Of the several gases in atmosphere, plant life mostly depends upon
Concentration of $O_2$
Availability of $CO_2$
Both $ (a) $ and $ (b)$
Concentration of $N_2$
O soil layer is rich in
Sheet erosion is caused by
Homeostasis is
The components of a soil are
Why do all the fresh water organisms have contractile vacuoles whereas majority of marine organisms lack them ?