Respiration in Plants

Respiration in Plants is a fundamental process where plants break down food molecules to release the energy required for their life activities. It’s crucial to understand that this is not the opposite of photosynthesis; rather, it’s a complementary process that occurs all the time, in every living cell. While photosynthesis only happens in the presence of chlorophyll and sunlight to make food, respiration occurs day and night in all living cells to unlock the energy stored within that food. The overall chemical equation involves combining glucose with oxygen to produce carbon dioxide, water, and a significant amount of energy. This energy is then used for various functions like absorbing nutrients, transporting materials, growing, and reproducing.

The process of respiration can be broken down into two main stages. The first stage, known as glycolysis, takes place in the cytoplasm of the cell. Here, a molecule of glucose is partially broken down without using oxygen, a process called anaerobic breakdown. This step releases a small amount of energy and results in a simpler compound called pyruvic acid. The second stage depends on the availability of oxygen. If oxygen is present, pyruvic acid is completely oxidized in the mitochondria—the powerhouse of the cell—through a process called aerobic respiration. This final step releases the bulk of the energy stored in the glucose molecule.

However, plants have adapted to survive in temporary low-oxygen conditions, such as waterlogged roots. In such cases, they switch to anaerobic respiration, also known as fermentation. Here, the pyruvic acid from glycolysis is converted into either ethanol and carbon dioxide or lactic acid. While this allows the plant to continue generating some energy, it is a much less efficient process, yielding far less energy per glucose molecule compared to aerobic respiration. This is why most plants rely primarily on aerobic respiration for their energy needs, using the oxygen they obtain not only from the air through stomata and lenticels but also from what is produced internally during photosynthesis.

• Multiple choice type

Question 1.

Glycolysis is a process ___________.

1. in which glycogen is broken down into glucose 
2. which occurs in mitochondria
3. in which glucose is broken down into pyruvate
4. that occurs next to the Krebs cycle

Question 2. 

One same common function is performed by?

1. Stomata and veins 
2. Stomata and lenticels
3. Lenticels and sepals
4. Lenticels and hydathodes

Question 3. 

Anaerobic respiration normally occurs in

1. Grass
2. Cactus
3. Coconut
4. Baker’s yeast

• Very short answer type

Question 1. 

Do the plants respire all day and night or only during the night?

Ans:

Plants engage in respiration continuously, throughout both the day and the night. It is a fundamental process for their survival, much like it is for animals.

The confusion often arises because people mix up respiration with photosynthesis. Here is the key difference:

• Respiration: This is the process of breaking down sugars to release energy that the plant needs for growth, repair, and all its cellular activities. It consumes oxygen and releases carbon dioxide. This happens 24 hours a day.
• Photosynthesis: This is the process where plants use sunlight, carbon dioxide, and water to create their own food (sugars) and release oxygen as a byproduct. This only happens during the day when sunlight is available.

Think of it this way:
During the day, a plant is both making food (photosynthesis) and using food (respiration). The rate of photosynthesis is typically so high that it masks the respiration process. The plant releases far more oxygen from photosynthesis than it consumes through respiration.

At night, when photosynthesis stops due to the lack of sunlight, the plant continues to use food (respiration). Since there is no photosynthetic process to mask it, the plant is only consuming oxygen and releasing carbon dioxide.

Question 2. 

1. Name the following: Energy currency of cell. 

2. Name the following: Oxidative breakdown of carbohydrates to release energy. 

3. Name the following: An organism which respires throughout life anaerobically. 

4. Name the following: A common phase in both aerobic and anaerobic respiration. 

5. Name the following: Aerobic respiration requires_________ . 

6. Name the following: A chemical which removes CO2 from the air.

Ans:

1. Adenosine Triphosphate (ATP)
2. Cellular Respiration
3. Yeast (Saccharomyces cerevisiae)
4. Glycolysis
5. Oxygen (or Dioxygen)
6. Soda Lime

Question 3. 

1. Mention if the following statement is true or false. If false, rewrite them correctly. 

Aerobic respiration of one mole of glucose yields 138 ATP.

True

False

2. Mention if the following statement is true or false. If false, rewrite them correctly. 

Anaerobic respiration in plants yields lactic acid.

True

False

3. Mention if the following statement is true or false. If false, rewrite them correctly.

Carbon dioxide readily dissolves in limewater. 

True

False

4. Mention if the following statement is true or false. If false, rewrite them correctly. 

All leaves of a green plant normally respire anaerobically at night.

True

False

Ans:

1. Statement: Aerobic respiration of one mole of glucose yields 138 ATP.
Answer: False
Correction: Aerobic respiration of one mole of glucose yields approximately 30–32 ATP.

2. Statement: Anaerobic respiration in plants yields lactic acid.
Answer: False
Correction: Anaerobic respiration in plants yields ethanol and carbon dioxide.

3. Statement: Carbon dioxide readily dissolves in limewater.
Answer: True
Correction: The statement is correct.

4. Statement: All leaves of a green plant normally respire anaerobically at night.
Answer: False
Correction: Leaves respire aerobically at night; anaerobic respiration occurs only during oxygen shortage.

• Short answer type

Question 1. 

What happens to the energy liberated during respiration?

Ans:

Energy Distribution

1. Stored as Chemical Energy (ATP): The majority of the usable energy is captured and stored in the high-energy phosphate bonds of ATP (Adenosine Triphosphate). This molecule acts as the immediate energy source for the cell. When energy is needed, ATP undergoes hydrolysis, breaking a phosphate bond to release energy and form ADP (Adenosine Diphosphate).
2. Lost as Thermal Energy (Heat): A considerable portion of the energy is inevitably released as heat due to the inefficiency inherent in all biological processes (in line with the second law of thermodynamics). This thermal energy is essential for regulating the body temperature in warm-blooded animals.

Function of ATP

The generated ATP is then used to fuel all cellular activities, including:

• Mechanical Tasks: Powering movement, such as muscle contraction.
• Active Transport: Moving substances against a concentration gradient across cell membranes.
• Chemical Synthesis: Driving the construction of complex molecules like proteins and DNA.

Question 2. 

Why is it usually difficult to demonstrate respiration in green plants?

Ans:

It is notoriously difficult to clearly demonstrate respiration in green plants because the process is effectively masked by a simultaneous and opposite metabolic activity: photosynthesis. For most of the day, when a plant is exposed to light, it is performing both functions at once. Respiration is a continuous process that breaks down food to release energy, consuming oxygen and producing carbon dioxide and water. Photosynthesis, on the other hand, uses light energy to build food, and in doing so, it consumes carbon dioxide and releases oxygen. The oxygen released by photosynthesis is often in much greater volume than the oxygen consumed by respiration. Therefore, if you try to test for the products of respiration during the day, the evidence is simply cancelled out or overshadowed. For example, a test for carbon dioxide production will yield a negative result because the plant is actively using up all the CO₂ it produces for photosynthesis.

To successfully demonstrate plant respiration, one must create experimental conditions that completely halt photosynthesis while keeping the plant alive and respiring. The most reliable method is to conduct the experiment in absolute darkness. By placing a healthy plant in a sealed, dark container for several hours, photosynthesis is forced to stop. In this setup, the plant continues to respire, leading to a net increase in carbon dioxide concentration and a decrease in oxygen levels inside the container. Using indicators like lime water (which turns milky in the presence of CO₂) can then conclusively prove that respiration is occurring. This highlights the core challenge: the visible “breathing” of a plant (gas exchange) is dominated by photosynthesis during the day, hiding the constant, vital process of respiration happening within its cells.

Question 3. 

Explain why respiration is said to be a reversal of photosynthesis.

Ans:

Respiration is called the reversal of photosynthesis because the processes use opposite reactions to achieve opposite goals.

• Photosynthesis is an energy-storing process. It uses light energy to build glucose (food) from carbon dioxide and water, releasing oxygen as a by-product.
• Respiration is an energy-releasing process. It breaks down that glucose using oxygen to release stored energy, producing carbon dioxide and water as waste.

In essence, the products of one process become the reactants for the other, effectively running the reaction in reverse to serve a different purpose for the organism.

Question 4. 

How is tilling of the soil useful for the crops growing in it?

Ans:

Tilling, or ploughing, is highly beneficial for crops as it fundamentally improves the soil condition where they grow. Its primary use is in turning the soil upside down, which serves several key purposes. This process effectively loosens compacted earth, creating a soft, crumbly structure that allows young and delicate crop roots to spread through the soil more easily and deeply in search of water and nutrients.

Furthermore, tilling plays a vital role in mixing essential elements back into the earth. It burrows weeds, old crop residues, and other organic matter deep into the soil, where they decompose and enrich it naturally. This action also exposes harmful insects, pests, and their eggs or larvae hidden in the topsoil to the sun and air, effectively eliminating them and protecting the new seeds. Additionally, the upturned soil allows for better air circulation and improves the water-holding capacity of the land, ensuring seeds have the oxygen and moisture they need to germinate strongly and healthily.

Question 5. 

Write the full forms of ATP and ADP.

Ans:

Full Forms:

• ATP is the abbreviation for Adenosine Triphosphate.
• ADP is the abbreviation for Adenosine Diphosphate.

Simple Explanation:

Think of your cell’s energy system like a rechargeable battery.

• ATP (Adenosine Triphosphate) is the fully charged battery. It’s the primary form of energy that your cells use to power everything they do, from moving a muscle to creating new molecules. The “Triphosphate” part means it has a chain of three phosphate groups, and the bond holding the last one is packed with potential energy.
• ADP (Adenosine Diphosphate) is what’s left—the drained battery. When a cell needs energy, it breaks the high-energy bond of the ATP molecule, releasing that stored power for work. This process removes one phosphate group, leaving behind ADP, which now has only two phosphate groups (hence “Diphosphate”).

Question 6. 

Can cell respiration occur in any organism at a temperature of about 65°C? Give a reason.

Ans:

Yes, cellular respiration can occur at around 65°C.

The reason is the existence of thermophiles, which are a type of extremophile microorganisms. These organisms, including certain species of bacteria and archaea, are specially adapted to thrive in high-temperature environments like hot springs. Their cellular enzymes and metabolic machinery are stable and function optimally at such high temperatures, unlike those of most other life forms which would be destroyed.

Question 7. 

1. Fill in the blank : _________ are the openings found on older stems. 

2. Fill in the blank : Glycolysis occurs in the _______of the cells.

3. Fill in the blank: _____________ is a respiratory substrate 

4. Fill in the blank: The rate of ____________ is more than the rate of ___________ in the daytime in the case of green plants. 

5. Fill in the blank:  _____________ is a chemical which absorbs oxygen from the air. 

6. Fill in the blank:____________ is used to create a vacuum to show anaerobic respiration.

Ans:

1. Lenticels are the openings found on older stems.
2. Glycolysis occurs in the cytoplasm (or cytosol) of the cells.
3. Glucose (or Carbohydrate or Fat) is a respiratory substrate.
4. The rate of photosynthesis is more than the rate of respiration in the daytime in the case of green plants.
5. Alkaline pyrogallol is a chemical which absorbs oxygen from the air.
6. A suction pump (or aspirator) is used to create a vacuum to show anaerobic respiration.

• Long answer type

Question 1. 

What is respiration? How are respiration and burning similar and how are they different?

Ans:

What is Respiration?

Respiration is the fundamental biochemical process that occurs within the cells of living organisms to release energy from nutrients, primarily glucose. It’s often called cellular respiration to distinguish it from the physical act of breathing.

Think of it this way: breathing (inhaling oxygen) is how we supply the raw material for the real energy-producing process happening inside every one of our cells. The core chemical equation for aerobic respiration (which uses oxygen) is:

Glucose + Oxygen → Carbon Dioxide + Water + Energy (ATP)

This energy, stored in a molecule called ATP (Adenosine Triphosphate), is what powers everything we do—from moving our muscles to thinking and growing.

How Respiration and Burning are Similar

At their core, respiration and burning (combustion) are chemically similar processes. Both are exothermic reactions, meaning they release heat energy, and they share the same fundamental chemical reaction:

1. Same Core Reaction: Both processes involve the oxidation of a fuel source (like glucose or wood) to produce carbon dioxide, water, and energy.
   • Burning: Wood (a carbohydrate) + Oxygen → Carbon Dioxide + Water + Heat & Light
   • Respiration: Glucose (a carbohydrate) + Oxygen → Carbon Dioxide + Water + Energy (ATP & Heat)
2. Oxidation: In both cases, the fuel is broken down and combined with oxygen. This chemical reaction is what releases the stored energy.
3. End Products: The final chemical products for both are carbon dioxide (CO₂) and water (H₂O), assuming the combustion or respiration is complete.

Differences

Feature	Respiration	Burning (Combustion)
Control	Controlled Biological Process (regulated by enzymes in steps).	Uncontrolled Physicochemical Process (no enzymes needed).
Occurrence	Occurs inside living cells (cytoplasm and mitochondria).	Occurs outside living systems (externally).
Energy Release	Slow and Stepwise release of energy.	Rapid and Single-step release of energy.
Energy Form	Energy is mainly stored as ATP (chemical energy), with some heat.	Energy is mainly released as Heat and Light.
Temperature	Occurs efficiently at body/room temperature.	Requires a high ignition temperature to start.

Question 2. 

How are aerobic and anaerobic respiration different in plants? 

Ans:

Feature	Aerobic Respiration	Anaerobic Respiration (Fermentation)
Oxygen Requirement	Requires O2​ as the final electron acceptor.	Does NOT require O2​ (occurs in its absence).
Location in Cell	Starts in the Cytoplasm (Glycolysis), continues in the Mitochondria (Krebs Cycle, ETC).	Occurs entirely in the Cytoplasm.
Glucose Breakdown	Complete oxidation of glucose.	Incomplete oxidation of glucose.
End Products	Carbon Dioxide (CO2​) and Water (H2​O).	Ethanol (Ethyl Alcohol) and Carbon Dioxide (CO2​).
Energy Yield (ATP)	High yield: typically 36–38 ATP per glucose molecule.	Low yield: only 2 ATP per glucose molecule (from Glycolysis).
Occurrence	Occurs continuously in all living cells (roots, stems, leaves) when oxygen is available.	Occurs only in O2​-starved tissues, such as waterlogged roots or deeply buried seeds.

Question 3. 

1. Describe one experiment you would perform to demonstrate the following phenomena: The germinating seeds produce heat. 

2. Describe one experiment you would perform to demonstrate the following phenomena: The germinating seeds to give out carbon dioxide. 

3. Describe one experiment each of you would perform to demonstrate the following phenomena: The germinating seeds can respire even in a total absence of air.

Ans:

1. Investigating Heat Release from Sprouting Seeds

Objective: To provide evidence that seeds undergoing germination release thermal energy as a result of respiration.

Core Concept: Cellular respiration is an exothermic biochemical process. As stored food in the seed is broken down to release energy, a portion of this energy is dissipated into the surroundings as heat. By monitoring temperature changes, we can observe this thermal release.

Items Needed:

• Two identical vacuum flasks (e.g., Thermos flasks), marked as X and Y.
• A substantial amount of pre-soaked, actively sprouting pea or bean seeds.
• An equal quantity of dry, inactive seeds (or seeds that have been boiled and cooled to halt all biological activity).
• Two laboratory thermometers.
• Absorbent cotton.
• A dilute antiseptic solution.

Methodology:

1. One set of seeds should be prepared a day in advance by soaking them in water. The control set should consist of dry, dormant seeds.
2. Fill Flask X completely with the moist, germinating seeds.
3. Fill Flask Y with the dry, non-germinating seeds.
4. Lightly seal the opening of each flask with a plug of cotton wool. This permits air circulation while reducing heat exchange with the external environment.
5. Carefully insert a thermometer into the center of the seed mass in each flask.
6. Note and record the starting temperature for both flasks.
7. Allow the setup to remain untouched for 48-72 hours in a stable location, after which the final temperatures are recorded.

What to Expect:
After the incubation period, the temperature inside Flask X (with sprouting seeds) will show a noticeable increase compared to its initial reading and to Flask Y. The temperature in Flask Y (with dry seeds) will show little to no change.

Interpretation:
The marked temperature rise in Flask X is a direct result of metabolic activity. The germinating seeds are respiring vigorously, a process that generates heat. The inert seeds in Flask Y, with minimal metabolic processes, do not produce detectable heat.

2. Detecting Carbon Dioxide Emission from Germinating Seeds

Objective: To confirm that carbon dioxide gas is a product of respiration in sprouting seeds.

Core Concept: Carbon dioxide (CO₂), when passed through limewater (a solution of calcium hydroxide), causes a chemical reaction that forms an insoluble white solid, calcium carbonate. This turns the clear limewater cloudy, providing a visible test for CO₂.

Items Needed:

• Two glass conical flasks.
• Two corks, each fitted with a bent glass delivery tube.
• Freshly germinating seeds.
• Dry, non-germinating seeds.
• Freshly prepared limewater.
• Two small test tubes.

Methodology:

1. Place a measured amount of germinating seeds into the first flask (Flask 1).
2. Place an equal amount of dry seeds into the second flask (Flask 2) as a control.
3. Insert a small test tube containing clear limewater into each flask, suspending it above the seeds.
4. Seal each flask securely with a cork that has a delivery tube attached. The free end of each delivery tube should be immersed in a separate test tube also containing fresh limewater.
5. Let the entire apparatus stand for several hours.

What to Expect:
The limewater in the test tube connected to Flask 1 (germinating seeds) will become distinctly milky. The limewater connected to Flask 2 (dry seeds) will remain clear and unchanged.

Interpretation:
The milky appearance is a positive indicator for carbon dioxide. This confirms that the germinating seeds are respiring and releasing CO₂ as a waste product. The dry seeds, with negligible respiration, do not release enough CO₂ to cause this change.

3. Demonstrating Respiration in the Absence of Atmospheric Oxygen

Objective: To show that sprouting seeds can respire without air by producing alcohol.

Core Concept: When deprived of free oxygen (anaerobic conditions), plant tissues such as germinating seeds can switch to a different respiratory pathway. This fermentation process breaks down sugar to produce ethanol (alcohol) and carbon dioxide, rather than the typical products of aerobic respiration.

Items Needed:

• A boiling tube or a small conical flask.
• Rapidly germinating pea seeds.
• Liquid paraffin (mineral oil).
• A tight-fitting rubber stopper.
• Acidified potassium dichromate solution.
• A dropper.

Methodology:

1. Place a generous amount of vigorously germinating seeds into the flask.
2. Add a small amount of water to the flask to maintain a moist environment, which is crucial for the seeds’ metabolic processes.
3. Slowly pour a layer of liquid paraffin over the seeds, ensuring it completely covers the water and forms a seal. This barrier effectively blocks atmospheric oxygen from reaching the seeds.
4. Close the flask very tightly with the stopper to create an airtight, oxygen-free system.
5. Keep this setup in a warm place for 24-48 hours.
6. After this period, carefully open the flask and gently waft the air from the mouth towards your nose to check for any aroma.
7. To chemically confirm, use a dropper to add a few drops of the liquid from the bottom of the flask into a fresh test tube containing the orange acidified potassium dichromate solution.

What to Expect:
Upon opening the flask, a characteristic alcoholic or fruity odour can be detected. Furthermore, when the liquid from the flask is added to the acidified potassium dichromate, the solution’s colour changes from orange to a blue-green.

Interpretation:
The colour change of the potassium dichromate solution is a specific test for the presence of ethanol (alcohol). Since the liquid paraffin seal prevented oxygen from entering, the production of ethanol conclusively proves that the seeds performed anaerobic respiration to meet their energy needs.

Question 4. 

1. How do the following structures help in respiration in plants? Lenticles _____________ 2. How do the following structures help in respiration in plants? Stomata _____________ 3. How do the following structures help in respiration in plants?  Root hairs ____________

Ans:

1. Lenticels:
Lenticels are raised, porous spots present on the bark of old stems and roots of woody plants. They function as tiny gateways for the direct exchange of respiratory gases between the internal tissues of the stem and the outside atmosphere. Since the bark is impermeable to gases, lenticels are essential as they allow oxygen to diffuse in to reach the living cells underneath for respiration. Simultaneously, the carbon dioxide produced as a waste product during this process diffuses out through these same openings.

2. Stomata:
They serve as the main sites for gas exchange in plants. During respiration, oxygen from the air enters the leaf’s internal spongy tissue through the stomatal pores, while carbon dioxide produced within the cells exits through them. The guard cells are remarkable as they can change shape to open or close the stomatal pore, thus regulating this exchange of gases, especially crucial during the night when photosynthesis has stopped.

3. Root Hairs:
Root hairs are delicate, hair-like outgrowths from the epidermal cells of a plant’s roots, significantly increasing the surface area for absorption. For the roots to respire, they require oxygen which is present in the air spaces between soil particles. Root hairs absorb this atmospheric oxygen that is dissolved in the soil moisture. This oxygen is then used for the respiration process within the root cells, providing the energy needed for active mineral uptake. Simultaneously, the carbon dioxide released from respiration diffuses out into the soil air through the thin membranes of the root hairs.

• Structured/Application/Skill type

Question 1. 

The following two chemical reactions are supposed to indicate a certain process occurring in the green plants under two different conditions:

(a) C6H12O6 + 6O2 → 6CO2 + _______ + 38 ATP

(b) C6H12O6 → ________ + 2 CO2 + 2 ATP

(i) Fill in the blank in each reaction.

(ii) Name the process represented by the two reactions.

(iii) What are the conditions under which the two reactions (a) and (b) are occurring respectively?

Ans:

(i) Filling in the blanks:

(a) The complete reaction is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP
(b) The complete reaction is: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + 2 ATP

(ii) Name of the process:

Both of these reactions represent different modes of cellular respiration. This is the biological process where cells break down glucose to release energy.

(iii) Conditions for the reactions:

Reaction (a) takes place when there is a plentiful supply of oxygen. This specific type is called aerobic respiration.

Reaction (b) occurs in environments that lack oxygen or have a very limited supply. This specific type is a form of anaerobic respiration, known as alcoholic fermentation.

Question 2. 

1. The following diagram refers to an apparatus which is used to demonstrate a physiological process:

What is the purpose of keeping potassium hydroxide solution in test tubes X and Y? 

2. The following diagram refers to an apparatus which is used to demonstrate a physiological process:

Why has the coloured water risen in tubing 1? 

3. The following diagram refers to an apparatus which is used to demonstrate a physiological process:

What is the purpose of keeping boiled peas soaked in a disinfectant in test tube Y?

4. The following diagram refers to an apparatus which is used to demonstrate a physiological process: 

Name the biological process which causes the above rise. 

5. The following diagram refers to an apparatus which is used to demonstrate a physiological process:

Define the biological process shown in the experiment.

Ans:

1.
The potassium hydroxide (KOH) solution is kept in the test tubes to absorb carbon dioxide (CO₂) produced by the respiring peas. KOH reacts with CO₂ to form potassium carbonate, thereby removing this gas from the air inside the apparatus.

2.
The coloured water rises in tubing 1 because the germinating peas in test tube X are respiring. They use up the oxygen present in the air of the test tube and produce carbon dioxide, which is immediately absorbed by the KOH solution. This creates a partial vacuum or a decrease in pressure inside test tube X, causing the coloured water from the beaker to be pushed up the tubing.

3. 

The boiled peas serve as a control for the experiment. Boiling kills the living cells, making the peas non-viable and unable to respire. Soaking them in a disinfectant prevents the growth of microorganisms. This setup ensures that any changes observed in test tube X are due to the respiration of the living peas and not some other external factor.

4.
The biological process that causes the rise of coloured water is Aerobic Respiration.

5.
Aerobic respiration is the process by which living cells break down glucose in the presence of oxygen to release energy, producing carbon dioxide and water as waste products.

Question 3. 

1. Given below is a set of six experimental set-ups (A-F), kept in this state for about 24 hours.

In how many flasks, the different plant parts have been kept under observation? 

2. Given below is a set of six experimental set-ups (A-F), kept in this state for about 24 hours.

What is the purpose of keeping a test-tube containing limewater in each flask?

3. Given below is a set of six experimental set-ups (A-F), kept in this state for about 24 hours.

In which tube/tubes the limewater will turn milky? 

4. Given below is a set of six experimental set-ups (A-F), kept in this state for about 24 hours.

What is the purpose of the set-up F? 

5. Given below is a set of six experimental set-ups (A-F), kept in this state for about 24 hours.

What conclusion can you draw from this experiment?

Ans:

1. In how many flasks, the different plant parts have been kept under observation?
   Different plant parts have been kept in five flasks (A, B, C, D, and E). Flask F is the control with no plant part.
2. What is the purpose of keeping a test-tube containing limewater in each flask?
   The purpose of the limewater is to detect the presence of carbon dioxide (CO₂). Limewater turns milky when carbon dioxide is passed through it, serving as an indicator for this gas.
3. In which tube/tubes the limewater will turn milky?
   The limewater will turn milky in all the flasks containing living plant parts: A, B, C, D, and E. This is because all living plant parts (fruits, leaves, roots) respire and release carbon dioxide. The limewater in flask F will remain clear.
4. What is the purpose of the set-up F?
   Set-up F acts as the control for the experiment. It shows that the milky appearance of limewater in other flasks is due to the respiration of the plant parts and not due to the atmospheric air inside the flask or any other external factor.
5. What conclusion can you draw from this experiment?
   The conclusion from this experiment is that respiration occurs in all living parts of a plant (fruits, leaves, and roots), as each of these parts releases carbon dioxide, which is a key product of the respiratory process.

Question 4. 

1. In order to study and prove a particular physiological process in plants, the following experiment was set up. Study the same and then answer the question that follows:  

Name the physiological process being studied. 

2. In order to study and prove a particular physiological process in plants, the following experiment was set up. Study the same and then answer the question that follows: 

What is the function of soda lime in the bottle ‘A’ and why is limewater placed in bottle ‘B’? 

3. In order to study and prove a particular physiological process in plants, the following experiment was set up. Study the same and then answer the question that follow:

What change would you expect to observe in bottle ‘D’? 

4. In order to study and prove a particular physiological process in plants, the following experiment was set up. Study the same and then answer the question that follow:

Represent the physiological process named in question 4.1 in the form of a chemical equation. 

5. In order to study and prove a particular physiological process in plants, the following experiment was set up. Study the same and then answer the question that follow:

In order to obtain accurate results, the bottle ‘C’ should be covered with black cloth. Why? 

6. In order to study and prove a particular physiological process in plants, the following experiment was set up. Study the same and then answer the question that follow:

If bottle ‘C’ was fitted with a 3-holed rubber stopper and a thermometer was introduced in such a way that its bulb reaches close to the germinating seeds, what would you observe? Why?

Ans:

1. Name the physiological process being studied.
The experiment is designed to investigate aerobic respiration in germinating seeds.

2. What is the function of soda lime in the bottle ‘A’ and why is limewater placed in bottle ‘B’?
The soda lime in bottle A acts as a chemical scrubber. Its job is to completely purify the incoming air by absorbing and removing any carbon dioxide present in it.
The limewater in bottle B serves as a visual checkpoint. Its clarity confirms that the air passing through to the seeds has been successfully stripped of carbon dioxide by the soda lime. If this limewater were to turn cloudy, it would indicate a failure in bottle A, meaning unpurified air is entering the main chamber.

3. What change would you expect to observe in bottle ‘D’?
You would observe the limewater in bottle D turning a milky or cloudy white.

4. Represent the physiological process named in question 4.1 in the form of a chemical equation.
The overall chemical equation for aerobic respiration is:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)
(Glucose + Oxygen produces Carbon Dioxide, Water, and usable Energy)

5. In order to obtain accurate results, the bottle ‘C’ should be covered with black cloth. Why?
Covering the flask with a black cloth is a crucial control measure to block out all light. This prevents the germinating seeds, which may develop small green parts, from performing photosynthesis. Photosynthesis would consume the carbon dioxide being produced by respiration, thereby masking the true amount of CO₂ generated and compromising the accuracy of the experiment.

6. If bottle ‘C’ was fitted with a 3-holed rubber stopper and a thermometer was introduced in such a way that its bulb reaches close to the germinating seeds, what would you observe? Why?
You would notice the thermometer’s reading gradually increasing over time. This occurs because respiration is an exothermic metabolic process. As the seeds break down glucose molecules to release stored energy, a considerable amount of this energy is liberated as heat, raising the temperature in their immediate surroundings.