Morphogenesis and form · Article

Physical forces and form

Physical forces and form is the idea that the shapes of cells and tissues follow in part from surface tension, internal pressure and mechanical stress. Early authors treated the cell as a liquid drop and asked what changes its surface energy.⁵ Recent authors ask how mechanical forces work together with chemical and electrical signals to set the size and shape of organs.⁶

Earliest held: 1859, Darwin
Most discussed in: On Growth and Form, 1992
In the library: 1,154 passages in 93 works
Rewritten: 2026-10-05

Surface tension and the cell

Verworn pictured amoeboid movement as a surface-tension effect. In his account, oxygen entering the biogen molecule at one point on the cell edge lowers the surface tension there, and the protoplasm bulges out at that point.¹ Bayliss asked where the energy of surface tension comes from. He judged that it is ultimately chemical, because it differs with the chemical constitution of the liquid.² He also described experiments by Hardy, in which stable hydrocarbons would not spread on water, while esters and glycerides lowered the surface tension greatly and spread widely.²

Limits of the surface-tension account

Hill tested the idea against muscle. He calculated that a single layer of lactic acid would have to raise surface tension by 4100 dynes per centimetre, about 55 times the value for water. He called this unreasonable as an explanation of the force a muscle develops.³ Thompson, in On Growth and Form, set out the conditions for the cell as a liquid drop.⁵ He made the account depend on whether small spherical cells can have local differences of surface tension. If they cannot, he said, division must be ascribed to changes in internal pressure or to electrical effects.⁴

Mechanics joined to signals

Recent authors treat mechanics as one input among several. Kamm and colleagues described the Drosophila wing disc, which grows from about 50 to about 50 000 cells and then stops. They proposed that its size reflects a balance between biochemical signals and tissue mechanics.⁶ Schofield and colleagues noted that some ion channels respond to mechanical forces in the membrane. This links membrane potential to mechanics.⁷ George and Bates put forward the hypothesis that forces between cells may guide ionic signalling in a tissue.⁸ Trewavas reported that root and shoot cells respond in opposite ways to tension and compression.⁹

SourcesEach quotation was checked word for word against the passage it opens.

the surface-tension would be locally diminished at any desired point of the periphery by the introduction of oxygen into the biogen-molecule ; the protoplasm would be bulged outVerworn, M., 1899 · General Physiology: An Outline of the Science of Life · open at passage 1419
There can be little doubt that it is ultimately chemical. The fact that it differs according to the chemical constitution of the liquid is sufficient to show this.Bayliss, W. M., 1915 · Principles of General Physiology · open at passage 212
It is obviously unreasonable, therefore, to regard a monomolecular layer of lactic acid as causing a change in surface tension large enough to explain the actual force developed by a muscle.Hill, A. V., 1926 · Muscular Activity · open at passage 139
If not, then changes in the conformation of the cell such as lead immediately to its division must be ascribed not to local changes in its surface-tension, but rather to direct changes in internal pressureThompson, D. A. W., 1992 · On Growth and Form · open at passage 445
what we have said may help us to understand the form of a cell,—considered, as with certain limitations we may legitimately consider it, as a liquid drop or liquid vesicleThompson, D. A. W., 1992 · On Growth and Form · open at passage 536
A model that has emerged from this system is that the organ size reflects an intricate balance between biochemical signals and tissue mechanics.Kamm RD, Bashir R, Arora N, Dar RD, Gillette MU, Griffith…, 2018 · Perspective: The promise of multi-cellular engineered living systems · open at passage 8
some ion channels can also respond to local mechanical forces within the membrane [45], thereby providing a direct link between MP, cell physiology and mechanical forces.Schofield Z, Meloni GN, Tran P, Zerfass C, Sena G, Hayashi…, 2020 · Bioelectrical understanding and engineering of cell biology · open at passage 14
Because many ion channels are sensitive to mechanical stresses, one hypothesis is that mechanical forces between cells within a tissue may guide ionic signaling.George LF, Bates EA, 2022 · Mechanisms Underlying Influence of Bioelectricity in Development · open at passage 58
Root and shoot cells respond in opposite ways to tension and compression.Trewavas A, 2026 · Aspects of plant intelligence (ii) · open at passage 81

Linked ideas

Ion channels and pumpsrelated to

Schofield and colleagues and George and Bates describe channels that respond to mechanical force, which ties mechanics to ionic signaling.

Resting membrane potentialrelated to

Mechanical forces on the membrane are described as a direct link to membrane potential; Thompson also raises surface distributions of electrical potential as a source of force.

Regenerationrelated to

Golding and colleagues discuss how material and mechanical forces shape cell responses during wound healing and limb regeneration.

Bioelectric prepatternin tension with

George and Bates ask what upstream information sets voltage across a tissue and propose mechanical forces as one answer, an alternative to a voltage prepattern.

Morphogenetic fieldparallels

Thompson's physical account of form, through surface tension and pressure, runs parallel to field accounts of how shape arises.

Vitalism and mechanismrelated to

Loeb says no chance coming together of physicochemical events builds each organism after a plan, which frames the form problem the vitalists raised.

Discontinuous variationrelated to

Thompson reads Bateson's discontinuous earwig distributions as differences of magnitude tied to growth over time, a different reading of the same data.

Synthetic living machinesrelated to

Gumuskaya and colleagues read the similarity of Xenobots and Anthrobots as showing generic laws of morphogenesis alongside species-specific genomic information.

Circumnutationrelated to

Bose ties circumnutation to growth in organs that are not perfectly radial, so the movement follows from how the organ grows.

Behaviour of single cellsprecursor of / follows

Verworn's surface-tension picture of amoeboid motion is an early physical account of single-cell movement.

Trial and errorparallels

Thompson uses trial and error as a drawing method for fitting coordinate systems to sections, a procedural sense of the phrase.

Determinism in physiologyparallels

Child's argument that constancy of pattern depends on developmental conditions bears on how form is explained.

Turing patterns, reaction-diffusion and autocatalysisprecursor of / follows

Thompson's On Growth and Form discusses catalysts formed by the reaction itself, and growth that accelerates as a result.

Inherency of form, mesoscopic materials and the physical origin of body plansprecursor of / follows

Thompson's physical treatment of surface tension and charge in drops anticipates the idea that physical effects shape living form.

The cell without a pumping membraneprecursor of / follows

Adsorption and surface energy, discussed by Bayliss, belong to the same early physical treatment of protoplasm.

Physical models of life: diffusion, osmotic growths and artificial cellsrelated to

Thompson's physical account of form, including liquid crystals, belongs to the same tradition as the osmotic growths.

Potassium channels and pigment pattern formationrelated to

The kcnk5b fin overgrowth and the Kcnj13 stripe change are both cases of channel genes altering the form of a zebrafish structure.

Where it is discussedPassages matching surface tension, mathematical, form of the, mechanical forces

1992	On Growth and Form · Thompson, D. A. W.	374
1915	Principles of General Physiology · Bayliss, W. M.	153
1899	General Physiology: An Outline of the Science of Life · Verworn, M.	58
1890	The Principles of Psychology, Vols. 1-2 · James, W.	55
1925	Elements of Physical Biology · Lotka, A. J.	48
1894	Materials for the Study of Variation Treated with Especial Regard to… · Bateson, W.	29
1930	The History of Biological Theories · Rádl, E.	28
1923	Protoplasmic Action and Nervous Action · Lillie, R. S.	28
1901	Regeneration · Morgan, T. H.	24
1957	An Introduction to the Study of Experimental Medicine · Bernard, C.	24