Respiration in plants
(i) All the parts of the plants perform respiration individually.
(ii) During respiration in plants there is a little transport of respiratory gases from one part of the plant to the other.
(iii) The respiration in plants occurs at a slow rate. Respiration in Animals
(i) An animal perfomrs respiration as a single unit.
(ii) Respiratory gases are usually transported over long distances inside an animal during respiration.
(iii) The respiration in animals occurs at a much faster rate.
(b) (i) During daytime when photosynthesis occurs, oxygen is produced. The leaves use some of this oxygen for respiration and the rest of oxygen diffuses out into the air. Carbon dioxide produced by respiration is all used up in photosynthesis by leaves during the daytime. Even more carbon dioxide is taken in from air. Thus, the net gas exchange in leaves during daytime is: Oxygen diffuses out; Carbon dioxide diffuses in.
(ii) At night time, when no photosynthesis occurs and hence no oxygen is produced, oxygen from air diffuses in leaves to carry out respiration. Carbon dioxide produced by respiration diffuses out into air. So, the net gas exchange in leaves at night is: Oxygen diffuses in; Carbon dioxide diffuses out.
(c) Exhaled air contains more carbon dioxide because during the respiration process when oxygen breaks down glucose, then a lot of carbon dioxide is produced hence the exhaled air has a higher proportion of the same.