Factors Affecting Photosynthesis//factors afffecting the rate of photosynthesis//external factors//enternal factors ///Blackman's low of limiting factors///

 

Factors Affecting Photosynthesis

 

Photosynthesis is affected by various factors. These factors are grouped into two categories the external and the internal factors, as follows-

1.    External factors or Environmental factors:

These include (a) Light, (b) Carbon dioxide, (c) Temperature, (d) Water, (e) Oxygen and (f) Mineral elements.

(   a) Light: 

Light is the ultimate source for photosynthesis in green plants. Plants getting average light for 10-12 hours a day show higher rate of Photosynthesis.

Chlorophyll (Photosynthetic pigment) absorbs blue and red light so plants show high rate of photosynthesis in blue and red light.

When light falling on a leaf about 80% is absorbed, and near about 15 to 18% is transmitted. Only a very small fragment of light is utilizes for photosynthesis.

Rate of photosynthesis increases with light intensity but a very high light intensity the cell exhibit photo-oxidation by solarization (If this continues for few hours the photosynthetic apparatus is destroyed like chlorophyll).

Requirement of light intensities are varies from plants to plants like some plants require low light intensity for optimum photosynthesis is called sciophytes.  On the other hand some plants require high  intensity for optimum photosynthesis are called Heliophytes.

  (b) Carbon dioxide:

The concentration of Carbon dioxide is very low in the atmosphere is about 0.03%.  

If increase the concentration of CO₂  rate of photosynthesis increase but  very high  concentration CO₂ becomes toxic to plants and inhibit photosynthesis.

(   c)  Tempertaure-

Usually the rate of photosynthesis increases by increase in temperature upto 40%.

At the above this temperature the rate of photosynthesis decreases and high temperature results into deactivation of enzymes.

Requirement of optimum temperature for photosynthesis is varies with the plant species.

Photosynthesis stops in many plants at 0°C but in some conifers it occurs even at -35°C and some algae undergo photosynthesis at 75°C.

d) Water:

Water is essential raw material in photosynthesis. Water deficiency decreases the rate of photosynthesis.

Water stress causes the stomata to close hence reducing the CO₂ availability. Besides this water stress also causes leaves wilt.

e) Oxygen:

Increase in oxygen concentration decreases the rate of photosynthesis as it results in photorespiration and oxygen competes with CO₂  and destroys the excited state of chlorophyll and thus inhibits photosynthesis.

f) Mineral elements:

Mineral elements like Mg, Cu, Cl, Mn, phosphorus closely associated with key reactions of photosynthesis. Deficiency of these minerals elements  reduces photosynthesis.

2. Internal Factors:

These include (a) Chlorophyll content, (b) Protoplasmic factor, (c) Accumulation of carbohydrates (d) Structure of Leaves.

a) Chlorophyll content:

Chlorophyll is an essential internal factor for photosynthesis.

Emerson found the direct relationship between chlorophyll  contents and the rate of photosynthesis.

 But   Willstatter and stall indicates that chlorotic leaves photosynthesize almost rapidly as the normal leaves.

b) Protoplasmic factor:

Some unknown protoplasmic factors are believed to affects the rate of photosynthesis.

c) Accumulation of Carbohydrates:

Accumulation of Carbohydrates in plant cell inhibits the photosynthetic rate.

If food materials are not translocated the process of respiration increases.

Due to which sugar is converted to starch which accumulates in the chloroplasts.

This reduces the effective surface in the chloroplast and the rate of photosynthesis is decreased.

d) Structure of Leaves:

In leaves position and distribution of stomata, intercellular spaces, vascular tissue etc. also affects the rate of photosynthesis.