Growth Rates and Growth Curves in Biology

• S-shaped logistic growth curve includes 3 phases:
• Lag phase - When some organisms are introduced in an area, the population growth begins slowly.
• Log phase - The conditions are ideal and the maximum growth rate is reached.
• Stationary phase - Growth rate begins to slow down as factors such as food, water and space become limiting.
  

The resources for the growth of most animal population are finite and become limiting sooner or later, thus the logistic growth model is considered more realistic. The equation for model gives a sigmoid shaped graph when plotted against the N in relation to time.  The equation is :

Annual rings are distinct and prominent in plants growing in temperate regions where climatic conditions vary sharply between seasons. In tropical regions, seasonal variations are not distinct, so annual rings are typically indistinct or absent.

In a typical sigmoid (S-shaped) growth curve, the growth rate is slow initially during the lag phase, accelerates exponentially to its maximum during the log (exponential) phase, and finally slows down in the stationary phase.

$G _1-$ phase is the period when the cell grows and carries out normal metabolism. 

Ectomycorrhiza is a symbiotic association between fungi and the roots of higher plants, where the fungal hyphae form a sheath around the root and inter-cellularly network in the cortex.

In most systems, the initial growth is slow (lag phase), and it increases rapidly thereafter,  at an exponential rate (log or exponential phase). Here, both the progeny cells following mitotic cell division retain the ability to divide and continue to do so. However, with limited nutrient supply, the growth slows down leading to a stationary phase. If we plot the parameter of growth against time, we get a typical sigmoid or S-curve. A sigmoid curve is a characteristic of living organism growing in a natural environment. It is typical for all cells, tissues and organs of a plant.

It is a 'S' shaped curve obtained when we plot growth against time. It is also called as sigmoid curve. This curve mainly shows four phases of growth -
1. Initial slow growth (lag phase) .

Relative growth rate is defined as the increase in size per unit time divided by the initial size, expressed as (1/W) * (dW/dt).

During pre-natal growth, there is an increase in the number of cells of the organism. So, this kind of growth is referred to as multiplicative or embryonic growth.
Hence, the correct answer is option (C), 'Multiplicative'.

Growth curve has three different phases as :
1. Lag phase (where cell prepares for growth),
2. Log phase (where cell actually grows) and
3. Stationary phase (growth ceases).
Thus, these three phases indicates different parameters of growth at different levels. Hence, the correct answer is option (A) - 'A growth parameter at various interval'.

Exponential growth is the increase in number or size at a constantly growing rate. It occurs when resources availability is unlimited each species has the ability to realise fully its potential to grow in number.

So, the correct option is 'All of the above'.

During the exponential or log phase of plant growth, the growth rate is at its maximum, representing the speedy or rapid growth phase where cells divide and increase in size at the fastest rate.

There are two types of population growth, geometric growth and logistic growth. Geometric growth is also called as exponential growth. Logistic growth is S shaped growth. Arithmetic growth is a linear growth. During cell division, cell divides into two. It increases cell number. During cell differentiation, cell specializes into different cell type. If division and differentiation are cocurrent then there will be negative control. It will regulate the cell division. Hence, the growth will be logistic.

In a sigmoid growth curve, there are three phases, lag phase, exponential phase and steady state phase. The upper limit of the curve is called as upper asymptote. It represents the period of equilibrium. At this stage, birth rate and death rate are at balance. It is said to be at equilibrium because at this stage, there is equilibrium between biotic potential and environmental resistance.

Ethylene is a gaseous hormone which stimulates the transverse growth but inhibits the longitudinal growth. Auxin delays the abscission of young leaves and provides nutrition to it so that they do not die down while ethylene increases the senescence of leaves and flowers and produces more gas which leads to loss of leaves.

J-shaped growth curve is a curve on a graph that records the situation in which, in a new environment, the population density of an organism increases rapidly in and exponential or logarithmic form, but then stops abruptly as environmental resistance or some other factor suddenly becomes effective. The actual rate of population change depends on the biotic potential and population size. It may be summarized mathematically as 

The stationary phase is the phase in which the growth of lant generally stops and the plant proceeds towards maturity it may occur due to the lack of nutrients majorly seen in the unfavourable season.

In geometrical growth both the progeny cells following mitotic cell division retain the ability to divide and continue to do so. However, with a limited supply of nutrients, the growth becomes slow which lead to the stationary stage. A sigmoid curve is the characteristic of organism living is the natural environment.

An auxanometer is a device used to measure the rate of growth in the length of a plant stem.