Respiration in Plants

1. The breakdown of glucose to carbon dioxide and water does not occur in a single step, but in a series of chemical steps. These steps occur in two major phases — (i) glycolysis (glucose → pyruvate) occurring in cytoplasm and (ii) Krebs cycle (pyruvate → CO₂ + 6H₂O + ATP) occurring in mitochondria.
2. Each breakdown step occurs due to a particular enzyme.
3. The energy liberated in the breakdown of glucose molecule is not all in the form of heat, but a large part of it is converted into chemical energy in the form of ATP.

The three inlets of oxygen for respiration in plants are:

1. Stomata in leaves.
2. Lenticels in stem.
3. General surface of the roots.

1. Aerobic respiration
   C₆H₁₂O₆ + 6O₂ $\xrightarrow{\text{enzyme}}$ 6CO₂ + 6H₂O + 38ATP

2. Anaerobic respiration
   C₆H₁₂O₆ ⟶ 2C₂H₅OH + 2CO₂ + 2ATP

Aerobic respiration is the primary and the most efficient way for plants to generate energy. On the other hand, anaerobic respiration is a backup mechanism for plants when oxygen is limited and occurs temporarily for short periods.

Bacteria and fungi.

In experiments on respiration, the seeds taken as control are boiled to kill them. It is done in order to compare the live seeds that can respire to dead seeds that cannot respire.

1. Soda lime is used to absorb any carbon dioxide released by the seeds.
2. Limewater is used to test for the presence of carbon dioxide as carbon dioxide turns limewater milky.

It is necessary that this experiment is carried out in dark in order to stop the process of photosynthesis so that the carbon dioxide liberated in respiration is not used up for photosynthesis.

We cannot use water because it contains dissolved gases such as oxygen and carbon dioxide.

In anaerobic respiration in plants, the end product is ethanol and carbon dioxide instead of lactic acid in animals.

in which glucose is broken down into pyruvate

Reason — Glycolysis is the first phase of respiration in which glucose is broken down into pyruvate.
Glycolysis occurs in the cytoplasm of the cell, not in mitochondria. The mitochondria are involved later in respiration. In this process, one molecule of glucose is converted into two molecules of pyruvate, releasing energy. Glycolysis occurs before the Krebs cycle, not “next to” it. It happens in the cytoplasm, while the Krebs cycle occurs in the mitochondria.

Stomata and lenticels

Reason — Stomata are tiny pores present on the surface of leaves and lenticels are present on stems.
Stomata help in gaseous exchange and transpiration. Veins transport water, minerals, and food. Lenticels help in gaseous exchange and sepals protect the flower bud.
Hydathodes are responsible for guttation.

Baker’s yeast

Reason — Anaerobic respiration normally occurs in fungi.
Grass performs aerobic respiration under normal conditions. Cactus also carries out aerobic respiration. It is adapted to dry conditions (CAM photosynthesis), but respiration still requires oxygen. Coconut plants respire aerobically like most plants under normal conditions.

38

Reason — Oxidation of 1 molecule of glucose gives 38 ATP.

In all the parts

Reason — Leaves respire through stomata, stems respire through lenticel and roots respire through their general surface.
Stomata are structures for gas exchange, not the site of respiration. Respiration occurs inside cells, not in stomata. Leaves do respire, but respiration is not limited to leaves. All living parts of the plant need energy. Lenticels also help in gas exchange in woody stems, but respiration does not occur only there.

Ethyl alcohol

Reason — Anaerobic respiration in plants leads to the formation of ethyl alcohol.
Soda lime is a chemical mixture used to absorb carbon dioxide in experiments. It is not a product of respiration. Limewater is a solution of calcium hydroxide used to test for carbon dioxide. It is not a product of respiration.

Cytoplasm

Reason — Glycolysis takes place in cytoplasm whereas Krebs cycle takes place in mitochondria.
Chloroplasts are involved in photosynthesis, not glycolysis. Mitochondria are the site of the Krebs cycle and electron transport chain, which occur after glycolysis. Glycolysis occurs in the cytoplasm of the cell.

Calcium carbonate

Reason — When carbon dioxide is passed through limewater (calcium hydroxide), it reacts to form calcium carbonate, a white precipitate that makes the solution turn milky.
Sodium carbonate is not formed in this reaction because limewater contains calcium, not sodium. Calcium chloride is formed in reactions involving hydrochloric acid, not carbon dioxide. Sodium chloride is unrelated to this reaction.

Glucose

Reason — Glucose is the simplest sugar. Any sugar first breaks to form glucose, which further breaks down to release energy.
Starch is a storage carbohydrate. It must first be broken down into glucose before it can be used in respiration. Oxygen is not a substrate; it is a reactant in aerobic respiration that helps release energy, but it is not the fuel. Sucrose is a sugar, but it must first be broken down into glucose and fructose before entering respiration.

Respiration

Reason — Respiration is a catabolic process because it breaks down glucose into simpler substances (carbon dioxide and water) and releases energy.
Photosynthesis is an anabolic process that leads to the formation of glucose while respiration (a catabolic process) leads to the breakdown of glucose molecules.

P — Glycolysis, Q — Kreb's cycle

Reason — In glycolysis glucose is broken down to form pyruvate and in Kreb's cycle it is completely oxidised to form CO₂, ATP, and NADH.
Glycogenesis is the process of forming glycogen from glucose (storage), not a step of respiration. Aerobic respiration and Anaerobic respiration are two different types of respiration, not sequential processes. Anoxybiotic respiration and Oxybiotic respiration are older terminology for anaerobic and aerobic respiration.

Sukhvinder and Aayush

Reason — Anaerobic respiration is the breakdown of glucose in the absence of oxygen. The end products vary depending on the organism:

• In plants and yeast:
  Glucose → Ethanol + Carbon dioxide + Energy
• In animals (like humans during vigorous exercise):
  Glucose → Lactic acid + Energy

As Aayush said Lactic acid so his answer is correct. Sukhvinder said Carbolic acid and lactic acid. Carbolic acid is wrong, but lactic acid is correct for animals. So, Sukhvinder's answer is partially correct.

1. Lenticels are the openings found on older stems.

2. Glycolysis occurs in the cytoplasm of the cells.

3. Glucose is a respiratory substance.

4. Rate of Photosynthesis is more than the rate of Respiration in the daytime in the case of green plants.

5. Pyrogallate of potash is a chemical substance which absorbs oxygen of the air.

6. Caustic potash (KOH) is used to create vacuum to show anaerobic respiration.

1. ATP (Adenosine triphosphate)
2. Respiration
3. Yeast
4. Glycolysis
5. Soda lime

Respiration is an essential life process for all living organisms. Therefore, plants also respire all day and all night.

1. False
   Corrected Statement — Aerobic respiration of one mole of glucose yields 38 ATP.

2. False
   Corrected Statement — Anaerobic respiration in plants yields ethanol.

3. True

4. False
   Corrected Statement — All leaves of a green plant normally respire aerobically at night.

(a) Respiration — Respiration is a catabolic process of releasing energy from glucose for carrying out life processes.

(b) Combustion — Combustion or burning is defined as a physio-chemical process in which energy is liberated in the form of heat and light.

(c) ATP — ATP is defined as energy currency of the cell as it acts as the immediate source of energy for different life processes.

(a) Glucose and Oxygen

(b) Carbon dioxide and water

(c) Bacteria and Fungi

Full form of ATP — Adenosine triphosphate

Full form of ADP — Adenosine diphosphate

The energy liberated in respiration is stored in the form of ATP inside the cells. Some part of it is lost as heat to the surroundings.

Tilling makes the soil porous and airy. The parts of the plant present below the ground receive adequate oxygen supply to respire. This way tilling facilitates faster crop growth.

During daytime, both photosynthesis and respiration take place in green plants. Evolution of carbon dioxide is an indicator used to demonstrate respiration in living organisms. However, the carbon dioxide produced during respiration is used up during photosynthesis. Consequently, there is no visible evolution of carbon dioxide during daytime, making it difficult to demonstrate respiration in green plants.

Cell respiration cannot occur in any organism at a temperature of about 65°C because the enzymes involved in respiration become inactivated at high temperatures.

(a) Difference between Aerobic and anaerobic respiration:

(b) Difference between Respiration and combustion:

(c) Difference between Stomata and lenticels:

(d) Difference between Photosynthesis and respiration:

(e) Difference between Anaerobic respiration in plants and animals:

Given below are the ways in which the following structures help in plant respiration:

(a) Lenticels — Lenticels are openings present on mature stems. They allow oxygen from the air to diffuse into the stem and carbon dioxide produced during respiration to diffuse out.

(b) Stomata — Stomata are pores present mainly on the leaves. They allow the exchange of respiratory gases, i.e., oxygen diffuses in and carbon dioxide diffuses out.

(c) Root hairs — Root hairs are in contact with air spaces present between soil particles. Oxygen diffuses through these air spaces into the root hairs and is used for respiration by root cells.

The differences between aerobic and anaerobic respiration in plants are as follows:

Respiration is said to be the reverse of photosynthesis due to the following reasons :

1. In respiration, organic food is broken down into inorganic substances, namely carbon dioxide and water. In photosynthesis, organic food is manufactured from inorganic substances, namely carbon dioxide and water.
2. In respiration, carbon dioxide is released whereas in photosynthesis, carbon dioxide is consumed.
3. Oxygen is consumed during respiration whereas oxygen is evolved during photosynthesis.
4. Energy is liberated during respiration whereas energy is absorbed during photosynthesis.

Oxidation of organic food particularly carbohydrates in living cells to release energy is called respiration.

Similarities between burning and respiration are —

1. Oxygen is required by both.
2. Energy is released by both.
3. The end products of both are water and carbon dioxide.

Differences between burning and respiration:

1. Aim — Experiment demonstrating the fact that germinating seeds produce heat.

Procedure —

1. Take two thermos flasks and mark them as 'A' and 'B'.
2. Take pea or bean seeds and soak them in water for more than 24 hours.
3. Divide the seeds into two equal groups.
4. Kill one group of seeds by boiling them and wash them with dilute formalin or carbolic acid to prevent bacterial decay.
5. Place the live germinating seeds in flask A and the boiled/killed seeds in flask B.
6. Introduce a thermometer into each of the flasks and seal their mouths with cotton wool.
7. Note the initial reading on each thermometer.

Inference —

1. A few hours later, the thermometer in flask A shows a higher reading, showing that germinating seeds produce heat during respiration.

2. Flask B shows no rise in temperature.

3. Aim — Experiment demonstrating the fact that germinating seeds produce Carbon dioxide.

Procedure —

1. Take two flasks and mark them as ‘A’ and ‘B’.
2. At the base of both the flasks, place wet cotton wool.
3. In flask A, take a few soaked pea seeds. In flask B, take an equal number of boiled seeds.
4. To flask B, add some carbolic acid so as to inhibit bacterial growth on the dead seeds.
5. Seal the flasks with corks and leave them undisturbed for a couple of days.
6. Observe the changes.

Inference —

1. After a few days, germination of seeds is observed in flask A.

2. Flask B shows no signs of seed germination.

3. The cork is removed to test the gases in each flask. The flask is tilted over a test tube containing limewater and the test tube is shaken.

4. The gas from flask A turns limewater milky, indicating the presence of carbon dioxide and showing that germinating seeds produce carbon dioxide.

5. The gas in the flask B shows no effect upon coming in contact with limewater, indicating absence of carbon dioxide.

6. Aim — Experiment demonstrating that germinating seeds can respire even in the complete absence of air

Procedure and Inference —

1. Fill a test tube with mercury and invert it into a beaker containing mercury.
2. Push some soaked and peeled pea seeds into the test tube before inverting it into the mercury beaker.
3. The seeds float up and remain completely surrounded by mercury.
4. After a few days, the mercury level falls and some gas collects in the test tube.
5. Introduce a stick or pellet of potassium hydroxide (KOH) into the test tube.
6. The gas in the tube is absorbed and the mercury level rises again, showing that the gas was carbon dioxide.
7. Consequently it is proved that the germinating seeds undergo respiration even in the total absence of air.

Below diagram shows the experimental set up (initial and final stages) to demonstrate anaerobic respiration in germinating seeds:

1. (a) 6H₂O
   (b) 2C₂H₅OH
2. (a) The process observed in this chemical reaction here is aerobic respiration
   (b) The process observed in this chemical reaction is anaerobic respiration
3. The reaction occurring in (a) can take place only in the presence of oxygen as it is aerobic respiration. The reaction occurring in (b) can take place even in the absence of oxygen as it is anaerobic respiration.

(a) Mercury is used because it excludes air and prevents oxygen from entering the test tube, thus creating anaerobic conditions. It also does not dissolve gases easily, so the gas released can collect at the top.
We cannot use air because it contains oxygen and would make respiration aerobic. Water is also not suitable because it contains dissolved gases and can dissolve carbon dioxide, preventing proper collection of the gas.

(b) The gas released by the germinating seeds is carbon dioxide.

(c) Yes, the experiment can be done without peeling the seeds, but peeling the seed coat hastens the outward diffusion of carbon dioxide.

(d) The gas released can be tested by introducing potassium hydroxide (KOH) into the test tube. KOH absorbs carbon dioxide, causing the mercury level to rise again. Alternatively, carbon dioxide can be confirmed by passing the gas through limewater, which turns milky due to the formation of calcium carbonate.

(e) A control set-up can be prepared in the same way, but with boiled and sterilised seeds instead of germinating seeds. Since boiled seeds are dead, they do not respire and no gas is produced.

(a) The experiment demonstrates that carbon dioxide is produced during the process of respiration in germinating seeds.

(b) Soda lime is placed in bottle ‘A’ to absorb any carbon dioxide present in the incoming air. Limewater is placed in bottle ‘B’ to confirm that the air entering bottle ‘C’ is free from carbon dioxide; therefore, the limewater in bottle ‘B’ remains clear.

(c) The limewater in bottle ‘D’ will turn milky. This happens because the germinating seeds in bottle ‘C’ give out carbon dioxide during respiration, and this carbon dioxide passes into bottle ‘D’.

(d) The chemical reaction is as written below:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38ATP (energy)

(e) Bottle ‘C’ is covered with a black cloth to prevent photosynthesis. This ensures that the carbon dioxide produced during respiration is not used up in photosynthesis.

(f) A rise in temperature would be observed. This is because germinating seeds respire and release some energy in the form of heat.

(a) Potassium hydroxide solution is kept in test tubes X and Y to absorb the carbon dioxide produced during respiration.

(b) In test tube X, the germinating peas respire and use up oxygen. The carbon dioxide produced is absorbed by potassium hydroxide. This reduces the volume and pressure of air inside the apparatus, so coloured water rises in tubing 1.

(c) Boiled peas soaked in a disinfectant are kept in test tube Y as the control. Boiling kills the peas, so they do not respire, and the disinfectant prevents bacterial growth.

(d) The biological process that causes the rise is respiration.

(e) Respiration is a catabolic process in which glucose is broken down in living cells to release energy for carrying out life processes.

(a) Different plant parts have been kept under observation in five flasks, A to E.

(b) Limewater is kept in each flask to test for the presence of carbon dioxide. It turns milky when carbon dioxide is present.

(c) The limewater will turn milky in flasks A, B, C, D and E because each of these flasks contains a plant part that respires and gives out carbon dioxide. The limewater in flask F will not turn milky because no plant part is present in it.

(d) In the experiment, the setup F depicts the experiment control, wherein all conditions are maintained in the same way except for the plant part that is absent in flask F.

(e) The experiment shows that all living plant parts respire and give out carbon dioxide during respiration.

A is true but R is false.

Reason — A is true as all parts of a plant respire continuously, both day and night, to produce energy.
R is false because all parts of a plant respire, not just leaves. Stems respire through lenticels, while roots respire through their general surface/root hairs.

Therefore, A is true but R is false is the correct option.

Both A and R are true and R is the correct explanation of A.

Reason — A is true as respiration is a catabolic process.
R is true as it breaks down glucose to release energy in form of ATP.

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

Both A and R are true and R is the correct explanation of A.

Reason — A is true as in anaerobic respiration in plants (e.g., yeast), the end products are ethyl alcohol and carbon dioxide.
R is true as in anaerobic respiration incomplete breakdown of glucose takes place.

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

Assertion (A): In many respects, respiration and photosynthesis in plants are distinctly opposite processes.

Reason (R): In photosynthesis, food is oxidised; whereas in respiration, food is manufactured.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

A is True but R is False.

Reason — A is True as photosynthesis and respiration are opposite processes.
R is False as in photosynthesis glucose is manufactured from carbon dioxide and water and energy, while in respiration glucose is broken down (oxidised) to obtain carbon dioxide water and energy.

Therefore, A is True but R is False is the correct option.

A is true but R is false.

Reason — A is true as the Krebs cycle occurs in the mitochondria and releases energy.
R is false because glycolysis occurs in the cytoplasm, while the Krebs cycle occurs in the mitochondria.

Therefore, A is true but R is false is the correct option.

A is False but R is True.

Reason — A is False as lenticels are the openings found on the surface of stem.
R is True as they help in gaseous exchange through diffusion.

Therefore, A is False but R is True is the correct option.

(a) These special pores found on the surface of stems are called lenticels and on the surface of leaves are called stomata.

(b) Yes, the main steps of respiration in plants are similar to those in humans. They include glycolysis and the Krebs cycle.

(c) The cell organelle which is mainly involved in the production of energy is mitochondria.

(d) The lower surface of leaves contains more number of these respiratory pores.
It is advantageous because it reduces water loss while still allowing gas exchange.

(e) Two more significant processes which occur through these pores are transpiration and exchange of gases required for photosynthesis.