Frank ICSE Class 10 Biology Solutions

Frank ICSE Class 10 Biology Solutions – Human Population

PAGE NO : 153
Solution 1:

1. Population: It is the total number of individuals of a species found in a particular area.
2. Sanitation: It refers to the formulation and application of measures intended to protect public health.
3. Deforestation: It is the removal of a forest or stand of trees from an area and thereafter that area is converted to a no forest use.
4. Birth control: It is an attempt to control the number of births in a family so that a couple may not have more than two children.
5. Rhythm method: It is a natural method of birth control in which the couple attempts sexual intercourse a week before and a week after the menstrual cycle.
6. Abstainence: It is the act or practice of refraining from sexual intercourse.
7. Test-Tube baby: A test tube baby is one which is developed from an egg that was fertilized outside the body and then implanted in the uterus of the biological or surrogate mother.
8. Birth rate: It is the total number of live births per thousand people of the population per year.
9. Death rate: It is the number of deaths per thousand people of the population per year.
10. Population density: It is the total number of individuals of a particular species in relation to unit area at any given time.
11. Natality: It is the number of live births per thousand people of the population per year.

Solution 2:
Growth rate

Solution 3:
Demography

Solution 4:
The two important methods for birth control are:

1. Vasectomy
2. Tubectomy

Solution 5:
The two reasons for the rapid increase of population in India recently:

1. Advancement of science and technology
2. Better health care facilities

Solution 6:
The age restrictions for marriages by law for boys and girls in India are:
Boys: 21 years
Girls: 18 years

PAGE NO : 154
Solution 7:

1. “Our resources cannot keep pace with the rising population”.
   • Population increases geometrically while food production is increasing arithmetically.
   • Rising population is putting heavy pressure on natural resources like water, land forest etc.
   • Fuel shortage is increasing day by day.
2. The three steps which may be taken towards controlling the rapid rise in human population in India are:
   • Education: People should be educated about the advantages of a small family.
   • Marriageable age: Population can be controlled by raising the age limit for marriage.
   • Family planning: Voluntary family planning using birth control measures and contraceptives can check the growth of population.

Solution 8:
The main drawbacks of a large population are that it may lead to shortage of basic resources like food, water, fuel etc without which life would become impossible. In addition, overcrowding can also cause epidemics, poverty, unemployment etc.

Solution 9:
The steps taken by the Indian government to control population are:

1. Establishment of health centers to advice and help people about family planning.
2. Free distribution of barrier contraceptives like condoms.

Solution 10:
The two advantages of a small family are:

1. Children can be provided with good health and good education along with the basic needs of life.
2. Living standards of the family can be high.

Solution 11:
Population explosion: The exceptionally high rate of population growth is known as Population explosion.
The consequences of Population explosion may be overcrowding, shortage of resources like food, water, land, fuel etc. It can also result in unemployment, poverty, social unrest, epidemic, violence etc.

Solution 12:
Population density: It is the number of people per square kilometer at any given time.
Tubectomy is the operation made in women to prevent the flow of eggs into the oviduct.

Solution 13:
Following are the two reasons for the decline in death rate in India in recent times:

1. Advancement in the field of medical science which leads to reduced morality rate.
2. Longevity provided by better food and health services.

Solution 14:
The symbol of family welfare in our country is an ‘Inverted Red Triangle’.

Solution 15:
Family welfare centres are set up in hospitals and other health centres to advocate small families and to promote family welfare and planning. These centres advice people on issues such as family planning, gap between successive children etc without any cost.

Solution 16:
Following are the methods of fertility control in men and women:
Men: Vasectomy is a method of fertility control in men. In this method, a small portion of vas deferens is cut and is tied at both the ends.
Women: Tubectomy is a method of fertility control in women in which the fallopian tubes are cut and are tied at both the ends.

Solution 17:
Tubectomy is the surgical method of contraception in human female.

Solution 18:

1. Population density
2. Mortality

Solution 19:
The resources cannot keep pace with the rising population because:

1. The demand of resources is much more than the supply. The population is growing at geometric progression (1, 2, 4, 8) while the production of food can increase only arithmetically (1, 2, 3, 4, 5).
2. New towns and cities coming up to accommodate the growing population are putting strain on the agricultural land.

Solution 20:

1. False
2. False
3. True
4. True
5. True

Solution 21:

1. 2011
2. Population density
3. females, males
4. two
5. Natality
6. Mortality
7. Age ratio

Solution 22:

1. 
2. Vasectomy
3. Vas deferens
4. Tubectomy
5. The part which is ligated in females is Fallopian tube. This is done to prevent the flow of eggs into the oviduct and its fusion with the sperm.

PAGE NO : 155
Solution 23:

1. (b) 20
2. (d) 35 years
3. (d) 7 billion
4. (c) 840 million
5. (c ) biotic potential
6. (c ) loss and gain are equal
7. (c) decrease in death rate and increase in longevity
8. (d) copper-T
9. (d) progesterone
10. (c) to prevent the presence of sperms in the semen

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Frank ICSE Class 10 Biology Solutions – Excretory System

PAGE NO : 97
Solution 1:
Separation and elimination of the metabolic nitrogenous wastes from the body is called excretion.
Kidneys, skin and lungs are important excretory organs.

Solution 2:
Carbon dioxide (CO2) and urine

Solution 3:
Ammonia is toxic in even small amounts and therefore it must be removed from the body. The urea cycle or the orinithin cycle, in the liver, involves the conversion of ammonia into urea. Then the urea is then transported to the kidneys where it is excreted.

Solution 4:
Nephron is the basic structural and functional unit of the kidney.
Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine.

Solution 5:

PAGE NO : 98
Solution 6:
Dialysis is a process of separation of toxic substances from the blood stream through a membrane by kidney machine or artificial kidney.

Solution 7:

1. Ammonotelic.
2. Ureotelic.
3. Uricotelic.
4. Liver.
5. Nephron.
6. Urinary Bladder.
7. Glomerulus.

Solution 8:

1. Vein
2. Heart
3. Haemoglobin
4. Glomerulus
5. Nerve
6. Brain

Solution 9:

1. Separation and elimination of the metabolic nitrogenous wastes from the body is called excretion.
2. Nephron.
3. The cortex of kidney shows dotted appearance because it contains numerous complex structures called nephrons.
4. Formation of urine and osmoregulation are important functions of kidney.

Solution 10:

1. (a) kidney
2. (a) pigeon
3. (c) haematuria
4. (d) anuria
5. (d) Nothing will happen
6. (a) liver
7. (b) urease
8. (b) vitamin C
9. (b) liver
10. (c) nephron
11. (b) renal papilla

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Frank ICSE Class 10 Biology Solutions – Circulatory System

PAGE NO : 90
Solution 1: Circulatory system: It is a system of organs that takes part in the flow of materials in the body of an organism inside an extracellular fluid.
Circulatory system in humans:

1. The right atrium receives deoxygenated blood from all the parts of the body through large veins called vena cava.
2. When the right atrium is full of blood, it contracts and the blood is forced into right ventricle.
3. When the right ventricle is full of blood, it contracts and the blood is pumped into the pulmonary trunk.
4. From right ventricle, the pulmonary artery carries the blood to the lungs for oxygenation.
5. The oxygenated blood returns to the heart via pulmonary veins that empty into the left auricle.
6. When the left auricle contracts, the blood passes into the left ventricle by the opening of bicuspid valve.
7. On contraction of the left ventricle, the blood is pumped into the artery called aorta.
8. The aorta branches into vessels which transports blood to the heart and all the body parts.

Solution 2:

1. The SA is also called the pacemaker because it establishes the basic frequency at which the heart beats. It starts each heart beat and sets the pace for the whole heart.
2. There is no mixing of deoxygenated and oxygenated blood in the human heart because of double circulation of blood where the blood passes twice through the heart and the right half of the heart is concerned with pumping deoxygenated blood while the left is concerned with pumping of oxygenated blood.
3. The closed circulatory system is more efficient than the open system because in closed system the blood flows inside arteries or veins all the time which stops the mixing of blood with other bodily fluids and helps the transport of the blood around the body.
4. The left ventricle possess a thicker wall than the right ventricle because it pumps the blood at a higher pressure since blood from the left ventricle goes to all areas of the body while the right ventricle only has to pump blood to the lungs which is a much shorter distance, therefore less pressure is required.

Solution 3:

Solution 4:
The functions of blood plasma : It transports gases and other materials, maintains blood pH, body immunity, body heat regulation and also regulates the osmotic pressure of the blood.

Solution 5:
Double circulation means during one circulation blood passes twice through the heart. It includes both pulmonary and systemic circulation. It is necessary as it keeps oxygenated and deoxygenated blood separate.

Solution 6:
The materials which are carried by the blood are: oxygen, carbon dioxide, water, digested food, organic wastes, hormones and antibodies.

Solution 7:
The main function of erythrocytes is to transport the respiratory gases – CO2 and O2.

Solution 8:

1. Fibrinogen
2. Phagocytosis
3. Haemoglobin
4. Auricular systole
5. Angiology
6. Pericarditis
7. Tricuspid valve
8. Foramen ovale
9. Polycythemia
10. Lubb

PAGE NO : 91
Solution 9:

1. Histone
2. Foramen ovales
3. Nerve
4. RBC
5. Albumin

Solution 10:

1. Inferior vena cava, superior vena cava and coronary sinus
2. Ventricles
3. Function of bicuspid valve: It prevents the reverse flow of blood from the left ventricle into the left auricle.
4. Function of tricuspid valve: It prevents the reverse flow of blood from the right ventricle into the right auricle.

Solution 11:

Solution 12:

1. (c) Pulmonary vein
2. (b) Thebasius valve
3. (d) Aorta
4. (e) Pulmonary arch
5. (a) Clotting

Solution 13:

1. (d) 5 l
2. (c ) Left ventricle
3. (b) Capillaries
4. (a) bone marrow
5. (c ) 120 days
6. (a) myogenic
7. (a) Eustachian valve
8. (c ) ventricle
9. (b) 70-80
10. (c ) Monocytes
11. (d) 90%
12. (c) William Harvey
13. (b) Spleen
14. (d) all the above
15. (d) O

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Frank ICSE Class 10 Biology Solutions – Principles of Genetics

PAGE NO:35
Solution 1:
Gregor Johann Mendel.

Solution 2:
Genetics is the branch of biology that deals with the study of transmission of characters from parents to offspring.

Solution 3:
The term heredity may be defined as the transmission of genetically based characteristics from parents to offspring.

Solution 4:
Monohybrid cross.

Solution 5:
Dihybrid cross ratio is 9:3:3:1.

Solution 6:

Solution 7:

1. Genotype – The genetic expression of a character in terms of alleles written in symbols is called genotype.
2. Phenotype – The physical or external and observable expression of a character is called phenotype.
3. Homozygous – Diploid condition where both the alleles are identical is called homozygous.
4. Heterozygous – Diploid condition where both the alleles are different is called heterozygous.
5. Allele – Alternative forms of the same gene which determine contrasting characters is called an allele.
6. Dominant – An allele which expresses itself externally when present in homozygous or heterozygous conditions.
7. Recessive – An allele which expresses itself externally when present in homozygous condition but remains suppressed in heterozygous condition.

Solution 8:
Gregor Johann Mendel was a biologist who carried out experiments on garden pea and derived a few fundamental principles in genetics. He is called the ‘Father of Genetics’.

Solution 9:
Mendel’s laws are:

1. Law of Dominance
2. Law of Segregation
3. Law of Independent Assortment

Solution 10:
Monohybrid cross is one where the parents used for hybridization differ in only one pair of contrasting characters or alleles.

Solution 11:

Solution 12:
The law of segregation explains that the characteristics of an organism are determined by internal alleles that occur in pairs. These allele pairs separate during meiosis in gamete formation and the pair gets restored upon random fusion in zygote.

Solution 13:
Law of segregation is also called the law of purity of gametes because the two members of a pair of factors do not blend but segregate or separate into different gametes.

Solution 14:
According to the law of independent assortment when there are two pairs of contrasting characters, the distribution of the members of one pair into the gametes is independent of the distribution of the other pair.

Based on dihybrid ratio of 9:3:3:1 in F2 generation, Mendel observed that when a plant with two dominant alleles was crossed with another having the corresponding recessive alleles it was possible to obtain new combinations of characters where a plant had one dominant and the other recessive allele. These were new recombinations were not present in either parent or F1 generation.

PAGE NO :36
Solution 15:
Importance of Mendel’s Laws:

1. Dominant and recessive characters can be found.
2. A hybrid with desired characters can be produced easily.
3. Crops can be improved.
4. Pure recessive characters can be used where needed.
5. Genotypes and phenotypes of next generation can be predicted even before cross is made.

Solution 16:
Exceptions to Mendel’s Laws:

1. Incomplete Dominance – In few cases, F1 generation has an intermediate phenotype between dominant and recessive alleles.
2. Linkage – Genes on the same chromosomes are said to be linked and are inherited together.
3. Multiple Allelism – Each character may have more than two alleles which can’t be explained by Mendel’s laws.

Solution 17:
Mendel performed his experiments on the garden pea plant or Pisum sativum.

Solution 18:
Sex chromosomes determine the sex of a child in humans.

Solution 19:

Solution 20:

Solution 21:
Mendel’s work did not receive much notice till 1900. Then three scientists: Hugo de Vries, Carl Correns and Erich von Tschermak working independently rediscovered his work and brought Mendel’s experiment to limelight.

Solution 22:

1. Autosomes – The chromosomes other than sex chromosomes present in the body are called autosomes.
2. Sex chromosomes – The chromosomes which determine the sex of an individual are called sex chromosomes.
3. Sex-linked characters – Such characters or traits that are controlled by genes occurring on sex chromosomes are called sex linked characters.

Solution 23:
The sex of the zygote is determined by the sperm which fertilizes the ovum. If an X bearing sperm fuses with an ovum in man, the offspring would be female and if a Y chromosome bearing sperm fuses with an ovum the offspring will be a boy.

Solution 24:
The inheritance of sex linked genes controlling sex linked characters is called sex linkage or sex linked inheritance.

Solution 25:
Haemophilia is X-linked inherited disease in which the diseased person is unable to synthesize a normal blood protein called Antihaemophilic globulin that helps in clotting. Haemophilia is also called Bleeder’s disease as the haemophilic person bleeds for a long time even from a minor cut.

Solution 26:
Colour blindness is a sex-linked inherited disease in which the diseased person is not able to distinguish between red and green colour.

Solution 27:
Cause of Haemophilia – Haemophilia is an X-linked inherited disease. Homozygosity for recessive haemophilia gene is must to be seen in a female while a single affected X chromosome makes the male a haemophilia victim.
Cause of Colour Blindness – Colour blindness is the effect of a recessive gene. In case of female, both the X chromosomes must have the recessive gene but as males have only one X chromosome, just a single affected chromosome causes colour blindness.

Solution 28:
More males are affected by sex linked diseases because they have a single X chromosome and the sex linked diseases occur due recessive gene on X chromosome.

Solution 29:
A man can never transfer a sex-linked gene directly to his son because the son inherits only the Y chromosome from his father and the sex linked diseases are present on the X chromosome.

Solution 30:
The progeny of the woman and the haemophilic man will have one son and one daughter as colorblind, one daughter as a carrier and one son will be normal.

Solution 31:
Haemophilia

Solution 32:
The inheritance of sex linked genes controlling sex linked characters is called sex linkage or sex linked inheritance.

Solution 33:

Solution 34:

PAGE NO :37

Solution 35:

1. Father is color blind.
2. 3 daughters and two sons.
3. Child 1 is color blind.
4. All daughters from 2-5 are carriers while all the sons are normal.
5. X chromosome.
6. Haemophilia.

Solution 36:

1. (b) garden pea
2. (d) 100%
3. (c) 7
4. (d) Mendel
5. (a) dominant
6. (c) Law of Independent Assortment
7. (a) alleles
8. (b) heterozygous
9. (a) dihybrid cross
10. (a) Czechoslovakia
11. (c) X and Y
12. (a) X chromosome
13. (b) autosomes
14. (b) one X chromosome
15. (b) X chromosomes in male
16. (c) 50%
17. (c) sons are colour blind and daughters are carriers
18. (b) daughter

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Frank ICSE Class 10 Biology Solutions – Structure of Chromosomes

PAGE NO-20:
Solution 1:
Chromatin is an extremely thin, long nuclear fibre occurring in the nucleus before cell division.

Solution 2:
In interphase, the chromatin appears as a network of long, extremely thin fibres.

Solution 3:
During prophase of mitosis, the chromatin fibres shorten and become thick to form chromosomes.
During metaphase, the chromosomes appear more distinct and clear and each consists of two parallel strands called chromatids joined by a centromere.

Solution 4:
Chromosomes are the thread like structures or chromatin material present inside the nucleus.
Chromosomes are so called because they take up certain basic dye and stain very rapidly. The word chromosome comes from two words “chromos” meaning colour and “soma” meaning body.

Solution 5:

1. Strasburger – He observed thread like structures during cell division.
2. Balbiani – Described rod like structures in nucleus before cell division.
3. Waldeyer – Coined the term ‘chromosomes’.
4. Sutton and Boveri – They described chromosomes as physical structures and transmitters of hereditary traits.

Solution 6:
Chromosomes are the thread like structures present in the nucleus of the cell. They are covered with a sheath made up of proteins and filled with granular matter called matrix. Inside the matrix, there are two threads called chromonemata.
The chromosome consists of two symmetrical strands called chromatids. Each chromosome consists of a distinct constriction called centromere which gets attached to the spindle network.

Solution 7:

1. Sheath – It is a proteinaeous covering present around the chromosomes.
2. Matrix – It is a granular matter present inside the sheath.
3. Chromonemata – They are the subunits of chromatids.
4. Centromere – A constriction in the chromosome is called centromere.
5. Secondary Constriction – A constriction other than primary constriction is called a secondary constriction.
6. Telomere – The ends of the chromosomes is termed as telomere.

Solution 8:
Chromosomes are best observed at metaphase

Solution 9:
The chromosomes other than sex chromosomes present in the human body are called autosomes.
22 pairs of autosomes are present in man.

Solution 10:
The chromosomes which determine the sex of an individual are called sex chromosomes.

Solution 11:
Sex chromosomes are significant as they determine the sex of an individual.

Solution 12:
In man, there is a pair of sex chromosomes. In males, it is X and Y while in female, the sex chromosomes are X and X which are identical to each other.

Solution 13:
Chromosomes are the main source of chemical information which determines that the cell should become like its parent cell.

During the developmental stage they also determine that the cells of the organism will give the animal or the plant, the characteristic features of its species.

Solution 14:
DNA and RNA are the two nucleic acids.
Frederick Miescher discovered DNA

Solution 15:
Nucleic acids are made up of three types of molecules:

1. a pentose sugar,
2. nitrogenous bases
3. a phosphate

Solution 16:
The chemical composition of chromosome consists of:

1. Approximately 40% of DNA
2. 50% of Histone proteins
3. 8.5% Non histone proteins
4. Metallic ions like magnesium and calcium in traces.

Solution 17:
Two nitrogenous bases present in DNA are:

1. Purines – Adenine and Guanine.
2. Pyrimidines – Cytosine and Thymine.

Solution 18:

Solution 19:
Features of DNA:

1. DNA consists of two strands which are spirally arranged around an axis. This is called a double helical arrangement.
2. Each DNA strand is made up of nitrogenous bases, pentose sugar and phosphate.
3. Sugars are pentose type; bases are adenine, guanine, cytosine and thymine.
4. Both strands are connected with hydrogen bonds. There are two bonds between adenine and thymine and three bonds between guanine and cytosine.
5. In the DNA, bases are inside and sugars are outside and two sugars are connected with phosphoric acid.
6. Each DNA strand replicates and from each replicated DNA a new DNA is formed. This is called replication of DNA.

Solution 20:
Watson and Crick described the detailed structure of DNA.

Solution 21:
Importance of DNA:

1. DNA is most important because it is the hereditary material.
2. It acts as the director of protein synthesis.
3. Some DNA of chromosomes forms nucleolus.
4. DNA in presence of enzymes forms mRNA which acts as messenger.

Solution 22:
The rungs of “DNA ladder” are made up of two types of nitrogenous bases:

1. Purines: Adenine and Guanine
2. Pyrimidines: Cytosine and Thymine.

Solution 23:
Repeating components of each DNA strand length wise are pentose sugar and phosphate group

Solution 24:

1. Interphase
2. histone proteins
3. RNA, DNA
4. Protein
5. Nitrogen

PAGE NO 21
Solution 25:

1. False
2. False
3. True
4. True

Solution 26:

1. This diagram represents the structure of chromosome.
2. ‘d’ is centromere which gets attached to the spindle fibres.
3. ‘b’ is heterochromatin which is darkly stained region when stained with acetocarmine and ‘c’ is euchromatin which when stained with acetocarmine or felugen gets lightly stained.
4. Waldeyer
5. Matrix
6. No, secondary constriction or ‘e’ is not present in all chromosomes.

Solution 27:

1. (d) chromatin
2. (c) Waldeyer
3. (a) centromere
4. (c) secondary constriction
5. (a) interphase
6. (d) prophase
7. (a) DNA and histones
8. (a) 46
9. (a) I shaped
10. (b) metacentric
11. (c) XY
12. (b) sex chromosomes
13. (a) Watson and Crick
14. (a) nitrogen base
15. (c) Uracil
16. (b) thymine
17. (a) DNA

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Frank ICSE Class 10 Biology Solutions – Cell Division

PAGE NO-11:
Solution 1:
Cell division is important for a variety of reasons. One reason is that cell division is important for the growth of an organism. It is also important for cells to divide so that they can remain efficient. As all the cells are produced by the division of pre-existing cells, so each organism needs new cells for growth, replacement, repair and reproduction.

Solution 2:
The cell cycle is a series of events that take place in a cell leading to its division and duplication

Solution 3:
Interphase is a long resting phase in the cell cycle during which the cell grows, multiplication of DNA, synthesis of RNA and proteins takes place. Thus interphase is important in the cell cycle as it allows the cell to grow and develop into a mature cell before it is able to reproduce.

Solution 4:
Meiosis results in the formation of ova.

Solution 5:

Solution 6:
In anaphase, the two chromatids separate at the centromere and begin to move in opposite direction towards either end of the spindle network called the poles. The chromosomes bend around the centromere showing a ‘V’ or ‘J’ or ‘L’ shaped structure based on the length of its arms.

Solution 7:
The different phases of mitosis are Prophase, Metaphase, Anaphase and Telophase.

Solution 8:
Mitosis takes place in the body cells or somatic cells of the organisms.

Solution 9:
Mitosis is important because:

1. It helps in the growth of tissues, organs and thus the entire organism.
2. It helps in the repair of damaged tissues and organs.
3. It is the method by which lower organisms reproduce.
4. It helps in the maintenance of the hereditary characters by the replication of chromosomes

Solution 10:
Some characteristic features of mitosis are:

1. It takes place in somatic cells.
2. Chromosome number is preserved.
3. Daughter cells produced are identical to the parent cell.
4. It results in increase in the number of cells.

Solution 11:
Few important characteristics of Meiosis are:

1. Meiosis occurs in germ cells only.
2. It results in the formation of gametes.
3. Chromosome number of the parent cell is halved.
4. Daughter cells differ from the parent cell.

Solution 12:

Solution 13:
In humans, meiosis occurs in testes producing sperms and in the ovaries resulting in ova.

Solution 14:
Significance of Meiosis:

1. Due to meiosis, chromosome number is reduced to half in gametes and chromosome number of species is maintained.
2. Genetic variations occur due to meiosis.
3. The zygote on fertilization gets one maternal and one paternal chromosome in each homologous pair.

Solution 15:
Significance of Crossing over:

1. As a result of crossing over, the paternal and maternal homologous chromosomes of an organism pair up and exchange certain portions of their chromatids which lead to genetic variations.
2. It makes the genetic information in each haploid cell unique

Solution 16:

Solution 17:
No, cytokinesis is not necessary after karyokinesis in meiosis I. It generally takes place at the end of meiosis II when the four daughter cells are formed.

Solution 18:

1. Karyokinesis – It is the nuclear division where nucleus divides into two.
2. Cytokinesis – It is the division of cytoplasm in which the entire cell splits separating each nuclei.
3. Chiasmata – is the point where two homologous non-sister chromatids exchange genetic material in chromosomal crossover during meiosis.

Solution 19:
In an animal cell, the cytoplasm between the two daughter nuclei constricts i.e. a furrow starts forming in the plasma membrane at the middle. This deepens towards the interior of the cell and the cytoplasm splits into two similar daughter cells.
In plant cells on the other hand, the constriction is not observed during cytokinesis. Instead a new cell wall is laid down along the equatorial region of the spindle network beginning at the centre. Thus, two distinct, daughter cells are cut off.

Solution 20:

Solution 21:
Meiosis is a reductional division as in meiosis the number of chromosomes of parent cell is reduced to half in the daughter cells. Now, this reductional division is significant because it restores the number of chromosomes in a species.

PAGE NO-12:
Solution 22:
Yes, meiosis is responsible for maintaining the chromosome number of a species as meiosis being a reductional division involves formation of daughter cells with half the number of chromosomes.

Solution 23:

1. If four cells undergo mitosis, eight daughter cells will be produced.
2. Sixteen daughter cells will be produced.
3. Eight daughter cells will be produced if four cells undergo amitosis.

Solution 24:

1. Mitosis
2. ATP
3. Homotypic
4. Reduction
5. Mitosis

Solution 25:

1. Anaphase in a plant cell
2. A – Spindle fibre
   B – Cell wall
3. The homologous daughter chromatids or chromosomes begin to move towards opposite poles.
4. This type of cell division occurs usually in the somatic cells.
5. Two daughter cells are formed from this type of cell division.
6. The dividing cell shown is a plant cell because of the presence of cell wall and the absence of centriole.

Solution 26:

1. A – Duplicated chromosomes
   B – Centromere
2. The structure C is Spindle fibre. Its function is to help in the movement of chromosomes.
3. The type of cell division is mitosis because all chromosomes appear to be same as there is no crossing over.
4. Metaphase.
5. Prophase occurs before metaphase and after metaphase anaphase takes place

Solution 27:

1. (c) Meiosis
2. (a) Mitosis
3. (c) Both of these
4. (a) 1/2
5. (b) Growth and repair
6. (a) Movement of chromosomes
7. (a) Meiosis
8. (d) Both (a) and (c)
9. (b) Chromatin
10. (c) Both (a) and (b)
11. (b) Metaphase
12. (a) Meiosis I
13. (d) One cell, two nuclei
14. (a) Meiosis
15. (d) Telophase
16. (d) Prophase
17. (c) Telophase

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