This document discusses various factors that affect the process of photosynthesis. It identifies external factors like carbon dioxide, light, temperature, water, and DCMU, as well as internal factors like the chlorophyll content of leaves. It explains that according to Blackman's law of limiting factors, the rate of a process is determined by the factor that is closest to its minimum value, and provides examples of how temperature and other conditions can limit photosynthesis. Key factors discussed in more depth include temperature, carbon dioxide, light, oxygen, and water.

1. FACTORS AFFECTING
PHOTOSYNTHESIS
Ms Saajida Sultaana Mahusook

2. There are various factors affecting photosynthesis
External Factors Internal Factors
•Carbon dioxide
•Light
•Temperature
•Water
•DCMU (3-(3,4-dichlorophenyl)-1,1-
dimethylurea).
•Chlorophyll content of leaves
•Protoplasmic factor
•Accumulation of byproducts
•Leaf anatomy
•Age of leaf
•Hormones

3. Blackman’s law of limiting factors
‘When a process is conditioned as to its rapidity by a
number of separate factors, the rate of the process is
limited by the pace of the slowest factor’.
 This implies that if more than one factor affects a
chemical process, then its rate will be determined by a
factor which is nearest to its minimal value. It is the factor
which directly affects the rate if its quantity is changed.
 Example: Despite the presence of a green leaf and
optimal light and CO2 conditions, the plant may not
photosynthesise if the temperature is very low. This leaf
will start photosynthesising if provided with the optimal
temperature.

4. TEMPERATURE
 The rate of photosynthesis increases with a rise in
temperature, over a range from 6°C to about 37°C. Above this
temperature, there is an abrupt fall in the rate and the tissue
dies at 43°C.
 High temperatures cause the inactivation of enzymes and
therefore affect the enzymatically controlled ‘dark’ reactions of
photosynthesis.
 The optimum temperature for the maximum falls between 20-
30°C.
 Above 25-30°C the maximum rate is not maintained as the
time factor begins to operate and the optimum temperature is
reduced from 37°C to 30°C.

6. CARBONDIOXIDE
 The concentration of CO2 in atmosphere varies
between 0.03% and 0.04%.
 Increase in the concentration of CO2 up to 0.05%
increases CO2 fixation.
 The increase in the amount of carbon dioxide
increases the photosynthesis.
 Higher concentrations have an inhibitory effect on
photosynthesis.

8. LIGHT
Solar radiation is the source of light for photosynthesis. The quality,
intensity and duration of light affect the rate of photosynthesis.
Quality of Light
 Light between the wavelength of 400 nm and 700 nm is the most
effective for photosynthesis and this light is called photosynthetically
active radiation (PAR). It is because the different rays of light are not
absorbed equally by the chlorophyll.
Intensity of Light
 Under low light intensity, the rate of photosynthesis is low.
 As the intensity of light increases, the rate of photosynthesis
increases. At very high light intensities, the rate of photosynthesis
decreases.
Duration of Light
 The extent of photosynthesis is more when a plant is exposed to long
periods of light.
 Uninterrupted and continuous photosynthesis for relatively long
periods of time may be sustained without any visible damage to the
plant.

9. OXYGEN
 Oxygen is essential for photosynthesis.
Photosynthesis does not take place in cells which
lack oxygen.
 The energy produced in oxygen respiration is
necessary for photosynthesis. Oxygen is required for
the production and maintenance of some substance.
 High concentrations of oxygen inhibit the rate of
photosynthesis. It promotes photorespiration.

10. WATER
 Water is one of the raw materials of photosynthesis.
The amount of water used in photosynthesis is very
small. Less than 1 % water is absorbed by the plant.
 But the water content of the leaf often acts as a
limiting factor indirectly. It maintains the turgor of the
assimilatory cells.
 The rate of photosynthesis decreases in the cells
which have lost their turgor, the loss of turgor of
guard cells closed the stomata. It reduces the rate of
photosynthesis.

11. DCMU
 DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is a
very specific and sensitive inhibitor of
photosynthesis.
 It blocks the plastoquinone-binding site of
photosystem II and prevents the flow of electrons
from PS II.

13. Reference:
 http://www.biologydiscussion.com/photosynthesi
s/15-main-factors-affecting-
photosynthesis/39944
 https://biologyboom.com/factors-affecting-
photosynthesis/
 https://www.tutorvista.com/content/biology/biolog
y-ii/nutrition/factors-affecting-photosynthesis.php
 https://www.topperlearning.com/study/cbse/class
-11-science/biology/chapter/photosynthesis-in-
higher-plants/factors-affecting-
photosynthesis/b101c3s1ch7505t15624

14. THANK YOU