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Lecture

BIOL 2060 Lecture Notes - Atriplex, Tonicity, Osmotic Concentration


Department
Biology
Course Code
BIOL 2060
Professor
Elizabeth Boulding

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Unit 2: Individuals:
Section 2.1: Homeostasis
Key Words:
-Regulators: Organisms that maintain constant internal environments despite varying
environmental conditions.
-Conformers: Organisms that allow their internal conditions to vary in parallel with the
environmental conditions.
-Homeostasis: maintenance of nearly constant internal environments in the midst of a
varying external environment.
-Negative feedback: Homeostatic control that returns internal conditions back to the
desired or normal state if they deviate because of external or internal influences.
-Positive feedback : Control in a system that reinforces a process in the same direction,
deviating farther away from the normal state.
Activity for Additional Learning:
1. What is homeostasis?
Homeostasis is the maintenance of nearly constant internal environments in the midst of a
varying external environment.
2. What is the difference between a regulator and a conformer?
Regulators are organisms that maintain homeostasis—that is, that have constant internal
environments despite varying environmental conditions, while conformers are organisms
that allow their internal conditions to vary according to the environmental conditions.
There is in fact a continuum between regulators and conformers. Perfect regulators have
precise control over their internal environments over their range of tolerance for a specific
condition, whereas perfect conformers have no response mechanisms with respect to that
condition
3. What is one advantage and one disadvantage of being a regulator?
One benefit is that when environmental conditions vary between wide extremes, regulators
can maintain their normal level of activity, food acquisition, and avoidance of predators. A
cost is the metabolic energy expended in activating and maintaining regulatory
mechanisms. Regulation is energetically expensive, and sufficient food supplies must be
available to support the organism’s demand for energy.

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4. What is one advantage and one disadvantage of being a conformer?
Conformers have lower energy expenditures, which is advantageous because they require
less food than does a regulator of similar size. The cost is that they are at the mercy of
their environment. When conditions are adverse, they must simply shut down and wait
with little activity until conditions improve
5. How do organisms use negative feedback to maintain homeostasis? Use
temperature regulation to illustrate the concept.
Negative feedback returns internal conditions back to the desired or normal state if they
deviate because of external or internal influences. For example, a person whose body
temperature increases while lying on a beach in the sun will use evaporative cooling
(sweating) to reduce body temperature back to the optimum.
6. Why is positive feedback rare in nature?
Examples of positive feedback are rare in nature because they are self-extinguishing; they
lead to the death of the organism rather than to its success
Section 2.2: Regulating Body Temperature
Key Words:
-Conduction: The movement of heat between objects in direct physical contact
-Convection: The process of heat flow or transfer to a moving fluid such as wind or
flowing water.
-Endotherm: An organism that relies mainly on internal sources of energy for
regulating body temperature.
-Ectotherm; An organism that relies mainly on external sources of energy for
regulating body temperature.
-Homeotherm; An organism that uses metabolic energy to maintain a relatively
constant body temperature.
-Poikilotherm: An organism whose body temperature varies directly with
environmental temperatures.
-Evaporation: The process by which a liquid changes from liquid phase to a gas.
-Metabolic heat: Energy released within an organism during the process of cellular
respiration.

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-Radiation: The transfer of heat through electromagnetic radiation, mainly infrared
light.
-Stored heat: Body temperature of an organism.
-Surface area to volume ratio: An allometric relationship that determines how quickly
ectotherms can gain and lose heat depending on their body size.
Activity for Additional Learning:
1. What is one cost of being a poikilotherm in terms of their enzymes?
For poikilotherms, internal temperatures are variable and thus stabilizing selection is
unlikely to be operating. Instead, many poikilotherms have redundant enzyme systems for
critical systems, each with different temperature optima. The cost involved is that these
enzyme systems require substantial energy in order to maintain function.
2. What mechanisms are used by endotherms to lower their body temperature?
Lowering the body temperature is more difficult than raising the body temperature, but can
be achieve through mechanisms such as panting, sweating, and altered body hair and
feather positioning (increasing energetic losses through convection, conduction,
evaporation and radiation).
3. Why can most endotherms live at ambient temperatures well below their body
temperature, but at only a limited range of temperatures above their body
temperature?
As a result of the limited effectiveness of the cooling mechanisms relative to the warming
mechanism, most endotherms are able to survive at ambient temperature well below their
set body temperatures while at only a limited range of temperatures above their set body
temperature. Endotherms tend to live closer to the upper end of their range of tolerance
than the lower end.
4. Provide examples of how ectotherms use behaviour to control their body
temperatures.
For example, many reptiles can be found laying still on roads, rocks and other exposed
objects early in the morning, exposing their bodies to the sun, resulting in an elevated
temperature. Furthermore, later in the day these animals are found in crevaces, cracks or
underground preventing their body temperature from reaching a lethal point.
5. Describe the adaptations arctic and alpine cushion plants use to regulate body
temperature. For each adaptation include the type of heat gain or loss that is
affected.
a. Darkly pigmented leaves:
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