Photosynthesis and its significance

Factors affecting photosynthesis rate

Solar energy conversion efficiency and its effect on photosynthesis

Effect of relative water content on photosynthesis

Effect of light intensity on photosynthesis

Effect of CO2 on photosynthesis

Photosynthesis limiting factors & limitations on photosynthesis

Conclusion

Photosynthesis

Carbon dioxide + water glucose + oxygensunlightsunlight

absorbed by chlorophyllabsorbed by chlorophyll

66COCO22 + + 66HH22O + energy O + energy C C66HH1212OO66 + + 66OO22

SIGNIFICANCE OF PHOTOSYNTHESIS

Makes organic molecules (glucose) out of inorganic materials (carbon dioxide and water).It begins all food chains/webs. Thus all life is supported by this process.It also makes oxygen gas.

Internal factorsInternal factors

a. Solar energyb. Waterc. Carbon dioxide d. Temperature ande. Minerals

a. Chlorophyllb. Leaf anatomyc. Accumulation of end productsd. Hormonese. RUBISCO Performancef. Rate of Chloroplast Electron

Transportg. Enzyme Activity of Calvin

Cycle

Major factors affect the rate of…?• CO2 concentration• Light intensity

• Moisture (H2O) content• Solar energy conversion

efficiency

The solar energy conversion efficiency is the fraction of light energy converted to chemical energy during photosynthesis.

Eight photons are needed to reduce one CO2 molecule to C6H12O6.

Theoretical maximum efficiency of solar energy conversion is approx. 11% considering 45% of incident radiation under PAR.

Observed solar energy conversion efficiency ranges from 3-6%. Sugarcane has the peak solar energy conversion efficiency of 7-8%.

If photosynthesis is inefficient the excess energy is dissipated as heat or fluorescence to avoid damage of radiation load.

SOLAR ENERGY CONVERSION EFFICIENCY

Breakdown of energetics of the photosynthesis process by Hall and Rao stated that;

100% sunlight 53% available photons (400-700nm) 37% absorbed photon energy 28.2% energy collected by chlorophyll 9% collected as sugar 5.4% net leaf efficiency (35-40% of 9% consumed by leaf in dark and photo respiration)

Many plants lose much of the remaining energy on growing roots. Most crop plants store ~0.25-0.5% of the sunlight in the sink. Sugar cane is exceptional in several ways, yielding peak storage efficiency of ~8%.

WATER CONTENT Water is a basic resource for photosynthesis. So its deficiency reduces photosynthetic rate.

In water stress condition stomata closes reducing transpiration and the gas exchange so reduced photosynthesis by CO2 starvation.

The photosynthetic rate of both the C3 and C4 plants decreases as their RWC and WP decreases.

Stomatal limitation and metabolic impairment decreases the potential rate of photosynthesis.

Stomatal limitation is considered to decrease both photosynthesis and CO2 concentration in the intercellular spaces of the leaves, which inhibits metabolism.

When RLW content decreased to less than 40% the plant cannot be restored (photosynthesis ~ 0).

LIGHT INTENSITY Increasing the light intensity on the plant will increase the rate of photosynthesis.

If a plant does not receive adequate light it will attempt to reach the light by growing taller.

Bright light is a basic element of photosynthesis, but variations in the colour of light have an effect on plants.

The colour that has the highest influence on photosynthesis is blue, which is why many plant growers use blue lights to grow indoor plants.

Red light is next best for photosynthesis and yellow light creates the lowest amount of light absorption.

violet blue green yellow orange red

wavelengthwavelength

Abs

orpt

ion

Light saturation point is the light intensity at which maximum photosynthesis rate observed.

Light saturation point is more in C4 than C3 crops.

Light compensation point is the light intensity at which rate of photosynthesis is equals to rate of respiration.

Light saturation point

CO2 is a basic resource of photosynthesis.

By increasing the amount of CO2, the rate of photosynthesis increases & its level determines the maximum rate of photosynthesis.

CO2 saturation range for most of the crops ranges from 500-1000ppm provided other factors are optimally available.

CO2 concentration at which the rate of CO2 utilized in photosynthesis equals to CO2 produced in respiration called CO2 compensation point.

CO2 saturation point is the CO2 concentration at which maximum photosynthesis observed and no more increase in photosynthesis recorded on increasing CO2 concentration.

CO2 saturation point is more in C3 plants, so the increasing CO2 concentration will increase the productivity and decrease the weed infestation as they are mostly C4 in nature.

CO2 compensation point- C3 and C4 plants

Reviewed that photosynthesis will be stimulated by 25–75% when the CO2concentration is doubled from 350ppm to 700ppm.

Some evidences showed that most plants undergo a gradual inhibition of photosynthesis during acclimation to enhanced CO2.

Differences in the long-term response to CO2 may be explained by differences in the sink-source status of plants, depending upon the species, the developmental stage, and the developmental conditions.

What is the ideal combination of factors for the maximum rate of photosynthesis?

PHOTOSYNTHESIS LIMITING FACTORS

enough light enough carbon dioxide

ideal temperature (not too hot or cold)

How is the rate affected if one of these factors is restricted?

If one of the factors is restricted, the rate of photosynthesis will be below the maximum possible rate.

The restricted factor controls how quickly photosynthesis occurs and so limits the rate. It is called the limiting factor.

Photosynthesis and light – limiting factorsHow does the amount of light affect the rate of photosynthesis on this labelled graph?

As the amount of light increases, so does the rate. The limiting factor is light.

light intensity

rate

of p

hoto

synt

hesi

s

Here, increasing the amount of light has no affect on the rate. The limiting factor is now carbon dioxide or temperature.

What must be increased for the rate to increase?

1

2

1

2

Photosynthesis and carbon dioxide – limiting factorsHow does the amount of carbon dioxide affect the rate of photosynthesis on this labelled graph?

As the amount of carbon dioxide goes up, so does the rate. The limiting factor is carbon dioxide.

concentration of carbon dioxide

rate

of p

hoto

synt

hesi

s

Here, increasing the amount of carbon dioxide has no affect on the rate. Light or warmth is now the limiting factor.What must be increased for the rate to increase?

1

2

1

2

LIMITATIONS ON PHOTOSYNTHESIS

• Photosynthesis is not perfect in C3 plants, it is only 1 - 4 % efficient and in C4 about 7%.

• Low efficiency due to photorespiration

• Photorespiration occurs when internal CO2

concentration becomes too low (drought);RUBISCO begins fixing oxygen.

On a bright sunny day, carbon dioxide is the limiting factor since air only contains 0.04% of the gas.

In the early morning and late afternoon, temperature and light are most likely to be limiting factors.

In order for a plant to achieve the maximum photosynthesis rate, carbon dioxide, water and sunlight need to be available in high levels.

SUMMARY OF PHOTOSYNTHESIS Photosynthesis is the conversion of radiant energy to chemical energy.

Consists of 2 stages of reaction; light reaction occurs in grana where photolysis of water and production of energy elements i.e. ATP and NADP and dark reaction occurs in stroma where reduction of CO2 to glucose occurs and dark reaction is light independent.

Among the factors affecting photosynthesis the most important factors are CO2, H2O and light.

The lower efficiency of C3 plants are due to high photorespiration than C4.

Nevertheless, PHOTOSYNTHESIS is still the most important biological process on earth.

“Look deep into nature, and then you will understand everything better.” Albert Einstein