Review
* Every organism begins its life as a single cell. This cell divides repeatedly to produce a cluster of cells. These cells form tissues and organs to perform different activities of life. This cell division essential for growth.
* There is always a wear and tear of cells during the normal body functions. These cells are replaced by new cells which are formed through division of their parent cells. Thus, cell division is needed for replacement of old cells.
* Cell division is also essential for repair of injuries and reproduction.
* There are two types of cell division-- Mitosis and Meiosis.
* In mitosis, two identical cells are produced by the division of one parent cell. Each daughter cell contains the same number of chromosomes as that of the parent cell.
* Mitosis is the cell division which occurs in 4 phases namely prophase, Metaphase, anaphase and telophase.
* In prophase, the chromosomes become short and thick which move towards the equator of the cell. Each chromosomes gets duplicated to form two chromatids.
* In Metaphase, the chromosomes arrange themselves on the equatorial plane. Each chromosomes gets attached to spindle fibre by centromere.
* In anaphase, the centrosome divide and the two sister chromatides of each chromosome separate are drawn apart towards opposite poles.
* Telophase is the last phase in which the chromatid becomes thinner and the nuclear membrane reappears. Nucleolus also reappears in each daughter nucleus.
* Mitosis is followed by the division of cytoplasm (cytokinesis). At the end of telophase, a furrow appears in the cell membrane at the middle, which depends and finally splits the cytoplasm into two, thus producing two new cells.
* Meiosis is the kind of cell division that produces the sex cells or the gametes. In this division, the number of chromosomes in the cell is halved.
* The meiosis is also called reduction cell division since the four daughter cells formed have half the number of chromosomes than the mother cell.
* There are two divisions of meiosis -- meiosis I (reduction division) and meiosis II (equational division).
* The mitosis (equational division) occurs in somatic cells while the memosis (reduction division) occurs in gamates.
** Significance of meiosis
a) mitosis plays an important role in vegetative growth, wound healing, repair and the regeneration.
b) It maintains the same chromosome number in daughter cells.
c) It maintains the proper size of an individual.
d) It helps in asexual reproduction, e g , binary fission in Amoeba.
** Significance of meiosis
a) It plays an important role in sexual reproduction, i.e., in the formation of gamets (sperms and ova).
b) It maintains the constant number of chromosomes in species.
c) It brings about recombination between a maternal and paternal genes theyby bringing in genetic variation within a Species. These variations are responsible for evolution.
* Chromosomes are long thread like structures made of DNA and proteins.
* A DNA molecule is made up of a double chain of a nucleotides in the form of helix. A nucleotide is a sugar molecules joined to a phosphate group and an organic base.
* The nucleotides bases in the helix pair up adenine to thymine (A - T) and cytosine to guanine (C - G).
* At replication, DNA strands separate and build up new chains on the exposed bases.
_____________+++++_______________
A) Fill in the blanks with suitable words in the following statements:
1) Meiosis takes place in the__, while mitosis takes place in the ___ cell of the body.
2) If a cell with two nuclei is spotted under a microscope, the cell is in __stage of cell division.
3) chromosome exhibit longitudinal splitting the two halves called ______.
4) Duplication of DNA occurs in the ___ of the cell cycle.
5) ______means splitting of nucleus.
6) The spindle fibres are made up of _____.
7) The chromatids are attached to each other at _____.
8) The process by which cells multiply is called_____.
9) The chromosome number is___ during meiosis.
10) The process by which gametes are formed is called _____.
11) ___is the indirect cell division. (Mitosis/meiosis).
12) The division of nucleus is called___. (Cytokinesis/karyokinesis).
13) the pairing of homologous chromosomes takes place in__ stage.(prophase/zygotene).
14) The growth of the organisms is achieved by___ division.(mitotic/meiosis).
B) NAME THE FOLLOWING:
1) division which brings about vegetative growth.
2) the phase in mitosis when the nucleolus starts disappearing.
3) the structure that attaches to the spindle during metaphase of Mitosis.
4) the structure from which spindle forms in an animal cell.
5) the shortest face of a mitosis.
6) the phase when to chromatids divides and two sister chromatids of each chromosomes separate and are drawn apart towards opposite poles.
7) the face of the cell cycle in which DNA replication takes place.
8) the phase of the cell cycle during which the cell grows.
9) the largest phase of a normal cell cycle.
10) the process during which the meiosis occurs in human beings.
11) the stage of meiosis at which there are two cells, each with sister chromatids aligned at the equator.
12) the shortest phase of cell cycle.
13) the type of the cell division occurs during growth of shoot.
14) the repeating component of each DNA strands lengthwise.
14) the structure that initiate cell division.
16) A membrane that disappears during later prophase.
17) A specific part of chromosome that determines hereditary characteristics.
C) MATCH THE FOLLOWING
1) daughter Chromosomes move opposite poles of the spindle.
2) chromosomes lose their distinctiveness and gradually become transformed into chromatin network.
3) Chromosomes become visible as fine long threads.
4) chromosomes become arranged in a horizontal plane at the equator.
a) Anaphase
b) Metaphase
c) Prophase
D) Telophase
D) DIFFERENCE BETWEEN:
1) chromosome /Chromatids
2) Interphase/Prophase
3) Karyokinesis/cytokinesis
4) Mitosis/meiosis
5) mitosis in animals/plants.
E) MULTIPLE CHOICE:
1) chromosomes are composed of:
a) proteins onley
b) DNA and proteins
c) DNA only d) RNA only.
2) Chromosome-replication occurs in:
a) Interphase. b) prophase
c) metaphase d) Telophase
3) function of Centrosome is:
a) initiation of cell division
b) inhabitation of cell division
c) to provide site for protein synthesis. d) none
4) Separation of chromosomes occurs during:
A) Anaphase. b) metaphase
c) prophase. d) Telophase
5) Parts of cells is associated with formation of spindle fibres are:
a) Microtubules b) golgy bodies
c) Centriole. d) microbodies
6) the first stage of cell division is:
a) prophase b) interphase
c) metaphase d) anaphase
7) the nucleic acid, which a chromosome is mainly composed of, is:
a) DNA b)RNA c) ATP d) AMP
8) chromosome arrange at equilateral plate of division spindle at:
A) anaphase b) telophase
c) telophase d) metaphase
9) separation of chromatids and their movement to opposite poles of division spindle occurs in :
a) prophase b) metaphase
c) telophase d) Anaphase
F) QUESTIONS :
1) What do you mean by cell cycle?
2) what type of cell division does occur in somatic cells of the body.
3) where does the meiosis occur in our body ?
4) What is interphase
5) What is the importance of meiosis in creating variations ?
6) Why is meiosis referred to as reduction division ?.
7) Mention three significant changes that occur in a cell during Interphase.
8) State how does meiosis maintain chromosome number in a species.
9) Given below is a set of five terms. Rewrite the terms in the correct order so as to be in logical sequence.
Metaphase, Telophase, Prophase, Anaphase.
10) What is the importance of Interphase for a cell division?
11) What is the significance of DNA replication during Interphase?
12) Give reason -- Gametes have a haploid Number of chromosomes.
G) QUESTIONS BASED ON DIAGRAMS:
1) Identify the stages of meiosis given below.
2) Figure shows a certain stages in cell division in a cell with four chromosomes.
b) Name structure C. What is its function ?
c) Name the type of division. Give a reason.
d) What is the diploid number for the organism from which the cell is taken ?
e) Name the stage before and the stage after the stage shown in the diagram.
.
3) Represents a stage during microtic cell division in an animal cell.
b) Name the parts labelled 1, 2 and 3.
c) What is the chromosome number of the cell ?
d) Draw a neat labelled stage diagram of the cell as it would appear in the next stage. Name the stage.
4) a) Draw a diagram of the nucleus of a cell, having chromosome number 6, as it would appear in the Metaphase stage of Mitosis and the label the following parts in the diagram.
i) Aster
ii) Achromatic spindle
iii) Chromatid
iv) Centrosome
b) Mention the difference between Mitosis and Meiosis with reference to
i) Number of daughter cell formed at the end of the division.
ii) The chromosome number of the daughter cell formed.
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