4.0    INTRODUCTION TO RESPIRATORY SYSTEM

The respiratory system is a biological system responsible for the exchange of gases — mainly oxygen and carbon dioxide – between an organism and its environment.

The respiratory system is essential for cellular respiration, the process by which cells generate energy. Without it, organisms would not be able to produce the energy needed for survival.

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          4.1     RESPIRATION

Respiration is the biochemical process by which living organisms convert glucose and oxygen into energy, carbon dioxide and water.

It can be classified into two main types – Aerobic respiration and anaerobic respiration.

• Aerobic Respiration – Occurs in the presence of oxygen.
• — Equation of aerobic respiration

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (ATP)

STAGES OF AEROBIC RESPIRATION

1.   Glycolysis – Occurs in the cytoplasm; glucose is broken down into pyruvate, producing a small amount of ATP.
2.   Krebs Cycle – Occurs in the mitochondria; pyruvate is further broken down, releasing carbon dioxide and transferring energy to electron carriers.
4. Anaerobic Respiration – Occurs in the absence of oxygen.Less efficient than aerobic respiration, producing less ATP.
5. TYPES OF ANAEROBIC RESPIRATION
6. Lactic Acid Fermentation – Occurs in animal cells; glucose is converted to lactic acid and energy.

— Equation for lactic acid fermentation

     C6H12O6 → 2C3H6O3 + Energy (ATP)

          4.2     COMPONENTS OF THE RESPIRATORY SYSTEM

• Nasal Cavity: Filters, warms, and moistens incoming air.
• Pharynx: The throat; a passage for air and food.
• Larynx: The voice box; contains vocal cords and is involved in sound production.
• Trachea: The windpipe; a tube that connects the larynx to the bronchi.
• Bronchi: Two main branches that lead to each lung.
• Bronchioles: Smaller branches of the bronchi that lead to the alveoli.
• Alveoli: Tiny air sacs where gas exchange occurs; surrounded by capillaries.
• Lungs: Organs that house the bronchi, bronchioles, and alveoli; responsible for gas exchange.

                    4.3     PROCESSES OF BREATHING

• Inhalation – Diaphragm contracts and moves down, expanding the thoracic cavity and drawing air into the lungs.
• Exhalation – Diaphragm relaxes and moves up, reducing the thoracic cavity volume and pushing air out of the lungs.

GAS EXCHANGE MECHANISM – Occurs in the alveoli through diffusion. Oxygen diffuses from alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli.

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          4.4     COMPONENTS OF RESPIRATORY SYSTEM IN PLANTS

• Stomata – Small openings on the surface of leaves that allow gas exchange.
• Guard Cells – Cells that surround stomata and regulate their opening and closing.
• Lenticels – Small openings on stems that allow gas exchange in woody plants.

PROCESS OF GAS EXCHANGE IN PLANTS – During the day, stomata open to allow carbon dioxide in for photosynthesis and release oxygen. At night, stomata may close to reduce water loss, and respiration occurs, consuming oxygen and releasing carbon dioxide.

          4.5     ORGANISMS AND THEIR RESPIRATORY SYSTEM

• Humans and Mammals – Use lungs; gas exchange occurs in alveoli.
• Birds – Unique system with air sacs for continuous airflow; efficient gas exchange.
• Reptiles – Use lungs; some can absorb oxygen through skin.
• Amphibians – Use lungs and skin; young use gills.
• Insects – Tracheal system delivers oxygen directly to tissues via spiracles.
• Arachnids (spiders) – Lung books.
• Protist (Amoeba, Paramecium) – Simple diffusion across body surface.
• Fungi (Mushroom, Yeast) – Absorption oxygen directly through hyphae or cell membrane.