Periods in Biological Definition

Punctuated equilibrium

... can occur relatively quickly, with long periods of little change— equilibria —in ... in small populations during geologically short periods of time, transitions between species are uncommon ... writing in The Origin of Species , "the periods during which species have undergone modification, ...

Thermoregulation

... burrows; in order to remain in "stasis" for long periods these animals must build up brown fat reserves ... (like siestas) and allows some mammals to survive periods of high temperature and little water (e.g. ... variation has been observed dependent on the periods of rest and activity, the maximum ranging from 10 ...

Growth curve

... growth Some growth curves for certain biological systems display periods of exponential growth . Typically, periods of exponential growth are of limited duration due to depletion of some ...

Activation energy

... is the point at which the original bonds have stretched to their limit. Transition states are only in existence for extremely brief (10 -15 s) periods of time. The energy required to reach the transition state is equal to the activation for that reaction. Multi-stage reactions involve a number of ...

Antibody

... binding with them. It is important to note that antibodies cannot attack pathogens within cells, and certain viruses "hide" inside cells for long periods of time to avoid them. This is the reason for the chronic nature of many minor skin diseases (such as cold sores ); any given outbreak is quickly ...

Charles Darwin

... insights into the areas he visited. From reading Charles Lyell 's Principles of Geology postulating gradual processes over huge periods of time, Darwin wrote home that he was ' seeing' land-forms as if he had the eyes of Lyell . He discovered fossils of gigantic extinct South ...

Extinction

... can kill off a species very rapidly, by killing all living members through contamination or sterilizing them. It can also occur over longer periods at lower toxicity levels by affecting life span, reproductive capacity, or competitiveness. DDT played such a role in killing off bald eagles ...

Memory B cell

... Memory B cells are B cells that although activated by the immune system, they are stored inside the circulatory system for later use, for long periods of time, possibly a whole lifetime. Like other cells such as helper T cells , killer T cells , and plasma cells they never become directly ...

Microbiology

... prokaryotes by binary fission . This allows for the propagation of genetically identical ( clonal ) populations. They may be frozen for long periods of time. Even if 90% of the cells are killed by the freezing process, there are millions of cells in a milliliter of liquid culture. These traits ...

Osmoregulation

... Certain plants develop methods of water conservation. Xerophytes are plants in dry habitats such as deserts which are able to withstand prolonged periods of water shortage. Succulent plants such as the cactus have water stored in large parenchyma tissues. Other plants have leaf modifications to ...

Protist

... are generally too small to be seen without a microscope. They are ubiquitous throughout aqueous environments and the soil, commonly surviving dry periods as cysts , and include several important parasites . Based on locomotion, protozoa are grouped into: Flagellates Move using flagella ...

Protist

... are generally too small to be seen without a microscope. They are ubiquitous throughout aqueous environments and the soil, commonly surviving dry periods as cysts , and include several important parasites . Based on locomotion, protozoa are grouped into: Flagellates Move using flagella ...

Vitamin

... Folkers and Alexander Todd in 1948 . Deficiency causes pernicious anaemia . It is the only water-soluble vitamin that can be stored for extended periods of time in the human body. Vitamin C ( Ascorbic acid ) Water Identified by James Lind in 1747 . Rediscovered by A. Hoist and T. ...