Ques 1: Write the molecular formula of first two members of homologous series having functional group -Cl.
Ans: The general formula for the homologous series of functional group −Cl is CnH2n+1Cl.
The two consecutive members of this series are:
a. CH3Cl (Chloromethane)
b. CH3CH2Cl (Chloroethane)
where n is 1 and 2 respectively
The molecular formula for both of them are CH3Cl and C2H5Cl.
Ques 2: Name the method by which Spirogyra reproduces under favourable conditions. Is this method sexual or asexual?
Ans: Under favourable conditions, Spirogyra reproduces by a process known as fragmentation. This is an asexual method of reproduction.
Ques 3: What is an ecosystem?
Ans: An ecosystem is a self sustaining system where biotic and abiotic organisms of various communities interact with each other. Ponds, forests, grasslands, etc are a few examples of ecosystem.
Ques 4: An object is placed at a distance of 30 cm in front of a convex mirror of focal length 15 cm. Write four characteristics of the image formed by the mirror.
Ans: Four properties of the image formed by the given convex mirror are:
(i) Image is always erect
(ii) Small in size
(iii) Virtual
(iv) Always forms behind the mirror between focus and pole.
Ques 5: What is sustainable management? Why is reuse considered better in comparison to recycle?
Ans: Sustainable management is a resource management technique which aims to conserve the resources, use them efficiently and avoid their misuse for individual purposes such that they are conserved for the future. Reuse is better than recycle because of the following reasons:
1. Recycling needs some processes to use the same material again.
2. Reuse saves energy by using material again without any changes.
3. Reuse prevents environmental pollution by not creating any waste.
4. Reuse saves cost as same material is used again without any process.
Ques 6: Management of forest and wild life resources is a very challenging task. Why? Give any two reasons.
Ans: Management of the forest and wildlife resources is considered as a challenging task because:
1. There are many stakeholders of forest. They are those people who are directly or indirectly involved in forest. Management of forest and wildlife has to take into account the interests of all these stakeholders which become a challenging task.
2. Industries would consider the forest as merely a source of raw material for its factories and huge interest-groups lobby the government for access to these raw materials at artificially low rates which further poses a challenge to manage the forest and wildlife resources.
Ques 7: Two carbon compounds X and Y have the molecular formula C4H8 and C5H12 respectively. Which one of these is most likely to show addition reaction? Justify your answer. Also give the chemical equation to explain the process of addition in this case.
Ans: Compound X has the molecular formula = C4H8 (CnH2n, alkene)
Compound Y has the molecular formula = C5H12 ( CnH2n+2, alkane)
C4H8 is unsaturated hydrocarbon, i.e. alkene (butene) and C5H12 is a saturated hydrocarbon, i.e. alkane (pentane).
Saturated compounds undergo substitution reaction.
Unsaturated compounds undergo addition reaction at the multiple bonds. For example, 1-butene and 2-butene will add a chlorine molecule (Cl2) to form 1,2-dichlorobutane and 2,3-dichlorobutane, respectively. The reaction will be:
CH3−CH2−CH=CH2 + Cl2 → CH3−CH2−CH(Cl)−CH2Cl
Or
CH3−CH=CH−CH3 + Cl2 → CH3−CH(Cl)−CH(Cl)−CH3
Ques 8: Write the names given to the vertical columns and horizontal rows in the Modern Periodic Table. How does the metallic character of elements vary on moving down a vertical column? How does the size of atomic radius vary on moving left to right in a horizontal row? Give reason in support of your answer in the above two cases.
Ans: In the Modern Periodic Table, there are 18 vertical columns known as Groups and 7 horizontal rows known as Periods.
As we move down the group, the electrostatic attraction between the nucleus and the outer-most electron decreases due to increase in the distance between them. This happens because, on moving down the group, a new shell is added. So the valence electron can be easily lost by the element. As we know, metallic character is characterised by the ease of loss of an electron, thereby, metallic character increases on moving down a group in the Modern Periodic Table.
When we move across a period, the number of electrons in the same shell increases. This leads to greater electrostatic attraction between the nucleus and the outer-most electron. This increased attraction pulls the outer-most electron closer to the nucleus, thereby decreasing the atomic size.
Ques 9: An element P (atomic number 20) reacts with an element Q (atomic number 17) to form a compound. Answer the following questions giving reason:
Write the position of P and Q in the Modern Periodic Table and the molecular formula of the compound formed when P reacts with Q.
Ans: Atomic number of element P = 20
Electronic configuration of element P = 2, 8, 8, 2
Atomic number of element Q = 17
Electronic configuration of element Q = 2, 8, 7
The position of P in the Modern
Periodic Table: Period (Number of shells) = 4
Group (Electrons in outer-most shell) = 2
The position of Q in the Modern Periodic Table:
Period (Number of shells) = 3
Group (Electrons in outer-most shell) = (10 + 7) = 17
When P reacts with Q, it looses the two valence electrons (valency 2). These two valence electrons are accepted by two Q atoms (valency 1). Hence, the formula of the compound formed between P and Q is PQ2.
Ques 10: What happens when:
(a) Accidently, Planaria gets cut into many pieces?
(b) Bryophyllum leaf falls on the wet soil?
(c) On maturation sporangia of Rhizopus bursts?
Ans: (a) When Planaria gets cut into many pieces, it will undergo a process known as regeneration due to which each piece will grow into a new Planaria organism.
(b) When Bryophyllum leaf falls on the wet soil, the buds that are produced in the notches along the leaf will develop into new plants by the process known as vegetative propagation.
(c) When the sporangia of Rhizopus bursts upon maturation, the spores present inside it spread in the open environment. Then, with the help of different agents, they are carried to different places and when they land on a favourable surface, they start growing and produce new organism.
Ques 11: State the basic requirement for sexual reproduction? Write the importance of such reproduction in nature.
Ans: The basic requirements for sexual reproduction to take place are involvement of two parents and fusion of their haploid gametes. In the sexual reproduction, a new individual is formed by the fusion of two haploid gametes, one from the male parent and the other from the female parent. Since the new individual formed is diploid in nature, the gametes must be formed by meoisis, so that chromosome number can be reduced to half. When fusion of gametes occurs, the two nuclei of these two gametes fuse and the chromosome number is then restored to normal. The zygote, thus, formed is diploid in nature.
Importance of sexual reproduction:
Sexual reproduction involves fusion of male and female gametes coming from both the parents. The fusion of these gametes results in genetic variations in the offsprings. This way sexual reproduction promotes diversity of characters in offsprings by providing genetic variations. These genetic variations, thus, lead to evolution of species as well as allow the organisms to become better adapted in the changing environment.
Ques 12: State the changes that take place in the uterus when:
(a) Implantation of embryo has occurred.
(b) Female gamete/egg is not fertilised.
Ans: (a) When the implantation has occured in uterus of the mother, the inner lining of the uterus thickens and is richly supplied with the blood vessels to provide nourishment to the growing embryo.
(b) If the egg is not fertilised, it lives for about one day. Since, the thickened uterus lining is no more required, it will slowly break down and comes out through the vagina as blood and mucous known as menstruation which lasts for about two to eight days.
Ques 13: Distinguish between the acquired traits and the inherited traits in tabular form, giving one example for each.
Ans: Differences between acquired and inherited traits are as follows:
| Acquired Traits | Inherited Traits |
| Acquired traits are those that are developed by an individual during his/her lifetime. | Inherited traits are the qualities or characteristics present in an individual since birth. |
| They are a result of changes in non-reproductive tissues (somatic cells). | They are a result of changes in the DNA. |
| They cannot be passed on to the progeny. | They are transmitted to the progeny. |
| Examples: Pierced ear, large muscle size, etc | Examples: Colour of eyes, skin or hair |
Ques 14: Explain with the help of an example each, how the following provide evidence in favour of evolution:
(a) Homologous organs
(b) Analogous organs
(c) Fossils
Ans: (a) Homologous organs: These organs are similar in form (or are embryologically same), but perform different functions in different organisms. These organs provide strong evidence in the favour of evolution. For example, the bone structure observed in the forelimbs of birds and bats, flippers of dolphins and arms of human beings are similar and have the same pentadactyl plan but they perform different functions.
(b) Analogous organs: These organs have different origin and different basic structure but perform same function. For example, wings of birds and wings of bats (bird wings are made of feathers while bat wings are the folds of skin) have different structure but perform same function of flying. Thus, these organs provide evidence for evolution that they are different in origin but evolve to perform same function to survive in hostile environmental conditions.
(c) Fossils: They are the impressions of dead organisms and they can tell a great deal about the changes that various species of organisms have gone through. For example, Archaeopteryx is a connecting link between birds and reptiles and it suggests that the present animals have evolved from the existing ones through the process of continuous evolution.
Ques 15: Due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens a certain defect of vision arises. Write the name of this defect. Name the type of lens required by such persons to improve the vision. Explain the structure and function of such a lens.
Ans: The defect caused due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens is presbyopia. Presbyopia is the defect of eye in which a person cannot see nearby objects comfortably and distinctly without corrective eye-glasses. A presbyopic eye has its near point greater than 25 cm and it gradually increases as the eye becomes older.
The type of lens required by such person to improve the vision is bifocal lens.
A bifocal lens consists of both convex lens and concave lenses. The convex lens used in bifocal lens is used to correct hypermetropia (far sightedness) and concave lens is used to correct myopia (short sightedness).
Ques 16: You have been selected to talk on 'ozone layer and its protection" in the school assembly on 'Environment Day.'
(a) Why should ozone layer be protected to save the environment?
(b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow friends that would also help in protection of ozone layer as well as the environment.
Ans: (a) Ozone layer is a rich zone of ozone found in upper atmosphere. It helps in shielding the Earth from the harmful UV radiations coming from sun. If ozone layer gets depleted, UV radiations can directly reach the Earth's surface and drastically affect the life on Earth. For instance, UV radiations coming from the Sun causes skin cancer. So, it is very important to protect the ozone layer so as to save our environment.
(b) The ozone layer can be protected by taking following measures: Some of the ways to help protect and stop the depletion of the ozone layer include not buying products in aerosol cans, maintaining air-conditioning filters and units. In order to halt the depletion of the ozone layer, countries around the world have banned the use of chlorofluorocarbons and other ozone-depleting substances. These compounds produce chlorine and bromine atoms high in the atmosphere, and these atoms react with ozone, destroying it. By reducing the use of fluorescent lights.
By minimising the use of vehicles to limit the emission of harmful gases that cause damage to the ozone layer, we can contribute to its protection.
