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The Biology Portal

Welcome to the biology portal. Biology is the science of life, from the Greek words bios (life) and logos (word). It is concerned with the characteristics and behaviors of organisms, how species and individuals come into existence, and the interactions they have with each other and with their environment. Biology encompasses a broad spectrum of academic fields that are often viewed as independent disciplines. Together, they study life over a wide range of scales. This Portal is updated on Wednesdays and Sundays.

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Chromatophores are pigment-containing and light-reflecting cells found in amphibians, fish, reptiles, crustaceans, and cephalopods. They are largely responsible for generating skin and eye colour in cold-blooded animals and are generated in the neural crest during embryonic development. Mature chromatophores are grouped into subclasses based on their colour (more properly "hue") under white light: xanthophores (yellow), erythrophores (red), iridophores (reflective / iridescent), leucophores (white), melanophores (black/brown) and cyanophores (blue). The term can also refer to coloured, membrane associated vesicles found in some forms of photosynthetic bacteria.

Some species can rapidly change colour through mechanisms that translocate pigment and reorient reflective plates within chromatophores. This process, often used as a type of camouflage, is called physiological colour change. Cephalopods such as octopus have complex chromatophore organs controlled by muscles to achieve this, while vertebrates such as chameleons generate a similar effect by cell signaling. Such signals can be hormones or neurotransmitters and may be initiated by changes in mood, temperature, stress or visible changes in local environment.

Unlike cold-blooded animals, mammals and birds have only one class of chromatophore-like cell type: the melanocyte. The cold-blooded equivalent, melanophores, are studied by scientists to understand human disease and used as a tool in drug discovery.

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Mayflies are insects assigned to the Order Ephemeroptera. They are related to dragonflies and damselflies. Their development takes place in freshwater and typically takes a year. During that time, they are known as "nymphs". The adults are short-lived, from a few hours to a few days depending on the species. About 2,500 species are known worldwide. Depicted here is a female subimago of the March Brown, Rhithrogena germanica, which is a faunistic rarity and on the red list of endangered species.


The plant shown is a horsetail, Equisetum arvense.


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