► Alveoli are the workhouses of respiratory system.
► The exchange of oxygen and carbondioxide takes place in alveoli.
► It takes up oxygen and gives out carbondioxide.

► Th foetus consists of multitude of cells of different shape, size and content.
► Foetal cells gradually attain change in structure and function.
► This process is known as cell differentiation.

i) How does excessive usage of mobile phone affect our eyes?
► Light emitted from mobile phone damage our eye's retina resulting in Macular degeneration which causes death of photoreceptor cell in the retina. Cell phone radiation can damage eyes and cause early cataracts. It also affects cornea, pupil and other ocular systems of the eye.
ii) What are the values shown by the teacher?
► The teacher is concerned about his student. His timely suggestion saved the boy from severe occular problems. The teacher insisted the boy to limit his video games and spend more time in outdoor games.

a) Why did the doctor advised him to go to the playground?
► Playing games in the playground regulates the breathing rate. It increases the capacity of lungs to hold more oxygen. Playground games may serve as a solution to minor respiratory problems in kids. It inhibits shallow breathing. So the doctor advised him to go to the playground.
b) What is the use of pranayamam?
► Pranayama ensures more oxygen to lungs and good for hearts too. In pranayama, the retention of breathe helps supply of oxygen and carbondioxide thus facilitates better work of lungs and helps brain to work more efficiently. Pranayama enhances autonomic nervous system which controls heart rate, glandular secretions, respiration, digestion and blood pressure.