In plants, respiration can be regarded as the reversal of the photosynthetic process. Like photosynthesis, respiration involves gas exchange with the environment. Unlike photosynthesis, respiration can occur at any time of day or night, and it occurs not just in the leaves, but also in the stem and roots. Plants breathe throughout their lives because the plant cell requires energy to exist; yet, plants breathe in a unique way known as cellular respiration.

Photosynthesis is a cellular respiration process in which plants create glucose molecules by collecting energy from sunlight and converting it to glucose. Plant breathing is demonstrated in a number of live studies. All plants respire in order to keep their cells active and alive.

What is Plant Respiration?

The method by which cells get chemical energy by the consumption of oxygen and the release of carbon dioxide is called respiration. In order to carry on respiration, plant cells require oxygen and a means of disposing of carbon dioxide just as animal cells do. In plants, every part such as root, stem executes respiration as plants do not possess any particular organs like animals for the exchange of gases.

Types of Respiration

There are two main types of respiration.

1. Aerobic Respiration
   This type of respiration takes place in the mitochondria of all eukaryotic entities. Food molecules are completely oxidised into carbon dioxide, water, and energy is released in the presence of oxygen. This type of respiration is observed in all the higher organisms and necessitates atmospheric oxygen.
2. Anaerobic Respiration
   This type of respiration occurs within the cytoplasm of prokaryotic entities such as yeast and bacteria. Here, lesser energy is liberated as a result of incomplete oxidation of food in the absence of oxygen. Ethyl alcohol and carbon dioxide are produced during anaerobic respiration.

Rate of Respiration

The volume of inspiration (inhale) and expiration (exhale) determines the normal rate of respiration. Respiratory rate is another name for breathing rate.

Factors affecting rate of Respiration

The rate of respiration has a considerable impact on the health and growth of plants. Plant physiology is a primary determinant of respiration rate, with each species respiring differently depending on its adaptations to the local environment. Plant respiration rates are influenced by a variety of external conditions, in addition to intrinsic variances across plant kinds. Agriculture and horticulture, as well as the ecology of natural regions and food preservation, could all be affected significantly.

Tissue Age & Stage of Life

One of the most critical elements regulating plant respiration is the life stage. A seed emits a burst of respiration after it has absorbed enough water to germinate and power its emergence from the seed casing. Branches expand and root tips burrow into the dirt as leaves emerge. As they utilise energy to grow, these sections begin to breathe rapidly. The rate of respiration decreases as the roots, branches, and leaves mature.

When fruits and seeds are maturing, respiration increases, and energy use peaks when the fruit is fully ripe. After this time, respiration decreases considerably, with many annual plants dying completely after fruiting, while perennials may lose older and damaged leaves.

Oxygen Content of the Atmosphere:

The percentage of oxygen in the surrounding atmosphere greatly influence the rate of respiration. But the reduction of the oxygen content of the air, however, causes no significant lowering in the respiratory rate until the percentage drops to about 10%. At 5% oxygen definite retardation of respiration occurs.

As shown in the graph, with the increase of oxygen concentration in the atmosphere, the rate of respiration also increases, but this effect is not as accelerating as might be expected. This response of plants and their parts depends upon several factors. The plant tissues which ordinarily have a low rate of respiration are not as seriously affected by low concentration of oxygen as those which have a higher rate of respiration.

In certain plants, like rice, on removal of oxygen the rate of respiration in terms of total carbon dioxide produced actually increases. This indicates that anaerobic respiration comes into action when oxygen is no longer available and that the plant, if it has to make up for the relative inefficiency of this system, has to respire faster.

Effect of Temperature:

1. Like most chemical reactions, the rate of respiration is greatly influenced by temperature. Estimation of Q 10 of the process for a rise in temperature from 8° to 18 °C gives a Q 10 of 2, indicating a chemical reaction.
2. If the rise is at a much higher starting temperature, say between 20° and 30°C, then the Q 10 may fall below 2. It should be borne in mind that different plants or plant parts may show considerable variation in regard to optimum temperature for respiration.
3. In certain cases the rate of respiration increases at lower temperature. E. F. Hopkins (1925) reported that the rate of respiration in white potatoes increases if the temperature in lowered to just abovezing point.
4. This increase in the rate of respiration is primarily due to increase in the quantity of respirable materials (such as soluble carbohydrates) which tend to accumulate in Irish potato at temperature slightly above 0°C.
5. At temperatures higher than the optimum for respiration, the rate of respiration (in terms of oxygen utilized and CO₂ produced) falls due to inter-conversions of respirable materials.
6. For instance, fats may be formed from carbohydrates by a reaction in which carbon dioxide is utilized and oxygen produced.
7. At very high temperatures, the rate of respiration falls significantly and may even come to standstill because of protoplasmic injuries.

Effect of Light:

Light has indirect effects on the rate of respiration. With the increase in light intensity, the temperature of the surrounding atmosphere also increases thus affecting the rate of respiration. Secondly, the quantity of respirable material in the plant largely depends upon the rate of photosynthesis which is directly influenced by light and thirdly, stomata remain open during daylight and hence rapid exchange of gases takes place through them.

Effect of Water Content:

Over a certain range, water content of the plant tissue greatly influence its rate of respiration. In most of the storage able seeds the moisture content is kept below the point which allows a rapid respiration. With the increase in moisture content, the rate of respiration is likely to go up with the result a rapid loss of viability will occur and at the same time the temperature will also rise and the grain may be spoiled.

Unlike most green tissues, xerophytes, lichens and leafy mosses (Sphagnum species) can be brought to an air-dry condition at low humidity without any apparent loss in their viability.

Effect of Carbon Dioxide Concentration:

The rate of respiration is normally not affected by an increase of carbon dioxide concentration in the surrounding atmosphere up to 19%, but as the concentration increases from 10% to 80%, a progressive decrease in respiration occurs.Specific response to higher CO₂ concentration varies with the particular kind of tissue and plant. The effect of CO₂ concentration is more significant when the temperature and oxygen supply are low. At a very high concentration of CO₂ the plant tissues are injured or even killed.

Protoplasmic Conditions:

The rate of respiration is higher in young growing tissues because they have more protoplasm than older tissues. Their faster rate of respiration helps the cells’ meristematic activities by supplying a lot of energy. The rate is affected by the degree of hydration of the protoplasm in the cells, and mechanical injury to plant tissues accelerates respiration.

Summary

In plants, respiration can be regarded as the reversal of the photosynthetic process. All plants respire in order to keep their cells active and alive. There are two main types of respiration – anaerobic and prokaryotic – both involve the exchange of gases with the environment. Respiratory rate is another name for breathing rate. Plant respiration rates are influenced by a variety of external conditions, in addition to intrinsic variances across plant kinds. Some of these factors are light intensity, carbon di oxide concentration, and water content.  Agriculture and horticulture could all be affected significantly by the rate of respiration of plants.

Frequently asked questions (FAQs)

Q1. What is the effect of carbon dioxide on the rate of respiration in plants?
Ans: As the carbon dioxide concentration increases, the rate of respiration in plants decreases. This is because high CO₂ concentration would result in the closing of the stomata. Thus the rate of respiration is inversely proportional to the concentration of carbon dioxide.

Q2. How does temperature affect the respiration rate of plants?
Ans: The increase in temperature enhances the rate of cellular respiration. It is due to the heat speeds up the reactions, which means the kinetic energy is higher. It means reactions speed up and the rate of cellular respiration increases.

Q3. What happens to a plant if the temperature is too high?
Ans: When soil temperature rises above an optimum threshold, plant water and nutrient uptake can be impeded, causing damage to plant components.

Q4. Does the rate of respiration change during day and night?
Ans: No. however, since plants only photosynthesise during the day, the relative release of CO₂ might be different.

Q5. Does CO₂ concentration affect respiration?
Ans: The rate of respiration is normally not affected by an increase of carbon dioxide concentration in the surrounding atmosphere up to 19%, but as the concentration increases from 10% to 80%, a progressive decrease in respiration occurs.Specific response to higher CO₂ concentration varies with the particular kind of tissue and plant.

Learn the Mechanism of Respiration

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