Aquatic ecology and Biodiversity

Unit 5- Productivity

5.1.2. Photosynthesis
Photosynthesis is an “anaerobic “process in which organic matter is synthesized from CO2 and water by green plants using radiant energy of the sun and liberate oxygen and energy as by product of photosynthesis
6C0₂+ 6H₂O ----------> C₆H₁₂O₆ + 6O₂ + Energy
Photosynthesis is the process by which plants, some bacteria, and some protistans use the energy from sunlight to produce sugar which cellular respiration converts into ATP, the "fuel" used by all living things. The conversion of unusable sunlight energy into usable chemical energy is associated with the actions of the green pigment chlorophyll.
We can write the overall reaction of this process as:
6H₂O + 6CO₂ ----------> C₆H₁₂O₆+ 6O₂
The above chemical equation translates as: Six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen.

The chlorophyll contained in specific chloroplasts in the plant cells. The important pigments are chlorophyll a, b, c, d etc. The cells also contain other pigments - carotenoids and xanthophylls and some algae contain phycobilins Plastids or chloroplast contains chromatophores which carry pigments. Chloroplasts vary in size, bounded by a double membrane and that stack of membranes present inside the chloroplast. The discs are the chlorophyll containing structures arranged as regular chlorophyll molecules.
Note: In blue green algae chlorophyll is arranged in a network of lamella inside the cell
Plants convert light energy into chemical energy by photosynthesis. The total amount of organic matter produced by plants in a unit area per unit time is referred to gross primary production. This is also called total production or productivity.

The total organic material stored in plants is called net primary production.

( P_n = P_g – R)

Net primary production = Gross production – respiration

(P_g = P_n-R)

6CO₂ + 6H₂O + light ---------->C₆H₁₂O₆+ 6O₂+ Energy Calories (Photosynthesis)
Carbon dioxide + water + sunlight + nutrients ----------> Simple sugar + oxygen
C₆H₁₂O₆ + 6O₂ ----------> 6CO₂ + 6H₂O + Energy calories (Respiration)
Simple sugar (food) + Oxygen → Carbon dioxide + water + energy (heat)
Where, P_g = gross primary production

P_n = Net primary production

R = Respiration

Thus, the amount of organic material produced in a unit area during a given period is called primary production. Productivity is expressed as grams C / m² / day.

If Pg = R – No storage

Pg < R – Productivity decreases

Pg > R- Productivity increases