The raw materials for photosynthesis are water and carbon (IV) oxide gas. For the process to take place, it requires the presence of light and chlorophyll.

Water and carbon (IV) oxide undergo several chemical processes in the presence of sunlight to form organic compounds( carbohydrates, lipids and proteins) and oxygen is given out as a byproduct.

General equation:

Carbon (IV) oxide + water ================ Glucose + Oxygen

6CO₂ + 6H₂O ================== C₆H₁₂O₆  + 6O₂

The process involves chemical reactions that can be outlined in two general stages. These are the light stage and dark stage.

The Light Stage (Light dependent stage)

• The chlorophyll molecules absorb light energy which is used to split water molecules into oxygen and hydrogen atoms. this process is called photolysis of water
• The hydrogen atoms that are produced by splitting of water enter the dark stage.
• some of the solar energy absorbed by chlorophyll molecules is used in the formation of energy rich Adenosine Triphosphate (ATP) which is later used in the dark stage.

The Dark Stage ( Light Independent Stage)

• This process involves carbon (IV) oxide combing with hydrogen atoms to form a simple sugar such as glucose. This process is known as carbon (IV) oxide fixation.

Carbon (IV) oxide  +  Hydrogen ions ======== simple carbohydrate  + water

CO₂ + 4H⁺ ============= (CH2O)₂ + H₂O

• The energy required for this reaction is provided by ATP from light stage reaction.

Factors affecting the rate of photosynthesis

Light intensity- the rate of photosynthesis increases with increase in light intensity, up to a certain point when it slows down and finally stops.

Carbon (IV) oxide Concentration- under controlled conditions like in a green house, an increase in carbon (IV) oxide concentration results in a linear increase in the rate of photosynthesis up to a certain level when it slows down and finally remains steady.

Temperature- photosynthesis is an enzyme controlled process. Enzyme controlled reactions are affected by temperature in the following ways:

At low temperature the rate of photosynthesis is low, as temperature increases the rate of photosynthesis increases up to about 40^oC.

Further increase in temperature above 40^oC, results in a sharp decrease in the rate of photosynthesis finally leading to cessation of photosynthesis. This is because excess heat denatures the enzymes that control the process of photosynthesis.

Water- plants need water for photosynthesis.

After reading the content above answer the following questions:

(a) Explain how chloroplasts are adapted to their photosynthetic functions.

(b) what is the importance of the light dependent reaction in the process of photosynthesis?

(c) what are the products of the light stage in photosynthesis?

(d) which gas is produced during photosynthesis?

(e) name the factors that affect photosynthesis in plants.

• Take 10 minutes to write your on the exercises response before clicking on the feedback.