rate and is also the measure of the ability of the plant to produce new plant material, referred to as efficiency index. Hence, the final size of W depends on the initial size, W . Figure . Constant linear growth, a plot of length L against time t Figure .
An idealised sigmoid growth curve typical of cells in culture, and many higher plants and plant organs Size/weight of the organ Exponential phase Lag phase Time Stationary phase Quantitative comparisons between the growth of living system can also be made in two ways : (i) measurement and the comparison of total growth per unit time is called the absolute growth rate. (ii) The growth of the given system per unit time expressed on a common basis, e.g., per unit initial parameter is called the relative growth rate. In Figure . two leaves, A and B, are drawn that are of different sizes but shows absolute increase in area in the given time to give leaves, A and B .
However, one of them shows much higher relative growth rate. Which one and why? . .
Conditions for Growth Why do you not try to write down what you think are necessary conditions for growth? This list may have water, oxygen and nutrients as very essential elements for growth. The plant cells grow in size by cell enlargement which in turn requires water. Turgidity of cells helps in extension growth.
Thus, plant growth and further development is intimately linked to the water status of the plant. Water also provides the medium for enzymatic activities needed for growth. Oxygen helps in releasing metabolic energy essential for growth activities. Nutrients (macro and micro essential elements) are required by plants for the synthesis of protoplasm and act as source of energy.
In addition, every plant organism has an optimum temperature range best suited for its growth. Any deviation from this range could be detrimental to its survival. Environmental signals such as light and gravity also affect certain phases/stages of growth. Figure13.
Diagrammatic comparison of absolute and relative growth rates. Both