Plant Growth and Development
Phases of plant growth and plant growth rate
Phases of growth and growth rate
- Formative phase is the phase of cell formation / cell division (or) meristematic phase and the cells of the region are rich in protoplasm with large nucleus and thin cellulosic wall.
- Enlargement phase show plastic extension via enzymatic loosening of micro fibrils and intussusception. The phase is also called as phase of cell elongation.
- Phase of differentiation occurs in a cell by attaining a particular shape, size, thickening and internal constitution, which can be also called as maturation phase.
- Increase in growth per unit time is called growth rate which is of 2 types (i) Arithmetic and (ii) Geometric rate.
- Arthmetic rate is found in root/ shoot elongation where the meristematic cells divide in such a way that one daughter cell remain meristematic while the other differentiates.
- Arthmetic growth rate can be expressed as Lt = L0 + rt
Lt = Length after time ; L0 = Length @ beginning; r = growth rate.
- Geometric growth is common in unicellular organisms when grown in nutrient rich medium.
- Geometric growth can't be sustained for longer time as some cells die due to limited availability of nutrients. Hence it leads to stationary phase.
- Plotting the growth against time will give a typical sigmoidal (or) s-curve.
- Absolute growth rate is the actual growth curve obtained by plotting growth against time which is commonly s-shaped , which can also be defined as total growth per unit time
- Relative growth rate is the growth per unit time per unit initial growth
- If there are 2 leaves which have growth 5cm2 in 1 day with the initial size of 10cm2 and 15cm2 of leaf A and B respectively. Their absolute growth rate is same, but the relative growth rate is faster in leaf 'A'.
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