JAMB Biology Note-Respiration

Sub Topics

a. Respiratory organs and surfaces
b. The mechanism of gaseous exchange in:
i. Plants
ii. Mammals
c. Aerobic respiration
d. Anaerobic respiration

Table of Contents

• Sub Topics
  • A. Respiration
    • i. Significance of Respiration
    • ii. The Chemical Processes in Respiration: Glycolysis and Krebs Cycle
    • iii. Experimental Setup for Gaseous Exchange, Heat Production, and Products of Respiration
  • B. Respiratory Organs and Surfaces
    • 1. Body Surface
    • 2. Gills
    • 3. Trachea
    • 4. Lungs
    • 5. Stomata
    • 6. Lenticels
  • C. Mechanism of Gaseous Exchange
    • i. Mechanism for Opening and Closing of Stomata
    • ii. Respiratory Movements in Animals
  • D. Role of Oxygen in the Liberation of Energy for Activities of Living Organisms
  • E. Types of Respiration
    • i. Aerobic Respiration
    • ii. Anaerobic Respiration (Fermentation)
  • Summary

A. Respiration

Respiration is a biochemical process through which cells release energy from organic compounds (mainly glucose) and use it to perform various cellular activities. Unlike breathing, which is the physical process of taking in oxygen and expelling carbon dioxide, respiration involves the breakdown of glucose to produce energy in the form of ATP (adenosine triphosphate). This energy is essential for maintaining cellular functions and supporting metabolic processes.

i. Significance of Respiration

• Energy Production: The primary purpose of respiration is to release energy stored in organic molecules, particularly glucose, and to convert this energy into a usable form (ATP) that powers cellular processes.
• Sustaining Life: ATP is needed for various cellular functions, including muscle contraction, protein synthesis, DNA replication, and active transport of molecules across membranes.
• Gaseous Exchange: In the process of respiration, organisms exchange gases—oxygen is used to oxidize glucose, and carbon dioxide is produced as a waste product. The balance of oxygen and carbon dioxide in the environment and within the cells is crucial for maintaining homeostasis.
• Heat Production: Respiration is also exothermic, meaning it releases energy in the form of heat. This helps maintain body temperature in warm-blooded organisms.

---

ii. The Chemical Processes in Respiration: Glycolysis and Krebs Cycle

Respiration occurs in several stages: Glycolysis, Krebs Cycle (Citric Acid Cycle), and Electron Transport Chain (ETC). Below are the simplified processes involved in Glycolysis and Krebs Cycle:

1. Glycolysis (Occurs in the cytoplasm)
   • Definition: The process by which one molecule of glucose (a 6-carbon compound) is broken down into two molecules of pyruvate (3-carbon compound).ATP Production: Glycolysis produces a small amount of ATP directly by substrate-level phosphorylation. It also produces NADH, which carries high-energy electrons to the electron transport chain.Steps:
     • Glucose (C₆H₁₂O₆) is phosphorylated using 2 ATP molecules to form a 6-carbon sugar phosphate.The 6-carbon sugar is split into two 3-carbon molecules of pyruvate.During the breakdown, 4 ATP molecules are produced (a net gain of 2 ATP), and 2 NADH molecules are generated, which will later be used in the electron transport chain for further ATP production.
   Overall Glycolysis Equation:

Glucose + 2 NAD⁺ + 2 ADP + 2 P_i → 2 Pyruvate + 2 NADH + 2 ATP + 2 H₂O

1. Krebs Cycle (Occurs in the mitochondria)
   • Definition: The Krebs cycle, also known as the citric acid cycle, is a series of reactions that further oxidize the pyruvate produced in glycolysis, releasing carbon dioxide and transferring energy to carrier molecules like NADH, FADH₂, and ATP.ATP Production: The Krebs cycle produces a small amount of ATP directly (through substrate-level phosphorylation), but its main role is to produce high-energy electron carriers (NADH and FADH₂) for the electron transport chain.Steps:
     • The 2 molecules of pyruvate are converted into acetyl-CoA before entering the cycle.Acetyl-CoA combines with oxaloacetate (a 4-carbon molecule) to form citrate (a 6-carbon molecule).Through a series of reactions, 2 carbon atoms are released as carbon dioxide, and high-energy molecules (NADH and FADH₂) are produced.ATP is synthesized directly in the cycle.The remaining molecule, oxaloacetate, is regenerated, allowing the cycle to continue.
   Overall Krebs Cycle Equation (per glucose molecule):

2 Acetyl-CoA + 6 NAD⁺ + 2 FAD + 2 ADP + 2 P_i + 4 H₂O → 4 CO₂ + 6 NADH + 2 FADH₂ + 2 ATP

---

iii. Experimental Setup for Gaseous Exchange, Heat Production, and Products of Respiration

Experiments can be conducted to study the gaseous exchange, the heat production, and the products of respiration. A simple experiment involves the use of an organism (e.g., a germinating seed or an animal like a small mammal) in a sealed container to measure oxygen consumption and carbon dioxide production.

1. Gaseous Exchange:
   • Setup: A small animal or plant is placed in a sealed chamber. Oxygen levels are measured before and after a set period to determine the amount of oxygen consumed. The amount of carbon dioxide produced is measured using a chemical indicator like sodium hydroxide that absorbs carbon dioxide.
   • Result: Oxygen is consumed, and carbon dioxide is produced, indicating that respiration is taking place. The balance of gases (oxygen consumption and carbon dioxide production) is a direct outcome of the metabolic processes in respiration.
2. Heat Energy Production:
   • Setup: A similar setup can be used to measure the heat produced during respiration. A calorimeter can be used to measure the temperature change in a controlled environment.
   • Result: Heat is produced during respiration as glucose is broken down and converted into ATP. The temperature of the container will rise as a result of this exothermic process.
3. Products of Respiration:
   • Primary Products: The primary products of respiration are carbon dioxide (CO₂) and water (H₂O), which are excreted as waste products.
   • ATP: The energy released during respiration is stored as ATP, which is then used for various cellular functions.
   • By-products: In the case of anaerobic respiration (e.g., in muscle cells during strenuous activity), lactic acid or ethanol may also be produced.

B. Respiratory Organs and Surfaces

Respiration in living organisms involves the exchange of gases (oxygen and carbon dioxide) between cells and their environment. Different organisms have developed specialized respiratory organs and surfaces adapted to their environment and metabolic needs.

1. Body Surface

• Organism: Invertebrates like earthworms and amphibians such as frogs.
• Mechanism: Oxygen diffuses directly through the moist skin (body surface) into the blood, and carbon dioxide diffuses out. This method is efficient in moist, low-oxygen environments but becomes inefficient as the size of the organism increases.

2. Gills

• Organism: Aquatic organisms like fish and amphibians (e.g., tadpoles).
• Mechanism: Gills consist of thin layers of tissue that allow for the diffusion of gases between the water and the bloodstream. Oxygen from the water diffuses into the gills, and carbon dioxide diffuses out into the water. Water flows over the gills, maintaining a constant supply of oxygen.

3. Trachea

• Organism: Insects like grasshoppers and cockroaches.
• Mechanism: The tracheal system consists of a network of tubes that carry air directly to the cells. Air enters the trachea through openings called spiracles and travels through smaller branches, reaching cells for gas exchange.

4. Lungs

• Organism: Terrestrial vertebrates like mammals (e.g., humans, lions), birds, and reptiles.
• Mechanism: Lungs are specialized organs for gas exchange, where oxygen from the air is diffused into the bloodstream, and carbon dioxide is diffused out. In mammals, air is inhaled into the lungs, where the alveoli (tiny air sacs) facilitate gas exchange due to their large surface area and thin walls.

5. Stomata

• Organism: Plants.
• Mechanism: Stomata are small pores located on the surface of leaves, stems, and other plant parts. These pores allow for gas exchange (oxygen and carbon dioxide) and water vapor release. The opening and closing of stomata are controlled by guard cells.

6. Lenticels

• Organism: Woody plants, particularly in stems and roots.
• Mechanism: Lenticels are small pores in the bark that allow for the exchange of gases between the plant and the surrounding environment. They are especially important for plants that do not have leaves during the winter or in submerged conditions.

---

C. Mechanism of Gaseous Exchange

i. Mechanism for Opening and Closing of Stomata

• Guard Cells: The stomata are surrounded by two specialized cells known as guard cells. The turgor pressure in the guard cells regulates the opening and closing of the stomata.
• Opening: When the guard cells take up water, they become turgid (swollen), causing the stomata to open and allow gases like oxygen and carbon dioxide to diffuse in and out.
• Closing: When the guard cells lose water, they become flaccid (shrunken), causing the stomata to close and prevent water loss.

ii. Respiratory Movements in Animals

Respiratory movements refer to the physical processes that facilitate the intake of oxygen and the expulsion of carbon dioxide.

• Mammals: In mammals, breathing involves inhalation and exhalation. During inhalation, the diaphragm contracts and moves downward, and the rib cage expands, creating negative pressure in the lungs. This allows air to flow in. During exhalation, the diaphragm relaxes, and the rib cage contracts, pushing air out.
• Fish: Fish use gill ventilation to maintain a constant flow of water over their gills, ensuring that oxygen diffuses into the gills, and carbon dioxide diffuses out.

---

D. Role of Oxygen in the Liberation of Energy for Activities of Living Organisms

Oxygen is crucial in cellular respiration, where it acts as the final electron acceptor in the electron transport chain. It combines with electrons and hydrogen ions to form water. Without oxygen, cells would have to rely on less efficient methods of energy production, such as anaerobic respiration, which produces far less energy.

• Role of Oxygen: Oxygen facilitates the complete breakdown of glucose (through aerobic respiration), which leads to the production of ATP, the energy currency of the cell.
• Effect of Insufficient Oxygen: Insufficient oxygen supply to muscles leads to lactic acid fermentation, which produces less ATP and causes muscle fatigue and cramping.

---

E. Types of Respiration

i. Aerobic Respiration

Aerobic respiration occurs in the presence of oxygen and involves the complete breakdown of glucose into carbon dioxide, water, and a large amount of ATP. This process occurs in the mitochondria of cells.

• Overall Reaction for Aerobic Respiration:

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ATP

• Significance: It produces a large amount of ATP and is the primary method of respiration in most multicellular organisms, especially in humans and animals.

ii. Anaerobic Respiration (Fermentation)

Anaerobic respiration occurs in the absence of oxygen and involves the partial breakdown of glucose. This process results in the production of energy (ATP), but far less than aerobic respiration. It produces lactic acid in animals and ethanol and carbon dioxide in yeast.

• Fermentation in Yeast: Yeast cells use fermentation to produce energy when oxygen is not available. This process breaks down glucose into ethanol and carbon dioxide.
• Reaction for Alcoholic Fermentation:

C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂ + ATP

• Economic Importance of Yeast:
  • Baking: Yeast is used in baking to cause dough to rise, as the fermentation process produces carbon dioxide gas.
  • Brewing: Yeast is used in the production of alcoholic beverages like beer and wine through fermentation.

---

Summary

• Respiratory organs are specialized for gas exchange, and organisms have evolved different mechanisms depending on their environment and size.
• Oxygen is essential for the efficient production of energy through aerobic respiration, while anaerobic respiration occurs when oxygen is scarce, producing less energy.
• Yeast fermentation is an example of anaerobic respiration with significant economic applications in baking and brewing.