1. Importance of Breathing
Breathing is essential for life as it provides energy required for daily activities like absorption, transport, movement, and reproduction. All living organisms need energy, and this energy comes from the food they consume.

2. Source of Energy
Energy is obtained by the oxidation (breaking down) of food (macromolecules). Green plants and cyanobacteria are unique because they can make their own food via photosynthesis, converting light energy into chemical energy stored in carbohydrates like glucose and starch.

3. Energy in Food

  • Not all cells in green plants perform photosynthesis. Only cells with chloroplasts, mainly in the outer layers, can do so.
  • Non-green parts of the plant (roots, stems, etc.) also need food for energy, which is transported from green parts where photosynthesis occurs.
  • Animals cannot make their own food (heterotrophic); they get energy from plants or other animals (herbivores or carnivores).
  • Fungi and other saprophytes depend on decaying organic matter for energy.
  • All energy ultimately comes from photosynthesis.

4. Photosynthesis vs. Respiration

  • Photosynthesis occurs in chloroplasts (in eukaryotes) and converts light energy into stored chemical energy.
  • Respiration, which occurs in cytoplasm and mitochondria, breaks down food to release energy. This energy is trapped in the form of ATP (adenosine triphosphate), the energy currency of cells.

5. Respiration Process

  • Respiration involves the oxidation of respiratory substrates (mainly carbohydrates), which releases energy in a controlled, stepwise manner, not all at once.
  • ATP is used to power various cellular processes. The carbon skeleton produced during respiration is used to build other molecules needed by the cell.

Do Plants Breathe?

  • Respiration in Plants: Plants do breathe, but in a different way compared to animals. They require oxygen (O₂) for respiration, and they also release carbon dioxide (CO₂) as a waste product.
  • Gas Exchange in Plants: Unlike animals, plants do not have specialized organs for breathing. They use stomata (tiny pores on leaves) and lenticels (openings in stems) for gas exchange.
  • Why No Specialized Organs: Plants can manage with fewer respiratory organs because:
    • Each plant part handles its own gas exchange needs.
    • Plants do not require as much gas exchange as animals.
    • The gases don’t need to travel far because plant cells are close to the surface, and air spaces in cells help with diffusion.

Respiratory Mechanism in Plants:

  • Glucose Oxidation: In plants, glucose is oxidized in a series of steps to release energy. However, the energy isn’t released all at once but is carefully used to make ATP, which can then power the plant’s functions.
  • Role of Oxygen: Oxygen is used in the process of respiration, and this can happen even in environments with low oxygen availability. Some organisms can also survive in conditions without oxygen (anaerobic conditions).

Glycolysis

1. What is Glycolysis?
Glycolysis is the breakdown of glucose into pyruvic acid. It is a key step in respiration and happens in the cytoplasm of the cell.

2. Steps in Glycolysis:

  • Initial Phase: Two ATP molecules are consumed to convert glucose into glucose-6-phosphate and then into fructose-6-phosphate.
  • Energy Production: During glycolysis, ATP and NADH (another energy carrier) are produced. This energy is released as glucose is converted into pyruvic acid.

3. Key Points:

  • ATP: 4 ATP molecules are produced, but 2 are used in the initial steps, so the net gain is 2 ATP molecules per glucose molecule.
  • NADH Formation: NAD+ is reduced to NADH as glucose is oxidized, which is crucial for later stages of respiration.

4. Fate of Pyruvic Acid:
Pyruvic acid, the product of glycolysis, can follow different pathways depending on oxygen availability:

  • Fermentation: In anaerobic conditions, pyruvic acid can undergo fermentation (either lactic acid or alcoholic fermentation).
  • Aerobic Respiration: In the presence of oxygen, pyruvic acid enters the Krebs cycle (aerobic respiration) to fully oxidize glucose into CO₂ and H₂O, releasing a significant amount of energy.

Summary of Key Points:

  • All living organisms need energy for their activities, and this energy comes from food.
  • Green plants make their own food through photosynthesis, while animals and other organisms rely on external sources.
  • Respiration involves breaking down food molecules (like glucose) to release energy, stored as ATP.
  • Plants do “breathe,” but in a less complex manner than animals, using stomata and lenticels for gas exchange.
  • Glycolysis is the first step of cellular respiration, breaking glucose into pyruvic acid and generating small amounts of energy.
  1. Fermentation:
    • Definition: In fermentation, glucose undergoes incomplete oxidation under anaerobic conditions (without oxygen) to produce pyruvic acid, which is then converted into CO2 and ethanol (alcohol) in yeast or lactic acid in some bacteria.
    • Key Enzymes:
      • Pyruvic acid decarboxylase and alcohol dehydrogenase are responsible for converting pyruvic acid into alcohol (in yeast).
      • Lactate dehydrogenase is responsible for reducing pyruvic acid into lactic acid (in muscles during exercise).
    • Energy Released: Fermentation produces very little energy (only about 7% of the energy in glucose), and this energy is not fully captured in ATP molecules.
    • Hazards: The products of fermentation (acid or alcohol) can be toxic at high concentrations (yeast dies at alcohol levels around 13%).
    • ATP Synthesis: For each glucose molecule fermented, only 2 ATP molecules are gained, but glycolysis consumes 2 ATP, resulting in a net of 0 ATP during fermentation.
  2. Aerobic Respiration:
    • Definition: In the presence of oxygen, glucose undergoes complete oxidation, releasing CO2, H2O, and a large amount of energy.
    • Location: Aerobic respiration occurs in the mitochondria of eukaryotic cells.
    • Steps Involved:
      • Pyruvate Transport: The product of glycolysis (pyruvate) is transported into the mitochondria.
      • Pyruvate Decarboxylation: Pyruvate is decarboxylated and converted into Acetyl CoA by the pyruvic dehydrogenase enzyme. This step produces NADH.
      • Krebs Cycle (TCA Cycle): Acetyl CoA enters the Krebs cycle, generating NADH, FADH2, and a small amount of ATP.
      • Electron Transport Chain (ETS): NADH and FADH2 transfer electrons through the electron transport system (ETS), where oxygen acts as the final electron acceptor to form water. This process generates a large amount of ATP (3 ATP from NADH and 2 ATP from FADH2).
      • Oxidative Phosphorylation: The energy from the ETS is used to synthesize ATP through a process called oxidative phosphorylation.
  3. Tricarboxylic Acid (TCA) Cycle:
    • Function: The TCA cycle begins with the combination of Acetyl CoA and oxaloacetic acid (OAA) to form citric acid. This cycle involves the release of carbon dioxide, the reduction of NAD+ to NADH, and the reduction of FAD to FADH2.
    • Energy Production: The cycle also produces GTP (which is converted to ATP).
    • Significance: It helps to regenerate oxaloacetate and supports the ongoing oxidation of acetyl CoA, ensuring a continuous flow of energy production.
  4. ATP Production:
    • Aerobic respiration produces a net gain of 38 ATP molecules per glucose molecule, with energy derived from NADH and FADH2. However, the exact ATP yield can vary due to transport inefficiencies and other cellular conditions.
  5. Fermentation vs. Aerobic Respiration:
    • Fermentation: Incomplete breakdown of glucose with a net gain of only 2 ATP per glucose molecule.
    • Aerobic Respiration: Complete breakdown of glucose, generating significantly more ATP (38 ATP), and is much more energy-efficient.
  6. Amphibolic Pathway:
    • The respiratory pathway is amphibolic, meaning it involves both catabolism (breaking down molecules for energy) and anabolism (synthesizing molecules like fats and proteins).
    • Fat and Protein Metabolism: Fatty acids and proteins can be converted into intermediates of the Krebs cycle, such as acetyl CoA and pyruvate.
  7. Respiratory Quotient (RQ):
    • The RQ is the ratio of CO2 produced to O2 consumed during respiration.
    • Carbohydrates: RQ = 1 (equal CO2 and O2)
    • Fats: RQ < 1 (since fats produce more CO2 per O2 consumed)
    • Proteins: RQ ≈ 0.9 (proteins have a different rate of oxidation).
  8. Summary:
    • Cellular respiration involves breaking down organic molecules (like glucose) to release energy.
    • The process can either be anaerobic (fermentation) or aerobic (using oxygen).
    • The final products of aerobic respiration are CO2, H2O, and a large amount of ATP.
    • The process is amphibolic, as it supports both breakdown and synthesis of molecules.

Additional Knowledge for Competitive Exams:

  • Fermentation and aerobic respiration are critical in understanding energy production in cells, especially in processes like exercise physiology, microbial fermentation, and energy metabolism.
  • The respiratory quotient is useful in calculating the type of substrate used (carbohydrates, fats, or proteins) and can be applied in biochemistry and ecology to understand how organisms use different energy sources.

These all are the notes of clhapter 12. And important questions are below HERE. *#THANKS FOR VISITING, VISIT AGAIN #* 😊

1. Why is breathing important?

Answer: Breathing is essential for life because it provides oxygen needed for respiration. Respiration is the process where energy is released from food. This energy is required for activities like moving, growing, reproducing, and maintaining body functions.

2. Where does energy come from in living organisms?

Answer: Energy comes from the food organisms consume. When food (like carbohydrates) is broken down, energy is released. Green plants can make their own food through photosynthesis, while animals get energy from plants or other animals.

3. Do plants need energy? How do they get it?

Answer: Yes, plants need energy too. They get energy from food made through photosynthesis. Photosynthesis happens in the green parts of plants, like leaves, where light is converted into chemical energy stored in sugars like glucose.

4. What is the difference between photosynthesis and respiration?

Answer: Photosynthesis is the process in plants where light energy is converted into chemical energy (stored in glucose). It happens in the chloroplasts. Respiration, on the other hand, occurs in all living organisms and breaks down food (like glucose) to release energy. Respiration happens in the cytoplasm and mitochondria.

5. Do plants breathe?

Answer: Yes, plants do breathe, but in a simpler way than animals. They take in oxygen for respiration and release carbon dioxide. Plants use stomata (tiny pores) on their leaves and lenticels (pores on stems) for this gas exchange.

6. What is glycolysis?

Answer: Glycolysis is the first step of respiration. It happens in the cytoplasm of the cell and involves breaking down glucose into pyruvic acid. This process releases a small amount of energy and produces ATP and NADH, which are used later for energy.

7. What happens to pyruvic acid after glycolysis?

Answer: Pyruvic acid can follow two pathways:

  • Fermentation: In the absence of oxygen (anaerobic conditions), pyruvic acid is converted into lactic acid or ethanol (alcohol).
  • Aerobic Respiration: In the presence of oxygen, pyruvic acid enters the mitochondria for complete breakdown in the Krebs cycle, releasing large amounts of energy.

8. What is fermentation?

Answer: Fermentation is a process where glucose is partially broken down without oxygen (anaerobic). This process produces very little energy and results in products like lactic acid (in muscles during exercise) or ethanol (in yeast). It only produces 2 ATP molecules per glucose molecule.

9. What is aerobic respiration?

Answer: Aerobic respiration occurs when oxygen is available. It involves the complete breakdown of glucose in the mitochondria, resulting in carbon dioxide, water, and a large amount of energy (ATP). It produces about 38 ATP molecules per glucose molecule.

10. How do fat and protein contribute to energy production?

Answer: Fat and proteins can also be used for energy. They are broken down into molecules like Acetyl CoA, which enter the Krebs cycle to produce ATP. This shows how respiration is amphibolic, meaning it breaks down molecules for energy and also synthesizes others.

11. What is the Respiratory Quotient (RQ)?

Answer: The Respiratory Quotient (RQ) is the ratio of carbon dioxide (CO₂) produced to oxygen (O₂) consumed during respiration.

  • For carbohydrates, RQ = 1 (equal CO₂ and O₂).
  • For fats, RQ < 1 (more CO₂ is produced than O₂ consumed).
  • For proteins, RQ ≈ 0.9 (proteins have a different oxidation rate).

12. What is the TCA (Krebs) Cycle?

Answer: The TCA cycle is a series of reactions in the mitochondria that helps break down Acetyl CoA into CO₂ and produces energy molecules like NADH, FADH2, and ATP. It is crucial for energy production during aerobic respiration.

13. What is oxidative phosphorylation?

Answer: Oxidative phosphorylation is the final step of aerobic respiration. It occurs in the mitochondria, where energy from NADH and FADH2 is used to generate a large amount of ATP. Oxygen acts as the final electron acceptor, forming water.

14. What are the differences between fermentation and aerobic respiration?

Answer: The key differences are:

  • Fermentation: Happens without oxygen, produces very little ATP (2 ATP per glucose), and produces products like lactic acid or alcohol.
  • Aerobic Respiration: Requires oxygen, produces much more ATP (38 ATP per glucose), and produces CO₂ and water as byproducts.

15. What is the role of enzymes in respiration?

Answer: Enzymes like pyruvic acid decarboxylase and lactate dehydrogenase help convert pyruvic acid into lactic acid or alcohol during fermentation. In aerobic respiration, enzymes help in breaking down glucose and transferring electrons during the electron transport chain.

Additional Knowledge for Competitive Exams:

  • Fermentation and aerobic respiration are crucial for understanding how energy is produced in cells. These processes are important in fields like exercise physiology (how muscles generate energy during exercise) and microbial fermentation (used in brewing, baking, etc.).
  • Respiratory Quotient helps scientists understand which type of molecule (carbohydrate, fat, or protein) is being used for energy, which is important in biochemistry and ecology.
  • Amphibolic pathways help in both breaking down molecules for energy (catabolism) and synthesizing new molecules (anabolism), which is key to maintaining life processes.