Vocal cords (vocal folds) in the larynx vibrate as air passes over them during exhalation, producing sound for voice. The pitch of sound is controlled by tension in the cords (tighter = higher pitch) and volume by airflow.

RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is the enzyme that fixes O₂ in photorespiration. When O₂ concentration is high relative to CO₂, RuBisCO's oxygenase activity dominates, initiating photorespiration.

Gas exchange in human lungs occurs at the alveoli — specifically across the thin alveolar epithelium and the rich network of capillaries overlying them. The total alveolar-capillary surface area is approximately 70 m².

This is the Bohr effect: as blood pH falls (more acidic, more CO₂), haemoglobin's O₂ affinity decreases and it releases more O₂ to tissues. Conversely at the lungs, low CO₂ and higher pH increase O₂ binding.

The larynx (voice box) is the complex cartilaginous structure at the upper end of the trachea. It contains the vocal cords, protects the airway during swallowing, and produces sound for speech.

Myoglobin is the oxygen-storing respiratory pigment in muscle cells. It has a single haem group and stores O₂ for use during intense muscle contraction when blood supply and haemoglobin cannot meet immediate demands.

Myoglobin has a higher affinity for O₂ than haemoglobin — its O₂-dissociation curve is hyperbolic rather than sigmoidal. This allows myoglobin to receive O₂ from haemoglobin and act as a muscle O₂ reserve.

Each alveolar sac (air sac) in human lungs consists of multiple alveoli — tiny, thin-walled (single layer of squamous epithelium) air pockets, each surrounded by a dense capillary network for gas exchange.

Emphysema is characterised by the progressive destruction and enlargement of alveoli. The loss of alveolar walls dramatically reduces the surface area for gas exchange, causing severe breathlessness and reduced exercise tolerance.

Total lung capacity (TLC) in adult humans is approximately 5 litres. Of this, about 1.2 litres is residual volume (air that cannot be expelled), and the remaining 3.8 litres is the vital capacity.

Birds have a very high metabolic rate — up to 3-4 times higher than mammals of similar size — due to the energy demands of flight and endothermy. This necessitates their highly efficient respiratory and circulatory systems.

The spongy texture of lungs is due to the millions of alveoli — tiny air sacs that make up most of the lung volume. Humans have approximately 300 million alveoli providing a total gas exchange surface of about 70 m².

Haemoglobin is the respiratory pigment in human red blood cells. It is a protein with four haem groups each containing iron (Fe²⁺) that binds one O₂. Haemocyanin (containing copper) is found in arthropods and molluscs.

Tuberculosis (TB) is caused by Mycobacterium tuberculosis, a slow-growing acid-fast bacterium. It primarily infects the lungs, causing granulomas (tubercles), tissue necrosis, and cavitation in advanced cases.

Parabronchi (also called air capillaries) are the tiny, thin-walled gas exchange tubes in bird lungs. Unlike mammalian alveoli (dead ends), parabronchi are open at both ends allowing continuous unidirectional airflow.

The Bohr effect: when CO₂ increases, blood pH decreases, which reduces haemoglobin's oxygen affinity, decreasing the oxygen tension (pO₂) at which HbO₂ releases O₂. This promotes O₂ delivery to metabolically active tissues.

During intense muscular activity, rising CO₂, falling pH, and rising temperature all reduce haemoglobin's affinity for O₂ (Bohr effect), causing it to release more O₂ to working muscles. This is a physiological adaptation.

Alveoli are the functional units of the lungs where gas exchange takes place. Each is a tiny (0.2mm) air-filled sac with walls one cell thick, surrounded by a dense network of blood capillaries for O₂/CO₂ exchange.

The tracheal tubes in cockroaches (and other insects) are lined by a thin layer of chitin (the same polymer forming the exoskeleton). This prevents tube collapse and provides structural support. The chitin is shed during moulting.

Inhalation (inspiration) is the active process of drawing air into the lungs by contracting the diaphragm and external intercostal muscles. Exhalation (expiration) is the passive release of air from the lungs.

Adult frogs use all three sites for gas exchange: lungs (during activity and warm weather), moist skin (cutaneous respiration, especially during hibernation), and the buccal (mouth) cavity lining.

When oxygen binds to haemoglobin in the lungs, oxyhaemoglobin (HbO₂) is formed. Each haemoglobin molecule can carry up to 4 oxygen molecules (one per haem group). This reaction is reversible in tissues.

Organismic (external) respiration refers to the mechanical process of breathing — ventilation of the lungs. It is distinguished from cellular (internal) respiration which is the biochemical process of ATP production in cells.

Lenticels are specialised pores in the bark (cork tissue) of older woody stems and roots that allow gas exchange. They appear as small raised dots on the bark surface and are loosely arranged to allow air diffusion.

Gas exchange in leaves occurs in the air spaces between mesophyll cells. CO₂ and O₂ diffuse through stomata into these intercellular spaces, then to and from the cells through the moist cell surface membranes.

Emphysema is a chronic lung disease (part of COPD) where the alveolar walls break down, merging small alveoli into larger, less efficient air spaces. This dramatically reduces the surface area for gas exchange, causing breathlessness.

Asthma is a chronic inflammatory airway disease with recurrent episodes (paroxysms) of wheezing, breathlessness, and airway obstruction, followed by recovery. It is triggered by allergens, exercise, cold air, or infection.

About 70% of CO₂ is transported as bicarbonate ions (HCO₃⁻) in plasma. CO₂ enters red blood cells, reacts with water (via carbonic anhydrase) forming H₂CO₃, which dissociates to H⁺ and HCO₃⁻ (Chloride shift).

Total lung capacity (TLC) in an average adult male is approximately 5 litres. This includes tidal volume (0.5L), inspiratory reserve volume (3L), expiratory reserve volume (1.1L), and residual volume (1.2L).

Metastasis is the process by which cancer cells break away from the primary tumour, enter blood or lymph vessels, and establish new tumours at distant sites. It is what makes cancer particularly dangerous and difficult to treat.

Lung cancer is the most deadly respiratory problem among smokers — cigarette smoke contains carcinogens that cause malignant transformation of bronchial epithelial cells. Smoking causes about 85% of all lung cancers.

During exercise, tidal volume increases from the resting 0.5 L to about 3 litres per breath, and breathing rate increases from ~12 to ~40 breaths/minute, greatly increasing ventilation to meet increased O₂ demand.

Myoglobin is called muscle haemoglobin because it is the oxygen-storing haemoglobin-like protein found in muscle cells. It gives red muscle its dark colour and provides O₂ reserves during intense contraction.

Myoglobin (muscle haemoglobin) has a higher affinity for O₂ than haemoglobin. It acts as an O₂ reservoir in muscles, storing O₂ when it is abundant and releasing it during intense muscle activity.

Oxyhaemoglobin (O₂-bound) is bright red; deoxyhaemoglobin is purple-red (darker). This colour difference is what makes arterial blood bright red and venous blood darker red — not blue as commonly depicted.

Haemoglobin increases blood's oxygen-carrying capacity about 70 times compared to simple dissolved O₂. Without haemoglobin, blood would need to flow 70 times faster to deliver the same amount of O₂ to tissues.

Haemoglobin's oxygen affinity is affected by: CO₂ concentration, temperature, and pH (all via the Bohr effect), and also by 2,3-BPG concentration. High CO₂, high temperature, and low pH all reduce O₂ affinity (promoting O₂ release in tissues).

At the normal arterial PO₂ of about 100 mmHg (in the lungs), haemoglobin is approximately 97-98% saturated with oxygen. This ensures maximum O₂ loading at the lungs for transport to tissues.

Pulmonary surfactant is a mixture of phospholipids and proteins produced by Type II pneumocytes in alveolar walls. It reduces surface tension preventing alveoli from collapsing during exhalation. Premature babies lack surfactant causing respiratory distress syndrome.

CO₂ concentration (and the resulting blood pH change) is the primary regulator of breathing, not O₂. Chemoreceptors in the medulla and peripheral chemoreceptors are more sensitive to CO₂/pH than to O₂ levels.

Breathing and ventilation both describe the mechanical process of moving air in and out of the lungs. Ventilation specifically refers to the bulk flow of air to maintain gas concentration gradients for diffusion in alveoli.

Bronchioles lack cartilage (unlike bronchi) — their walls contain smooth muscle that can contract (bronchoconstriction in asthma) or relax (bronchodilation). Their diameter is controlled by the autonomic nervous system.

Alveoli are the functional units of the lungs where actual gas exchange occurs. Each alveolus is a tiny air sac (0.2mm diameter) surrounded by capillaries. Humans have ~300 million alveoli with a total surface area of ~70m².

Birds have the most advanced and efficient respiratory system — a unique flow-through system with parabronchi and air sacs ensuring continuous unidirectional airflow, extracting oxygen even on inhalation AND exhalation.

Pulmonary respiration specifically refers to gas exchange through the lungs. In adult frogs, the simple sac-like lungs handle pulmonary respiration, though most gas exchange occurs through the skin (cutaneous respiration).

Most birds have 9 air sacs (1 interclavicular, 2 cervical, 2 anterior thoracic, 2 posterior thoracic, 2 abdominal). These act as bellows creating a continuous unidirectional air flow through the parabronchi for efficient gas exchange.

The nasal cavity performs three functions on inhaled air: filtration (by hairs and mucus trapping particles), humidification (mucous membranes add moisture), and warming (extensive blood supply warms cold air to body temperature).

The complete air passage in humans: nostrils → nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → alveolar ducts → alveolar sacs (clusters of alveoli where gas exchange occurs).

In birds, gas exchange occurs primarily in the parabronchi — tiny parallel tubes in the lungs through which air flows continuously (not in and out like mammals). Air sacs act as bellows, not gas exchange sites.

Fish have a single-circuit (single loop) circulatory system: heart → gills → body → heart. Blood passes through the heart only once per circuit. Mammals and birds have a double circuit (pulmonary + systemic).

The active site of RuBisCO can bind both CO₂ (for photosynthesis/carboxylation) and O₂ (for photorespiration/oxygenation). The relative concentrations of CO₂ and O₂ determine which reaction predominates.

In cockroaches, tracheae branch repeatedly into progressively finer tracheoles (< 1µm diameter) that penetrate directly into tissues and muscle cells. Tracheoles are the actual sites of gas exchange at the cellular level.

Photorespiration reduces photosynthetic efficiency in C3 plants by approximately 25-50% under normal conditions. C4 and CAM plants evolved mechanisms to minimise photorespiration by concentrating CO₂ around RuBisCO.

Gas exchange in earthworms occurs entirely through the skin (cutaneous respiration). The skin must remain moist for gas diffusion. Earthworms have a dense network of capillaries just beneath the skin surface.

In photorespiration, glycolate (produced in chloroplasts when O₂ is fixed) moves to peroxisomes where it is oxidised and converted to glycine (an amino acid). Glycine then moves to mitochondria where CO₂ is released.

Gas transport in plants occurs through: intercellular air spaces (within leaves and stems), stomata (main entry/exit points for CO₂ and O₂ in leaves), and lenticels (pores in bark of stems and roots).

RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) has a dual function: it acts as a carboxylase (fixes CO₂) in photosynthesis and as an oxygenase (fixes O₂) in photorespiration, depending on CO₂/O₂ ratios.

Photorespiration releases CO₂ — the reverse of what photosynthesis aims to achieve. RuBisCO fixes O₂ to RuBP forming glycolate, which is converted back to CO₂ in peroxisomes and mitochondria, wasting energy.

Intercellular air spaces in leaf mesophyll comprise approximately 40% of the total leaf volume. This large internal air space facilitates rapid diffusion of CO₂ to photosynthetic cells and O₂ away from them.

Photorespiration occurs in C3 plants when RuBisCO reacts with O₂ instead of CO₂, releasing CO₂ without producing ATP or sugar. It occurs in bright light and reduces photosynthetic efficiency.

During a forceful cough, a person can expel approximately 2-2.5 litres of air at velocities up to 160 km/h. This forceful expulsion clears mucus and foreign particles from the airways.

Birds have the most efficient respiratory system of all vertebrates. Their unique flow-through system with air sacs ensures a unidirectional flow of fresh air past parabronchi at all times, enabling sustained high-altitude and high-activity flight.

Tuberculosis (TB) is caused by the bacterium Mycobacterium tuberculosis. It primarily affects the lungs (pulmonary TB) and is spread by airborne droplets from infected persons. It remains a major global health problem.

Cockroaches (insects) ventilate their tracheal system through rhythmic body movements (abdominal pumping). Contraction and relaxation of abdominal muscles compresses and expands the tracheal system, moving air in and out.

The primary purpose of cellular respiration is the liberation of energy (as ATP) from organic molecules. It involves both the consumption of oxygen and production of CO₂, but energy release is the fundamental goal.

Vocal cords (vocal folds) are located in the larynx — the cartilaginous voice box. They vibrate when air passes over them during exhalation to produce sound. The glottis is the opening between the vocal cords.

Total lung capacity (TLC) — the maximum amount of air the lungs can hold when fully inflated — is approximately 5 litres in an average adult male. In females it is slightly less (about 4.2 L).

Both human trachea and insect tracheae are derived from ectoderm (embryonic outer layer) — this is their common developmental origin. In insects, the tracheal system invaginates from the body surface (ectoderm).

Mitochondria are the chief site of cellular respiration in plants (and all eukaryotes). They carry out the Krebs cycle and oxidative phosphorylation to produce ATP from glucose oxidation.

Rising blood CO₂ (and falling pH) stimulates chemoreceptors in the medulla oblongata and carotid/aortic bodies, which send signals to increase breathing rate and depth to expel excess CO₂.

In sneezing, irritants in the nasal passages trigger a reflex that forcibly expels air through the nasal cavities to clear them. In coughing, air is expelled through the larynx and mouth to clear the lower airways.

Adult frogs breathe using three methods: lungs (primary during activity), moist skin (especially during hibernation underwater), and the buccopharyngeal lining. The relative contribution varies with conditions.

Earthworms perform cutaneous (skin) respiration. They have no specialised respiratory organs — gas exchange occurs entirely through the moist, thin body surface richly supplied with blood capillaries.

The mammalian larynx is distinctive in possessing a thyroid cartilage — the large shield-shaped cartilage forming the anterior wall of the larynx (forming the 'Adam's apple'). This is unique to mammals.

Expiration (exhalation) occurs when the diaphragm and intercostal muscles relax. This decreases thoracic volume, increases pressure in the lungs, and forces air out. Normal expiration is passive (no muscle contraction needed).

The larynx (voice box) contains the vocal cords — two folds of mucous membrane stretched across the laryngeal cavity. Air vibrates them to produce sound during speech.

Tidal volume is the amount of air inhaled and exhaled during normal, quiet breathing — approximately 0.5 litres (500 mL) per breath in adults. Vital capacity is the maximum air that can be exhaled after maximum inhalation.

Coughing is a reflex action that forcibly expels air from the lungs through the trachea and bronchi, clearing mucus, foreign particles, and microorganisms that may have entered the airways.

Adult frogs use multiple respiratory organs: lungs (pulmonary respiration), moist skin (cutaneous respiration), and the lining of the buccopharyngeal (mouth/throat) cavity. All three contribute to gas exchange.

During breathing (inhalation/inspiration), the diaphragm contracts and flattens, intercostal muscles raise the rib cage, increasing thoracic volume, reducing air pressure, and drawing air into the lungs.

In earthworms, gaseous exchange occurs through the moist general body surface (cutaneous respiration). Oxygen diffuses in and CO₂ diffuses out through the thin, moist, well-vascularised skin.

Bronchioles branch progressively and their finest branches (alveolar ducts) terminate in groups of tiny air sacs called alveoli. Each cluster of alveoli is called an alveolar sac. Humans have about 300 million alveoli.

Aquatic animals (fish, aquatic insects) extract dissolved oxygen from water for cellular respiration. Gills are the primary organs for absorbing dissolved O₂ and releasing CO₂ into water.

The pleural cavity contains pleural fluid — a thin lubricating liquid that reduces friction between the pleural membranes during breathing. It also creates surface tension that keeps the lungs expanded.

Tracheoles are the smallest branches of the tracheal system in insects. They are extremely thin (less than 1 µm diameter), permeable, and penetrate directly into tissues for gas exchange at the cellular level.