Respiration in Plants

Edited By Irshad Anwar | Updated on Oct 18, 2024 11:33 AM IST

Respiration in plants is the biochemical process where energy is released from organic compounds for physiological functions. Respiration in plants is different than in animals as the mechanism and the 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 article covers the process, types, and importance of respiration in plants which is crucial from an exam point of view.

Important Topics of Chapter Respiration in Plants

Cellular Respiration
Aerobic And Anaerobic Respiration
Respiration in Root, stem and Leaves
Important Concept- glycolysis, fermentation, Krebs cycle

Overview of the Chapter

The Respiration in Plants chapter explains how energy is released in plants by breaking down glucose. It differentiates between aerobic and anaerobic respiration and explains glycolysis, the Kreb cycle as well and oxidative phosphorylation. An outline of the formation of ATP along with the roles of the mitochondria and all those involved in the plant respiratory pathways is described. It also mainly focuses on the factors of respiration as well as makes a distinction between respiration and photosynthesis.

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.

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As you can see, there are several ways to breathe:

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

Oxygen + Glucose → Water + Carbon Dioxide with Energy

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

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Respiration Definition Plants

Respiration in plants is the breakdown of glucose to give energy for performing cellular activities. These reactions take place through aerobic or anaerobic pathways, where oxygen plays a role in aerobic respiration but is not present in anaerobic respiration.

Do Plants Breathe?

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 at night rises. Consequently, flowers are damaged and plant growth is impaired.

Types of Respiration in Plants

There are two major forms of respiration by plants:

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

NCERT Notes Subject Wise Link:

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.

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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.
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.

Respiration in the Leaf

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

NCERT Solutions Subject-wise link:

Cellular Respiration in Plants

The details are given below:

Glycolysis

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

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.

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.

Comparison between Photosynthesis and Respiration

The table below shows the difference between photosynthesis and respiration:

Feature	Photosynthesis	Respiration
Occurs in	Chloroplasts	Mitochondria
Energy Source	Light	Glucose
Reactants	Carbon dioxide, water, light	Glucose, oxygen
Products	Glucose, oxygen	Carbon dioxide, water, ATP
Function	Converts light energy to chemical energy	Converts chemical energy to usable energy
Time of Occurrence	Only in the presence of light	Continuously, day and night
Electron Carrier Molecules	NADP+	NAD+ and FAD

Plant Adaptations to Achieve Efficient Respiration

Plants develop several adaptations to carry out respiration efficiently in different conditions:

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 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.

Exam Tips and Strategies for Respiration in Plants

Here are the tips and tricks to prepare for Respiration in Plants:

Mnemonics

Steps of Aerobic Respiration (Glycolysis, Krebs Cycle, ETC)

"Great Kids Enjoy Outdoors"

Glycolysis
Krebs Cycle
Electron Transport Chain (ETC)
Oxidative Phosphorylation

Stages of Glycolysis

"Paddy Produces Two Powerful Fruits"

Phosphorylation
Priming
Two 3-carbon sugars
Pyruvate
Formation of ATP

Note-Making

Charts and Tables: Prepare charts that explain the differences between aerobic and anaerobic respiration

Diagrams: Prepare diagrams on how the mitochondria are structured and what occurs in glycolysis

Multimedia

Watch animations showing the process of aerobic and anaerobic respiration in plants

Flashcards

Use flashcards with the keywords to learn, such as glycolysis, Krebs cycle, and electron transport chain.

NCERT Exemplar Solutions Subject-wise link:

Types of Questions and Weightage of Respiration in Plants in Exams

Exam Type	Types of Questions	Weightage
CBSE Board Exams	Short answers on respiration types, diagram explanations	4-6%
NEET	MCQs on steps of respiration, ATP production, and anaerobic products	2-3%
AIIMS	Assertion and reason questions on respiration processes	2-3%
Nursing Entrance Exams	Scenario-based questions on plant survival in low-oxygen	1-3%
Paramedical Exams	True/False on anaerobic respiration products	1-3%

Prescribed Books for Respiration in Plants

The main and most recommended learning resource for Respiration in Plants is the NCERT Biology class 11 textbook covering all concepts as per the CBSE syllabus. For further understanding, "Trueman's Elementary Biology, Volume 1" can be referred to. The other useful book is "Pradeep's Biology" which is also known for its detailed explanation and plenty of solved examples. You can access a variety of videos, articles and mock tests on this chapter from the careers360 platform.

Best Book for NEET Biology Class 11

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