Question

Show with the help of a sketch that the plants are the ultimate source of food.

Answer 1

Hint: Plants are autotrophs. The autotrophic mode of nutrition refers to the formation of one's own food with the help of inorganic sources of energy.

Complete answer:
Plants are autotrophic organisms that synthesize their own food with the help of carbon dioxide, chlorophyll, water, and sunlight. The food produced by them is the source of energy for the entire food chain present on this earth except for the saprophytic food chain. Thus, they act as the ultimate source of food.
- Photosynthesis is the natural process of conversion of solar energy into chemical energy. It results in the formation of organic compounds like carbohydrates. It can be represented chemically as:
$\begin{matrix} { 6CO }_{ 2 } \\ Carbon\quad dioxide \end{matrix}+\begin{matrix} { H }{ _{ 2 }{ O } } \\ Water \end{matrix}\xrightarrow [ Light ]{ } \quad \begin{matrix} { C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 } \\ Glucose \end{matrix}\quad +\quad \begin{matrix}{ 6O }_{ 2 } \\ Oxygen \end{matrix}$

- It is mainly responsible for the formation of oxygen that sustains all life forms on the earth.
- The plants contain membrane- bound organelles known as chloroplasts. They consist of a stack of membranous cells called grana. Each cell of a granum is called a thylakoid that contains the chlorophyll molecules.
- Different types of pigments present in plants are chlorophyll a, b, c, d, xanthophylls, and carotenoid.
- Chlorophyll ‘a' forms the reaction center in the plastids and is the primary chlorophyll pigment, rest all are accessory pigments.
- Chlorophyll ‘b’ is responsible for absorbing the sunlight and passing it to the reaction center.
- The process can be differentiated into two phases- Light- dependent reactions and Light independent reactions.
- The light reaction involves the photolysis of water. The sunlight breaks the water molecule into hydrogen, oxygen, and electrons. The hydrogen and electrons produced are used to produce NADPH from NADP and ATP from ADP. 
- The NADPH and ATP are then transferred to the Light independent reactions that include conversion of carbon dioxide into organic compounds like sugars.
- The primary sugar produced during photosynthesis is glucose. It remains stored in the form of starch in different parts of the plant.

Note: Chlorophyll a is present in all photosynthesizing organisms Chlorophyll b is present in higher plants, pteridophytes, bryophytes, and blue- green algae. Chlorophyll c and d are found in brown algae; diatoms and red algae respectively. Whereas, Chlorophyll e is present in the algae of class Xanthophyceae such as Vaucheria and Botrydium.