# CBSE Class 10 Science SA-II Board Exam 2017: Marking Scheme

Sep 18, 2017 17:01 IST
CBSE Class 10 Science Marking Scheme 2017

We bring here the CBSE Class 10 Science SA-II Board Exam 2017 Marking Scheme that released by the board itself. This marking scheme has key answers (or values point) along with mark wise break up of every answer which gives better idea about the division of marks inside a question.

Importance of CBSE Class 10 Science Board Examination Marking Scheme:

Every year CBSE Board releases the marking scheme which was used while checking the answer booklets of CBSE Board Examinations.  CBSE does this with a purpose of helping its students get an idea to frame a perfect answer that contains every important key point.

The word limit while answering questions of CBSE board examination is the most crucial factor. With the help of key answers in marking scheme, students will easily understand the criteria of word limit of answers to be written in CBSE Board Exams.

A few sample questions and their key points from the CBSE Class 10 Science Board Exam 2017: Marking Scheme, are given below:

Q. Write the molecular formula of the 2nd and the 3rd member of the homologous series whose first member is methane.

Ans.

C2H6, C3H8 (&frac12; + &frac12;)

Q. In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer ?

Plants → Deer → Lion

Ans.

1000000 J (1)

Q. State two advantages of conserving (i) forests, and (ii) wild-life.

Ans.

• Conserving forests helps in (i) retaining sub soil water and (ii) checking floods / any other (&frac12; x 4)
• Conserving wild life helps in (i) maintaining ecological balance and (ii) protecting the nature (or any other) (&frac12; x 4)

Q. Write  the  number  of  periods  and  groups  in  the  Modern  Periodic  Table. How does the metallic character of elements vary on moving

(i) from left to right in a period,and

Ans.

• Periods – 7, Groups – 18 (&frac12; + &frac12;)
• Metallic character decreases along the period because effective nuclear charge increases on the valence electrons hence decrease in tendency to lose electrons. (&frac12; + &frac12;)
• Metallic character increases down a group because effective nuclear charge experienced by valence electrons decrease, hence tendency to lose electron decreases. (&frac12; + &frac12;)

Q. Reproduction is one of the most important characteristics of living beings. Give three reasons in support of the statement

Ans.

• For continuation of species / perpetuation of species. (1)
• It promotes diversity of characters / helps to show the variationswhich enhances the survival chances. (1)
• Increases population of a species / any other answer (1)

Q. What is vegetative propagation? State two a dvantages and two disadvantages of this method.

Ans.

• Vegetative propagation – A process in which any vegetativepart of a plant (root, stem or leaf) gives rise to a new plant under appropriate conditions. (1)
• Two advantages :- (i) Large number of plants obtained in a short interval. (ii) Propagation of seedless plants is made possible / any other advantage. (&frac12; + &frac12;)
• Two disadvantages :- (i) No genetic variations, so, less adaptability to the environment. (ii) The disease of plants gets transferred to the offsprings. (&frac12; + &frac12;)

Q. List  three  techniques  that  have  been  developed  to  prevent  pregnancy. Which one of these techniques is not meant for males ? How does the use of these techniques have a direct impact on the health and prosperity of a family?

Ans.

• Three techniques – Barrier method, chemical method, surgical method (&frac12; x 3)
• Chemical method (&frac12; )
• It maintains health of the woman, parents can provide more attention to children / more resources are available to the family / any other. (&frac12; x 2)

Q. (a) Write  the  functions  of  each  of  the  following  parts  in  a  human female reproductive system :

(i)Ovary

(ii)Uterus

(iii)Fallopian tube

(b)Write the structure and functions of placenta in a human female.

Ans.

(a)  Functions :

• (I) Ovary:

(i) Production of female hormones / estrogen /

progesterone

(ii) Production of female gamete/egg/ germ cells (&frac12; + &frac12;)

• (II) Uterus:-

(i) Implantation of zygote / embryo

(ii) Nourishment of developing embryo (&frac12; + &frac12;)

• (III) Fallopian tube :-

(i) Transfer of female gamete from the ovary

(ii) Site of fertilisation (&frac12; + &frac12;)

(b)  Structure of placenta :- It is a special disc like tissue embedded in mother’s uterine wall and connected to the foetus / embryo. (1)

Functions of placenta :- It provides a large surface area for glucose and oxygen / nutrients to pass from mother’s body to the developing / developed embryo / foetus and also helps in passing the waste from the foetus / embryo to the mother’s body. (1)

CBSE Class 10 Science SA II Board Exam 2017: Marking Scheme

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