Metabolism, Plant Tissues, and Respiration
Metabolism: Catabolism and Anabolism
Catabolism is the transformation of biomolecules into simple and complex molecules, storing chemical energy released as phosphate bonds and ATP molecules. This process destroys molecules with high-energy covalent bonds through exothermic chemical reactions. Catabolism is the reverse of anabolism.
Anabolism or biosynthesis is a part of metabolism responsible for synthesizing complex organic molecules (biomolecules) from simpler ones or nutrients. It requires energy (endergonic reactions), unlike catabolism.
Plant Conducting Tissues
Phloem: This tissue conducts sap from photosynthetic organs to all parts of the plant. It includes two types of conducting cells: sieve cells and sieve tube elements. Its main feature is the presence of sieve areas with pores that connect the cytoplasms of neighboring cells. These are living cells.
Gas Exchange in Plants
Plants exchange gases with the atmosphere during both photosynthesis and cellular respiration:
- During photosynthesis, plants take in carbon dioxide and release oxygen.
- During cellular respiration, they take in oxygen and release carbon dioxide.
During the day, plants perform both cellular respiration and photosynthesis, but photosynthesis dominates. Therefore, the plant as a whole takes in carbon dioxide and releases oxygen.
During the night, plants only perform cellular respiration, so they take in oxygen and release carbon dioxide.
Angiosperms are a phylum of flowering plants with eggs enclosed in an ovary. When fertilization occurs, the egg matures and becomes the fruit.
Some features of angiosperms are:
They have fruits that cover and protect the seeds, and facilitate their dispersion.
They have modified leaves that form the calyx and corolla, facilitating fertilization.
All have showy flowers.
They have diverse forms in roots, stems, and leaves, enabling them to adapt to various environments.
Examples: poppy, daisy, apple, lily, fig trees, vines, rose, clover, geranium, narcissus, poplar, ash, birch, acacia, orange.
Gymnosperms are a phylum of flowering plants or spermatophytes with naked eggs, i.e., not protected within an ovary. Therefore, they do not have fruit, as fruit forms from the walls of an ovary.
Examples: pine, fir, cypress, juniper, ginkgo, spruce, yew, Douglas fir, larch, hemlock, redwood, juniper, chalchal, Curibaya, pinsapo.
Excreted Substances
Major excretion products include urea, mineral salts, and substances that cannot be degraded by our cells, such as certain drugs and food additives. Most of these substances are eliminated through the urinary system (urine), while the rest is eliminated through the skin (sweat) and eyes (tears).
The Alveoli
The alveoli are the terminal sacs in the bronchial tree where gas exchange occurs between inspired air and blood.
There are approximately 750,000,000 alveoli in the two lungs. If stretched out, they would cover about 70 square meters.
The alveoli are lined with fluid and surfactant. There are about 300 million of them throughout the respiratory tract, located at the ends of pulmonary bronchioles, also called terminal bronchioles. They facilitate gas exchange between blood and air due to differences in the concentration of gases needed by the body (oxygen and carbon dioxide).
The Nephron (Kidney)
The nephron (kidney) is the basic structural and functional unit of the kidney, responsible for purifying blood. Its main function is to filter blood, regulate water and soluble substances, reabsorbing what is needed and excreting the rest as urine. It is mainly located in the renal cortex.
The Neuron
The neuron is considered the fundamental structural and functional unit of the nervous system. Different nervous system structures are based on groups of neurons. The neuron is the functional unit because it can be isolated as a single component and perform the basic function of the nervous system: transmitting information as nerve impulses.
- Overall, the function of the neuron is to transmit information.
- That information is transmitted as nerve impulses.
- The impulse travels in one direction: it begins in the dendrites, passes through the soma, and along the axon to another neuron, muscle, or gland.
- The nerve impulse is electrochemical, i.e., an electric current is produced by gradients of concentrations of chemicals with electric charges.
Types of Respiratory Systems
Tracheal Respiration
This type of respiration is common in insects and other terrestrial arthropods.
It consists of a series of tubes, the tracheae, formed by invaginations of the integument. Air enters through small holes on the body surface called stigmata.
The tracheae branch and decrease in diameter until they directly contact the cells, where gas exchange occurs by diffusion. Therefore, a circulatory system is not needed for gas transport. Figure 1.
Branchial Respiration: Gills are characteristic of aquatic animals, such as some annelids, mollusks, crustaceans, echinoderms, and fish. Gases are transported into cells through the circulatory system. Gills are projections of the outer surface of the body or the lining of the intestine to the outside of the animal and are evolutionarily derived by evagination. There are two types of gills: external and internal. External gills are more evolutionarily primitive. External gills have the advantage that simple movement mobilizes water, but they can be easily damaged by external agents. Internal gills are located in a protective cavity, requiring a ventilation system for gas exchange. Pulmonary Respiration: Lungs are invaginations of respiratory surfaces surrounded by capillaries. They are thin-walled sacs that facilitate gas exchange and connect to the outside world via a series of ducts. Cutaneous Respiration: This type of respiration occurs through the skin and is typical of many invertebrates, such as annelids (worms), some mollusks, and in vertebrates, amphibians use it as a complement to their gills (when larvae) or lungs (as adults). The skin used for gas exchange should be formed by a thin layer of very wet cubic epithelial cells, such as those in our mouth cavity. This allows the diffusion of carbon dioxide into the liquid cell and then into the air, while oxygen diffuses in the opposite direction.