Why Are Plants Green? Essay

Well you are spot on about it being chlorophyll inside the chloroplasts that gives a plant the green colour. There are other pigments in the leaves too, such as xanthophylls (yellows) and carotenoids (yellows, oranges and reds). These pigments are also used in photosynthesis but occur in lesser quantities than the green chlorophyll. The combinations of the different pigments make different shades of green. Now the reason that plants look green is that they are trying to obtain energy from the sun using a particular part of the light spectrum, mainly the red and infra red wavelengths.

If you remember from your physics classes the colour you see is the colour that is reflected from the object, the other colours are absorbed. So in the case of green plants, the green wavelength is reflected and all the other colours, especially reds and blues, are absorbed to drive the energy cycle in the plants. Chlorophyll does best in the red (around 670 nm) and blue (around 500 nm) areas of the spectrum.

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That’s why many plants have the additional pigments (xanthophylls and carotenoids) called accessory pigments that feed light energy to chlorophyll “a” from light. Chlorophyll is almost useless in the green part of the spectrum, and doesn’t absorb that colour. That is why most plants are green. WHY IS FIRE HOT ? When a fuel is burnt, a lot of heat is produced. Now let us understand why combustion of fuels results in liberation of heat or why fire is hot. When a chemical reaction occurs, rearrangement of bonds takes place.

Certain old bonds are cleaved (broken) and certain new bonds are formed. Cleavage of bonds requires energy whereas during the formation of bonds energy is released. The amount of energy required breaking a bond or the amount of energy released during the formation of a bond depends upon the nature of atoms involved in the bond. The reaction in which the energy released during the formation of new bonds is more than the energy required to break the old bonds are accompanied by the evolution of heat and are called exothermic reactions.

On the other hand, reactions in which the energy released during the formation of new bonds is less than the energy required to break the old bonds are accompanied by the absorption of heat and called endothermic reactions. The reaction involving combustion of fuels are highly exothermic because in case of combustion the energy released during the formation of bonds in the product of combustion (CO2 and H2O) is very large as compared to the energy required for breaking bonds in fuel molecules and oxygen molecules. This is why the combustion of fuel produces lot of heat and fire is hot.


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