CBSE Class 10 Sample Paper Science Solution - For 2023 Boards

(a) How are variations useful for species if there is drastic alteration in the niches?

(b) Explain how the uterus and placenta provide necessary conditions for proper growth and development of the embryo after implantation?




  • If the niche were drastically altered , the population could be wiped out due to the population's inability to suddenly adapt to the changes.
  • However, if some variations were to be present in a few individuals in these populations, there would be an increased chance for the population to survive
  • Variation is thus useful for the survival of species over time.


After fertilisation and formation of the embryo, the uterus is prepared to receive the embryo and to support the development of the foetus .

  • The lining of the uterus thickens and is richly supplied with blood to nourish the growing embryo. 
  • The embryo gets nutrition from the mother’s blood with the help of placenta . It is embedded in the uterine wall
  • It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces , which surround the villi. 
  • This provides a large surface area for glucose and oxygen absorption by villi to pass from the mother to the embryo. 
  • The developing embryo also generates waste substances which can be removed by transferring them into the mother’s blood through the placenta

The child is born as a result of rhythmic contractions of the muscles in the uterus which begin when it has matured (takes nearly 9 months).


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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo