(i) H- bonding in water molecules of ice creates a lot of vacant spaces. As, a result density of ice is less than that of water . hence, it floats on the surface of water .In winters, when the temperature is very low, generally upper layer of water in the lake freezes. The aquatic life remains protected in the water underneath. 

(ii) in the vascular plants, the movement of water through the plant;s xylem and other vessels takes place through hydrogen bonding.water molecules are not only hydrogen bonded to each other but also to the cellulose cell comprising the wall of the plant cells. As a result, capillary action is set in which allows plant to pull up water into the roots. Furthermore, hydrogen bonding can create a long chain of water molecules which can overcome the force of gravity and travel upto the high altitude of the plants 

(iii) the secondary structure of the protein involves interaction (mainly hydrogen bond) between the neighbouring polypeptide backbones which contain N-H bonded pairs and O- atoms. Consequently, H-atom bonded to N in one polypeptide backbone can form H-atom with O atom in another chain and vice-versa. Though they are relatively weak, these bonds offer a great staibility to secondary protein structure because they repeata great number of times.hydrogen bonding plays an important role in DNA base pairing