Photosynthesis 1

Photosynthesis – the process via which plants use simple inorganic molecules in the presence of sunlight to make complex organic food.

Worded equation: carbon dioxide + water >>>>> glucose + water

Chemical Equation: 6CO2 + 6H2O >>>>> C6H12O6 + 6O2

The above reaction can only occur in the presence of sunlight, chloropyll and enzymes.

Photosynthesis is also know as autotrophic nutrition. Before we go any further let us contrast autotrophic nutrition and heterotrophic nutrition.


Autotrophic nutrition
Includes all plants and some protists (those containing chlorophyll)
Uses inorganic CO2 and H2O to make complex food (glucose)
Energy source from sunlight
Building up process: photosynthesis

Heterotrophic nutrition
Includes animals, some protists, fungi, bacteria, viruses
Uses complex organic molecules (fats, proteins, carbohydrates)as food
Energy source from food
Process: intake of food, digestion and assimilation

There are different categories of heterotrophic nutrition and these include:
1. Holozoic: digestion assimilation and absorption occurs inside the body. Eg. Most animals and some protists such as the Amoeba sp.
2. Saprophytic: digestion occurs outside the body as enzymes are passed out from the body onto the food.
3. Parasitic: organisms which exhibit this type of nutrition, usually has no digestive system as they obtain digested food from other organisms (host).


Photosynthesis occurs in chlorophyll molecules and has 2 stages:

1. The light dependent (light) stage: UV rays from the sun splits water molecules into hydrogen and oxygen. The oxygen is released into the atmosphere as waste via the stomata. While the hydrogen is used in the light independent stage.

2. The light independent (dark) stage: hydrogen is chemically combined with carbon dioxide in the presence of enzymes to form glucose. (This can occur with or without light as it occurs independent of light).

N.B.
1.The UV rays from the sun breaks the bonds that holds the atoms in a water molecule together thus separating them.
2. The enzymes are need to increase the rate of reaction so it can occur in a timely manner.

What happens to glucose after it is made?

The fate of glucose after it is made:
1. Some is used in respiration to provide energy need by the plants.
2. Some is converted to sucrose for transport around the plant.
3. Some is used to make other substances need for the plants survival eg. hormones, vitamins, lipids, proteins ect.
4. The excess is converted to starch for storage.