`star` Growth rates
`star` Growth Conditions


● The `color{violet}"increased growth"` per unit time is termed as `color{Brown}"growth rate"`.

● Thus, `color{violet}"rate of growth"` can be `color{violet}"expressed mathematically"`.

● An organism, or a `color{violet}"part of the organism"` can produce more cells in a `color{violet}"variety of ways"`.

● The `color{violet}"growth rate"` shows an increase that may be `color{vBrown}"arithmetic or geometrical"`.

● In `color{Brown}"arithmetic growth"`, following `color{violet}"mitotic cell division"`, only `color{violet}"one daughter cell"` continues to divide while the `color{violet}"other differentiates"` and matures.

● The `color{violet}"simplest expression"` of arithmetic growth is exemplified by a `color{violet}"root elongating"` at a `color{violet}"constant rate"`.

● On `color{violet}"plotting"` the `color{violet}"length of the organ"` against `color{violet}"time,"` a `color{Brown}"linear curve"` is obtained.

● `color{violet}"Mathematically"`, it is expressed as

`L_t` = `L_0` + `rt`
`L_t` = length at time `t`
`L_0` = length at time ‘zero’
`r` = growth rate / elongation per unit time.

● Let us now see what happens in `color{Brown"geometrical growth"`.

● In `color{violet}"most systems,"` the`color{violet}" initial growth is slow"` (`color{Brown}"lag phase"`), and it `color{violet}"increases rapidly"` thereafter – at an `color{violet}"exponential rate"` (`color{violet}"log or exponential phase"`).

● Here, both the `color{violet}"progeny cells"` following mitotic cell division retain the `color{violet}"ability to divide"` and continue to do so.

● However, `color{violet}"with limited nutrient supply"`, the growth slows down leading to a `color{Brown}"stationary phase"`.

● If we plot the `color{violet}"parameter of growth"` against time, we get a t`color{violet}"ypical"` `color{Brown}"sigmoid or S-curve"`

● A `color{violet}"sigmoid curve"` is a characteristic of `color{violet}"living organism"` growing in a `color{violet}"natural environment"`.

● It is typical for all `color{violet}"cells, tissues"` and `color{violet}"organs of a plant"`.

● The `color{violet}"exponential growth"` can be `color{violet}"expressed"` as

`W_1` = `W_0e^(rt)`
`W_1` = final size (weight, height, number etc.)
`W_0` = initial size at the beginning of the period
`r` = growth rate
`t` = time of growth
`e` = base of natural logarithms

● Here, `color{Brown}"r"` is the `color{violet}"relative growth rate"` and is also the measure of the `color{violet}"ability of the plant"` to produce new plant material, referred to as `color{Brown}"efficiency index"`.

● Hence, the `color{violet}"final size"` of `W_1` depends on the i`color{violet}"nitial size"`, `W_0`.

● `color{violet}"Quantitative comparisons"` between the `color{violet}"growth of living system"` can also be made in two ways :

(i) `color{violet}"Measurement"` and the `color{violet}"comparison"` of total growth per unit time is called the `color{Brown}"absolute growth rate"`.

(ii) The `color{violet}"growth"` of the `color{violet}"given system"` per `color{violet}"unit time"` expressed on a common basis, e.g., per unit initial parameter is called the `color{Brown}"relative growth rate"`.

● In Figure `color{violet}"two leaves,"` `color{vBrown}"A and B,"` are drawn that are of `color{violet}"different sizes"` but shows absolute `color{violet}"increase in area"` in the given time to give `color{violet}"leaves"`, `A_1` and `B_1`.

● However, one of them shows much `color{violet}"higher relative growth rate"`.


● There are `color{violet}"many necessary conditions"` for growth.

● This list may have `color{violet}"water, oxygen"` and `color{violet}"nutrients"` as very `color{Brown}"essential elements"` for growth.

● The plant cells `color{violet}"grow in size"` by `color{violet}"cell enlargement"` which in turn requires `color{Brown}"water."`

● `color{violet}"Turgidity of cells"` helps in `color{violet}"extension growth"`.

● Thus, `color{violet}"plant growth"` and `color{violet}"further development"` is intimately linked to the `color{violet}"water status"` of the plant.

● `color{violet}"Water"` also provides the `color{violet}"medium for enzymatic activities"` needed for growth.

● `color{Brown}"Oxygen"` helps in releasing `color{violet}"metabolic energy essential"` for growth activities.

● `color{Brown}"Nutrients"` (macro and micro essential elements) are `color{violet}"required by plants"` for the synthesis of `color{violet}"protoplasm"` and act as `color{violet}"source of energy"`.

● In addition, `color{violet}"every plant organism"` has an `color{vBrown}"optimum temperature"` range best suited for its growth.

● Any `color{violet}"deviation"` from this range could be `color{violet}"detrimental to its survival."`