Saturday, 30 November 2013

ICSE solved Question Paper


                                                             UNIT TEST-I (Answer Key)                             Dt.22/07/2013
                                                                   Subject: Biology
Attempt all the following questions:
I.                    Name the following:
a)      The stage of Mitosis where sister chromosomes separate from their paired condition
Ans.   Anaphase
b)  The dominant trait of flower position in pea plant
Ans.  Axillary
c)       Type of cell division which occur in meristamatic tissue of the plant body
Ans. Mitosis
d)      The complementary base pair of Thymine in a DNA molecule
Ans.   Adenine
e)      The only condition in which the recessive character can be expressed
Ans. Homozygous

II.                  Fill up the blanks with appropriate  words:

a)      Removal of anthers of a bisexual flower to carry out artificial cross pollination is known as emasculation.
b)      Scientific name of Pea plant is  Pisum sativum.
c)       A phase of Mitosis which is reverse of prophase is Telophase.
d)      The repeating small and similar components of each strand of DNA are known as Nucleotides.

III.                Define the following terms:
a)      Karyotype
The  diagrammatic representation of all the chromosomes of an individual according to their size and shapes  is known as karyotype.
b)      Allelomorph
The alternative form of a gene which occupy the same position on the chromosome but alters the character in a different way.
c)       Homologous chromosomes
A pair of chromosomes which are similar in all respects such as size, shape, length etc. and each of them are derived from a parent.
d)      Mutations
The sudden changes which occur in the genetic constitution of an individual or in the number or structure of chromosomes are known as mutations.
e)      Cell Cycle
The sequence of events which occur between one cell division and other is known as Cell cycle.
IV.                Write the difference between the following pairs of terms:
a)      Phenotype and Genotype
Ans.  Phenotype: The external appearance of an individual irrespective of its genetic constitution is known as Phenotype.
Genotype: The genetic constitution of an individual is known as genotype.
b)      Character and Trait
Ans. Character:  Any heritable feature of an individual is known as Character.
Trait: The alternative form of a character is known as Trait.
C) Gene and Genome
Gene: Gene is a specific part of the chromosome which decides a particular character in the individual.
Genome: All the genes present in a haploid set of chromosomes of an individual is known as Genome.
d)Pure Breed and Hybrid
Pure Breed:  Plants bred true for the same feature for several generations without any change through controlled breeding.
Hybrid: Offspring  obtained by crossing two genetically different plants.  
E)Karyokinesis and Cytokinesis
Karyokinesis: The division of nucleus into two daughter nuclei is known as Karyokinesis.
Cytokinesis: The division of cytoplasm into two daughter cells is known as cytokinesis.
V.                  Answer  the following questions on Mitosis Cell division:
I)                    Why mitosis is known as “equational division”?
Ans. The two daughter  cells formed  are exact similar copies of the parent cell with the same number of chromosomes.
ii) Draw a neat labeled diagram of an animal cell in Anaphase of Mitosis starting with a cell of six chromosomes. Label the parts centromere, chromatid, spindle fibers, aster in your drawn diagram.

iii) State four important features which occur in prophase of mitosis.
Ans. 1. Chromatin get resolved and condensed to  form visible chromosomes.
2. Centrosome split into two bits and move to opposite poles to form asters.
3. Chromosomes split longitudinally to form two chromatids and which are held together by centromere.
4. Nuclear membrane and nucleolus disappear.
iv) Write any two differences between mitotic  cell division of a plant cell and animal cell.
Ans. Plant Cell: 1. Aster formation do not occur in cell division.
2. Cytokinesis occur by cell plate formation
Animal cell: 1. Aster formation  occur in cell division.
2. Cytokinesis occur by furrow formation.
VI) The following diagram represents an important event which occur in Meiotic Cell division. Study the same carefully and answer the questions that follow:

a)      What is the important event that was depicted in the above diagram? Define it.
Ans. The event that was depicted in the diagram is Crossing over.
Crossing over: The overlapping of non-sister chromatids  along the length of the homologous pair of chromosomes in meiosis is known as crossing over.
b)      What do you understand by the term “Chiasma” and mention its importance.
Ans. The ‘X’ shaped marking formed due to overlapping of non-sister chromatids during crossing over in meiosis is known as chiasma.  Chiasma is the region where exchange of genetic materials occur.
c)       “Gametes must be produced through meiosis for sexual reproduction.”  Why is it so?
Ans. The original chromosome number will be halved during gamete formation in meiosis. When gametes with haploid number fuse in fertilization, the original number of chromosomes will be restored.
d)      Write  any two differences between Mitosis and Meiosis cell division.
Ans. Mitosis:  1. In mitosis full set of chromosomes are passed on to the daughter cells.
2. Mitosis occurs in somatic cells.
3. Mitosis cell division results in two daughter cells.
Meiosis:  1. In meiosis, only half set of chromosomes are passed on to the daughter cells.
2. Meiosis occurs in reproductive cells.
3. Meiosis cell division results in four daughter cells.
e) What are diploid and haploid cells? Give an example of each.
Ans.   A cell with two sets of chromosome is known as diploid cell. Ex: Zygote cell, somatic cell.
A cell with one set of chromosomes is known as haploid cell. Ex: Unfertilized egg cell, sperm cell
VI)A pea plant having pure round seeded nature is crossed with a pea plant having wrinkled seeded nature
a)      Give a phenotype of F1 progeny by using  Punnet checker board.
Ans.    F1 Progeny:


All the progeny of F1 generation are phenotypically round in nature.
b)      Give the F2 progeny produced upon by the self pollination of F1 progeny with the help of Punnet checker board.
F2 Progeny:


c)       Give the Phenotypic and genotypic ratio of F2 generation.
Ans.  Phenotypic ratio:   3(Round) : 1(Wrinkled)
Genotypic Ratio: 1(Pure Round):2(Mixed Round):1(Wrinkled)
d)      Name and explain the laws induced by Mendel on the basis of the above experiments conducted by him.
Ans. 1. Law of Dominance:  Every character is influenced by a pair of factors.  Of these, the dominant factor gets expressed and the recessive factor gets suppressed. This is known as Law of dominance.
2. Law of segregation or Law of Purity of Gametes:  Every character is influenced by a pair of  factors. These factors they get separated during the formation of gametes and move into two different gametes without blending or  mixing.

Sunday, 24 November 2013

Why fresh water fish thrown in salt water will die?

Why fresh water fish thrown in salt water will die?

The cells of the fresh water fish are accustomed to maintain hypotonic condition in their cells. But when the fish is thrown in sea water , the condition which prevail outside the fish is hypotonic. Due to difference in concentration between inside and outside the fish, water from its dilute region (from inside the cells) move to concentrated region (to outside surrounding of the fish)  through exosmosis. Due to this the cells of the fish become  plasmolysed  and get killed.