Question

What is the various factors which affect the rate of photosynthesis 0?

Answer 1

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Here is your answer,
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Various external factors which affect the rate of photosynthesis are :-
1. Light
2. Carbon-dioxide
3. Temperature
4. Water

Internal factors affecting photosynthesis are :-
1. Chlorophyll
2. Accumulation of photosynthesis products .
3. Presence of ions

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Answer 2

NCERT based Answer for Class 11 Biology Students

Following are the factors which affect the rate of photosynthesis:

Light:  

 Light quality, light intensity and light duration affect photosynthesis.

 Light saturation occurs at 10% of full sunlight.

 Hence except for plants in shade or in dense forest, light is rarely a limiting factor in nature.

 At higher light intensities, the rate of  photosynthesis decreases because of two reasons:

• Other factors become limiting.

• Destruction of chlorophyll occurs in presence of O2 and is called photo oxidation.

Note: Carotenoids play a protective role by absorbing excess light and diverting it away from chlorophyll, preventing photooxidation.

Temperature:

 Dark reactions are more sensitive to temperature than light reactions.

 Affinity of enzyme RuBisCO for CO2 reduces at higher temperature.

 C3 plants have lower temperature optimum.

 In C4 plants, rate of photosynthesis increases with increasing temperature.

 Temperature optimum for photosynthesis differs as the habitat changes.

• Tropical plants have higher temperature optimum.

• Temperate plants have lower temperature optimum.

CO2 concentration:

 It is major limiting factor.

 The concentration of CO2 is very low in atmosphere (0.03 to 0.04%).

 Increase in concentration upto 0.05% can cause an increase in CO2 fixation rate.

Note:

 C3 and C4 plants respond differently to CO2 concentrations.

 C4 plants show saturation at about 0.036% while C3 plants show saturation beyond 0.045%.

 Thus, current level of atmospheric CO2 is limiting to C3 plants.

 The increased rate of photosynthesis in C3 plants at higher CO2 level would be due to two factors:

• High availability of substrate (CO2) for carboxylation reaction.

• Reduced photorespiration due to more available CO2 to RuBisCO.

 Some C3 greenhouse crops such as tomatoes and bell pepper are grown in CO2 enriched atmosphere that leads to higher yields.

Soil water:

 If soil water becomes limiting, plants undergo water stress.

 Under water stress, the rate of photosynthesis declines because of two factors:

• Stomatal closure and resultant decrease in CO2 supply.

• Reduced leaf water potential.

 Low leaf water potential reduces leaf expansion by causing wilting. This results in significant reduction in photosynthetic surface area.

Nutrient supply:

 Among various nutrients, nitrogen has a direct relationship with photosynthesis.

 Nitrogen is a basic constituent of chlorophyll and all enzymes involved in carbon reactions.

 Any reduction in nitrogen supply has an adverse effect on photosynthesis.

Leaf factor:

 If a leaf undergoes senescence (ageing), loss of chlorophyll occurs.

 Photosynthetic enzymes also get deactivated, resulting in reduced photosynthesis in a senescent leaf.

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