Get complete information on the role of external factors on respiration

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Temperature:

The influence of temperature on respiration is the same as on other metabolic processes. Plants generally are capable of respiring in the temperature range between 0-45° C. Within this range any increase or decrease of temperature would have a similar effect on respiration.

In several experiments it has been noticed that the increase in the rate of respiration follows the Vant Hoffs law that the rate of reaction is doubled for every 10°C increase of temperature, if no other factor is limiting. In general an optimum temperature of 30°C is most suitable for respiration. Beyond this range there is no further increase but the rate flattens until 45°C when it starts declining.

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Light:

It is generally believed that the influence of light on respiration is indirect even though physiologists like Emerson and Lewis (1943) have re­ported that illuminated Chlorella cells have a higher rate of respiration than those kept in darkness. A similar effect on barley seedlings has been ob­served by Johnson (1944).

But there is no stoppage of respiration indirectly by governing the supply of reparable materials via photosynthesis. Another influence of light is that by increasing temperature, it increases the rate of respiration.

Oxygen concentration:

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Oxygen is a must for aerobic respiration, though it is not necessary for anaerobic respiration. Since the concentration of O2 in the atmosphere is constant, slight variations in O2 concentration do not seem to have a lasting influence on respiration. But if the concentration of O2 below 2.0% it will retard the rate of respiration as there is rise in CO2 level due to fermentation.

Carbon dioxide concentration:

The atmosphere has a carbon dioxide concentration of 0.03% and it is almost constant. Hence generally its influence on respiratory rate is negligible. However any increase in the carbon diox­ide concentration has a retarding influence on respiration. Soil has a higher concentration of CO2 than atmosphere due to the activity of microbes. Hence seeds sown in such a soil generally fail to germinate. Ploughing the soil increases the aeration and enhances the rate of germination.

Decrease in respiration due to increased CO2 concentration may be used to preserve vegetables and fruits (in CO2 rich atmosphere) by keeping the rate of respiration at minimum. This is not however practised as a higher CO2 concentration may prove to be poisonous. Higher CO2 concentration also affects all other vital activities which require biological energy.

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Water:

Hydration of the medium is a basic requirement for all the meta­bolic activities and respiration is no exception. The rate of respiration is minimum in dry seeds, and as soon as they come in contact with water the rate of respiration registers a marked increase. Respiratory enzymes be­come active only in a hydrated medium. Water maintains proper turgidity of the cells and provides a suitable environment for respiratory reactions.

Injury:

The works of Hopkins (1927) and others have demonstrated that injury enhances the rate of respiration. It has been observed that sugar con­tent of cells near the wounded region increases preparatory rate of respira­tion. In the wound healing process new cells have to be added, with the result there is increased metabolic activity, thereby accounting for increased respiratory rate. Potato tubers cut into pieces show enhanced rate of respira­tion due to the conversion of starch into sugars.

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