31.

Write two examples each of sexually transmitted diseases caused by (i) virus, (ii) bacteria. Explain how the transmission of such diseases be prevented?       

Tabulate two distinguishing features between acquired traits and inherited traits with one example of each.

The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it. Justify this statement with the help of flow chart showing determination of sex of a newborn.

Mention the types of mirrors used as (i) rear view mirrors, (ii) shaving mirrors. List two reasons to justify your answers in each case.

An object of height 6 cm is placed perpendicular to the principal axis of a concave lens of focal length 5 cm. Use lens formula to determine the position, size and nature of the image if the distance of the object from the lens is 10 cm. 

State the difference in colors of the sun observed during sunrise/sunset and noon. Give explanation for each. 

(a) What is an ecosystem? List its two main components.  

(b) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Explain.

(a) Define the term 'isomers'.        

(b) Draw two possible isomers of the compound with molecular formula C₃H₆O and write their names.

(c) Give the electron dot structures of the above two compounds.

(a) List three distinguishing features between sexual and asexual types of reproduction.

(b) Explain why variations are observed in the offspring of sexually reproducing organisms? 

(a) Identify A, B and C in the given diagram and write their functions.          

(b) Mention the role of gamete and zygote in sexually reproducing organisms.