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7.3.2.3. Factors influencing photosynthesis

Factors influencing photosynthesis

For photosynthesis to take place, photosynthetic pigments need to capture the energy of light, in addition to H2O and CO2. There are factors that make photosynthesis more or less efficient.

Some of the factors that influence photosynthesis are:

a)  CO2 concentration. With high light intensity, photosynthesis increases if the concentration of CO2  in the air is high, until it reaches a limit at which it stabilizes.

b)  O2 concentration. The higher the oxygen concentration in the air, the lower the photosynthetic performance, due to photorespiration processes.

c)  Water shortageThe scarcity of water in the soil and of water vapor in the air decreases the photosynthetic performance. Thus, in the absence of water, the stomata are closed to prevent desiccation, and the entry of CO2 is less.

d)  Temperature. Each species is adapted to live within a range of temperatures. Within this range, the higher the temperature, the higher the efficiency of the enzymes and, therefore, the higher the photosynthetic yield. If the temperature limits are exceeded, enzymatic disturbances occur and performance decreases. If protein denaturation occurs, the plant dies.

e)  Lighting timeThere are species in which, the longer the hours of light, the higher the photosynthetic yield. Others, on the other hand, require nocturnal periods.

f)  Luminous intensity. Each species is adapted to live within a range of light intensity. There are penumbra species and photophilic species. Within each interval, the higher the illumination, the higher the performance, until certain limits are exceeded, in which the irreversible photo-oxidation of the photosynthetic pigments occurs. For the same light intensity, C4 plants show higher performance than C3 plants and never reach light saturation.

g) Color of light. The chlorophyll a and chlorophyll b absorb light energy in the blue and red spectrum region; the carotenes and xanthophylls in blue; the phycocyanins in orange; and phycoerythrins, in the green. All of these pigments pass the energy on to the target molecules. The least usable monochromatic light in organisms lacking phycocyanins and phycoerythrins is green light.

Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU)

Andalusia, model 5, 2015, option A, question 4.

In a greenhouse it is decided to increase the photosynthetic activity of the plants. For this, the plants are divided into two groups, one that is grown in a compartment enriched in CO2 at the usual temperature, while a second group of plants is grown under the same CO2 conditions as the previous one but at a low temperature.

How will CO2 enrichment affect plants in the first group? [0.5].

Reasonably explain which group of plants will show the best performance in photosynthesis [0.5].