Respiration in Plants

What Is Respiration in Plants?

Respiration is the process by which cells gain chemical energy by consuming oxygen and releasing carbon dioxide. The respiration in plants involves oxygen and carbon dioxide, just like animal cells. Since plants do not have specific organs that allow for gas exchange, every part of the plant, including its roots and stems, performs breathing. Respiration and breathing occur through lenticels in hard and woody stems. In all trees, there are tiny pores, known as lenticels, found on the bark.

Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

Therefore, it may conclude from the equation above that respiration causes carbon dioxide to be released and oxygen to be consumed.

Do Plants Breathe?

When we look at the plants, we might say that they do not breathe because they lack lungs or any other visible breathing system like animals. However, plants do breathe, but in a different way. Here are some important points to explain this concept further.

• Plants "breathe" in the sense that they are capable of exchanging gases with the environment.

• Gas exchange is required for respiration and photosynthesis.

• Plants take up oxygen and give out carbon dioxide through stomata, lenticels, and root cells.

• Breathing ensures the supply of oxygen for cellular respiration.

• Efficient gas exchange is important for metabolic activities going on in a plant and overall plant health.

Types of Respiration in Plants

Like other living organisms also need energy to perform important life processes, which they receive through respiration. There are two main forms of respiration in plants, i.e. aerobic respiration and anaerobic respiration.

Aerobic Respiration

• Involves the presence of oxygen.

• It includes glycolysis, the Krebs cycle, and the electron transport chain.

• It results in the production of carbon dioxide, water, and a significant portion of ATP.

• The amount of ATP obtained is utilized in accomplishing the activities essential for living organisms.

• This is especially beneficial while making and preserving plant tissues.

Anaerobic Respiration

• It can happen in the absence or when there is little oxygen.

• Commonly found in waterlogged soils or during intense metabolic activity.

• Yields far less energy than aerobic respiration.

• Forms waste products like ethanol and lactic acid, which can be toxic if accumulated.

Respiration in Different Plant Parts

In contrast to animals, plants do not possess specialised respiratory organs, rather gas exchange occurs through various plant tissues.

Root Respiration

• The root system is responsible for respiration in plants. Soil contains oxygenated air and root hair helps absorb oxygen into the roots.

• Air diffuses between soil particles, allowing oxygen to enter into root hairs. During respiration, oxygen is transported from root hairs to all parts of the roots.

• Then the root hairs produce carbon dioxide gas during respiration, in the opposite direction from the roots.

• Plants are prone to dying if they are watered over for a long period of time. Water blocks the air between soil particles

• Hence the roots cannot perform aerobic respiration because oxygen is not freely available.

• Germinating seeds have a seed coat that prevents oxygen from entering them, so they respire anaerobically during the early stages of seed germination.

Stem Respiration

• Lenticles on the bark of woody stems provide a surface for the exchange of gases.

• In herbaceous stems, it takes place directly through the epidermal cells.

• Oxygen is absorbed through lenticels and diffuses through to the inner tissues.

• Carbon dioxide, which is the product of cellular respiration, diffuses out through the same openings.

• Stem respiration is essential to produce energy in cells of the stem for its growth and transport of nutrients and water.

Leaf Respiration

• Gas exchange is controlled by the stomata on the leaf surface.

• The thin, flat nature of the leaves allows for efficient gas diffusion in plants.

• During the day, the stomata are open. This allows the take-up of carbon dioxide needed for photosynthesis and oxygen to be released.

• Oxygen is also taken up for respiration, and carbon dioxide, which is a byproduct of respiration, diffuses out.

Cellular Respiration in Plants

Cellular respiration is a process by which glucose is broken down to release energy by plants. This energy is used for various purposes like growth, repair, and transport of nutrients. The details are given below:

Glycolysis

• Glycolysis occurs in the cytoplasm.

• Glucose is broken down into two molecules of pyruvate.

• Yields a net gain of 2 ATP and 2 NADH molecules.

• It is an anaerobic process.

Krebs Cycle (Citric Acid Cycle)

• Krebs cycle occurs in the mitochondrial matrix

• Pyruvate is first converted into acetyl-CoA, which subsequently enters the cycle.

• Yields CO2, NADH, FADH2 and 2 ATP per glucose molecule.

• Completes oxidation of glucose derivatives.

Electron Transport Chain (ETC)

• The electron transport chain occurs in the inner mitochondrial membrane

• NADH and FADH2 donate electrons to the chain.

• Electrons pass through protein complexes, driving proton pumping.

• Protons flow back through ATP synthase, generating 34 ATP molecules.

Factors Affecting Respiration in Plants

The rate of respiration is always constant, it is affected by different internal and external factors. Understanding these factors will help in getting to know the health of a plant and its responses to environmental stress. Several factors can influence the process of respiration in green plants:

Temperature

• An increase in temperature normally increases respiration rates to a certain optimum value.

• Very high temperatures can cause the denaturation of enzymes involved in respiration.

Oxygen Concentration

• Oxygen should be optimally present for aerobic respiration.

• Low oxygen conditions promote anaerobiosis.

Sufficient Water

• Water should be optimally present to carry out enzymatic activities and other cellular activities.

• Drought stress reduces the ability of the plant cells to respire.

Light

• It indirectly affects respiration, as light is essential for photosynthesis and consequently determines the level of carbohydrate availability.

• Plants respire at all times, but they will only photosynthesise in the light.

Nutrients

• Metabolic nutrients, particularly nitrogen, potassium, and phosphorus.

• Scarcity of any required nutrient will limit both respiration and.

Comparison Between Photosynthesis & Respiration

The table below shows the difference between photosynthesis and respiration:

Plant Adaptations for Efficient Respiration

Plants acquire different adaptations to perform respiration efficiently in different conditions. This is because the plants do not have any specialized respiratory organs like animals. Hence, they depend on various structures and physiological mechanisms to ensure smooth gas exchange and cellular respiration.

• Aerenchyma tissues in roots that allow the exchange of gases in waterlogged soils. The large surface area of roots readily absorbs oxygen.

• Laterally flattened types of leaves increase the time for gas exchange.

• In aquatic plants, leaves float on the water surface while air-filled cavities above ground ensure oxygen supply.

• Desert plants have reduced stomata openings with thick cuticles to reduce loss of water and promote respiration.

• Mangrove trees respire with the help of pneumatophores. A plant's respiration occurs throughout the day and night, resulting in carbon dioxide.

Respiration NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Types of respiration

• Respiration in different plant parts

• Cellular respiration in plants

Practice Questions for NEET

Q1. The structures present in plants for the purpose of gaseous exchange are

1. Lenticels

2. Stomata

3. Nostrils

4. Both a and b

Correct answer: 4) Both a and b

Explanation:

Unlike animals, plants do not have specialized organs for gaseous exchange. Instead, they rely on structures like stomata, tiny openings found on the surfaces of leaves, and lenticels, small pores present on stems and woody parts. These structures allow the exchange of oxygen, carbon dioxide, and water vapour, enabling plants to carry out processes like photosynthesis and respiration effectively.

Hence, the correct option is 4) Both a and b

Q2. Respiratory pathway is called as amphibolic pathway because

1. It includes catabolic reactions

2. It includes anabolic reactions

3. It includes catabolic and anabolic reactions both

4. None of these

Correct answer: 4) None of these

Explanation:

Catabolic Role: In the respiration context, catabolism is the breakdown of glucose and other substrates for energy (ATP) through glycolysis, citric acid cycle, or oxidative phosphorylation. That energy would play an important role in lots of cell functions.
Anabolic Role: The respiratory pathway supplies intermediates for anabolic processes, such as amino acid synthesis, fatty acid synthesis, and nucleotide synthesis. These can be diverted out of the ways of catabolic reactions to be used in support of the synthesis of complex molecules needed for cell growth and repair.
It will then be possible to consider that as an amphibolic pathway, therefore, the respiratory pathway is an essential part of maintaining cellular metabolism through the production of energy and biosynthesis processes. This further provides a holistic view of metabolic flexibility within biochemical pathways and their interrelations.

Hence, the correct answer is option 4) None of these.

Q3. Which of the following exhibits the highest rate of respiration?

1. Growing shoot apex

2. Germinating seed

3. Root tip

4. Leaf bud

Correct answer: 2) Germinating seed

Explanation:

Germination is the process that has the maximum growth rate as compared to other options and has the highest respiration rate. During germination, the seed undergoes rapid metabolic activity to support cell division and elongation, resulting in a high growth rate. The increased respiration rate provides the necessary energy (ATP) for these intense developmental processes.

Hence, the correct answer is option 2) Germinating seed.

Also Read:

• MCQs on Respiration in Plants

• TCA Cycle

• Amphibolic Pathway

Recommended Video on Respiration in Plants