Pulmonary and Plant Respiration, Animal and Plant Excretion
Pulmonary Respiration
In pulmonary respiration, gas exchange is performed in the lungs. The lungs are connected to the outside through the mouth and nostrils, and continue via the pharynx, larynx, trachea, and bronchi. This type of respiration occurs in vertebrates: amphibians, reptiles, birds, and mammals.
Evolution of the Pulmonary Respiratory System
- Increasing the area of gas exchange (e.g., amphibians).
- Acquisition of ventilation mechanisms. In reptiles, birds, and mammals, the process of air entering and leaving the lungs is called ventilation.
- Improvement in pulmonary circulation. Birds and mammals have a complete circulatory system.
Models of Lung Respiratory Systems
- Birds: The lungs have several extensions in pouches called air sacs.
- Mammals: Lungs have numerous tiny air sacs called alveoli, through whose walls oxygen and carbon dioxide diffuse between blood and air.
Plant Respiration
Plants do not require specialized respiratory organs because their oxygen needs are lower than those of animals. Plant tissues are relatively close to the surface, and during photosynthesis, oxygen is released as carbon dioxide is consumed. Cellular respiration in plants consumes oxygen and releases carbon dioxide.
Animal Excretion
Excretion in animals is the elimination of waste products through the excretory system.
Waste Products
- Carbon dioxide and water: CO2 is removed by the respiratory surfaces. Water vapor is removed through the same surfaces.
- Nitrogenous products: Nitrogen from the metabolism of proteins and nucleic acids is excreted as ammonia, urea, or uric acid.
Nitrogenous Waste Classification
- Ammoniotelic: Aquatic animals.
- Ureotelic: Sharks, amphibians, some reptiles (turtles), and mammals.
- Uricotelic: Insects, most reptiles, and birds.
Excretory Systems
Invertebrates
- Protonephridia: Found in flatworms, these are highly branched tubes.
- Metanephridia: Found in annelids and mollusks, these consist of a coiled tube with two openings: the external opening (nephridiopore) and the internal opening (nephrostome).
- Malpighian Tubules: Found in insects, these are thin tubes open at one end to the digestive tract.
- Green Glands (Antennal Glands): Found in crustaceans.
Vertebrates
Their excretory organs are the kidneys, which are composed of numerous nephrons. A kidney can be distinguished externally by:
- Renal capsule
- Renal cortex
- Renal medulla
- Renal pelvis
Structure of the Kidney and Nephron
- Bowman’s capsule: Surrounded by capillaries called the glomerulus.
- Proximal tubule
- Loop of Henle
- Distal convoluted tubule: Empties into the collecting tubule.
Other Excretory Structures
- Sweat glands: produce sweat.
- Liver: produces bile pigments (bilirubin).
Urine Formation
- Glomerular filtration: Pressure differences between the glomerular capillaries and the interior of Bowman’s capsule cause a filtration of substances, creating a filtrate similar in composition to blood plasma.
- Tubular reabsorption: Many usable substances in the filtrate are reabsorbed in the tubules of the nephron.
- Secretion: Some substances can pass from the capillaries into the interior of the tubule.
At the end of the process, urine is formed. Urine travels through the ureters to reach the bladder and is eliminated through the urethra.
Plant Excretion
Plants have no specialized excretory structures. They produce fewer waste products, and not all waste products are removed to the exterior.
Waste Products
- Gaseous substances: Carbon dioxide and ethylene are removed through stomata or lenticels.
- Liquid substances: Essential oils, resins, and latex.
- Solids: Calcium oxalate accumulates as crystals.