Respiration in Plants

Respiration in plants is the biochemical process where energy is released from organic compounds for physiological functions. Respiration in plants is different from that in animals as the mechanisms and types of respiration are different in the plant kingdom. This chapter of biology is from the Class 11 syllabus and is important for the students who are preparing for competitive exams such as NEET, AIIMS nursing, and paramedical.

This Story also Contains

1. Respiration in Plants
2. Do Plants Breathe?
3. The Role of Air and Temperature in Respiration
4. Types of Respiration in Plants
5. Cellular Respiration in Plants
6. Factors Affecting Respiration in Plants
7. Comparison between Photosynthesis and Respiration
8. Plant Adaptations to Achieve Efficient Respiration
9. Recommended Video on Respiration in Plants

This article will help in exploring the process of respiration in plants. While most people associate respiration mainly with animals or humans, plants also undergo cellular respiration for their survival and growth. Together, this will help to understand how plants maintain their metabolism, grow, repair, and adapt to different environmental conditions.

Respiration in Plants

Respiration is the process by which cells gain chemical energy by consuming oxygen and releasing carbon dioxide. The respiration of plant cells involves oxygen and carbon dioxide, just like that of 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.

C₆H₁₂O ₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)

Oxygen + Glucose → Water + Carbon Dioxide with Energy

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 don't 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.

• In contrast to animals, plants do not possess specialised respiratory organs; in them, gas exchange takes place through various plant tissues.

• 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.

The Role of Air and Temperature in Respiration

Plants breathe 24 hours a day, but the night respiration process is more obvious when photosynthesis ends. The temperature should be much cooler at night compared to the daytime because plants can be stressed.

Put yourself in the shoes of a marathon runner. When a runner runs, his/her breathing rate is higher than when they are standing still; this results in an increase in his/her respiration and an increase in body temperature. When plants grow, their respiration is higher than when they are standing still. The respiration rate increases and the temperature increases when the temperature rises at night. Consequently, flowers are damaged and plant growth is impaired.

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 Roots

• The root system are responsible for plant respiration. Soil contains oxygenated air that is already present in the spaces between soil particles. A root hair present on the roots helps absorb oxygen into the roots.

• There is direct contact between the root hairs and them. Root hairs are actually lateral tubules that arise from the outer epidermal layers of a root. Plant roots respire through underground spaces.

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

• The same root hairs produce carbon dioxide gas during respiration, which is released in the opposite direction from the roots. The roots are thus completed in their respiration process.

• Plants are prone to dying if they are watered over for a long period of time. Water exercises all the air between soil particles as a result of too much water. 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.

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

• Supports the energy requirements of photosynthesis in higher plants.
• It thus becomes essential for the maintenance of cellular processes and the general health of the leaf.

The Process of Respiration in Stems

• Lenticels 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.

The Rate of Transpiration in Leaves

• 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 pathway

• Location: cytoplasm

• Glucose is broken down into two molecules of pyruvate.

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

• Is an anaerobic process.

Krebs Cycle (Citric Acid Cycle)

• Location: 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)

• Location: 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

Respiration is a biochemical process that provides the energy that plants need for their growth, development, and other cellular activities. However, the rate of respiration doesn't always remain 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 and Respiration

Oxygen and glucose are produced from carbon dioxide and water in the photosynthesis process. Oxygen and glucose are converted into water and carbon dioxide in the cellular respiration process. This process generates by-products such as water and carbon dioxide. ATP is the energy produced by this process. The table below shows the difference between photosynthesis and respiration:

Plant Adaptations to Achieve Efficient Respiration

Plants acquire many 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.

Root Respiration

• Aerenchyma tissues in roots that allow the exchange of gases in waterlogged soils.

• The large surface area of roots readily absorbs oxygen.

Leaf Respiration

• Stomata control the gas exchange; open during the day and close at night.

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

Aquatic Plants

• Leaves float on the water surface while air-filled cavities above ground ensure oxygen supply.

Desert Plants

• Reduced stomata openings with thick cuticles to reduce loss of water and promote respiration.

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