Gravitational biology is the study of the effects

gravity In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

has on

living organisms An organism is any living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have been pro ...

. Throughout the history of the Earth life has

evolved Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

to survive changing conditions, such as changes in the

climate Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteoro ...

and

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

. However, one constant factor in evolution since life first began on Earth is the

force In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...

of gravity. As a consequence, all

biological process Biological processes are those processes that are necessary for an organism to live and that shape its capacities for interacting with its environment. Biological processes are made of many chemical reactions or other events that are involved in ...

es are accustomed to the ever-present force of gravity and even small variations in this force can have significant impact on the health and function and the system of organisms.

Gravity and life on Earth

The force of gravity on the surface of the Earth, normally denoted ''g'', has remained constant in both direction and magnitude since the formation of the planet. As a result, both

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

and

animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...

life have evolved to rely upon and cope with it in various ways. For example, humans employ internal models in motor planning that account for the effects of gravity on gross and fine motor skills.

Plant use of gravity

Plant

tropism In biology, a tropism is a phenomenon indicating the growth or turning movement of an organism, usually a plant, in response to an environmental stimulus (physiology), stimulus. In tropisms, this response is dependent on the direction of the s ...

s are directional movements of a plant with respect to a directional stimulus. One such tropism is

gravitropism Gravitropism (also known as geotropism) is a coordinated process of differential growth by a plant in response to gravity pulling on it. It also occurs in fungi. Gravity can be either "artificial gravity" or natural gravity. It is a general feat ...

, or the growth or movement of a plant with respect to gravity. Plant roots grow towards the pull of gravity and away from sunlight, and shoots and stems grow against the pull of gravity and towards sunlight.

Animal struggles with gravity

Gravity has had an effect on the development of animal life since the first single-celled organism. The size of single biological cells is

inversely proportional In mathematics, two sequences of numbers, often experimental data, are proportional or directly proportional if their corresponding elements have a constant ratio. The ratio is called ''coefficient of proportionality'' (or ''proportionality ...

to the strength of the

gravitational In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force be ...

field exerted on the cell. That is, in stronger gravitational fields the size of cells decreases, and in weaker gravitational fields the size of cells increases. Gravity is thus a limiting factor in the growth of individual cells. Cells which were naturally larger than the size that gravity alone would allow for had to develop means to protect against internal sedimentation. Several of these methods are based upon

protoplasm Protoplasm (; ) is the part of a cell that is surrounded by a plasma membrane. It is a mixture of small molecules such as ions, monosaccharides, amino acids, and macromolecules such as proteins, polysaccharides, lipids, etc. In some definitions ...

ic motion, thin and elongated shape of the cell body, increased

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...

, and a reduced range of

specific gravity Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...

of cell components relative to the ground-plasma."Gravitational Zoology: How Animals Use and Cope with Gravity" Ralf H. Anken, Hinrich Rahmann. 2001. The effects of gravity on multicellular organisms is considerably more drastic. During the period when animals first evolved to survive on land some method of directed locomotion and thus a form of inner skeleton or outer skeleton would have been required to cope with the increase in the apparent force of gravity due to the weakened upward force of

buoyancy Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...

. Prior to this point, most lifeforms were small and had a worm- or jellyfish-like appearance, and without this evolutionary step would not have been able to maintain their form or move on land. In larger terrestrial

vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

gravitational forces influence

musculoskeletal system The human musculoskeletal system (also known as the human locomotor system, and previously the activity system) is an organ system that gives humans the ability to move using their Muscular system, muscular and Human skeleton, skeletal systems. ...

s, fluid distribution, and

hydrodynamics In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids – liquids and gases. It has several subdisciplines, including (the study of air and other gases in ...

of the circulation.

References

{{Authority control Gravity Astrobiology

Gravity and life on Earth

Plant use of gravity

Animal struggles with gravity

See also

References