Chapter 6: Respiration in Organisms
6.1 Why Do We Respire?
Cellular Respiration
- Cell: The smallest structural and functional unit of an organism.
- Cellular Respiration: The process of breakdown of food in the cell with the release of energy.
- Aerobic Respiration: Breakdown of glucose in the presence of oxygen to release carbon dioxide, water, and energy.
- Anaerobic Respiration: Breakdown of food without using oxygen, yielding alcohol, carbon dioxide, and energy (e.g., in yeast).
- Anaerobes: Organisms like yeast that can survive in the absence of air.
Anaerobic Respiration in Muscles
- Occurs during heavy exercise when oxygen supply is limited.
- Glucose breaks down into lactic acid and energy.
- Accumulation of lactic acid causes muscle cramps. Relief is obtained via hot water baths or massages which improve blood circulation and oxygen supply.
6.2 Breathing
Mechanism of Breathing
- Breathing: Process of taking in air rich in oxygen (inhalation) and giving out air rich in carbon dioxide (exhalation).
- Breathing Rate: Number of times a person breathes in a minute. Average adult at rest: 15-18 times/minute.
- A single breath consists of one inhalation and one exhalation.
6.3 How Do We Breathe?
Human Respiratory System
- Pathway: Nostrils → Nasal Cavity → Windpipe → Lungs (located in the chest cavity).
- Diaphragm: A large, muscular sheet forming the floor of the chest cavity.
- Inhalation: Ribs move up and outwards; diaphragm moves down. Chest cavity expands, drawing air into the lungs.
- Exhalation: Ribs move down and inwards; diaphragm moves up. Chest cavity contracts, pushing air out.
- Sneezing: Expels foreign particles (dust, pollen) trapped in the nasal cavity to ensure clean air enters the body.
6.4 What Do We Breathe Out?
Composition of Inhaled and Exhaled Air
- Inhaled Air: 21% Oxygen, 0.04% Carbon Dioxide.
- Exhaled Air: 16.4% Oxygen, 4.4% Carbon Dioxide.
- Exhaled air contains moisture which condenses on cool surfaces (like a mirror).
- Carbon dioxide in exhaled air turns lime water milky.
6.5 Respiration in Other Animals
Insects, Earthworms, and Frogs
- Cockroach: Breathes through small lateral openings called spiracles connected to a network of air tubes called tracheae.
- Earthworm: Exchanges gases directly through its moist, slimy skin.
- Frogs: Possess lungs but can also breathe through their moist, slippery skin.
6.6 & 6.7 Underwater and Plant Respiration
Breathing Under Water
- Fish: Use gills (richly supplied with blood vessels) to absorb oxygen dissolved in water.
Respiration in Plants
- Plants take in oxygen and release carbon dioxide for cellular respiration.
- Stomata: Tiny pores on leaves used for gas exchange.
- Root Hairs: Absorb air from the spaces present between soil particles.