07 Plant Growth and Mineral Nutrition - part 04 - Growth Rate and types of growth

07 Plant Growth and Mineral Nutrition - part 04 - Growth Rate and types of growth


Growth Rate and types of growth : 

Growth rate : 
  • It is the increased growth per unit time. 
  • It is also called efficiency index. 
  • Rate of growth can be measured by an increase in the size and area of different plant organs like leaf, flower and fruits. 
  • The ratio of change in the cell number (dn) over the time interval (dt) is called Absolute growth rate (AGR). 
  • Alternatively, it is the measurement and comparison of total growth per unit time.
  • The AGR, when divided by total number of cells present in the medium, gives Relative growth ratio (RGR). 
  • Alternatively, RGR refers to the growth of a particular system per unit time, expressed on a common basis or it is the ratio of growth in the given time/ initial growth. 
  • AGR and RGR are useful in describing the dynamics of cell growth in culture. 
Types of growth : 
  • There are two types of growth viz- 
  1. Arithmetic growth and 
  2. Geometric growth. 
1. Arithmetic growth : 
  • Here, rate of the growth is constant and an increase in the growth occurs in arithmetic progression. i.e. 2, 4, 6, 8 cms etc.
  • In this type of growth, the rate of growth is constant. 
  • After mitosis one of the daughter cell continues to divide and the other cell takes part in the differentiation and maturation. 
  • e.g. elongation of root at a constant rate, best explains arithmetic growth. 
  • Linear curve is obtained when growth rate is plotted against the time. 
  • Arithmetic growth is expressed mathematically by an equation, 
  • It is expressed as, Lt = Lo + rt Where 
  1. Lt = Length at time `t' 
  2. Lo = Length at time `Zero' 
  3. r = Growth rate 
  4. t = Time of growth 
  • When graph of length (L) is plotted against the time (t), a linear curve is obtained as indicated in the diagram. 
2. Geometric growth : 

  • Cell divides mitotically into two. 
  • Here, both the daughter cells continue to divide and redivide repeatedly.Such growth is called geometric growth. 
  • Here, growth rate is slow initially but later on there is a rapid growth at exponential rate. 
  • Geometric growth can be expressed mathematically by an equation.
  • We can also observe quantitative comparison between the growth of living system in two ways. 
  • Measurement and comparisons of total growth per unit time is called the Absolute growth rate(AGR) 
  • The growth of the given system per unit time expressed on a common basis per unit initial parameter is called the Relative growth rate(RGR).
  • In the above example, two leaves `A' and `B' are of different sizes but show same absolute increase in area in a given time. 
  • Both leaves grow and increase their area by 5cm2 to produce `A' and `B' leaves. 
  • `A' leaf of 5cm2 in size grows 5cm2/ day then its RGR would be 100%.
  •  If the leaf is 50cm2 in size and the growth rate/day is 5cm2 then its RGR would become 10%. 

Comments

Post a Comment

Popular posts from this blog

6. Biomolecules - part 01 - Carbohydrates

Image
  6. Biomolecules - part 01 - Carbohydrates Introduction : Our planet is having a wide diversity of living organisms that are classified as - unicellular  (consisting of a single cell; including bacteria and yeast) or  multicellular  having many cells (e.g. plants and animals).  living organisms have cell as the basic structural and functional unit.  The cells have protoplasm containing numerous chemical molecules, the biomolecules. Biochemistry  : Biochemistry is  biological chemistry  that provides us the idea of the chemistry of living organisms and molecular basis for changes taking place in plants, animals and microbial cells.  It develops the foundation or understanding  all biological processes  and communication within and between cells as well as chemical basis of inheritance and diseases in animals and plants. Chemical analysis of all living organisms indicates presence of the most common elements like  carbon, h...
Read more

6. Biomolecules - part 02 - Lipids

Image
  6. Biomolecules - part 02 - Lipids B. Lipids : These are group of substances with greasy consistency with  long hydrocarbon chain containing carbon, hydrogen and oxygen. In lipids, hydrogen to oxygen ratio is  greater than 2:1  (in carbohydrates it is always 2:1). Lipid is a broader term used for fatty acids and their derivatives.  They are soluble in organic solvents (non-polar solvents).  Fatty acids are organic acids which are composed of hydrocarbon chain  ending in carboxyl group (-COOH).  They can be  saturated fatty acids  with no double bonds between the carbon atoms of the hydrocarbon chain.  Palmitic and stearic acids  found in all animal and plant fats are examples of saturated fatty acids. Unsaturated Fatty Acids  are with one or more double bonds between the carbon atoms of the hydrocarbon chain.  Oleic acid  found in nearly all fats and  linoleic acid  found in many seed oils are example...
Read more

6. Biomolecules - part 05 - Enzymes

Image
  6. Biomolecules - part 05 - Enzymes Enzymes : Thousands of different chemical reactions take place automatically at a given time in a tiny living cell. The reactions take place at the body temperature.  If these enzymes were not present in the cell, either the reactions would not occur or if they occur they would occur at a  very very slow rate . Know the scientists : German chemist  Edward Buchner  discovered enzymes by accident.  Buchner discovered that living cells were not necessary but that  yeast  extract could bring about fermentation.  He then coined the term Enzyme (Gk. En = in, zyma = yeast i.e. in yeast). This term is now commonly used for all biocatalysts. Each enzyme catalyzes a small number of reactions, specifically perhaps only one. Substrate :  The substance upon which an enzyme acts is termed as the substrate.  Endo-enzymes :  The enzymes which act within the cell in which they are synthesizedare known as en...
Read more