BOTANY Higher Secondary Second Year - Textbooks Online

5. PLANT PHYSIOLOGY
Plant physiology is the branch of biological science, which deals with
the functioning, and interrelationships of cells, tissues and organs of plants.
Green plants have the capacity of harvesting light energy for life energy,
making use of inorganic raw materials. Most of the living organisms
including man depend upon this energy rich compounds of plants. Plants
not only provide food but also supply required oxygen for breathing.
Besides synthesizing organic compounds, plants carry other natural
phenomena of living organisms such as respiration, growth and
development. In this chapter, we study these natural phenomena operating
in plants. Though the plants do not have respiratory, circulatory and
digestive systems like animals, all these functions are carried out at cellular
level.
5.1. Enzymes
Enzymes are biological catalysts, which activate various biochemical
reactions of a living cell in a highly specific and precise manner. Enzymology
is the study of enzymes. The name enzyme was coined by Kuhne in 1878.
Pasteur recognised that some microorganisms like yeasts have got a capacity
to cause fermentation in wine. In 1897, Buchner discovered that yeast
extract could bring about fermentation of grape juice, like the living yeast
cells. He also observed that the extract has lost its catalytic activity on
boiling. He coined the word zymase for the active principle involved in
the fermentation. The substance on which the enzyme acts is called substrate.
Enzymes are essentially proteins but all proteins are not enzymes.
+
Apoenzyme Prosthetic group Holoenzyme
Fig. 5.1. Protein and nonprotein part of an enzyme
168