Plant Waste, Respiration, and Vertebrate Urine Formation

Plant Waste Products

Gaseous substances: These include carbon dioxide and ethylene. Carbon dioxide is removed via stomata and lenticels, while ethylene is found in ripe fruits.

Liquid substances:

• Essential oils are expelled to the outside (ciliary ganglion) or stored (oleifera bags).
• Resins accumulate in the resin canals.
• Latex is stored within laticiferous channels.

Solid substances: Calcium oxalate accumulates as crystals in cell vacuoles.

Plant Respiration

Plants, like most living organisms, require oxygen for cellular respiration. As photosynthetic organisms, they also require carbon dioxide to synthesize their own organic matter. The addition of these gases does not require a respiratory apparatus as in animals, due to the following peculiarities:

• The oxygen requirement of plants is lower.
• Living plant tissues are relatively close to the exterior.
• Among the cells that form tissues, numerous intercellular spaces allow gases to diffuse freely.

Despite these features, plants utilize small organs such as stomata on leaves and green stems, and lenticels on woody stems.

Relationship Between Photosynthesis and Cellular Respiration

Cellular respiration is a light-independent process, meaning plants consume oxygen 24 hours a day. In contrast, oxygen production during photosynthesis only occurs during daylight hours. During photosynthesis, oxygen is released, and large amounts of carbon dioxide are taken in. Some of the oxygen is used in cellular respiration, and the rest is released to the exterior. During cellular respiration, plants consume oxygen and release carbon dioxide. The most important aspect of this relationship is not the release of oxygen but that plants assimilate carbon dioxide in the form of tissues and organs that do not pass into the atmosphere.

Urine Formation in Vertebrates

The process of urine formation can be divided into three stages:

1. Glomerular filtration: This occurs in Bowman's capsule, where most serum components (nutrients, water, salts), urea, and uric acid leak from the capillaries into the capsule's interior.
2. Resorption: This takes place in the tubules, which recover beneficial substances from the glomerular ultrafiltrate. These substances pass into the capillaries surrounding the nephron.
3. Secretion: This is a process by which substances that did not pass through ultrafiltration are removed. It usually involves active transport and includes ions, drugs, or toxic substances.

From the kidney, urine flows from the renal pelvis into the ureters and then to the bladder. From the bladder, urine passes through the urethra and exits the body.