1.  What are the characteristic features of living organisms?

All living organisms show one or more of the following general characteristics.  They all
(i) Breathe
(ii) Grow
(iii) Move
(iv) Respond to outside change
(v) Need food
(vi) Reproduce

2.  Why the visible changes in an organism are not the defining characteristics of life?

These visible changes are not the defining characteristics of life because not all organisms show all these characteristics and some of these characteristics can only be observed over a period of time.  For e.g., a tree when observed do not show visible movements for breathing, growth, nutrition or reproduction still we all categorize trees under living thing.

3.  Why are viruses considered a borderline between living and non-living?

Viruses are considered a borderline between living and non-living because they show molecular movements only when they infect other living cells.  Outside these cells they show all characteristics of non living things.

4.  What are molecular movements?  Why are these needed for life?

Molecular movements are the invisible movements occurring inside  the living cells due to chemical reactions. These movements together over a period of time result in visible movements of life like growth.  Molecular movements drive the life processes at cellular level.

5.  What are life processes?

All living organisms require various maintenance functions in order to continue living and prevent damage and breakdown.  The processes that together perform this maintenance job are called life processes.

6.  Give examples of some life processes taking place in all living organisms.

Nutrition, respiration, transportation and excretion are examples of life processes taking place in living organisms.

7.  Why do all life processes need energy?  How do living organisms fulfill this requirement?

Life processes prevent damage and breakdown of living organisms.  This requires constant building up of new material and repair of the older ones. Hence, life processes need energy to perform these tasks.
Living organisms fulfill their energy requirements by taking energy from an outside source.