8. Respiration and circulation

All living organisms require energy to carry out various life processes. The energy that is stored in the body in the form of complex organic compounds (potential energy) is however not usable by the organisms unless it is converted into usable form. This conversion is achieved through the process of respiration.

Respiration: It is a biochemical process of oxidation of organic compounds in an orderly manner for the liberation of chemical energy in the form of ATP.

For this, the process of gaseous exchange takes place between the organism and the environment. The site of gaseous exchange is called the respiratory surface.

Organs of Respiratory Exchange:

 Respiratory exchange is a simple physical process. For efficient gaseous exchange, the respiratory surface should have the following features: -

a. It should have a large surface area.

b. It should be thin, highly vascular and permeable to allow exchange of gases.

c. It should be moist.

Gaseous exchange in plants:

1.      The shape and structure of plants facilitate gaseous exchange by diffusion.

2.       A terrestrial flowering plant has many air spaces between the cells of stem, leaf and root.

3.       These air spaces are continuous. Oxygen diffuses into the air space through stomata (the pores on leaves and young stems), carbon dioxide and water vapour diffuse out.

4.      In the aerated soil, the oxygen dissolves in the film of moisture or water around the root tissue and enters it by diffusion.  

5.      Woody flowering plants (trees and shrubs) have an external impervious bark. Here, gaseous exchange occurs through small pores in the stem surface, called lenticels.

Respiration in Animals:

1.      As compared to plants, animals show wide variety of respiratory surfaces or organs.

2.      The respiratory surfaces differ in various animals.

3.      In animals, depending upon the complexity of organization and the surrounding medium, certain parts of the body have become specialized into different types of respiratory organs.

4.       In the higher animals, these respiratory organs are also associated with a transport system.

07. Plant Growth and Mineral Nutrition

Introduction :-

         Growth is one of the characteristic features of living organisms. Growth as a phenomenon has two aspects viz. quantitative and qualitative. 
        Quantitative aspect :- It is about the  increase in the length, breadth, size, volume, body mass or dry weight and number of cells. Growth as  a quantitative  change is a final end product of successive metabolism.
       Qualitative aspect :- It is  about the change in the nature of growth where development is an ordered change or progress while differentiation leads to higher and more complex state. 
      Growth thus can be defined as permanent, irreversible increase in the bulk / mass of an or-ganism, along with the change of form.
       In multicellular (vascular) plants, growth is indeterminate and occurs throughout the life indefinitely.

Root and stem show indefinite or indeterminate growth.
While, in organs like leaves, flowers and fruits, growth is determinate. i.e. they grow up to certain genetically destined size.
In unicellular plants, growth  is  uniform  and  determinate.

     Growth is restricted to some specific region called meristems.  Meristems are of three types based on location viz. Apical, Intercalary and Lateral.