Flashcards in Chapter 2 Deck (20):
For aquatic organisms, how can the viscosity of water both hinder and facilitate movement?
Describe how water changes in mineral content as one moves from rainwater to lake water and, eventually, to ocean water.
Why might bodies of water with low pH pose a danger to organisms that live in them?
Explain the relationship between soil particle size and field capacity of soil.
Explain why the availability of water to plants is highest in soils with particle sizes intermediate between sand and clay.
How can we be sure that root pressure is not sufficient to explain the movement of water in trees?
For saltwater and freshwater fish, describe what would happen if they lacked their adaptions to control the movement of water and salts across their external surface.
Describe the costs and benefits associated with the different nitrogen products excreted by fish, mammals, and birds.
Water is the basic medium of life. It is abundant over most of the earth's surface, it is liquid within the range of temperatures usually encountered there, and it is a powerful solvent. These properties of water make it an ideal medium for living systems.
Water conducts heat rapidly and resits changes in temperature and state. Temperatures are therefore relatively evenly distributed throughout bodies of water.
Water is denser, and provides more buoyancy, than air, but it is also more viscous and therefore impedes movement.
All natural waters contain dissolved substances picked up in the atmosphere or from soils and rocks through which water flows.
The concentration of hydrogen (H+) ions in a solution is referred to as acidity and is expressed as pH. Most natural waters have pH values between 6 (slightly acidic) and 9 (slightly alkaline)
Because water clings tightly to the surfaces of soil particles, its availability depends in part on the physical structure of soil. Soils containing a high proportion of small clay particles hold water more tightly than do sandy soils. The force by which soil holds water is called water potential of the soil. Most plants cannot remove water from soils with a water potential more negative than -1.5 megapascals (Mpa). This water potential is referred to as the wilting point of the soil.
Plants extract water from soils by maintaining high solute concentrations in their root cells to generate high osmotic potentials.
According to the cohesion-tension theory, water is drawn from the roots to the leaves of a plant by a gradient in water potential generated by transpiration- the evaporation of water from leaf cell surface. When under water limitation, plants can reduce transpirational water losses by closing their stomates.
Terrestrial animals reduce their use of water for eliminating excess salts by concentrating salts in their urine or by excreting them through salt glands.
To maintain salt and water balance, freshwater animals, which are hyperosmotic, retain salts while excreting the water that continuously diffuse into their bodies.
Marine animals, which are hypo-osmotic, actively exclude salts. Some marine animals increase the concentrations of solutes, such as urea and amino acids, in their body fluids to match the osmotic potential of seawater and this reduce the movement of water out of their bodies.