Which two processes are responsible for keeping the percentage of atmospheric oxygen at relatively constant levels ?

Respiration and Photosynthesis

They include lobsters and crabs

The virus is considered to be are living item since they have hereditary material dnas or rnas. they can imitate and change. they respond to boosts, for example, radiation, chemicals, and warmth. they have antigenic properties. they are proficient to duplicate with a same hereditary constituent.