College Biology: Photosynthesis
Photosynthesis and transpiration rate of detached leaves of pea (Pisum sativum L. cv. Iłowiecki) exposed to solution of Pb(NO3)2 at 1 or 5 mmol·dm−3 concentrations were inhibited. The higher concentration of this toxicant decreased photosynthesis and transpiration rates 2 and 3 times respectively, and increased respiration by about 20 %, as measured after 24 hours of treatment. Similarly to Pb(NO3)2, glyceraldehyde solution, an inhibitor of phosphoribulokinase, at 50 mmol·dm−3 concentration decreased the rates of photosynthesis and transpiration during introduction into pea leaves. The rate of dark respiration, however, remained unchanged during 2 hours of experiment.
High School Biology - Photosynthesis
In other words, respiration is the opposite of photosynthesis.Respiration doesn’t depend on light; it goes on 24 hours a day, so that plants and animals have enough energy to perform the basic functions that keep them alive.However, during the day, the amount of oxygen plants release as part of photosynthesis makes the amount of oxygen they consume for respiration seem negligible.At night, when photosynthesis can’t take place, plants continue to consume oxygen but they don’t release any back into the room.
Dissolved oxygen concentration in ponds fluctuates on a 24-hour basis. This fluctuation is called a diurnal oxygen cycle. Dissolved oxygen increases during daylight hours when photosynthesis is occurring and decreases at night when respiration continues but photosynthesis does not.