1. Chemical Reactions and Equations

2. Acids , Bases and Salts.

3. Metals and Non-metals

4. Carbon and its Compounds

5. Periodic Classification of Elements

6. Life Processes.

7. Control and Coordination

8. How do Organisms Reproduce.

9. Heredity and Evolution

10. Light- Reflection and Refraction

11. Human eye and colourful world

12. Electricity.

13. Magnetic effects of electric current

14. Sources of Energy

15. Our Environment

16. Management of natural resources

9. Heredity and Evolution

CHAPTER  9.
HEREDITY AND EVOLUTION
PAGE No: 143

1. If a trait A exists in  10% of a population of an asexually reproducing species and a trait B          exist in 60% of the same population. Which trait is likely to arisen earlier ?

The trait B is likely to be arisen earlier. 
The population of trait B is much greater than the population of A. 
Trait A is a new trait which only spread to only 10% of the population by reproduction.

2. How does the creations of variations in a species promote survival?

Sexual reproduction give rise to subtle variations in new individuals. Hence different variant emerges in the species. The variant which are suitable to the environment will survive and the others will perish.
If the environment in which the organism lives get drastically altered, the organisms cannot survive .But if there are some variants which can survive in the changed environment, these organism would reproduce and continue the species
Example : The bacteria living in water would die due to increase in temperature because of global warming. But the variants which can resist high temperature would survive. 

PAGE No: 147

1. How do Mendel's experiments show that traits may be dominant or recessive?

In the F2 generation 
The traits which are present in 75% of the individuals are dominant and the traits which are present in 25% of the individuals are dominant

2. How do Mendel's experiments show that traits are inherited independently?

Mental crossed contrast characters  of two traits of  pea plants.  The F1 progeny showed only the dominant characters. But in the F2 progeny the traits from the parents as well as new traits where shown. This shows that the traits are inherited independently 

This happens during the gamete formation where the genes separates independently

3. A man with blood group A marries a woman with blood group O and there daughter has a blood group O. Is this information enough to tell you which of the traits blood group A or blood group O is dominant? Why or whynot?

From the information given we cannot conclude whether the blood group A or blood group O is dominant.

Either can be possible because each individual carries two factors. Recessive charactor will only appear when the two traits are similar. Here two cases arrise

Case 1
Blood group A is dominant and blood group O is recessive
Here father is AA  or AO and mother is  OO
When A is considered to be dominant over O , the combinations such as AO, OO,AO, AO,AO,AO,AO and  OO
Since two of the combinations are OO, the daughter can have blood group O

Case 2

Blood group O is dominant and blood group A is recessive
Here father is AA  and mother is OA or OO
When O is considered to be dominant over A , the combinations such as OA,OA,OA,AA,OA,OA,OA and AA
Since six of the combinations are OA, the daughter can have blood group O

4. How is the sex of the child determined in human beings?

In human beings 23 pairs of chromosome  are present. Out of that 22 pairs are the characters of the parents other than sex chromosome  The 23rd pair is called the sex chromosome.

Woman have XX chromosome  as sex chromosome and it is perfectly matched.
Men have XY chromosome as sex chromosome , and it is mismatched as Y chromosome is shorter than X chromosome .

All the children inherit from there mother regardless of whether they are boys or girls. This means that the sex of the child will be determined from what they inherit from there father.

 A child who inherits a X chromosome from the father will be a girl and the child who inherits a Y chromosome from the father will be a boy.

PAGE No: 150

1. What are the different ways in which individuals with a particular trait may increase in a population ?

When a variation occurs and it  results in the better survival of the organism in a existing environment. These traits will be selected naturally. Hence more individuals with that particular trait will increase in a population.

2. Why are traits acquired during  the life time of an individual not inherited? 

The traits acquired during the life time is known as acquired characters.
 These characters are not inherited because these affects the somatic cells and not the germ cells .Hence the change in character cannot be passed to next generation. Thus the acquired characters would die with the death of the person

Example : The scar that a soldier gets in a battle field

3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

If some natural calamity occurs , since they are limited in numbers they would get killed and extinct.

Moreover since there are less numbers, they breed among themselves and there is less chances for variations.

If a deadly disease affect the tiger all the tigers may die as there would be less variation in the genotype to survive the disease

PAGE No: 151

1. What factors could lead to the rise of a new species ?

The factors which affects the rise of new species are
  1. Genetic Variation
  2. Natural selection
  3. Reproductive isolation.
  4. Speciation 

2. Will geographical isolation be a major factor in the speciation of a self pollinating plant species? Why or why not?

No.
As the plant is self pollinating it would be less affected by geographical isolation.
In contrast  in a cross pollinated species,geographical isolation is a major factor which would result in the accumulation of variations.

3. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?

No.
Asexually reproducing organism have very little variations over generations. The change resulting from geological isolation would not be passed to the next generation. 

PAGE No: 156

1. Give an example of characteristics being used to determine how close two species are in evolutionary terms ?

Structure of fore limb of animals such as frog, lizard, bird and humans are homologous . That is  they all have same structure in order to do different functions. From this we can assume that they all have a common ancestor

2. Can the wing of a butterfly and the wing of a bat be considered a homologous organs?  Why or why not?

No.

The wing of a butterfly and the wing of a bat are used for the same function , that is flying.
But the structures of there wings are very different.

Hence they are not considered as homologous organs but as analogous organs

3. What are fossils ? What do they tell us about the process of evolution?

PAGE No: 158

1. Why are human beings who look so different from each other in terms of size , colour and looks said to belong to the same species?

2. In evolutionary terms, can we say which among  bacteria, spiders, fish and chimpanzees have a better body design ? Why or why not?

PAGE No: 159

EXERCISES

1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make up of the tall parent can be depicted as

2. An example of  homologous organs is

3. In evalutionary terms , we have more in common with

4. A study found that children with light coloured eyes are likely to have parents with light coloured eyes. On this basis can we say anything about whether the light eye colour trait is dominant or recessive?  Why or why not?

5. How are the areas of study - evolution and classification- interlinked?

6. Explain the terms analogous and homologous organs with examples

7. Outline a project which aims to find the dominant coat colour in dogs.

8. Explain the impotence of fossils in deciding evolutionary relationships

9. What evidence do we have for the origin of life from inanimate matter?




10. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?



11.  How is the equal genetic contribution of male and female parents ensured in the progeny?


12. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement Why or why not?

5 Periodic Classification of Elements

CHAPTER  5.
PERIODIC CLASSIFICATION OF ELEMENTS
PAGE No: 81

1. Did Dobereiner's triads also exist in the columns of Newlands Octave? Compare and findout.

Yes. one of the Dobereiner's triads exist in the columns of Newlands' octave .
Li, Na & K are found in the first column of Dobereiner's triads whereas the same elements in the same order are placed in the second column of Newlands' octave.

2. What were the limitations of Dobereiners classification?

Dobereiner could classify only three triads from the elements known at that time.

It is not found useful since all of the elements known at that time could not be arraigned in triads

3.  What were the limitations of Newlands Law of  Octaves?

1. It was applicable to only lighter elements up to calcium having atomic mass 40u.
     After calcium , the first and eighth element did not show similar properties.
    Eg : Cr ( chromium ) & Y  ( yttrium) placed in the same column, but having different properties

2. It is assumed by Newlands that only 56 elements existed in nature and no new elements would be        discovered in the future. But later several new elements were discovered, whose properties does          not fit into Law of Octaves.

3.  Some similar elements are seperated from one another while some dissimilar elements was placed       in the same column
      Eg: Fe ( iron) is placed away from Co ( cobalt )and Ni ( nickel)
      Co and Ni  do not resembles halogens( F, Cl, Br) , but placed in the same column

 4. When noble gases were discovered, it is the first and the ninth element which has similar                      properties and not the eighth element.

PAGE No: 85

1. Use Mendeleev's Periodic table to predict the formulae for the oxides of the following elements
    K, C, Al, Si, Ba

  Element                      Group             Oxide Formula                     Oxide

 K (Pottasium)            group I                    R2O                                   K2O

C ( Carbon)                 group IV                RO2                                  CO2


Al ( Aluminium)         group III                R2O3                                 AL2O3 

Si (Silocon)                 group IV                RO2                                  SiO2

Ba (Barium)                group II                  RO                                   BaO

2 . Besides Gallium which other element have since been discovered that were left by Mendeleev in  his Periodic Table? ( any two)

Eka - Boron  in Mendeleev 's periodic table  was found out and named as  Scandium
Eka - Aluminium   in Mendeleev 's periodic table  was found out and named as Gallium
Eka - Silicon  in Mendeleev 's periodic table  was found out and named as Germanium

3. What were the criteria used by Mendeleev in creating his Periodic Table

Mendeleev used atomic masses, physical properties  and chemical properties  as the criteria for creating his periodic table. Here the elements where arraigned in the order of increasing atomic masses

Mendeleev's Periodic law states that physical and chemical properties of the elements are the periodic functions of there atomic masses

4. Why do you think the Noble gases are placed in a separate group?

Noble gases were discovered very late because they are inert and present in extremely low concentration in atmosphere.
It includes Helium, Neon, Argon, Krypton and Xenon

But when they were discovered they could be placed in a new group with out disturbing the existing Mendeleev's table

It is named as zero group which is added later by  Ramsay

PAGE No: 90

1. How could the Modern Periodic Table remove various anomalies of Mendeleev's Periodic Table?

1. Placement of Hydrogen with alkali metals is justified on the basis of its electronic configuration.

2. In modern periodic table elements with similar valence electrons fall in the same group.Hence are      arraigned in the gradation of chemical and physical properties.

3. All the isotopes of the same element has a single position on modern periodic table, since the               elements are arraigned in the order of atomic number

4. Prediction of properties of elements could be made with precision when elements are arranged on        the basis of increasing atomic number.

2. Name two elements you would expect to show chemical reaction similar to magnesium. What       is the basis of your choice?

Calcium and Beryllium
It belongs to the II group of Modern periodic table, and having two electrons in there outermost shell.
Since all  these elements have two electrons in the outermost shell, they show similar properties.

They are called as Alkaline earth metals . These include Beryllium, Magnesium, Calcium, Strontium, Barium and Radium

3. Name
(a) Three elements that have a single electron in there outermost shell

Lithium, Sodium, Potassium, Rubidium , Cesium and Francium. These belongs to the first group of the periodic table and called as Alkali Metals

(b)  Two elements that have two electrons in there outer most shell.

Beryllium, Magnesium, Calcium, Strontium , Barium and Radium.  These belongs to the second group of the periodic table and called as Alkaline earth  Metals

(c) Three elements with filled outermost shell

Helium , Neon, Argon, Krypton, Xenon and Radon  These belongs to the eighteenth group of the periodic table and called as Noble gas

4 (a) Lithium , sodium , potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements.

Yes , there are similarity in the atoms of these elements.
Let us examine the balanced equations

2Li(s)   + 2H₂O(l)       à      2LiOH  (aq) + H₂(g)

2Na (s)   +  2H₂O (l)    à     2NaOH (aq)  + H₂(g)

2K (s)  +  2H₂O(l)      à      2KOH (aq) + H₂(g)

From this we can understand that all these elements  has the valency 1. From its electronic configuration, it is evident that all the elements are similar with one electron  in its outermost shell. Hence it belongs to I group. This group is called as alkali metals.

(b) Helium is an unreactive gas  and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

The elements helium and neon belongs to noble gas that is  18th group of the periodic table.

The elements of this group have completely filled valence shell.
Now we can examine their electronic configuration

He :  2
Neon : 2, 8

Now it is evident that the similarity in their atom is the completely filled valence shell.

5. In the modern periodic table, which are the metals among the first ten elements?

Li(Lithium) , Be( Beryllium)

6. By considering the positions in the periodic table, which one of the following elements would you expect to have maximum metallic characteristic?
Ga  ,   Ge  ,  As,  Se  , Be

Be 

Metallic character decreases from left to right. Here beryllium is on the most left among the elements given,

EXERCISE 

PAGE No: 91

1. Which of the following is not a correct statement about the trends when going from left to right across the periods of periodic table?

(a) The elements become less metallic in nature  ✅
(b) The number of valence electron increases✅
(c) The atoms loose their electrons more easily❌
(d) The oxides become more acidic✅

2. Element X forms a chloride with the formula XCl₂, which is  solid with high melting point . X would most likely to be in the same group of the periodic table as

(b)Mg

3. Which element has

(a) Two shells both of which are completely filled with electrons

Neon.  Electronic configuration  2,8

(b)  The electronic configuration 2,8,2

Mg

(c) A total of three shells with four electron in its valence shell

Silicon   Electronic configuration 2,8,4   

(d) A total of two shells with three electrons in its valence shell

Boron      Electronic configuration 2,3

(e) Twice as many electrons in its second shell as in its first shell

Carbon    Electronic configuration 2,4 

4.(a) What property do all elements in the same column of the periodic table as boron have in common?

All the elements of boron family has a valency of  three and are known as boron family. It includes  Boron, Aluminium, Gallium, Indium and Thallium .
Here Boron is a metalloid where us all others are metals.

(b) What property do all elements in the same column of the periodic table as fluorine have in common?

All the elements of fluorine family has a valency of one and are known as halogens. It includes  Fluorine, Chlorine, Bromine, Iodine and  Astatine
All the elements in this group are gases.
They are highly reactive.
The most reactive element fluorine belongs to this family.

5. An atom has electronic configuration 2,8,7

(a) What is the atomic number of the element?

17 and the element is  Chlorine

(b) To which of the following elements would it be chemically similar ( Atomic number is given in parenthesis)
N(7)         F(9)          P(15)          Ar(18)

The electronic configuration of the given elements are as a follows

N(7)     :  2,5
F(9)      : 2,  7
P(15)     :  2, 8, 5
Ar(18)   : 2, 8, 8

Here F(9) only has seven electrons in its valence shell as that of the given element chlorine

6. The positions of three elements A, B and C  in the periodic table are shown below

Group  16                      Group  17
 -----                                  ------
------                                  A
------                                -----
  B                                     C

(a) State whether A is ametal or non-metal

Non metal

(b) State whether C is more reactive or less reactive than A

Less reactive than A

(c)  Will C be larger or smaller in size than B?

C is smaller than B

(d) Which type of ion, cation or anion, will be formed by element A?

Anion, 17th group is halogens and having a valence of 1 and form ionic bonds

7. Nitrogen ( atomic number 7 ) and phosphorus ( atomic number 15) belong to group 15 of the periodic table . Write the electronic configuration of these two elements.Which of these will be more electronegative? Why?

Electronic configuration

Nitrogen : 2,5

Phosphorus : 2,8,5

Nitrogen is more electronegative than phosphorous.

In a periodic table electronegativity decreases from top to bottom. Here nitrogen is above phosphorous in the group 15 of the periodic table

8. How does the electronic configuration of an atom relates to its position in the modern periodic table?

Groups / Column :  Valence electron determines the group number of the element

Periods / Rows  :  Number of shells determines in which period the elements belongs.

The group number of the elements having more than two valence electrons is the number of valance electrons plus ten 

9. In the modern periodic table , calcium ( atomic number 20) is surrounded with elements with atomic number 12, 19,  21  and 38. Which of these have physical and chemical properties resembling calcium?

Electronic configuration  of calcium is 2,8,8,2

Electronic configuration of the given elements are 

Magnesium ( 12)  : 2, 8, 2

Potassium   ( 19)    : 2,8,8,1

Scandium  ( 21)    :  2,8,8,3

Strontium (32)    : 2, 8, 18,2

Magnesium and strontium shows same physical and chemical properties as calcium.

These three elements belongs to the same group with valence electrons two

10. Compare and contrast the arrangement of elements in Mendeleevs periodic table and Modern periodic table

Mendeleev’s Periodic table	Modern Periodic Table
Based on Atomic mass	Based on Atomic Number
In a group all elements does not have same number of valence electrons	In a group all elements have same number of valence electrons
Law states that the physical and chemical properties of elements are periodic functions of their atomic mass	Law states that the physical and chemical properties of elements are periodic functions of their atomic number
The elements having same physical and chemical properties may not fall in a group	The elements having same physical and chemical properties fall in a group
The real elements and its isotopes may not be placed in the same position	The real elements and its isotopes are placed in the same position
A precise prediction of properties of elements is not possible	A precise prediction of properties of elements is possible

11. The Human Eye and Colourful World

CHAPTER  11.
THE HUMAN EYE AND COLOURFUL WORLD
PAGE No: 190

1. What is meant by power of accommodation of eye ?

The ability of the eye lens to adjust its focal length is called the power of accommodation of eye. It is the maximum variation of its power for focusing on near and far objects. For normal eye , the power of accommodation is about four dioptres.

2. A person with a myopic eye cannot see objects beyond 1.2 metes distinctly. What should be        the type of corrective lens used to restore proper vision?

Concave lens ( diverging )of suitable wavelength should be used.

3. What is the far point and near point of the human eye with normal vision? 

For a human eye with normal vision, the far point is at infinity and the near point is at 25cm from the eye.

4. A student has difficulty reading the blackboard while sitting in the last row. What could be        the defect the child is suffering from ?. How can it be corrected?

The child is suffering from myopia. It can be corrected by using a concave lens ( diverging lens ) of suitable power.

EXERCISES
PAGE No: 197

1. The human eye can focus objects at different distances by adjusting the focal length of the           eye lens. This is due to 

Accommodation

2. The human eye forms the image of an object at its

Retina.

3. The least distance of distant vision for a young adult with normal vision is about

25 cm

4. The change in focal length of an eye lens is caused by the action of the

Ciliary  muscles

5. A person needs a lens of power -5.5 dioptres for correcting his distant vision. For correcting        his near vision he needs a lens of power +1.5 dioptres .What is the focal length of the lens            required for correcting (i) distant vision and (ii) near vision.

(i) The power of the lens used for distant viewing is  -5.5 D
     Power = 1/f

Focal length = 1 / Power  = 1 / -5.5   =   -0.181818m

 ie  Focal length  = -18.1818cm

Since focal length is negative the lens used is concave

The person should use a concave lens of focal length 18.1818cm

(ii)  The near viewing section of the lens is corrected by power = +1.5 D

     Power = 1/f

Focal length = 1 / Power  = 1 / 1.5   =   0.67 m
 ie  Focal length  = 67 cm

Since focal length is positive the lens used is convex

The person should use a convex lens of focal length 167 cm

6. The far point of a myopic person is 80 cm in front of the eye. What is the nature and power         of  the lens required to correct the problem

Since this person is having myopia, the lens used is concave.
The far point distance (v)and the distance of the object at infinity (u), both are negative, since they are in front of the lens

u = -80     v = infinity

By lens formula  1/f  = 1/v - 1/u

1/f  = 1/-80  -  1/infinity  =  -1/80  + 0   =  -1/80

Hence f = -80 cm

Power = 1/f  ( f in meter )

P = (1/ -0.8 ) D  =  -1.25D

Negative sign again indicates the lens is concave

The person should use a concave lens of 1.25 D

7. Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye       is 1 m .What is the power of the lens required to correct this defect?. Assume that the near point of     eye  is   25 cm

The near point distance of hypermetropic eye  (v)and the near point distance of a normal eye  (u), both are negative, since they are in front of the lens

u = -25 cm     v =  -100 cm

By lens formula  1/f  = 1/v - 1/u

1/f  = 1/-100cm  -  1/-25cm  =  = 3/100cm

Hence f = 100/3 cm  = 33.3cm

Power = 1/f  ( f in meter )

P = (1/ 0.333 ) D  =  3D

Positive  sign again  indicates the lens is convex

The person should use a convex lens of 3 D

8. Why is a normal eye not able to see clearly the objects placed closer than 25cm? 

The least distance of distinct vision for a normal eye is 25 cm.

When an object is placed less than  25cm , the ciliary muscles cannot bulge the eye lens anymore, and hence cannot be focused  on the retina and a blurred image is seen

9. What happens to the image distance in the eye when we increase the distance of an object from the  eye?

For a normal eye the image distance is fixed. It is equal to the distance of retina from the eye lens.

When we increase the distance of an object , to make the image distance constant, the adjustment is made on the focal length of the eye lens by the help of ciliary muscles

10. Why do stars twinkle

Due to the atmospheric refraction the star twinkles.

When the star light enters the earths atmosphere it undergoes continuous refraction before it reaches the earth. The atmospheric refraction occurs in a medium of gradually changing refractive index . Since the atmosphere bend the starlight , the position of the star is slightly different from its original position when  viewed from here

The stars appear a little higher when viewed from the horizon and the apparent position of the star keeps on changing because of the change in physical features of the atmosphere like density, temperature etc

As a result the fluctuating image  of the star makes them twinkle to the observer

11. Explain why the planets do not twinkle

Planets do not emit light. They become visible due to the reflection of light falling on them.
The planets are closer to the earth and are considered as an extended source of light.

The fluctuations of the light coming from a large number of point sources due to refraction gets nullified.Hence no twinkling of planets can be seen.

12.  Why does the sun appears reddish early in the morning

During the sun set and sun rise the sun is closer to the horizon. The solar rays have to travel a longer distance as compared to than at noon when the sun is overhead.
Most of the shorter wave length colours like blue gets scattered by the particles such as dust , humidity and molecules of the air
The longer wave length colour like orange and  red are least scattered
Hence the red colour  reaches the observers eye and so the red colour at dawn and dusk

13. Why does the sky appear dark instead of blue to an astronaut? 

At a huge height there is not much atmosphere for the light rays to scatter. Hence the sky appears dark for an astronaut.