Plants use the glucose produced during photosynthesis to fuel their respiration. Respiration in Plants can take place in the plant’s living cells. Respiration is also vital in each cell’s carbon balance, as well as in ecosystems and the global carbon cycle. Do you realise that plants and people are similar in certain ways? Plants, like people, breathe. All living organisms require oxygen to survive. Plants, unlike animals and humans, do not have specialised respiratory organs.

In plants, the process of respiration involves combining the sugars created during photosynthesis with oxygen to generate energy for plant growth. Respiration is the exact opposite of photosynthesis in many respects. Plants make their own nourishment to survive in the natural world.

Read this article to know more about respiration in plants, definition, types, respiration in various parts of a plant, etc.

What is Respiration?

Respiration is the most vital, cellular, enzymatically controlled, catabolic process, which involves the liberation of energy by the breakdown of food substances inside the living cells. To continue respiration, plant cells need oxygen and a means of discarding carbon dioxide. To fulfill their energy, they need every part of the plants, i.e., stems, leaves and roots independently take oxygen from the air, use it to gain energy, and liberate carbon dioxide.

Chemical Equation of Respiration

The overall reaction for aerobic respiration occurring in plants can be summarised by the chemical equation as follows:

C₆H₁₂O₆ + 6O₂ —-> 6CO₂ + 6H₂O + Energy (in form of ATP)

In this process, the glucose is broken down by oxygen to produce carbon dioxide and water molecules. The energy is stored in special molecules called ATP or Adenosine Triphosphate. ATP provides energy directly to all plant cells.

The compounds which are oxidised throughout this process are known as respiratory substrates. All the three nutritional components of food, i.e., carbohydrates, fats, and proteins, can function as respiratory substrates. The most common substrate for respiration is glucose. Depending upon the substrates employed, respiration is of two types:

a) Floating respiration: In this process, carbohydrates and fats are employed as substrates.
b) Protoplasmic respiration: In this process, proteins are employed as respiratory substrates. As proteins are rarely stored in cells, protoplasmic respiration uses cellular proteins. This disturbs metabolisms and cellular machinery, causing permanent injury and even death of cells.

Study Mechanism of Respiration

Types of Respiration

There are two types of respiration, depending on the absence or presence of oxygen.

• 1) Aerobic respiration
• 2) Anaerobic respiration

1) Aerobic Respiration

• a. In aerobic respiration, organic food is completely oxidised with the help of oxygen into carbon dioxide, water and energy are released as end products.
• b. Aerobic respiration takes place inside the mitochondria.
• c. In aerobic respiration, glucose metabolism occurs in three different steps:
  • i. Glycolysis or EMP pathway,
  • ii. Krebs cycle or TCA cycle or Citric Acid cycle and
  • iii. Electron transport chain or terminal oxidation or oxidative phosphorylation.
• d. One molecule of glucose is completely oxidised with the help of 6 molecules of oxygen, resulting in the formation of 6 carbon dioxide molecules and 6 water molecules.

2) Anaerobic respiration

• a. Anaerobic respiration is a process when glucose is incompletely broken down in the absence of oxygen.
• b. The common products of anaerobic respiration are CO₂, ethyl alcohol, and other organic matter such as citric acid, oxalic acid, lactic acid, etc.
• c. Anaerobic respiration occurs in the cytoplasm of various organisms such as Yeast, bacteria, and parasitic worms. In RBCs, mitochondria are absent, and hence they cannot carry out aerobic respiration. Similarly, white muscle fibres and muscles during strenuous activity do not receive adequate oxygen and thus undergo anaerobic respiration.
• d. Anaerobic respiration yields much less energy due to the partial breakdown of glucose.
• e. In microorganisms’ anaerobic respiration is called fermentation; fermentation is of four types:
  • i. Alcoholic Fermentation: It is common in Yeast. The alcoholic fermentation process is involved in brewing industries for producing beverages such as whisky, rum, beer, etc. The finished products are ethyl alcohol, carbon dioxide and energy.
  • ii. Butyric Acid Fermentation: It is common in Clostridium. In rotten butter, this type of fermentation occurs.
  • iii. Lactic Acid Fermentation: In the milk industry, it occurs in the presence of lactic acid bacteria, Lactobacillus acidophilus. In this type of fermentation, pyruvic acid acts as an H-acceptor and receives two H-atoms from NADH + H⁺ and changes into lactic acid. Even such type of fermentation in the white muscle fibres of the vertebrates or even during strenuous muscle activity.
  • iv. Acetic Acid Fermentation: This pathway is common in acetic acid bacteria. The products obtained are carbon dioxide and acetic acid.
• f. It is a low energy-producing process. Only 59 Kcal of energy is produced in anaerobic respiration.

Fig: Aerobic and Anaerobic Respiration

Respiration in Roots

 Fig: Respiration in Roots

Roots are the underground part of a plant. It absorbs oxygen with the help of root hair (a lateral tubular outgrowth of the external epidermal cells of a root). Carbon dioxide produced in the root cells at the time of respiration goes out through the root hair by diffusion. If we water a potted plant for a long time, then that plant may die. This is because too much water expels all the air in between the soil particles. Due to this, oxygen will not be available to the roots for aerobic respiration.

Respiration in Stems

Fig: Respiration in Stems

The living cells are arranged in thin layers inside and beneath the bark in stems. Lenticels are the openings or pores which are mainly present in the bark and woody stems of flowering plants. Lenticels help in the gaseous exchange between the intercellular spaces of the inner tissues of the stem and outer atmosphere.

Respiration in Leaves

 Fig: Respiration in Leaves

Stomata are the tiny pores present in large numbers on the surface of leaves. They help in the exchange of gases during respiration. The kidney-shaped cells that are present surrounding the stomata are known as guard cells. The oxygen present in the atmosphere enters into a leaf through stomata and reaches all the cells by the process of diffusion. This oxygen is used in respiration within the cells of the leaf. The carbon dioxide which is produced during respiration diffuses out from the leaf into the atmosphere through the stomata.

Summary

Respiration is the most vital, cellular, enzymatically controlled, catabolic process, which involves the liberation of energy by the breakdown of food substances inside the living cells. The respiration process in plants occurs using various respiratory substrates, the most common being glucose. The chemistry of respiration is generally the opposite of photosynthesis. Respiration in plants mainly occurs in the living parts of the cell. During respiration, plants exchange gases mainly through stomata and lenticels.

FAQs on Respiration in Plants

We have provided some frequently asked questions here:

Q.1. Where does aerobic respiration take place?
Ans: Aerobic respiration takes place inside the mitochondria.

Q.2. What are lenticels?
Ans: Lenticels are the openings or pores which are mainly present in the bark and woody stems of flowering plants.

Q.3. What are guard cells?
Ans: The kidney-shaped cells that are present surrounding the stomata are known as guard cells.

Q.4. What is respiration?
Ans: Respiration is the most vital, cellular, enzymatically controlled, catabolic process, which involves the liberation of energy by the breakdown of food substances inside the living cells.

Q.5. Mention the most common substrate of respiration?
Ans: Glucose is the most common substrate of respiration.

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