Innovations in Biotechnology and Medical Sciences

How plants dissipate excess sunlight as heat?

Note4Students

From UPSC perspective, the following things are important :

Prelims level : Read the attached story

Mains level : Not Much

Photosynthesis is a life-sustaining process by which plants store solar energy as sugar molecules. However if sunlight is in excess it can lead to leaves being dehydrated and damaged.

What is Photosynthesis?

  • Photosynthesis is the process used by plants, algae and certain bacteria to harness energy from sunlight and turn it into chemical energy.
  • There are two types of photosynthetic processes: oxygenic photosynthesis and anoxygenic photosynthesis.
  • The general principles of anoxygenic and oxygenic photosynthesis are very similar, but oxygenic photosynthesis is the most common and is seen in plants, algae and cyanobacteria.
  • During oxygenic photosynthesis, light energy transfers electrons from water (H2O) to carbon dioxide (CO2), to produce carbohydrates.
  • Ultimately, oxygen is produced along with carbohydrates. Oxygenic photosynthesis is written as follows:

6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2 + 6H2O

Here, six molecules of carbon dioxide (CO2) combine with 12 molecules of water (H2O) using light energy. The end result is the formation of a single carbohydrate molecule (C6H12O6, or glucose) along with six molecules each of breathable oxygen and water.

How do plants dissipate heat?

  • To prevent such damage, plants dissipate extra light as heat.
  • While this was known there has been a debate over the past several decades over how plants actually do so.
  • Now for the first time researchers have directly observed one of the possible mechanisms through which plants dissipate extra sunlight.
  • The new research has been able to determine–by using a highly sensitive type of spectroscopy–that excess energy is transferred from the pigment chlorophyll, which gives leaves their green colour, to other pigments called carotenoids.
  • The carotenoids then release the energy as heat. After the carotenoids accept excess energy, most of it is released as heat, thus preventing damage to the cells.

Why does plant dissipate light?

  • During photosynthesis, light-harvesting complexes play two seemingly contradictory roles.
  • They absorb energy to drive water-splitting and photosynthesis, but at the same time, when there’s too much energy, they have to also be able to get rid of it.
  • Plants quickly adapt to changes in sunlight intensity. Even in very sunny conditions, only 30 per cent available sunlight is converted into sugar, and the rest is released as heat.
  • The excess energy, if not released, leads to the creation of free radicals that can damage proteins and other important cellular molecules.

Significance of the research

  • So far, it had been difficult to observe the heat dissipation phenomenon, given that it occurs on a very fast time scale, in femtoseconds or quadrillionths of a second.
  • Using the new technique, researchers could observe that chlorophylls absorb red light and carotenoids absorb blue and green light, thus being able to monitor energy transfer.
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