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Chapter 7 -- Part 3
Part of the rise in SMT can be explained by two effects.
The water is bound into the narrower capillaries when the soil loses water.
As the water'sMoisture content decreases, sections of water become isolated and tend to form droplets.
The droplets may be small.
The pressure needed to draw the water out of the droplet is about 14.2 atm.
The material composition of the capillary surface affects the strength of capillary action.
The SMT in clay may be ten times higher than in loam under similar conditions.
There is a limit to the amount of pressure that roots can produce.
wheat can't get enough water to grow if the SMT goes above 15 atm.
In hot dry climates where vegetation requires more water, plants may be able to grow at an SMT of 2 atm.
The ability of a plant to survive depends on the amount of water in the soil.
A plant can thrive in a clayey soil with twice the water content.
The other aspects of SMT are treated in exercises.
About 3% of insects are aquatic.
Their lives are associated with water in one way or another.
Many insects are able to use the surface tension of water for movement.
The surface tension of the water makes it possible for insects to stand on it.
There is an insect on the water.
The surface of the water is depressed when an insect lands on it.
The legs of the insect must not be wet by water.
Water-repulsive property can be provided by a waxlike coating.
Some assumptions are needed to perform quantitative calculations.
Let's assume that the dimensions of the cube are the same as the dimensions of the legs in contact with water.
The insect's mass is 2 x 10-2 g.
The myosin-actin units are about 1mm long.
The myosin-actin structure is damaged when Ca2+ ion is released into it.
The sliding of the threads through each other is caused by the shortening of the myosin-actin structure.
The contraction of the muscle is the result of this process.
A contracting motion must be produced by a force along the myosin-actin threads.
The force is not fully understood.
The force may be due to surface tension, which is present in liquid and tissue cells.
The motion of the threads is similar to the movement of a liquid.
The movement is due to the attraction between the two types of thread.
The surface attraction may be caused by a release of Ca2+ ion.
The force per square centimeter of muscle tissue could be generated by the surface tension proposed in this model.
We can conclude that surface tension could be the source of muscle contraction because this is below surface tensions.
The mechanism should not be taken too seriously.
The actual processes in muscle contraction are much more complex and cannot be reduced to a simple surface tension model.
Surfactants lower the surface tension of liquids.
The word implies that the end of the molecule is attracted to water, while the end of the molecule is not.
Nature and laboratory synthesis produce many different types of surfactants.
The surface structure of water is disrupted by an alignment.
The surface tension of water can be reduced by a small amount of surfactant molecule.
The end of the liquid is aligned with the surfactants.
The surface tension of the oil is reduced.
soaps and detergents are used to wash away oily substances.
The oil has a surface tension.
As a result, the oil breaks up into small droplets.
The small oil droplets are suspended in the water and can be washed away.
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