent decrease and the chromosomes uncoil and separate.
  • The separation is however incomplete and paired chromosomes are in contact with each other at one or more points, called Chiasmata.
  • Each homologous chromosome split longitudinally except in the centromere region.
  • Now each bivalent is composed of four chromatids and therefore is known as bivalent tetrad.

ii. Cytokinesis:
The division of cytoplasm is called cytokinesis. It continues with the last stage of nucleus division in mitosis and meiosis. Soon the cytoplasm of the cell also divides and two daughter cells are formed. Thus telophase may or may not be accompanied by cytokinesis and daughter cell formation.
OR
Cytokinesis is the part of the cell division process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the last stage of nuclear division in mitosis and meiosis.

iii. Bivalent:
During second sub-stage i.e Zygotene of prophase I of meiosis I, the Homologous (Similar structure) chromosomes, which comes from the mother (by ovum) and father (by sperm) are attracted towards each other and their lengthwise pairing takes place. The pairing of homologous chromosomes is known as synapsis, while the paired homologous chromosomes are known as bivalent.
OR
During prophase I of meiosis I, homologous chromosomes pair and from synapses. The paired chromosomes are called bivalents. The bivalent has two chromosomes and four chromatids, with the chromosome coming from each parents

iv. Chiasma:
In sub-stages of meiosis I, the synaptic forces of attraction between each bivalent decrease and the chromosomes uncoil and separate. The separation is however incomplete and paired chromosomes are in contact with each other at one or more points, called Chiasmata. The homologous chromosomes exchange their parts of chromatid at Chiasmata.
OR
A chiasma is the point of contact, the physical link, between two chromatids belonging to homologous chromosomes. At a given chiasma, an exchange of genetic material can occur between both chromatids.

v. Chromatids Or Sister Chromatids:
In the beginning of cell-division each chromosome is consist of two genetically identical copies of thread attach with each other called chromatids or sister chromatids. They contain hereditary material called gene (DNA).
OR
A chromatid is one half of a duplicate chromosome. Before replication, one chromosome is composed of one DNA molecule. In replication, the DNA molecule is copied, and the two molecules are known as chromatids.
OR
Each of the two thread like strand into which a chromosome divides longitudinally during cell division is called chromatid. Each contains a double helix of DNA.

vi. Diakinesis:
  • It is the final sub-stage of Propahse I of meiosis I, followed by diplotene.
  • During this sub stage; nucleoli and nuclear membrane are disappeared, whereas Mitotic Apparatus (spindle) is completed.
  • Chiasmata moves from the centromere towards the ends of the chromosomes like a zipper. This type of movement of chiasmata is known as Terminalization.
  • At the end of Diakinesis chromatids still remain compacted at their ends.

vii. Terminalization:
During the Diakinesis, final sub-phase of prophase I of meiosis, Chiasmata moves from the centromere towards the ends of the chromosomes like a zipper. This type of movement of chiasmata is known as Terminalization.

viii. Necrosis:
The type of cell death which is caused by external factors i.e infection, toxin and tumor i.e accidental cell death, is known as necrosis.

ix. Crossing Over:
The homologous chromosomes exchange their parts of chromatid at Chiasmata. This exchange of segments of chromatids at chiasmata between the homologous chromosomes is called Crossing Over.

x. Centromere:
The region or point in which the chromatids are linked together are called centromere. The centromere is the specialized DNA sequence of a chromosome that links a pair of sister chromatids (a dyad). During mitosis, spindle fibers attach to the centromere via the kinetochore. Centromeres were first thought to be genetic loci that direct the behavior of chromosomes.

4. Distinguish between the following in tabulated form:
  1. Prophase and Prophase-I
  2. Prophase and Telophase
  3. Apoptosis and Necrosis

Ans: i. Difference between Prophase and Prophase I
S.No. Prophase Prophase I
1. It is a phase of mitosis. It Is a phase of meiosis.
2. It is a short phase and occurs only once and is not divided in any sub-phase. It Is a long phase and is divided into the sub phases.
3. Pair formation (synapsis) in between homologous chromosomes does not occur as there is no attraction between them. Pair formation (synapsis) due to attraction occurs in between homologous chromosomes.
4. Chiasma is not formed. Chiasma is formed.
5. Crossing over does not occur. Crossing over occurs.
6. Part exchange does not occur in the chromosome. So gene arrangement remains unchanged. Part exchange occurs, which changes the gene arrangement of the chromosomes.

Difference between Prophase and Teloohase
S.No. Prophase Telophase
1. Prophase is the first stage of karyokinesis during mitosis Telophase is the final stage of karyokinesis during meiosis and mitosis
2. In prophase the chromatin condenses to form the chromosomes In telophase the daughter chromosomes enlongate and overlap each other to form chromatin.
3. Spindle fibres appear around the poles. Spindle fibres disappear around the poles.
4. Nuclear envelope and nucleolus degenerate (disappear) completely. Nuclear envelope and nucleoli reappear and two daughter nuclei are formed.
5. Cell organelles disorganized and there is no difference between the cytoplasm and nucleoplasm. Cell organelles are reformed and nucleoplasm appears in chromatin making it distinct from other cytoplasmic area.
6. In prophase the nuclear content is not initiated to be distributed. In telophase the nuclear content get equally distributed to become the part of daughter cells.
7. The viscosity of cytoplasm increases. The viscosity of cytoplasm decreases.

Difference between Apoptosis and Necrosis
S.No. Apoptosis Necrosis
1. Apoptosis is a programmed cell death Necrosis is the premature death of cells.
2. It is always natural. It is pathological and is caused by factors external to the cell or tissue, such as infection, toxins or trauma.
3. It is genetically controlled. It is not genetically controlled.
4. It is highly time regulated event. It is an unregulated event.
5. They do not require any treatment.  They always require proper treatment.
6. It is usually beneficial to the organism. They are determinal to the organism.
7. Nucleus gets fragmented Nucleus gets disorganized
8. Chromatin condensation is a hallmark of apoptosis. No chromatin condensation occurs

5. Write short answers of following questions:
(i) Why meiosis-I is called reduction division?
Ans: Meiosis is called reduction division because it reduces the number of chromosomes from diploid to haploid i.e. it gets reduced from 2N to IN (e.g. 46 to 23 chromosomes in human being) so as to maintain the species specific number 46 chromosomes(23 pairs) from generation to generation.

(ii) Why mitosis is necessary for growth?
Ans: Mitosis is a way of making more cells that are genetically the same as the parent cell. It plays an important part in the development of embryos, and it is important for the growth and development of our bodies as well. Mitosis produces new cells, and replaces cells that are old; lost or damaged.
OR
Mitosis is necessary for growth as it is responsible for development and growth of organisms by increasing number of exact copies of cells. It enables the organisms to grow from a single cell to a complex multicellular organism. Cell replacement is also done by mitosis.

(iii) How number of chromosomes remains constant from generation to generation?
Ans: Constant number of chromosomes:
Meiosis maintains chromosome number constant from generation to generation. It is due to the fact that meiosis reduces the diploid number of chromosomes to half i.e. haploid in the gametes. During fertilization the diploid number of the chromosomes is restored. e.g. There are 23 pairs of chromosomes in human cell which remain constant.

(iv) Why interphase is called as phase of high metabolic activities?
Ans: Interphase is the phase of the cell cycle. It includes sub-stages the G1 (the cell grows), S (replicates its DNA) and G2 (prepares for mitosis). G1 the sub-phase of interphase is called as phase of high metabolic activities because it is the period of extensive metabolic activity, in which:
Cell grows in size, specific enzymes are synthesized and DNA base units are accumulated for the DNA synthesis.

(v) Why interphase between meiosis-I and meiosis-II is short?
Ans: Interphase is a short period of interphase before meiosis II, if it occurs. Interphase is a stage associated with replication of DNA, and growth. Once meiosis II starts, the purpose is to produce a haploid gamete. So there is no further need of replication or growth. Hence between meiosis I and meiosis II, interphase is short.

6. Write detailed answers of the following questions:
(i) Describe various stages of mitosis with suitable diagrams.
Ans: MITOSIS:
In this type of cell division a parent cell divides into two daughter cells in a way that the number of chromosomes in the daughter cells remains the same as in the parent cell. i.e. diploid mother cell producing diploid somatic (daughter) cell.

Phases Of Mitosis:
Although mitosis is a continuous process, but for the study point of view we can divide it into two phases
  • (a) Karyokinesis - nuclear division
  • (b) Cytokinesis - cytoplasmic division

(a) The karyokinesis:
It can be divided further for convenience into four phases which are:
  1. Prophase
  2. Metaphase
  3. Anaphase and
  4. Telophase

1. Prophase:
  1. During early prophase chromatin material condenses and become visible as thick coiled, thread like structures called chromosomes.
  2. Each chromosome at this stage is already double, consists of two chromatids.
  3. The chromatids are attached to each other at centromere.
  4. The nuclear membrane and nucleolus gradually disappears.
  5. At the same time centrosome divides to form two centrioles, each moves towards the opposite pole of the animal cell and forms the star shaped aster and spindle fibres.
  6. In plant cells, the centrioles and asters are absent.

Metaphase:
  1. During this phase each chromosome arranges itself on the equator of the spindle and becomes more visible.
  2. Each chromosome is attached to separate spindle fibre by its centromere, from each pole..

Anaphase:
  1. In this phase the spindle fibre contract.
  2. Centromere of a chromosome divides and the chromatids of each chromosome separates from each other and begin to move towards the other poles.
  3. In this way one set of the chromatids (each chromatid is now an independent chromosome) move towards one pole while the other set towards the other pole.

Telophase:
  1. This is a stage when the chromatids (now called chromosomes) reach at the respective poles and their movement ceases.
  2. Each pole receives the same number of chromosomes.
  3. The nuclear membrane is reformed around each set of chromosomes.
  4. Nucleolus also reappears.
  5. In this way two daughter nuclei formed in each cell. Each daughter nucleus has the same number of chromosomes as were present in the parent cell.

(b) Cytokinesis:
  1. The division of cytoplasm is called cytokinesis. It continues with the last stage of nucleus division.
  2. Soon the cytoplasm of the cell also divides and two daughter cells are formed.
  3. Events In Animal Cell:
    * In animal cell cytokinesis takes place by developing a constriction in the middle between the two nuclei.
    * This constriction become deep to divide cytoplasm in two equal halves.
    * As a result two daughter cells are formed.
  4. Events In Plant Cell:
    * In plant cells cytokinesis occurs by developing cell plate (cell wall) in the center of the cell (equatorial region).
    * This wall extends towards the periphery of the cell and finally completes the formation of two daughter cells.
  5. In this way the daughter cells become the exact copies of their parent cell.


(ii) Describe stages of meiosis-I with suitable diagrams.
Ans: Meiosis I (First Meiotic Division) First meiotic division is the reduction division during which the chromosomes number is reduced to half. Meiosis I consists of:
  • Prophase I
  • Metaphase I
  • Anaphase I and
  • Telophase I

Prophase I:
It consists of the longest phase of meiosis. It can be subdivided into following sub stages:
  1. Leptotene
  2. Zygotene
  3. Pachytene
  4. Diplotene
  5. Diakinesis

1. Leptotene:
During this sub stage following changes occur;
  • The chromatin network break into specific number of long thin beaded thread called leptotene.
  • Each thread has two morphologically similar leptene in each cell called homologous structure.

2. Zygotene:
  • During this sub stage the Homologous (Similar structure) chromosomes, which comes from the mother (by ovum) and father (by sperm) are attracted towards each other and their lengthwise pairing takes place.
  • The pairing of homologous chromosomes is known as synapsis, while the paired homologous chromosomes are known as bivalent.

3. Pachytene:
  • The synaptic forces of attraction between each bivalent decrease and the chromosomes uncoil and separate.
  • The separation is however incomplete and paired chromosomes are in contact with each other at one or more points, called Chiasmata.
  • Each homologous chromosome split longitudinally except in the centromere region.
  • Now each bivalent is composed of four chromatids and therefore is known as bivalent tetrad.

4. Diplotene:
  • The homologous chromosomes exchange their parts of chromatid at Chiasmata.
  • This exchange of segments of chromatids at chiasmata between the homologous chromosomes is called Crossing Over.

5. Diakinesis:
  • During this sub stage; nucleoli and nuclear membrane are disappeared, whereas Mitotic Apparatus (spindle) is completed.
  • Chiasmata moves from the centromere towards the ends of the chromosomes like a zipper.
  • This type of movement of chiasmata is known as Terminalization.
  • At the end of Diakinesis chromatids still remain compacted at their ends.
(Note: Below Diagram is only for explanation)👇

Metaphase I:
Following changes occur in this phase:
  • The bivalent line up at the equatorial plane.
  • The centromere of each chromosome attaches with same fibres of spindle.

Anaphase I:
  • At this stage one chromosome from each member of homologous pair (bivalent) begins to separate and move towards its respective pole by the contraction of spindle fibers.
  • The actual reduction occurs at this stage because half the number of chromosomes moves to each pole.
  • Moreover as a result of crossing over the two chromatids of a chromosome do not resemble with each other in the genetic terms.

Telophase I:
  • The nuclear membrane form around the chromosomes at each pole and chromosomes become uncoil.
  • The nucleolus reappears and thus two daughter nuclei formed.

Cytokinesis:
Telophase may or may not be accompanied by cytokinesis and daughter cells formation.

STAGES OR PHASES OF Meiosis I (First Meiotic Division)



OR
(Note: Below Diagram is only for explanation)👇

SHORT QUESTION & ANSWERS

Q.1: Name types of chromosomes?
Ans: Types Of Chromosomes:
The chromosomes are of different types, depending upon position of centromere. These types are:
  1. Metacentric: Chromosomes with equal arms.
  2. Sub-meta centric: Chromosomes with un equal arms.
  3. Acrocentric or sub-telocentric: Rod like chromosomes with one arm very small and other very long. The centromere is subterminal.
  4. Telocentric: Location of centromere at the end of chromosomes.

Q.2: What is the difference between mitosis and meiosis?
Ans: Difference Between Mitosis And Meiosis:
S.No Mitosis Meiosis
1. Mitosis occurs in asexual reproduction. Meiosis occurs in sexual reproduction.
 It  takes place in Somatic Cells It takes place in Germ Cells
2. Result in 2 daughter cells are formed, which  are genetically identical Result in 4 daughter cells are formed, which  are genetically different.
3. It involves one cell division. It involves two successive cell divisions.   meiosis I (reduction) and meiosis II (simple mitosis).
4. No Pairing of Homologous / no synapsis / no bivalent formation Paring of homologous / synapsis / bivalent  formation.
5. No recombination or crossing occur. Recombination or crossing over occur.
6.  Number of chromosomes remains the same Number of chromosomes reduced to half 
7. Chiasmata absent  chiasmata formed during prophase I.
 8.  Mother Cells can be either haploid or diploid  Mother Cells always diploid
9. It takes part in cellular reproduction, general growth, repair of the body, healing and repair Genetic It takes part in the formation of gametes and maintains chromosome number from  generation to generation.
10. Prophase stage is short prophase stage is longer in meiosis I.



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Biology For Class IX - Chapter No.5 - CELL CYCLE - Questions and Answers

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CHAPTER 5
CELL CYCLE
Questions And Answers

Q.1: How were chromosomes discovered?
Ans: Discovery Of Chromosomes:
The term Chromosomes is given by German embryologist Walter Fleming in 1882 when he was examining the rapidly dividing cells of salamander larvae after treating with Perkin's Aniline. He observed that chromosomes colour is much darker than the rest of organelles.
The term chromosomes is misnomer because its means coloured body later it was found that chromosomes are colourless bodies.

Q.2: Define chromosomes and its types?
Ans: Chromosomes:
Chromosomes are thread like structure appear at the time of cell division. They are found in specific numbers, made up of chromatin material in eukaryotic cell. They contain heredity units called Genes.
Chromosomes are made up of DNA and basic protein, Histones, appear during the cell division in the shape of rod. It has two parts arms and centromere.


Types Of Chromosomes:
The chromosomes are of different types, depending upon position of centromere. These types are:
  1. Metacentric: Chromosomes with equal arms.
  2. Sub-meta centric: Chromosomes with un equal arms.
  3. Acrocentric or sub-telocentric: Rod like chromosomes with one arm very small and other very long. The centromere is subterminal.
  4. Telocentric: Location of centromere at the end of chromosomes.


Q.3: What are chromatids or siseter chromatids?
Ans: Chromatids Or Sister Chromatids:
In the beginning of cell-division each chromosome is consist of two genetically identical copies of thread attach with each other called chromatids or sister chromatids.

Q.4: Briefly describe the formation of chromosome.
Ans: Formation of chromosome:
Each chromosomes in eukaryotes are composed of chromatin fiber, which is made of nucleosomes.  Chromatin fibers are packaged by proteins (histones) into a condensed structure called chromatin. Chromatin allows the very long  and complex DNA molecules to fit into the cell nucleus. There is also less amount of RNA present.
During cell division chromatin condenses further to form microscopically visible chromosomes. The structure of chromosomes varies through the cell cycle. During cell cycle chromatin material replicate, divide and passed successfully to their daughter cells for survival of their progeny. Some time cell-division is also responsible for genetic diversity.

Q.5: Define cell cycle and its phases? Draw labelled diagram of cell cycle?
Ans: CELL CYCLE:
"The sequence of changes which occurs between one cell division and the next is called Cell Cycle.”
The cell cycle undergoes a sequence of changes, which involve period of growth, replication of DNA followed by cell division. This sequence of changes is called cell cycle.

PHASES OF CELL CYCLE:
It has two phases:
  1. Interphase: which is the period of non-division.
    The period of cell cycle between two consecutive divisions is called Interphase. It is a period of growth and synthesis of DNA. During this period the cell prepares itself for the M- phase.
    The Interphase is divided further into three sub-phase:
    1. G1 - phase OR (Gap one) phase
    2. S - phase OR (Synthesis) phase
    3. G2 -phase OR (Gap one) phase

  2. M-phase: which is a period of cell division. There are two types of cell division.
    i. Mitosis
    ii. Meiosis

CELL CYCLE


Q.6: Define interphase and its sub-phases?
Ans: INTERPHASE:
The period of cell cycle between two consecutive divisions is called Interphase. It is a period of growth and synthesis of DNA. During this period the cell prepares itself for the M- phase.

Sub-Phases Of Interphase:
The Interphase is divided further into three sub-phase:
  1. G1 - phase
  2. S - phase
  3. G2 -phase

1. G1-(Gap one) phase:
It is the period of extensive metabolic activity, in which:
  • Cell grows in size, specific enzymes are synthesized and DNA base units are accumulated for the DNA synthesis.
  • At a point in G1, the cell may enter into a phase called G0 (G-knot) where cell cycle stop. It remains for days, weeks or in some cases even for the life time of the organism.

2. S-(Synthesis) phase:
During this phase, replication of DNA occurs. As a result of it chromatin material is duplicated.

3. G2–(Gap two) phase: (Pre-Mitotic Phase):
The following changes occur during this phase:
  • Cell grows in size
  • cell organelles are replicate in numbers as well as enzyme require for cell-division also synthesized during this phase.

Q.7: Define Mitosis? Describe the phases of mitosis. Draw a neat and labelled diagram?
Ans: MITOSIS:
In this type of cell division a parent cell divides into two daughter cells in a way that the number of chromosomes in the daughter cells remains the same as in the parent cell. i.e. diploid mother cell producing diploid somatic (daughter) cell.

Phases Of Mitosis:
Although mitosis is a continuous process, but for the study point of view we can divide it into two phases
  • (a) Karyokinesis - nuclear division
  • (b) Cytokinesis - cytoplasmic division

(a) The karyokinesis:
It can be divided further for convenience into four phases which are:
  1. Prophase
  2. Metaphase
  3. Anaphase and
  4. Telophase

1. Prophase:
  1. During early prophase chromatin material condenses and become visible as thick coiled, thread like structures called chromosomes.
  2. Each chromosome at this stage is already double, consists of two chromatids.
  3. The chromatids are attached to each other at centromere.
  4. The nuclear membrane and nucleolus gradually disappears.
  5. At the same time centrosome divides to form two centrioles, each moves towards the opposite pole of the animal cell and forms the star shaped aster and spindle fibres.
  6. In plant cells, the centrioles and asters are absent.

Metaphase:
  1. During this phase each chromosome arranges itself on the equator of the spindle and becomes more visible.
  2. Each chromosome is attached to separate spindle fibre by its centromere, from each pole..

Anaphase:
  1. In this phase the spindle fibre contract.
  2. Centromere of a chromosome divides and the chromatids of each chromosome separates from each other and begin to move towards the other poles.
  3. In this way one set of the chromatids (each chromatid is now an independent chromosome) move towards one pole while the other set towards the other pole.

Telophase:
  1. This is a stage when the chromatids (now called chromosomes) reach at the respective poles and their movement ceases.
  2. Each pole receives the same number of chromosomes.
  3. The nuclear membrane is reformed around each set of chromosomes.
  4. Nucleolus also reappears.
  5. In this way two daughter nuclei formed in each cell. Each daughter nucleus has the same number of chromosomes as were present in the parent cell.

(b) Cytokinesis:
  1. The division of cytoplasm is called cytokinesis. It continues with the last stage of nucleus division.
  2. Soon the cytoplasm of the cell also divides and two daughter cells are formed.
  3. Events In Animal Cell:
    * In animal cell cytokinesis takes place by developing a constriction in the middle between the two nuclei.
    * This constriction become deep to divide cytoplasm in two equal halves.
    * As a result two daughter cells are formed.
  4. Events In Plant Cell:
    * In plant cells cytokinesis occurs by developing cell plate (cell wall) in the center of the cell (equatorial region).
    * This wall extends towards the periphery of the cell and finally completes the formation of two daughter cells.
  5. In this way the daughter cells become the exact copies of their parent cell.


Q.8: Write down importance or significance of mitosis?
Ans: Importance Or Significance Of Mitosis:
Mitosis plays an important role in the life of an organism.
  • It occurs in all type of somatic cell.
  • It is responsible for development and growth of organisms by increasing exact copies of cells.
  • With few exception all kinds of asexual reproduction and vegetative propagation take place by mitosis.
  • The production of new somatic cells, such as blood cells depends on mitosis.
  • The healing of wounds, repair of wear and tear within organism is also dependent upon the mitotic division.

Q.9: What do you know about cell death Or Is cell death is beneficial? Define ways of cell death?
Ans: CELL DEATH:
Cell in an organism depends upon various extra cellular signals for its regulated and controlled activities. It means all the activities even the death of cells is programmed.
Programmed cell death helps in proper control of multicellular development, which may lead to deletion of entire structure, e.g. the tail of developing human embryo, or some part an organ which is more required like tissue between developing digits.

Ways Of Cell Death:
There are two ways of cell death in Multicellular organisms:
  1. Apoptosis
  2. Necrosis
1. APOPTOSIS or Self - Destruction (Autophagy):
“Programmed change which lead to sequence of physiological changes in cell by which cells commit suicide collectively called Apoptosis”.

2. NECROSIS:
This type of cell death which is caused by external factors i.e infection, toxin and tumor i.e accidental cell death.

Q.10: Define meiosis? Briefly describe the phases of meiosis.
Ans: MEIOSIS (Reduction Division):
Meiosis is a type of cell division in which single cell divides into four daughter cells and number of chromosomes becomes half in each daughter cell.
  • In animal, meiosis takes place in germ cell to produce gametes i.e. Sperms and Eggs
  • In plants, it takes place in spore mother cells (S.M.C) to produce spores.

PHASES OF MEIOSIS:
Events of Meiosis:
Meiosis is a series of two divisions:
  1. MEIOSIS I and
  2. MEIOSIS II
which result in the formation of four haploid cells.

Meiosis I (First Meiotic Division)

First meiotic division is the reduction division during which the chromosomes number is reduced to half. Meiosis I consists of:
  • Prophase I
  • Metaphase I
  • Anaphase I and
  • Telophase I

Prophase I:
It consists of the longest phase of meiosis. It can be subdivided into following sub stages:
  1. Leptotene
  2. Zygotene
  3. Pachytene
  4. Diplotene
  5. Diakinesis

1. Leptotene:
During this sub stage following changes occur;
  • The chromatin network break into specific number of long thin beaded thread called leptotene.
  • Each thread has two morphologically similar leptene in each cell called homologous structure.

2. Zygotene:
  • During this sub stage the Homologous (Similar structure) chromosomes, which comes from the mother (by ovum) and father (by sperm) are attracted towards each other and their lengthwise pairing takes place.
  • The pairing of homologous chromosomes is known as synapsis, while the paired homologous chromosomes are known as bivalent.

3. Pachytene:
  • The synaptic forces of attraction between each bivalent decrease and the chromosomes uncoil and separate.
  • The separation is however incomplete and paired chromosomes are in contact with each other at one or more points, called Chiasmata.
  • Each homologous chromosome split longitudinally except in the centromere region.
  • Now each bivalent is composed of four chromatids and therefore is known as bivalent tetrad.

4. Diplotene:
  • The homologous chromosomes exchange their parts of chromatid at Chiasmata.
  • This exchange of segments of chromatids at chiasmata between the homologous chromosomes is called Crossing Over.

5. Diakinesis:
  • During this sub stage; nucleoli and nuclear membrane are disappeared, whereas Mitotic Apparatus (spindle) is completed.
  • Chiasmata moves from the centromere towards the ends of the chromosomes like a zipper.
  • This type of movement of chiasmata is known as Terminalization.
  • At the end of Diakinesis chromatids still remain compacted at their ends.
(Note: Below Diagram is only for explanation)👇

Metaphase I:
Following changes occur in this phase:
  • The bivalent line up at the equatorial plane.
  • The centromere of each chromosome attaches with same fibres of spindle.

Anaphase I:
  • At this stage one chromosome from each member of homologous pair (bivalent) begins to separate and move towards its respective pole by the contraction of spindle fibers.
  • The actual reduction occurs at this stage because half the number of chromosomes moves to each pole.
  • Moreover as a result of crossing over the two chromatids of a chromosome do not resemble with each other in the genetic terms.

Telophase I:
  • The nuclear membrane form around the chromosomes at each pole and chromosomes become uncoil.
  • The nucleolus reappears and thus two daughter nuclei formed.

Cytokinesis:
Telophase may or may not be accompanied by cytokinesis and daughter cells formation.

STAGES OR PHASES OF Meiosis I (First Meiotic Division)



OR
(Note: Below Diagram is only for explanation)👇

Interphase:
  • Following Telophase I (If this stage occurs), there is a short period called Interphase before meiosis II.
  • It is similar to Interphase between Mitotic divisions except that DNA replication does not occur.
  • Replication of DNA is unnecessary because each chromosome already has two chromatids.

Meiosis II (Second Meiotic Division)

The second meiotic division is actually the mitotic division which divides each haploid cell formed during meiosis I into two daughter haploid cells.
The second meiotic division includes:
  1. Prophase II
  2. Metaphase II
  3. Anaphase II
  4. Telophase II

1. Prophase II:
  • The spindle Fibres are formed.
  • The nuclear membrane and the nucleolus disappear.

2. Metaphase II:
  • The chromosomes are attached to half spindle fibers by their centromere and get arranged at equatorial plane.
  • Each chromosome attach with separate fiber of spindle.

3. Anaphase II:
  • The spindle fibers attached to the centromeres shorten and the chromatids of chromosomes are pulled away from one another.
  • This movement continues until one complete set of chromosomes is positioned at each pole of the cell.

4. Telophase II:
  • The spindle fibers disappear completely and chromosomes begin to uncoil.
  • They become longer and indistinct and form group at each pole.
  • Around each group nuclear envelope is formed.

Cytokinesis:
After the kayrokinesis in each haploid meiotic cell the cytokinesis i.e. division of cytoplasm occurs and thus four haploid cells are formed.

STAGES OR PHASES OF Meiosis Ii (Second Meiotic Division


OR
(Note: Below Diagram is only for explanation)👇

Q.11: What happens in absence of meiosis?
Ans: In the absence of meiosis number of chromosomes would have been doubled giving rise to abnormal growth, changes in species characteristics and or may prove fatal.

Q.12: What are the significance of meiosis?
Ans: Significance of Meiosis:
  1. Constant number of chromosomes:
    Meiosis maintains chromosome number constant from generation to generation. It is due to the fact that meiosis reduces the diploid number of chromosomes to half i.e. haploid in the gametes. During fertilization the diploid number of the chromosomes is restored.

  2. Responsible for genetic variation among species:
    By crossing over, the meiosis provides an opportunity for the exchange of the genes between homologous chromosome and thus cause the genetic variations among the species. The variations are the raw material of the evolutionary process.

Q.13: What do you mean by Meiotic error OR Explain phenomenom of non-disjunction.
Ans: Meiotic errors - Non-Disjunction:
In normal course of meiosis, the two chromosomes of each homologous pair separates and enter into two gametes, but sometimes a pair of homologous chromosomes fails to separate from one another, during miosis I. This phenomenon is called Non-disjunction.
Non-disjunction produce gametes with abnormal number of chromosome i.e either with less or extra chromosome. If such abnormal gametes fuse with normal gametes, the resulting zygote will also have abnormal number of chromosome.



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Biology For Class IX - Chapter No.5 - CELL CYCLE - MCQs and Fill In the Blanks

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CHAPTER 5
CELL CYCLE

Multiple Choice Questions (MCQs)
Encircle the correct Answer:
1. Which processes involve mitosis?
(a) Growth, reduction division and asexual reproduction
(b) Growth, repair and asexual reproduction ✓
(c) Growth, repair and semi conservative replication
(d) Growth, reduction division and repair

2. What occurs in metaphase of mitosis?
(a) Chromosome line up on the equator of the cell ✓
(b) Chromatids reach the poles of the spindle
(c) Chromatids separate and move to opposite poles
(d) Chromosomes start to coil up and become visible

3. Select the mismatched:
(a) Anaphase 4 Chromatids move
(b) Prophase 4 Centriole move
(c) Telophase 4 Nuclear membrane disappear ✓
(d) Metaphase 4 Chromosome line up

4. Which process occurs during prophase of mitosis in an animal cell?
(a) Division of centromeres
(b) Formation of chromosomes ✓
(c) Replication of DNA
(d) Separation of centrioles

5. Sequence of physiological changes by which cell commit suicide.
(a) Apoptosis
(b) Necrosis
(c) Autophagy
(d) Both Apoptosis and Autophagy ✓

6. Choose the Incorrect statement regarding meiosis.
(a) Maintain chromosome number from generation to generation
(b) Reduces the diploid number of chromosomes to half
(c) Takes place in germ cell to produce gametes
(d) Production of new somatic cells from germ cells ✓

7. A type of cell division in which spore mother cell produce spores
(a) Amitosis
(b) Mitosis
(c) Meiosis ✓
(d) Both Amitosis and Meiosis

8. Stage of mitosis in which chromatids reach the poles and their movement ceases.
(a) Prophase
(b) Metaphase
(c) Anaphase
(d) Telophase ✓

9. Stage of meiosis in which centromeres shorten and the paired chromatids are pulled away from one another.
(a) Anaphase-II ✓
(b) Metaphase-II
(c) Telophase-Il
(d) Prophase-II

10. Phenomenon in which pair of homologous chromosomes fails to separate called:
(a) Non-disjunction ✓
(b) Terminalization
(c) Synapsis
(d) Linkage

11. In 1882, the term 'chromosomes' was given by German embryologist:
(a) Walter Fleming ✓
(b) Leeuwenhoek
(c) Carolus Linnaeus
(d) Ernst Hackle

12. Chromosomes contain heredity units called:
(a) Chitin
(b) Apoptosis
(c) Genes ✓
(d) Diplotene

13. A chromosome has:
(a) two parts ✓
(c) four parts
(b) three parts
(d) five parts

14. The chromosomes are of different types, depending upon:
(a) size of chromosomes
(b) shape of chromosomes
(c) length of its arms
(d) position of centromere ✓
15. Chromosomes with equal arms are called:
(a) sub-meta centric
(b) metacentric ✓
(c) sub-telocentric
(d) telocentric

16. Chromosomes with unequal arms are known as:
(a) sub-meta centric ✓
(b) metacentric
(c) sub-telocentric
(d) telocentric

17. Rod like chromosomes with one arm very small and other very long.
(a) sub-meta centric
(b) metacentric
(c) sub-telocentric ✓
(d) telocentric

18. Location of centromere at the end of chromosomes.
(a) sub-meta centric
(b) metacentric
(c) sub-telocentric
(d) telocentric ✓

19. Each chromosome in eukaryotes is composed of:
(a) chitin
(b) chromatin fiber ✓
(c) genes
(d) diplotene

20. In the beginning of cell-division each chromosome is consist of two genetically identical copies of thread attach with each other called:
(a) chromatids ✓
(b) chromatin fiber
(c) genes
(d) diplotene

21. Chromatin fiber is made of:
(a) chromatids
(b) nucleosomes ✓
(c) chromatin
(d) diplotene

22. Chromatin fibers are packaged by protein into a condensed structure called:
(a) chromatids
(b) nucleosomes
(c) chromatin ✓
(d) diplotene

23. The sequence of changes which occurs between one cell division and the next is called:
(a) interphase
(b) cell cycle ✓
(c) M-phase
(d) G-phase

24. A cell cycle has:
(a) two phase ✓
(b) three phases
(c) four phases
(d) five phases

25. It is the period of non-division.
(a) M-phase
(c) S-phase
(b) G-phase
(d) interphase ✓

26. It is the period of cell division.
(a) M-phase ✓
(b) G-phase
(c) S-phase
(d) interphase

27. The period of cell cycle between two consecutive divisions is called:
(a) M-phase
(b) G-phase
(c) 5-phase
(d) interphase ✓

28. It is the period of growth and synthesis of DNA.
(a) M-phase
(b) G-phase
(c) interphase ✓
(d) G2 phase

29. The interphase is divided further into:
(a) two sub-phases
(b) three sub-phases ✓
(c) four sub-phases
(d) five sub-phases

30. It is the period of extensive metabolic activity.
(a) G3-phase ✓
(b) G2-phase
(c) S-phase
(d) prophase

31. At a point in G1-Phase, the cell may enter into a phase where cell cycle stop, known as:
(a) G2-Phase
(b) S-Phase
(c) Anaphase
(d) G-Phase ✓

32. During this phase, replication of DNA occues.
(a) G2-Phase
(b) S-Phase ✓
(c) Anaphase
(d) G-Phase

33. If the number of chromosomes in the daughter cells remains the same as in the parent cell, this type of cell division is called:
(a) cytokinesis
(b) meiosis
(c) mitosis ✓
(d) metaphase

34. Although mitosis is a continuous process, but for the study point of view it is divide into:
(a) two phases ✓
(b) three phases
(c) four phases
(d) five phases

35. In mitosis, the phase of nuclear division is:
(a) Anaphase
(b) Telophase
(c) Cytokinesis
(d) Karyokinesis ✓

36. In mitosis, the phase of cytoplasmic division is called:
(a) Anaphase
(b) Telophase
(c) Cytokinesis ✓
(d) Karyokinesis

37. The mitosis phase, Karyokinesis, can be divided further for convenience into:
(a) two phases
(b) three phases
(c) four phases ✓
(d) five phases

38. In prophase of mitosis chromatin network becomes thick and thread like structure is called:
(a) chromosomes ✓
(b) chromatid
(c) centromere
(d) centrosome

39. During this phase each chromosome arranges itself on the equator of the spindle.
(a) Prophase
(b) Metaphase ✓
(c) Anaphase
(d) Telophase

40. Chromatids of each chromosome begin to move towards opposite pole in:
(a) Prophase
(b) Metaphase
(c) Anaphase ✓
(d) Telophase

41. In mitosis, the nuclear membrane is reformed and two daughter nuclei formed during:
(a) Prophase
(b) Metaphase
(c) Anaphase
(d) Telophase ✓

42. In mitosis, cytoplasm divides and two daughter cells are formed during:
(a) prophase
(b) cytokinesis ✓
(c) telophase
(d) metaphase

43. In animal cell, cytokinesis takes place by developing a:
(a) cell boundary
(b) cell plate
(c) constriction ✓
(d) divider

44. In plant cells, cytokinesis occurs by developing:
(a) cell boundary
(b) cell plate ✓
(c) constriction
(d) divider

45. The production of somatic cells, such as blood cells, depends on:
(a) mitosis ✓
(b) meiosis
(c) cytokinesis
(d)Allofthem

46. The healing of wounds, repair of wear and tear within organism is dependent upon:
(a) pachytene
(b) diplotene
(c) mitotic division ✓
(d) meiotic division

47. Programmed changed which lead to sequence of physical changes in cell by which cells commit suicide collectively called:
(a) apoptosis ✓
(b) necrosis
(c) diakinesis
(d) interphase

48. Cell death caused by external factors is called:
(a) apoptosis
(b) necrosis ✓
(c) diakinesis
(d) interphase

49. Cell division in which single cell divides into four daughter cells and number of chromosomes becomes half in each daughter cell is called:
(a) cytokinesis
(b) diakinesis
(c) mitosis
(d) meiosis ✓

50. In animals, meiosis takes place in germ cell to produce:
(a) gametes ✓
(b) spores
(c) only eggs
(d) only sperms

51. Meiosis is a series of two divisions which result in the formation of:
(a) two haploid cells
(b) three haploid cells
(c) four haploid cells ✓
(d) five haploid cells

52. Meiosis I consists of:
(a) two phases
(c) four phases ✓
(b) three phases
(d) five phases

53. It consists of the longest phase of meiosis:
(a) Prophase I✓
(c) Anaphase I
(b) Metaphase I
(d) Telophase I

54. During the first sub stage of prophase I, the chromatin network break into specific number of long thin beaded thread called:
(a) diplotene
(b) pachytene
(c) leptotene ✓
(d) zygotene

55. During this sub stage of prophase I, lengthwise pairing of chromosomes takes place.
(a) diplotene
(b) pachytene
(c) leptotene
(d) zygotene ✓

56. The pairing of homologous chromosomes is known as:
(a) bivalent
(b) synapsis ✓
(c) autophagy
(d) apoptosis

57. The paired homologous chromosomes are known as:
(a) bivalent ✓
(b) synapsis
(c) autophagy
(d) apoptosis

58. During pachytene sub-phase, the separation of paired chromosomes is incomplete and they are in contact with each other at one or more points called:
(a) synapsis
(b) leptotene
(c) chiasmata ✓
(d) centromere

59. Each bivalent is composed of four chromatids and is known as:
(a) bivalent
(b) bivalent tetrad ✓
(c) synapsis
(d) centromere

60. The homologous chromosomes exchange their parts of chromatid at:
(a) synapsis
(b) leptotene
(c) chiasmata ✓
(d) centromere

61. The exchange of segments of chromatids at chiasmata between the homologous chromosomes is called:
(a) cutting over
(b) taking over
(c) passing over
(d) crossing over ✓

62. During this sub-stage of prophase I, nucleoli and nuclear membrane are disappeared.
(a) diakinesis ✓
(b) diplotene
(c) zygotene
(d) leptotene

63. During this sub-stage of prophase I, chiasmata moves from the centromere towards the ends of the chromosomes like a zipper.
(a) Zygotene
(b) pachytene
(c) diplotene
(d) diakinesis ✓

64. In this phase of meiosis, the bivalent line up at the equatorial plane.
(a) Prophase I
(b) Metaphase I ✓
(c) Anaphase I
(d) Telophase I

65. In this phase of meiosis, chromosomes become uncoil, nucleolus reappears and two daughter nuclei formed.
(a) Prophase I
(b) Metaphase I
(c) Anaphase I
(d) Telophase I ✓

66. In this sub-phase, the spindle fibres are formed; nuclear membrane and the nucleolus disappear.
(a) Prophase II ✓
(b) Metaphase II
(c) Anaphase II
(d) Telophase II

67. The chromosomes are attached to half spindle fibres by their centromere and get arranged at equatorial plane during:
(a) Prophase II
(b) Metaphase II ✓
(c) Anaphase II
(d) Telophase II

68.It maintains chromosomes number constant from generation to generation.
(a) Anaphase I
{b) Anaphase II
(c) Mitosis
(d) Meiosis ✓

69. Meiotic error, where a pair of homologous chromosomes fails to separate from one another called:
(a) non-junction
(b) disjunction
(c) non-disjunction ✓
(d) None of these

70. It produce gametes with abnormal number of chromosomes with less or extra chromosomes.
(a) non-disjunction ✓
(b) crossing over
(c) Karyokinesis
(d) inter-phase

2. Fill in the blanks:
(i) Chromosomes are thread like structures appear at the time of cell division.
(ii) Sequence of changes which occurs between one cell division and the next is called cell cycle.
(iii) The two chromatids are attached to each other at centromere.
(iv) Chromosomes in the cell which are similar to each other in shape and size are called homologous pair.
(v) Chromosomes with one arm very small and other very long called Acrocentric.
(vi) Chromosomes consist of two genetically identical copies of thread called chromatids.
(vii) Period of extensive metabolic activity, in which cell grow, enzymes are synthesizes G1 phase.
(viii) In animal meiosis produces gametes.
(ix) During metaphase homologous chromosomes arrange themselves on the equator of the spindle.
(x) Cell death which is caused by external factor called necrosis.
11. Chromosomes are made up of chromatin material in specific number in Eukaryotic cell.
12. Chromosomes are made up of DNA and histone protein.
13. There are four types of Chromosome i.e Metacentric, Submetacentric Aerocentric and Telocentric.
14. Sequences of change occur between two successive Cell division called cell-cycle.
15. Cell-cycle is mainly consist of two phases i.e cell-division and inter phase.
16. Inter phase is divided further into three sub phases G1, S and G2 phases.
17. Mitosis is the type of cell division, where a parent cell divides into two daughter cells, with same number of chromosomes as the parent cell contain.
18. Meiosis is the type of cell division in which a single cell divides into four daughter cells and number of chromosomes become half of the parent cell.
19. In plant meiosis division takes place in spore mother cells to produce gametes and spores respectively.
20. Meiotic error, where a pair of homologous Chromosomes fails to separate form one another called non disjunction.
21. Non disjunction produce gametes with abnormal number of chromosomes with less or extra chromosomes.
22. Cell-death occur in two ways.
23. Apoptosis is programmed cell death, which help in proper control of development.
24. Necrosis is cell death occur by external factor or accidental cell death.




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Monday 24 May 2021

Urdu Salees (Asan Urdu) (for Sindhi medium candidates) - For Class SSC - Part 2 (Science Group) - Solved Model papers 2020 - 2021- AS PER CONDENSED SYLLABUS

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Urdu Salees (Asan Urdu)
(for Sindhi medium candidates)
For Class X Or SSC - Part 2 (Science Groups)
Solved Model papers 2020 -2021
As Per condensed Syllabus








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