Photobiology: Definition, Types, and Examples


This biology subdiscipline focuses on the biology of light. This discipline studies the effect of light and various factors associated with it like its duration and intensity and their effect on biological processes.

Subdisciplines of Photobiology

Photobiology is a multidisciplinary subject with specialty areas. Photophysics focuses on the physical aspects of light as a wave and as a photon and studies its effect at atomic and molecular levels. Photochemistry specializes in the chemical molecular reaction that occurs after photon absorption.

Photobiology Research Topics

This discipline researches the interaction of light with biological entities and their detrimental and beneficial effects. Main concepts and topics related to this are discussed below:

i. Photosynthesis

Light is an essential abiotic physical factor that directly and indirectly affects organisms and the surroundings they live in. Some organisms like photoautotrophs are dependent on light to derive their energy through photosynthesis and synthesize food. Thylakoid membranes have photosystems with pigments that are capable of extracting energy from photons and absorbing it.

The absorbed energy or photon is passed from pigments in the antenna complex to the reaction center that has the main pigment chlorophyll a. Here in the reaction center, it sets a redox chain concerned with electron transport. A primary acceptor accepts an electron from chlorophyll a and passes into ETC.

The flow of electrons in the Electron Transport Chain helps in the generation of energy through the generation of a proton gradient according to Chemiosmotic theory. These reactions occur in the Photosystem II reaction center. In photosystem I, there is a cyclic flow of electrons due to which no NADPH is formed.

ii. Phototropism

In this kind of tropism, biological entities like plants can respond to light stimuli. The response can be negative or positive based on the fact whether the organism moves or grows towards the light source or away from it. The shoots of plants demonstrate positive tropism as they grow towards the light to increase photosynthesis yield and rate.

The light triggers a plant hormone auxin that bends growing shoots in direction of light by promoting localized cell elongation. Light also influences the growth of root so it is correctly oriented towards the soil. Red light is responsible for positive phototropism in roots while white or blue light results in negative phototropism.

iii. Diurnal Rhythms

Organisms have an internal biological rhythm that is mediated by a biological clock synchronized by a diurnal rhythm. Animals exhibit certain behavioral patterns and certain physiological responses in a diurnal rhythm. For instance, in the daytime, the loa loa releases their microfilariae into the peripheral blood. Nocturnal organisms are active at night time while diurnal animals are active predominantly at day time.

iv. Bioluminescence

It is the property by which living beings emit light. Organisms that show this property include Aequorea Victoria, dinoflagellates, firefly squid, and honey fungus. Luciferase enzyme is the photoprotein that catalyzes the biochemical reaction for the emission of light. Luciferin substrate is oxidized in the presence of this enzyme, which leads to its excitation and release of a photon to go back to a stable state. Some can produce their light with the help of this enzyme and others like squid exhibit bioluminescence by forming a symbiosis with bioluminescent organisms.

v. Skin Pigmentation

It also manifests the regulatory effects of light. Melanocytes synthesize melanin pigment responsible for skin color in humans. Melanin is synthesized by tyrosine oxidation and its polymerization. This reaction is mediated by light exposure. Prolonged exposure to the sun can increase melanin production.

vi. Photomedicine

This is a special application of the field of photobiology. Cell death can be induced in cancerous cells by making them photosensitive using a photosensitizing drug. This is referred to as photodynamic therapy where photons are used to treat a condition and it is not a recent event.

The light source determines the effect of light on health in general. Not only humans are sensitive to light. Almost all organisms are susceptible to light be it bacteria, protists, and algae, or multicellular organisms.

Animal behavior depends on light’s intensity so artificial lighting in wildlife needs to be regulated as otherwise, it can cause light pollution.

Galacto Oligosaccharide
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