# Life (Biology) - *See also:* [[Life (The duration of one's being alive)]]. - *See also:* [[Classification of (these) living things]] (an attempt to classify the creatures found within these notes) --- ## The nature and diversity of life ### Characteristics of life Life has been defined as “[[2024-0802. Life is 'a state of physical entities that utilize substances derived from outside themselves for the purposes of growth, the repair of their own structure, and the maintenance of their functional systems, and that also reproduce'.|a state of physical entities that utilize substances derived from outside themselves for the purposes of growth, the repair of their own structure, and the maintenance of their functional systems, and that also reproduce]].”[^1] Or, to put it more simply: life is matter with the “[[2024-0802. Life is a quality that distinguishes matter with biological processes from matter without; it is 'defined descriptively by the capacity for homeostasis, organisation, metabolism, growth, adaptation, reproduction, and response to stimuli'.|capacity for homeostasis, organisation, metabolism, growth, adaptation, reproduction, and response to stimuli]]”.[^2] #### History of (the study of) “life” [[2025-0324. The Aristotelian concept of 'the soul as the essential distinction between living and nonliving things' dominated the European view for centuries.|The Aristotelian concept of 'the soul as the essential distinction between living and nonliving things' dominated the European view for centuries.]][^3] It was [[René Descartes (Philosopher)|Descartes]], in the 1600s, who proposed “[[2025-0324. Descartes, in the 1600s, proposed that the 'the human body works like a machine and the organism’s physiological functions can be explained as operating in a way mechanically similar to clocks'.|the human body works like a machine and the organism’s physiological functions can be explained as operating in a way mechanically similar to clocks.]]”[^4] --- ### The origin and evolution of life - [[Origin and evolution of life]] - [[Evolution (Biology)]] --- ### Classification of living things - Classification of living things - [[Taxonomy (Biology)]] + [[Three-domain system]] + [[Classification of (these) living things]] --- ## The molecular basis of life [[2024-0815. Molecules are the chemical building blocks of all body structures.|Molecules are the chemical building blocks of all body structures.]][^4] > All life forms require certain core chemical [[Elements (Chemical)|elements]] for their biochemical functioning.[^5] These core chemical elements include [[carbon]], [[hydrogen]], [[nitrogen]], [[oxygen]], [[phosphorus]], and [[sulphur]]: “the elemental macronutrients” of all organisms.[^6] Together, these make up [[nucleic acids]], [[proteins]], and [[lipids]]—the “bulk of living matter.”[^7] Five of these six elements comprise the chemical components of [[DNA]]; the exception is sulphur.[^8] --- - [[Vital processes (Biology)]] - [[Organic chemistry]] - Metabolism (bioenergetics and biosynthesis) - Molecular biology --- ## The structures and functions of organisms - Structures and functions of organisms - Cellular biology - [[Form and function (Biology)]] - [[Homeostasis (Biology)]] - [[Anatomy and physiology]] - [[Nutrition]] - [[Infants--Nutrition]] - Respiration - [[Reproduction and sex]] - Development: growth, differentiation, morphogenesis - Hereditary: the transmission of traits --- ## The behaviour of organisms - [[Behaviour]] - Nature and patterns of behaviour - Development and range of behavioural capacities: individual and group behaviour --- ## The biosphere - [[Biosphere]] - Ecology - Populations and communities - Disease and death - Ecosystems - [[Human ecology]] [^1]: Michael Allaby (ed.), *A Dictionary of Ecology*, 5th ed. (Oxford: Oxford University Press, 2015), s.v. ‘life’. [^2]: ‘Kingdom (biology)’, *Wikipedia*, updated 31 March 2024, https://en.wikipedia.org/wiki/Kingdom_(biology) [^3]: Nelson R. Cabej, ‘[[Cabej. ‘Epigenetics of Reproduction in Animals’, 2013.|Epigenetics of Reproduction in Animals]]’, in *Building the Most Complex Structure on Earth* (Elsevier, 2013), p. 59. [^4]: Nelson R. Cabej, ‘[[Cabej. ‘Epigenetics of Reproduction in Animals’, 2013.|Epigenetics of Reproduction in Animals]]’, in *Building the Most Complex Structure on Earth* (Elsevier, 2013), p. 59. [^5]: ‘Life’, *Wikipedia*, updated 22 March 2025, https://en.wikipedia.org/wiki/Life. [^6]: ‘Life’, *Wikipedia*, updated 22 March 2025, https://en.wikipedia.org/wiki/Life. [^7]: ‘Life’, *Wikipedia*, updated 22 March 2025, https://en.wikipedia.org/wiki/Life. [^8]: ‘Life’, *Wikipedia*, updated 22 March 2025, https://en.wikipedia.org/wiki/Life.