Ecology: biology of interaction. 5.13. Biological effects of electromagnetic radiation
Terrestrial organisms live in an environment saturated with EM radiation of various wavelengths and intensities. It should be noted that humanity has added many artificial sources to the natural ones, especially in the radio range. The diversity of effects of this radiation on organisms has not yet been fully studied.
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5.12. Solar Radiation Composition
D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Chapter 5. Autecology and Fundamentals of the Environment
5.14. Absorption of solar radiation by the atmosphere
5.13. Biological Effects of Electromagnetic Radiation (EMR) EMR has numerous diverse effects on organisms. The reader of this text perceives it through sight. Their body exchanges infrared radiation with surrounding objects. In summer, they got a tan from the sun. Bright sunlight improves their mood, and in darkness, they feel sleepy. They need to protect themselves from contact with radioactive objects – sources of ionizing radiation. Sometimes they underwent diagnostic procedures during which their body was X-rayed... Terrestrial organisms live in an environment saturated with EMR of various wavelengths and intensities. It should be noted that humanity has added numerous artificial sources to natural ones, especially in the radio range. The diversity of these radiations' effects on organisms is not yet fully understood. Without claiming completeness, the following biological effects associated with electromagnetic radiation from the Sun and other sources can be named. 1. Photosynthesis. The synthesis of organic substances from inorganic ones using light energy. In its most general form, the equation for photosynthesis can be written as 6CO2 + 12H2O = C6H12O6 + 6O2 + 6H2O. The energy required for this reaction is captured and converted by the chlorophyll molecule. Chlorophyll has absorption maxima in the red and blue parts of the spectrum, but thanks to a significant number of accessory pigments that capture light quantum energy and transfer it to chlorophyll, plants can use the entire visible spectrum, as well as parts of the IR and UV ranges. 2. Visual Perception. Vision is one of the main channels for obtaining information for humans and many other species. The evolution of visual organs begins with the primitive photosensitivity of the body surface of many animals and leads to highly sophisticated camera eyes of vertebrates and cephalopods, as well as compound eyes of arthropods. Photoreceptors can be sensitive to the entire visible range (in vertebrates, they are called rods) or only to a specific part of the spectrum (cones). In nocturnal animals, for whom overall eye sensitivity is more important, vision is typically black and white. Animals that live in wood, or fly or swim in water bodies under good lighting, more often have color vision. 3. Heating upon absorption of light and infrared radiation. An important method of thermoregulation in many animals. It is less important for homeothermic animals than for poikilothermic ones, but it is also widespread among them (each of us has had to warm ourselves in the sun's rays or by the fire or fireplace). 4. Phototaxis. Movement towards a light source (positive phototaxis) or away from it (negative phototaxis). 5. Phototropisms. Orientation relative to a light source. Characteristic of sessile animals and plants. Growth movements lead to movement towards light (positive phototropism, characteristic of stems) or away from it (negative phototropism, as for roots). Photonasty – movements of plant organs caused by changes in light intensity. Associated with growth processes and changes in turgor. 6. Compass Reactions. Many species strive to maintain a constant angle relative to the direction of light rays when moving. The spiral movement of moths towards a candle flame is an example of these reactions. Orientation towards the Sun and stars is common among various animals. Insects are capable of seeing the plane of polarization of light radiation and, using it, orient themselves by the Sun even in conditions of complete cloudiness. 7. Regulation of Daily Activity. In a significant portion of animals, the daily cycle depends on the level of illumination. The dynamics of day and night changes set circadian biological rhythms. Internal rhythm drivers play a major role in maintaining these biorhythms. Shifts in circadian rhythms under experimental conditions prove that normally they are constantly corrected by the changes in day and night. Daily rhythms should not be confused with seasonal ones, often regulated by photoperiodism. 8. Photoreactions. In many cases, visible light is a factor that stimulates seed germination or the formation of fruiting bodies in fungi. In humans, as likely in other vertebrates, there are reactions that depend on the overall illumination level, rather than the dynamics of day and night changes or the duration of the light day. In darkness, the activity of the epiphysis (pineal gland, a remnant of the parietal eye) increases. In many vertebrates with a reptilian level of organization, the parietal eye assesses the flow of light and thermal energy heating the body. The epiphysis secretes the hormone melatonin, which affects the hypothalamus-pituitary system and, through it, suppresses the activity of the reproductive system. 9. Phytochrome Regulation in Plants. The protein phytochrome plays a key role in regulating the physiological processes of many plants. It acts as a 'switch' that changes the course of reactions in plant cells (e.g., ensuring the transition from growth to reproduction). Under red light, phytochrome is activated and initiates many cellular reactions. Transition to the inactive form occurs in darkness or under far-red light. 10. Ionization by Radiation. Interacting with substance molecules, a short-wavelength radiation quantum transfers its energy to them, ionizing them. The ionizing effect of radiation significantly depends on its wavelength. In small doses, ionizing radiation is absolutely necessary, and without it, even cell division does not occur. Its optimal level corresponds to the natural background. Small doses exceeding the background, with short-term exposure, show a pronounced stimulating effect. Large doses cause radiation sickness, accompanied by cell death in intensely dividing tissues and disruption of many life functions due to the accumulation of ionized molecules in cells. 11. Photochemical Reactions. In a broad sense, photochemical reactions should include photosynthesis; however, due to the importance of this process for the biosphere as a whole, we have considered it separately. Using light or ultraviolet radiation energy, other reactions can occur, the most important of which is the synthesis of vitamin D (ergocalciferol) from its precursor. Thus, using the energy of an ultraviolet quantum, this important regulator of calcium and phosphorus metabolism is formed not only in human skin but also in plant tissues. 12. Disinfection by Ultraviolet Light. UV radiation is weakly ionizing and has low penetrating power. In macroorganisms, ultraviolet light penetrates only the surface layers of the integument, while microorganisms are penetrated through and through. Therefore, doses of ultraviolet light that are relatively safe for large organisms have a strong disinfecting effect. This is used in hospitals for disinfection with an ultraviolet lamp. 13. Tanning and Sunburns from Ultraviolet Radiation. Although ultraviolet light is absorbed by the skin, it can still penetrate to a depth where living and dividing cells are located. It is precisely this ability that explains why vitamin D can be formed in human skin. Europeans have white skin specifically so that this vitamin can still be formed under conditions of low ultraviolet irradiation. At the same time, excessive UV irradiation of skin cells can damage their genetic apparatus and cause skin cancer. This is why the body itself destroys (through programmed cell death, apoptosis) those cells that have been excessively exposed to ultraviolet radiation. The local reaction associated with cell death is called sunburn. When the body has received enough vitamin D, to reduce the adverse effects of ultraviolet exposure, the synthesis of the dark pigment melanin increases in the skin, which provides tanning and absorbs ultraviolet light. Additional Materials: Educational Model: The Effect of EMR on Organisms Educational Model: Engelmann's Experiment Educational Model: Photosynthetic Pigments of Plants Column: About Skin Color: An experience of discussing a human adaptation with justification of far-reaching conclusions about the specifics of ecological factor action Column: And About Skin Color: Why We Are White and Why We Tan
5.12. Solar Radiation Composition
D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Chapter 5. Autecology and Fundamentals of the Environment
5.14. Absorption of solar radiation by the atmosphere