Chapter 4 Summary
CONCEPT 4.1 Each species has a range of environmental tolerances that determines its potential geographic distribution.
- The physical environment affects a species’ ability to obtain energy and resources, thereby determining its growth and reproduction and, more immediately, its ability to survive the extremes of that environment. The physical environment is therefore the ultimate constraint on a species’ geographic distribution.
- Individual organisms can respond to environmental change through acclimatization, a short-term response that enhances the organism’s ability to survive, grow, and reproduce under stressful environmental conditions.
- A population may respond to unique environmental conditions through natural selection for physiological, morphological, and behavioral traits, known as adaptations, that enhance its survival, growth, and reproduction under those conditions.
CONCEPT 4.2 The temperature of organisms is determined by exchanges of energy with the external environment.
- Temperature exerts important controls on physiological processes through its effects on enzymes and membranes.
- Gains of energy from and losses of energy to the external environment determine an organism’s temperature. Modifying this exchange of energy with the environment allows an organism to control its temperature.
- Terrestrial plants modify their energy balance by controlling transpiration, increasing or decreasing absorption of solar radiation, and adjusting the effectiveness of convective heat loss.
- Animals modify their energy balance mainly through behavior, adjusting the effectiveness of convective heat loss, and for endothermic animals, generation of internal heat.
CONCEPT 4.3 The water balance of organisms is determined by exchanges of water and solutes with the external environment.
- Water flows along energy gradients determined by solute concentrations (osmotic potential), pressure or tension (pressure potential), and the attractive force of surfaces (matric potential).
- Plants and microorganisms can influence water potential by adjusting the solute concentration in their cells (osmotic adjustment).
- Terrestrial organisms can alter their gains or losses of water by adjusting their resistance to water movement, as by the opening or closing of stomates in plants or variations in the thickness of skin in animals.
- Aquatic animals that are hypoosmotic to the surrounding water must expend energy to excrete salts against an osmotic gradient. On the other hand, aquatic animals that are hyperosmotic to their environment must take up solutes from the environment to compensate for solute losses to the surrounding water.
